[The detection of the sites of mediator release in a motor nerve ending]

A model of the postsynaptic current generation in response to a release of the quantum mediator from the nerve terminal is suggested. In its terms the law of the current density attenuation is determined as j = I/rb, where I is the current density in the site of generation, while j--current densities at the distance r from the site of generation. Experiments with extracellular recording have shown that coefficient b equals approximately 1. Assuming that sites of the quantum release and a site of the postsynaptic current generation are spatially identical, the new method is suggested to determine coordinates of the transmitter release sites in the motor nerve terminal. This method consists in the measuring of a uniquantal signal amplitude by three extracellular microelectrodes, arranged at a distance of 5-10 microns from each other. The construction of spatial pictures of the transmitter secretion on the basis of the analysis of several hundreds of signals in the cutaneous pectoris frog muscle has shown that release sites are organized in groups transversal to the nerve terminal. It is supposed that these groups of sites reflect the transmitter secretion in the active zones of the nerve ending. Advantages, shortcomings and errors of the method are shown.