Effects of naloxone and levallorphan on the spinal cord reflex potentials under the spinal ischemic condition in cats.

The spinal reflex potentials elicited by electrical stimulation of the tibial nerve were recorded from the lumbo-sacral ventral root in spinal cats. When the thoracic aorta and the bilateral internal mammary arteries were occluded for 10 min, the potentials were completely depressed. Reappearance of these potentials could be observed at about 10 min after removal of the occlusion and they gradually recovered. Intravenous injection of naloxone (1 or 10 mg/kg) or levallorphan (0.1 mg/kg) together with removal of occlusion significantly promoted the recovery of the polysynaptic reflex potential. Morphine (5 mg/kg) showed no particular effect on the recovery of potentials. Furthermore, pretreatment with morphine (5 mg/kg) did not influence the effects of these opioid antagonists. These results suggest that naloxone and levallorphan may preserve or potentiate the interneuronal activities of the lumbo-sacral spinal cord under the ischemic condition and that the effects may not be mediated through morphine-like opioid receptors.