Chronic stress may not be a factor in the behavioral response to chronic lithium in ICR mice

Background: Lithium (Li) is the prototypic mood-stabilizing drug, but the individual response to Li is highly heterogeneous. Some evidence suggest interactions between Li and stress, and it is possible to hypothesize that lithium's effects are modified by stress conditions. The current study examines the interaction between 2 chronic stressors, constant light (CL) and restrain and the behavioral responses to chronic Li in female and male mice. Methods: Female and male ICR mice were exposed to 3 weeks of either (1) CL; (2) daily restrain or (3) no stress control. One week after the start of the stress intervention, mice started chronic oral Li treatment or control. After 2 weeks of stress and Li, mice were tested in a number of behavioral tests including spontaneous activity, sweet solution preference, plus-maze and forced swim test. Results: There were no effects of stressors on behavior. Effects of Li were demonstrated in males but not females with no interactions between stress and Li. Conclusions: The behavioral effects of Li in this study were not affected by stress. The lack of effects of the stressors themselves on behavior suggests that the application of more intrusive stressors might be needed to further explore the issue.