PRESYNAPTIC NATURE OF NEUROMUSCULAR DEPRESSION

Abstract

The nature of neuromuscular depression, i.e., the gradual decline in size of e.p.p.''s (excitatory postsynaptic potentials) during repetitive stimulation, was investigated in curarized nerve-muscle preparations of the frog and rat. The sensitivity of the end-plate to ionophoretic micro-application of ACh remains entirely unchanged even when the size of e.p.p. is greatly reduced after repetitive junctional activities. It is concluded that the principal cause of neuromuscular depression is the gradual decrease of transmitter release per nerve volley, probably in consequence of partial exhaustion of the store of available transmitter, and that the desensitization of end-plate by ACh does not play any appreciable part in neuromuscular depression.