CLINICAL RESEARCH POSTER PRESENTATION ABSTRACTS
Please note: All posters will be displayed in Salons 10-12.

FRIDAY, 10:15-11:00 AM

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Berman SM, Jarcho J, Suyenobu B, Chang I, Naliboff B, Mayer EA*.

Brain activity associated with placebo-mediated symptom improvement in irritable bowel syndrome.

UCLA Center for Neurovisceral Sciences & Women's Health emayer@ucla.edu *Presenting author

Irritable bowel syndrome (IBS) is a common functional syndrome characterized by chronic abdominal pain/discomfort associated with altered bowel habits. In recent clinical IBS trials, placebo effects ranging from 30-40% were maintained over 3 months.

Although neurobiological mechanisms underlying the placebo effects are not well understood, several recent brain imaging studies have found evidence for activation of a corticolimbic pontine network, including rostral anterior cingulate and medial prefrontal cortices (rACC/mPFC), the ventrolateral prefrontal cortex and pontine regions. To see if the placebo response in IBS patients is also associated with increased activity in this brain network, we studied the brain response (O-15 PET) to rectal distensions and anticipation of distensions, before and after a train of repeated noxious sigmoid distensions in 37 IBS patients (50% female). Patients were tested before and after 3-week treatment with the 5-HT3 receptor antagonist Alosetron (n=20), or placebo (n=17). We assessed behavioral and physiological correlates of IBS symptom improvement in each group. Symptom improvement after placebo was associated with attenuated perceptual responses after sigmoid distension. Placebo responders felt fewer unpleasant sensations and this was associated with increased activity in rACC/mPFC (p<.01). In contrast, the primary effect of Alosetron on brain response was to reduce activity in the amygdala (p<.03) and other 5- HT3 receptor rich limbic structures. These effects were strongest at baseline and prior to the noxious sigmoid distension. Our findings suggest that patients whose symptoms improve on placebo and those who improve on an active drug activate different brain networks to achieve subjective relief. The increased activation of rACC associated with the placebo is consistent with several other recent brain imaging studies and may suggest increased endogenous opioid release in this mu-opioid rich brain region.

 

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