A neuropharmacological analysis of the pacemakers and conducting tissues of Hydra attenuata

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1. Extracellular recordings from preparations in which sections of endoderm have been removed reveal that rhythmic potentials are conducted by the endoderm while tentacle pulses and contraction burst pulses are still able to be propagated by the ectoderm. 2. Nicotinic agents and the serotonergic inhibitor, methysergide decrease the number of contraction burst pulses/h/animal. Atropine increases them. 3. This effect is due to the reduction of the number of pulses/contraction burst as well as the number of bursts/h for the nicotinic agents. For atropine it is due to an increase in the number of pulses/burst, not in the number of bursts/hour. 4. For methysergide, the decrease in contraction burst pulse activity is due to a significant reduction in the number of contraction bursts/hour. 5. Atropine, curare and TEA cause a marked reduction of CBP amplitude. 6. With one exception nicotinic blocking agents significantly increased the frequency or rhythmic potentials. Atropine appeared to reduce RP frequency. The adrenergic inhibitor, and one of the two serotonergic blocking agents, p-chlorophenyl alanine, significantly increased RP frequency. © 1978 Springer-Verlag.

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Journal of Comparative Physiology □ A