Orally administrated fatty acids enhanced anorectic potential but did not activate central fatty acid sensing in Senegalese sole post-larvae

Abstract

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), α-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 FAsensing mechanisms ( fat/cd36-pg4l, fas, cpt1.1, cpt1.2, cpt1.3, sur, pparα and lxrα).

Appetite-Controlling Endocrine Systems in Teleosts

“…In Atlantic cod larvae, Kortner et al (42) showed that the expression levels of cck and npy were diet-specifically modulated and followed the same expression profile as the genes coding for digestive enzymes, suggesting a close connection between appetite control and digestion processes. Recently, two studies in Senegalese sole larvae have analyzed the effect of fatty acids ingestion in the control of food intake (378, 379). The administration of several fatty acids (leate, linoleate, α-linolenate, or eicosapentaenoate) in sole post-larvae enhanced the expression of the anorexigenic neuropeptides cart4 and pomcb and decreased the orexigenic npy , with no major discrepancies between the different fatty acids tested (378).…”

“…Recently, two studies in Senegalese sole larvae have analyzed the effect of fatty acids ingestion in the control of food intake (378, 379). The administration of several fatty acids (leate, linoleate, α-linolenate, or eicosapentaenoate) in sole post-larvae enhanced the expression of the anorexigenic neuropeptides cart4 and pomcb and decreased the orexigenic npy , with no major discrepancies between the different fatty acids tested (378). However, the transcriptional analysis of several anorexigenic: pyya, pyyb, glp1, cckl, cart1a, cart1b, cart2a, cart4, pomc-a, pomc-b, crf ; and orexigenic: gal, npy, agrp2 factors showed a dissimilar response to feeding times and dietary fatty acid composition (cod liver oil, linseed oil, soybean oil, or olive oil) that was generally not in agreement with their putative function (40).…”

“…Furthermore, the response of npy, pyy, pomc-c , and cart to food deprivation and refeeding in Atlantic halibut larvae did not appear to be coordinated (35), lacking a consistent expression pattern to explain their contribution to appetite control in early larvae as it was for Senegalese sole larvae (40). In addition, the differences observed between both studies in Senegalese sole larvae may be explained by the different approaches used: use of complex diets fed through the whole larval and post-larval stage (379) versus a tube-fed single meal of pure fatty acids solution (378). …”