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eNeuro. 2020 Feb 13;7(1). pii: ENEURO.0081-19.2020. doi: 10.1523/ENEURO.0081-19.2020. Print 2020 Jan/Feb.

Cannabinoid Signaling Recruits Astrocytes to Modulate Presynaptic Function in the Suprachiasmatic Nucleus.

Author information

1
Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR 97239.
2
Department of Behavioral Neuroscience, Oregon Health and Science University, Portland, OR 97239.
3
Oregon Institute of Occupational Health Sciences, Oregon Health & Science University, Portland, OR 97239 allenc@ohsu.edu.

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.

KEYWORDS:

GABA; astrocyte; circadian rhythm; endocannabinoid; suprachiasmatic nucleus

PMID:
31964686
DOI:
10.1523/ENEURO.0081-19.2020
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