Effect of neuropeptide y on food intake in bullfrog larvae

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