The human gut is colonized by microorganisms in a similar number as the cells of the human body.
“Microbiota” refers to these microorganisms, and it maintains a symbiotic relationship with the host, contributing to essential functions such as food digestion, energy harvest and storage, the function of the intestinal barrier, and the immune system and protection against pathogenic organisms. Prenatal and postnatal factors can alter the composition of the microbiota, such as stress and diet or the use of antibiotics (see image).
For instance, stress during pregnancy can alter the composition of vaginal microbiota, which affects the composition of the microbiota of the newborn and is related to gastrointestinal (GI) symptoms and allergic reactions. Interestingly, there is a bidirectional communication between the GI tract and the central nervous system (the gut-brain axis) that involves neuronal and metabolic pathways, immune and endocrine mechanisms. Changes in the composition of the microbiota can lead to altered development of the brain and increased risk of psychiatric and neurodevelopmental disorders, such as anxiety, depression and autism (see image).
Depression is one of the most recurrent stress-related disorders that highly impacts the quality of life. Fecal samples of patients with depression have a decreased microbial richness and diversity than controls. The use of probiotics have been shown to help with sad mood and negative thoughts, which may be a potential preventive strategy for depression.
Autism is characterized by impaired communication, poor social engagement and repetitive behaviours, with frequent GI symptoms. We know that the bacteria composition is more diverse in autistic individuals than in unaffected subjects.
For other psychiatric disorders, such as Attention deficit/hyperactivity disorder (ADHD) and Schizophrenia, there is indirect evidence for a role of the microbiota, but more studies are needed.
This connection between the gut and brain is two way communication, and is known as “The Gut-Brain Axis.”
Our knowledge of the impact of gut microbiota on brain function is growing fast, which may pave the way to possible applications for the treatment of psychiatric and neurodevelopmental disorders.
Authors Judit Cabana, Bru Cormand, and Noelia Fernandez Castillo are in the Department of Genetics, Microbiology & Statistics, University of Barcelona, Catalonia, Spain
More information can be found in: Felice VD, O’Mahony SM. The microbiome and disorders of the central nervous system. (2017) Pharmacol Biochem Behav. Sep;160:1-13.