Effects of Naloxone and Levallorphan on the Spinal Cord Reflex Potentials under the Spinal Ischemic Condition in Cats

Abstract

ABSTRACT-The spinal reflex potentials elicited by electrical stimulation of the tibial nerve were re corded from the lumbo-sacral ventral root in spinal cats. When the thoracic aorta and the bilateral in ternal mammary arteries were occluded for 10 min, the potentials were completely depressed. Reap pearance 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 poten tial. Morphine (5 mg/kg) showed no particular effect on the recovery of potentials. Furthermore, pre treatment with morphine (5 mg/kg) did not influence the effects of these opioid antagonists. These re sults 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.

Effects of GABAergic Drugs on the Recovery of Reflex Potentials after Spinal Cord Ischemia in Cats

“…An occlusion of 10 min was repeated at an interval of more than 110 min. We have previously reported that the recovery process of the reflex potentials was reproducible when the occlusion was repeated two or three times under this experimental condition (11). In other words, there were no significant differences in the recovery of the amplitude of MSR potentials and the area of PSR potentials among the first, second and third occlusion.…”

“…Since levallorphan is a K-opiate receptor agonist and a p-opiate receptor antagonist, they concluded that c-opiate receptor stimulation may be beneficial for protection against ischemic neural tissues. In our previous study (11), morphine failed to affect the recovery of PSR potentials after a brief spinal cord ischemia, although naloxone and levallorphan promoted the recovery. Therefore, it is unlikely that naloxone improved the functional recovery by antagonizing opiate receptor, although we can not completely exclude this possibility from the present study.…”

“…We have previously reported that not only naloxone but also levallorphan promoted the recovery of the polysynaptic reflex (PSR) potentials after spinal cord ischemia in spinal cats (11). However, the underlying mechanism(s) of the beneficial effect of naloxone on the neurological recovery remain unclarified.…”