CRESPI, E.J.*; DENVER, R.J.; Univ. of Michigan, Ann Arbor: Corticotropin-releasing hormone regulates locomotion and foraging behaviors in spadefoot toad (Spea hammondii) tadpoles and juveniles

Corticotropin-releasing hormone (CRH) and corticosterone (CORT) are primary components of the vertebrate stress axis and are involved in food intake regulation. We investigated the effects of CRH and CORT on foraging behavior in spadefoot toad (Spea hammondii) tadpoles and juveniles to assess the function of these hormones throughout development. We administered intracerebroventricular (icv) injections of ovine CRH or a CRH receptor antagonist, αhelical CRH_(9-41)(ahCRH) to tadpoles and, one hour later, observed behavior for a 2-minute period. In premetamorphic tadpoles (Gosner stage 33), icv injections of CRH increased swimming while ahCRH reduced movement compared with controls. Injections of CRH in prometamorphic tadpoles (Gosner stage 37) increased swimming but also reduced feeding. Injections of ahCRH increased feeding, suggesting that in later-staged tadpoles basal (i.e., unstressed) CRH secretion modulates feeding by exerting a tonic suppressive effect on appetite. Injections of ahCRH also stimulated prey catching behavior in Spea juveniles. By contrast to the inhibitory effects of CRH on food intake, we found that CORT treatments caused an increase in feeding. We also observed an increase in feeding 6h after icv CRH injection. This increase was associated with elevated whole-body CORT concentrations and was blocked by treatment with the glucocorticoid receptor antagonist RU486. Our results show that both CRH and CORT affect feeding behavior in Speatadpoles as they do in juveniles and other adult vertebrates. Our results also suggest that the anorectic effect of CRH during the initial �fight or flight� stress response may be balanced by a CORT-mediated increase in food intake during the recovery phase. (supported by NSF grant IBN 9724080 to R.J.D.)