In order to more objectively evaluate drug effects in the forced swimming test proposed by Porsolt et a I. u as a screening method for antidepressants, vibrations of the wall of a tank caused by rats trying to escape from water were recorded. Locomotor activity was also measured in an activity cage. Male Wistar rats were forced to swim once daily for 15 min in a tank of 25 °C water filled to a depth of 20 cm. After 4 d sessions of swimming, drugs were administered i.p. 3 times (24, 5 and 1 h prior to the test session). On day 5,45 min after the last injection of a test drug, locomotor activity was measured for 15 min and then the rat was subjected to the forced swimming test. All antidepressants tested, dose-dependently increased tank vibration. Nomifensine, atropine, methamphetamine, chlorpheniramine and diazepam increased locomotor activity. The remaining drugs had no effect or reduced locomotion. In addition, the pattern of the tank vibrations, caused by rats treated with most drugs, like atropine, showed a burst during the first 5 min followed by sporadic vibrations. Nomifensine and methamphetamine, on the other hand, caused vibrations throughout the 15 min test session. A specific effect of antidepressants was revealed by this forced swimming test in combination with the measurement of locomotor activity.
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