Retinal innervation of the inferior colliculus in rat and monkey.

Visual pathways were studied using horseradish peroxidase (HRP) as an anterograde tracer after intraocular injections in rats and monkeys. Retinal axons continue caudally from the stratum opticum of the contralateral superior colliculus at the medial and lateral sides of the superior colliculus. Fibers near the midline spread out as a flat sheet within the pericentral nucleus of the inferior colliculus. The optic axons travel through the dorsal pericentral nucleus and some reach the posterior pericentral nucleus, but their numbers diminish along the route, suggesting that the fibers terminate. The fact that a similar pathway was observed in rodent and primate suggests that the retino-pericentral nucleus pathway exists in other mammals.