Temporal and spatial layout of endocannabinoid system components in the mouse suprachiasmatic nucleus

Environmental light serves as the main entraining signal for the central circadian pacemaker, the suprachiasmatic nucleus of the hypothalamus (SCN). To shift clock timing with the changing environment, minute adjustments are necessary and the endocannabinoid system (ECS) acts as a neuromodulatory signaling mechanism in the SCN. These systems exert bidirectional effects on one another, still, limited knowledge exists about the role of endocannabinoids in circadian rhythm regulation. Therefore, we investigated the temporal and spatial molecular layouts of the ECS in the SCN of male and female C57BL/6J mice. We utilized laser capture microdissection and quantitative RT-PCR to investigate the ECS temporal layout in the SCN, detected 13 of 19 examined ECS components, and followed up with two 24-hour time course experiments, one under 12:12 light/dark and one under constant dark conditions. All enzymatic machinery related to endocannabinoid synthesis and degradation investigated were found present; however, only cannabinoid receptor 1 (Cnr1) was detected from the 6 ECS related receptors investigated. Cosinor analysis revealed circadian rhythms in many components in both sexes and lighting conditions. Next, we investigated the spatial localization of ECS components in the SCN with RNAscope in situ hybridization. Some genes, such as Cnr1, were more highly expressed in neurons with others, such as Fabp7, were elevated in astrocytes. Cnr1 levels were highest in neurons that do not express the neuropeptides Avp or Vip, and lowest in Vip neurons. Our results support the idea that locally regulated ECS signaling through neuronal CB1 modulates circadian clock function.