Bidirectional Pathway Between Depression and Inflammatory Bowel Disease

Although in the past, scientists have the well understanding of both depression and inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), it is only few decades that the relationship between them has been discussed. Neither depression nor IBD can bring catastrophic damages to a person's life, but many tested evidences illustrate that they have the similar remission and relapse pattern, namely attenuating and exacerbating at the same time. By finding the common pathways or the pertinent effects shared by depression and IBD, we can better understand the etiologies to both of them. There are few studies indicating that the common immune-inflammatory, oxidative and nitrosative stress (O&NS), auto-immune, and tryptophan catabolite (TRYCAT) pathways are present in depression and IBD. Moreover, the paramount part of brain and intestine is the gut-brain axis (GBA). Mounting evidence and an experiment indicate the interlaced consequences from dysfunction of the gut-brain axis, and the inflammatory disease has an impact on the key structure of GBA, amygdala, and the dysfunction of which will change the emotional processing. However, although there is result demonstrating that in depression, levels of TNF α x, IL-6, and β are elevated, the reason is still unclear, and the measurement of cytokines cannot be directly linked to the assessment of depression. In conclusion, the relationship between depression and IBD still has many uncertainties.