The antinociceptive actions of dexmedetomidine on dorsal horn neuronal responses in the anaesthetized rat.
The actions of the selective alpha 2-adrenoceptor agonist dexmedetomidine were examined on the nociceptive C and innocuous A beta fibre-evoked responses of dorsal horn neurones to transcutaneous electrical stimulation in the intact anaesthetized rat. C fibre-evoked responses were dose dependently reduced by intrathecal dexmedetomidine--to a maximum 86 +/- 6% inhibition by 10 micrograms of the agonist. The ED50 for inhibition of C fibre responses was estimated to be 2.5 micrograms. A beta-evoked responses were inhibited to a lesser degree--a maximum 54 +/- 8% inhibition after 10 micrograms dexmedetomidine. The antinociceptive effects of dexmedetomidine were reversed by the alpha 2-adrenoceptor antagonist atipamezole and the opioid antagonist naloxone. The results are discussed with reference to adrenergic and opioid mechanisms in the spinal cord.
Department of Pharmacology, University College London, U.K.
A F
AF
Sullivan
E A
EA
Kalso
H J
HJ
McQuay
A H
AH
Dickenson
D000200:Action Potentials / Q000187:drug effects; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000700:Analgesics / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000758:Anesthesia; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D007093:Imidazoles / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008297:Male; D020926:Medetomidine; D009270:Naloxone / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D009619:Nociceptors / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects* / Q000502:physiology
D000317:Adrenergic alpha-Antagonists; D000700:Analgesics; D007093:Imidazoles; C050701:atipamezole; D009270:Naloxone; D003000:Clonidine; D020926:Medetomidine