The connection between the trillions of microbes residing in our gut and depression is well established. However, an ancient dilemma needs to be addressed; do changes in the gut microbiota lead to the development of depression or does depression causes changes to the gut microbiota?
By Gal Winter Ziv
There are trillions of microbes living in our bodies, the vast majority of them reside in the gut and is collectively termed the gut microbiome. Research has identified the gut microbiome to be a powerful modulator of many physiological processes and a valuable indicator of health status.
The brain modulates gut microbes
Furthermore, a direct communication system between the gut and the brain has been characterized which is able to deliver signals in both directions, gut to brain and brain to gut. Through this communication system, the gut microbes have the capacity to modulate and also be modulated by brain behaviour. As such, the gut microbiome is strongly linked with mood-relating behaviours including depression.
Chicken and egg dilemma
While the link between gut microbiome and depression is well supported by research, a major question needing to be addressed is the causality in the connection between the two: do changes in the gut microbiota lead to development of depression or does depression causes changes to the gut microbiota?
In a review article published in Reviews in the Neurosciences, the authors address this question by examining a theoretical ‘chronology’, reviewing the evidence supporting two possible sequences of events.
First, the article examines the hypothesis by which alterations in the gut microbiota might contribute to depression. Then the opposite hypothesis is examined by which depressive states might induce modification of the gut microbiota and eventually contribute to more severe depression.
Interestingly, the feasibility of both sequences is supported by pre-clinical trials. For instance, research in animal models has shown an onset of depressive behaviour following faecal transplantations from patients diagnosed with depression.
On the other hand, mental induction of stress and depressive behaviour in rodents resulted in alterations of gut microbiota. Synthesis of these chronology dynamics raises important research directions to further understand the role that gut microbiota play in mood-relating behaviours, which holds substantial potential clinical outcomes for persons who experience depressive disorders.
A fundamental factor in onset of depression
The gut microbiota is proving to be a fundamental factor in the onset of depression and other chronic conditions. As such, understanding the role that gut microbes play in the development of these diseases holds major potential clinical outcomes in both prevention and treatment of mood disorders.
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