Involvement of α-adrenergic receptors in the amnestic and anti-amnestic action of acth, β-endorphin and epinephrine

Abstract

The post-training administration of ACTH 1–24 (0.2 μg/kg), human β-endorphin (1.0 μg/kg) or epinephrine HCI (5.0 μg/kg), intraperitoneally, caused retrograde amnesia for a step-down inhibitory avoidance task in rats, and their pre-testing administration reversed this effect. The concomitant administration of the α 2-adrenergic receptor blocker, yohimbine HCl (2.0 mg/kg), antagonized both the post-training amnestic and the pre-testing anti-amnestic effects of the three substances. The anti-amnestic effect of epinephrine, but not that of ACTH or β-endorphin, was also antagonized by the α 1-adrenergic receptor blocker, prazosin HCl (2.0 mg/kg). These findings suggest that α 2-adrenergic receptors are involved both in the amnestic and in the anti-amnestic effect of ACTH, β-endorphin and epinephrine at the doses used, and that, in the case of the antiamnestic effect of epinephrine, α 1 receptors also are involved. It seems likely that memory regulation by post-training and pre-testing ACTH and β-endorphin requires the concomitant activity of α 2-adrenergic mechanisms, either central or peripheral.