Structure of the rat behaviour in the forced swimming test.

Forced swimming test (FST) or 'behavioural despair' test is a useful screening for antidepressant drugs. The FST predictability has been improved by a number of procedural modifications. Description of the behavioural microstructure in FST may help to delineate innovative protocols. Thus, counts of all behaviours emitted during FST in rats (four-month-old Wistar male, n = 63) were recorded and examined by Markovian sequential analysis (MSA) and principal components analysis (PCA). In a second experiment, rats (n = 28) were tested in an open field test (OFT) followed a week later by FST; behaviours in both tests were recorded and analysed by two correlation methods (Pearson's test and sliding window correlation). The descriptive ethological analysis displayed counts of swimming and immobility increased over the course of the test, whereas climbing behaviour decreased. The MSA revealed the occurrence of immobility was predicted by swimming, climbing, and diving behaviours whereas the immobility predicted the occurrence of swimming behaviour and headshakes. The PCA showed duration of immobility and climbing loaded into one component and duration of immobility and swimming loaded into another one. Low as well high levels of climbing behaviour were positively correlated with motor activity in the OFT. In brief, the present data suggest there are at least two different factors that grouped variables related to the behavioural despair in the FST. In addition, altered motor activity could be predicted by the frequency of climbing behaviour recorded in the FST.