EVIDENCE FOR A SUPRASPINAL MECHANISM IN THE OPIOID-MEDIATED ANTINOCICEPTIVE EFFECT OF KETAMINE

Systemic ketamine (50 or 160 mg/kg, i.p.) produced an antinociceptive effect in rats on the tail flick test. This effect of ketamine was inhibited by injection of naloxone (27 nmol) into the lateral ventricle. Intrathecal ketamine (3-mu-m) produced a slight but significant antinociceptive effect on the tail flick test, which was not affected by injection of naloxone (27 nmol) into the lateral ventricle. Antinociception was not produced by injection of ketamine into the lateral ventricle (3-mu-m) or the rostral ventromedial medulla RVM (30 nmol). The role played by spinal and supraspinal opioid receptors in ketamine-induced antinociception is discussed.