Pirenperone does not attenuate morphine analgesia in spinal rats.

The selective serotonin type-2 (S2) receptor blocker pirenperone (0.24 mg/kg, SC) attenuates morphine-produced tail-flick antinociception in intact rats, but not in rats with transected spinal cords. These results suggest that S2 receptor blockade does not affect intraspinal opioid antinociception. Together with evidence that there are virtually no S2 receptors in the dorsal spinal cord, supraspinal S2 receptors are implicated in the mediation of morphine-produced antinociception.