title: Dextromethorphan and levorphanol on dorsal horn nociceptive neurones in the rat.
abstract: Intrathecal administration of dextromethorphan and levorphanol and intravenous injection of dextromethorphan were tested on the electrophysiological response of deep multireceptive dorsal horn neurones to peripheral stimuli. Both blockade of C-fibre input to the cells and wind-up, the increase in C-fibre firing with repeated stimulus, were recorded. Intrathecal injection of levorphanol (0.25-100 micrograms) had a typical opioid effect, blocking the C-fibre input. Its affect on wind-up was dose-dependent, paralleled precisely the blocking effect on the C-fibre input and both effects were reversed by naloxone. Unlike levorphanol and other opiates, intrathecal administration of dextromethorphan (50-500 micrograms) blocked the C-fibre input and A beta response in parallel and was not reversed by naloxone. Wind-up was reduced by a maximum of 56% at the largest dose tested. Intravenous injection of dextromethorphan (5 mg/kg) also produced a reduction in wind-up but not in the C-fibre response.
authors.affiliation: Department of Pharmacology, University College London, U.K.
authors.forename: A H
authors.initials: AH
authors.lastname: Dickenson
authors.forename: A F
authors.initials: AF
authors.lastname: Sullivan
authors.forename: L C
authors.initials: LC
authors.lastname: Stanfa
authors.forename: H J
authors.initials: HJ
authors.lastname: McQuay
mesh_terms: D000818:Animals; D003915:Dextromethorphan / Q000494:pharmacology*; D004594:Electrophysiology; D007278:Injections, Spinal; D007981:Levorphanol / Q000008:administration & dosage / Q000494:pharmacology*; D009412:Nerve Fibers / Q000187:drug effects; D009413:Nerve Fibers, Myelinated / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D009619:Nociceptors / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000166:cytology* / Q000187:drug effects
chemical_list: D007981:Levorphanol; D003915:Dextromethorphan