[Electrophysiological and morphological study of the synaptic organization of the tonic muscle fibers in the frog].

The histochemical and electrophysiological investigation of tonic muscle fibers was performed in the frog m. cruralis. Cholinesterase activity studies in tonic fibers revealed 4 to 14 synapses aggregated in groups. A number of synapses were in positive correlation with the muscle fibers length. In MPSP recording, the distribution of amplitude, periods of growth and of half-time decay had a nonsymmetrical form. At the scatter diagrams of MPSP amplitude recorded by two intracellular microelectrodes, two to six signal groups were revealed in single synapses at different distances from the site of recording. The groups were represented by different number of signals of various duration. Similar groups of signals were also found in evoked PSP, the number of such groups depending upon the intensity of nerve stimulation. The synapses formed by a single motor axon seem to congregate in certain areas of tonic fibers and to be functionally heterogeneous. Intracellular recording revealed only a part of the tonic fibre synapses.