The differential effects of chronic imipramine or citalopram administration on physiological and behavioral outcomes in naïve mice

Tricyclics and selective serotonin reuptake inhibitors (SSRIs) are probably the most widely employed reference antidepressants in animal studies on depression. Using imipramine and citalopram, we sought to assess which drug would be more appropriate as pharmacological reference in paradigms of depression in C57BL6N mice by measuring their effect on liquid consumption, home cage activity, body weight and long-term memory in naive animals treated with each compound at generally used dose of 15 mg/kg/day. Continuous logging of home cage movement, weekly monitoring of vertical activity in a novel cage, and body weight was recorded during four-week treatment period and for four weeks after discontinuation of the antidepressant; sucrose preference was evaluated at weekly intervals during drug administration. A novel object recognition memory test was performed in mice treated the antidepressants for two weeks. Compared to control, imipramine-treated mice displayed increased sucrose and water intake, as well as enhanced home-cage and novelty exploration activities, and reduced body weight. Imipramine also impaired learning in the object recognition task, but citalopram diminished object exploration sufficiently to invalidate the test. Citalopram-treated animals demonstrated no changes in a sucrose test and had elevated body mass. Thus basic physiological and behavioral outcomes in naive mice were significantly altered by the chronic administration of imipramine and, to a lesser extent, citalopram. As altered variables are crucial for the evaluation of antidepressant-like effects in mice, our data suggest that, at commonly used doses, both drugs must be applied in mouse models of depression with caution.