Structure and distribution of the mRNAs encoding pituitary adenylate cyclase-activating polypeptide and growth hormone-releasing hormone-like peptidein the frog, Rana ridibunda

The structure of the neuropeptide pituitary adenylate cyclase-activating po lypeptide (PACAP) has been characterized in several species including proto chordates, fish, amphibians, birds, and mammals. Although PACAP has been sh own to stimulate frog pituitary and adrenal cell activity, the structure of the PACAP precursor and the expression of its gene have not yet been repor ted in any amphibian species. In this study, we have characterized two cDNA variants encoding PACAP of the frog Rana ridibunda, one of which encodes a second peptide exhibiting strong homologies to growth hormone-releasing ho rmone (GHRH) of fish and mammals. Northern blot and reverse transcriptase-p olymerase chain reaction (RT-PCR) analyses revealed that PACAP/GHRH-like pe ptide mRNAs are predominantly expressed in the brain and spinal cord and, t o a lesser extent, in the neurointermediate lobe of the pituitary. Other ti ssues including the testis and the distal lobe of the pituitary do not expr ess the PACAP precursor gene. The distribution of PACAP/GHRH-like peptide m RNAs in the frog brain has been determined by in situ hybridization histoch emistry. High levels of expression were found in the accessory olfactory bu lb, the distal pallium, the ventral part of the magnocellular preoptic nucl eus, the ventral hypothalamic nucleus, the posterior tuberculum, and the ve ntral habenular nucleus. These data contribute to the understanding of the evolution of the PACAP and GHRH genes in vertebrates and provide the anatom ical bases to elucidate the roles of PACAP and the GHRH-like peptide in amp hibians. (C) 2000 Wiley-Liss, Inc.