Researchers found that a peptide similar to the skin‑tanning drug melanotan‑I can shrink appetite when directly injected into the brain of goldfish, showing that the appetite‑controlling system using melanocortin signals is ancient and works across species.

Posttranscriptional processing of proopiomelanocortin (POMC) yields melanocortin peptides, which are involved in the regulation of energy balance in mammals. The sequence preservation of the main brain melanocortin, alpha-melanocyte-stimulating hormone (alpha-MSH), suggests a conserved function throughout vertebrate evolution. We studied the involvement of the central melanocortin system in the control of food intake in the goldfish. In situ hybridization studies done following molecular cloning of POMC mRNA demonstrated positive POMC mRNA cell bodies exclusively expressed within the mediobasal hypothalamus, in the anterior, posterior and inferior part of the lateral tuberal nucleus and the medial region of the lateral recess nucleus. POMC expression is localized in brain areas appropriate for involvement in food intake and neuroendocrine regulation. Progressive fasting did not affect POMC mRNA expression levels. Intracerebroventricular administration of [Nle(4), D-Phe(7)]-alpha-MSH (NDP-alpha-MSH), a universal melanocortin agonist, within nanomolar range, dose-dependently inhibited food intake 2 h after treatment. The results show for the first time a functional melanocortin system in fishes that participates in central regulation of food intake. The conserved central expression pattern of POMC mRNA and role of MSH peptides in physiological regulation of food intake suggests that melanocortin functions were gained early in vertebrate evolution.