Orally administered fatty acids enhance anorectic potential but do not activate central fatty acid sensing in Senegalese sole post-larvae

Studies in fish have reported the presence and function of fatty acid (FA)-sensing systems comparable in many aspects to those known in mammals. Such studies were carried out in juvenile and adult fish, but the presence of FA-sensing systems and control of food intake have never been evaluated in early life stages, despite the importance of establishing when appetite regulation becomes functional in larval fish. In this study, we aimed to elucidate the possible effects of different specific FAs on neural FA-sensing systems and neuropeptides involved in the control of food intake in Senegalese sole post-larvae. To achieve this, we orally administered post-larvae with different solutions containing pure FA - oleate (OA), linoleate (LA), alpha-linolenate (ALA) or eicosapentaenoate (EPA) - and evaluated changes in mRNA abundance of neuropeptides involved in the control of food intake and of transcripts related to putative FA-sensing systems, 3 and 6 h post-administration. The changes in neuropeptide gene expression were relatively consistent with the activation of anorectic pathways (enhanced cart4 and pomcb) and a decrease in orexigenic factors (npy) following intake of FA. Even though there were a few differences depending on the nature of the FA, the observed changes appear to suggest the existence of a putative anorectic response in post-larvae fish to the ingestion of all four tested FAs. However, changes in neuropeptides cannot be explained by the integration of metabolic information regarding FAs in circulation through FA-sensing mechanisms in the brain. Only the reduction in mRNA levels of the FA metabolism gene acc in OA-treated (6 h), ALA-treated (3 h) and EPA-treated (3 and 6 h) post-larvae could be indicative of the presence of a FA-sensing system, but most genes either were not significantly regulated (fat/cd36-lmp2, acly, kir6.x, srebp1c) or were affected in a way that was inconsistent with FA-sensing mechanisms (fat/cd36-pg4l, fas, cpt1.1, cpt1.2, cpt1.3, sur, ppar alpha and lxr alpha).