INNERVATION OF ORBITAL AND CHOROIDAL BLOOD-VESSELS BY THE PTERYGOPALATINE GANGLION IN PIGEONS

Orbital and choroidal blood vessels in mammals are known to receive a parasympathetic innervation from the pterygopalatine ganglion, which a ppears to utilize vasoactive intestinal polypeptide (VIP) and nitric o xide (NO) to increase choroidal blood flow. The present studies were u ndertaken to elucidate the anatomical and neurotransmitter organizatio n of the pterygopalatine ganglion input to orbital and choroidal blood vessels in pigeons. Single-or double-label immunohistochemistry were employed on paraformaldehyde-fixed cryostat sections of the pigeon eye and surrounding orbital tissue to localize 1) VIP+ neurons and fibers ; 2) choline acetyltransferase (CHAT)-containing cholinergic neurons a nd fibers; 3) axons containing the 3A10 neurofilament-associated antig en; and 4) neuronal NO synthase (nNOS)-containing neurons and fibers. NOS+ neurons and fibers were also identified by NADPH-diaphorase histo chemistry in sections and whole-mount specimens. The pterygopalatine g anglion was found to consist of an interconnected series of three to f our main microganglia of about 50-200 neurons each and numerous lesser microganglia. The major microganglia of the pterygopalatine network i n pigeon lie along the superior aspect of the Harderian gland, with ma ny additional fibers and microganglia of the network encircling the gl and. Neurons of all microganglia were extremely rich in VIP, nNOS, and NADPH-diaphorase and moderate in CHAT. The majority of the pterygopal atine ganglion neurons were observed to co-contain VIP and nNOS. Axons labeled for VIP, nNOS, NADPH-diaphorase, or the 3A10 antigen could be traced from the pterygopalatine ganglion network to perivascular fibe r plexi on orbital blood vessels. These orbital vessels, many of which enter the choroid posteriorly and nasally, appear to be a conduit by which pterygopalatine postganglionic fibers reach the choroid. The pte rygopalatine postganglionic fibers were also seen to innervate the Har derian gland and contribute branches to the nearby ophthalmic nerve. W ithin the choroid, VIP+ fibers were widely scattered and sparse but we re most abundant in nasal choroid. A few VIP+ and NADPH-diaphorase+ ne urons were also observed in the choroid. These results suggest that pt erygopalatine ganglion neurons of birds use VIP and NO to exert vasodi latory control over blood flow to and within the avian choroid. (C) 19 97 Wiley-Liss, Inc.