Cerebral glucose utilization during stage 2 sleep in man

[Contribution of positron emission tomography in the study of wakefulness and sleep. Status of the question]

Positron emission tomography (PET) allows the exploration of cerebral physiological and biochemical processes in vivo in man. Sleep studies using this technique first demonstrated that cerebral metabolic rates for glucose decrease during slow wave sleep in comparison with wakefulness whereas, during paradoxical sleep, the cerebral glucose metabolism is as high as during wakefulness. At present, several laboratories are currently exploring the regional modifications of cerebral blood flow during sleep. The results are partial and preliminary but seem to show a relative decrease in frontal cortex blood flow during slow sleep. This short review also considers some PET studies of sleep deprivation and sleep related pathologies.

Adenosine inhibition of mesopontine cholinergic neurons: implications for EEG arousal

Increased discharge activity of mesopontine cholinergic neurons participates in the production of electroencephalographic (EEG) arousal; such arousal diminishes as a function of the duration of prior wakefulness or of brain hyperthermia. Whole-cell and extracellular recordings in a brainstem slice show that mesopontine cholinergic neurons are under the tonic inhibitory control of endogenous adenosine, a neuromodulator released during brain metabolism. This inhibitory tone is mediated postsynaptically by an inwardly rectifying potassium conductance and by an inhibition of the hyperpolarization-activated current. These data provide a coupling mechanism linking neuronal control of EEG arousal with the effects of prior wakefulness, brain hyperthermia, and the use of the adenosine receptor blockers caffeine and theophylline.