Experimental design. The experiment compared gene expression in sleep and sleep-deprived animals in two peripheral organs (heart and lung). (A): Groups of mice were either allowed uninterrupted sleep or were sleep-deprived via gentle handling. Baseline animals were sacrificed at zeitgeiber time 0 (ZT0 - lights on) and diurnally matched animals from both groups were sacrificed after 3, 6, 9, and 12 hours. Animals were only fed during the lights-off (dark) period for 14 days prior to study to prevent differential food intake. (B): Activity was monitored by a non-invasive locomotor monitoring system. Sleep was considered to be present when there was 40 seconds or more of continuous inactivity. Sleep was assessed in undisturbed control mice across the entire 24 hour cycle. The percentage of each hour that control mice slept is plotted as a function of time. Data shown are mean ± standard deviation. In the three-hour-blocks preceding sample collection at ZT3, ZT6, ZT9, and ZT12, animals in the undisturbed sleep group slept for 58%, 77%, 79%, and 61%, respectively, of the available sleep opportunity.