ANTINOCICEPTIVE EFFECTS OF COMBINING LOW-DOSES OF NEUROLEPTIC DRUGS AND FENTANYL IN SHEEP

Effects of low doses of the neuroleptic drugs droperidol and zuclopent hixol, combined with a subanalgesic dose of the opioid mu-agonist, fen tanyl, on mechanical nociceptive thresholds were evaluated in sheep. I ntravenously administered droperidol (5 mug/kg of body weight) did not induce any change in the nociceptive thresholds when administered alo ne, but caused marked increase in threshold responses when combined wi th a subanalgesic dose of fentanyl (5 mug/kg). Similarly, a combinatio n of IV administered zuclopenthixol (100 mug/kg) and fentanyl induced significant (P < 0.05) antinociceptive effects, whereas zuclopenthixol administered iv alone had no effect on the threshold responses. Intra thecal administration of a low dose of droperidol (5-mug total dose) c ombined with IV administered fentanyl also increased mechanical thresh olds significantly (P < 0.05). These results indicate that interaction s exist between dopaminergic and opioid systems in the processing of n ociceptive information and that these effects may, at least partially, be mediated spinally.