Sleep-promoting effects of DORA-22 in normal rats are diminished during the inactive phase. Vehicle (20% Vitamin E TPGS, p.o.) and DORA-22 (30 mg/kg) were administered to rats during the mid-active phase (arrow, ZT 17:00; n = 13) (A) or 1 h before the inactive phase (arrow, ZT 23:00; n = 8) (B) in a balanced cross-over design. Values represent mean time in sleep stage over 30-min intervals over 3 days of consecutive treatment. Gray shading denotes the dark or active period. AW, active wake; QW, quiet wake. Time points at which significant differences exist between vehicle and DORA-22 responses are indicated by gray vertical lines and tick marks (short, medium, long marks: P < 0.05, 0.01, 0.001, respectively).