INTRACELLULAR RECORDING AND STIMULATION OF A SINGLE IDENTIFIED NEURON IN AN INTACT PREPARATION OF APLYSIA CALIFORNICA
The activity of neuron R15, located in the abdominal ganglion of Aplysia californica, was studied in a preparation in which the sensory inputs were left intact and the hemolymph was undisturbed. Bursting pacemaker activity (BPA) was studied while exposing the animal to varying concentrations of sea water or varying temperatures. The effect of inhibition of R15 activity was examined by measuring changes in ion and metabolite concentration in the hemolymph. This approach was used to understand the functional significance of R15 activity in the whole animal.^ Bursting pacemaker activity was present in 70% of the cases studied. Substitution of 93% sea water for normal sea water produced a hyperpolarization of R15 which either silenced the cell or significantly increased in interburst interval in 9 out of 12 trials. Excitatory activity from head ganglia acted to antagonize this inhibitory response. Also, 83% and 50% sea water hyperpolarized cell R15. In all cases, this effect was reversible.^ In experiments where R15 was hyperpolarized for 30 minutes, it was found that hemolymph K('+) concentration increased from 11.7 (+OR-) 0.5mM to 13.2 (+OR-) 0.3mM in 2.5 hours after inhibition. Na('+) values were unchanged by hyperpolarization of R15. Ammonia levels also increased 69.6 (+OR-) 16.8% from 0.14 (+OR-) 0.01 to 0.20 (+OR-) 0.03mM. Amino acid analysis revealed a 367% rise in taurine, a 130% rise in lysine, a 75% rise in glutamic acid, and a 120% rise in histidine. All values were obtained by comparisons with controls. These results demonstrate wide-ranging physiological effects from a relatively short period of hyperpolarization in a single neurosecretory cell.^ The temperature sensitivity of BPA in R15 before and after excision of the abdominal ganglion did not reveal evidence for in situ compensation. Differences in BPA occurred at warmer temperatures (12-18(DEGREES)C) where there was suppression of activity in the in situ cell. Cooling of the hemolymph proceeded along an exponential time course with a time constant of 128.2 minutes. After severing the aorta, reexposure of the animal to the same temperature conditions resulted in a cooling rate with a time constant of 50.0 minutes. Although R15's thermosensitivity is present in the whole animal, it is buffered from transient temperature change by a previously undescribed mechanism.^ The results show that BPA is not an artifact of ganglion isolation and that there is a role for R15 in osmoregulation. Lowered environmental temperatures would not be expected to have a significant effect upon BPA in cell R15 because of an unidentified mechanism which buffers hemolymph temperature. ^
GAYNE M BABLANIAN,
"INTRACELLULAR RECORDING AND STIMULATION OF A SINGLE IDENTIFIED NEURON IN AN INTACT PREPARATION OF APLYSIA CALIFORNICA"
Dissertations and Master's Theses (Campus Access).