Dexmedetomidine and ST-91 analgesia in the formalin model is mediated by alpha2A-adrenoceptors: a mechanism of action distinct from morphine.
Br J Pharmacol
; 155(7): 1117-26, 2008 Dec.
Article
em En
| MEDLINE
| ID: mdl-18846040
ABSTRACT
BACKGROUND AND PURPOSE:
Intrathecal administration of alpha(2)-adrenoceptor agonists produces potent analgesia. This study addressed the subtype of spinal alpha(2)-adrenoceptor responsible for the analgesic effects of i.t. dexmedetomidine and ST-91 in the formalin behavioural model and their effects on primary afferent substance P (SP) release and spinal Fos activation. EXPERIMENTALAPPROACH:
The analgesic effects of i.t. dexmedetomidine and ST-91 (alpha(2) agonists) were tested on the formalin behavioural model. To determine the subtype of alpha(2)-adrenoceptor involved in the analgesia, i.t. BRL44408 (alpha(2A) antagonist) or ARC239 (alpha(2B/C) antagonist) were given before dexmedetomidine or ST-91. Moreover, the ability of dexmedetomidine and ST-91 to inhibit formalin-induced release of SP from primary afferent terminals was measured by the internalization of neurokinin(1) (NK(1)) receptors. Finally, the effects of dexmedetomidine on formalin-induced Fos expression were assessed in the dorsal horn. KEYRESULTS:
Intrathecal administration of dexmedetomidine or ST-91 dose-dependently reduced the formalin-induced paw-flinching behaviour in rats. BRL44408 dose-dependently blocked, whereas ARC239 had no effect on the analgesic actions of dexmedetomidine and ST-91. Dexmedetomidine and ST-91 had no effect on the formalin-induced NK(1) receptor internalization, while morphine significantly reduced the NK(1) receptor internalization. On the other hand, both dexmedetomidine and morphine diminished the formalin-induced Fos activation. The effect of dexmedetomidine on formalin-induced Fos activation was reversed by BRL44408, but not ARC239. CONCLUSION AND IMPLICATIONS These findings suggest that alpha(2A)-adrenoceptors mediate dexmedetomidine and ST-91 analgesia. This effect could be through a mechanism postsynaptic to primary afferent terminals, distinct from that of morphine.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Clonidina
/
Agonistas alfa-Adrenérgicos
/
Dexmedetomidina
/
Agonistas de Receptores Adrenérgicos alfa 2
Tipo de estudo:
Prognostic_studies
Limite:
Animals
Idioma:
En
Revista:
Br J Pharmacol
Ano de publicação:
2008
Tipo de documento:
Article