Abstract
Circadian rhythms are 24-h cycles in physiology regulated by the suprachiasmatic nucleus (SCN) in the brain, where daily cues act on SCN neurons to alter clock timing. Cannabinoid signaling modulates SCN neuronal activity, although the mechanism remains unclear. We propose that neuronal activity generates endocannabinoid release, activating astrocyte Ca2+ signaling, which releases adenosine and activates adenosine-1 receptors (A1Rs) on the presynaptic axon terminals, decreasing GABA release. We demonstrated, in mice, that activation of cannabinoid-1 receptors (CB1R) with the agonist WIN 55,212-2 (WIN) reduced the miniature GABA receptor-mediated postsynaptic current (mGPSC) frequency by a mechanism that requires astrocytes and A1R. WIN activated an intracellular Ca2+ signaling pathway in astrocytes. Activating this intracellular Ca2+ pathway with designer receptors exclusively activated by designer drugs (DREADDs) also decreased the mGPSC frequency and required A1R activation. The frequency of spontaneous Ca2+ events, including those induced by depolarization of a postsynaptic SCN neuron, was reduced by blocking CB1R activation with AM251, demonstrating neuronal endocannabinoid signaling modulates astrocytic Ca2+ signaling in the SCN. Finally, daytime application of WIN or adenosine phase advanced the molecular circadian clock, indicating that this cannabinoid signaling pathway is vital for the timing of circadian rhythms.
Footnotes
The authors declare no competing financial interests.
This work was supported by National Institutes of Health (NIH) Grants NS036607 and NS103842 (to C.N.A.), an Oregon Institute of Occupational Health Sciences Summer Student Research Award (A.N.G.), and the National Institute on Drug Abuse Training Grant Postdoctoral Fellowship T32DA007262 (to L.M.H.). The imaging work was supported by the NIH Grant P30 NS061800 and used resources in the Advanced Light Microscopy Core at The Jungers Center acquired under NIH Grant S10 RR025440.
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