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Mice were trained in an automated visual-discrimination task. When injected with cycloheximide before training, mice showed: (a) some impairment of memory within minutes after the beginning of training, (b) gradual development of total amnesia in less than 3 hr or in more than 6 hr after training, depending on the extent of training, and (c) spontaneous recovery of memory within 3 days after training. The results are consistent with the operation of three processes of memory storage: (i) a short-term process that is independent of protein synthesis, (ii) a long-term that is dependent on protein synthesis, and (iii) a slow-developing memory storage that becomes apparent during the days after training.

Cycloheximide, when injected subcutaneously or intracerebrally, produces changes in the activity level of mice. Isocycloheximide, injected intracerebrally, produces identical effects on activity, but it does not produce inhibition of cerebral protein synthesis or amnesia. Amphetamine, in doses that can antagonize the amnesic action of cycloheximide, does not antagonize the effect of cycloheximide on activity. Effects of cycloheximide on activity do not appear to be responsible for its amnesic action.