Circadian and Homeostatic Control of Rapid Eye Movement
(REM) Sleep: Promotion of REM Tendency by the
Suprachiasmatic Nucleus
Sarah W.
Wurts1, 2 and
Dale M.
Edgar1
1 Sleep and Circadian Neurobiology Laboratory, Sleep
Disorders Research Center, Department of Psychiatry and Behavioral
Sciences, Stanford University School of Medicine, Stanford, California
94305, and 2 Interdepartmental Graduate Program for
Neuroscience, University of California, Los Angeles, California 90095
The daily timing of rapid eye movement (REM) sleep reflects an
interaction between the circadian pacemaker located in the suprachiasmatic nucleus of the hypothalamus (SCN) and a homeostatic process that induces compensatory REM sleep in response to REM sleep
loss. Whether the circadian variation in REM sleep propensity is caused
by active promotion, inhibition, or passive gating of REM sleep
homeostasis by the SCN is unknown. To investigate these possibilities,
compensatory responses to 24 hr REM sleep deprivation (RSD) were
compared between SCN-lesioned (SCNx) and sham-lesioned rats at
different times of day in constant dark. The attempts to enter REM
sleep (REM tendency) increased during RSD in all rats and were
modulated by circadian phase in sham-lesioned, but not SCNx rats. REM
sleep homeostasis interacted with circadian time, such that REM
tendency doubled during the rest phase in sham-lesioned rats relative
to SCNx rats (F(6,93) = 17.9;
p = 0.0001). However, REM tendency was
indistinguishable between SCNx and sham-lesioned rats during the
activity phase, suggesting the SCN does not inhibit REM tendency at
this time. By contrast, the amount of compensatory REM sleep examined
2, 6, 12, or 24 hr after RSD did not depend on circadian phase. Thus,
transitions into REM sleep are facilitated by the SCN during the rest
phase, but the amount of REM sleep, once initiated, is determined
primarily by homeostatic mechanisms. This work supports a role for the
SCN in the active promotion of REM sleep at specific times of day.
Key words:
electroencephalogram; sleep homeostasis; REM sleep
propensity; paradoxical sleep; active sleep; desynchronized sleep; circadian rhythm; suprachiasmatic nucleus; rat
Copyright © 2000 Society for Neuroscience 0270-6474/00/20114300-11$05.00/0
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