Roles of stress hormones in food intake regulation in anuran amphibians throughout the life cycle

Towards understanding the ontogeny of energy balance regulation in vertebrates we analyzed the responses of corticotropin-releasing factor (CRF) and corticosterone to food deprivation in the Western spadefoot toad (Spea hammondii) at three developmental stages: premetamorphic tadpole, prometamorphic tadpole, and juvenile. Corticosterone responses to 5 days of food deprivation varied among developmental stages. Both pre- and prometamorphic tadpoles increased whole-body corticosterone content with food deprivation, but the magnitude of the response of premetamorphic tadpoles was significantly greater. By contrast, juvenile toads decreased plasma corticosterone concentration. Similarly, brain CRF peptide content tended to increase in food-deprived tadpoles but did not change in food-deprived juveniles. Therefore, there is an ontogenetic difference in the way the hypothalamic-pituitary-interrenal (HPI) axis responds to food deprivation in amphibians. In tadpoles, the HPI axis is activated in response to fasting as is seen in birds and mammals, and may be associated with mobilization of stored fuels and increased foraging. Juvenile toads do not respond to food deprivation by activating the HPI axis, but instead pursue a strategy of energy conservation that involves a reduction in plasma corticosterone concentration.