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Nested calcium dynamics support daily cell unity and diversity in the suprachiasmatic nuclei of free-behaving mice

Abstract : The suprachiasmatic nuclei (SCN) of the anterior hypothalamus host the circadian pacemaker that synchronizes mammalian rhythms with the day–night cycle. SCN neurons are intrinsically rhythmic, thanks to a conserved cell-autonomous clock mechanism. In addition, circuit-level emergent properties confer a unique degree of precision and robustness to SCN neuronal rhythmicity. However, the multicellular functional organization of the SCN is not yet fully understood. Indeed, although SCN neurons are well-coordinated, experimental evidences indicate that some neurons oscillate out of phase in SCN explants, and possibly to a larger extent in vivo. Here, to tackle this issue we used microendoscopic Ca2+i imaging and investigated SCN rhythmicity at a single cell resolution in free-behaving mice. We found that SCN neurons in vivo exhibited fast Ca2+i spikes superimposed upon slow changes in baseline Ca2+i levels. Both spikes and baseline followed a time-of-day modulation in many neurons, but independently from each other. Daily rhythms in basal Ca2+i were highly coordinated, while spike activity from the same neurons peaked at multiple times of the light cycle, and unveiled clock-independent coactivity in neuron subsets. Hence, fast Ca2+i spikes and slow changes in baseline Ca2+i levels highlighted how multiple individual activity patterns could articulate within the temporal unity of the SCN cell network in vivo, and provided support for a multiplex neuronal code in the circadian pacemaker.
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https://hal.archives-ouvertes.fr/hal-03784377
Contributor : Nathalie C. Guerineau Connect in order to contact the contributor
Submitted on : Thursday, October 6, 2022 - 1:38:23 PM
Last modification on : Wednesday, October 12, 2022 - 3:59:56 AM

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Lama El Cheikh Hussein, Pierre Fontanaud, Patrice Mollard, Xavier Bonnefont. Nested calcium dynamics support daily cell unity and diversity in the suprachiasmatic nuclei of free-behaving mice. PNAS Nexus, 2022, 1 (3), ⟨10.1093/pnasnexus/pgac112⟩. ⟨hal-03784377⟩

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