The bacteria in your gut (known as the microbiota) are the new cool. And, by cool, I mean the bogeyman for everything that is wrong with you. That is not to say they aren’t very, very important; but the science exploring the role of the complex colonies of microbes residing inside your gut and comprising ten times as many cells as in your actual body is still developing and enormously complex.
In this study, the researchers found that mice lacking a gut microbes exhibited different behavior than mice with gut microbes. They found that inoculating the gut shortly after birth removed this difference, but that inoculating later on did not. The authors reasonably conclude that the presence/absence of the gut microbiota affects neural development in a way that affects their behavioral measures. They further showed that these behavioral changes are correlated with changes in gene expression and neurochemistry. Reasonable enough.
What piqued my curiosity was the speculation on the part of the authors as to mechanisms through which this influence might be affected. They suggest three causes, all direct:
- Modulation of proteins affecting the development of synapses.
- Modulation of neurotransmitters in the gut affecting vagal nerve signaling.
- Production of neurotoxins that affect neural tissue development.
To me, this list seemed incomplete. During my PhD, one of our neighboring labs was run by Jeff Gordon, a prominent researcher in the gut microbiota field; and one of the things I learned during many seminars by his lab members (its a very big lab) is that the presence and composition of the gut microbiota affects the nutrition that the host receives from its food[4-6].
Furthermore, we know malnutrition can affect brain development, suggesting that the nutritional resources available during postnatal development could affect brain development more subtly. This hypothesis also has the advantages of being simple and working within the known functions of the digestive tract and microbiota. But, its not very cool.
- Very technically, they reside outside of you as your gut is technically on your outside. Weird, huh?
- A number which appears to be mostly pulled out of thin air due to the unknowability of the denominator and the assumptions that contribute to the numerator.
- Rochellys Diaz Heijtz, Shugui Wang, Farhana Anuar, Yu Qian, Britta Björkholm, Annika Samuelsson, Martin L. Hibberd, Hans Forssberg, and Sven Pettersson. Normal gut microbiota modulates brain development and behavior. PNAS published ahead of print January 31, 2011, doi:10.1073/pnas.1010529108
- Turnbaugh PJ, Ley RE, Mahowald MA, Magrini V, Mardis ER, Gordon JI. An obesity-associated gut microbiome with increased capacity for energy harvest. Nature444, 1027-1031 (21 December 2006) | doi:10.1038/nature05414
- Bäckhed F, Ley RE, Sonnenburg JL, Peterson DA, Gordon JI. Host-bacterial mutualism in the human intestine. Science 25 March 2005: Vol. 307 no. 5717 pp. 1915-1920. DOI: 10.1126/science.1104816
- Hooper LV, Midtvedt T, Gordon JI. How host-microbial interactions shape the nutrient environment of the mammalian intestine. Annu Rev Nutr. 2002;22:283-307.