Scientists at the Science Foundation Ireland-funded APC Microbiome Institute at University College Cork, Ireland, have shown that, at least in mice, gut bacteria play a key role in regulating abdominal pain and its associated changes in the brain and spinal cord.

Visceral pain is a global term used to describe pain originating from the internal organs of the body, which affects a significant proportion of the population and is a common feature of functional gastrointestinal disorders such as irritable bowel syndrome (IBS). Currently, the treatment strategies for visceral pain are unsatisfactory, with the development of novel therapeutics hindered by a lack of detailed knowledge of the underlying mechanisms, although alterations of the Gut-Brain axis has been implicated.

The human gut is home to over 100 trillion bacteria and other microorganisms collectively known as the microbiota. The gut microbiota is involved in critical processes such as digestion, metabolism, immune responses and absorption of nutrients. Until recently, little was known about how the microbiota influences the nervous system; however, it is becoming increasingly clear that gut microorganisms can influence the brain and behavior.

Profs. John Cryan and Ted Dinan along with postdoctoral fellow Dr. Monica Tramullas and research scientist Pauline Luczynski, have unraveled a novel mechanism underlying how visceral pain can emerge. They have shown that mice that grow up without microbes (germ-free mice) were more sensitive to visceral pain stimuli. These animals also showed corresponding changes in genes in their spinal cord. In the brain, germ-free mice had changes in areas involved in the descending pain modulation and its emotional regulation.

Of great interest, colonisation of germ-free mice with gut bacteria reversed these changes which suggest that there is potential to reverse the changes with microbiota-based interventions. Prof. Cryan, says "we are very excited about these data, although the microbiota has long been thought to play a key role in pain modulation, the current study proves it categorically and offers insights into some of the potential neurobiological mechanisms at play."

The data have implications for our understanding of IBS and supports the concept of targeting the microbiota to modulate pain symptoms in this and other gastrointestinal disorders.

The research has been published in the journal eLife.