The melatonin receptor MT1 is required for the differential regulatory actions of melatonin on neuronal 'clock' gene expression in striatal neurons in vitro.

Through inhibitory G protein-coupled melatonin receptors, melatonin regulates intracellular signaling systems and also the transcriptional activity of certain genes. Clock genes are proposed as regulatory factors in forming dopamine-related behaviors and mood and melatonin has the ability to regulate these processes. Melatonin-mediated changes in clock gene expression have been reported in brain regions, including the striatum, that are crucial for the development of dopaminergic behaviors and mood. However, it is not known whether melatonin receptors present in striatum mediate these effects. Therefore, we investigated the role of the melatonin/melatonin receptor system on clock gene expression using a model of primary neuronal cultures prepared from striatum. We found that melatonin at the receptor affinity range (i.e., nm) affects the expression of the clock genes mPer1, mClock, mBmal1 and mNPAS2 (neuronal PAS domain protein 2) differentially in a pertussis toxin-sensitive manner: a decrease in Per1 and Clock, an increase in NPAS2 and no change in Bmal1 expression. Furthermore, mutating MT1 melatonin receptor (i.e., MT1 knockouts, MT1(-/-)) reversed melatonin-induced changes, indicating the involvement of MT1 receptor in the regulatory action of melatonin on neuronal clock gene expression. Therefore, by controlling clock gene expression we propose melatonin receptors (i.e., MT1) as novel therapeutic targets for the pathobiologies of dopamine-related behaviors and mood.