The relationship between anxiety and depression in animal models: a study using the forced swimming test and elevated plus-maze

ABSTRACT

The present study evaluated the correlation between the behavior of mice in the forced swimming test (FST) and in the elevated plus-maze (PM). The effect of the order of the experiments, i.e., the influence of the first test (FST or PM) on mouse behavior in the second test (PM or FST, respectively) was compared to handled animals (HAND). The execution of FST one week before the plus-maze (FST-PM, N = 10), in comparison to mice that were only handled (HAND-PM, N = 10) in week 1, decreased percent open entries (HAND-PM 33.6 + or - 2.9; FST-PM 20.0 + or - 3.9; mean + or - SEM; P<0.02) and percent open time (HAND-PM 18.9 + or - 3.3; FST-PM 9.0 = or - 1.9; P<0.03), suggesting an anxiogenic effect. No significant effect was seen in the number of closed arm entries (FST-PM 9.5 (7.0-11.0); HAND-PM 10.0 (4.0-14.5), median (interquartile range); U = 46.5; P>0.10). A prior test in the plus-maze (PM-FST) did not change percent immobility time in the FST when compared to the HAND-FST group (HAND-FST 57.7 + or- 3.9; PM-FST 65.7 + or - 3.2; mean + or - SEM; P>0.10). Since these data suggest that there is an order effect, the correlation was evaluated separately with each test sequence FST-PM (N = 20) and PM-FST (N = 18). There was no significant correlation between percentage immobility time in the FST and plus-maze indexes (percentage time and entries in open arms) in any test sequence (r -0.07 to 0.18). These data suggest that mouse behavior in the elevated plus-maze is not related to behavior in the forced swimming test and that a forced swimming test before the plus-maze has an anxiogenic effect even after a one-week interval