Objectives: 

We aimed to evaluate in a teleost model (rainbow trout) the presence of putative components of fatty acid sensing mechanisms (as described in mammalian models) and their response to enhanced levels of circulating FA.

Materials: 

Fish received IP 10 ml•kg-1 injection of saline solution alone (control) or containing oleic acid (60 or 300 mg•kg-1) or octanoic acid (6 or 3 mg•kg-1).Blood, hypothalamus,hindbrain and Brockmann bodies(BB) samples were taken 6h after treatment to assess enzyme activities, tissue metabolites and mRNA levels. A second set of fish received IP 10 ml•kg-1 injection of saline solution alone (control) or containing oleic acid (60 or 300 mg•kg-1) or octanoic acid (60 or 300 mg•kg-1).Food intake was registered for 3 days before treatment and then 6 and 24 h after IP treatment.Then, fish received IP 10 ml•kg-1 injection of saline solution alone (control) or containing C75 (5 mg•kg-1) or TOFA (5 mg•kg-1) or TOFA/C75 (5 mg•kg-1 each). FI was registered for 3 days before treatment and then 6 and 24 h after IP treatment.

Results: 

The increase in circulating LCFA or MCFA levels in rainbow trout elicited an inhibition in food intake and induced in hypothalamus a response compatible with fatty acid sensing in which fatty acid metabolism was involved.Food intake was inhibited when the fatty acid metabolism was perturbed and changes in mRNA levels of specific neuropeptides such as NPY and POMC were also noticed. This response seems to be 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 could be also present in this tissue.

Conclusions: 

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.