Cover legend: Two cultured mouse cortical astrocytes stained with glial fibrillary acidic protein (GFAP, grayscale) and 4′,6-diamidino-2-phenylindole (DAPI, blue). These cells show circadian rhythms in ATP release that depend on a functional clock and on IP₃-dependent signals. For more information, see the article by Marpegan et al. in this issue (pages 8342–8350).