Influence of antidepressants on the stress-coping strategy of mice following repeated forced swim testing

The forced swim test is a commonly used animal model to evaluate antidepressant drug effects. A pre-exposure to swimming in a drug free condition is suggested to increase passive behaviour, which is interpreted as behavioural despair and part of the stress coping strategy. In this experiment the influence of different durations of pre-exposure on antidepressant effects was investigated. DBA/2 (DBA) and BL/6J (BL6) mice were orally administered with antidepressants in different treatment schemes. To additionally investigate the development of an altered swimming strategy we conducted up to four test sessions every 24h on the days to follow. The experiments proved that in DBA and BL6 mice passive behaviour was increased by pre-exposing the animals to the test and further, antidepressants induced a change in the coping strategy by reducing passive behaviour. Thereby we found no difference between 5 or 15 minutes of pre-exposure. Furthermore, we found that DBA and BL6 mice responded in a different way to the repeated swimming and to the application of antidepressants. BL6 mice developed a robust behavioural strategy which was resistant to further antidepressant treatment. In DBA mice behaviour was more influenceable, as the development of behavioural despair could be alleviated by antidepressants also after repeated swim test exposures.