Differences between the effects of two meclofenoxate doses on active training for two-way avoidance in rats

Male Wistar rats were trained for active two-way avoidance in a shuttle-box apparatus for five consecutive days. Meclofenoxate, in doses of 100 and 300 mg/kg i.p., was applied in two separate groups of rats, 60 min before the beginning of the training. Meclofenoxate (Mf), applied in a dose of 100 mg/kg, slightly improved the avoidance training, whereas in a dose of 300 mg/kg it "deteriorated" learning during the last two training days. Retrospective analysis of the experimental results showed that Mf caused a dose-dependent increase in the percentage of rats who were "poor learners", compared with the percentage of "poor learners" among the controls. On the other hand, the Mf-treated "good learners" manifested an essentially better capacity for avoidance training, compared with the control "good learners". The data obtained suggest that Mf increases the adaptational capacities of rats trained for active avoidance possibly in two different ways: in part of the animals it causes improvement of the conditioned reflex activity, in another part of the animals it increases their resistance to the stressogenic stimuli used during such a training.