CNS depressants: effects on post-synaptic pharmacology.

(1) The effects of 5 anesthetics (chloralose, chloroform, ethanol, pentobarbital and urethane) and one anticonvulsant (diphenylhydantoin) were studied on the membrane properties and post-synaptic responses of crustacean neuromuscular junction preparations and molluscan neurons to putative transmitters and peptides. (2) In crustacean preparations pentobarbital selectively depressed, in a dose-dependent, reversible manner, post-synaptic, Na+-dependent, depolarizing responses to the putative transmitter glutamate without altering post-synaptic, Cl(-)-dependent inhibitory responses to the putative transmitter gamma-aminobutyric acid. (3) The effects of all the agents on post-synaptic pharmacology of a molluscan neurosecretory cell were studied either by causing the cell to hyperpolarize to about--100mV through repeated application of acetylcholine (ACh) in a K+-free, Ca++-containing solution or by hyperpolarization through injection of intracellular current in a K+-free solution. Effects of these agents on post-synaptic responses on other molluscan neurons were studied using intracellular current injection to manipulate membrane potential. (4) All of the agents tested selectively depressed the depolarizing Na+-K+-dependent post-synaptic responses of the neurosecretory cell to ACh in a dose-dependent reversible manner without appreciably altering the membrane properties of the cell (over the potential range of the ACh responses). (5) Pentobarbital did not alter the inversion potential of the ACh response. (6) Reciprocal plot analysis of all of the agents tested revealed that the antagonism of the ACh response was primarily non-competitive. (7) None of the agents tested altered hyperpolarizing, K+-dependent responses to dopamine and glutamate on the neurosecretory cell, nor did they affect either the induction or enhancement of BPP activity by the vertebrate peptide vasopressin on this cell.