AGA Abstracts of placebo analgesia between IBS and healthy subjects. AIM: To test the hypothesis that IBS and controls display different neuro-network in visceral placebo analgesia. METHODS: 1. Fourteen IBS (F=10, 36.3 ± 11.5 yrs) and 13 controls (F=8, 36.5 ± 9.9 yrs) were enrolled. 2. Psychophysical inventories [Hospital Anxiety and Depression Scale (HADS), visual ana- logue scale (VAS) and short-form McGill questionnaire (SF-MPQ], and brain activity [using 3T fMRI] upon placebo treatment and upon anticipation were assessed in response to CRD. 3. Placebo treatment consisted of a standard instruction by stating the effectiveness of a newly-developed drug (saline actually) to relieve visceral pain. RESULTS: 1. IBS patients had higher HADS-anxiety score (IBS vs. controls: 8.21 ± 3.37 v.s 5.69 ± 3.40, p=0.04) and lower pain threshold upon CRD (mild pain: 29.4 ± 7.4 vs. 35.7 ± 7.9 , p=0.02; moderate pain: 39.7 ± 7.4 v.s 47.8 ± 8.3 mmHg, p=0.02) than controls. 2. Placebo treatment decreased the VAS score and SF-MPQ parameters upon CRD in both IBS and controls. 3. Comparable placebo analgesic effect was observed in both IBS and controls evidenced by similar VAS reduction after placebo (IBS vs. control= 20.8 ± 14.2 vs. 24.8 ± 10.8, p=0.2) 3. In healthy subjects, placebo analgesia was accompanied by reduced neuronal activities in the visceral pain matrix including thalamus, somatosensory cortices, insula, prefrontal, and anterior cingulate cortex. In IBS, reduced neuronal activity was observed in only posterior cingulate gyrus (area 29) and thalamus after placebo treatment. 4. During anticipation, dorsal lateral prefrontal cortex (DLPFC) activation was noted in controls, while more extended neuronal activation involving emotional circuit (PFC, bilateral insula, anterior/posterior cingulate , and bilateral parahippocampal gyrus) was observed in IBS patients. CONCLUSION: 1. Both IBS patients and controls achieve comparable placebo analgesia under experimentally- induced CRD. 2. Though both groups display similar placebo effect psychophysically, the central representations in response to placebo and anticipation are different. 858 Reduced Structural Connectivity Between Amygdala and Prefrontal Cortex in Patients With Irritable Bowel Syndrome: A Diffuse Tensor Imaging Study Jennifer S. Labus, Eduardo Vianna, Johanna M. Jarcho, Kirsten Tillisch, Joshua A. Bueller, Emeran A. Mayer Background: Irritable bowel syndrome (IBS) patients have increased engagement of an emotional arousal circuit [which includes the amygdala and locus coeruleus (LC)] during expectation of visceral pain and altered functional connectivity within prefrontal-limbic- pontine pain modulation circuits during rectal distension. In addition, IBS patients show an increase in left dorsolateral prefrontal cortex (dlPFC) for both grey matter and cortical thickness. Aims: In this pilot study, we sought to determine the anatomical connectivity of the amygdala, a key structure within the emotional arousal circuits, in IBS patients and healthy controls (HC), and to test the hypothesis that previously reported differences in cortico-limbic functional and effective connectivity are associated with group-based structural differences between these regions. Methods: Diffusion weighted images were obtained from 7 IBS and 9 age-matched HCs. Estimation of amygdala-seeded tracts was performed using probabilistic tractography in FSL. In order to verify differences in fiber connectivity between groups, we performed a permutation test using all resulting fiber tracts from each subject using a significance threshold of p<0.05 level and 5000 permutations. Results: HCs showed amygdala connectivity with a number of brain regions including lateral prefrontal cortices, frontal pole, insula cortex, anterior portion of the superior and mid-temporal gyrus, caudate, putamen, thalamus, dorsal brainstem (including the LC), periaqueductal gray area, and cerebellum.). IBS presented a similar pattern of amygdala connectivity. However, in compar- ison to HCs, there was significantly reduced connectivity (i.e., less fibers) between the amygdala and the dlPFC. In a direct group comparison, significantly less fibers connected the amygdala and the dlPFC. No differences were observed between the amygdala and other nodes of the emotional arousal circuit (dorsal pons, ACC subregions). Discussion: This pilot study supports previously specified amygdala-ACC anatomical connectivity comprising the emotional arousal circuitry. There were no disease-based differences in these emotional arousal circuits. However IBS patients showed reduced structural connectivity between amygdala and dlPFC compared to HCs. These findings may be related to the previously reduced functional connectivity between lateral PFC and amygdala, and the alterations in cortical thickness of this brain region. Inadequate inhibitory control of emotional arousal circuits by the lateral PFC may play a role in central pain amplification and altered autonomic control of the GI tract. 859 Abnormal Brainstem Responses to Auditory Stimuli in Female Patients With Irritable Bowel Syndrome Cecilia Grinsvall, Caroline Wass, Johan Källstrand, Sara Nehlstedt, Sören Nielzén, Iris Posserud, Jan Svedlund, Magnus Simren Background: Patients with irritable bowel syndrome (IBS) have demonstrated abnormalities in central nervous system functions important for sensory information processing. The auditory brainstem response (ABR) audiometry method may be used to assess the activity of the auditory system; from the acoustic nerve to the medial geniculate body in thalamus. By altering the used target tone, different parts of the auditory system can be evaluated. Aim: To further investigate sensory information processing in patients with IBS, using an ABR paradigm. Method: Thirty-six female IBS patients (mean age 34 (19-62) years), and 23 female controls (mean age 35 (17-63) years) underwent ABR audiometry including 13 different sounds. The sounds were constructed to examine the response to different frequen- cies, amplitudes, forward masking, backward masking and habituation. The masking effect was defined as the difference in response (i.e. the amplitude of the EEG curve) to an auditory stimuli, i.e. the “pulse alone condition”, compared with the response to a pulse plus masker noise i.e. “masking condition”. The brainstem audiograms were average representations of 1024 auditory stimuli. Extreme values, with a narrow time interval to perceive the small peaks in the ABR-curve, as a measure of activity, were assessed. The coordinates were then compared between IBS-patients and controls. In addition the IBS patients completed the Hospital Anxiety and Depression scale (HAD). Results: There was a clear difference in the masking effect when comparing IBS patients to healthy controls (p<0.005).The effect of masking in the control group was decreased activity (p<0.005) in the brainstem at pontine- S-118 AGA Abstracts and midbrain-level, quantified as number of sub-peaks in masking condition compared to in reference condition. In the IBS-group this effect was absent, and instead there was a tendency towards increased activity (p=0.19). The abnormal masking response in patients with IBS was negatively correlated to severity of anxiety (r = -0.62, p<0.01). Furthermore, the number of extreme values in the response to a complex sound were less in the IBS group than in the control group (46 ± 12 vs. 53 ± 12; p<0.05), indicating less activity, or less synchronized activity in the brainstem auditory system of IBS patients. Conclusions: In this study we have demonstrated that female IBS patients have abnormal brainstem response to auditory stimuli, reflecting aberrant brainstem function. The IBS patients seem to lack the normal masking response present in healthy control subjects. Abnormal processing of sensory information at the brainstem level might be of importance for symptom generation in IBS. 860 Ameliorating Effects of Mirtazapine on Visceral Hypersensitivity in Rats With Neonatal Colon Sensitization Jieyun Yin, Weifeng Wang, John H. Winston, Ruixing Zhang, Jiande Chen Antidepressants are widely prescribed for patients with irritable bowel syndrome (IBS) in clinical practice. Presently, a newer clinical generation antidepressant, mirtazapine, a noradrenergic and specific serotonergic agent, becomes favorable in the clinic. However, it is unknown the role of mirtazapine on visceral hypersensitivity and gastric motility. The aim of this study was to investigate the effects of mirtazapine on visceral hypersensitivity and gastric emptying in an established rodent model of IBS. Methods: twenty colonic sensitized rats (injected with acetic acid during the neonatal period) and 10 matched controls (injected with saline) were used. Visceral sensitivity during colorectal distension (CRD) was assessed by the measurement of abdominal electromyogram (EMG) with the pressures of 20, 40 and 60mmHg. In colonic sensitized rats, mirtazapine with doses of 1mg/kg, 5mg/ kg and 10mg/kg were administered orally 1.5 hrs before the recording on separate days in a randomized order. In the control session, saline was adminstered. In the normal rats, only two sessions (mirtazapine 10mg/kg and saline) were studied. In another study, 16 colonic sensitized rats were divided into two groups to investigate the effect of mirtazapine on gastric emptying. One hour after oral mirtazapine (10mg/kg) or saline, 1.5 ml phenol red solution mixed with 1.5% methylcellulose was fed by gavage and then the rats were terminated 30min later. Gastric retention was assessed by calculating the phenol red amount in the stomach. Results: 1) Rats treated with acetic acid showed a significantly higher visceral sensitivity during CRD compared to the normal rats (P<0.01). 2) Mirtazapine with at a dose of 10mg/kg significantly reduced visceral hypersensitivity in the colonic sensitized rats. The EMG during CRD at 20, 40, 60 mmHg were 7.2 ± 1.2, 17.6 ± 2.0 and 26 ± 2.5 respectively in the saline session, and substantially reduced to 3.1 ± 0.8, 10 ± 1.8 and 12.6 ± 2.2 (P < 0.03 vs corresponding saline). Similar findings were noted at doses of 5mg/kg and 1mg/kg. In the normal rats, mirtazapine was found to reduce visceral sensitivity only during CRD at 60 mmHg (12.5±3.1 vs. 8.7±1.9, P=0.02). 3) Mirtazapine 10mg/kg significantly accelerated gastric emptying. The gastric emptying was increased from 77 ± 3.5% in the saline group to 87.9 ± 3.5% in the mirtazapine group (P=0.045). Conclusions: Mirtazapine reduces visceral sensitivity in a rodent model of visceral hypersensitivity and accelerates gastric emptying. These findings suggest mirtazapine may have a therapeutic potential for treating patients with IBS. 861 Mucosal Administration of 5-HT 4 Receptor Agonists Enhances Colonic Motility, Inhibits Colonic Hypersensitivity, and Activates 5-HT Release Jill M. Hoffman, Onesmo B. Balemba, Anthony C. Johnson, Karl R. Tyler, Hong Zhao, James Galligan, Beverley Greenwood-Van Meerveld, Gary M. Mawe 5-HT 4 receptor agonists, administered systemically, are effective for treatment of constipation, and they alleviate abdominal pain in constipation-predominant irritable bowel syndrome. However, concerns about adverse reactions have restricted their availability, thus limiting treatment options. 5-HT 4 agonists are thought to act via presynaptic facilitation of transmitter release by myenteric neurons. We tested the hypothesis that luminal administration of 5- HT 4 agonists could act locally to promote motility and reduce visceral hypersensitivity, possibly via serotonin (5-HT) release from enterochromaffin (EC) cells. RT-PCR was used to confirm mucosal expression of the 5-HT 4 receptor in colonic samples. Propulsive motility was evaluated in isolated segments of guinea pig distal colon, viscero-motor responses (VMR) recorded in a conscious rat model of acute colonic hypersensitivity, and 5-HT release measured by continuous amperometry in segments of guinea pig ileum. Transcripts for the 5-HT 4 receptor were detected in mucosal samples from mouse ileum and colon, and human rectum. In motility studies, the 5-HT 4 agonists tegaserod and ATI-7505 (10-100 nM) acceler- ated propulsive motility when administered directly into the lumen, but not upon bath application. This motility enhancement was blocked by the 5-HT 4 antagonist, SB204070 (10 nM). In VMR studies, tegaserod administered orally (1 or 10 mg/kg) or via an intra- colonic catheter (0.1 or 1 mg/kg) attenuated colonic hypersensitivity to a nociceptive stimulus. The effect of intra-colonic administration was significantly greater and detected at a lower dose than oral administration. Cisapride (1 μM) caused a significant increase in the oxidation current when applied directly to the mucosal surface of guinea pig ileum, indicating that 5-HT 4 receptor activation elicits 5-HT release from EC cells. In summary, mucosal application of 5-HT 4 agonists had a prokinetic action and reduced visceral hypersensitivity, and this effect may involve 5-HT release from EC cells. It is interesting to note that serosal application of 5-HT 4 agonists, which allow access of the drugs to the myenteric plexus, did not promote motility. Furthermore, colonic administration was more potent and effective than oral/ systemic administration in alleviating hypersensitivity. Collectively, these data support the concept that 5-HT 4 agonists can elicit their effects within the lumen of the colon, indicating that targeted delivery of these drugs may restore altered motility and colonic hypersensitivity, while limiting bioavailability and minimizing adverse side effects. This work was supported by NIH grants DK62267 and R21HD056197.