1. We tested two hypotheses: that respiration and metabolism are subject to
circadian modulation in wakefulness, non-rapid-eye-movement, (NREM) steep
and rapid-eye-move ment (REM) sleep; and that the effects of steep on breat
hing vary as a function of time of day.
2. Electroencephalogram (EEG), neck electromyogram (EMG) and abdominal body
temperature (T-b) were measured by telemetry in six male Sprague-Dawley ra
ts. The EEG and EMG were used to identify steep-wake states. Ventilation ((
V) over dot(1)) and metabolic rate ((V) over dot(CO2)) were measured by ple
thysmography. Recordings were made over 24 h (12:12 h light:dark) when rats
were in established states of wakefulness, NREM steep and REM steep.
3. Statistically significant circadian rhythms were observed in (V) over do
t(1) (V) over dot(CO2), and in each of the wakefulness, NREM steep and REM
steep states. Amplitudes and phases of the circadian rhythms were similar a
cross sleep-wake states.
4. The circadian rhythm in (V) over dot(1) was mediated hy a circadian rhyt
hm in respiratory frequency (f(R)). Tidal volume (V-T) was unaffected by ti
me of day in all three, sleep-wake states.
5. The 24 h mean (V) over dot(1) was significantly greater during wakefulne
ss (363.5 +/- 18.5 ml min(-1)) than during NREM steep (284.8 +/- 11.1 ml mi
n(-1)) and REM steep (276.1 +/- 13.9 nil min(-1)). (V) over dot(CO2) and V-
T each significantly decreased from wakefulness to NREM sleep to REM steep.
f(R) was significantly lower in NREM steep than in wakefulness and REM ste
ep.
6. These data confirm that ventilation and metabolism exhibit circadian rhy
thms during wakefulness, and NREM and REM sleep, and refute the hypothesis
that state-related effects on breathing vary as a function of time of day.
We conclude that the effects of circadian rhythms and sleep-wake state oil
respiration and metabolic rate are additive in the rat.