Journal of Molecular Neuroscience Copyright © 2005 Humana Press Inc. All rights of any nature whatsoever reserved. ISSN0895-8696/05/25:215–224/$30.00 Journal of Molecular Neuroscience 215 Volume 25, 2005 ORIGINAL ARTICLE Receptors for VIP and PACAP in Guinea Pig Cerebral Cortex Effects on Cyclic AMP Synthesis and Characterization by 125 I-VIP Binding Jolanta B. Zawilska,* ,1,3 Agnieszka Dejda, 1 Pawel Niewiadomski, 3 Illana Gozes, 4 and Jerzy Z. Nowak, 1,2 1 Centre for Medical Biology, Polish Academy of Sciences, 93-232 Lodz, Poland;Departments of 2 Pharmacology and 3 Pharmacodynamics, Medical University of Lodz, Lodz, Poland; and 4 Department of Clinical Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 69978, Israel Received February 18, 2004; Accepted August 22, 2004 Abstract Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in guinea pig cerebral cortex were characterized by (1) radioreceptor binding of 125 I-labeled VIP (human/rat/porcine), and (2) cyclic AMP (cAMP) formation. Saturation analysis of 125 I-VIP binding to mem- branes of guinea pig cerebral cortex resulted in a linear Scatchard plot, suggesting the presence of a single class of high-affinity receptor-binding sites, with a K d of 0.63 nM and a B max of 77 fmol/mg protein. Various peptides from the PACAP/VIP/secretin family displaced the specific binding of 125 I-VIP to guinea pig cerebrum with the relative rank order of potency: chicken VIP (cVIP) ≥ PACAP38 ≈ PACAP27 ≈ guinea pig VIP (gpVIP) ≥ mam- malian (human/rat/porcine) VIP (mVIP) > peptide histidine-methionine (PHM) > peptide histidine-isoleucine (PHI) > secretin. Analysis of the competition curves revealed displacement of 125 I-VIP from high- and lower- affinity binding sites, with IC 50 values in the picomolar and the nanomolar range, respectively. About 70% of the specific 125 I-VIP-binding sites in guinea pig cerebral cortex were sensitive to Gpp(NH)p, a nonhydrolyzable analog of GTP. Pituitary adenylate cyclase-activating polypeptide 38 (PACAP38), PACAP27, cVIP, gpVIP, mVIP, PHM, and PHI stimulated cAMP production in [ 3 H]adenine-prelabeled slices of guinea pig cerebral cortex in a concentration-dependent manner. Of the tested peptides, the most effective were PACAP38 and PACAP27, which at a 1 μM concentration produced a 17- to 19-fold rise in cAMP synthesis, increasing the nucleotide pro- duction to approx 11% conversion above the control value. The three forms of VIP (cVIP, mVIP, and gpVIP) at the highest concentration used, i.e., 3 μM, produced net increases in cAMP production in the range of 8–9% con- version, whereas 5 μM PHM and PHI, by, respectively, 6.7% and 4.9% conversion. It is concluded that cerebral cortex of guinea pig contains VPAC- type receptors positively linked to cAMP formation. In addition, the observed stronger action of PACAP(both PACAP38 and PACAP27), when compared to any form of VIP, on cAMP production in this tissue, suggests its interaction with both PAC 1 and VPAC receptors. Index Entries: VIP receptors; PACAP receptors; cAMP; guinea pig cerebral cortex. Introduction Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) belong to a superfamily of structurally related bioac- tive polypeptides, which also includes secretin, glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide, *Author to whom all correspondence and reprint requests should be addressed. E-mail: jzawilska@pharm.am.lodz.pl