[Laminar analysis of the synaptic organization of the frog optic tectum].

Distribution of axo-axonic and axo-dendritic synapses, nervous terminals and neuron somata in the depth of the optic tectum was studied in frog Rana temporaria L. in norm and 6-9, 60 and 134 days after contralateral eye enucleation. In outer plexiform layer 9 density of synapses was found to be maximal near the surface of the tectum; it decreased in deeper levels. In the outer zone of layer 9 (about 0.30 micrometer from the surface) many axo-axonic synapses were found. Terminals of myelinated optic fibres of large diameter ("dark" terminal degeneration) were widely distributed in layer 9. Density of axo-dendritic synapses in deep plexiform layer 5 was similar to that in layer 9. Numerous nervous terminals containing not only light synaptic vesicles, but also granular vesicles were seen in layer 5 and in adjacent zones.