0042 EEP-PROMOTING GABAERGIC NEURONS IN THE PARAFACIAL ZONE PLAY A ROLE IN ANESTHETIC-INDUCED UNCONSCIOUSNESS IN MICE

Abstract

Abstract Introduction Although the precise mechanisms by which anesthetics induce unconsciousness are unknown, there is evidence that shared brain circuits are engaged during sleep and general anesthesia. The parafacial zone (PZ) of the brainstem has recently been identified as a sleep-promoting region. Specifically, GABAergic neurons in the PZ (PZ-GABA) are active during non-REM sleep. The role of sleep-promoting PZ-GABA during anesthetic-induced hypnosis is unknown. We hypothesized that PZ-GABA are active during general anesthesia and contribute to anesthetic-induced hypnosis. Methods Adult C57BL6 mice (n = 3) were subjected to two-hour exposures of a hypnotic dose of an inhaled general anesthetic (isoflurane 1.2%) in oxygen, a non-immobilizer, F6, that lacks hypnotic properties (1,2-dicholorohexafluorocyclobutane 3%) in oxygen, or oxygen alone. The brains were harvested immediately following these exposures. The sections of brain were immunostained for c-Fos and GAD. To study the role of PZ-GABA in isoflurane-induced hypnosis, ablation of PZ-GABA was performed in adult bitransgenic Vgat-ires-Cre;Ai6 mice in which GABAergic neurons express a fluorescent reporter (n = 5 per group). Anesthesia sensitivity was evaluated weekly for four weeks after the virus injections by assessing the presence of a righting reflex during the exposures. Results In the PZ, a hypnotic dose of Isoflurane selectively activated GAD-positive GABAergic neurons compared to mice treated with F6 and oxygen. (P < 0.01 for both F6 and oxygen vs. Isoflurane, one-way ANOVA) Furthermore, mice lacking PZ-GABA demonstrated resistance to anesthetic induction, decreased sensitivity during the maintenance phase, and consistently increased the propensity to emerge from anesthesia. (For both induction and emergence, the upper 95% CI of EC50 at baseline was lower than the lower 95% CI at all time points after the injections. For maintenance phase, P < 0.05 for baseline vs. 1-week, one-way ANOVA) Conclusion PZ-GABA was active during isoflurane exposure. Moreover, the absence of PZ-GABA resulted in resistance to isoflurane-induced hypnosis. These findings suggest that PZ-GABA, a sleep-promoting region in the brainstem, plays an important role in general anesthesia. Support (if any) NIH (T32HL7713-27, T32 NS091006), ATS-ASPIRE