Decreased Neuroplasticity May Play a Role in Irritable Bowel Syndrome: Implication From the Comorbidity of Depression and Irritable Bowel Syndrome

TO THE EDITOR: It is with great interest that we read the paper entitled " Post-traumatic Stress Disorder Is Associated With Irritable Bowel Syndrome in African Americans " by Iorio et al. 1 The authors investigated the potential association between irritable bowel syndrome (IBS) and post-traumatic stress disorder (PTSD) in an urban African American (AA) population. The results demonstrate that those with IBS were much more likely to suffer from PTSD; PTSD is independently associated with depression and anxiety; and the majority of individuals with IBS suffered from depression, and anxiety was the second most common in IBS patients. Then it is concluded that PTSD is independently associated with IBS. The authors also emphasized the relation between hypothalamic-pituitary-adrenal (HPA) hormones , such as corticotropin-releasing hormone, adrenocortico-tropic hormone and cortisol, and IBS. Although the authors pointed out that this study specifically addressed AA and could not be extrapolated to other races, we believe that it enlightened the relation between stress and IBS in the whole population. Neuroplasticity is the ability of the nervous system to respond to intrinsic or extrinsic stimuli by reorganizing its structure, function and connections. 2 The nervous system monitors and coordinates internal organ function, therefore we have proposed that neuroplasticity may also be associated with the pathogenesis of other diseases besides neuropsychiatric diseases. 3 IBS has been generally considered to be caused by alterations in the brain-gut axis. 4 Thus neuroplasticity may be related to the pathogenesis of IBS. Neuroplasticity is disrupted in mood disorders and depression is a disorder of decreased neuroplasticity. 3,5 It is widely accepted that stress triggers the activation of the HPA axis and causes the brain to be exposed to corticosteroids, affects neuro-behavioral functions with a strong down-regulation of hippo-campal neurogenesis, and is a pivotal risk factor for depression. Brain-derived neurotrophic factor (BDNF) is a critical cytokine in neuronal survival, morphogenesis, and plasticity. BDNF expression is regulated by stress-responsive corticosteroids, and increased glucocorticoid exposure induces a reduction in BDNF level. Most of the circulating BDNF is produced in the brain and passes through the blood-brain barrier. Serum BDNF level is believed as a biomarker for depression. A meta-analysis showed a significant reduction of serum BDNF level in depression. 3 Shortened and reduced complexity of dendritic trees have been found in the hippocampus and the prefrontal cortex in depression. Antidepressant treatment increases the expression of BDNF and can enhance neuroplasticity. 5 Besides depression, …