Ontogeny of pituitary adenylate cyclase-activating polypeptide (PACAP) and its binding sites in the rat brain.

Endogenous levels of pituitary adenylate cyclase-activating polypeptide (PACAP) and its binding site densities were measured in eight brain regions in rats of different ages (2-240 days) by sandwich-enzyme immunoassay and autoradiography. PACAP levels were quite low at day 2, peaked in 30-60 days, and then remained constant in most regions. Such ontogenetic changes are similar to those of vasoactive intestinal polypeptide (VIP) and classical neurotransmitters. PACAP-binding sites were already dense at day 2 and varied only slightly up to day 240. These results suggest that PACAP may have modulatory effects on brain development.