Abstract
Effects of physostigmine and nicotine on learned immobility in the forced swimming test. The learned immobility hypothesis in the forced swimming test (FST) suggests that the subjects learn to be immobile in the first session, the second one being a retention test. In the frame of this interpretation, the effects of two memory enhancers, the cholinergic agonists physostigmine (0.1, 0.2 and 0.3 mg/kg) and nicotine (0.15 and 0.6 mg/kg), were studied in mice. After a 24 day interval, the animals were exposed to the second session, and a loss of the learned immobility (similar swimming activity in both sessions) was observed in control groups, 0.1 and 0.2 mg/kg of physostigmine, and 0.15 mg/kg of nicotine groups. Retention of immobilily (a decrease in the swimming activity in the second session) was observed with the highest doses of physostigmine and nicotine. The effects of both drugs on FST provide support to the learned immobility hypothesis, and cannot be interpreted in the light of the "behavioural despair" hypothesis.
