Are non-communicable diseases communicable? The role of the microbiome in mental illness

How do gut microbes affect the brain?

Microbial composition, immune activation, Vagus nerve signaling, tryptophan metabolism, and microbial metabolites are contributory factors to the effects of gut microbes on brain function and behaviour,¹ explained Professor Taylor.

Gut microbes produce neurotransmitters and modulate neurotransmitter receptors^2–4

Gut microbes produce neurotransmitters that modulate behavior including norepinephrine² and serotonin,³ and modulate the expression of neurotransmitter receptors, including mu-opioid and cannabinoid receptors.⁴

Most research so far has been preclinical, said Professor Taylor, and it is not clear how to extrapolate the data to clinical care.

[For more on these mechanisms, click here]

Links between the gut microbiome and bipolar disorder

Gut microbiota of people with bipolar disorder differs from that of healthy controls⁷

Research results demonstrating preliminary signals linking the gut microbiome to bipolar disorder include the following:

• patients recently discharged following hospitalization for mania whose treatment included probiotic supplementation had a lower rate of rehospitalization⁵
• patients with bipolar disorder compared to healthy controls had:
  
  • a significantly decreased fractional representation (p<0.001) of Faecalibacterium⁶ 
  • significantly more of the phylum Actinobateria and class Coriobacteria⁷
• a negative correlation between microbial alpha‐diversity and illness duration⁷

Is depression communicable?

Depression is associated with decreased gut microbiota diversity

The role of the gut microbiome in a range of psychiatric disorders, including depression and anxiety, has become a major focus of scientific interest, for more click here.

Depression is associated with decreased gut microbiota richness and diversity, said Professor Taylor, and this may play a causal role in the development of depressive features:⁸

• fecal microbiota transplantation (FMT) that increases microbiota diversity improves depressive and anxiety symptoms⁹
• microbiota-depleted rats who receive FMT from people who have major depressive disorder (MDD) develop behavioral and physiologic features characteristic of depression, including anhedonia and anxiety-like behaviors, as well as alterations in tryptophan metabolism⁸

For more information on the microbiome and brain disorders, please click here