Golgi and electron-microscopic golgi-GABA immunostaining study of the avian optic tectum.

The neuronal structures and their possible connections in the optic tectum of chicks were studied by using Golgi impregnation, in light microscopy, and Golgi-GABA immunogold staining in electron microscopy. The terminals of the optic fibers displayed different patterns and orientation in various laminae of the avian optic tectum. The shape of the branching and the terminals of the optic fibers conformed to the postsynaptic neuronal structures. In Golgi preparations, the terminals in tectal layers 4 and 5 seemed to be located rather densely, and they contact, among other things, the 'dendritic terminal sections' of large ganglion cells of layer 13 of the tectum. This connection could be responsible for direct optic transmission via ganglion cells to the nucleus rotundus. Additionally, the contacts established by optic terminals in these layers with the tectal neurons arranged with their dendrites parallel to the surface of the tectum, could provide the structural basis for an inhibitory system. The terminals of isthmic nuclei were found in this optic lamina, too. The optic terminals in layer 7 contacted the dendritic side branches of some radial tectal neurons.