Activation of alpha 2-adrenergic receptors decreases nerve trauma-induced afferent barrage but not autotomy.
Effects of the selective alpha 2-adrenoceptor agonist, medetomidine, on a compound volley of a tibial nerve stimulation-evoked spinal reflex, pain-induced phrenic motor responses and on postoperative neuropathic pain behavior were studied in rats. Medetomidine (0.3 mg/kg) decreased the amplitude of the compound volley recorded from peroneal nerve in response to tibial stimulation in pentobarbital (40 mg/kg) anesthetized rats. Atipamezole, an alpha 2-adrenoceptor antagonist (1.5 mg/kg) fully restored the response when given 60 min after the medetomidine administration. Pain-evoked phrenic motor responses were completely inhibited upon combination anesthesia by pentobarbital (40 mg/kg) and medetomidine (0.3 mg/kg) (PB+M) but not upon plain pentobarbital anesthesia (50 or 60 mg/kg) (PB50,PB60). To study the effect of medetomidine on postoperative neuropathic pain behavior (autotomy), transection of sciatic nerve was done under PB+M, PB50 or PB60 anesthesia. No differences between the groups were found in the postoperative pain behavior during eight-week follow up. The results show that activation of alpha 2-adrenergic receptors by medetomidine under pentobarbital anesthesia mitigates trauma-induced afferent barrage, whereas it does not reduce the subsequent autotomy.
Taira
T
T
Institute of Biomedicine, University of Helsinki, Finland.
Tanila
H
H
Jyväsjärvi
E
E
Pertovaara
A
A
Kauppila
T
T
D058647:Adrenergic alpha-2 Receptor Agonists; D000344:Afferent Pathways / Q000187:drug effects; D000818:Animals; D003714:Denervation; D004558:Electric Stimulation; D007093:Imidazoles / Q000494:pharmacology*; D007274:Injections, Intraperitoneal; D008297:Male; D020926:Medetomidine; D009068:Movement / Q000502:physiology; D010146:Pain / Q000503:physiopathology*; D010791:Phrenic Nerve / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012652:Self Mutilation / Q000503:physiopathology; D013116:Spinal Cord / Q000187:drug effects*; D013979:Tibial Nerve / Q000502:physiology; D014947:Wounds and Injuries / Q000503:physiopathology*
D058647:Adrenergic alpha-2 Receptor Agonists; D007093:Imidazoles; D020926:Medetomidine