Effect of glucose on memory : examination of possible mechanisms

Previous research has shown that ingestion of sucrose or injection of glucose following a learning experience can improve an animal's memory for that experience. The present work was directed towards elucidating the mechanisms by which sucrose and glucose produce this effect. Memory was tested by determining the effects of post-training injections of various substances on a conditioned emotional response. Glucose itself exerted a dose-dependent bidirectional action on retention. This action was shown not to depend on particular blood glucose levels. Insulin did not improve retention at any of the doses tested. Fructose, a sugar that does not cross the blood-brain barrier produced a dose-response effect on retention similar to that of glucose suggesting that fructose and glucose may act through a common peripheral mechanism. The observation of a memory improvement following injections of either 2-deoxyglucose or 3-O-methylgucose, two non-metabolized glucose analogs, suggested that the effect of glucose on retention may be due to an action on glucose transport and not to any metabolic effects of glucose. Two peripheral organs were examined for their possible involvement in the memory-improving action of glucose. This action was shown not to be dependent on the adrenal medulla which has been implicated in the action of other mnemoactive treatments. Partial denervation of the liver produced a partial attenuation of the effect of glucose on retention. The results are discussed in terms of the action of reinforcers on endogenous physiological mechanisms that modulate memory consolidation