Short-term homeostasis of REM sleep throughout a 12:12 light:dark schedule in the rat.

Study Objectives: Intervals extending from the end of a rapid eye movement (REM) sleep episode until the triggering of the next tend to be longer when they follow a longer REM sleep episode. A short-term REM sleep homeostatic process has been hypothesized to explain this effect. The present study assessed and modeled the REM sleep episode-interval relationship and compared its expression at different phases of a 12:12 light: dark schedule.

Design: Chronically implanted rats were continuously recorded for 3 consecutive days. Automated state scoring in 15-second epochs determined lengths of REM sleep episodes and intervals and non-rapid eye movement sleep and wakefulness content of intervals.

Setting: Individual sound-attenuated temperature-regulated boxes.

Participants: 16 Sprague-Dawley rats.

Interventions: Scheduled 12:12 light:dark cycle.

Measurements And Results: The effect of REM sleep episode length is evidenced by a rising trend in the means and robust means of intervals and non-rapid eye movement content that follow REM sleep episodes of a given length. The relationship of robust means of intervals and REM sleep episode length was best fitted by a Gompertz sigmoid function. The parameters of the Gompertz equation were modulated throughout the 24 hours, presenting the highest amplitude and earliest rise in hours 1 to 4 after lights on and the lowest amplitude at the start of lights off. The modulation was also evident when only intervals with less than 3 minutes of wakefulness were considered.

Conclusions: Short-term REM sleep homeostasis is modulated throughout the 24 hours under a 12:12 light:dark regime. Its assessment may provide a useful measure of REM sleep propensity, regulation, and recurrence.