CRESPI, EJ; DENVER, RJ; Univ. of Michigan, Ann Arbor: Role of corticotropin-releasing hormone (CRH) in the regulation of food intake in Xenopus laevis

In mammals CRH is known to be a regulator of food intake and energy balance. We tested the hypothesis that CRH is involved in the regulation of food intake in amphibians by (1) administering intracerebral ventricular (ICV) injections of CRH to juvenile Xenopus laevis to determine if CRH suppresses food intake as shown in other vertebrates, and (2) measuring brain CRH mRNA in animals that differed in time since feeding to determine if CRH gene expression is affected. We predicted that if CRH is involved in reducing food intake, then CRH mRNA levels would increase after feeding and decrease after periods of food deprivation. We used semi-quantitative RT-PCR to measure CRH mRNA in the anterior hypothalamus (preoptic area), where CRH neurons respond to environmental stressors in amphibians, and the mid-posterior hypothalamus (MPH), where feeding regulation centers occur in other vertebrates. In Xenopus, CRH neurons have been found in the MPH but the functional role of these neurons is unknown. We found that ICV injections of CRH significantly reduced food intake, suggesting that CRH has a conserved function in the regulation of food intake among vertebrates. As predicted, CRH mRNA levels significantly decreased in both brain regions after long-term food deprivation (14 and 31 d). By contrast, CRH mRNA in the MPH significantly decreased 24h after a meal relative to pre-feeding levels, then tended to increase during short-term food deprivation (3-4 d). Although the functional significance of these CRH gene expression fluctuations remains unknown, these data are the first to suggest that CRH neurons in Xenopus respond to energy balance and may be involved in the regulation of food intake. (EJC supported by NIH postdoctoral training grant. Supported by NSF grant IBN9974672 to RJD.)