LARSON, ET; SCHJOLDEN, J; SCHI�TH, H; LARHAMMAR, D; WINBERG, S; Uppsala University: Melanocortin peptides influence appetite in rainbow trout.

Melanocortin peptides (α-MSH, β-MSH, γ-MSH, ACTH) are a series of peptides cleaved from the precursor proopiomelanocortin (POMC). In mammals, melanocortins influence appetite, learning, sexual and social behavior. Food intake in mammals is influenced via both the MC4 and MC3 receptor subtypes which both seem to inhibit appetite with the MC4 having a stronger effect. Rainbow trout were used to investigate if the melanocortin system influences appetite in teleosts. Fish were allowed to acclimate to individual aquaria for one week during which baseline food intake values were determined. MC agonists, antagonists or saline were then delivered directly into the third cerebral ventricle. Food intake was measured at 2 hours post injection. We used two antagonists, HS024, specific for MC4 and SHU9119, which acts on both MC3 and MC4. We also used MTII, a general MC agonist. All three substances affected feeding in a dose-dependent manner. HS024 was the most effective increasing food intake almost trifold over baseline at the highest dose. SHU9119 acted with about half the efficiency of MS024. MTII showed a dose dependent inhibition of food intake with the highest dose resulting in food intake roughly one-third of baseline. These results indicate that the melanocortin system is important for appetite regulation in teleosts and that the MC4 receptor is a key player. This information can be used to improve fish growth and performance in aquaculture. Supported by the Swedish Research Council for Environment, Agricultural Sciences, and Spatial Planning (FORMAS).