Clonidine inhibits itch-related response through stimulation of α(2)-adrenoceptors in the spinal cord in mice.

The present study investigated whether clonidine - an α(2)-adrenoceptor agonist known to relieve pain - is able to suppress itch-related behavior in mice. An intraplantar injection of serotonin induced biting (an itch-related response), which was inhibited by intraperitoneal and intrathecal, but not intraplantar or intracisternal, clonidine injections. The effect of intrathecal clonidine was inhibited by intrathecal injections of phentolamine (a non-selective α-adrenoceptor antagonist) and yohimbine (a selective α(2)-adrenoceptor antagonist), but not by prazosin (a selective α(1)-adrenoceptor antagonist). The effect of intraperitoneal clonidine was also inhibited by intrathecal yohimbine. These results suggest that clonidine is an effective antipruritic agent and that the effect is mainly mediated by the stimulation of α(2)-adrenoceptors in the dorsal horn.