tokens: METHODS AND RESULTS : To test whether clonidine elicits pharmacological effects independent of alpha2 - adrenoceptors , we have generated mice with a targeted deletion of all 3 alpha2 - adrenoceptor subtypes ( alpha2ABC -/-). Alpha2ABC -/- mice were completely unresponsive to the analgesic and hypnotic effects of clonidine ; however , clonidine significantly lowered heart rate in alpha2ABC -/- mice by up to 150 bpm .