Reticular modulation of breathing during sleep and anesthesia.

Although sleep and anesthesia are distinctly different states of consciousness, they manifest some common physiologic traits, including respiratory depression. Support is lacking for the concept of any unitary mechanism causing the loss of wakefulness and the respiratory depression associated with sleep or anesthesia. A recently emerging view is that brain mechanisms, which have evolved to generate naturally occurring states of consciousness, are preferentially involved in generating traits characterizing some anesthetic states. The brain stem reticular formation mediates four functions of direct relevance for sleep and anesthesia. Recent work is selectively reviewed showing that brain stem cholinergic and monoaminergic neurons alter breathing while modulating behavioral states, muscle tone, cardiopulmonary control, and pain sensation. The ability of these four functions to influence breathing also makes clear their potential to serve as confounding variables in experimental models from which they are ignored or systematically excluded.