DIFFERENTIAL EXCITATORY AND INHIBITORY EFFECTS OF OPIATES ON NON-NOCICEPTIVE AND NOCICEPTIVE NEURONS IN SPINAL-CORD OF CAT

Morphine, levorphanol, dextrorphan and naloxone were applied microelectro-phoretically to cells identified as either having nociceptive inputs or non-nociceptive inputs in the dorsal horn of the cat. Morphine excited non-nociceptive cells and depressed nociceptve cells. Naloxone reversed morphine excitations on non-nociceptive cells, but only reversed about one-third of morphine depressions on nociceptive cells. Levorphanol depressed nociceptive cells, whilst dextrorphan ejected with similar currents caused less depression or had no effect. It is concluded that excitation of non-nociceptive cells may constitute a spinal action relevant to the analgesic action of opiates, acting synergistically with a depressant effect on nociceptive neurones. © 1978.