Biol. Pharm. Bull. 30(12) 2399—2401 (2007)

roles in several psychiatric disorders, including depression and anxiety. Obsessive compulsive disorder (OCD) is classified as an anxiety disorder characterized by obsession or compulsion. The burying of harmless objects like marbles by mice may reflect the formation of compulsive behavior. Marble burying behavior in mice is recognized as an animal model for OCD. It has been reported that marble burying behavior is inhibited by anxiolytics such as diazepam. This behavior is also attenuated by treatment with selective serotonin reuptake inhibitors (SSRIs). We previously reported that several SSRIs, fluvoxamine, sertraline and paroxetine inhibit marble burying behavior in mice. SSRIs, including fluvoxamine or citalopram, are effective for OCD in humans and are used as standard drugs for the treatment for OCD. These findings suggest that serotonergic activity may be closely related to OCD and marble burying behavior in mice may also be derived from defect of 5-HT. Milnacipran is an antidepressant, which selectively inhibits the reuptake of both 5-HT and noradrenaline, that is, milnacipran is a serotonin and noradrenaline reuptake inhibitor (SNRI). Tricyclics including imipramine also inhibits the reuptake of both noradrenaline and 5-HT, although they have anti-cholinergic activity, which leading to several side effects. In contrast, milnacipran improves depression without anti-cholinergic activity. Therefore, there is increasing interest in milnacipran for the treatment of depression. However, it has not yet been clarified whether milnacipran is effective in OCD. Therefore, in the present study, we investigated the effects of milnacipran on the OCD model, marble burying behavior in mice, and compared with the effects of a SSRI, fluvoxamine.