Etomidate Modulates the Tactile Stimulation-Evoked Field Potential Responses in Cerebellar Granule Cell Layer in vivo in Mice

Etomidate (ET) produces sedation by binding on the γ-aminobutyric acid type A (GABA_A) receptors. We previously found that ET inhibited cerebellar Purkinje cells activity via both GABA_A and glycine receptors in vivo in mice, suggesting that ET modulated sensory information synaptic transmission in cerebellar cortex. In this study, we investigated the effect of ET on the sensory stimulation-evoked responses in the cerebellar granule layer (GL) in urethane-anesthetized mice, using electrophysiological and pharmacological methods. Our results showed that cerebellar surface perfusion of ET (100 μmol/L) significantly decreased amplitude and area under the curve (AUC) of the sensory stimulation-evoked excitatory component (N1) in the cerebellar GL. Application of GABA_A receptor antagonist, SR95531 (20 μmol/L) significantly attenuated, but not abolished the ET-induced decrease in amplitude and AUC of facial stimulation-evoked responses. However, application of a mixture of SR95531 (20 μmol/L) and cannabinoid 1 receptor (CB1) antagonist, AM-251 (5 μmol/L), completely blocked the ET-induced decrease in amplitude and AUC of facial stimulation-evoked responses. Furthermore, application of the CB1 receptor agonist, WIN55212-2, induced a decrease in amplitude and AUC of N1 in the absence of GABA_A receptors activity, as well occluded the ET-induced depression of N1. Moreover, the ET-induced changes in amplitude and AUC of N1 in absence of GABA_A receptors activity were abolished by a specific protein kinase A (PKA) inhibitor, KT5720. These results indicate that ET facilitates CB1 receptors in the absence of GABA_A receptors activity, resulting in a depression of the sensory stimulation-evoked synaptic transmission via PKA signaling pathway in mouse cerebellar GL.