Distribution of spontaneous release along the frog neuromuscular junction.

A new method, called the spatial decay method, is described. This method permits to localize the site of occurrence of the spontaneous release producing each miniature end-plate potential (MEPP) recorded at the frog neuromuscular junction (nmj). The method requires simultaneous intracellular recording at both distal ends of the nmj. The electrodes are positioned using Nomarksi optics. The assumptions that the MEPP amplitude is maximum in front of its release site and decays exponentially toward the recording electrodes placed distally, permit the calculation of the position of the release site producing each MEPP recorded intracellularly. The spatial decay method indicates that the occurrence of spontaneous release is not uniformly distributed along the frog nmj.