Amphetamine, epinephrine, and glucose enhance memory storage when administered shortly after training. Amphetamine enhancement of memory storage may be mediated by peripheral epinephrine actions, and epinephrine enhancement of memory storage may involve increases in blood glucose levels. Amphetamine and possibly epinephrine also enhance memory retrieval when administered shortly before testing. To examine the parallels in pharmacological enhancement of memory storage and retrieval, we tested the effects on memory of injections of amphetamine (1.0 mg/kg), epinephrine (0.05 mg/kg), or glucose (100 mg/kg) administered prior to retention tests in mice. Mice were trained in a one-trial inhibitory (passive) avoidance task. Thirty minutes prior to testing, each mouse received an injection of saline, amphetamine, epinephrine, or glucose. In a second experiment, rats were trained on a one-trial inhibitory avoidance task and were administered glucose (100,250, or 500 mg/kg) prior to testing. The results indicate that amphetamine, epinephrine, and glucose all significantly enhanced learned performance, supporting the view that similar neuroendocrine systems may contribute to both memory storage and retrieval. In addition, these findings provide another demonstration that peripheral glucose injections modify behavior.
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