Role of activation of VGLUT2 neurons in vagal nodose ganglion in dexmedetomidine-caused bradycardia in mice / 中华麻醉学杂志

ABSTRACT

Objective:To evaluate the role of activation of vesicular glutamate transporter 2 (VGLUT2) neurons in vagal nodose ganglion in dexmedetomidine-caused bradycardia in mice.Methods:Ninety-six SPF healthy male VGLUT2-cre mice, aged 10 weeks, weighing 20-25 g, were divided into 6 groups ( n=16 each) by the random number table method: normal saline control group (NS group), dexmedetomidine group (Dex group), viral control + chemogenetic control + dexmedetomidine group (eGFP-NS+ Dex group), viral transfection + chemogenetic control + dexmedetomidine group (hM4Di-NS+ Dex group), viral control + chemogenetic inhibition + dexmedetomidine group (eGFP-CNO+ Dex group) and viral transfection + chemogenetic inhibition + dexmedetomidine group (hM4Di-CNO+ Dex group). Dexmedetomidine 100 μg/kg was intraperitoneally injected in Dex group. The equal volume of normal saline was intraperitoneally injected in NS group. AAV2/9-hSyn-DIO-hM4Di-eGFP was injected in the right nodose ganglion in hM4Di-NS+ Dex group and hM4Di-CNO+ Dex group, and AAV2/9-hSyn-DIO-eGFP was injected in the right nodose ganglion in eGFP-NS+ Dex group and eGFP-CNO+ Dex group, allowing the virus expression for 21 days. On the 22nd day after virus injection, clozapine-n-oxide (CNO) 5 mg/kg was intraperitoneally injected in hM4Di-CNO+ Dex group and eGFP-CNO+ Dex group, the equal volume of normal saline was intraperitoneally injected in hM4Di-NS+ Dex group and eGFP-NS+ Dex group, 1 h later the efficacy of CNO reached the peak, and then dexmedetomidine 100 μg/kg was intraperitoneally injected. The respiratory rate, heart rate, SpO 2 and discharge frequency of the right vagal nodose ganglion were synchronously measured by multi-channel electrophysiology in vivo. The expression of phosphorylated extracellular signal-regulated kinase (pERK) and VGLUT2 and co-expression of pERK and VGLUT2 in the right vagal nodose ganglion were detected by immunofluorescence assay. Results:Compared with NS group, the percentage of heart rate variation and neuron firing frequency after administration were significantly increased, and pERK expression was up-regulated in the other five groups ( P<0.05). Compared with Dex group, the percentage of heart rate variation and neuron firing frequency after administration were significantly decreased, and pERK expression was down-regulated in hM4Di-CNO+ Dex group, and no significant change was found in the parameters mentioned above in hM4Di-NS+ Dex group, eGFP-NS+ Dex group and eGFP-CNO+ Dex group ( P>0.05). Compared with hM4Di-CNO+ Dex group, the percentage of heart rate variation and neuron firing frequency after administration were significantly increased, and pERK expression was up-regulated in eGFP-CNO+ Dex group ( P<0.05). There was no significant difference in the percentage of respiratory variation and SpO 2 among the six groups ( P>0.05). The expression of VGLUT2-positive neurons was abundant in nodose ganglia, and the co-expression rate of pERK and VGLUT2 was nearly 90%. The co-expression rate of pERK and VGLUT2 decreased to about 30% after inhibition of VGLUT2 neurons in ganglion. Conclusions:The mechanism by which dexmedetomidine causes bradycardia is associated with activation of VGLUT2 neurons in vagal nodose ganglia in mice.