Enhanced lipid levels inhibit food intake in fish but no studies have characterized the possible mechanisms involved. We hypothesize that the presence of fatty acid sensing mechanisms could be related to the control of food intake. Accordingly, we evaluated in hypothalamus, hindbrain and Brockmann bodies (BB) of rainbow trout changes in parameters related to fatty acid metabolism, transport of FA, nuclear receptors and transcription factors involved in lipid metabolism, and components of the KATP channel after IP administration of different doses of oleic acid (long-chain fatty acid, LCFA) or octanoic acid (medium-chain fatty acid, MCFA). The increase in circulating LCFA or MCFA levels elicited an inhibition in food intake and induced in hypothalamus a response compatible with fatty acid sensing in which fatty acid metabolism, binding to CD36 and mitochondrial activity are apparently involved, which is similar to that suggested in mammals except for the apparent capacity of rainbow trout to detect changes in MCFA levels. Changes in those hypothalamic pathways can be related to the control of food intake since food intake was inhibited when FA metabolism was perturbed (using FAS or ACC inhibitors) and changes in mRNA levels of specific neuropeptides such as NPY and POMC were also noticed. This response seems exclusive of the hypothalamus, since the other centre controlling food intake (hindbrain) was unaffected by treatments. The results obtained in BB suggest that at least two of the components of a putative fatty acid sensing system (based on fatty acid metabolism and binding to CD36) could be present. Therefore, the present study provides, for the first time in fish, evidence for a specific role for FA (MCFA and LCFA) as metabolic signals in hypothalamus and Brockmann bodies where the detection of those FA can be associated with the control of food intake and hormone release.
- rainbow trout
- fatty acid
- lipid sensing
- Brockmann bodies
- Copyright © 2012, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology