Vasoactive intestinal polypeptide and the ocular innervation.

The indirect immunofluorescence technique with antisera to vasoactive intestinal polypeptide (VIP) stains peripheral nerve fibers in both the anterior segment and the posterior segment of rat, guinea pig, cat, and rhesus monkey eyes. While immunoreactive corneal nerves are lacking, all four species have a prominent innervation of the superficial limbal blood vessels. The aqueous humor outflow apparatus of the rat, guinea pig, and cat, but not the monkey, contain VIP-like immunoreactive nerves. All four animals have immunoreactive iris nerve fibers, tending either to surround large blood vessels or to lie as free stromal nerves. Only in the cat are immunoreactive nerve fibers seen within the iris muscles. A modest number of VIP-like immunoreactive nerves are present in the ciliary body of all four animals; immunoreactive nerve fibers within the ciliary processes occur only in the rat and guinea pig. VIP-like immunoreactive nerves are found in the choroid of all four animals. An association of immunoreactive nerve fibers to uveal melanocytes also is apparent. The present findings expand several prior immunohistochemical studies of mammalian eyes in which the VIP-like immunoreactive nerves to the choroid was emphasized.