Repeated Forced Swim Stress Induces Learned Helplessness in Rats

Abstract

The goal of our study was to determine if another form of inescapable, uncontrollable stress, milder than repeated electric shock, could induce learned helpless (LH) behavior in rats and if antidepressant drugs can prevent this behavior. Rats were first exposed to repeated forced swim stress (RFS) and 24 hr after last swim, rats were tested for escape behavior [Escape Latency (EL) and % Escape Failure (EF)] in a shuttle‐box. RFS segregated the stressed rats into two clusters based on EL and EF. One cluster, LH, showed increased EL (27.1 ± 1.4 s) and EF (82.7 ± 8 %) compared to controls (11.1 ± 1.3 s; 11.7 ± 4.3%), showing stress susceptibility. The other cluster, non‐helpless (NH), showed EL (8.8 ± 2.4s) and EF (11.5 ± 5.3%) similar to the controls. All RFS rats performed similar to controls in the open field and elevated plus maze tests, suggesting the absence of locomotion deficits or increased anxiety. In rats pretreated for 10 days with desipramine (DMI), no increased EL or EF were observed in the shuttle‐box after RFS. DMI also prevented a reduction in GRK3 in the locus coeruleus observed after RFS in untreated LH rats. These data suggest that, like inescapable unpredictable shock, RFS can induce LH in rats, which is prevented by DMI pretreatment. Hence, RFS is another inescapable stress paradigm that can identify stress‐susceptible and stress‐resilient populations in rats. (Supported by NARSAD)