Gut Microbes Regulate Nerve Cell Myelination (Animal Model)

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.

Reference

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

http://www.nature.com/tp/journal/v6/n4/full/tp201642a.html

Serum Vitamin D Predicts Cognitive Performance in Adults

Much of the research on the relationship between vitamin D and cognitive function has been conducted on older people or individuals who have a diagnosis of Alzheimer’s Disease or other dementia. This is because older people are less able to synthesise vitamin D in their skin and because dementia is typically a disease of aging. A study published in August 2015 looked at the relationship between vitamin D status and cognitive function in two cohorts of healthy individuals; those aged 30-60 and 60+. Research on disease-free groups is important because it allows us to look at the potential effect that nutritional deficiency has on the general population and on sub-clinical (no diagnosis) functioning. That is to say that we can learn more about how dietary insufficiencies might be affecting the general population long before disease onset. This information allows us more opportunity to intervene with treatment.

In this study of vitamin D in the blood were strongly associated with the degree of cognitive impairment on tests of visual spatial memory (recalling and recreating a complex shape) and processing speed. In this study lower levels of vitamin D were associated with poorer performance on these tests even in people aged 30.  This study complements a growing body of research that is demonstrating a relationship between vitamin D status and brain function (including influence on mood and anxiety disorders).

There is also growing concern worldwide about the ‘pandemic’ of vitamin D deficiency and the many health concerns it is associated with such as osteoporosis, fractures, and increased risk of some cancers and autoimmune diseases. It is estimated that at least 50% of people are vitamin D deficient and the situation is worse for those of with dark skin as the melanin pigment blocks the action of vitamin D synthesis in the skin. Food sources of vitamin D include oily fish (salmon, sardines and mackerel), eggs and fortified cereals, though few people are eating sufficient amounts of these foods to keep their levels topped up, and vegetarians and vegans need to be very thoughtful about their food/supplement choices to ensure adequate levels.

Reference

Darwish, H., Zeinoun, P., Ghusn, H., Khoury, B., Tamim, H., and Khoury, S. J. (2015). Serum 25-hydroxy vitamin D predicts cognitive performance in adults. Neuropsychiatric Disease and Treatment, 11, 2217–2223.