But just in case the signal does make it up the second neuron to the brain, opioids have another role to play. As well as the ascending pathway, which takes pain information to the brain, there is another pathway, going in the opposite direction, which interacts with it. Opioids act on a region of the brain called the periaqueductal gray (PAG), to activate this descending pathway. Once activated, the descending pathway releases chemicals including GABA, serotonin, noradrenaline and more opioids into the synapse between the sensory neurons and the neuron that would carry the signal up the
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