Neuropeptide Y stimulates food intake and regulates metabolism in grass carp, Ctenopharyngodon idellus

Abstract

Neuropeptide Y (NPY) has been established as an important regulator of food intake in mammals. However, the involvement of NPY in the feeding behavior of fish has not yet been fully understood. The present study investigated the role of NPY in food intake in grass carp. The full-length cDNA sequence of gc-NPY was 797bp, and an ORF of 96 amino acids, including the 28-residue signal peptide and 36-residue mature peptide, which had high identities to the NPY of cyprinid fishes. Two receptors Y1 and Y5 which mediate the appetite-stimulating effects of NPY in mammals lost from some of the euteleost genomes. However, sequences of other NPY receptors Y8a and Y8b were obtained from the ESTs library of grass carp in our previous studies. NPY and both Y8 receptors were predominantly expressed in the brain. Cumulative food intake was significantly increased by intracerebroventricular administration of NPY during a 72-h observation period. For better understanding of NPY's action in grass carp, the mRNA levels of appetite regulators, energy metabolism genes and key digestive enzymes were assessed. The results showed that the mRNA levels of Y8b were significantly increased, while the expressions of cholecystokinin (CCK), cocaine and amphetamine regulated transcript (CART), pituitary adenylate cyclase-activating peptide (PACAP), leptin, leptin receptor (leptinR) and leptin receptor overlapping transcript protein (LEPROT) were significantly decreased after NPY injection. In addition, the marked stimulation of insulin-like growth factor1 (IGF1), insulin-like growth factor 1 receptor (IGF1R), lipoprotein lipase (LPL), Stearoyl-CoA desaturase 1 (SCD1), amylase and trypsin mRNA levels in liver were caused by NPY administration, and the mRNA level of uncoupling protein 1(UCP 1) tended to decrease but not significantly. These results indicate that NPY acts as an orexigenic factor in the grass carp, and Y8b may involve in the feeding regulation. NPY not only affects food intake, but also has marked effects on energy metabolism in grass carp. Moreover, NPY seems to closely interact with other appetite regulators, and the present results provide novel insight into these complex interactions. Further understandings of appetite regulation in fish ultimately have the potential to yield methods for improving feed efficiency in aquaculture.