[The detection of the sites of mediator release in a motor nerve ending]. / Vyiavlenie tochek osvobozhdeniia mediatora v dvigatel'noi nervnoi terminali.

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.

[An analysis of mediator secretion in the active zone of the motor nerve ending]. / Analiz sekretsii mediatora v aktivnoi zone dvigatel'nogo nervnogo okonchaniia.

The topography of transmitter release sites at the motor-nerve terminal of the cutaneous-pectoris frog muscle has been determined using three extracellular electrodes. It is shown that release sites are united in groups arranged transversally to the nerve endings and reflecting the transmitter release in the active zones (AZ) of the nerve terminal. The quantitative analysis of revealed groups has permitted concluding that the maximal level of secretion is at the centre of AZ, decreasing to the edge and aside from AZ. At the low extracellular Ca2+ concentration all the AZ take part in the spontaneous release process, while in the evoked one--only some of AZ. Advantages of the three-microelectrode method over the two-microelectrode one are analyzed. It is found that the transmitter secretion in spatially isolated AZ leads to the polymodality in uniquantal signal amplitude distribution at extracellular recording. The role of AZ in the transmitter release process is discussed.