Quantitative RTPCR analysis of circadian clock gene expression in the spleen. Plotted open circles represent the mean ± SEM in each experimental group. The dashed line represents the fitted plot of cosinor analysis utilizing linear harmonic regression. Values are represented as the number of transcript copies/1000 Gapdh transcripts. Abscissa labels indicate ZT time values every 3 hrs under LD 12:12 conditions; ZT0 = lights on; ZT12 = lights off. Open bar on the bottom of the x-axis indicates the light period, while crosshatched indicates darkness. The cry and per genes harbor daily oscillations ~2-5 fold in amplitude with higher abundances occurring during the late night for cry1 (pANOVA < .001; pcosinor = .009), cry2 (pANOVA = .003; pcosinor < .001), per2 (pANOVA < .001; pcosinor = .005), and per3 (pANOVA < .001; pcosinor = .008). Clock and the bmals, also express a daily pattern of rhythmicity in the spleen. Clock mRNA attained maximal abundance during the early night (pANOVA < .001; pcosinor < .001) while bmal1 is highest during the late night to early day period (pANOVA = .007; pcosinor = .01). Bmal2 showed increased expression during the nighttime (pANOVA = .01; pcosinor = .03), however it was not as robust as other clock genes nor in excess of a 2-fold rhythm.