[Numerical characteristics of the structure of the vesicular apparatus of the synapses in the dorsal horn of the cat spinal cord].

Numerical parameters characterizing the structure of vesicular apparatus of presynaptic terminals were determined on the basis of the morphometrical investigation of the ultrastructure of 135 synapses from the dorsal horn of the cat spinal cord. Statistical estimates of the number of vesicles in the terminal was obtained (mean value 470). Bimodality of distribution of distances from a centre of each vesicle to the nearest site of the active zone has been demonstrated, that is regarded as a possible structural correlate of the two-pool model of the transmitter storage. The possibility of classification of synapses according to the spatial distribution of vesicles, relations between such distribution and parameters of the transmitter release and storage are discussed.