Neuropeptide Y (NPY) is involved in the regulation of a variety of physiological events including pituitary hormone secretion, energy balance, and feeding behavior. The aim of the research project is to study the functional relationship between energy balance, hypothalamic orexigenic NPY and pituitary luteinizing hormone (M) secretion in fish, using the sea bass (Dicentrarchus labrax L.), as the experimental model. Some good evidences have been already found finding that in juvenile sea bass, under negative energetic balance imposed by chronic fasting, LH secretion ""in vivo"" is dose dependently enhanced in response to NPY. These data will be pursued by investigating the mRNA expression and peptides levels of NPY, GnRH (brain gonadotropin-releasing hormone) and LH as well as effects of NPY on LH - GnRS axis under negative or positive energetic balance. This investigation will be screened throughout different periods of starvation, and reproductive stage in male and female sea bass in order to understand possible sexual dimorphism and influences of the sexual cycle in these processes. Finally, the presence of leptin, the product of obesity (ob) gene in mammals, and the functional studies on the effect of leptin on energetic homeostasis, food intake and neuroendocrine function will be investigated.