Naloxone and experimental spinal cord injury: Part 1. High dose administration in a static load compression model.

Previous studies by other investigators using a dynamic weight drop injury model in cats or rats have demonstrated a beneficial effect of naloxone in promoting motor recovery after experimental spinal cord injury. The effective doses ranged from 0.8 mg (total dose) in rats to a high dose of 10 mg/kg in cats. We report here an evaluation of high dose naloxone (10 mg/kg) in a model of cord injury in rats using a static load compression technique. After induction of injury at T-12, naloxone (10 mg/kg) was administered by the intraperitoneal route, followed by five additional bolus injections over the course of the next 2 days. Animals were randomly assigned to this treatment regimen (n = 10) or to a saline control group (n = 10). The animals were observed for 4 weeks, with testing of recovery of hind limb motor function (Tarlov score and on an inclined plane). Although there were slight differences in recovery, the overall evaluation showed no statistically significant difference between the naloxone-treated and control groups. The spinal cords of the sacrificed animals were studied morphometrically; there was no statistically significant difference between the residual gray and white matter at the site of cord injury between the treated and control groups. Naloxone did not seem to promote recovery of motor function in this model of spinal cord injury.