Knockdown of Clock in the Ventral Tegmental Area Through RNA Interference Results in a Mixed State of Mania and Depression-Like Behavior

Background: Circadian rhythm abnormalities are strongly associated with bipolar disorder; however the role of circadian genes in mood regulation is unclear. Previously, we reported that mice with a mutation in the Clock gene (Clock Delta 19) display a behavioral profile that is strikingly similar to bipolar patients in the manic state. Methods: Here, we used RNA interference and viral-mediated gene transfer to knock down Clock expression specifically in the ventral tegmental area (VTA) of mice. We then performed a variety of behavioral, molecular, and physiological measures. Results: We found that knockdown of Clock, specifically in the VIA, results in hyperactivity and a reduction in anxiety-related behavior, which is similar to the phenotype of the Clock Delta 19 mice. However, VTA-specific knockdown also results in a substantial increase in depression-like behavior, creating an overall mixed manic state. Surprisingly, VTA knockdown of Clock also altered circadian period and amplitude, suggesting a role for Clock in the VTA in the regulation of circadian rhythms. Furthermore, VTA dopaminergic neurons expressing the Clock short hairpin RNA have increased activity compared with control neurons, and this knockdown alters the expression of multiple ion channels and dopamine-related genes in the VTA that could be responsible for the physiological and behavioral changes in these mice. Conclusions: Taken together, these results suggest an important role for Clock in the VTA in the regulation of dopaminergic activity, manic and depressive-like behavior, and circadian rhythms.