Distribution of vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide receptors (VPAC(1), VPAC(2), and PAC(1) receptor) in the rat brain

Abstract

To examine the distributions of VIP/PACAP receptors (VPAC(1), VPAC(2), and PAC(1) receptors) in the brain and to identify the cell types that express these receptors, we performed immunohistochemistry and double immunofluorescence in the rat brain with specific antibodies. The immunohistochemistry revealed that the receptors had distinctive, complementary, and overlapping distribution patterns. High levels of the V-PAC(1) receptor were expressed in the cerebral cortex, hippocampal formation, deep cerebellar nuclei, thalamus, hypothalamus, and brainstem. The VPAC(2) receptors were concentrated in the cerebral cortex, hippocampal formation, amygdalar regions, cerebellar cortex, deep cerebellar nuclei, hypothalamus, and brainstem. On the other hand, the PAC(1) receptors had a more restricted distribution pattern in the brain, and high levels of the PAC(1) receptors were confined to the cerebellar cortex, deep cerebellar nuclei, epithalamus, hypothalamus, brainstem, and white matter of many brain regions. Also, many fibers expressing the PAC(1) receptors were observed in various areas, i.e., the thalamus, hypothalamus, and brainstem. The double immunofluorescence showed that the VIP/PACAP receptors were confined to the neuroglia as well as the neurons. All three types of the VIP/PACAP receptors were expressed in the astrocytes, and the PAC(1) receptors were also expressed in the oligodendrocytes. These findings indicate that VIP and PACAP exert their functions through their receptors in specific locations in different combinations. We hope that this first demonstration of the distributions of the VIP/PACAP receptors provides data useful in the investigation of the mechanisms of the many functions of VIP and PACAP in the brain, which require further elucidation. (C) 2004 Wiley-Liss, Inc.