Effects of imipramine on the nocturnal behavior of bilateral olfactory bulbectomized rats

Experiments were performed to characterize the circadian behavior of bilateral olfactory bulbectomized (OB) rats and to investigate the effects of imipramine on that behavior. OB and sham-operated (SO) rats were housed individually for 2 weeks in activity monitors on a 13-hr light/11-hr dark cycle. OB rats were significantly more active than SO rats during the dark phase of the cycle, and both groups of rats were equally inactive during the light phase. Seven daily injections of imipramine [10.0 mg/kg, intraperitoneally (IP)] significantly reduced the nocturnal activity of OB rats, such that OB rats displayed nocturnal activity equivalent to SO rats. Abnormally high nocturnal activity is another important characteristic of the OB rat. This behavioral characteristic may prove to be valuable for the evaluation of novel antidepressive compounds.