Arousal, orexins and anesthesia

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In the past two decades, genetic studies have revealed mechanisms that regulate circadian and sleep neurophysiology. They promise to unveil mechanisms of anesthetic-induced unconsciousness as well. Sensitivity to anesthetics varies across a population with some individuals requiring a higher dose to achieve a given depth of anesthesia. Anesthetic resistance may present in humans as awareness under anesthesia. One form of hypersensitivity may present as delayed emergence from anesthesia and js seen in a subset of narcoleptic patients with impaired orexin signaling. The central hypothesis of this grant is that inhaled anesthetics exert specific effects upon the endogenous neural circuitry regulating sleep and wakefulness. During induction and maintenance of anesthesia, we hypothesize that inhaled anesthetics produce their hypnotic effects through activation of the ventral lateral preoptic area (VLPO), the central sleep-active region of the brain. Emergence from anesthesia should depend upon re-activation of orexinergic (Ox) neurons, a wake-promoting and sustaining region of the brain. In aim 1 of this grant, we will map neural activation through c-Fos protein immunohistochemistry¿the same methodology used initially to find arousal state- dependent nuclei. We hypothesize that c-fos mRNA and protein levels will be induced in VLPO and repressed in Ox neurons during inhaled anesthesia; and that these changes must reverse during normal emergence from anesthesia. In aim 2, we will evaluate the contribution of Ox neurons to induction and emergence from inhaled anesthesia using behavioral (loss of righting reflex) as well as electroencephalographic (EEC) assays. We hypothesize that mice with genetically and pharmacologically impaired orexin signaling will show delayed emergence from anesthesia. Finally, in aim 3, we will demonstrate that administration of orexin agonists speeds emergence from anesthesia. We hypothesize that orexin agonists should also produce c-fos neuronal activation patterns that attenuate (or reverse) both inhaled anesthetic-induced activation of VLPO and inhibition of Ox neurons. As an anesthesiologist formally trained in neuroscience and mouse genetics, Dr. Kelz is firmly committed to a career in academic anesthesia. His ultimate career goal is to improve perioperative patient care through a better understanding of the mechanisms by which anesthetics suppress consciousness. This proposal will enhance his training toward that end by providing formal education in sleep neurobiology (including EEG and EMG acquisition and analysis), stereotactic surgerical techniques necessary for pharmacologic studies, and advanced molecular biology. His co-mentors have established records of nuturing junior faculty. Together with his current skill set, these new tools will help transition him towards becoming an independent physician-scientist by bridging the interface between sleep neurobiology and anesthetic action.