Lieu: Brunoy
Abstract: Daily torpor is an
energy-saving process which evolved as an extension of non-rapid eye movement
(NREM) sleep mechanisms. In many heterothermic species there is a relation
between torpor expression and the repartition of the different behavioural
states of sleep. Despite the presence of sleep during this period of
hypothermia, torpor induces an accumulation of sleep debt which results in a
rebound of sleep in mammals. We aimed to investigate the expression of
sleep-wake rhythms during daily torpor at various ambient temperatures in a
non-human primate model, the grey mouse lemur (Microcebus murinus). Cortical activity was measured with telemetric
electroencephalography (EEG) recordings in prefrontal cortex during torpor
episode and the next 24h following hypothermia. Grey mouse lemurs were divided
into two groups: the first submitted to normal ambient temperatures (25°C)
whereas the second were placed at lower ambient temperatures (10°C). Contrary
to normal ambient temperatures, sleep-wake rhythms were maintained during
torpor until Tb of the animals reached 21°C. Below this temperature, NREM and
REM sleep strongly decreased or were absent whereas the EEG became isoelectric.
The different states of sleep were proportional to Tbmin during
prior torpor in contrary to active phases. Ours results showed that temperature
was a determining factor for the quality and quantity of sleep. Low
temperatures were inconsistent with the recovery function of sleep.
Heterothermy caused a sleep debt thus there was a rebound of sleep at the
beginning of euthermia to compensate the lack of sleep.