Interaction Between Nigro-Striatal Lesions and Drugs Affecting Dopamine Receptors

Lesioning the nigro-striatal dopamine neuron system produces aphagia and adipsia with an intensity proportional to the size of the lesion. Those rats which received small lesions produced by a 1 mA current for a 15 second duration of the nigro-striatal system initially lost weight and then spontaneously recovered from that loss. Pretreatment with alpha-methyl-para-tyrosine (50 mg/kg) or haloperidol (0.4 mg/kg) given twice a day for a three-day period prior to lesioning facilitated the recovery. When large lesions (2mA for JO sec) were used to destroy this dopaminergic neuron system, a severe aphagia and adipsia resulting in death occurred in all saline treated animals . Haloperidol (2 mg/kg) or morphine sulfate (JO mg/kg) injected twice a day for six days preceding extensive nigrostriatal destruction promoted survival. The pharmacological denervation of dopaminergic receptors produced by haloperidol, morphine sulfate, or alpha-methyl-para-tyrosine prior to surgical destruction pf the nigro-striatal pathway i? felt to facilitate recovery. Symptoms of morphine withdrawal such as, wet shakes, ptosis, weight loss and hypothermia were enhanced when lesions were made in the nigro-striatal tract prior to and following the production of morphine dependence. This exacerbation of the primary abstinence syndrome was seen at either of two different terminal doses of morphine sulfate.

Lesions made prior to the production of dependence.
Lesions made after the production of morphine dependence. The exis te nce of the nigro-striatal pathway arising in the substantia nigra and terminating in the neostriatum is well established by histological (Anden et al., 1964;Anden ~al., 1965), biochemical (Anden et al., 1964;Poirier and Sourkes ,. 1965) and electromicroscopic (Hokfelt and Ungerstedt, 1969) determinations. The nigro-striatal neuron system is known to regulate the dopamine content o:f the neostriatum (Anden. et al., 1964;Anden et al., 1965). The phy-, siological importance of this system is evident froffi its involvement in mo t or function, mental processes, thei'moregulation and normal feeding behavior (Anden et al., 1966b;Fuxe et al., 1 970). The function of this dopamine system is particularly int eresting in connection with the actions of a number of ps y c h opharmacological agents such a s apomorphine (Anden et al., 1967;Ernst, 1967), morphine (Puri et al., 1973) and neuro1.eptics (Anden et al., 1971) which are known to in:f'luence do p aminergic function. The objective of this study is to investigate the interaction between the effects of lesioning the nigro-striatal neuron system and pharmacological agents affecting dopamine receptors.
The ascendi ng fibers of the nigro-striatal system originate mainly from the dopamine cell bodies situated in the zona compac ta of the substantia nig ra. The fibers be-1 come aggregated in a bundle situated just medial and ventromedial to the lernniscus medialis in the area of the nucleus ventralis tegmenti. This bundle lies dorso medial to the ventral part of the crus cerebri in the H 2 area of Forel before it enters the ro s tral part of the crus cerebri. After entering the crus cerebri the tract diverges into the internal capsule to innervate the neostriatum (Anden et al., 1964;Anden et al., 1965;Poirier and Sourkes, 1965;Faull and Laverty, 1969). This system is of great importance for normal movements and postures. The symptoms of rigidity, hypokinesia and tremor found in parkinsonism are probably due to the degeneration of the nigro-striatal system (Hornykiewicz, 1966). The pathophysiology of schizophrenia may be in part due to the activity of dopamine at its receptor sites in the striatum (Klawans et al., 1972). A role for dopamine neurons in thermoregulation has been suggested since apomorphine decreases body temperature via a central action (Fuxe and Sjogrist, 1972). The ni g ro-striatal neurons appear to be necessary for normal eating and drinking behavior (Ungerstedt, 1970(Ungerstedt, , 1971Oltsman and Harvey, 1972).
Unilateral lesions of the corpus striatum or the nigrostriatal dopamine system are known to produce asymmetric movements and postures (Poirier et al., 1965;Anden et al., 1966). Lesioned animals show a pro~ounced rotational behavior which is linked to differences in dopamine receptor activity on two sides of the brain (Anden et al., 1966a).
Three to four days after unilateral removal· of the nigrostriatal system there is a lack of orienting response to all sensory stimuli on the side contralateral to the lesion (Ungerstedt,197J). The period from five days to two months after the operation is characterized by partial recovery of sensory function (Ungerstedt, 1973). Degeneration of thenigro-striatal system, bilaterally, in the rat has been shown to result in the development of adipsia and aphagia (Ungerstedt et al., , 1971). Stricker (1972, 1973) have al s o found that depletion of brain dopamine was critical for the production of adipsia and aphagia. The adipsic and aphagic syndrome seen after nigro-striatal destruction is severe and if not force-fed animals die several days after lesioning (Ungerstedt, 1970(Ungerstedt, , 1971Oltsman and Harvey, 1972). Force-fed animals recover from aphagia and adipsia, in a predictable sequence of stages culminating in the ability to maintain their body weight on food pellets and water . Recovery of feeding behavior has been suggested to involve a denervation supersensitivity mechanism (Glick~ al., 1 9 72). Supersensitivity may be defined as the phenomenon in which the amount of a neurotransmitter required to produce a given biological response is less than normal. Thus, the one consistent sign of supersensitivity is a shift to the left of the dose response curve (Fleming~ al., 1973).
Supersensitivity in addition to being a useful model in explaining recovery of feeding behavior has also been forwarded to ' explaining dependence on narcotics (Jaffe and Sharpless, 1968;Collier, 1969). Based upon results from morphine withdrawal aggression it has been suggested that central dopamine receptors are supersensitized during chronic morphine administration. Morphine withdrawal aggression in dependent animals can be selectively potentiated by dopaminergic stimulating agents and blocked by drugs which block dopamine receptors (Puri~ al., 1971;Lal and Puri, 1972;Puri and Lal, 1973). Further evidence for the interaction between brain dopamine and morphine comes from biochemical studies. Acute morphine elevates brain hornovanillie acid and J-4 dihydroxyphenylacetic acid (Fukui and Tagaki, 1972; Kus c hinsky and Hornykiewicz, 1972), increases the synthesis of labeled dopamine from labeled tyrosine in brain (Clouet and Ratner, 1970;Fukui et al., 1972;Smith ~ al., 1970Smith ~ al., , 1972' and accelerates the disappearance of dopamine after the administration of alpha-methyl-paratyrosine (Gunne ~ aJ_., 1969;Puri et al., 1973). Based upon these studies it was proposed that acute administration of morphine blocks dopamine receptors. Chronic administration of morphine therefore wo-uld produce a persistent bJ_ockade of dopamine receptors and cause the development of latent supersensit i vity of central dopamine receptors. This supersensitivity may therefore contribute to the morphine withdrawal synd rome.
Treatment with haloperidol (Gia.nutsos et al., 197 4 a, 1975) and methy l-para-tyrosine (Tarsy and Baldessarini, 1973) has also been shown to produce a supersensitivity of dopamine receptors in the central nervous system. Haloperidol is a potent neuroleptic that is known to block dopamine receptors (Janssen, 1967;Anden et al., 1971). The dopamine receptor supersensitivity produced by chronic administration . of haloperidol is manifested by an enhanced stereotypy and aggression in response to small otherwise ineffective doses of apomorphine (Gianutsos .!:..! al.,l974a). Apomorphine has been sho>\TI to effectively decrease turnover of dopamine in haloperidol-treated rats at doses which were without effect in drug-naive rats (Gianutsos et~., 1975). A shift in the dose response curve in the direction of increased sensitivity was found in response to apomorphine, a dopaminergic stimulant, after withdrawal of chronically administered alpha-methyl-para-tyrosine (Tarsy and Baldessarini, 1973).
Alpha-methyl-para-tyrosine is a well known inhibitor of catecholamine synthesis (Nagatsu et al., 1964). Apomorphine, which has been used in these studies to show increased sensi ti vi ty, is believed to stimulate the dopaminergic receptors in the central nervous system (Anden et al., 1967;Ernst, 1967). Biochemical studies have shmvn that apomorphine decreases the turnover rate o~ striatal dopamine; this effect is completely blocked by haloperidol (Anden et al ., 1967;Persson, 1970;Anden and Becard, 1971;Lahti et al., 1972;Puri, 1973).
This investigation is focused on the nigro-striatal neuron system and dopaminergic supersensitivity. These factors were studied in relation to aphagia, adipsia and the morphine withdrawal syndrome. Nigro-striatal lesions will be made and body weight changes recorded. Frio~ to the production of the lesion, animals will be treated with either saline, alpha-methyl-para-tyrosine, a blocker of catecholamine synthesis (Nagatsu et al., 1964), haloperidol, a dopaminergic blocking agent (Janssen, 1967;Van Rossum, 1967;Anden et al., 1970), or morphine which may also block dopaminergic receptors (Puri et~.,l97J). Drug treated and cbntrol groups will be compared with respect to lesion induced weight changes and lethality.
Nigro-striatal lesions will be produced both prior to and subsequent to the production of morphine dependence.
After the abrupt termination of morphine injections subjects will be observed for the symptoms of morphine withdrawal.
Narcotic withdrawal symptoms will be compared between lesioned and non-lesioned groups. The dopaminergic stimulating agent apomorphine (Anden et al., 1967;Ernst, 1967) will be administered to both intact and nigro-striatal lesioned morphine withdrawn subjects to further assess the role of dopamine receptor activity in the abstinence phenomena.
In order to determine if the results are specific for the dopaminergic system the medial fore brain bundle, a nor-adrenergic and serotonergic neuron system, will also be lesioned after the production of dependence and abstinence signs observed.
This research has the following significance. First-ly, evidence for the role of the nigro-str{atal dopamine neurons in aphagia and adipsia will be gathered. Secondly, it will clarify the role of receptor supersensitivity in recovery from nigro-striatal lesioning and in the morphine withdrawal syndrome. 'Ihirdly, it will give insight into the role of this dopamine system in narcotic dependence. II.

LITERATURE SURVEY
A. Central Ne rvous Syst e m Dopaminergic Pathways The dopamine neuron system discovered so far are two large ascending fiber systems and one small dopamine neuron system. The existence of these dopaminergic pathways has been demonst ra ted through studies employi ng lesions, stimulating electrodes, biochemical and histochemical techniques.
Based upon these studies the following dopaminergic pathways have been described:  (Anden et ~.-, 1966b;.

9
Lesions placed at the level of the rostral hypothalamus which specifically interrupt the pathway to the mesolimbic area are found to modify neuroleptic catalepsy.
These lesions caused an initial potentiation followed by a reduction in the cataleptic effect of neuroleptic agents but cause a potentiation of cholinergic catalepsy at all times of testing (Costall and Naylor, 1974). The mesolimb- ic area thus appears to be involved with the mediation of neuroleptic catalepsy and the cholinergic dopaminergic balance controlling cataleptic beha~~br ~ould also appear to involve the mesolimbic dopamine neurons (Costall and Naylor, 1974a). Lesions of the dopaminergic mesolimbic innervation partially reduce morphine catatonia (costall and Naylor, 1974b). · Although stereotypy has been considered by many purely in terms of extrapyramidal actions, studies employing apomorphine and ET 495 have shown that mesolimbic functions are important for the initiation of stereotyped responses (Costall and Naylor,197Jc). Ablation of the mesalimbic innervation reduce the weaker components of methylphenidate stereotypy (Costall and Naylor, 1974c).

2) Tubero-infundibular Dopamine Neurons
The tubero-infundibular dopamine neurons have their cell bodies mainly localized to the anterior part of the nucleus annuatus and anterior periventricular nuclei. The axons of this system run ventrally toward the lateral b6rder of the median eminence (Fuxe, 1963;I<'uxe andHokfelt, 1966, 1969). In the external layer of the medial eminence, the axons give rise to a densely packed plexus of dopaminergic nerve terminals, which exerts ah axo-axonic influence in the layer (Hokfelt, 1967).
This very short dopaminergic intrahypothalamic system regulates the discharge of the releasing and inhibiting factors from the median eminence . The re-lea8e of dopamine in the median eminence acts locally on terminals storing luteinizing hormone releasing factor (LHRF) to inhibit the release of LHRF from the medial eminence. This system also participates in mediating the negative feedback action of estrogen and testosterone on gonadotropic secretion, because estrogen and testosterone markedly increase the turnover of the tubero-infundibular dopamine neurons of castrated rats, resulti·ng in increased release of dopamine in this area (Fuxe et al., 1967. The blockade of ovulation by synthetic estrogen and its derivatives may at least partly be mediated via activation of the neuron system . This system is also highly sensitive to prolactin, which markedly increases the turnover of dopamine in the tubero-infundibular dopamine neurons (Fuxe andHokfelt, 1969, 1970).

J) Nigro-neostriatal Dopamine Neurons
The nigro-neostriatal system seems to originate mainly in the pars compacta of the subst a ntia nigra (Anden, 1964). Support for this comes from fluorescence microscopy and the high dopamine content observed in this area (Hornykiewicz, 1963). Unilateral pars compacta lesions result in a sixty per cent lowering of the dopamine level in the corpu~ striatum of the operat~d side when compared with the unoperated side (Faull and Laverty, 1969). The caudate nucleus and putamen shows a fairly strong green to yellow fluorescence due to the high dopamine content. This fluorescence was reduced in animals with lesions of the substantia nigra.
A clear correlation was found between the fluorescence reduction and the extent of destruction of the pars compacta (And en, 1964). Some cell bodies are also found in the zona reticulata and the pars lateralis of the substantia nigra, which also belong to the nigro-neostriatal dopamine neurons . Recently, studies after removal of the nucleus caudatus putamen suggest that the cell bodies in the ventrolateral part of the midbrain tegrnentum belong to this large uncrossed neuron system, inasmuch as they show marked reduction in fluorescence intensity and signs of atrophy after such operations . There is now a virtually complete picture of the distribution of these dopamine fibers. Upon leaving the pars compacta of the substantia nigra, most of the nigro-neostriatal dopamine fibers become aggregated in a bundle which ascends just medial and dorso medial to the ventral part of the crus cerebri.
At the level of the posterior part of the medial eminence, the bundle turns to the ventralrostral part of the crus cerebri and enters and diverges into the rentrolenticular part of the internal capsule. Running rostrally and dorsally in the internal capsule, the fibers then ascend in the fibers of the internal capsule to innerva te the neostriatum (Anden et al., 1965).
Biochemical and histochemical investigation have yielded some quantitative data on the unilateral nigro~neo-  York, 1967;York 1970).
Following the application of dopamine iontrophoretically from multibarrel micropipette assemblies ne a r caudate cells, the rate of discharge of fifty to sixty per cent of these neurons is depressed, while the spike rate of approximately ten per cent of the cells is facilitated. Electrical stimulation of substantia nigra evokes depressant and facillatory responses from individually recorded nucleus neurons (Connor, 1968(Connor, , 1970. Catecholamine involvement in the phenomenon of intracranial self stimulation is well known. Until recently, the major role has been assigned to noradrenergic nerves. This has been challenged by neuroanatomical and histochemical evidence of a possible dopaminergic involvement in intracranial self-stimulation (Phillips and Fibiger, 1973). When the facilatory effects of d and l isomers of amphetamine on self-stimulation were assessed, it was found that the two isomers were equipotent (Phillips and Fibiger,l97J). These data would seem to indicate that the dopaminergic systems in part subserves positiv~ reinforcement. b.

Motor functions
The nigro-neostriatal neurons play an important role in normal movement and postures. Degeneration of the systern is believed to be the cause of symptoms such as rigidity, hypokinesia and tremors found in parkinsonism (Hornykiewicz, 1966).
In agreement with this it has been found possible to restore normal motor functions in Parkinsonian patients by treatment with L-dopa (Cotzias et al., 1967).
The drug-induced stimulation of the nigro-neostriatal pathway causes an induction of locomotion, stereotyped behaviors and finally compulsive gnawing (Randrup and Munkvad, 1968;. Thus the changes in these behaviors involve the stimulation of dopaminergic receptors. Similar results were obtained when animals were treated with L-dopa, the precursor of dopamine, following dopa decarboxylase illl'J.ibi ti on. Locomotor activity was markedly increased (Bartholini et al., 1969;Butcher et al., 1970). The increase in locomotor activity is mainly composed of stereotyped movements (Butcher et al., 1970). The systemic administration of apomorphine produces stereotyped behavior in rats which is characterized by continuous and compulsive sniffing, licking and gnawing (Ernst, 1965).
The results of several studies have supported the hypothesis that stereotyped behaviors induced by apomorphine or by amphetamine is due to increased dopamine receptors activity in the neostriatum (Ernst, 1969;. Unilateral lesions of the corpus striatum or the nigrbstriatal dopamine system are known to produce asymmetries in movemen t and posture (Poiri~r et al., 1965;Anden t l al., i966a) . The difference between the two sides of the brain may be further aggravated by treatment with drugs that release dopamine from the non-lesioned side. Such animals show a pronounced rotational behavior (Anden et al., 1966a). The rotational behavior is further linked to the differences in dopamine levels on the two sides of the brain by finding that tinilateral striatal injections o f dopamine cause the rats t o turn or slowly rotate away from the side where dopamine was injected (Ungerstedt et al., 1969). Spontaneous rotatio ns toward the intact side is seen twenty-four to thirty-four hours after a lesion of the nigrostriatal dopamine s y stem.
The direction of the rotation as well as the time p o int of its occurrence is indicative of a degeneration release of dopamine from_ the lesioned side (Ungerstedt, 1973). In a chronically lesioned animal there is a striking difference bet ween the effects of dopamine-releasing drugs and dnpamine receptor-stimulating drugs. Amphetamine causes the ani mal to rotate toward its lesioned side, apomorphine causes . it to r o tate toward its intact side (Ungerstedt, 1973). These r esuJ_ts indicate that amphetamine preferenti-ally influences the non-lesioned side, whereas apomorphine exerts its strongest effect on the denervated side. c.

Mental functions
It is now accepted that stereotyped behavior induced by amphetamine or apomorphine is principally due to the increased dopaminergic neurotransmission in the neostriatum.
Stereotyped behavior is also often seen in patients with schizophrenia. (Snyder, 1971) and it has, therefore, been assumed to be partly due to an abnormal increased activity of nigro-neostriatal dopamine neurons .
This view is substantiated by the fact that neuroleptics which are potent antipsychotic drugs block dopaminergic neurotransmission (Corrodi et al., 1971).

d. Autonomic functions
The observation that dopamine increases cardiac output and increases systemic blood pressure (Noyer et al., 1971) suggest that dopaminergic neurons may play a role in central vasomotor mechanism. Since the administration of dopaminergic blocking agents such as spiroperdal and pimozide decrease blood pressure .
e. Sensory neglect following removal of the nigrostriatal dopamine system Three to four days after ~ unilateral removal of the nigrostriatal system there is an almost complete lack of orienting response to all sensory stimuli on the side contralateral to the J.esion, while the animal reacts in an es-sentially normal way to stimuli-to the side ipsilateral to the lesion (Ungerstedt, 1973). Simple reflexes like the withdrawal reaction or the corneal reflex, are normal on both side_s. The period from five days to two months after the operation is characterized by partial recovery of sensory functions. Even two months after the operation none of the anim~ls show normal responses on the side contralateral to the lesion. The sense of smell seems to recover first, then vision and yet none of the animals regained a normal reaction to touch (Ungerstedt, · 1973).

Striatal Dopamine System
Detailed mapping of the central monoamine pathways (Ungerstedt, 1971) show the dopamine axons to be located in a dense bundle in the lateral hypo thalamus before entering into the crus cerebri.
There is a vast literature in the field of physiological psychology and especially in connection with consumatory behavior where the effects of lesions and stimulations in this area are carefully studied. However, the dopamine system has received little or no attention, probably because detailed inf'orma tion of its anatomy has been lacking.
A great deal has been learned concerning the changes in food and water r egulation follo wing lateral h y pothalamic · lesions; little is known concerning the spe cific anatomical structures or systems involved. Several investigations have suggested that the critical areas for producing the lateral hypothalamic syndrome may be outside or include only a lateral segment of the lateral hypothalamus (Morgane, 1961;Gold, 1967;Grossman and Grossman, 1971;Wampler, 1971). Gold (1967) outlined a critical forebrain area for producing aphagia and adipsia. This area included a portion of the g1obus pallidus, the medial portion of the internal capsule.
It is known that several fiber systems pass through these three a reas which regulate the telancephalic content of norepinephrine , dopamine and serotonin. The nigro-striatal bundle, a fiber system that regulates the dopamine content of the neostriatum, passes · through each of the three areas described by Gold (1967).
_ Electrocoagulation in the lateral hypothalamus interrupting the axons of the nigro-striatal dopamine pathway cause the dopamine terminals in the corpus striatum to degenerate thus resulting in a decrease in the dopamine content of the neostriatum (Poirier et al., 1967;Faull and Laverty, 1969;Moore et al., 1971;Ungerstedt, 1971). Symptoms of adipsia and aphagia appear after the lesions; since other than dopamine neurons may have been destroyed the results may not be due to interruption of dopamine fibers alone.
The technique of int~ocerebral injections of 6-hydroxydopamine permits a more selective degeneration ·of dopamine and noradrenergic pathways (Ungerstedt, 1971). The development of adipsia and aphagia was correlated to the histochemical effects of the 6-hydroxydopamine lesions.
Adipsia and aphagia always followed a complete bilateral degeneration of the nigro-striatal dopamine system regardless if the 6-hydroxydopamine was injected into the substantia nigra, the area ventralis tegmenti or the lateral hypothalamus (Ungerstedt, 1970(Ungerstedt, , 1971. However, where the ascending noradrenergic pathways were lesioned no adipsia and aphagia developed in spite of the fact that most of the hypothalamus degenerated (Ungerstedt, 1971). In agreement with ~r~vious reports, intraventricular administration of 6-hydroxydopamine in monoamine oxidase inhibited · animals or bilateral injections of 6-hydroxydopamine into substantia nigra produced aphagia and adipsia (Fibiger ~al., 1973). Oltsman and Harvey (1972) found that electrolytic lesions of the lateral hypothalamus which destroyed the dopaminergic nigrostria tal tract produced severe aphagia and adipsia.
The adipsic and aphagic syndrome seen after nigro-striatal destruction is severe. -ungerstedt ( 1970, 1971) found that if not supported, the animals died four to five days after lesions. Their condition was generally worse than that which is seen where a normal animal is deprived of food and water (Ungerstedt, 1971). Oltsman and Harvey (1972) also reported a severe aphagia and adipsia after nigro-striatal lesioning.
Recovery of food and water intake is re~orted to have occurred within ten days of intraventricular 6-hydroxydopamine (Zigmond and Stricker, 1972;Fibiger et al., 1973).
Nigral injections of 6-hydroxydopamine produce a more severe effect with recovery failing to occur during a three month period (Fibiger et al., 1973). Animals with nigro-striatal lesions show deficits in water regulation and food intake as have been found in lateral hypothalamic lesioned animals (Oltsman and Harvey, 1972;Fibiger et al., 1973;Marshall and Teitbaum, 1973). Rats with nigro-striatal destructions progress through the same sequence of stages in the recovery of feeding as do rats with lateral hypothalamic lesions . Ungerstedt· (1970Ungerstedt· ( , 1971) has shown that adipsia and aphagia is the result of a loss in striatal dopamine. Zigmond and Stricker ( . 1972, 1973) have also found that depletion of brain dopamine was more critical for producing symptoms of the lateral hypothalamic sundrome than was depletion of brain norepinephrine. Glick et al., (1974) have found lesion-induced weight loss to be highly correlated with depletion of striatal dopamine but not telencephalic norepinephrine. In rats with severe dopamine depletions, the degree of weight loss was related more to the striaturn with the highest remaining level of dopamine suggesting that a critical level of doi:>amine in one striatum may be essential for lateral hypothalamic recovery. Zigmond and Stricker (1973) have also.
r~ported that residual brain catecholamines appear to make a significant contribution to the recovery of ingestive behavior in rats with either 6-hydroxydopamine or electrolytic lesions. Rats after intraventricul a r 6-hydroxydopamine or lateral hypothalamic lesions decrease food and water intake markedly after the administration of methyl-para-tyrosine a t doses that did not affect the ingestive behaviors df controlled rats (Zigmond and Stricker, 1973). These results suggest that recovery from aphagia and adipsia is dependent upon compensatory processes occurring with the damaged systerns. Severa.l mechanisms have been proposed which might account for this compensation, such as an increa.se in catecholamine turnover in terminals of remaining fibers (Bloom et al., 1969;Uretsky ~al., 1 9 71), an increased sensitivity of postsynaptic receptors (Ungerstedt, 1971;Uretsky and Schoenfeld, 1971;Schoenfeld and Uretsky, 1972), and sprouting of new terminals f rom transceted axons Nygren et al., 1971) • , Recently, various kinds of chemical treatments have been found to attenuate the severity of the aphagia and adipsia following bilateral lesions of the lateral hypothalamus.
Recovery of feeding behavior has been facilitated by systemic injections of either methyl-p-tyrosine or insulin for a few days prior to surgery.
Rats with bilateral hypothalamic lesions die of starvation within seven days of surgery. But when these rats are pretreated with methyl-p-tyrosine they spontaneously eat, drink and gain weight after surgery (Glick et al., 1972). These data suggest that recovery of functions after lateral hypothalamic damage involves denervation supersensitivity since, methyl-p-tyrosine should have pharmacologically produced a partial denervatio~ of neurons subserving recovery. Glick and Greenstein (1972) have also suggested that recovery from lateral hypothalamic lesions may involve the sprouting of intact inputs to the remaining lateral hypothalamic noradrenergic neurons. They found that if frontal cortical lesions were produced thirty days prior to lateral hypothalamic lesioning recovery was facilitated.
The period of recovery after bilateral electrolytic lesions of the lateral hypothalamus is shortened if insulin is given for five days before surgery (Balagura et al., 1973). Recovery of feeding has also been facilitated when rats are reduced by food deprivation to seventy-five per cent of their normal body weight. This food deprivation facilitated recovery has been shown for lateral hypothalamic lesions 2J (Powley-Keesey, 1970) and 6-hydroxydopamine treatment (Myers and Martin,l97J).
Enhanced recovery of feeding after hypothalamic damage .has been reported ~n response to an intraventricular injection of nerve growth factor (Berger et aJ_., 1973). These authors speculate that nerve growth factor may facilitate behavj_oral recovery by promoting the development of supersensi tivity to norepinephrine and possibly also by stimulating the growth of regenerating noradrenergic neurons in the brain.
Postoperative alpha-methyl-para-tyrosine treatment has been sho>vn to facili:tate survival but the dose of alphamethyl-para-tyro sine which will produce this effect ;_s critical (Glick and Greenstein, 1974). Initially, alphamethyl-para-tyrosine improved feeding mechanisms involving catecholamine and thereby promoted the development of denervation supersensitivity which became behaviorally manifested after the effect of alpha-methyl-para-tyrosine on catecho lam ine synthesis had subsided (Glick and Greenstein, 1974). Electrical stimulation through the same electrodes that induced aphagia by means of a mechanical lesion has been shown to shorten the post lesion recovery period (Harrell et al •. , 1974). Alte ration of the esculent property of the diet given f'ollow ing lateral hypothalamic lesioning has also been shown. to e f:t·ect recovery from the syndrorne (Myers and Martin, 1973). Recovery of a postoperative weight loss following bilateral ablations of frontal cortex in rats is quicker when food pellets are scattered on the cage floor than when pellets were available only in attached food hoppers (Glick and Greenstein,197J). The period of recovery after bilateral electrolytic lesions of the lateral hypothalamus in r ats is lengthened if gluc agon is given during the preoperative period (Balagura et a l., 197J). Bilateral lesions made in the habenular nuclei had little effect on recovery of feeding following lateral hypothalamic lesions (Mok et ·al., 1973), thus suggesting that the habenular nucleus is not a crucial part of the feeding syst.em which mediates the recovery from the lateral hypothalamic syndrome.

C. Cortical Dopaminergic Terminals
For a number of years it had been generally assumed that all catecholaminergic cortical nerve terminals were nor-adrenergic. However, high concentrations of dopamine have been found in the cortex of various species (Bertler and Rosengren, 1959;Valzelli and Garatlini, 1968). It appears that most of the dopamine found in the cortex of the rat is not localized in nor-adr e nerg ic terminals. Lesions of the dorsal nor-adrenergic system or a combined lesion of the dorsal and the ventral nor-adrenergic systems, which both significantly decrease the cortical levels of norepinephrine, did not induce a parallel reduction in cortical dopamine content (Thierry!:..!. al.,197Jb). These findings strongly suggest the existence of dopaminergic neurons in the cortex. Further evidence for the e xistence of dopaminergic terminals in the rat cortex is taken from the fact that cortical synaptosomes have the ability to synthesize JR-dopamine from JR-tyrosine (Thierry t l al.,197Ja).
The destruction of ascending noradrenergic pathways which abolishes the in vitro synthesis of JR-norepinephrine did not abolish the synthesis of JR-dopamine (Thierry et al.,197Ja). Also, a specific dopamine reuptake process has been demonstrated in the cerebrc'fl ·cortex of normal rats and rats whose ascending noradrenergic pathways have been selectively destroyed (Tassin et al., 1974). Visualization of these dopaminergic terminals has been achieved by combined pharmacological and histochemical methods (Lidbrink t l al., 1974). The occurrence of dopaminergic nerve endings was further ~upported by the demonstration of a dopaminergic receptor in the cortex. Specifically, dopamine was found to activate an adenylate cyclase systern and this effect was inhibited by the dopamine receptors blocker haloperidol {van Rungen and Roberts, 197J).

D. Recovery Mechanism Within the Central Nervous System
Recovery from central nervous system lesions appears to be dependent on compensatory processes occurring within the damaged system. Several mechanisms have been proposed which might account for this compensation; such as an increase in catecholamine turnover in terminals of remaining fibers, an increase in sensitivity of postsynaptic receptors and sprouting of new terminals from transected axons.

1) Catecholamine Turnover
Reduced accumulation of intraventricularly administered 3 H-l-norepinephrine was seen in the brain of rats who were treated with intraventricular injections of 6hydroxydopamine.
The loss of catecholamine uptake sites produced by the 6-hydroxydopamine pretreatment was probably responsible for the reduction in accumulation (Uretsky et al., 1971) • . The rate constant of disappearance of 3 H-norepinephrine was used to estimate the fraction of the endogenous norepinephrine pool turning over per unit of time.
An increase in the rate constant in the pons-medulla region was seen in 6-hydroxydopamine treateci·rats.
An increase in the rate constant may indicate that norepinephrine containing neurons which survive the degeneration effects of 6-hydroxydopamine show an increase in their physiological state of activity to compensa t e for the loss of neuronal function after degeneration ( Uretsky ~al., 1971). Alternatively, the noradrenergic neurons which have a higher turnover than average may survive the effects of 6-hydroxydopamine. An increase in the ratio of homovanillic acid to the dopamine content in the striatum on the side lesioned with 6-hydroxydopamine has also been found (Agid et al., 1974).
These results indicate a hyperactivity of the remaining dopaminergic neurons following partial degeneration of the nigrostriatal pathway.

2) Postjunctional Supersensitivity
Supersensitivity may be defined as the phenomenon in which the amount of a substance required to produce a given Thus, the one shift in the maxi-biological response is less than normal.
consistent sign of supersensitivity is a mum response to a drug (Fleming et al., 1973). An apparent change in sensitivity of the postjunctional element to nerve impulses could result from any one of several changes in the transmission apparatus. There could be a change in the postjunctional element so that it actually became more sensitive to the transmitter (Thesleff, 1960). The mechanism inactivating the transmitter could change so that it is removed from its site of action more slowly (Trendelenburg, 1963). Prejunctional elements could increase their capacity to deliver transmitter or change their recovery process to repetitive stimulation (Sharpless, 1969). Many of these changes are known to occur in disused or denervated peripheral structures.
There is evidence that spinal motor neurons become more reactive to a variety of stimuli following cord section (Cannon and Rosenblueth, 1949;Stavraky, 1961), and destruction of sensory nerve fibers (Cannon · and Rosenblueth, 1949;Stavraky, 1961;Loeser and Ward, 1967). Several weeks after a tenotomy, which relieves tension on muscle spindles and thus reduces the activity of Group la sensory fibers, monosynaptic discharge elicited by stimulating Group la fibers had greatly increased j_n strength (Beranek and Hnik, 1959;Kozak and Westerman, 1961).
Supersensitivity of the temperature regulating center of the hypothalamus has been shown to develop in response to chronic administration of scopola~ine (Friedman and Jaffe · , 1969;Friedman et al., 1969). When scopolamine was administered to mice for various periods ranging from five days to four weeks and then withdrawn, an exaggerated hypothermic response to pilocarpine and other centrally acting cholinergic drugs was seen. Sharpless and Halpern (1962) found that in the isolated cerebral cortex of the cat supersensitivity emerged in two to three weeks after surgical denervation. Supersensitivity to metamphetamine has been shown to occur after treatment with alpha-methyl-para-tyrosine (Paschel and Nintemon, 1966).
Following intraventricular administration of 6-hydroxy-dopamine which destroys catecholamine containing nerve terminals, L-dihydroxy-phenylalanine (dopa) produces a marked increase in the locomotor activity of treated rats, while it has little effect on the activity of untreated rats (Uretsky and Schoenfeld, 1971). These results suggest the enhanced effects of L-dopa may be due to a central supersensitivity to catecholamine. The behavtoral response to apomorphine is altered by 6-hydroxydopamine pretreatment while lowering the ED 50 for apomorphine (Schoenfeld and Uretsky, 1972). A modified response to apomorphine, administered directly into the striatum has also been reported in reserpine-treated rats . Jalfre and Haefely (1971) have reported that 6-hydroxydopamine treated rat.s s howed increased motor activity after low doses of apomorphine which were inefr ective in normal ani-

mals.
A shift i n the dose-response curve in the direction of increased sens itivity was found in response to apomorphine after withdrawal of chronically administered reserpine, alpha-methyl-para-tyrosi.ne or chlorpromazine (Tarsy and Baldessarini,l97J). Chronic administration of haloperidol has been shown to result in a supersensitivity of dopamine receptors .. This supersensitivity is manifested by an enhanced stereotypy and aggression in response to small, otherwise ineffective doses of apomorphine (Gianutsos et al., 1974). Apomorphine has been shown to effectively decrease turnover of dopamine in haloperidol treated rats at doses which were without effect in drug-naive rats (Gianutsos et al. , 1971+) • Chronic den ervation of the rat pineal gland leads to an increase in the cyclic AMP response to norepinephrine within three weeks (Weiss and Costa, 1967). Pineal denervation has been shown to also induce supersensitivity in the postsynaptic beta adrenergic receptor site on the pineal cell to catecholamines. Elevation of adenosine cyclic 3', 5' monophosphate was also seen in response to denervation and this resulted in the superinduction of N-acetyl-transferase in the p i neal gland (Deguchi and Axelrod, 1973). The responsiveness of the pineal beta adrenergic receptor has been found to cha nge sensitivity, in response to diurnal changes (Rom~ro and _.<\xelrod, l974). An increase in the cyclic AMP response to norepinephrine has been found to occur· in the hypothalamus, cerebrum and brainstem of rats treated seven days beforehand with 6-hydroxy-dopamine (Palmer,l972). Prior to destruction of the dopamin~rgic innervation in the striqtum by 6-hydroxydopamine or chronic inhibition of dopamine synthesis by alpha-methyl-para-tyrosine fails to alter dopamine stimulated cyclic AMP formation.
These results indicate that dopamine sensitive adenyl c·yclase does not ap~ear to increase during dopaminergic denervation supersensitivity (Von Voigtlander et al.,l97J).
A model proposed for physical dependence and associated tolerance is what Emmlin (l961) called the supersensi--tivity 0£ pharmacological denervation.
According to the disuse theory of physical dependence, presence of the drug entity is only indirectly responsible for the development of dependence; the direct or proximal cause is depression of nervous activity for long periods of time (Sharpless, 1969).
Withdrawal phenomena generally seem to represent rebound effects, opposite in character to those produced by the drug itself, as if depressed pathways· become hyperexcitable during withdrawal and stimulated pathways become -depressed (Sharple~s, 1969). Sharpless and Halpern (1962) suggest that supersensitivity of receptors might underly the convulsions resulting from withdrawal of barbituates after the induction of physical dependence. It has also been suggested to account for physical dependence and tolerance towards morphine (Jaffee, 1965;Collier, 1966). The effectiveness of apomorphine and amphetamine in enhancing morphine withdrawal aggression when given in otherwise ineffective doses has led Lal and co-workers to suggest receptor supersensitivi ty during narcotic dependence (Lal et al., 1971;Lal and Puri, 1972;Puri and . Lal, l97J).

3) Evidence for Regeneration Axon Sprouting of Central Catecholamine Neurons
For many years a general conclusion of neurohistological investigators was that adult manunal cerebral nerve fibers show only feeble and abortive regenerative growth when sev~red (Cajal, 1928;Clark, l94J).
ported sprouting from cut central Thus, many have reaxons, but this process soon terminated and the newly formed axons sprouts were described as degenerating within a few weeks.
There is now d a ta to suggest the brain may be capable of some plastic modifications in response to deafferenting lesions; there is now evidence for more persistent a nd functional regeneration.
It is well known that upon severing or traumatizing a monoamine nerve axon or an axon collateral, the transmitter accumulates within the axon itself (Dahlstrom and · Fuxe, 1964;. In fact, it is this phenomenon that has permitted the mapping out of catecholamine-containing fibers tracts in the central nervous system. The intraaxonal catecholamines accumulate very rapidly after the injury and remain approximately twelve days after which they gradually disappear . During the seventh to nineteenth days after electrolytic lesions in the mesencephalon of the r~t a type of densely packed, delicate, fl .uorescent, vancose fiber become visible in the vicinity of the axonal accumulations ).
This increase is ascribed to _regeneratio:h or sprouting of catecholamine fibe~s ~t the border of the l~sion.  . Reinnervation of the distal part of the spinal cord by new noradrenergic fibers following 6-hydroxydopamine denervation has been shown (Nygren et al., 1971). Reinnervation was attributed to resrilt from outgrowth of axotomized fibers, but growth in the form of collaterals . sprouting from a few possibly surviving fibers in the distal region may be invalved. A normal pattern of innervation was seen within one to two months after denervation (Nygren et al., 1971).
After a unilateral entorhinal lesion (a major extrin-sic afferent to the hippocampal formation), a new fiber projection from the remaining contralateral entorhinial cortex grows to reinnervate the dentate gyrus.  (1960). Another case of significant neuronal regeneration has been reported in the hypothalamohypophys ial tract after pituitary stalk transection in the ferret (1968). Lesioned central catecholamine neurons in the rostral mesencephalon show a considerable capac~ty for growth into smooth muscle transplants and into and along the walls of cerebral blood vessels ).

E. Morphine and Brain Dopamine
The relationship between neurotransmitters in the brain and the pharmacological activity of narcotic analgesics has received considerable attention in the last several years. dopamine is seen to correspond to analgesia produced by morphine (Takagi et al., 1966). The acute adininistration of morphine has been shown by others to cause a similar decrease of brain dopamine as well as norepinephrine in mice (Reis et al., 1969;Rethy et al., 1971.). In rats, there was no difference in the brain dopamine levels one hour after an acute dose of morphine (Gunne et al., 1969;Wantanabe et al., 1969;Johnson and Clouet, 1973;Puri et al., 1973}.  C-catecholamine was seen in the whol.e brain of mice after JO mg/kg or 100 Iµg/kg of morphine (Smith~ al., 1970(Smith~ al., , 1972 shown to occur to this effect of morphine (Smith~ al., 1972). Clouet and Ratner (1970) (Gauchy et al., 1973). These results indicate that morphine stimulated dopamine synthesis.
Increased release of newly synthesized JH-dopamine was also seen which was evidenced by a greater accwnulation of JHdopamine in incubating mediwn of slices of morphine pretreated rats (Gauchy ~al., 1973). Similar results of increase in the synthesis of dopamine and reversal by naloxone were also observed by Loh et al. (1973).
Another pharmacological approach to study catecholamine turnover is the use of a catecholamine synthesis in-3,7 hibitor, alpha-methyl-para-tyrosine. Acute administration of morphine has been found to cause an accelerated depletion of brain dopamine after catecholamine synthesis inhibi"tion~ This effect is interpreted as an increased activity within the ascending dopamine neuron system (Gunne et al., 1969).
Similarly, Puri et al . (1973) · have sho·wn °a faster depletion of striatal dopamine by morphine in methyl-para-tyrosine treated rats, suggesting an increased dopamine turnover. Kuschinsky (1973) has also shown morphine to significantly increase the depleting effect of methyl-para-tyrosine.
In rats, the catalepsy induced by analgesic doses of morphine has been shown to parallel a dose-dependent increase in the concentrations of homovanillic acid, a dopamine metabolite, in the striatum (Kuschinsky t l al., 1972and Ahtee et al., 1973. In the who le mouse brain Fukui and Tukagi ·(1972) have found a significant rise in the dopamine metabolites, homovanillic. acid and J,4-dihydroxyphenyl acetic acid, with analgesic doses of morphine.
This increase in homovanillic acid is explained by an increased dopamine turnover, thus a rise in dopamine utilization in the striata (Kuschinsky, 1973 andKuschinsky et al. , 1974). The catalepsy and the ri$e in striatal homoyanillic acid concentrations produced by morphine were inhibited by naloxone   Subanalgetic levels of morphine have been shown to produce mixed inhibitions of dopamine transport into slices from the mouse brain cortex and uncompetitive inhibition in the diencephalon. Increased concentrations of morphine produced a greater effect on dopamine affinity rather than reaction velocity which was observed in the cortex although inhibition remained mixed.
Morphine did not modify the activity of tyrosine hydroxylase in brain homogenates.
In vivo experiments show a significant increase in brain tyrosine hydroxylase activity after morphine. The authors suggest that an acceleration of dopamine biosynthesis may be due to the activation of feedback mechanism in vivo.
----Furthermore, a significant increase in the specific activity of brain tyrosine was observed after morphine, by other investigators and they also found this effect was blocked by the morphine antagonist, naloxone .

2) Effects of Chronic Morphine
Gunne (1963) noted no change in dopamine content in the telencephalon of dogs treated daily for seventy to nine~ ty days with increasing doses of morphine up to 120 mg/kg~ Dopamine was also found unchanged in various brain regions of the morphine dependent monkey (Segal~ al., 1962;Segal. -et al., 1972). During chronic administration of morphine its effect on brain dopamine disappear~d and the impulse flow became . normal within ascending dopamine neurons system (Gunne et al., 1969). ---In rats, there was a slight increase in the brain levels_ of dopamine after chronic administration _ of morphine (Sloan et al., 1963;Johnson and Clouet, 1973).
The increase in brain dopamine concentrations was suggested to be attributed to the increase in the syni;besis of dopamine after chronic administration of morphine (Clouet and Ratner, 1970;Johnson and Clouet, 1973). The incr-ease in dopamine synthesis was suggested to be associated with the increase in tyrosine hydroxylase activityafter chronic mor-· phine (Reis~ al., 1970). Contrary to these findings Smith et ~· (1972)  is interesting to note that the excretion of dopamine was reported to be increased in rats (Sloan and Eisen.men, 1968) and male human volunteers (Weil-Malberbe ~al., 1965) ·during the addiction phase.

3) Effect of Morphine Withdrawal
Gunne (1963) reported that brain dopamine was decreased seventy-two hours after morphine withdrawal. At this period dogs exhibited moderate to severe abstinence. Maynert and Klingman (1962) observed similar findings during withdrawa l in dogs and rabbits but observed no change in brain dopamine on rats during withdrawal from morphine. Abrupt withdrawal has been shown to reduce activity in the brain dopamine neu-

rons.
Histochemical results showed that methyl-para-tyrosine did not cause any effect within the dopamine or noradrenergic neurons that could be distingui.shed from the effect of synthesis inhibition alone. Nalorphine-injuced abstinence caused increased activity within the noradrenaline neuron system in practically all parts of the brain (Gunne et al., 1969). Contrary to this study a transient increase in dopamine levels was reported in rats and mice after naloxone induced withdrawa l (Iwamoto~ al., 1973), which is suggested to be responsible for the stereotyped jumping in mice and rats during withdrawal. In rats, brain dopamine and norepinephrine levels decreased during withdrawal from morphine when compared with chronic morphine levels (Sloan et al., 1973). The striatal dopamine turnover in morphine dependent animals was shown not to differ from the turnover in non-dependent animals when measured one, twenty-four and seventy-two hours after the last morphine injection (Puri, 1973). Also, dopamine levels were 4'.3 replenished at a more rapid rate during morphine withdrawal after the administration of reserpine (Gunne et al., 1970).
The urinary excretion of dopamine in rats was increased during withdrawal with peaks occurring on the third and eighth day (Sloan and Eiseman, 1968). In humans, however, ·the urinary excretion of dopamine was found to be decreased during the withdrawal phase (Weil-Malherbe .£.!_al.,

1965).
Upon withdrawal from morphine, aggregation of the dependent rats elicited intense aggression. Pretreatment of the withdrawn rats with L-dopa, amphetamine or apomorphine before aggregation enhanced the aggressive response~ severalfold.
Haloperidol, a dopaminergic blocking agent, blocked the aggressive behavior (Lal et al., 1971;Puri et al., 1971;Lal and Puri, 1972;Puri and Lal, 1973;Gianutsos et al., 1974). These data are interpreted to suggest a dopaminergic basis ()f morphine withdrawal aggression and the development of a latent supersensitivity of dopaminergic neuropathways during morphine dependence.

F. Apomorphine and Brain Dopamine
In both the central nervous system and in the periphery, apomorphine is believed to stimulate the dopaminergic receptors (Anden et al., 1967;Ernst, 1967). Biochemical studies have shown that apomorphine decreases the turnover rate of striatal dopamine.
Similarly, there was a decrease in the rate of form~tion of homovanillic acid {Roos, 1965{Roos, , 1969Lahti et al., 1972). The administration of apornorphine can also result in the decreased accumulation of dopa after the administration of NSD 1025 (Koe, 1973). The biochemical changes of brain dopamine produced by apomorphine were completely blocked by haloperidol (Anden et al., 1967;Persson, 1970;Anden and Bedard, 1971 Fuxe and ' Ungerstedt, 1969).
produce hypothemia in mice.

Apomorphine has been shown to
This hypothemic effect is antagonized by haloperidol and pimozide, indicating that dopaminergic mechanisms are involved in temperature control {Fuxe and Sjoqrist, 1972). In a number of rats apomorphine consistently facilitated sel f -st imulation but inhibited this behavior in others {Broekkamp and van Rossum, 1974).
These results indicate that apornorphine is able to replace the reinforcing action of intracranial rewarding stimulation.

G. Neuroanatomical Pathways Related to Morphine Dependence and Abstinence
Physical dependence on morphine is characterized by the appearance of abstinence signs when morphine intake is abruptly terminated or when an opioid antagonist is admin- The caudate nuclei has also been implicated as important in mediating the altered reaction to pain induced by morphine (Glick, 1974). Bilateral lesions of the caudate nuclei were shown to produce a persistent potentiation if the effect of morphine on ~scape luten_cies (Glick, 1974). These studies indicate that although the opioid molecule may act on a common biochemical element in different tissues, the amount and the coupling of the biochemical element of specific tissue functions determine the specificity of opioid actions.
The central sites related to physical dependence have been studied by localized manipulations of brain tissue.
Wikler (1948,1952) reported that removal of the cortex in dogs did not attenuate the abstinence syndrome but that spinal cord sections interfered with some withdrawal signs.
This work has been confirmed by the demonstration that morphine dependence has a supraspinal and spinal component (Martin and Eades, 1964). It has been reported that bilateral rostral cingulomotomy markedly attenuates abstinence phenomena after withdrawal of morphine in monkeys and a variety of opioid analgesis in patients with intractable pain. Foltz et al., 1957;Wilker (1972)  .. (Kerr and Pozuelo, 1971}. Subsequent studies carried out in monkeys showed that lesions of the hypothalamus, amygd a la and septal nuclei, even if the tolerance for morphine and severity of the withdrawal had been modified the lesion had little or no effect on the craving for morphine, as the animals continued self-injected approximately the same amount of' morphine sulfate as they did before receiving their lesion (Kerr and Pozuelo, 1971). Lesions placed sterotaxically in monkeys in the organs of the nigro-striatal system and the nucleus tegementi ventralis, known to be mainly dopaminergic pathways, · abolish craving for marphine and the phenomena of withdrawal, as evidneced, respectively, by lack of bar pressing and by absence of the manifestations of withdrawal (Pozuelo and Kerr, 1972).
Further evidence for the involvement of dopamine pathways in morphine abstinence has been shown by Gianutsos et al. (1973, l974b). They have found that electrolytic lesioning abolished the morphine withdrawal aggression in thirty day abstinent rats while lesioning of the medial forebrain bundle was ineffective in blocking the aggression (Gianutsos et al., 1973, l974b).
A central component to morphine dependence has been suggested by the studies by Eidelberg and Barstow (1971) in the monkey and by Wantanabe (1971) in the rat showing that dependence on morphine can be induced by chronic intracranial applications of chronic intracranial applic a tions of mor-

phine.
These investigations also demonstrated that withdrawal could be precipitated by administration of opioid antagonist into the ventricular fluids. Herz et al. (1972) reported that withdrawal signs were elicited in the morphine dependent rabbits after administration of nalorphine into the fourth ventricle. Wei et al. (1972Wei et al. ( , 1973 have found that meidal thalamus and areas in the diencephalic~mesen cephalic junction are more sensitive than neocortical, hippocampal, striatal, hypothalamic and mesencephalic structures to naloxone precipitated withdrawal. Their investigation indicates that the medial thalamus and rostral mesencphalic structures are involved in precipitated abstinence behaviors -n e oc ort ical, hippocampal, hypothalamic, s_tria tal and tegmental are a s of the brain are relatively insensitive to naloxone precipitated withdrawal. The regional application of naloxone to the brain to precipitate abstinence signs indicates that the site of adaptation to morphine has neuroanatomical specificity.
Wei concluded from these results that medial thalamic nuclei and closely adjacent structures may be the primary sites for the development of opioid dependence.
The medial thalamus is also believed to play a role in tolerance.
Morphine sulfate administration results in d~astic alterations in brain bioelectrical activity.
After repeated drug administrations EEG effects disappear (Teitelbaum et al., 1974). An intense morphine response was seen after the administration of a single dose of morphine to tolerant rats with lesions of the medial thalamus. Despite extensive damage to the medial and lateral habernular nuclei, the faciculus retroflexus, and dentate gyous, naloxone still reversed the effect of morphine (Teitelbaum et al., 1974). It appears that medial thalamic lesions have little effect on precipitated withdrawal while they have a drastic effect on sensitivity to morphine in tolerant rats.
Recently the occurrence of opioid receptor binding has been reported -its localization in the nervous tissue (Pert and Snyder, 1973). Their studies of the tissue distribution provide evidence for the locus of the pharmacologications of opioids.
curred in the brain.
The greatest amount · of binding oc-Within the brain the opioid receptor binding revealed the greatest amount of binding in the corpus striatum where binding exceeded that of the cerebral cortex more than fourfold.
Of the known neurotransmitters only dopamine and acetycholine are found in high concentrate in the corpus striatum.
Other areas to show binding were the midbrain cortex, brainstem, and the cerebellum, in that order.
Several studies have taken the approach of lesioning discrete brain areas and then administering chronic morphine; upon the termination of morphine withdrawl symptoms are recorded. It has been found that rats with bilateral lesions in the anterior cingulate cortex show less opiate directed behavior following passive morphine injections Marques 1971, 1974). Less withdrawal induced weight loss is seen in rats with posterior medial forebrain bundle lesions. These lesioned rats conslime morphine solution much more readily than controls (Glicks and Charap, l97J Recently it was found that a strongly reducing congener of serotonin, synthesized by Schlossburger and Kuck (1960), 5,6-dihydroxytryptamine (5,6-DHT) induces a selective chemical destruction of brain 5-HT nerve terminal (Baum-garten~ al., 1971) thus reducing brain serotonin contents.
The antinociceptive effect of morphine is not significantly changed by 5,6-DHT pretreatment (Blasing, l97J). The intracerebral administration of 5,6-DH'T in the mouse inhibited the development of tolerance to and physical dependE-nce on morphine induced by morphine pellet implantation (Ho et al., 1972).

2) 6-Hydroxydopamine
Intraventricular administration of 6-hydroxydopamine (6-0HDA) markedl y reduces brain catecholamines (Bloom ~ al., 1969). Morphine administration one week following intraventricular administration of 6-0HDA has been found to increase morphine induced analgesia when measured by the tail-flick response. 'Die bilateral administration of 6-0HDA into the medial hypothalamic areas at the level of the ventricular or t he dorsomedial hypothalamic nuclei also markedly augmented morphine's effect on the tail-flick latency.
In addition to these neuroanatomical structures, when 6-0HDA was injected into the medial forebrain bundle morphine effec t on the tail-flick latency was enhanced.
This data would seem to indicate that 6-0HDA induced depletion of norepinephrine in the hypothalamus potentiates morphine analgesia whereas depletion of dopamine in the caudate nucleus _decreases morphine analgesia.
The involvement of brain dopamine in the morphine antinociceptive effect has also been shown in other studies.
Rats treated intracisternally at two week~ o1 age with 6-0HDA which depleted both brain norepinephrine and dopamine showed antagonism of morphine antinociception six weeks later when measured by the hot-·plate and tail-flick tests.
Preferential depletion of brain dopamine by desinethylimipramine and 6-0HDA in these rats produced greater antagonism of morphine antinociception in the tail-fl.ick test and complete antagonism in the hot-plate test (Elchisak et al., 1973 ) . A reduced analgesic response to morphine has been found in both tolerant and nontolerant mice after the intracerebral administration of 6-0HDA without modifying the · brain uptake of morphine (Friedler et al., 1972). A decrease in sensitivity to morphine has also been reported for tolerant and nontolerant rats following pretreatment by 6-0HDA (Bhargava ~al., 197J).
The morphine dependent state has also been found to be altered by 6-0HDA. Precipitated abstinence, measured by naloxone indu~ed withdrawal jumping in mice was enhanced by 6-0HDA pretreatment; weight loss after abrupt withdrawal was also increased by 6-0HDA (Friedler et al., 1972). Intraventricular injection of 6-0HDA has been found to exacerbate morphine withdrawal in the rat (Bhargava et al., 1973).
The intraventricuJ_ar administration of 6 -0HDA caused a marked depletion of brain-norepinephrine in saline treated rats and in rats treated either chronically or with a single dose of morphine. The increase in brain dopamine seen twenty-four hours after the administration of 6-0HDA to control rats ·was not observed when 6-0HDA was administered to rats previously treated with morphine -a decrease in brain dopamine was observed in these rats. One week after treatmeni, with 6-0HDA both brain noradrenaline and morphine con-cen~rations markedly decreased. While chronic morphine treatment with morphine caused no significant effect on the depletion of brain norepinephrine after 6-0HDA, chronic treatment with morphine did inhibit the depletion of brain dopamine (Nakamura e t al., 1972). These results are interpreted to suggest that chronic treatment with morphine may induce changes in the uptake process of the nigrostriatal system.

A. Animals
Male hooded rats of the Long-Evans strain, r~ndom-bred, weighing 250-400 grams were obtained from Charles River  In the investigation of recovery from nigro-striatal lesions, haloperidol, morphine sulfate and alpha-methylpara-tyrosine were administered intraperitoneally twice a day for a three or six day period with the last injection being given 24 hours prior to surgery.

E. Measurement of Withdrawal Symptoms
Abstinence symptoms were measured after the aburpt termination of chronic morphine administration and the lesioning of various brain regions. Symptoms were measured once every 24 hours for the first 72 hours after the withdrawal of morphine and/or brain lesioning. In addition to these initial observations the occurrence of withdrawal symptoms in brain lesioned subjects was measured three weeks following the pro- In those experiments where the lesion was directed at the medial forebrain bundle microscopic examination showed the damage to be localized to this area. In some cases some slight damage to the immediately adjacent nigro-striatal fibers cannot be ruled out.

2) Neurochemical Effects of the Lesion
In order to further confirm the site of the lesion to the nigro-striatal dopamine neuron system the dopamine concentration in the corpus striatum was determined spectrofluorometrically following either a lmA 15 second or 2mA JO second brain lesion.
To evaluate dopamine levels after nigro-striatal lesioning the animals were starved for 18-24 hours prior to being sacrificed by decapitation. The brains were rapidly removed from the cranium and the two cerebral hemispheres These changes in dopamine levels are shown in Figure 4. The results achieved here correspond well with those of other i nvestigators (Faull et al., 1969;Anden, e .t al., 1972;Agid et al., 1974).

G. Statistical Analysis
An analysis of variance for repeated measures was used to test for significant differences between treated and control conditions in the nigro-striatal lesion induced weight loss experiments.
The two-tailed Student's ' t ' test for independent means was used to test for the differences between the means of -lesioned and non-lesioned groups in the morphine withdrawal experiments. The level of significance was chosen to be p L0.05 for rejection of the null hypothesis.
The results obtained from the effect of drugs pretreatment on survival after extensive ni-g ro-striatal lesions was analyzed by the Chi-Square test.

FIGURE l. Typical Cross Section of Rat Brain Showing
Nig~o-Striatal Ue~tru6tion.  (Morgane, 1961;Gold, 1961;Grossman and Grossman, 1971;Wampler, 1971). These critical areas include portions of the globus pallidus, the medial portion of the internal capsule, and a small portion of the lateral hypothalamus area adjacent to the internal capsule. Several fiber systems pass through these areas and are known to regulate the content of norepinephrine, dopamine and serotonin in the telencephalon. One such fiber system, the nigro-striatal bundle (NSB), regulates the dopamine content of the neostriatum (the caudate and putamen). Nigrofugal fibers · pass through areas described as critical for producing the LR .syndrome. Rats sutaining a complete electrolytic (Oltsman and Harvey, 1972) lesion of the NSB or chemic a l lesion (Ungerstedt, 1970(Ungerstedt, , 1971) of the NSB show a severe aphagia and adipsia resulting in death, unless the animals are force-fed.
When animals that have received lateral hypothalamus lesions are force-fed they gradually recover from their feeding deficits (Teitelbaum and Epstein, 1962). The basis of recovery after lateral hypothalamic lesioning is not known des:")ite much investigation. A denervation supersensitivity model may be useful in explaining recovery (Sharpless,1 964 ).
If a supersensitivity phenomenon were the factor responsible for the recovery of food regulating behavior, then certain results could be predicted; namely, neurons which were made supersensitive at some time prior to destruction of the NSB could then be expected to facilitate recovery.
Administration of alpha-methyl-para-tyrosine (MPT), a known blocker of catecholamine synthesis (Nagatsu et al., 1964) will produce a partial denervation of catecholamine pathways (Tarsy and Baldessarini, 1973). Recent research has shown that pret reatment with MPT before lesioning of the lateral hypothalamus facilitates recovery from the syndrome (Glick et al., 1972). However, MPT blocks the synthesis of all the catecholamines, and further, the lesion used by Glick et al. (1972)  was given 24 hours before surgery.

The last injection
Throughout the experiment the rats were house:l individually and given free a ccess to dry food and water. Force feeding was not attempted. Body weights were taken daily during both pre-and post-lesion periods. The occurrence of a death in either the experimental or contr~l groups was recorded.
A represent ative group of surviving rats were sacrificed 16 days after the production of the lesion and the lesion si . te determined by histological procedures as described in Chapter III.

C. · Results
Those animals receiving partial (lmA 1.5 sec ) nigrostriatal lesions continued to lose body weight until the fifth post-operative day as can be seen from Table 1.
Analysis of variance for repeated measures (Winer, 1962) showed that tho~e groups pretreated with alpha-methyl-para-tyrosine or haloperidol lost significantly (p L 0.05) less body weight than did saline controls. The extent of total weight loss was diminished in these drug treated animals as evidenced by their higher percentage body weights as compared to saline treated controls. These re3ults are shown in Figure 4. The saline treated controls showed a greater loss in gram of body weight indicating that the drug treated group began to recover earlier.
These results are SLurunarized in Figure 5.
When a current of 2mA for a JO second duration was employed to make a more extensive lesion of the nigro-striatal tract the resulting aphagia and adipsia produced death in all saline treated controls. These results are shown in Table 2. All of the rats in the control group died within two weeks of the lesion, -nearly half of them in less than eight days. Percentage body weight changes were similar for both treated and control groups for the first six postlesion days as can be seen in Figure 6. From the 9th to the 14th post-operative day, the saline treated rats showed a greater loss in grams of body weight than did the groups 1.
Weights are expressed as means and standard errors of percent weight relative to preoperative weight. Number of subjects per condition is indicated in parentheses.

2.
Each subject was lesioned bilaterally using 1 mA for 15 sec.
An analysis of variance for repeated measures 14 comparing the haloperidol and control conditions on days 2 through 7 indicated a significance (F=7.6, p L.05 for df = 1, 14).
..... l. Weights are expressed as means and standard errors of percent weight relative to preoperative weight. Number of subjects per condition is indicated in parentheses.
2. Each subject was lesioned bilaterally using 2 mA for JO sec.
J. 60 mg/kg/day of morphine sulfate was given i.p. for 6 days.
A significantly greater number of rats pretreated with morphine or haloperidol were still alive on the 15th postoperative day when compared to saline treated controls (morphine vs saline p L 0. 001 and haloperidol vs saline p L o. Ol by the Chi-Square test). These data are shown in Figure 8.

D. Discussion
Tne extent of weight loss in the lesioned animals was dependent upon the amount of nigro-striatal damage. These results support previous suggestions (Oltsman and Harvey, 1972;Ungerstedt, 1970Ungerstedt, , 1971) that the destruction of the riigro-striatal pathway is critical fcir the production of the lateral hypothalamic syndrome. Facilitations of recovery f'rom the syndrome produced by large lateral hypothalamic lesions has previously been demonstrated with methyl-paratyrosine treatment (Glick et al., 1972), and the present results show an analogous effect of methyl-para-tyrosine on recovery from nigro-striatal damage of a less extensive area. Recovery was also facilitated by pretreatment with haloperidol. Lethality from massive nigro-striatal damage was reduced if subjects were treated with haloperidol" or morphine for a six-day period prior to surgery.
A definite mechanism underlying recovery from the destruction of the nigro-striatal pathway cannot as yet be  (Cannon and Rosenbleuth, 1949;Stovraky, 1961;Glick et al., 1972); s~condly the re g enera tive sprouting from transected axons (Katzman e t a l., 1971; Nygren e t al., 1971); third and lastly is an increase in catecholamine turnover in surviving neurons (Bloom et al., 1969;Uretsky et al., 1971;Agid et al., l97J). Any or all of these changes are likely to promote recovery. All the drugs found active in promoting recovery have one property in common, that is, they produ.ce dopamine deficiency at receptor sites. Alpha-methyl-paratyrosine is a well-knoi.m i;nhibitor of catecholamine synthesis (Nagatsu et al.; haloperidol blocks dopamine receptors directly (Janssen, 1967;Van Rosswn, 1967;Anden et al., 1970) and morphine blocks dopamine receptors indirectly, possibly through an effect on non-dopaminergic neurons - (Puri et al.,l97J). The other pharmacological effects of the drugs employed in this study are not common to all three drugs.
A drug induced deficiency of receptor activity can cause both an increase in receptor sensitivity as a consequence of pha rmacological denervation (Sharpless, 1964) and stimulate n e uronal feedback mechanism (Fuxe and Ungerstedt,197 0). Chronic treatment with haloperidol (Gianutsos et a l., l974a, 1975), methyl-para-t yrosine (Tarsy and Baldessareni, 1973), and morphine sulfate (Puri and Lal, 1973 ) is known to cause supersensitivity of dopamine receptors in the central nervous system. Both haloperidol and morphine sulfate increase dopamine synthesis in the nigro-striatal system (Janssen, 1967;Gunne et al., 1969;Puri~ al., 1973). The pretreatment with these drugs, that increase neurotransmitter synthesis, could promote the development of a compensatory change in the level of activity of the surviving dopamine containing neurons (Bloom et al., 1969;Uretsky et al., 1971;Agid et al., 1973).  (Puri et al., 1971;Lal and Puri, 1972;Puri and Lal, 1973). Haloperidol, a drug with some specificity for blocking dopamine receptors (Janssen 1967;Von Rossum, 1967;Anden et al., 1970) has been reported -to reduce morphine withdrawal syndrome in animals and humans (Lal et al., 1971;Kark alas and Lal, 1972). Haloperidol also reduces the self a dministration of morphine in addicted rats (Hanson and Cimine-Venema, 1972) and monkeys (Pozuelo and Kerr, 1972). Lesions placed stereotaxically in monkeys in the origin of the nigro-striatal system and the nucleus tegmenti ventralis, known to be mainly dopaminergic pathways, abolish craving for morphine and the phenomena of withdrawal, as evidenced, respectively by lack of bar pressing and by lack of withdrawal manifestations (Pozuelo and Kerr, 1972). Further evidence for the involvement of dopamine pathways in morphine abstinence has been shown by Gianutsos et al. (1973Gianutsos et al. ( ,1974. They have found that electrolytic lesioning of the nigro-striatal bundle abolished morphine withdrawal aggression in thirty-day abstinent rats while lesioning of the medial forebrain bundle was ineffective in blocking the aggression (Gianutsos et al., 1973(Gianutsos et al., , 1974b. Further evidence for the interaction between brain dopamine and morphine comes from biochemical studies. Acute morphine elevates brain homovanillic and 3-4 dihydrophenylacetic acid (: Fukui and Tugaki, 1972;Kuschinsky and Hornykiewicz, 1972), increase the synthesis of labeled dopamine from labeled tyrosine in the brain (Clouet and Ratner, 1970;Fukui et al., 1972;Smith et al., 1970Smith et al., , 1972 and accelerates the disappearance of dopamine after the administration of .alpha-methyl-para-tyrosine (Gunne ~al., 1969;Puri et al., 1973). These observations strongly suggest the involvement of dopaminergic pathways in morphine action and dependence.
In order to understand the role of the nigro-striatal dopaminergic pathways in morphine dependence, this study in- In order to determine if the results were specific for the dopaminergic system the medial fore brain bundle, a noradrenergic and serotonergic neuron system, was also lesioned after the production of dependence and abstinence signs observed. It was hypothesized that nigro-striatal lesions would modify the withdrawal symptoms that involved dopaminergic mechanisms.

B. Method
Male hooded rats were housed in individual cages during the addiction and withdrawal phases of these experiments.
Brain lesions were made under anesthesia either prior to or following the production of dependence. At the completion of each experiment a representative group of animals were sacrificed for histological localization of the lesion site.
Rats were made dependent upon morphine by injecting them intraperitoneally with systematically increasing doses 8() of morphine sulfate three times a day. The starting dose of 15 mg/kg/injection was increased by 15 mg/kg every day until a dose of 405 mg/kg was reached.
In those rats who received a terminal dose of 200 mg/ kg orily two injections a day were given twelve hours apart.
The starting dose of 10 mg/kg/injection was increased by 10 mg/kg every day until a dose of 200 mg/kg was reached. They were maintained at this dose for at least five days after which no morphip.e was injected.
Abstinence symptoms were measured after the abrupt termination of chronic morphine admi ni stration. Symptoms were measured once every 24 hours for the first 72 hours after morphine withdrawal. The rats were removed from their home cages and placed individually into novel cages. Symptoms were measured for JO minutes; prior to observation rats were weighed and then rectal temperature taken. The abnormal behavior noted during the observation period consisted of wet shakes, writhing, ptosis and piloerection. Aggression in response to social grouping was measured seventy-two hours after the last morphine sulfate injection. A more detailed description of these procedures can be found in Chapter III.  9.

1) Modification of' Narcotic Withdrawal
10. All data are expressed in terms of means and standard errors unless otherwise indicated.
The number of animals employed in each group is indicated as the denominator of the fraction used to express the occurrence of piloerection.
Ptosis time is expressed in seconds, weight loss in grams and hypothermia in degrees centigrade.  withdrawal showed a reduction in rearing and vocalization in the lesion addicted groups.

4.
These results are shown in Table   The  Increased hypothermia was observed in rats withdrawn from 405 mg/kg/day but this increase failed to achieve significance.
These results are summarized in Table J. b. Lesions made after the production of morphine dependence. ' lesion effect was observed for wet shakes and writhing in non-addicted rats.
Weight loss was also seen in non-addieted lesioned rats. These results are summarized in Table   5. Seventy-two hour morphine withdrawal aggression was apparently increased by the lesion, as showTI in Table 4.

5.
Significantly different from non-lesioned controls based on Student's It I test ( p .L 0. 001 ) • 6. All data are expressed in terms of means and standard errors unless otherwise indicated.
The number of animals employed in each group is indicated as the denominator of the fraction used to express the occurrence of piloerection~ Ptosis time is expressed in seconds, weight loss in grams and hypothermia in degrees centigrade • These data are shown in Table 5. · The lesioned groups showed significantly less 72 hour morphine withdrawal aggression. These data are given in Table 4 .

2.
Effect of large nigro-striatal lesions Weight loss was also seen in non-addicted lesioned rats.
These results are summarized in Table 6. Morphine withdrawal aggression was decreased by the lesion as shown in Table   4.
A similar lesion effect was seen in rats dependent up -

7.
All data are expressed in terms of means and standard errors unless otherwise indicated. The nwnber of animals employed in each group is indicated as the denominator of the fraction used to express the occurrence of piloerection. Ptosis time is expressed in seconds, weight loss in grams and hypothermia in degrees centigrade.
l02 after being injected with apomorphine, re-observed. The results for this experiment are given in  Table   5.) The effect of an injection of apomorphine (l.25 mg/kg) on the withdrawal syndrome in rats with nigro-striatal lesion made after the terminal dose of morphine is shown in

2.
Rats were dependent upon 405 mg/kg/day of morphine sulfate, injections were given three times a day.

J.
Significantly different from pre-drug based on Paired 't' test (p Lo.05).

5.
All data are expressed in terms of means and standard errors unless otherwise indicated.
The number of animals employed in each group is indicated as the denominator of the fractions used to express the occurrence of piloerection.
Ptosis time is expressed in seconds, weight loss in grams and hypothermia in degrees centigrade.  J. Rats were dependent upon 405 mg /kg/day of morphine sulfate, injections were given twice a day.

5.
All data are expressed in terms of means and standard errors unless otherwise indica.ted. The number of animals employed in each group is indicated as the denominator of the fractions used to express the occurrence of pilo e rection.
Ptosis time is expressed in seconds , weight loss in grams and hypothermia in degrees centigrade.
f-' 0 +-1. Effect of small medial fore brain bundle lesions Withdrawal symptoms were found to be modified by small (lmA 15 sec ) medial fore brain bundle lesion when they were made after the terminal dose of morphine; these results are shown in Table 10.
The Student's ' t ' test was used to analyze the difference between the mean of the lesioned groups and that of the non-lesioned addicted con- The lesion by itself produced ptosis and weight loss in non-addicted rats. Medial fore brain bundle lesions were found to decrease soci~l aggression seen at 72 hours of withdrawal; these results are shown in Table 4.

2.
Effect of large medial fore brain bundle lesions The effect of large (2mA JO sec ) medial fore brain bundle lesion on morphine withdrawal are shown in  Ptosis and weight loss resulted from lesioning non-addicted rats.
Morphine withdrawal a g gression was decreased by these _large medial fore brain bundle.
ized in Table 4.
These results are sununarb. Small lesions made during the withdrawal period The effects of small (lmA 15 sec ) medial fore bra in bundle lesions made at 48 hours on narcotic withdrawal symptoms at 72 hours are sununarized in Table 11. Statistical significance was determined by the Student's ' t ' test.
Ptbsis time, weight loss and hypothermia were found to significantly (p Lo.01) increase in medial fore bra in bundle lesioned rats as compared to non-lesioned addi c ted controls.

D. Discussion
The results from these experiments sugg e s t a role for dopaminergic nigro-stria tal fibers in mori:,hine ivi thdrawal .
Nigro-striatal lesioning prior to the production of mor-  1. lmA 15 sec medial fore brain bundle lesions.

2.
Twenty-four hours after medial fore bra in bundle lesioning.
J. Seventy-two hours after the last injecti on of morphine sulf'ate, 135 mg/kg.

4.
Seventy-two hours after the last injection of morphine sulfate, 135 mg/kg, and twenty-four hours after the production of the lesion.

5.
Significantly different from non-lesioned addic ted controls by the Student's It I test (p L 0,02).

6.
Significantly different from non-lesioned addicted controls by the Student's It I test (p L0 .01).
7. All data are expressed in terms of means and standard errors unless otherwise indicated.
The numb er of animals employed in e2ch group is indicated as the denominator of the fractions used to express the occurrence of piloerection.
Ptosis time is expressed in seconds, weight loss in grams and hypothermi a in degrees centigrade.
withdrawal period, 48 hours after the terminal dose of morphine, resulted in increased wet shakes,ptosis time and weight loss.
Several mechanisms may possibly underly the enhanced withdrawal symptoms in nigro-striatal lesioned subjects.
An increased denervation supersensitivity, changes in receptor activity and alterations in the balance between several putative neurotransmitters are mechanisms worthy of consideration.
One possible explanation for the enhanced withdrawal symptoms induced by nigro-striatal lesioning can be offered in terms of a denervation supersensitivity • . It is a well recognized phenomenon that after pharmacological or surgical denervation in the peripheral nervous system, the response of the target organ to a transmitter can be greatly augmented.
Analogously, it has been suggested that physical dependence might be a manifestation of a central denervation supersensitivi ty and as a result the withdrawal phenomena would reflect a state of rebound hyperexcitability (Jaffee and Sharpless, 1968). If the withdrawal symptoms that were seen to increase involve dopaminergic pathways, then nigro- The effect of these drugs was interpreted to indicate an antagonism of withdrawal. Herz ~ al., (1974) have shown that the administration of ct-amphetamine, cocaine, L-dopa increased levallophan precipitated withdrawal jwnping and decreased wet shakes. The effect of these drugs was interpreted as a potentiation of withdrawal since similar changes in withdrawal occurred when. withdrawal was precipitated in highly dependent rats (Herz et al., 1974).
Following their logic it would be concluded that nigro-st~iatal lesions reduce narcotic withdrawal. This conclusion does not seem to be justified in view of the fact that rats receiving a terminal dose of 405 mg/kg/day of morphine show a higher occurrence of wet shakes than those dependent upon 200 mg/kg/day of morphine. It has been reported that rats de~endent upon JO or 120 mg/kg/day of morphine show no wet shakes upon withdrawal of the drug (Akera and Brady, 1968). The increase in wet shakes se e n in those rats receiving a higher terminal dof.e of morphine tends to parallel a general increase in other s~nptoms.
Additional support for the role of denervation supersensitivity and receptor activity in the expression of withdrawal symptoms comes from the effect of the lesion by itself. Nigro-striatal lesioning produced some symptoms similar to those of narcotic withdrawal. Lesioned animals showed wet shakes, writhing, piloerec t ion, ptosis and weig;ht loss. The appearance of these withdrawal like symptoms is thought to be due to a decrease impulse flow in the nigro-striatal system and a resultant denervation supersensitivity.
It should be pointed out that the increase in withdrawal symptoms in the animals lesioned after the production of dependence cannot totally be explained in terms of the lesion effect a lone. Lesioning t he nigro-striatal pathway prior to the production of dependence results in llJ increased withdrawal signs when the effect of the lesion alone is virtually non-exist e nt.
Alterations in the balance between several putative neurotransmitters have been reported to occur during morphine withdrawal (Merali ~al., 1974). shown that nigro-striatal fibers are functionally connected with a serotonergic system (Cools~ al., 1974). It is thus possible that the nigro-striatal les i on induced increases in withdrawal symptoms are the result of alterations in serotonergic and dopamine rgic neuronal systems.
The intense morphine withdrawal a ggression observed in response to social g rouping 7 2 hours after the termination of morphine injections was reduced by the production of partial nigro~striatal lesion prior to the production of dependence.
Similarly, when lesions of the nigro-striatal tract were made after the terminal dose of morphine there was a general decrease in the aggressive response of these animals. One notable exception occurred when a small (lmA 15 sec.) lesion was placed in rats dependent upon 200 mg/kg/day morphine after the last injection.
It should be noted that these results are of a preliminary nature and further investigation is needed. These results are thus in agreement with those of Gianutsos ~ ~· (1973Gianutsos ~ ~· ( , 1974b,who have shown that nigro-striatal lesioning blocked morphine withdrawal aggression in thirty-'-day abstine nt rats. It has been previously hy;iothesized that social aggression during acute w. ithdrawal was caused by the hyperactivity of dopaminergic receptors which have become supersensitized during chronic morphine administration (Lal .~~., 1971;Lal and Puri, 1972;Puri and Lal, 1973). The decrease in aggression.appears to result from the degeneration of dopamine neurons produced by the lesion, thus leaving little or no transmitter to be released onto supersensitized receptors.
Destruction of the medial fore brain bundle in morphine dependent rats resulted in increased ptosis, temperature and weight loss. Although wet shakes were seen to increase at both 48 hours and 72 hours, the increase was significant only at 48 hours. Seventy-two hour withdrawal ptosis, weight and temperature loss were significantly increased when lesions were produced during the withdrawal period. Wet shakes were not affected by these 48 hour lesions~-These experiments with the medial fore brain bundle suggest a role for nor-adrenergic and serotonergic mechanisms in narcotic with~ drawal, especially ptosis, weight a n d temperature loss. The involvement of the medi a l fore brain b undle in n a rcotic withdrawal has been previously sug gested (Glick et al., 1973;Herz et al., 1974). It appears that wet shakes are more dependent upon dopaminergic mechanisms, since medial · fore brain bundle lesions were effected in significantly increasing wet shakes at only one time interval. A role for this noradren- These results correspond well with those of other investigators (Faull~ al., 1969;Anden ~al., 1972;Agid et al., 1974).
Lesioning of the nigro-striatal pathway resulted in aphagia and adipsia, indicated by a loss of body weight.
The histological examination of · the lesion site and the de~ crease in corpus striatal dopamine produced by the lesion indicates that the extent of weight loss was dependent upon the amount of nigro-striatal damage. Administration of haloperidol or alpha-methyl-para-tyrosine prior to the production of small (lmA 15 sec) ni gr o-striatal lesions lessened the loss in body weight produced by the lesion.
Lethality and the loss of body weight were reduced in those animals who were pretreated with haloperidol and morphine ll-1 prior to receiving a large (2mA JO sec ) nigro-striatal le- sion.
An increase in receptor sensitivity, regnerative sprouting from transected axons and an increase in catecholamine turnover are several possible mechanisms which may be involved in the recovery of body weight following nigrostriatal lesioning.
Morphine withdrawal wet shakes, ptosis, weight loss and hypothermia were increased when nigro-striatal lesions were made either prior to or following . the production of morphine dependence. Similar changes were observed when the lesion was made during the withdrawal period. Apomorphine effectively induced withdrawal wet shakes in both in~act and nigro-striatal lesioned subjects. Several mechanisms which may be responsible for the enhanced withdrawal symptoms in these lesioned subjects are an increased denervation supersensi tivi ty, changes in receptor activity and alterations in the balance between several putative neurotransmitters.
Noradrenergic mechanism also appears to be involved in the narcotic withdrawal syndrome since destruction of the medial fore brain bundle in morphine dependent rats resulted in increased ptosis, weight loss and hypothermia.
This study suggests a role for nigro-striatal fibers in the regulation of body weight and some of the symptomol- The symptoms of morphine withdrawal were intensified when the nigro-striatal pathway was destroyed prior to or following the production of dependence. Withdrawal wet shakes, ptosis, weight loss and temperature loss were seen to significantly increase. Apomorphine produced a significant decrease in wet shakes in both lesioned and nonlesioned dependent rats. These results suggest that withdrawal wet shakes are dependent upon dopaminergic mechanism. A denervation supersensitivity mechanism, changes in receptor activity and alterations in the balance between several putative neurotransmitters are mechanisms which may be useful in explaining the increased withdrawal phenomena.
The effect of unilateral substantia nigra lesions on apomorphineinduced increases in neostriatal acetylcholine levels.