SEGMENTAL EFFECTS ON MOTOR FUNCTION FOLLOWING DIFFERENT INTRATHECAL RECEPTOR AGONISTS AND ANTAGONISTS IN RABBITS

Background: The occurrence of motor impairment after intrathecal drug administration is infrequently reported in the literature and the meth ods of determining motor function vary. Methods: Motor function was ex amined in rabbits after a wide dose range of a variety of intrathecall y administered opioid agonists, alpha-adrenergic agonists, non-competi tive NMDA antagonists, a benzodiazepine agonist, a sigma agonist, para cetamol, isotonic and acidified saline. The opioids, sigma agonist and NMDA antagonists were additionally examined following pretreatment wi th naloxone. The opioid antagonists naltrindole and MR2266 (delta-and kappa-opioid receptor antagonists, respectively) were administered bef ore the delta agonist and the kappa agonist. The alpha(2)-adrenergic a ntagonist yohimbine was given before administration of dexmedetomidine and xylazine. Motor function was evaluated by a five-point scale of m otor impairment ranging from normal function to total paralysis of the hindlegs. Results: DPDPE (delta agonist),paracetamol, naloxone, naltr indole, yohimbine, isotonic and acidified saline did not affect motor function. MR2266 produced minor motor impairment. The alpha-adrenergic agonist dexmedetomidine reduced motor function slightly and dose inde pendently. The remaining compounds affected motor function in a dose-d ependent fashion. High doses of morphine produced hypersensitivity and myoclonus. An irreversible paralysis of the hindlegs was observed fol lowing intrathecal administration of the sigma agonist SKF10047 in hig h doses. Naloxone and MR2266 attenuated the effects of U50488H (kappa agonist). Conclusion: The present results reveal a dose-dependent redu ction in motor function after intrathecal administration of some of th e investigated compounds. The mechanisms behind these effects appear t o be multifactorial. (C) Acta Anaesthesiologica Scandinavica 41 (1997) .