Corticotropin-releasing hormone (CRH) is recognized as the key hypothalamic regulator of the mammalian stress response. Within the hypothalamic-pituitary-adrenal axis (HPA), hypothalamic CRH is the principal hormone controlling pituitary ACTH secretion. At other sites in the central nervous system, CRH is thought to act as a neurotransmitter to mediate stress-related behavioral, autonomic, and immunological responses. The effects of CRH are mediated by two classes of CRH receptors and are modulated by a CRH-binding protein. Several years ago, a new mammalian CRH-like ligand was identified by Vaughan and colleagues. This 40 amino acid neuropeptide, called urocortin, is 43 percent identical to CRH and binds to both of its receptors, albeit with a higher affinity to CRHR2. Because CRH and urocortin can bind to and activate both CRH receptors, iv or icv administration of urocortin results in very similar physiological responses to those observed with CRH. Since urocortin is colocalized with CRH receptors in a number of sites, the investigator hypothesize that urocortin mediates or modulates some of the physiological effects previously thought to be mediated by CRH. The proposed work will specifically examine the in vivo role of urocortin in the CNS and pituitary. Based upon physiological experiments and neuroanatomical data, the investigator hypothesizes that urocortin acts in the brain to modulate feeding and drinking behavior, anxiogenic behavior, and autonomic function. Also it appears that urocortin might act in a paracrine fashion in the anterior pituitary to modulate basal or CRH-mediated ACTH secretion. To test these hypotheses, the investigator will further characterize the expression of urocortin mRNA in the adult mouse CNS and pituitary under basal and altered physiological states (stress, altered glucocorticoid status, food or water deprivation) using in situ hybridization and RNAase protection assays. Second, she will create an inducible brain-specific urocortin knockout mouse and characterize the physiological and behavioral changes resulting from the lack of urocortin expression in the CNS. Third, primary anterior pituitary cultures will be used to test the role of pituitary urocortin in basal and stimulated ACTH secretion from corticotropes. Finally, the investigator will examine the molecular mechanisms responsible for regulation of urocortin expression in cultured cells and in transfection assays. These studies will allow a more accurate determination of the physiological role(s) of urocortin in CNS and pituitary, and to differentiate its roles from those of CRH. As dysregulation of CRH activity is thought to be important in major depression, anxiety disorders, and anorexia, a clearer understanding of the role(s) of urocortin in CNS and pituitary sites may be important to our understanding of the pathophysiology of these human disease states.
