Intrathecal clonidine suppresses noxiously evoked activity of spinal wide dynamic range neurons in cats.

The analgesic effectiveness of perispinal clonidine administration prompted us to evaluate clonidine effects on spinal dorsal horn wide dynamic range neurons. Intrathecal clonidine produced a dose-dependent (10 and 30 micrograms), yohimbine-reversible suppression of noxiously evoked activity in decerebrate, spinal cord-transected cats. In addition, combining ineffective intrathecal doses of morphine (25 micrograms) and clonidine (5 micrograms) produced statistically significant, reversible suppression of noxiously evoked activity. The time course of suppression was similar to that observed behaviorally. These results support the role of spinal alpha 2-adrenergic receptors in clonidine analgesia.