The cholinergic nature of the cercal nerve‐giant fiber synapse in the sixth abdominal ganglion of the American cockroach, <i>Periplaneta americana</i> (L.)

Abstract

Abstract The effects of cholinergic drugs on transmission at the cercal nervegiant fiber synapse in the desheathed sixth abdominal ganglion of the American cockroach, Periplaneta americana (L.) were evaluated. When due consideration was given to slow diffusion rates of drugs into the ganglion, and to the enzymic hydrolysis of exogenously applied choline esters by endogenous cholinesterase, the synapse was found to respond in ways consistent with cholinergic transmission. Botulinus toxin, magnesium, and hemicholinium‐3, all working presynaptically blocked transmission. Atropine, D ‐tubocurarine, and hexamethonium produced non‐depolarizing blockade at concentrations of 10 −7 M or 10 −6 M . Atropine and d‐tubocurarine also blocked the action of exogenously applied acetylcholine. Postsynaptic responses were obtained from acetylcholine (10 −7 M ), acetyl ß‐methyl choline (10 −8 M ), and nicotine (10 −8 M ). The results were discussed with respect to criteria which have been proposed for the indentification of transmitters. It was concluded that considering all of the information available on the cercal nerve‐giant fiber synapse, the transmitter is almost certainly Ach.