The gurgling workings of the lower digestive tract may not be the first place you might think to look when hunting for a miracle cure for cognitive decline, but recent research suggests the bowel could be more linked to the brain than we might like to admit.
A new study suggests faecal transplants - the transfer of stool from a donor into the gastrointestinal tract of another person - could one day be used as a therapy to restore the mental capabilities of elderly people.
The technique is already recognised as a means of treating certain gastrointestinal infections and other conditions, with the introduction of the foreign faeces acting to repopulate the essential microbes in the gut.
But the new research indicates this process could also stimulate certain brain activity which affects learning and memory.
The team of researchers, from the University of East Anglia, the University of Florence and the Quadram Institute in Norwich found in a study on mice, faecal transplants from older mice to younger mice altered their gut microbiome, which in turn impacted their spatial learning and memory.
The team now hope that by reversing the process, medical science could one day see faecal transplantation being used to combat cognitive decline among the elderly.
Dr David Vauzour, from UEA's Norwich Medical School, said: “Ageing is an inevitable process that starts immediately after birth and ultimately leads to physical health problems as well as a decline in psychological well-being and cognitive function.
“Research has shown that the aging process may be linked with age-related changes in our gut microbiota.
“Recently, the existence of two-way communication between the gut and the brain - known as the ‘gut-brain axis’ - has emerged as an important player in shaping aspects of behaviour and cognitive function.
“We wanted to see whether transferring gut microbes from older to younger mice could affect parts of the central nervous system associated with ageing.”
The research team performed faecal transplants from older adult mice to younger adult mice and then assessed the young adults for markers such as anxiety, exploratory behaviour and memory.
After the transplantation, the team found significant differences in the young mice’s microbial profiles.
While the young adults showed no significant changes in markers of anxiety, explorative behaviour or locomotor activity, they did show impaired spatial learning and memory as measured in a maze test.
The scientists found these changes were paralleled by changes in the expression of proteins associated with synaptic plasticity and neuro transmission - both of which affect the nervous system, and there were also measurable alterations to cells in the hippocampus - the part of the brain - responsible for functions including learning and memory.
Dr Vauzour said: “Our research shows that a faecal transplantation from an old donor to a young recipient causes an age-associated shift in the composition of gut microbiota.
“The procedure had an impact on the expression of proteins involved in key functions of the hippocampus - an important part of the brain that has a vital role in a variety of functions including memory, learning but also in spatial navigation and emotional behaviour and mood.
“In short, the young mice began to behave like older mice, in terms of their cognitive function.”
Professor Claudio Nicoletti, from the University of Florence, Italy, said: “While it remains to be seen whether transplantation from very young donors can restore cognitive function in aged recipients, the findings demonstrate that age-related shifts in the gut microbiome can alter components of the central nervous system.
“This work highlights the importance of the gut-brain axis in ageing and provides a strong rationale to devise therapies aiming to restore a young-like microbiota to improve cognitive functions and quality of life in the elderly,” he added.
“Manipulating the microbiome is increasingly being seen as a way of improving or maintaining human health, and these results are an exciting indication of its potential for helping us age healthily,” said Professor Arjan Narbad from the Quadram Institute.
“We have established an FMT service on the Norwich Research Park to treat serious gut infections and now want to explore in humans its effectiveness in combating a number of age-related conditions, including cognitive decline.”
The research is published in the journal Microbiome.