[Does the plasticity of central nervous system synapses have a morphological basis?].

The sensorymotor area of the cerebral cortex of the laboratory rat was repeatedly electrically stimulated after 10-minute intervals which led to progressive lengthening of the self-sustained after-discharges (SSAD). One minute, 10 minutes and one hour after completion of the third SSAD the authors examined by an electron microscope synapses type I according to Gray from the IInd cortical layer of the sensorymotor area of the contralateral hemisphere. One minute after termination of the fit a marked drop of the number of granular synaptic vesicles was noted in the immediate vicinity of the synaptic cleft, as well as in the whole synapsis, which correlates very closely with the reduced excitability of tissue during this period. Ten minutes after the end of the fit the number of vesicles rises markedly in both evaluated areas. This finding again corresponds well to the functional state, i.e. an increased excitability. One hour after the end of SSAD no changes in the number of vesicles near the synaptic cleft was found which might be associated with a greater functional capacity of the synaptic apparatuses. The results confirmed the idea on the synaptic apparatus as a structure which reflects from the morphological aspect very accurately changes of the functional state of the central nervous system.