Dexmedetomidine Inhibition of GABA Neurons in the Ventral Tegmental Area Attenuates the Depth of Sedation in Mice.

INTRODUCTION: Dexmedetomidine is a sedative anesthetic with a unique ability to produce an arousable state of sedation. However, the neural mechanisms underlying this arousable sedation remain incompletely understood. Previous studies have implicated dopaminergic neurons in the ventral tegmental area (VTA) in mediating this effect, but the upstream neural circuit mechanisms remain unclear. Furthermore, although VTA GABAergic neurons exert robust inhibitory effects on dopaminergic neurons, their specific role in dexmedetomidine-induced arousable sedation remains unclear.

METHODS: Vgat-Cre transgenic mice were used to investigate the role of VTA GABAergic neurons in dexmedetomidine-induced arousable sedation. Electroencephalography (EEG), fiber photometry, calcium imaging, GABA neurotransmitter sensing, chemogenetic manipulation, and immunohistochemistry were used to assess neuronal activity, GABAergic signaling, and behavioral responses to dexmedetomidine.

RESULTS: Fiber photometry using the calcium indicator GCaMP6m revealed that dexmedetomidine inhibited VTA GABAergic neurons. Fiber photometry with the GABA neurotransmitter sensor iGABASnFR demonstrated that dexmedetomidine increased GABAergic input to VTA GABAergic neurons. Chemogenetic manipulation combined with EEG demonstrated that activating VTA GABAergic neurons deepened dexmedetomidine-induced sedation, whereas inhibiting these neurons attenuated sedation.

CONCLUSION: These findings suggest that dexmedetomidine increases GABAergic input to VTA GABAergic neurons and suppresses their activity, potentially contributing to its arousable sedative effects. Further studies are needed to establish the causal role of this neural circuit mechanism.