Non-uniform distribution of miniature endplate potential amplitudes along the length of the frog neuromuscular junction.

We studied the amplitude distribution of miniature endplate potentials (MEPPs) as a function of the release site position along the frog neuromuscular junction. Following intracellular recordings with two electrodes each located at one distal end, we used the spatial decay method to evaluate the release site position of each MEPP and the MEPP amplitude in front of its release site. Nitroblue-tetrazolium-cholinesterase staining was performed for further morphological correlation. Our results indicate that MEPP amplitude distributions are skewed to the left for distal regions, while MEPP amplitudes are more widely distributed for the proximal regions (i.e. near the last myelinated segment). This suggests that distal regions produce predominantly MEPPs with a small amplitude whereas proximal regions produce MEPPs of all sizes (small to large).