Effect of Opioids on the CNS

As discussed earlier, opioid receptors exist at specific locations throughout the CNS and possibly in peripheral nerve tissues as well. In the spinal cord, these receptors are concentrated on the neurons responsible for transmitting nociceptive input to higher (supraspinal) levels.33 Opioid receptors have likewise been identified in several locations of the brain that are associated with pain transmission and interpretation. 

These areas include the periaqueductal gray region of the spinoreticular tract, medial thalamic nuclei, hypothalamus, limbic system, and several other areas.33,65,75 

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