Autoradiographic evidence for a projection from the pretectal nucleus of the optic tract to the dorsal lateral geniculate complex in the cat.

A pathway from the pretectal region to the dorsal division of the lateral geniculate body has been studied by autoradiography in adult cats following injection of tritium-labeled amino acids into the meso-diencephalic border zone. The findings suggest that the pretecto-geniculate connection arises in the ipsilateral nucleus of the optic tract (NOT) and terminates in the principle dorsal layers of the geniculate body (A and A1), in lamina C and most massively in the medial interlaminar nucleus. In the A layers and lamina C, the pretectal fibers from a relatively even matting with partial interruptions occurring at the interlaminar leaflets. The ventral C layers do not appear to receive a substantial pretectal input as they were only weakly labeled, and partly in a perforant fiber pattern, after injections confined to the pretectum. Topographic ordering of the projection was evident at least along the medial to lateral axis of the NOT, fibers from the medial part terminating caudally, and those from the lateral part rostrally, within the lateral geniculate complex. The laminar pattern of termination correlates closely with the distribution of retinal Y-cell input and acetylcholinesterase activity in the geniculate body but contrasts sharply with the pattern of termination of tecto-geniculate fibers. Of potential importance in considering the functional significance of the pretecto-geniculate pathway is the fact that the NOT has been implicated in the mechanism of optokinetic nystagmus and the fact that the pathway terminates within the layers of the lateral geniculate body known to provide the main geniculo-cortical input to layer IV of the striate cortex.