Stress exerts a profound effect on the gut and altered stress response is associated with functional disorders, including irritable bowel syndrome (IBS). Brain corticotropin-releasing factor (CRF) and CRF receptor 1 (CRF1) play an important role in the colonic motor, anxiogenic and endocrine responses to stress, while activation of CRF2 restrains the behavioral and endocrine responses to stress. The objectives, based on our preliminary data, are to test in conscious rats the novel concept that peripheral CRF2 impedes the CRF1 receptor-mediated stress- and CRF-induced colonic motility and visceral hyperalgesia as part of a stress-coping mechanism.
Specific aim 1 will establish that peripheral activation of CRF2 counteracts the stimulatory effect of CRF and stress on colonic motor function. This will be achieved by: 1) characterizing, in vivo and in vitro, the inhibitory action of peripheral CRF2 agonist, urocortin 2 (Ucn 2) on CRF1 preferential agonist, oCRF1- and stress-induced colonic motor stimulation; and 2) determinining the neuromediators involved in CRF2 action and the chemical coding of cells expressing CRF2 in the colonic tissue.
Specific aim 2 will demonstrate that peripheral CRF2 activation blunts colorectal distention (CRD) and stress-induced visceral pain. This will be achieved by: 1) assessing the inhibitory effect of peripheral injection of Ucn 2 against CRD and stress-induced enhanced visceral pain ; and 2) identifying the neuronal and chemical pathways by which Ucn 2 attenuates the visceral pain response to CRD and stress. The mechanisms involved in the CRF2 mediated modulation of visceral pain will be determined by functional (visceral pain to CRD) and electrophysiological (in vitro colonic afferent activation by distention) measurements, as well as induction of Fos and activation of Erk in the lumbo-sacral spinal cord. Novel tools such as RNAi to silence colonic CRF and CRF2 receptor gene, ultrasonomicrometry for in vitro motility measurements and laser capture microdissection techniques to determine tissue distribution of CRF2 and ligands, highly selective CRF receptor and ligand antibodies and CRF2 antagonists will be used in these studies. The elucidation of the effects and mechanisms through which peripheral CRF2 dampen stress- and CRF-related colonic motor alteration and visceral hypersensitivity will have important clinical implications in functional disorders such as IBS, for which a link between stress, CRF signaling pathway and symptoms are increasingly recognized.
