CRESPI, E.J.*; VAUDRY, H.; DENVER, R.J.; Univ. of Michigan, Ann Arbor; Univ. of Rouen, France; Univ. of Michigan, Ann Arbor: Development of neuroendocrine controls of food intake in amphibians

Almost all studies on the neuroendocrine controls of food intake have been conducted on juvenile or adult animals; thus, little is known about the roles of hormones in energy balance regulation in larval or fetal life stages. These controls may be especially important in vertebrates with free-living larval forms such as fish and amphibians. Towards understanding the ontogeny of neuroendocrine regulation of food intake in amphibians, we investigated the effects of neuropeptides known to regulate food intake in mammals in larval and juvenile stages of the Western spadefoot toad, Spea hammondii. As in many other anurans, S. hammondii tadpoles are herbivorous grazers, but juveniles and adults are carnivorous predators, suggesting that neuroendocrine regulation of food intake may differ among life stages. Previously, we showed that intracerebroventricular (i.c.v.) injection of corticotropin-releasing factor and related peptides inhibited food intake in both tadpoles and juveniles. In this study, we tested the hypothesis that neuropeptide Y (NPY) stimulates appetite in larval and juvenile S. hammondii, as it does in other adult vertebrates. We found that i.c.v. NPY injection stimulated food intake and prey catching behavior in juveniles. Paradoxically, NPY inhibited food intake in a dose-dependent manner in prometamorphic tadpoles. Furthermore, injections of a NPY receptor antagonist stimulated food intake in tadpoles, suggesting that endogenous NPY secretion suppresses appetite. We discuss this developmental reversal in NPY function in spadefoot toads in the context of the ontogeny of foraging behavior regulation in amphibians and the evolution of energy balance signaling pathways in vertebrates. (Supported by NSF grant IBN 0235401 to R.J.D.)