The upper layers of the superior colliculus of the rat: A Golgi study

Abstract A number of questions deriving from a previous electron microscopic study of the superficial layers of the rat superior colliculus pointed out the need for a comprehensive study of the cell types of the superior colliculus and their detailed morphology. In the present Golgi study the cells of the superficial layers of the superior colliculus were found to be of five major types; marginal cells, horizontal cells, narrow field vertical cells, wide field vertical cells, and stellate cells. Some of these categories were further subdivided. Each cell type has a distinctive set of dendritic field characteristics, a regional distribution, and consistent axon characteristics. The horizontal cells were found to have a preference in the orientation of their dendrites along the vertical and horizontal axes of the visual field projection upon the superior colliculus. It is argued that the horizontal cells are the presynaptic elements in the majority of the dendrodendritic synapses.