The dendritic architecture of the visual pretectal nuclei of the rat: a study with the Golgi-Cox method.

The dendritic architecture of the neurons of the visual pretectal nuclei in the rat was studied with the Golgi-Cox method. The olivary pretectal nucleus (PO) is characterized by distinctive neurons with a gnarled, tufted, richly branched dendritic arbor forming a dense neuropil within the nucleus. The distinct dendritic morphology of the olivary pretectal neurons enables this nucleus to be identified at all levels of the pretectum in Golgi-impregnated preparations. Rostromedially, the PO is surrounded by peripheral neurons whose dendrites wrap around the surface of the PO. The nucleus of the optic tract (NTO) contains three types of cells: (1) superficial horizontal cells whose dendrites extend out transversely; (2) large multipolar neurons whose dendrites spread out predominantly in a transverse plane, and (3) small to medium multipolar neurons with varying dendritic architecture. The posterior pretectal nucleus (PP) is composed predominantly of (1) multipolar cells with horizontally and vertically oriented dendrites extending out transverse to the optic axons; (2) piriform cells with dendrites extending dorsally toward the brachium; and (3) small multipolar neurons. The presence of superficial horizontal and large multipolar neurons in the NTO distinguishes the NTO from the PP in Golgi preparations. The horizontally oriented dendrites of many of the multipolar neurons in the PP give this nucleus an appearance distinct from that of the NTO. The differences in dendritic morphology between the visual pretectal nuclei in the rat permit identification of these nuclei at all levels within the pretectum. The boundaries of these nuclei, as determined in the Golgi-Cox preparations, correlate quite well with the boundaries defined by studying retinal projections (Scalia and Arango, '79).