Studies on memory: spontaneous return of memory in 6-hydroxydopamine-treated mice and its relation to cycloheximide-induced transient amnesia.

We suggested previously that cycloheximide-induced transient amnesia was due in part to side-effects of the antibiotic on the central adrenergic system at the time of testing and that spontaneous return of memory depended upon recovery of the adrenergic system. To test these possibilities, mice chronically depleted of brain catecholamines (CAs) by 6=hydroxydopamine (6-OHDA) were trained in an avoidance-discrimination task and tested for spontaneous return of memory. Contrary to our hypothesis, amnesia at 24 hr after training was followed by recovery of memory by 72 hr, which indicates that recovery of memory can occur independently of adrenergic recovery. Injection of alpha-methyl-para-tyrosine immediately after training prevented return of memory at 72 hr, suggesting that the residual CAs remaining after 6-OHDA are necessary for memory to spontaneously return at this time.