Neuroinflammation, Gut-Brain Axis and Depression

Abstract

Psychiatric diseases are the manifestations that result from the individual's genetic structure, physiology, immunology and ways of coping with environmental stressors. The current psychiatric diagnostic systems do not include any systematic characterization in regard to neurobiological processes that reveal the clinical picture in individuals who got psychiatric diagnosis. It is obvious that further research in different areas is needed to understand the psychopathology. The problems in the functions of immune system and the correlation of neuroinflammatory processes with psychiatric disorders have been one of the main research topics of psychiatry in recent years and have contributed to our understanding of psychopathology. Recent advances in the fields of immunology and genetics as well as rapidly increasing knowledge on the effects of immunological processes on brain functions have drawn attention to the correlations between psychiatric disorders and immune system dysfunctions. There are still unfilled gaps in the biology, pathophysiology, and treatment of major depressive disorder, which is quite prevalent among the psychiatric disorders, can lead to significant disability, and frequently has a recurrent course. It appears that low-grade chronic neuroinflammation plays a key role in forming a basis for the interaction between psychological stress, impaired gut microbiota and major depressive disorder. In this review, the role of neuroinflammation in the etiopathogenesis of depression and the mechanism of action of the gut-brain axis that leads to this are discussed in the light of current studies.

The mechanism of electroacupuncture for depression on basic research: a systematic review

“…EA can reduce corticotropin-releasing hormone (CRH) mRNA expression in the hypothalamus and the expression of CRH and adrenocorticotropic hormone (ACTH) in the hypothalamus and pituitary gland, thereby reducing cortisol expression in the adrenal glands and inhibiting the HPA axis. Monoamine neurotransmitters (serotonin, dopamine and noradrenaline) play an important role in depression and normal mood development [ 48 ]. EA can restore synaptic plasticity by regulating the expression of monoamine neurotransmitters in the hippocampus and then alleviate depression symptoms.…”

Indoxyl sulfate caused behavioral abnormality and neurodegeneration in mice with unilateral nephrectomy

“…Disturbed gut microbiota has a huge impact on the abundance and types of microbiota-derived molecules, including neurotransmitters, short-chain fatty acids, bile acids, and indole metabolic derivatives [ 45 – 48 ]. By competing with the biosynthesis of serotonin from tryptophan, intestinal microorganisms cause metabolic breakdown of tryptophan to indole derivatives via enzyme tryptophanase [ 46 , 47 ]. The production of indole derivative indoxyl sulfate is elevated in disturbed gut microbiota and is decreased by probiotics [ 12 ].…”

Insights into the Authentic Active Ingredients and Action Sites of Oral Exogenous Glutathione in the Treatment of Ischemic Brain Injury Based on Pharmacokinetic-Pharmacodynamic Studies

“…Accumulating evidence reveals a close linkage of brain injury and gastrointestinal dysfunction. The influence of the gastrointestinal tract on the brain of human has been noted since the 19th century, and the neuroinflammation hypothesis has been advocated since the 21 st century (Evrensel et al, 2019). The structure and function of the brain can be modulated by the gut; conversely, the brain regulates the gut microenvironment and microbiota composition (Maqsood and Stone, 2016;Zhao et al, 2018).…”