Ultrastructural changes in synapses of the rabbit sensomotor cortex during stimulation of the reticular formation

Abstract

Ultrastructural changes were studied in synapses of the sensomotor cortex of rabbits during short-term (25 stimuli during 1 day) and long-term stimulation of RF (400 stimuli in the course of 7–8 days). 1. Short-term stimulation of RF led to the development and increased complexity of structures of the synapses, in the form of the appearance of numerous axon terminals forming several active zones with the postsynaptic neuron, and to an increase in the number of synaptic vesicles in the axon terminals. 2. During long-term stimulation of RF further transformations took place in the synapses, namely an increase in the area of the active zones and a decrease in the number of synaptic vesicles in the axon terminals. 3. The submicroscopic changes observed in the synaptic apparatus during stimulation of RF are regarded as a process of intensification of the functional activity of the synaptic apparatus of the sensomotor cortex with the bringing of new interneuronal connections into operation. 4. Structural and functional transformations in the synaptic apparatus of rabbits take place throughout the cross-section of the sensomotor cortex, but predominantly at the upper level (layers I–IV), which suggests that nonspecific afferent endings are distributed throughout all layers of the sensomotor cortex but are represented chiefly in the upper layers.