University of Queensland researchers have explained a key mechanism by which the stress hormone noradrenaline, which floods the bloodstream during stressful events, affects the brain's pain-processing pathway to produce such analgesia.

Pankaj Sah and colleagues studied a region of the amygdala, the brain's emotion-processing region known to mediate the emotional and stress-related aspects of pain. Researchers have long known that amygdala-based processes are controlled by neurons originating in the brain stem and are regulated by noradrenaline. Sah and his colleagues found noradrenaline suppressed the transmission of pain messages to the amygdala.

"Our results show that an important mediator of stress-induced analgesia could be the potent modulation by noradrenaline of (pain) inputs in the central amygdala," the scientists said.

The study, which included Andrew Delaney and James Crane of the Queensland Brain Institute, was reported in the journal Neuron.