LOCALIZATION AND GENE-EXPRESSION OF THE RECEPTOR FOR PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE IN THE RAT-BRAIN

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a recent ly identified member of the secretin/vasoactive intestinal polypeptide (VIP) family. There are at least two types of receptor for PACAP: typ e I (PACAPR), which specifically binds PACAP; and type II (VIP/PACAPR) , which binds both PACAP and VIP. The localization of PACAPR in the ra t brain was determined by in situ hybridization and immunocytochemistr y. We raised antisera against a synthetic peptide that corresponds to the carboxy-terminal cytoplasmic domain which is found in all subtypes of PACAPR in order to localize PACAPR-like immunoreactivity (PACAPR-L I) in the rat brain. In general, the distribution of PACAPR-LI correla ted well with the distribution of PACAPR transcripts. Particularly str ong PACAPR mRNA expression was detected in the olfactory bulb, hippoca mpus, cerebellum and hypothalamus and moderate labeling was detected i n other scattered regions. At the cellular level, PACAPR-LI appeared t o be concentrated predominantly in neuronal perikarya and dendrites. A t the ultrastructural level, strong immunostaining for the PACAPR was found in plasma membranes, rough endoplasmic reticulum, cytoplasmic ma trix, and at synapses. This study provides the basis for a better unde rstanding of the functions of PACAP in the rat brain. (C) 1997 Elsevie r Science Ireland Ltd.