The Effects of NPY and Insulin on Food Intake Regulation in Fish1

Abstract

Recent abundant studies report that in rodents starvation induces in- creased neuropeptide Y (NPY) mRNA expression and peptide secretion in the hy- pothalamus which reduces autonomic nervous activity and promotes food intake, and intracerebroventricular (ICV) injection of NPY has potent orexigenic effects. Conversely, the effect of insulin in the central nervous system is to inhibit food intake and NPY biosynthesis and secretion. In mammals body fatness is regulated and insulin acts as one intake inhibitory signal related to fatness. In salmon (On- corhynchus sp.) we have demonstrated a rise in NPY-like mRNA expression and a coincident decrease in plasma insulin levels during 2 to 3 weeks of starvation. Additionally, experimentally manipulating body fatness with high and low fat diets has demonstrated that body fatness affects food intake in teleost fishes, raising the possibility that NPY and insulin act to regulate their food intake. Therefore, we hypothesized that as in rodents, ICV treatment with NPY would stimulate food intake while ICV insulin would reduce food intake. Preliminary results suggest that ICV NPY administration does stimulate food intake in channel catfish (Ictal- urus punctatus), but central injection of insulin has no effect. Results of treatments with the sulfated octapeptide of cholecystokinin and the recombinant fragment of rat leptin 2256 are also discussed.