Effect of different glycaemic conditions on gene expression of neuropeptides involved in control of food intake in rainbow trout; interaction with stress.

To assess mechanisms relating to food intake and glucosensing in fish, and their interaction with stress, we evaluated changes in the expression of orexigenic (NPY) and anorexigenic (POMC, CART and CRF) peptides in central glucosensing areas (hypothalamus and hindbrain) of rainbow trout subjected to normoglycaemic (control), hypoglycaemic (4 mg insulin kg(-1)) or hyperglycaemic (500 mg glucose kg(-1)) conditions for 6 h under normal stocking density (NSD; 10 kg fish mass m(-3)) or under stress conditions induced by high stocking density (HSD; 70 kg fish mass m(-3)). Hyperglycaemic NSD conditions resulted in decreased mRNA levels of NPY and increased levels of CART and POMC in the hypothalamus as well as increased mRNA levels of CART and CRF in the hindbrain compared with hypo- and normoglycaemic conditions. HSD conditions in normoglycaemic fish induced marked changes in the expression of all peptides assessed: mRNA levels of NPY and CRF increased and mRNA levels of POMC and CART decreased in the hypothalamus, whereas the expression of all four peptides (NPY, POMC, CART and CRF) decreased in the hindbrain. Furthermore, HSD conditions altered the response to changes in glycaemia of NPY and POMC expression in the hypothalamus and CART expression in the hypothalamus and the hindbrain. The results are discussed in the context of food intake regulation by glucosensor systems and their interaction with stress in fish.