Abnormal and Behavioural Psychology

The Brain-Body-Microbial Communities: A Crosstalk and Stress Exchange Beyond the “Gut hypothesis”

Abstract

Afifi MA, Jiman-Fatani AA, Tonkal AM and Jamjoom MB

For many decades, the consequences of “stress” have been perceived as a “unidirectional” pathway where some stressful life conditions cause “mental stress” that activates the brain’s stress response systems, which sequentially affect many of the major body systems especially gastrointestinal tract. The striking upsurge in incidence of neuropsychiatric and neurodevelopmental disorders, in the last five decades, appeals to a crucial “bidirectional” interaction between the nervous system with other body systems. Such fast expansion of these disorders enforces also a causal role for environmental insults inflicted by the changing ecosystems as well as the modernization of human life style including lavish use of antibiotics, high hygiene standards and predominant utilization of urban western diet. It is also becoming clear that several neurological and psychiatric disorders are more and more being linked to a wide range of systemic dysfunctions including, most notably, immunological impairments and microbial manipulation. We believe that nervous system development and function are not only highly coupled with other physiological body systems but also with non-physiologic microenvironments created by pathogenic agents or dormant commensals. Direct or bystander effects of certain infectious agents or complex microbiome communities on brain development and function could modulate and evoke deviated behavioral responses and abnormal psychological outcomes. We think a better understanding of the basic components of this bidirectional interaction and the comprehensive characterization of the involved pathways will produce significant insights into the way nervous system diseases evolve and yield a novel array of therapeutic strategies. Here, we discuss different aspects of the dynamic crosstalk between the nervous system and microenvironments created by long-lasting pathogenic infections or by permanent commensal microbial communities. To pursue this goal, we review hypotheses and evidences that link certain pathogens or microbiome compositions to the development of neuropsychiatric diseases and/or neurodevelopmental disorders in genetically predisposed persons.