YAO, M*; WESTPHAL, N; DENVER, RJ; Univ. of Michigan; Univ. of Michigan; Univ. of Michigan: Acute stress-induced elevation in corticotropin-releasing hormone expression in Xenopus laevis.

Corticotropin releasing hormone (CRH) plays a central role in the regulation of neuroendocrine, autonomic, and behavioral responses to physical and emotional stress. In nonmammalian vertebrates, CRH may regulate both the thyroid and interrenal axes, and can mediate environmental effects on amphibian metamorphosis. Towards understanding the evolution of this ancient signaling pathway we conducted immunohistochemistry (IHC) to map the neuroanatomical distribution of CRH perikarya and fibers in juvenile Xenopus laevis brain. We observed specific, CRH immunoreactivity (CRH-ir) in several hypothalamic, thalamic, limbic, brain stem and spinal cord nuclei, and in the median eminence. CRH-ir in the frog brain follows a conserved, vertebrate pattern of expression. To determine if acute physical stress alters CRH-ir, we exposed juvenile frogs to shaking stress and conducted IHC morphometric analysis. Shaking stress for 4.5 hr increased plasma corticosterone and produced a robust increase (240% of control in the periventricular zone, and 457% of control in the subventricular zone) in CRH-ir in the ventral preoptic nucleus, but not in other brain regions. We sequenced 1 kb of 5’-flanking DNA of two Xenopus CRH genes and examined the conservation of regulatory sequences in the frog genes with those of mammalian CRH promoters. We found highly conserved consensus AP1 and CRE sequences in Xenopus and mammals, to which Fos-Jun or phosphorylated CREB, respectively, could bind to regulate CRH gene expression. We hypothesize that the basic regulatory elements of the CRH gene responsible for tissue specific and stress-induced expression arose early in vertebrate evolution. (supported by NSF grant IBN9974672 to RJD).