Actions of morphine and met-enkephalin-amide on nociceptor driven neurones in substantia gelatinosa and deeper dorsal horn.

Simultaneous recordings of responses of substantia gelatinosa and deep dorsal horn neurones to thermal noxious cutaneous stimulation were made in spinalized cats anaesthetized with urethane/chloralose. Morphine, whether applied iontophoretically in the substantia gelatinosa (50-200 nA) or injected intravenously (1.0-1.5 mg/kg), enhanced the responses of the substantia gelatinosa cells while depressing those of deep cells. Met-enkephalin-amide (50-200 nA) also had similar reciprocal actions. Naloxone counteracted these effects of the agonists. The results support our previous proposal that the opiates facilitate the activity of a substantia gelatinosa system that controls the responses of deep dorsal horn neurones to pain.