Some Features of the Formation of Contact between the Chemical Synapses and the Membrane of Astrocytes in the Primary Somatosensory Cortex of the Rat Brain

The aim of the study was to investigate the relationship between the average size of the active synapse zone and the frequency of synapse-astrocyte membrane contact in the layers of the rat cerebral cortex. The material for the study included 40 μm frontal sections of the primary somatosensory cortex of five outbred male white rats. Astrocytes were labeled for TEM by incubating the sections with primary antibodies to the s100β protein and secondary antibodies conjugated with horseradish peroxidase, followed by label development in a reaction with DAB. Two hundred fifty images with a 25 000× magnification were made for each layer. The length of the synaptic cleft was measured in the images, and the number of synapses forming contact with the astrocyte membrane was counted. The proportion of chemical synapses making contact with the astrocytic membrane in the rat primary somatosensory cortex showed a direct relationship to the average synaptic cleft length only in layers one through four. The data obtained suggest that contact is formed by a combination of a random membrane encounter followed by selective fixation or repulsion of the astrocytic membrane by various factors, only partly determined by the size of the chemical synapse.