PRESYNAPTIC NATURE OF NEUROMUSCULAR DEPRESSION

Abstract

1. The nature of neuromuscular depression, i. e., the gradual decline in size of e. p.p.'s during repetitive stimulation, was investigated in curarized nervemuscle preparations of the frog and rat.2. 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.3. When the transmitter-receptor reaction is enhanced or depressed presynap tically, the degree of neuromuscular depression is correspondingly augmented or reduced, whereas the depression is little modified when the reaction is altered postsynaptically.4. 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.