LAUSR

Abstract Neuropeptide Y (NPY), melanin-concentrating hormone 1 (MCH1), and cholecystokinin (CCK) are appetite-regulatory hormones. To understand the regulation of npy, mch1, and cck mRNA expression by dietary nutrients, the following two experiments were performed in the marine, carnivorous yellowtail (Seriola quinqueradiata). Juvenile yellowtails were fed one of four different diets for one week in Experiment 1—high protein-based diets combined with either fat (HF diet) or carbohydrates and low protein-based diets combined with either fat (LF diet) or carbohydrates. After feeding, serum non-esterified fatty acid concentration increased in the HF and LF groups, and serum free amino acid concentration increased in all dietary groups. In post-feeding fish, serum glucose concentration increased only in the HF group. The highest npy and cck mRNA levels in the forebrain were observed in the HF group, among the four dietary groups before feeding. Furthermore, a significant decrease in the npy mRNA level in the forebrain, after feeding, was observed only in the HF group. A similar trend was observed for cck and mch1 levels in the forebrain. Pyloric cecal cck increased significantly after feeding, in the LC group. Following the intraperitoneal administration of glucose in Experiment 2, the npy and mch1 mRNA expression levels in the forebrain decreased significantly. These results suggest that NPY and MCH1 levels in yellowtail are mainly regulated by the serum glucose concentration derived from the feed, and they work as feeding stimulators.