Effect of Methylphenidate on Retention and Retrieval of Passive Avoidance Memory in Young and Aged Mice

Background: Several studies showed that dopamine and norepinephrine improve retention and retrieval of memory. Methylphenidate is an enhancer of dopamine and norepinephrine in brain. Objectives: In the present study, the effect of methylphenidate was evaluated on retention and retrieval of memory in young and aged mice using passive avoidance apparatus. Materials and Methods: Animals were divided into groups (n = 8) as follows: test groups received electric shock plus methylphenidate (2.5, 5 and 10mg kg-1, i. P.), control group received electric shock plus normal saline and blank group received only electric shock. In all groups, step-down latency for both retention and retrieval test of memory was measured. Methylphenidate was administered immediately after receiving electric shock in the retention test, but methylphenidate was administered 23.5 hours after receiving electric shock in the retrieval test. Results: The mean of step-down latency on day 4 was significantly higher compared to day 2 (P < 0.05) in all young and aged groups of mice. The best response was attained with 5 mg/kg of methylphenidate. In memory retention test, the mean of step-down latency in young groups that received 2.5 and 5 mg/kg methylphenidate was significantly longer(P < 0.05) than aged groups. However, this difference was not significant in memory retrieval test. Conclusions: Methylphenidate may improve memory retention and retrieval