To determine whether immortalized cells derived from the rat SCN (SCN 2.2) retain intrinsic rhythm-generating properties characteristic of the SCN, oscillatory properties of the SCN2.2 transcriptome were analyzed and compared to those found in the rat SCN in vivo using rat U34A Affymetrix GeneChips. In this comparison, adult male Long-Evans rats (175-200g; N=45) were housed under a standard 12h light:12h dark photoperiod (LD 12:12; lights-on at 0600 hr). At 1800 hr (circadian time [CT] 12), animals were exposed to constant darkness (DD) and 12 hours later (0600 hr or CT 0), sacrificed under isoflurane anesthesia at 6-hr intervals (N=5) for 48 hours by decapitation using an infrared viewer. After the eyes were removed in the dark, SCN tissue was immediately dissected under dim light, frozen in liquid nitrogen, and stored at –80C. SCN tissue from individual animals was separately homogenized in TRIzol reagent by aspiration through a 25-gauge needle and then extracted cellular RNA for all animals at each timepoint was pooled into a single sample. RNA samples were subjected to on-column treatment with DNAse-1 to digest genomic DNA and then were stored at –80°C before routine processing for GeneChip analysis.
