Electrophysiological characteristics of crayfish inhibitory.

Parameters of IPSPs and characteristics of inhibitory neuromuscular transmission in the dactylopodite-opener muscle of the crayfish pincer at various rhythms of activity were studied by intracellular recording. The presynaptic conduction nature of high-frequency (pessimal) blockade of the inhibitory system was demonstrated. Transformation of the rhythm of stimulation correlated with a decrease in conduction velocity along the inhibitory axon and (or) its branches. At high frequencies of stimulation the mean quantum composition of IPSPs of the potentiation plateau before the beginning of rhythm transformation was lower than at lower frequencies. No signs of exhaustion of mediator reserves were found in the course of high-frequency activity. It is concluded that the mechanism of secretion of inhibitory mediator is more reliable than the function of conduction of the presynaptic nervous impulse. The possible functional significance of the comparatively low reliability of function of crustacean nerve fibers is discussed.