RESEARCHERS AT NUI Galway have made an important discovery in the study of pain and the human brain.

The team – David Finn, Gemma Ford, Siobhan Kieran, Kenneth Dolan, and Brendan Harhen - have had their findings published in the leading journal Pain which shows for the first time that the hippocampus of the brain has an active role to play in suppressing pain during times of stress.

The hippocampus is usually associated with memory.

The work was carried out by the researchers in Pharmacology and Therapeutics, and the Centre for Pain Research at the National Centre for Biomedical Engineering Science, NUI Galway.

In times of immense stress or fear, pain transmission and perception can be suppressed in humans and other animals.

This survival response can help us cope with, or escape from, potentially life-threatening situations.

An increased understanding of the biological mechanisms involved in this so-called fear-induced analgesia is important from a fundamental physiological perspective and may also advance the search for new therapeutic approaches to the treatment of pain.

Dr David Finn, Co-Director of the Centre for Pain Research at NUI Galway, and study leader, explained:

The body can suppress pain when under extreme stress, in part through the action of marijuana-like substances produced in the brain. What we have now identified for the first time, is that the brain’s hippocampus is an important site of action of these endocannabinoids during the potent suppression of pain by fear.

Finn said it advances our fundamental understanding of the neurobiology of pain and may facilitate the identification of new therapeutic targets for the treatment of pain and anxiety disorders.

Working with Dr Finn, first author Dr Gemma Ford was able to demonstrate that inhibition of the enzyme that breaks down one of these endogenous marijuana-like substances in the hippocampus had the effect of enhancing stress-induced pain suppression.

Further experimentation revealed that these effects were mediated by the cannabinoid CB₁ receptor and were likely to be mediated by stress-induced increases in levels of endocannabinoids in the hippocampus.

The research took us about two years and the team were working towards a hypothesus that the hippocampus had a role in reducing pain while the body was under stress.

It was carried out on pre-clinical models so there is now the potential for research to be carried out on humans at some point, although it would be ”much more difficult to do technically”, said Dr Finn.

Within the pain field that should be quite an important discovery and should generate some further interest in research around the world. The next step might be to try and see whether that translates to humans.

One could follow up with imaging studies in humans to investigate whether that part of the brain is active during stress induced analgesia in humans and try to understand its role in people.

For example, he said research could potentially be done in pain patients to see whether those suffering from chronic pain have any alterations to that region during stress or following stress.

The type of pain that was tested by the NUI Galway researchers was a persistent pain of the inflammatory type.

Dr Finn explained that blocking pain during times of stress can have an evolutionary survival role.

If you have suffered an injury which is causing you pain and you are at the same time in a threatening situation or stressful situation, you want to be able to get out of there and escape and survive.

Situations where this might come into play are soldiers on the battle field who don’t feel pain in their wounds, or sports people on the pitch who don’t feel the pain of injuries until the game is over.

“It allows you to cope with a threatening situation or stress for a period of time and suppress the pain until you have escaped,” said Dr Finn.

The research was funded by a grant from Science Foundation Ireland.