Learned immobility is also involved in the forced swimming test in mice

Abstract

A modified version of the forced swimming test (FST) was utilised in order to test, for the first time in mice, the learned immobility hypothesis. From this point of view, the subjects learn to be immobile in the first session, being the second one a retention test. The development of habituation was observed by repeating the test. The forgetting was studied by allowing different time intervals between the first and the second session. A decrease in the activity was observed with intervals of up to 18 days, but not with longer intervals of 21 or 24 days. Scopolamine (1 or 2 mg/kg), a cholinergic antagonist, did not modify the swimming activity in the second session. Physostigmine, a cholinergic agonist, at a dose of 0.05 mg/kg was ineffective, and at a dose of 0.2 mg/kg decreased the swimming activity in the second session. These data extend to mice the findings previously obtained in rats, and lend additional support to the learned immobility hypothesis in the interpretation of the behaviour found in the FST.