Role of the G protein-coupled receptors GPR84 and GPR119 in the central regulation of food intake in rainbow trout.

We evaluated the role of the G protein-coupled receptors GPR84 and GPR119 in food intake regulation in fish using rainbow trout (Oncorhynchus mykiss) as a model. In the first experiment, we assessed the effects on food intake of intracerebroventricular treatment with agonists of these receptors. In the second experiment, we assessed the impact of the same treatments on mRNA abundance in the hypothalamus and hindbrain of neuropeptides involved in the metabolic control of food intake (npy, agrp1, pomca1 and cartpt) as well as in changes in parameters related to signalling pathways and transcription factors involved in the integrative response leading to neuropeptide production. Treatment with both agonists elicited an anorectic response in rainbow trout attributable to changes observed in the mRNA abundance of the four neuropeptides. Changes in neuropeptides relate to changes observed in mRNA abundance and phosphorylation status of the transcription factor FOXO1. These changes occurred in parallel with changes in the phosphorylation status of AMPKα and Akt, the mRNA abundance of mTOR as well as signalling pathways related to PLCβ and IP3. These results allow us to suggest that (1) at least part of the capacity of fish brain to sense medium-chain fatty acids such as octanoate depends on the function of GPR84, and (2) the capacity of fish brain to sense N-acylethanolamides or triglyceride-derived molecules occurs through the binding of these ligands to GPR119.