Brain can suppress pain when under extreme stress by producing marijuana-like chemicals, scientists have found.
Researchers from National University of Ireland Galway (NUI Galway) led by Dr David Finn found suppression of pain during times of fear involves complex interplay between marijuana-like chemicals and other neurotransmitters in a brain region called the amygdala.
The study builds on previous breakthrough findings from Finn's research group on the role of marijuana-like chemicals in the brain's hippocampus in pain suppression during fear.
Pain is both a sensory and an emotional experience and is subject to modulation by a number of factors including fear and stress. During exposure to a high-stress environment or stimulus, pain transmission and perception can be potently suppressed.
This important survival response can help us cope with or escape from potentially life-threatening situations. One brain region that is integral to the processing and expression of both emotional responses and pain is the amygdala.
Working with Finn, first author Dr Kieran Rea was able to confirm the amygdala as a key brain region in the suppression of pain behaviour by fear (so-called fear-induced analgesia).
Fear-induced analgesia was associated with increases in levels of marijuana-like substances known as endocannabinoids in the amygdala.
Moreover, fear-induced analgesia was prevented by injecting a drug that blocked the receptor at which these endocannabinoids act into the amygdala.
Further experimentation revealed that these effects involved an interaction between endocannabinoids and the classical neurotransmitters GABA (Gamma-amino butyric acid) and glutamate.
An increased understanding of the biological mechanisms involved in 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.
"The body can suppress pain when under extreme stress, in part through the action of marijuana-like substances produced in the brain," Finn said.
"This research provides information on the complex interactions between multiple neurotransmitter systems including endocannabinoids, GABA and glutamate in times of stress and pain," he said.
The study was published in the journal Pain.