Miniature endplate potentials related to neuronal injury

Intracellular recordings were made in vivo from muscle fibers of anesthetized or spinalized frogs. Characteristic 'spontaneous' miniature endplate potentials were rarely recorded in intact muscles by comparison with muscles acutely denervated in the same animals. It is concluded that little or no spontaneous quantal release of transmitter occurs in vivo, in contrast with isolated preparations. The presence effectively 'silent' endplates was confirmed by evoking quantal release with hypertonic saline.