Opiate receptors for behavioral analgesia resemble those related to the depression of spinal nociceptive neurons.

With naloxone as antagonist, a dose-ratio analysis of the depression by morphine of nociceptive neurons in the spinal cord reveals that this opiate depression of single unit activity has the same pharmacological properties as observed with morphine analgesia. This suggests that the opiate receptor, mediating the observed cellular depression, and those mediating analgesia are presumably the same.