Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2005 Jan 12;25(2):404-8.
doi: 10.1523/JNEUROSCI.4133-04.2005.

Circadian rhythm generation and entrainment in astrocytes

Laura M Prolo  1 , Joseph S Takahashi, Erik D Herzog
Affiliations

Circadian rhythm generation and entrainment in astrocytes

Laura M Prolo et al. J Neurosci. .

Abstract

In mammals, the master circadian pacemaker is considered the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN consists of a heterogeneous population of neurons and relatively understudied glia. We investigated whether glia, like neurons, rhythmically express circadian genes. We generated pure cultures of cortical astrocytes from Period2::luciferase (Per2::luc) knock-in mice and Period1::luciferase (Per1::luc) transgenic rats and recorded bioluminescence as a real-time reporter of gene activity. We found that rat Per1::luc and mouse Per2::luc astroglia express circadian rhythms with a genetically determined period. These rhythms damped out after several days but were reinitiated by a variety of treatments, including a full volume exchange of the medium. If cultures were treated before damping out, the phase of Per1::luc rhythmicity was shifted, depending on the time of the pulse relative to the peak of Per1 expression. Glial rhythms entrained to daily 1.5 degrees C temperature cycles and were significantly sustained when cocultured with explants of the adult SCN but not with cortical explants. Thus, multiple signals, including a diffusible factor(s) from the SCN, are sufficient to either entrain or restart circadian oscillations in cortical glia.

PubMed Disclaimer

Figures

Figure 1.
Figure 1.
Glia express circadian periodicity independent of interactions with neurons. Inset, All cells stained for GFAP (green), indicating that the culture contains only astrocytes. Cells were counterstained with the nuclear dye DAPI (blue). Cortical glia (100,000) were plated at 1300 cells/mm2. Scale bar, 40 μm. Representative cultures of pure rat (Per1::luc, top left) and mouse (Per2::luc glia, top right) show circadian rhythms and a gradual decrease in the overall bioluminescence level with time since plating. Detrended data from the same cultures (bottom) illustrate that the peak-to-trough amplitude of bioluminescence decreases with time in vitro.
Figure 2.
Figure 2.
Phase-response of oscillating and damped glia. Rhythms in oscillating glia show a phase-dependent response to a medium change, whereas rhythms in damped glia are either reinitiated or resynchronized to the same phase by a medium change regardless of the circadian time of the pulse. A, Representative traces of bioluminescence from glial cultures that experienced a medium change while oscillating (left) or after dampening (right). Arrowheads indicate the time of the medium change for each culture, and squares show the phase of subsequent peaks. As an example, the medium was changed 36 h after plating (gray arrowhead), resulting in the times of peak daily expression for one culture (gray squares). B, The times of peak Per1::luc expression for each culture plotted against the times of their medium change (diagonal line). This “wedge” plot shows that, for example, the pulse given to oscillating glia 36 h (pulse time 12) after plating (gray arrowhead) delayed the Per1::luc rhythm (gray squares) relative to glia pulsed 40 h (time 16) after plating. In contrast, pulses given to damped glial cultures resulted in Per1::luc peaking ∼28 h after the medium change regardless of the time of the pulse (open squares). C, Representative traces of Per1::luc activity from an oscillating (top) and damped (bottom) glial culture during the 24 h over which cultures experienced a timed medium change. D, Phase-response curves to medium changes for oscillating (filled squares) and damped (open squares) glia derived from the data in B. Oscillating glia show lower amplitude, phase-dependent responses to medium changes than the high amplitude, phase-resetting responses seen in damped cultures. Error bars represent SEM.
Figure 3.
Figure 3.
Glia entrain to a temperature cycle. A, Representative bioluminescence recordings from glia cultured in a 1.5°C temperature cycle (top) or at constant temperature (bottom). Glia responded to a daily decrease in temperature (gray rectangles) by increasing levels of Per1::luc expression. Eight days after plating, glia that experienced the temperature changes continued to oscillate, whereas glia that did not experience the temperature cycles damped. B, Times of peak expression for glia that experienced either cyclic (filled squares) or constant (open squares) temperature. Cooling to 35.3°C (gray rectangle) on day 4 after plating caused a peak in Per1::luc expression 11 h after the previous phase, 6 h after the warm-to-cool transition. By the fourth day of the temperature cycle, Per1::luc reliably peaked ∼8 h after the warm-to-cool transition. After returning to constant temperature, glia free ran from this new phase. Error bars represent SEM.
Figure 4.
Figure 4.
The adult SCN appears to sustain circadian rhythms in glia. A, Representative Per1::luc bioluminescence recording from glia plated alone or cocultured with an explant of SCN or cortex from an adult or neonatal rat. B, The distribution of the number of circadian cycles expressed by glial cultures for each of the conditions presented in A. The mean duration of rhythmicity after 10 d of recording (triangles) was increased when glia were cocultured with an adult SCN. Error bars represent SEM.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Abe M, Herzog ED, Yamazaki S, Straume M, Tei H, Sakaki Y, Menaker M, Block GD (2002) Circadian rhythms in isolated brain regions. J Neurosci 22: 350-356. - PMC - PubMed
    1. Abrahamson EE, Moore RY (2001) Suprachiasmatic nucleus in the mouse: retinal innervation, intrinsic organization and efferent projections. Brain Res 916: 172-191. - PubMed
    1. Albus H, Bonnefont X, Chaves I, Yasui A, Doczy J, van der Horst GT, Meijer JH (2002) Cryptochrome-deficient mice lack circadian electrical activity in the suprachiasmatic nuclei. Curr Biol 12: 1130-1133. - PubMed
    1. Allen G, Rappe J, Earnest DJ, Cassone VM (2001) Oscillating on borrowed time: diffusible signals from immortalized suprachiasmatic nucleus cells regulate circadian rhythmicity in cultured fibroblasts. J Neurosci 21: 7937-7943. - PMC - PubMed
    1. Balsalobre A, Damiola F, Schibler U (1998) A serum shock induces circadian gene expression in mammalian tissue culture cells. Cell 93: 929-937. - PubMed

Publication types

MeSH terms

LinkOut - more resources