PITUITARY ADENYLATE CYCLASE-ACTIVATING PEPTIDE-IMMUNOREACTIVE NERVE-FIBERS IN THE CAT EYE

Purpose: To study the occurrence and distribution of the neuropeptide pituitary adenylate cyclase-activating peptide (PACAP) in ocular and o rbital structures of the cat. Methods: Immunocytochemistry to localize PACAP and double immunostaining to detect co-localization of PACAP wi th other neuropeptides. Results: Numerous PACAP-immunoreactive nerve f ibers were observed in the lacrimal gland, choroid and retroocular art eries. There was a sparse supply of PACAP-containing nerve fibers in t he iris, ciliary body and conjunctiva. Subpopulations of PACAP-contain ing nerve fibers stored vasoactive intestinal peptide (VIP) or calcito nin gene-related peptide (CGRP). Around 10% of the ganglion cells in t he sphenopalatine ganglion harbored PACAP immunoreactivity. In the tri geminal ganglion around 5% of the neuronal cell bodies and in the cili ary ganglion only occasional ganglion cells contained PACAP immunoreac tivity. PACAP immunoreactivity co-localized with VIP in the sphenopala tine ganglion and with CGRP in the trigeminal ganglion. Conclusion: PA CAP-containing nerves in the eye and associated structures demonstrate a distribution pattern resembling that of VIP. Subpopulations of nerv e fibers containing PACAP immunoreactivity store VIP or CGRP immunorea ctivity. Neuronal PACAP in the eye and orbit may take part in regulati on of smooth muscle tone, glandular secretion and sensory processing.