Microbiota and Behavior
By Adam Granot
It’s hard to believe that anything has the ability to live within the mammalian GI tract but of course life persists and flourishes. Like the mitochondria and chloroplasts before it, these living microscopic organisms seem to have found unique relationships with their mammalian hosts where neither it nor its host faces harm but rather each acquires benefit. The mutualistic nature of this interaction begins during birth as the soon to be newborn slides through many steadfast colonies of microbial growth, rapidly and densely populating the newborn along the way. From this point, the newborn picks up even more of these lifelong stowaways throughout their formative years and into their early pubescent years while eating, drinking and interacting with their environments. The isolated and unwavering internal environment presented to these various bacteria and fungi provides clear benefit—ample food, sex and a relatively safe environment from predation. Less enchantingly, the host gets help breaking down food, reabsorbing nutrients and regulating immunology. As research into microbial microbiomes heats up, it’s becoming more apparent that these living creatures may have an effect on a person’s mood, behavior, memory and cognition and appear to be as unique to the host as is the host’s own finger print.
But what happens if the balance in these relationships breaks down over time? Like an old man stripped of his wheelchair, he’s left coping in a world his body is not accustomed or prepared to handle. Recently, the idea of the gut-brain axis has been picking up more steam. While only a few years ago, it was thought the gut’s major role in the body, outside of food digestion, dealt with holding upwards of 90% of the body’s immunological response, today there is evidence to suggest that the gut has more of an intimate role in the body and can be viewed as an individual’s metagenome. Researchers have reported links between microbiota and obesity, brain development, behavior and depression (1-4). It seems that mammalian bodies have become so dependent on these intestinally-intrepid travelers that development of gut dysbiosis appears to have a role in predicting early onset Alzheimer’s disease, abnormal neurological developments and even a wide range of autism disorders (5).
In their landmark experiment, Rochellys Heijtz and her team breed two varieties of mice; those who presented with expected gut flora and those raised in sterile condition presenting as germ-free and lacking gut microbiota. When compared, she found that the control mice, those with expected gut inhabitance, displayed increased clumsy motor activity and increased anxiety (2). While this experiment highlights the microbial ability to have an effect on host behavior, it also suggests the acquisition of bacteria may be negative as it may make a host more prone to possible agitation, nervousness and increases in anxiety; however, growing up in a sterile environment is impractical and unrealistic. In a germ filled world, obtaining a balanced and effective gut colony is extremely important. With estimates of 1 in 88 births during 2008 presenting with autistic indicators, any help in preventing or even treating the proliferation of the spectrum could be very powerful to the advancement of mankind (6).
Elaine Hsiao, a researcher at Caltech, has suggested that mutualistic fauna affect a variety of complex behaviors, including social, emotional and anxiety like behavior and contribute to brain development and function; over time, these fauna strengthen the gut wall, allowing for gut permeability if gut imbalances occurs. Her team amazingly relieved symptoms plaguing 8 week old mice exhibiting core communicative, social and stereotypic impairment associated with Autistic Disorders through the injection of Bacteroides fragilis, a common bacteria found in the human colon (6). While this does not present a cure for autism, it does highlight the power of probiotics. Research from Finland over 15 years ago found early evidence for the ability of probiotics to modulate immunity, restore the gut and alter behavior. Kallimoki et al. found that administration of various bacteria in the Lactobacillus genus decreased chances that at risk children would develop atopic eczema by 50% when compared to the control group (7). Still probiotics don’t work 100% of the time. With well over tens of trillions of bacteria currently residing in the human GI tract, space is limited and hard to come by. Like trying to find a hotel late in the holiday season, if probiotics aren’t administered early then vacancy is very hard to come by, ultimately causing the probiotics to be expelled and unused.
It seems to me with the rise of C-section births and antibiotic use across western medicine in recent years, along with the rise in antibacterial washes and ultra-hygienic mentalities, we’re playing with fate. If children are not presented with sufficient microbial life to balance their gut early on, devastating results can ensue. Is it possible that a baby born from a mother with an incomplete but compensatory gut fauna be at a higher risk of acquiring gut instability and developing various social, behaviors and cognitive deficits? If children stop eating dirt off their dirty hands, breast feeding or playing in the mud, are the evolutionarily durable relationships developed between humans and our small companions altering? Western medicine needs to open their eyes and stop prescribing antibiotics to please their patients so haphazardly, while understanding a prescription for a probiotic regiment is not just recommended but is needed to replace the lost bacteria when antibiotics are warranted (8). Although hard to imagine, it’s starting to seem more and more that our brains are not the center of our cognition and consciousness, but rather that is just our perception. If these microbes play such an important role in determining who we are, who’s to say they aren’t as much a part of us as mitochondria are now a part of our cells?
1. Manco, M. (2012). “Gut Microbiota and Developmental Programming of the Brain: From Evidence in Behavioral Endophenotypes to Novel Perspective in Obesity.” Cellular and infection Microbiology. (2)109: 1-3
2. Heijtz R, D. et al. (2011). “Normal Gut Microbiota Modulates Brain Development and Behavior.” Nueroscience. (108):3047-3052
3. Dinan T, G. Cryan J, F. (2013) “Melancholic Mircobes: A Link Between Gut Microbiota and Depression.” Neurogastroenterology and Motility. (25)154: 713-719
4. Putignani, L. et al. (2014). “The Human Gut Microbiota: A Dynamic Interplay with the Host from Birth to Senescence Settles during Childhood.” Pediatric Research. (76):2-14
5. Bhattacharjee S. Lukiw, W. (2013) “Alzheimer’s Disease and the Microbiome.” Cellular Nueroscience. (7):1-4
6. Hsiao E,Y. et al. (2013). “Microbiota Modulate Behavioral and Physiological Abnormalities Associated with Neurodevelopmental Disorders.” Cell. (155):1451-1463
7. Kallimomaki M. (2001) “Probiotics in Primary Prevention of Atopic Disease: A randomised Placebo-Control Study.” The Lanclet. (357)9262:1076-1079
8. Nami Y, et al. (2015) “Probiotics or Antibiotics: future challenges in medicine.” Journal of Medical Microbiology. (64):136-147
My name is Adam Granot and I'm currently enrolled as a senior at Muhlneberg College, apart of the class of 2016.
With dreams of being an emergency room pediatric physician one day, I plan on taking a year off to travel the world after graduation before returning for medical school. I'm an avid runner (when not injured) and swimmer (wen not injured). I also enjoy hiking, skiing/boarding and cooking when I have the time and energy.
I'd like to spend a few years volunteering overseas in a doctors without borders style program one day. Go Mules!