by Kaitlyn May
This area of research has been overlooked for years, largely because of the difficulties of studying these species in a lab; the majority of the microbes of the human system cannot survive in a petri dish. A key finding—the discovery of a way to sequence DNA from these microbes—served as a catalyst to the development of this area of research. Even then, little thought was given to the influence of the microbiome on the brain. Prior research indicated that the blood-brain barrier acted as a “sift” for the brain, only allowing small molecules to pass through.
The New York Times article goes through seminal studies in this line of research. Each study relates various aspects of the microbiome to a different neurological disorder, such as Alzheimer’s, depression, autism, or seizures. The majority of these studies examine individual strains of bacteria in mouse models. For example, Dr. Costa-Mattioli at Baylor College of Medicine used mouse models of autism to examine how differences in the microbiome affected autism symptomatology. Dr. Costa-Mattioli found that the animals lacked Lactobacillus and adding this strain of bacteria to their diet reduced repetitive and anti-social behaviors. He researches revealed that the bacteria communicated to nerve endings in the intestines, and that these signals would be sent from gut to brain, where they would affect the production of the oxytocin hormone that promotes social bonds.
Similarly, examination of the role of the microbiome in epileptic mice on a ketogenic diet identified a key role of the microbiome. A ketogenic diet has long been a key treatment for individuals with epilepsy, as the diet reduces seizures. When this diet was fed to epileptic mice raised free of microbes, these mice did not see a reduction in seizures. However, if they received stool from mice who were on a ketogenic diet, there seizures were reduced. This was because it is the microbiome which communicates to the brain. The research identified two types of gut bacteria which thrive in mice on a ketogenic diet and are potentially the key bacterium which communicate with neurotransmitters to halt electrical activity in the brain. This research could eventually replace diet therapy for epileptics with a pill containing the bacteria needed to communicate to neurotransmitters in the brain.
The Penninsi article dives deeper into the relationship between the microbiome and depression. This article details a study that identified the absence of several species of gut bacteria in people with depression, namely Coprococcus and Dialister bacteria. These species were not missing in subjects with a high quality of life, and this persisted in participants of different ages, genders, or different antidepressant use. It is unclear whether the absence is a cause and effect, or a confound, but they were able to demonstrate that gut bacteria affected nerve cell function. Unlike the studies in the New York Times article which examined mice, the Penninsi article demonstrates this effect in humans. These findings could eventually influence treatments for depression. Oral probiotics, for example, could begin to be an accepted treatment for individuals with depression.
1. How might this area of research influence your field?
2. How does this research change the way that you think of the brain?