The mind-body connection garners a lot of attention these days, with explosive and ever-emerging research demonstrating the importance of seeing the body as a whole, rather than fractured systems. When talking about the brain, it’s hard to ignore the gut. The gut-brain axis is a good example of this; with the ability of the gut microbiota to bidirectionally communicate with the brain through the vagus nerve. Also, 95% of serotonin is found in the gut’s enterochromaffin cells.
Our bodies are comprised of trillions upon trillions of bacteria, or microorganisms, the majority of which reside in our gut. These bacteria are responsible for various supporting functions in the body; ranging from digestion and immune system functioning to metabolic support, but exactly how do they impact the brain?
Current research points to the gut microbiota as a significant determinant in brain health. In a study evaluating the effect of the gut microbiota on the brain development in humanized germ-free mice, they found the gut bacteria influence neuronal development, neurotransmission pathways, oligodendrocyte development and neuroinflammation markers. In this study, the pregnant germ-free mice were colonized with either microbiota from a preterm infant with good growth (M-H) or a preterm infant with poor postnatal growth (M-L).
Although the microbiota did not seem to alter brain fatty acid composition or short chain fatty acid production, a decreased nuclear protein antigen (NeuN) and reduced (myelin basic protein) MBP expression in the cortex suggest that gut bacteria influence neuronal development and the myelination process. A delayed oligodendrocyte development and brain myelination were also strongly associated with poor microbiota.
In addition to neuronal development, myelination process and oligodendrocyte development, the microbiota impacted glutamatergic, GABAergic and dopaminergic pathways. Glutamine and γ-aminobutyric acid (GABA) are the main neurotransmitters in the central nervous system, involved in over 85% of the synaptic transmissions related to learning and memory, and motor and sensory activities. Dysfunction of these pathways can lead to cognitive deficits as well. Other studies have shown that microbiota alterations are critical to the development of neuronal circuits, but this study looked at the expression of synaptic transmission plasticity-related genes by reverse transcription polymerase chain reaction (RT-PCR) and found the microbiota very much impacted those neurotransmitter pathways. See chart here. Also, the low microbiota (M-L) was associated with decreased serotonin and dopamine pathways compared to the high microbiota (M-H). Neurotransmitter modulation by gut bacteria is a burgeoning and exciting new field of study. The trillions of bacterial are not only important for immune and metabolic health, but have been found to play a key role in the central nervous system and neurotransmitter health.
Finally, when colonized with samples from a preterm infant with poor growth (M-L), interleukin1β (IL-1β) and TNF (major regulators of neuroinflammation) were measured and found to be higher when compared to M-H. Neuroinflammation can be deleterious to a developing brain, so demonstrating that a healthy microbiota can better manage inflammation is very important clinical data.
Overall, this study shows that early microbiome colonization patterns definitely influence brain development, with future studies necessary to elucidate exactly which microbes and microbial metabolites alter brain function. Many studies suggest the gut’s influence on neurodegenerative health or how dysbiosis may contribute to neuropsychiatric disorders. The gut’s critical role in anxiety, depression and overall neurological health is indisputable.
Since an infant’s microbiota may strongly influence brain health, optimizing those early hours, weeks and months with microbial colonization might at least benefit the preterm infants to help steer brain development and neurological outcomes.
Some beneficial probiotic strains include:
Saccharomyces boulardi. Indicated to improve intestinal microbalance in the gut, supporting immunity by boosting intestinal secretion of IgA. S. bouladii (for short) has also been suggested to stimulate and activate bacterial toxins, helping to optimize detoxification and boost immunity, as well as cell growth and differentiation.
Lactobacillus aciophilus DDS-1. Supports a healthy balance of beneficial (good) bacteria in the gut, helping to optimize immune function. L.acidophilus, DDS-1 also helps in promoting the production and use of B vitamins (B6, B12 and folic acid), aiding in energy production.
Lactobacillus plantarum. Aids in further supporting immunity, and most notably healthy inflammatory response in the gut. This optimal strain helps in also promoting the integrity of the GI lining, and therefore supporting absorption of vitamins, essential omega-3 fatty acids and antioxidants. All of which are essential to our overall health and energy levels.
Lactobacillus brevis. This beneficial strain is often found in insufficient amounts in the gut, and is valuable in supporting digestive and immune health. Less than optimal nutrition and lifestyle factors are the contributing factors to this bacteria is found to be compromised in the gut.
Bifidobacterium longum. Indicated to promote sufficient absorption of vital nutrients, support healthy GI functioning, as well as inhibits the growth of harmful bacteria. Additionally, this valuable strain has a valuable role in scavenging free radicals, having powerful antioxidant benefits in the body.
Lactobacillus rhamnosus LB3. Creates favorable environment for balancing intestinal microbiota. Demonstrates induction of antibody production. Increases production of key cytokines such as IFNs, TNF, and NK cells for immune system health.
Lactobacillus delbrueckii LE. Exhibits superior immune modulating properties. Stimulates production of key cytokines IFNs, TNF, NK cells, IL-1, IL-2, IL-6 and IL-10. Found to improve immune system functioning by showing antagonistic activity towards opportunistic pathogens, particularly prevalent in the ear, nose and throat. Activates immunocompetent cells by CD25 antigens and stimulates B cell lymphocyte production.