NITRERGIC AND VIPERGIC NEURONS IN THE CHOROID AND CILIARY GANGLION OFTHE DUCK ANIS-CARINA

Immunohistochemistry for neuronal nitric oxide synthase (nNOS) and vas oactive intestinal peptide (VLP), and NADPH diaphorase histochemistry, were applied to investigate neurons in the choroid and the ciliary ga nglion of the muscovy duck Anis carina. Up to 1000 neurons in the chor oid stained for NADPH diaphorase and showed virtually complete colocal ization for nNOS immunoreactivity. Almost all of them co-stained for V IP, while about 90% of VIP immunoreactive cell bodies showed colocaliz ation for nNOS. Two-thirds of the neurons were located, mostly singly, at nodes of a wide-meshed nerve plexus in the suprachoroid and were o nly rarely grouped in ganglia of up to 3 neurons. Numerous varicose nN OS/NADPH-diaphorase-positive nerve fibers were seen around large arter ial blood vessels. These fibers derived mainly from paravascular cell bodies that represented about one-third of all choroidal neurons and a lso displayed costaining for nitrergic markers and VIP. Colocalization of nNOS/NADPH-d and VIP could be demonstrated in most of the perivasc ular fibers, while slightly more VIP-positive axons in the suprachoroi d plexus did not costain for nNOS/NADPH-d. Small-caliber blood vessels and those localized in the choriocapillaris were not endowed with VIP /nNOS/NADPH-diaphorase-positive fibers. A few reactive neuronal cell b odies were also found in ciliary nerves, while most ciliary axons were unstained. In the ciliary ganglion a small subpopulation of neurons s howed VIP/nNOS/NADPH-diaphorase colocalization. There were also nNOS/N ADPH-d-positive cap-like terminals on ciliary ganglion cells. The pres ence of VIP/nNOS/NADPH-diaphorase positive neurons and nerve fibers in both the choroid and ciliary ganglion, and in the choroidal perivascu lar plexus, indicates peripheral nitrergic and VLPergic control of blo od flow in the choroid of the duck.