Helospectin-like immunoreactivity in the rat eye and pterygopalatine ganglion

Helospectin I and II, nearly identical peptides isolated from lizard venom, show close sequence homology with vasoactive intestinal peptide (VIP). In mammals, the helospectins have been localized immunohistochemically to neurons of the brain, digestive tract and respiratory system, commonly co-existing with VIP. Using an antiserum that recognizes both forms of the peptide, we localized helospectin-like immunoreactivity in the rat eye and pterygopalatine ganglion. In the eye, helospectin-positive nerve fibers were evident mostly in the choroid, associated with small arterial vessels or distributed diffusely in the stroma; they were only occasionally seen in the anterior uvea. All of the helospectin nerve fibers also appeared to be immunoreactive for VIP. In the pterygopalatine ganglion, the principal source of VIP-containing innervation of the posterior uvea, approximately 25% of ganglion cells were helospectin-positive; all helospectin-reactive cells were also strongly positive for VIP. This immunohistochemical localization of helospectin indicates possible involvement in ocular autonomic functions, particularly regulation of blood flow.