Alpha-2 agonist-induced memory impairment is mediated by the alpha-2A-adrenoceptor subtype.

The activation of 2-adrenoceptors has been reported to impair memory functions in both rats and humans. The 2-adrenoceptor subtype responsible for this detrimental effect is still unknown. The effect of the 2-agonists clonidine and guanabenz on memory processes, in dependence to the time of administration, was evaluated in the mouse passive avoidance test. Clonidine (0.02–0.2 mg kg−1 i.p.) and guanabenz (0.1–0.3 mg kg−1 i.p.) induced amnesia in a dose-dependent manner. From time–course experiments emerged that the impairment of memory function was detectable only when clonidine and guanabenz were administered 60 min before or immediately after the training test, respectively. This detrimental effect was prevented by pretreatment with the 2-antagonist yohimbine (1–3 mg kg−1 i.p.) and by the 2A-antagonist BRL-44408 (0.3–1 mg kg−1 i.p.). By contrast, the 2B,C antagonists ARC-239 (10 mg kg−1 i.p.) and prazosin (1 mg kg−1 i.p.) did not revert the amnesia induced by both clonidine and guanabenz. At the highest effective doses, clonidine and guanabenz were devoid of behavioral side-effects as well as maintained unaltered the motor coordination, as revealed by the rota-rod test. Furthermore, none of the compounds used modified the spontaneous motility as indicated by the Animex apparatus. These results indicate that clonidine and guanabenz impaired memory processes in amouse passive avoidance paradigm through the selective activation of the 2A-adrenoceptor subtype.