Ceramide counteracts the effects of ghrelin on the metabolic control of food intake in rainbow trout

In mammals ceramides are involved in the modulation of the orexigenic effects of ghrelin (GHRL). We previously demonstrated in rainbow trout that intracerebroventricular (ICV) treatment with ceramide (2.5 µg/100g fish) resulted in an anorexigenic response, i.e. a response opposed to that described in mammals where ceramide treatment is orexigenic. Therefore, we hypothesize that the putative interaction between GHRL and ceramide must be different in fish. Accordingly, in a first experiment we observed that ceramide levels in hypothalamus of rainbow trout did not change after ICV treatment with GHRL. In a second experiment, we assessed if the effects of GHRL treatment on regulation of food intake in rainbow trout changed in the presence of ceramide. Thus, we injected ICV GHRL and ceramide alone or in combination to evaluate in hypothalamus and hindbrain changes in parameters related to metabolic control of food intake. The presence of ceramide generally counteracted the effects elicited by GHRL on fatty acid sensing systems, the capacity of integrative sensors (AMPK, mTOR, and SIRT-1), proteins involved in cellular signaling pathways (Akt and FoxO1), and neuropeptides involved in the regulation of food intake (AgRP, NPY, POMC, and CART). The results are discussed in the context of regulation of food intake by metabolic and endocrine inputs.