Pituitary adenylate cyclase-activating polypeptide receptors during development: Expression in the rat embryo at primitive streak stage

The distribution and localization of the pituitary adenylate cyclase-activa ting polypeptide (PACAP) receptor [the PAC(1) receptor (previously called t he type 1 PACAP receptor or PVR1), which binds PACAP, but not vasoactive in testinal peptide, with high affinity] were first investigated in rats with in situ hybridization for its messenger RNA, and with immunohistochemical m ethods during prenatal and postnatal development. The expression of PACAP r eceptor messenger RNA was first detected in the rat embryo at the primitive streak stage as early as embryonic day 9, and it was intensely expressed i n the neural plate. PACAP receptor messenger RNA was also intensely express ed in the neuroepithelia of the mesencephalon and rhombencephalon at embryo nic day 11, and expressed in the basal telencephalon, hippocampal formation neuroepithelium, cortical neuroepithelium and cerebellar neuroepithelium a fter embryonic day 13. It was also expressed in the olfactory bulb neuroepi thelium after embryonic day 16, and in mature regions of the older embryos. In postnatal developing brains. PACAP receptor messenger RNA was intensely expressed in the olfactory bulb, hippocampal formation, cerebellum and oth er scattered regions. The localization of PACAP receptor-like immunoreactiv ity coincided well with that of the gene transcripts. We also used reverse transcription-polymerase chain reaction methods to determine the expression of the splice variants of the PACAP receptor gene. At each ontogenetic sta ge of the rat from embryonic day 9 to postnatal day 60, two major products were detected with reverse transcription-polymerase chain reaction, a thick band (303 base pairs) corresponding to the short splice variant of the rec eptor that lacks both the "hip" and "hop" cassettes, and a thin band (387 b ase pairs) corresponding to the splice variant that contains one cassette o f "hop" or "hip". There was no evidence for the other larger splice variant s. Some of the amplified products were sequenced and found to have the exac t sequences of "PACAP receptor" and "PACAP receptor-hop1", which are couple d to different signal transduction pathways. These results indicate that the PACAP receptor is actively expressed in dif ferent neuroepithelia from early developmental stages and expressed in vari ous brain regions during prenatal and postnatal development, and that the m ajor splice variants are "PACAP receptor" and "PACAP receptor-hop1". The in itial mapping of ontogenetic localization of the PACAP receptor provides th e basis for a better understanding of the functions of PACAP and its recept ors during the development of the brain. (C) 1999 IBRO. Published by Elsevi er Science Ltd.