Clonidine and the hyper-responsiveness of dorsal horn neurones following morphine withdrawal in the spinal cat.

In barbiturate-anaesthetized spinal cats, exaggerated responses of dorsal horn neurones to impulses in unmyelinated primary afferents, were produced by administering naloxone after iontophoretic administration of morphine in the substantia gelatinosa. Clonidine, given both intravenously (5-10 micrograms/kg) and iontophoretically into the substantia gelatinosa, reduced cell responses to pre-naloxone values. The action of clonidine was reversed by idazoxan. This spinal action of clonidine may be an important component in the suppression of the opiate withdrawal syndrome observed in the whole animal.