Substance P-like immunoreactivity in the central retinal artery of the rabbit.

Substance P-like immunoreactive nerve fibers were identified in the central retinal artery of therabbit using the peroxidase-antiperoxidase method. The fibers were seen to encircle the central retinal artery throughout its course in the main trunk of the optic nerve. No labeled fibers were seen in the central retinal vein or in the retinal blood vessels. It appears, therefore, that the central retinal artery and the retinal blood vessels are innervated by different nerve systems: the central retinal artery by one of the peripheral nerves, and the retinal vessels by the central nervous system.