The Anorexigenic Action of the Octadecaneuropeptide (ODN) in Goldfish is Mediated Through the MC4R- and Subsequently the CRH Receptor-Signaling Pathways

Intracerebroventricular (ICV) administration of the octadecaneuropeptide (ODN), a peptide derived from diazepam-binding inhibitor, reduces food intake in goldfish as in rodents. However, the neurochemical pathways involved in the anorexigenic action of ODN have not yet been identified in goldfish. Alpha-melanocyte-stimulating hormone (α-MSH), corticotropin-releasing hormone (CRH), and CRH-related peptides play a major role in the control of food consumption in goldfish. In this species, the anorexigenic action of α-MSH is mediated via the CRH/CRH receptor neuronal system. Therefore, in the present study, we examined whether the anorexigenic effect of ODN in goldfish could be mediated through α-MSH and/or CRH neuronal pathways. ICV injection of ODN (10 pmol/g body weight (BW)) significantly reduced food intake, and the anorexigenic effect of ODN was suppressed by ICV preinjection of the melanocortin 4 receptor (MC4R) antagonist HS024 (40 pmol/g BW) or the CRH receptor 1/receptor 2 antagonist α-helical CRH(9–41) (100 pmol/g BW). ICV injection of ODN (10 pmol/g BW) induced a significant increase of proopiomelanocortin mRNA level but had no effect on CRH mRNA level, while ICV injection of the MC4R agonist, melanotan II (100 pmol/g BW), significantly enhanced CRH mRNA expression. These results suggest that, in goldfish, the anorexigenic action of ODN is mediated by the MC4R- and subsequently through the CRH receptor-signaling pathways.