Induction of c-fos Messenger Ribonucleic Acid in Neuropeptide Y and Growth Hormone (GH)-Releasing Factor Neurons in the Rat Arcuate Nucleus Following Systemic Injection of the GH Secretagogue, GH-Releasing Peptide-6
In this study we investigated the neurochemical identity of the arcuate cells activated following GH-releasing peptide-6 (GHRP-6) injection by comparing, on consecutive sections, the distribution c-fos messenger RNA (mRNA) with that of mRNAs for peptides synthe- sized in arcuate cells, including neuropeptide Y (NPY), GH-releasing factor (GRF), tyrosine hydroxylase, POMC, and somatostatin. Rats bearing chronically implanted jugular catheters were injected with either 50 mg GHRP-6 or vehicle. Thirty minutes later they were terminally anesthetized and perfused with fixative. Paraffin-embed- ded sections of 7 mm thickness were processed using in situ hybrid- ization for either c-fosmRNA or mRNAs for the neurochemical mark- ers. In GHRP-6-treated rats the mean (6 SEM) number of cells expressingc-fosmRNAinthearcuatenucleus(23 62cells/sectionper rat; n 5 5) was significantly higher than for vehicle-treated controls (2 6 1 cells/section per rat; n 5 5; P , 0.001, Mann-Whitney U test). Superimposed camera lucida maps indicated that, in GHRP-6-in- jected rats, neurochemically identifiable cells expressing c-fosmRNA also express NPY mRNA (51 6 4%), GRF mRNA (23 6 1%) tyrosine hydroxylase mRNA (11 6 3%), POMC mRNA (11 6 2%), or soma- tostatin mRNA (4 6 1%). Thus, the majority of cells expressing c-fos mRNA following GHRP-6 injection are NPY and GRF-containing cells. (Endocrinology 138: 771-777, 1997)