Impact of intestinal disorders on central and peripheral nervous system diseases

Brain injuries and neurological diseases have a significant impact on the gut microbiome and the gut barrier. Reciprocally, gut disorders, such as Inflammatory Bowel Syndromes (IBS), can affect the development and pathology of neurodegenerative and neuropsychiatric diseases, although this aspect is less well studied and is the focus of this review. Inflammatory Bowel Syndrome (IBS) is a chronic and debilitating functional gastrointestinal disorder afflicting an estimated 9-23% of the world's population. A hallmark of this disease is leaky gut, a pathology in which the integrity of the gut blood barrier is compromised, causing gut contents such as immune cells and microbiota to enter the bloodstream leading to low-grade systemic inflammation. The increased levels of inflammation associated cytokines in circulation has the potential to affect all organs, including the brain. Although the brain is protected by the blood brain barrier, inflammation associated cytokines can damage the junctions in this barrier and allow brain infiltration of peripheral immune cells. Central inflammation in the brain is associated with various neurodegenerative disease such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, and neuropsychiatric disorders, namely, depression, and anxiety. Neurodegenerative diseases are of particular concern due to the anticipated rise in the population of the elderly and consequently, the prevalence of these diseases. Additionally, depression and anxiety are the most common mental illnesses affecting roughly 18% of the American population. In this review, we will explore the mechanisms by which IBS can influence the risk and severity of neurological disease.