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

The activation of alpha(2)-adrenoceptors has been reported to impair memory functions in both rats and humans. The alpha(2)-adrenoceptor subtype responsible for this detrimental effect is still unknown. The effect of the alpha(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 alpha(2)-antagonist yohimbine (1-3 mg kg(-1) i.p.) and by the alpha(2A)-antagonist BRL-44408 (0.3-1 mg kg(-1) i.p.). By contrast, the alpha(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 a mouse passive avoidance paradigm through the selective activation of the alpha(2A) -adrenoceptor subtype. (C) 2004 Elsevier B.V. All rights reserved.