GABAA Receptor Subtypes Regulate Stress-Induced Colon Inflammation in Mice

BACKGROUND & AIMS: Psychological stress, in early life or adulthood, is a significant risk factor for inflammatory disorders, including inflammatory bowel diseases. However, little is known about the mechanisms by which emotional factors affect the immune system. gamma-Aminobutyric acid type A receptors (GABA(A)Rs) regulate stress and inflammation, but it is not clear whether specific subtypes of GABA(A)Rs mediate stress-induced gastrointestinal inflammation. We investigated the roles of different GABA(A)R subtypes in mouse colon inflammation induced by 2 different forms of psychological stress. METHODS: C57BL/6J mice were exposed to early-life stress, and adult mice were exposed to acute-restraint stress; control mice were not exposed to either form of stress. We collected colon tissues and measured contractility using isometric tension recordings; colon inflammation, based on levels of cluster of differentiation 163 and tumor necrosis factor messenger RNA (mRNA) and protein and myeloperoxidase activity; and permeability, based on levels of tight junction protein 1 and occludin mRNA and protein. Mice were given fluorescently labeled dextran orally and systemic absorption was measured. We also performed studies of mice with disruption of the GABA(A)R subunit alpha 3 gene (Gabra3(-/-) mice). RESULTS: Mice exposed to early-life stress had significantly altered GABA(A)R-mediated colonic contractility and impaired barrier function, and their colon tissue had increased levels of Gabra3 mRNA compared with control mice. Restraint stress led to colon inflammation in C57/BL6J mice but not Gabra3(-/-) mice. Colonic inflammation was induced in vitro by an alpha 3-GABA(A)R agonist, showing a proinflammatory role for this receptor subtype. In contrast, alpha 1/4/5-GABA(A)R ligands decreased the expression of colonic inflammatory markers. CONCLUSIONS: We found stress to increase expression of Gabra3 and induce inflammation in mouse colon, together with impaired barrier function. The in vitro pharmacologic activation of alpha 3-GABA(A)Rs recapitulated colonic inflammation, whereas alpha 1/4/5-GABA(A)R ligands were anti-inflammatory. These proteins might serve as therapeutic targets for treatment of colon inflammation or inflammatory bowel diseases.