TRIAZOLAM-INDUCED SLEEP IN THE RAT - INFLUENCE OF PRIOR SLEEP, CIRCADIAN TIME, AND LIGHT DARK CYCLES

Rats entrained to 12-h on /12-h off light schedule and injected with triazolam 0.4 mg/kg at the mid-point of their activity phase (6 h after lights out: circadian time = CT-18) had a stronger hypnotic response than animals free-running in constant dark injected at the equivalent circadian time. In contrast, entrained rats injected 5 h after lights on (CT-5) showed increased wake after injection relative to baseline, largely due to REM sleep inhibition. Hypontic efficacy was found to be inversely related to prior accumulated sleep. During the 6 h before injection, entrained rats injected at CT-18 slept significantly less than the free-running rats, which in turn slept significantly less than entrained rats injected at CT-5. Taken together, the results suggest that the amount of prior sleep was a more important influence on the response to triazolam than either light/dark per se or circadian phase. Methodologically, automated sleep scoring was found to be an efficient corroborated by concurrent independent physiological variables and spectral analysis.