RESUMO
Experiments were performed to determine whether growth hormone-releasing hormone (GHRH) mRNA displays diurnal variations in the hypothalamus and cortex of the rat. Levels of GHRH and beta-actin mRNA were measured from hypothalamic and cortical extracts using the reverse transcriptase polymerase chain reaction method in rats sacrificed at 4 h intervals across a 12:12 h light:dark cycle. Hypothalamic GHRH mRNA peaked around the light onset, declined during the light period, and stayed low in the dark. Variations in hypothalamic beta-actin and cortical GHRH mRNA levels were not observed. beta-Actin mRNA expression in the cortex was higher in the dark than in the light period. The results demonstrate that hypothalamic GHRH mRNA displays diurnal variations.
Assuntos
Córtex Cerebral/metabolismo , Ritmo Circadiano/fisiologia , Hormônio Liberador de Hormônio do Crescimento/metabolismo , Hipotálamo/metabolismo , Animais , Masculino , Reação em Cadeia da Polimerase , Ratos , Ratos Sprague-DawleyRESUMO
Vasoactive intestinal peptide (VIP), the structurally homologous pituitary adenylate cyclase-activating peptide (PACAP) and the pituitary hormone, prolactin (PRL) enhance rapid eye movement sleep (REMS). VIP and PACAP are both inducers of PRL gene expression and release in the pituitary gland. Little is known about PRL regulation in the brain although it is hypothesized that the REMS-promoting activity of i.c.v. administered VIP may be mediated via the activation of cerebral PRL. To test whether VIP or PACAP in fact increase intracerebral mRNA, the peptides (VIP: 30 or 300 pmol; PACAP: 220 pmol) were injected i.c.v. into rats at dark onset. 1 h later, cDNA was synthesized from purified hypothalamic mRNA. Standardized amounts were analysed for PRL using the polymerase chain reaction followed by Southern blotting and hybridization. Compared with beta-actin mRNA levels, both VIP and PACAP increased PRL mRNA levels in a dose-dependent fashion though VIP was more effective on a molar basis. The previously reported alternatively spliced PRL mRNA (lacking exon 4) was not detected. The data support the hypothesis that the REMS-promoting activity of central VIP and PACAP might be mediated by cerebral PRL.