The prefrontal cortex (PFC), the foremost part of the brain, is the seat of what is called ‘executive function’. Executive functions are the higher order tasks of the brain (beyond regulating the systems and processes of the body) such as attention, planning, decision-making, memory, managing social interactions, making moral judgements and anticipating the consequences of a particular behaviour. The PFC also plays an important role in emotional functioning; regulating fear, anxiety, normal guilt, and PFC dysfunction is implicated in the development of mental disorders such as schizophrenia and autism spectrum disorders.
New research from University College Cork has uncovered an important role of the gut microbiome on the structure and functions of neurones in the PFC. In this study the researchers compared the brains of mice raised in ‘germ free’ conditions (i.e. no gut microbiome) with mice raised conventionally and those who spent the first part of their lives germ-free then were later introduced to the conventionally-raised animals, which would lead to some colonisation of the gut microbiome.
They found that over 221 genes behaved differently in the brains of the germ-free and ex-germ-free mice compared to those raised conventionally. The germ-free vs the conventional mice made up the biggest difference accounting for 190 of the 221 differently expressed genes. Many of these genes were involved in the task of myelination and these changes were confined to the PFC region of the brain. Myelin is the fatty sheath that surrounds a nerve cell, like the protective plastic coating around an electrical wire. Myelin aids the conductivity of the nerve cell, helping it to send messages faster and more efficiently. Failure in myelination is the cause for the loss of muscle function and control in Multiple Sclerosis, for example. This study was looking at the underlying biological mechanism so the researchers did not make any comment on the potential implications of these changes other than to note previous research showing increased anxiety in germ-free mice and stating ‘Our results further highlight the microbiota as a viable therapeutic target in psychiatric disorders’. They also note that the unusual changes in the myelin of the germ-free mice was corrected in the ex-germ-free mice, indicating that later colonisation of the gut microbiome normalised myelin gene expression in this important region of the brain.
Hoban, A. E., Stilling, R. M., Ryan, F. J., Shanahan, F., Dinan, T. G., Claesson, M. J., Clarke, G. & Cryan, J. F. (2016). Regulation of prefrontal cortex myelination by the microbiota. Translational Psychiatry, 6, e774. doi:10.1038/tp.2016.4