Hypothalamo-retinal centrifugal projection in the dog.

Horseradish peroxidase (HRP)-filled neurons and their processes were consistently detected in the ventral portion of the dog hypothalamus after intraocular injection of HRP. The number of HRP-filled neurons decreased in parallel with the extent of the resection of the optic nerve. HRP-filled neurons were never detected in specimens with a complete resection of the optic nerve. These findings strongly indicate that these HRP-filled neurons in the ventral hypothalamus are the source of centrifugal fibers to the retina.