Memory retention test performance in mice: improvement by chronic oral cholinergic drug treatment

Mice consumed solutions containing 0, 0.025, 0.050 or 0.075 mg/ml of arecoline hydrobromide (ARE) one week prior to training (T-maze, footshock, active avoidance) and a total of two weeks prior to testing memory retention. The mean daily doses of ARE were estimated to be 0, 157, 302, or 500 micrograms per mouse, respectively. An inverted-U dose-response curve was obtained; the best retention test performance was by the group receiving 0.050 mg/ml of ARE. Measures of activity and weight taken over the experiment indicated no significant differences between ARE groups and the control group; thus no apparent toxicity. Separate groups of mice consumed 0 or 0.050 mg/ml of ARE for one week, then were trained to a criterion of 5 avoidances in 6 training trials. There were no significant differences in trials to first avoidance response or to criterion. Thus the enhanced retention test performance of the 0.050 mg/ml ARE group reflected improved memory processing rather than better learning.