Amphetamine enhances memory retention and facilitates norepinephrine release from the hippocampus in rats

The present study investigated the effects of intrahippocampal amphetamine on memory retention and the role of hippocampal norepinephrine (NE) in memory consolidation in rats. One-way inhibitory avoidance learning paradigm was adopted. Animals were trained to avoid the foot shock. The latency to step into the shock compartment was recorded as the retention measure. The ceiling score (full retention) was 600 s. Results indicated that intra-hippocampal injections of amphetamine produced a dose-dependent enhancement of memory retention with doses at 0.6 micrograms and 1.6 micrograms reaching a significant effect. The beta-adrenergic blocker propranolol, at a dose which did not affect retention alone (80 ng), antagonized the memory-enhancing effect of amphetamine. Along with this memory-enhancing effect, amphetamine also elevated the level of NE release, and this effect was significant in animals not showing a full retention score (nonresponders) than in animals showing a full retention score (responders), as assayed by in vivo microdialysis. Within the control group, the responders also had a higher level of NE than the nonresponders. All these results are probably due to the fact that responders have a higher level of NE release than nonresponders. The effect of amphetamine on NE release is, therefore, not as obvious in responders. These results together support our hypothesis that NE plays a facilitatory role in the memory process and amphetamine enhances retention performance, at least in part, through facilitation of hippocampal NE release.