Brazilian Journal of Medical and Biological Research Joey Miller Effects of Caffeine on Learning and Memory in Rats Tested in the Morris Water Maze Angelucci, M.E.M.; Cesário, C.; Hiroi, R.H.; Rosalen, P.L.; Da Cunha, C. Brazilian Journal of Medical and Biological Research Vol. 35 (10), October 2002, pp. 1201-1208

Hypothesis Caffeine will have an improving effect on memory functions.

Structure Subjects 13 Groups of 12 Adult Male Wistar Rats (240-300 g) Tools Morris Water Maze (Spatial Version) Training and Test Sessions Training Sessions – 6 Trials Test Sessions– 3 Trials (48 Hours after Training Session.)

Independent Variables Administration Time 3 Levels: Pre-Training, Post-Training, Pre-Test Amount of Caffeine (0-30 mg/kg, ip, in .1 ml/100 g Body Weight) Pre-Training – Saline, 3, 10, 30 mg/kg Post-Training – Saline, .3, 3, 10, 30 mg/kg Pre-Test – Saline, 3, 10, 30 mg/kg

Dependent Variables Memory and Learning Test and Training scores on tests of: Distance Traveled (cm) Escape Latency (seconds)

Theoretical Constructs Learning Memory Acquisition Memory Retention and Retrieval

Operational Definition Learning Training Portion Measurements of Distance traveled and Escape Latency during Training. Memory Test Portion Measurements of Distance traveled and Escape Latency during Testing.

Statistical Analysis ANOVA Two-way Training and Test Data analyzed separately Number of Trials as repeated measure Differences between groups were evaluated by the post hoc Duncan test.

Results Caffeine improved memory retention but not memory acquisition (learning). Post-Training Administration Improved memory retention at doses of .3-10 mg/kg, but not at doses of 30 mg/kg Pre-Test Administration Small increase in memory retrieval Pre-Training Administration Did not alter performance in Training or Test sessions

Results Pre-Training Administration Treatment did not affect training for treatment and interaction treatment vs. repeated measure (P≥0.2), or test scores (P≥0.2). Post-Training Administration During Training no difference among groups for latency (p≥0.2) and Traveled Distance (p=.10). Repeated Measure: latency and traveled distance, p≤0.001 Treatment: latency, p≤0.05; traveled distance, p=.18 Interaction Treatment vs. Repeated Measure: latency, p≤0.01; traveled distance, p≤0.05 Test Sessions showed that .3-10 mg/kg of caffeine improved retention (P≤0.05 Post Hoc Duncan Test). While the dose of 30 mg/kg had no effect (p=.14 Post Hoc Duncan Test).

Results Pre-Test Administration Groups did not differ in training sessions for latency, and it had no effect on retention. The shape of the retention (test) curve implied the low doses of caffeine tend to improve memory retrieval (interaction treatment vs. repeated measure, traveled distance: p≤0.05, latency: p≥0.2)

Conclusion Effect of caffeine was more evident when administered after training. This suggests an effect on memory consolidation. Ineffective when administered before training. Suggesting that it does not affect working memory and memory acquisition. The effect of Pre-Testing administration suggest improvement in memory retrieval (for spatial memory tasks).

Conclusion The improving effect of caffeine in smaller doses, and impairment or no effect at higher doses, suggest an effect on more than one type of receptor. Effects of caffeine are better explained as antagonists of the Adenosine A2 receptors

Discussion Well conducted study Good attempts at controlling confounding variables Applicable to human species? It was noted that rats have similar hippocampal memory systems Would the results for female rats have been the same? How would subjects under different natural conditions respond? How would prior caffeine use effect these results?