Neurochemical perspectives on the control of breathing during sleep.

A specific depression of minute ventilation occurs during sleep in normal subjects. This sleep-related ventilatory depression is partially related to mechanical events and upper airway atonia but some data also indicate that it is likely to be centrally mediated. This paper reviews the anatomical and neurochemical connections between sleep/wake- and respiratory-related areas in an attempt to identify the potential implication of sleep-related neurochemicals (serotonin, catecholamines, GABA, acetylcholine) in the sleep-related hypoventilation. The review of available data suggests that the sleep-related ventilatory depression depends upon the enhanced GABAergic activity together with a loss of suprapontine influence depending on the cessation of activity of the reticular formation. During REM sleep, an additional inhibitory activity emerges from the pontine cholinergic neurons, which contributes to the breathing irregularities and the associated depression of minute ventilation and ventilatory response to chemical stimuli. This model may contribute to a better understanding of the neurochemical environment of respiratory neurons during sleep, which remains a question of importance regarding the numerous pathological states that are linked to specific perturbations of breathing control during sleep.