Neurobiological features common to memory modulation by many treatments

Evidence reviewed here suggests that many treatments that retroactively enhance or impair memory in rats and mice may act by releasing epinephrine from the adrenal medulla: (1) When administered shortly after training, epinephrine injections modulate memory storage processes; (2) plasma epinephrine levels assessed shortly after training predict later performance of learned responses in several situations; and furthermore, (3) peripherally administered adrenergic antagonists block the effects on memory of epinephrine and of many other treatments that enhance and impair memory. In addition, the rapid forgetting exhibited by juvenile and aged rodents can be retarded (i.e., memory is improved) by posttraining epinephrine injections, suggesting that age-related memory deficits may reflect inadequate functions of those neuroendocrine systems responsible, in part, for regulating memory storage. These results, together with the additional finding that epinephrine enhances the establishment of a neurophysiological analogue of memory, long-term potentiation, suggest that the hormone regulates neurobiological processes responsible for memory formation.