[The effect of light stimulation in the pre- and postnatal periods on the synaptic ultrastructure in the chick hyperstriatum].

Morphometric analysis of synapses in the medial parts of the ventral and accessorium hyperstriatum in the right and left hemispheres in chicks has been performed after rhythmic optic stimulation from the 18th day of incubation, flickering stimulation at the 11-12th hour after hatching, as well as in chicks reared under normal illumination and those kept in darkness within the first two days after hatching. Numeric density of synapses, mean dimensions of postsynaptic thickenings, the number of synaptic vesicles per active zone in presynapses and mean length of the whole axodendritic contact were determined in ultrathin sections. The data obtained indicate that early visual experience significantly affects the synaptic structures in both parts of the brain. A discussion is made of the plasticity of synapses during stimulation, morphological and functional relationships between hyperstriatal areas in relation to different aspects of processing and storage of visual information.