Endogenous state-dependency:memory regulation by post-training and pre-testing administration of ACTH, beta -endorphin, adrenaline and tyramine.

The post-training amnestic effect of ACTH, beta-endorphin, adrenaline or tyramine on a step-down inhibitory avoidance task in rats was reversed by the administration of the same drugs prior to testing. Each drug was more effective as an anti-amnestic agent when the amnesia was induced by post-training administration of the same drug than of one of the others. alpha 2-Adrenergic receptors were shown to be involved in the amnestic and anti-amnestic actions of all the drugs and alpha 1 receptors to be involved in the anti-amnestic action of adrenaline and tyramine. These findings support the concept that memory depends on the relationship between the neurohumoral and hormonal states both after training and at the time of testing. These drugs would have limited value as contextual cues, and the mechanisms sensitive to their influence should be those involved in the availability of stored information for retrieval.