The presence of PACAP and VIP was demonstrated in all the four levels ofthe photoneuroendocrine system (PNES) with the use of immunohistochemistry (IHC), radioimmunoassay (RIA),anterograde and retrograde tracing techniques, and cell immunoblot assay (CIBA). Both peptides play aphysiological role in the PNES. According to our results both PACAP and VIP are involved in the regulationof the gonadotrop hormone secretion and their inhibitory role may be mediated through the neuronal chainof the PNES.

Keywords: Neuropeptides, Neurosecretory Systems, Research Support, Non-U.S. Gov, Vasoactive Intestinal Peptide