Maudsley reactive and nonreactive rats in the forced swim test: comparison in fresh water and soiled water.

Maudsley reactive (MR) and nonreactive (MNRA) and Sprague-Dawley (SD) male rats were tested for their immobility response in the forced swim test when the water was fresh or soiled by a rat of the same or other strain. For all strains, rats tested in soiled water were less immobile than rats in fresh water. The three strains did not differ as producers of soiling substance, but did differ in their response to it. The MR strain was least responsive, whereas the MNRA and SD did not differ from one another. These results support a previous study suggesting that MR rats are more immobile than MNRA rats in the forced swim test. The interpretation of these findings regarding the use of the Maudsley rat strains as an animal model for studying anxiety and/or depression is discussed.