Internal temperature variations during the sleep-wake cycle in the rat

Area of Science:

• Physiology
• Neuroscience
• Sleep Science

Background:

• Internal body temperature exhibits diurnal variations linked to physiological processes.
• Understanding thermoregulation during sleep is crucial for comprehending overall physiological regulation.

Purpose of the Study:

• To elucidate the relationship between internal temperature variations (brain and subcutaneous) and behavioral states (sleeping and waking) in rats.
• To investigate the correlation between local cerebral blood flow (CBF) and brain temperature during different sleep stages.
• To examine the link between whole-body thermogenesis (VO2) and subcutaneous temperature variations.

Main Methods:

• Chronic measurement of local cerebral blood flow (CBF) using a thermal clearance method.
• Monitoring of brain (cerebellum, hypothalamus) and subcutaneous temperatures in rats.
• Quantification of whole-body thermogenesis (VO2) and sensible heat loss.

Main Results:

• Cerebral blood flow (CBF) remained high during slow wave sleep (SWS), decreased at the onset of wake (W) and paradoxical sleep (PS), with an overshoot at the end of PS.
• Subcutaneous temperature correlated with thermogenesis (VO2) and sensible heat loss, showing distinct patterns across W, SWS, and PS.
• VO2 was highest during W, decreased during SWS, and was minimal during PS, while sensible heat loss showed inverse trends.

Conclusions:

• Observed variations in brain and subcutaneous temperatures align with changes in heat gain and loss during sleep-wake cycles.
• A close relationship exists between vigilance states and internal temperature rhythms, suggesting circadian influence, though the precise interaction requires further study.