The microbiome: A key regulator of stress and neuroinflammation

Abstract

There is a growing emphasis on the relationship between the complexity and diversity of the microorganisms that inhabit our gut (human gastrointestinal microbiota) and health/disease, including brain health and disorders of the central nervous system. The microbiota-gut-brain axis is a dynamic matrix of tissues and organs including the brain, glands, gut, immune cells and gastrointestinal microbiota that communicate in a complex multidirectional manner to maintain homeostasis. Changes in this environment can lead to a broad spectrum of physiological and behavioural effects including hypothalamic-pituitary-adrenal (HPA) axis activation, and altered activity of neurotransmitter systems and immune function. While an appropriate, co-ordinated physiological response, such as an immune or stress response are necessary for survival, a dysfunctional response can be detrimental to the host contributing to the development of a number of CNS disorders.In this review, the involvement of the gastrointestinal microbiota in stress-mediated and immune-mediated modulation of neuroendocrine, immune and neurotransmitter systems and the consequential behaviour is considered. We also focus on the mechanisms by which commensal gut microbiota can regulate neuroinflammation and further aim to exploit our understanding of their role in stress-related disorders as a consequence of neuroinflammatory processes.

Parasites, stress and reindeer: infection with abomasal nematodes is not associated with elevated glucocorticoid levels in hair or faeces

“…Furthermore, the gut microbiota forms part of a complex network with bidirectional communication, dubbed the gut–brain axis. Signals/changes on either end of the axis have the potential to influence the hypothalamic–pituitary–adrenocortical axis and, thus, GC levels (Palma et al ., 2014; Rea et al ., 2016). Indeed, studies have shown that germ-free animals have elevated corticosterone levels compared with animals with gastrointestinal bacteria (reviewed by Rea et al ., 2016).…”

“…Signals/changes on either end of the axis have the potential to influence the hypothalamic–pituitary–adrenocortical axis and, thus, GC levels (Palma et al ., 2014; Rea et al ., 2016). Indeed, studies have shown that germ-free animals have elevated corticosterone levels compared with animals with gastrointestinal bacteria (reviewed by Rea et al ., 2016). Thus, it is possible that by removing parasites native to the host population, we caused a distruption in the gut microbiota leading to the observed increase in GC levels in the treated group.…”

May the Force Be With You: The Light and Dark Sides of the Microbiota–Gut–Brain Axis in Neuropsychiatry

“…The brain’s resident immune cells—the microglia—are also found to be under the regulation of the microbiota [105, 106]. Consequently, the bacterial commensals in our gut have the potential to control the neuroinflammatory response that is often found to be exaggerated in psychiatric and neurodegenerative conditions [107, 108].…”

Alternatives to Antibiotics: Phage Lytic Enzymes and Phage Therapy

“…Advantageously, bacteriophages are more specific for certain bacterial strains, such as Clostridium difficile that causes intestinal infections or diarrhea following antibiotic treatment [48]. Also, phage therapy is more sparing than antibiotic-based therapies [49,50].…”