Scientists have acknowledged a relationship and communication between the gastrointestinal tract and the brain for over 100 years. Studies from the early 19th century demonstrated that the emotional state of a person can alter function of the gut. In 1830, William Beaumont monitored gastric secretions through a fistula and observed a relationship between changing moods and gastric secretions.[1]

Modern scientists have now turned the tables towards investigating the theory of ‘bottom up control’ – the idea that microbiota of the gut can influence brain function.

Current research shows natural microbes inhabiting the gut seem to play an integral part in controlling the permeability of the blood brain barrier, thus shielding the brain from harmful substances.

An intact blood brain barrier acts as a guard to regulate the passage and exchange of nutrients and molecules between the circulatory system and the brain parenchyma. It is vital for healthy brain development and function as well as maintaining homeostasis of the central nervous system.

A recent study, published in Science Translational Medicine, demonstrated that the movement of molecules across the blood brain barrier can be influenced by gut microbes, supporting previous evidence that alterations in gut microbiota can have an effect on the development and function of the brain.[2]

Researchers from the Karolinska Institute in Sweden, compared the integrity and development of the blood brain barrier between two groups of mice. Group 1 were raised in an environment exposed to normal bacteria and group 2 were kept in a sterile environment.

One author, Dr Viorica Braniste, stated that the results “showed that the presence of the maternal gut microbiota during late pregnancy blocked the passage of labelled antibodies from the circulation into the brain parenchyma of the growing foetus. In contrast, in age matched foetuses from group 2 mothers, these labelled antibodies easily crossed the blood brain barrier and was detected within brain parenchyma.”

Senior researcher Professor Sven Pettersson added “given that the microbiome composition and diversity change over time, it is tempting to speculate that the blood brain barrier integrity may also fluctuate depending on the microbiome.” These outcomes also further highlight the significance of maternal microbes during early life.

REFERENCES

  1. Foster JA. Gut feelings: bacteria and brain. Cerebrum 2013;2013:9. [Full text]
     
  2. Braniste V. The gut microbiota influences blood-brain barrier permeability in mice. Sci Transl Med 2014;6(263):263ra158. [Full text]

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