Papers of the Week

Inflammatory bowel disease (IBD), mainly comprising Crohn's disease and ulcerative colitis, is characterized by chronic inflammation in the digestive tract. Approximately 60% of the patients experience abdominal pain during acute IBD episodes, which severely impairs their quality of life. Both peripheral and central mechanisms are thought to be involved in such abdominal pain in IBD. Although much attention has been paid to peripheral mechanisms of abdominal pain in IBD pathophysiology, the involvement of supraspinal mechanisms remains poorly understood. To address this issue, we investigated regional brain activity in response to colorectal distension (CRD) in normal and IBD model rats using voxel-based statistical analysis of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) PET imaging. The rat IBD model was generated by colorectal administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS), a chemical compound widely used to generate colitis. Tissue damage and inflammation were induced and dynamically changed with time after TNBS injection, while CRD-induced visceromotor response showed corresponding temporal changes. We found that characteristic brain activations were observed in response to visceral innocuous and noxious CRD and supraspinal nociception shared some physiological sensory pathway. Moreover, widespread brain regions were activated, and the functional coupling between the central medial thalamic nucleus (CMT) and anterior cingulate cortex (ACC) was enhanced after noxious CRD in IBD model of rats. Increased brain activity in the anterior insular cortex (aINS) and ACC positively correlated with noxious CRD-induced pain severity in normal and IBD rats respectively. These findings suggest that the pain matrix was shifted following persistent colonic inflammation, and thalamocortical sensitization in the pathway from CMT to ACC might be a central mechanism of the visceral hyperalgesia in IBD pathophysiology.