[Changes in the synaptic vesicles of cat motor cortex axon terminals upon stimulation]

The relation of the synaptic vesicle size to the distance between the vesicle and the synapse active zone was studied in the axon terminals at the motor cortex neuron spines and dendrites of resting cats (under moderate barbiturate anesthesia) and after prolonged repetitive stimulation of the somatosensory SII area. Thes sizes of the vesicles belonging to any of the three strata observed in the terminal section profile under the electron microscope were registered as a decrementing variation sequence. The predominance of small vesicles in stratum I adjoining to the synapse active zone was found by means of the statistical analysis (symbol criterion and criterion chi2), both in the control and experimental material. A significant gradient of the vesicle size diminution from peripheral stratum III to stratum I as well as vesicle size decrease both in stratum I and intermediate stratum II in comparison with the control developed after the cortico-cortical projection stimulation. The functional role of this phenomenon is discussed.