Galanin-like peptide (GALP) mRNA expression is restricted to arcuate nucleus of hypothalamus in adult male rat brain

Galanin-like peptide (GALP) is a novel 60-amino acid neuropeptide, isolated from porcine hypothalamus and subsequently identified in rats and humans, which has reported selectivity for the Gal-R2 galanin receptor [Ohtaki T et at: J Biol Chem 1999; 274: 37941-37045]. In the current study, the regiona l and cellular distribution of GALP mRNA in rat brain has been investigated by in situ hybridization of [S-35]-labelled oligonucleotide probes. In a t horough screening of adult male rat brain, GALP mRNA expression was detecte d only throughout the rostrocaudal extent of the arcuate nucleus (ARC) with the most abundant hybridization signal in the posterior, periventricular z ones. GALP mRNA-positive neurons were mostly localized in the ventromedial division of the ARC, with many closely adjacent to the wall of the third ve ntricle. Smaller numbers of labelled neurons were also found in ventrolater al areas. The distribution of GALP mRNA was somewhat complementary to that for galanin (GAL) mRNA in the ARC, but contrasted with the broad distributi on of this transcript throughout the hypothalamus. GAL mRNA was also distri buted along the rostrocaudal extent of the ARC, but was most abundant in th e anterior to middle levels and in ventrolateral regions. Interestingly, so matostatin mRNA expression appeared to overlap the distribution of GALP mRN A in posterior, ventromedial regions of the ARC. Thus, in adult rat brain G ALP mRNA expression was restricted to a discrete subpopulation of neurons i n the ARC, with a unique localization pattern unlike GAL or many other know n peptide and transmitter-containing cells in this region. GALP could, howe ver, be co-expressed in sub-populations of other neuronal phenotypes (e.g. somatostatin neurons) or within cells that express Gal-R2 receptors. In vie w of the established anatomy and function of the ARC and the restricted loc alization of GALP mRNA, this novel peptide is likely to play a role in regu lation of anterior pituitary hormone secretion, or in regulation of other h ypothalamic peptide and transmitter systems. Copyright (C) 2000 S. Karger A G. Basel.