General anesthesia and ascending arousal pathways.

摘要

The ability to produce a reversible loss of consciousness is the denning characteristic of general anesthetics. It is also the most fascinating and elusive. Although the molecular targets of many anesthetics have been identified, they are widely distributed in the central nervous system. Therefore, identifying the locus of action of these drugs in the brain represents a major challenge. The neuronal mechanisms of sleep, a physiologic state that involves a loss of consciousness, provide one obvious avenue of enquiry. Brain imaging and electroencepha-lographic studies give a broad characterization of the anesthetic state and show clear similarities with the sleeping brain. However, natural sleep and wakefulness are controlled by multiple arousal pathways, as well as by the intimate connectivity between the thalamus and cortex. Anesthetics could cause a loss of consciousness by pressing a switch in any (or all) of these regions, for example by disrupting intracortical connectivity by directly triggering burst firing in the thalamus or by inhibiting ascending arousal pathways. An interesting study presented by Luo and Leung in this issue of Anes-thesiology is the latest evidence that the ascending control of natural sleep-wake cycles may be targeted in drug-induced loss of consciousness.