Sleep deprivation alters mRNA levels of per1, per2, and dbp. (A) RT-PCR analysis of the expression of five 'clock'-genes in the mouse cortex across four experimental conditions [C = control; R = recovery sleep; SD = sleep deprived; ZT = Zeitgeber time (i.e., 6 or 10 h after light-onset)]. g3pdh expression was used as an internal standard. Bars depict mean ± 1 SEM. Asterisks denote significant differences (P < 0.05) between the experimental and corresponding control group (Student-Newman-Keuls post-hoc tests; 1-way ANOVA factor 'condition': P < 0.05, for per1,2, and dbp only; n = 7/condition) (B) per1 mRNA falls significantly in rat cortex during a 2-h recovery period (R) subsequent to 6 h SD ending at ZT6 (P < 0.05, t-test). Northern analysis was performed on cortex of five sleep-deprived rats and five rats that were allowed 2 h of recovery sleep (ZT8).