Effect of neuropeptide Y on food intake in bullfrog larvae

Neuropeptide Y (NPY) is a potent orexigenic neuropeptide implicated in appetite regulation in mammals. However, except for teleost fish such as the goldfish and zebrafish, the involvement of NPY in the regulation of feeding in non-mammalian vertebrates has not been well studied. Anuran amphibian larvae feed and grow during the pre- and pro-metamorphic stages, but, thereafter they stop feeding as the metamorphic climax approaches. Therefore, orexigenic factors seem to play important roles in pre- and pro-metamorphic larvae. We investigated the role of NPY in food intake using bullfrog larvae including pre- and pro-metamorphic stages, and examined the effect of feeding status on the expression level of the NPY transcript in the hypothalamus. NPY mRNA levels in hypothalamus specimens obtained from larvae that had been fasted for 3 days were higher than those in larvae that had been fed normally. We then investigated the effect of intracerebroventricular (ICV) administration of NPY on food intake in the larvae. Cumulative food intake was significantly increased by ICV administration of NPY (5 and 10 pmol/g body weight, BW) during a 15-min observation period. The NPY-induced orexigenic action (10 pmol/g BW) was blocked by treatment with a NPY Y1 receptor antagonist, BIBP-3226 (100 pmol/g BW). These results indicate that NPY acts as an orexigenic factor in bullfrog larvae.