Researchers at UQ’s Queensland Brain Institute (QBI) have discovered a new brain mechanism that plays an important role in regulating how we experience pain.
Scientists from QBI’s synaptic plasticity laboratory discovered the new mechanism while studying the amygdala – the part of the brain that deals with our emotional responses.
QBI has one of the relatively few laboratories around the world currently looking at how the amygdala deals with pain inputs.
According to QBI’s Dr Andrew Delaney, there are essentially two aspects to pain.
“You have a sensory component that tells you where you are hurting and what sort of hurt you’ve had, and there’s the emotional response you have to that event,” he said.
“The sensory part of pain is quite well understood, but until now very little had been done to look at the emotional part of pain.”
QBI scientists used an anatomical technique which involved labelling the neurons in what is essentially the brain’s pain-relay station [the parabrachial nucleus] to identify target cells in the amygdala that receive inputs during pain.
Researchers were able to record electrical responses in the amygdala when the pain inputs were stimulated electrically.
“People have long thought there’s a connection between your experience of pain and the emotional state that you’re in,” Dr Delaney said.
Historically, this has been borne out by first-hand reports from people who have suffered a traumatic injury during the height of combat and yet gone on to all but ignore their injury for some time.
A similar phenomenon happens on the sporting field where, during the game’s emotional zenith, a player injures a knee or ankle but manages to finish the play or walk off.
For many years, this was thought to be a spinal cord effect, whereby the release of hormones during heightened emotions inhibit the transmission of pain – sometimes called the “gate theory” of pain.
“Our findings indicate that there is also an interaction between the stress pathways in the brain and the pain pathway that targets the amygdala,” Dr Delaney said.
“This seems to indicate that during times of stress, our emotional response to pain may also be modulated, perhaps reducing the emotional impact of a painful experience.”
The QBI scientists have shown, for the first time, that the stress hormone noradrenaline acts as a fast modulatory transmitter in the brain, and that the way this transmitter works at these pain synapses was by scaling down the size of the pain inputs.
Such a mechanism had not previously been identified in the brain, and it is one which is ideally suited to providing strong control over the activation of the emotional response, even when strong painful input activates the pathway to the amygdala.
According to QBI’s Head of Synaptic Plasticity, Professor Pankaj Sah, people who suffer chronic pain have higher incidence of anxiety disorders, conditions known to involve dysfunctional processing in the amygdala.
“This study reveals an important site for interaction between the pain and emotional systems of the brain, potentially offering a key connection to how this might be occurring,” he said.
“Ultimately understanding how these systems interact at the synaptic level might reveal the nature of these dysfunctional states and offer an insight into how we might better treat such conditions.”
The research – “Noradrenaline Modulates Transmission at a Central Synapse by a Presynaptic Mechanism” – is published in the journal Neuron and is downloadable here.
Source : Queensland Brain Institute
