Reserpine and Ketamine Effects on Temporal Discrimination in Female Rats

Depression has been indicated to induce alterations in the perception of time. Ketamine, a noncompetitive N-methyl-D-aspartate (NMDA) antagonist has been shown to produce rapid and robust antidepressant effects in patients whom are suffering from major depressive disorder. The present study examined the effects of a sub-anesthetic dose of ketamine (5.0 mg/kg) on time perception in depressed rodents. Female rats were trained on a fixed interval procedure. Following the temporal training, depression was induced by a daily injection of reserpine (0.2 mg/kg i.p.) for two weeks. Reserpine has been found to inhibit vesicular monoamine transporter, and as a result, depletes brain monoamines. Depressed state was confirmed by a forced swim test 24hours after the last reserpine injection. Followed by an injection of either ketamine or saline. After 24 hours, animals were retested in the fixed interval procedure and the forced swim test. Reserpine induced depression, as determined by the force swim test, but it did not cause distortion in time perception in the fixed interval procedure. In addition, a single injection of ketamine significantly increased escaping behavior in the force swim test. In cases of depression in which time perception is affected, treatments focusing on the monoamine system might not be effective. In future studies, focusing on commonly reported symptoms for depression, such as time disruption, might shed light on what type of treatment is effective.