AGA Abstracts 11.3% in group C. Conclusions BT monotherapy had a significantly lower risk of radiation proctopathy compared to BT in combination with EBRT. BT followed by EBRT boost increased endoscopic severity of radiation proctopathy compared to BT boost after EBRT. These findings may allow one to decrease rectal morbidity caused by radiotherapy for prostate cancer. Mo2028 A Functional Approach to Improve Barrier Function in Irradiated Mice Lauren Vaught, Liangjie Yin, Astrid Grosche, Amy Zhang, Paul Okunieff, Sadasivan Vidyasagar Tight junctions are formed by mature enterocytes and create an efficient barrier that has the necessary machinery for electrolyte and nutrient absorption. Radiotherapy causes epithe- lial barrier dysfunction leading to increased macromolecular translocation into the systemic compartment causing endotoxemia and inflammatory response. Recently, it was shown that glucose and some amino acids (AAs) activated active anion secretion and/ or increased paracellular permeability, whereas our mitigating amino acids mixture (MAAM) comprised of lysine, glycine, tryptophan, tyrosine, aspartic acid, isoleucine, threonine, valine, and serine increased electrolyte absorption and decreased paracellular permeability. The mechanism by which these amino acids tightened the mucosal barrier was not known. Therefore, studies were undertaken to determine the mechanism by which MAAM tightened the mucosal barrier. NIH Swiss mice were irradiated using a 137 Cs source. Radiation dose-dependent and time-dependent (0, 6, 12, 24, 48, 72, and 144 hr after irradiation) changes in transepithe- lial electrical resistance (TEER) and dilution potential (DP) and the relative permeability of Cl - and Na + (PCl/PNa) were measured. Transmission electron microscopy (TEM) images, Western blot analysis, and immunohistochemistry (IHC) for the cell junction protein complex (Claudin 1, 2, 5, Nectin, and E-cadherin) were performed at similar time points. Radiation resulted in a dose-dependent increase in conductance (43.3 ± 1.2, 29.5 ± 1.2, 48.2 ± 2.3, 48.9 ± 1.7, 38.7 ± 1.2 mS at 0, 1, 3, 5, 7 Gy, respectively). Similarly, time-dependent changes in conductance showed a maximal increase occurring in the first 6 hr (46.3 ± 1.5); there was no significant difference with increasing time after irradiation. Treatment with MAAM resulted in a significant decrease in conductance. DP studies showed that MAAM restored ion selectivity. TEM showed disruption of the cell junction complex and formation of clear space between the cells as early as 6 hr after irradiation. The changes persisted for the duration of the experiment (6 days). MAAM prevented cell junction disruption in mice; this was identifiable at 6 hr after irradiation. Western analysis and IHC showed a radiation dose-dependent increase in Claudin 1, 2, 5, Nectin, and E-cadherin except at 7 Gy. MAAM further increased Claudin 1, 2, 5, Nectin, and E-cadherin across all radiation doses. MAAM treatment decreased paracellular permeability. TEM showed disruption of the cell junction complex that peaked at 6 hours and was corrected using MAAM. Western analysis and IHC showed that radiation-induced alterations in the cell junction protein complex were further corrected in the MAAM group. We conclude that the disruption in the barrier results from changes in the cell junction complex and that MAAM restores the barrier function by correcting these changes. Mo2029 Differential Activity of NHE3 and NHE2 in the Small Intestine of Irradiated Mice Liangjie Yin, Lauren Vaught, Amy Zhang, Paul Okunieff, Sadasivan Vidyasagar Introduction: The major functions of the gastrointestinal (GI) tract are the mucosal barrier and the absorption of nutrients, electrolytes, and water. Electrolyte absorption occurs in fully mature and differentiated villus cells via coupled sodium-hydrogen exchange (NHE3) and chloride bicarbonate exchange (Cl-HCO3). Radiation targets rapidly dividing cells, such as cancer cells, and clonogenic cells located in the crypts, causing a decrease in proliferation, maturation, and differentiation that causes villus shortening. A decrease in villus height is therefore responsible for the diarrhea associated with radiation exposure. Also, it was previ- ously shown that radiation increases intracellular calcium oscillations and cyclic adenosine monophosphate (cAMP) levels in enterocytes. Elevated intracellular cAMP is known to inhibit NHE3 and increase NHE2 activity. However, the effect of radiation on NHE3 and NHE2 is not known. Therefore, we investigated the effect of radiation on NHE2 and NHE3 activity in the GI tract. Methods: NIH Swiss mice were irradiated using a 137 Cs source. The small intestinal mucosa of mice with 0, 1, 3, 5, or 7 Gy were studied on day 6. 22 Na flux studies were undertaken to measure Na absorption. Relatively specific NHE2 inhibitor 5-(N-Ethyl- N-isopropyl)amiloride (EIPA) and NHE3 inhibitor 5-(N,N-Hexamethylene)amiloride (HMA) were used to determine their activity. Immunohistochemistry and Western blot analysis were performed to study NHE2 and NHE3 protein and expression levels. Results: Radiation increased basal short circuit current (I sc ) in a dose-dependent fashion until 5 Gy. At 7 Gy there was a marginal decrease when compared to 5 Gy. Isotope flux studies showed a radiation dose-dependent decrease in Na absorption. The addition of EIPA or HMA did not decrease the basal I sc across all radiation doses. HMA-inhibitable flux decreased with increas- ing radiation dose, while EIPA-inhibitable flux increased with increasing radiation dose. IHC showed that NHE3 and NHE2 expression occurs mostly along the brush boarder membrane of villus epithelial cells. NHE3 expression and its protein levels decreased with increasing radiation doses, while NHE2 expression and protein levels increased with increas- ing radiation doses. The maximal increase in NHE2 protein level was detected at 7 Gy. Conclusions: Radiation decreases sodium absorption and results in decreased expression of NHE3. A small but significant portion of the sodium flux in the small intestine of irradiated mice was maintained by NHE2 activity. NHE2 activity in the presence of radiation suggests a less efficient but alternate mechanism for sodium absorption. S-774 AGA Abstracts Table 1 Mo2030 Neurobiology of Psychological Resilience in Irritable Bowel Syndrome (IBS) and Inflammatory Bowel Disease (IBD) Patients Lisa A. Kilpatrick, Arpana Gupta, Aubrey D. Love, Jennifer S. Labus, Mher Alaverdyan, Kirsten Tillisch, Bruce D. Naliboff, Emeran A. Mayer BACKGROUND: Resilience is commonly defined as the process of adapting well in the face of adversity. Stressful life events have been associated with the onset or symptom exacerbation of gstrointestinal disorders such as IBS as well as inflammatory bowel disease IBD. A better understanding of the neural circuitry associated with enhanced or deficient resilience holds promise for the development of new interventions to improve health. AIMS: To examine structural brain changes associated with psychological resilience in male and female IBS and IBD patients compared to healthy controls (HCs). We hypothesized that reduced resilience in pain populations would be associated with alterations in emotion- arousal related brain regions. METHODS: 48 HCs (33 female), 54 IBS patients (43 females) and 27 IBD patients (14 females) completed MRI scans and resilience questionnaires. The questionnaires consisted of the Brief Resilience Scale (BRS) and the Connor-Davidson Resili- ence (CD-RISC) scale. The CD-RISC was comprised of 4 factors representing (1) persistence, (2) emotional/cognitive control, (3) ability to bounce back, and (4) sense of control/meaning of one's life. Volume measures for 165 brain regions were calculated and entered into partial least squares (PLS) analyses with the behavioral data. RESULTS: Male and female IBS patients demonstrated significantly reduced psychological resilience, particularly in terms of ‘bounce back'. While male IBD patients did not differ from HCs in terms of resilience; female IBD patients showed significantly reduced BRS scores. PLS identified a brain-behavior pattern (accounting for 34.4% cross-block variance; p=.05) demonstrating that reduced resilience in male IBS patients was related to decreased volume of a set of brain regions including: precuneus, rectal gyrus, anterior cingulate gyrus, postcentral gyrus and postcentral sulcus and increased volume of the brainstem. Male HCs and IBD patients did not demonstrate this brain-behavior pattern. For female subjects, PLS identified a brain-behavior pattern (accounting for 40.2% cross-block variance, p=.05) demonstrating that resilience in female HCs was associated with increased volume of the cerebellum and postcentral sulcus and decreased volume of the precuneus, insula, and orbital gyri. Female IBS patients failed to demonstrate this brain-behavior pattern while female IBD patients showed a similar pattern to HCs in terms of BRS but not CD-RISC. DISCUSSION: Reduced psychological resilience was more prominent in IBS patients than in IBD patients, particularly for males. IBS males demonstrated a relationship between reduced psychological resilience and decreased volume of brain regions associated with autonomic and emotional-arousal functions. Female subjects demonstrated different brain-behavior patterns, highlighting a need to consider sex in resili- ence research. Mo2031 Involvement of Catechol-O-Methyltransferase Genetic Reduction in Murine Intestinal Dysmotility: A Possible Link Between Psychiatric Disorders and Irritable Bowel Syndrome Valentina Caputi, Ilaria Marsilio, Lucia Cavallo, Stefania A. Frizzo, Francesca Marinelli, Maddalena Mereu, Isabella Lante, Genny Orso, Francesco Papaleo, Maria Cecilia Giron Introduction. Irritable bowel syndrome (IBS) is a still poorly understood functional disorder, associated with significant psychological distress and psychiatric comorbidities in the absence of organic disease. Aim. Since psychiatric disorders and pain syndromes are associated to low catechol-O-methyltransferase (COMT) activity and these conditions are both related to IBS we assessed whether COMT genetic reduction affects enteric nervous system (ENS) homeostasis and intestinal function. Methods. Female COMT heterozygous (COMT +/- ) and wild-type (COMT +/+ ) mice (12±2 weeks) were used and their genotypes were confirmed by PCR on mouse tail DNAs. In isolated ileum segments, mounted vertically in organ baths, changes in muscle tension were recorded by isometric transducers following charbacol (0.001-100 μM) or 60 mM KCl treatment, electric field stimulation (EFS, 1-40 Hz, in presence or absence of 1 μM tetrodotoxin or atropine) or non-adrenergic non-cholinergic (NANC) neurotransmission (EFS=20 Hz, 1 μM atropine and 1 μM guanethidine, with and without 0.1 mM L-NAME). In ileum whole mount preparations changes in neuronal markers, such as HuC/D and betaIII-tubulin, and in glia markers, S100beta and glial fibrillary acidic protein (GFAP) were determined by confocal immunofluorescence. Acetylcholinesterase and NADPH-diaphorase biochemical assays together with nNOS immunohistochemistry were performed to evaluate the integrity of ENS neurochemical code. Gastrointestinal transit were assessed after 30 minutes post intragastric administration of a fluorescent labeled dextran probe. Results. In vitro contractility studies have shown altered receptor and not-receptor mediated responses (-41±8% of Emax for carbachol and -38±5% of contraction to KCl, respectively) together with an altered neuronal cholinergic and nitrergic transmission (- 33±6% and +56±11% at 20 Hz, respectively) in COMT +/- mice. In the ENS of COMT +/- mice the ileal distribution of S100beta and GFAP immunoreactivity was found significantly increased in myenteric ganglia. A reduced staining of acetylcholinesterase + fibers (-26±3%) and NADPH-diaphorase + neurons (-23±4%) together with an altered distribution of nNOS immunopositive neurons was found in COMT +/- mice compared to wild-type animals. The