Gut-Brain Axis and its Neuro-Psychiatric Effects: A Narrative Review

Abstract

The gut microbiota regulates the function and health of the human gut. Preliminary evidence suggests its impact on multiple human systems including the nervous and immune systems. A major area of research has been the directional relationship between intestinal microbiota and the central nervous system (CNS), called the microbiota-gut-brain axis. It is hypothesized that the intestinal microbiota affects brain activity and behavior via endocrine, neural, and immune pathways. An alteration in the composition of the gut microbiome has been linked to a variety of neurodevelopmental and neurodegenerative disorders. The connection between gut microbiome and several CNS disorders indicates that the focus of research in the future should be on the bacterial and biochemical targets. Through this review, we outline the established knowledge regarding the gut microbiome and gut-brain axis. In addition to gut microbiome in neurological and psychiatry diseases, we have briefly discussed microbial metabolites affecting the blood-brain barrier (BBB), immune dysregulation, modification of autonomic sensorimotor connections, and hypothalamuspituitary-adrenal axis.

Bacillus subtilis-Based Probiotic Improves Skeletal Health and Immunity in Broiler Chickens Exposed to Heat Stress

“…Impaired gut microbiota (dysbiosis), alterations in the richness and diversity of microbiota, leads to the pathophysiological processes of various diseases in humans and animals [ 20 , 21 , 22 , 23 , 24 ]. The modulation of the gut microbiota by the administration of probiotics, as well as prebiotics and synbiotics, has become a biotherapy strategy for preventing and treating many diseases, from stress-related irritable bowel syndrome to neuropsychiatric disorders [ 25 , 26 , 27 ]. Probiotics (direct-fed microbials) can restore the ecologic stability of gut microbiota by inhibiting pathogens, promoting the growth of beneficial bacteria, and releasing bioactive and immunomodulatory factors to improve the function of the hypothalamic–pituitary–adrenal axis (one of the major stress response systems) and immunity via the microbiota–gut–brain axis and or the microbiota–gut–immune axis [ 28 , 29 ].…”

COVID-19: The Significance of Platelets, Mitochondria, Vitamin D, Serotonin and the Gut Microbiota

“…Furthermore, since about 95% of the body's serotonin is produced by ECs in the GIT that is taken up by circulating platelets [186], it may also support how antidepressants may have a beneficial effect on the outcome of COVID-19 in patients via the gut-brain axis [183].…”

“…Even though SARS-CoV-2 could directly infect neurons [2], neurological symptoms usually are non-specific and not all symptoms are associated with direct infection of cells in the nervous system. SARS-CoV-2 caused neurological diseases may result from disturbances of the gut microbiota that perturb bi-directional signaling systems such as the gut-brain axis or the lung-gut-brain axis, in addition to the more explored mechanisms including coagulation dysfunction, cardio-vascular comorbidities, and others [156,167,183,222]. We agree with the assumption introduced by others that platelet hyper-reactivity via increased platelet-platelet and platelet-leukocyte interactions may have a key role in the pathophysiology of COVID-19 and that the supposed cytokine storm is probable due to endothelial dysfunction and related systemic inflammation [4,38,78].…”

“…As mentioned above in the previous section regarding gut dysbiosis, there is growing evidence that SARS-CoV-2 infection can affect the digestive system and produce intestinal disorders in about 30% of the infected patients [181,182]. SARS-CoV-2 could perturb gut microbial systems that may be involved in the pathogenesis of neuropsychiatric symptoms via the gut-brain axis [183]. Bostancıklıoğlu [184] proposed that SARS-CoV-2 invasion of the gastrointestinal system starts with oral invasion and probably exists before the brain invasion.…”

Promising Intervention Approaches to Potentially Resolve Neuroinflammation And Steroid Hormones Alterations in Alzheimer’s Disease and Its Neuropsychiatric Symptoms

“…GM modulates important processes, such as microglia maturation and activation, neurogenesis, myelination, synaptic pruning, and BBB permeability. The GM-brain axis links GM and the brain via metabolic, endocrine, neural, and immune pathways that are crucial for the maintenance of brain homeostasis [ 68 ]. Emerging evidence indicate that gut dysbiosis may aggravate Aβ aggregation and neuroinflammation in the development of AD [ 69 ].…”