Using Optogenetic And Neural Circuit Tracing Techniques To Study The Function Of Vestibular Nuclei

Glutamatergic and GABAergic neurons represent the main component of the Medial Vestibular Nuclei(MVN).We assessed the functional role of glutamatergic and GABAergic neuronal populations in the vestibular nuclei in the maintenance of gait and balance,by opto-genetically stimulating the vestibular nuclei of VGlu T2-cre and GAD2-cre mice.The result demonstrated the VN glutamatergic,but not GABAergic subpopulation are responsible for immediate and strong posture-locomotor deficits,comparable to unilateral Vestibular Deafferentation Syndrome(u VDS).In addition,during optogenetic stimulation the mice's supporting surface area dramatically increased for VN-VGlu T2+ animals,and rapidly come back to baseline level after stimulation,still comparable to u VDS,whilst it remained unchanged during all the experiment for VN-GAD2+ animals.Finally,in VN-VGLu T2+ animals posturolocomotor parameters such as immobility and velocity remained present immediately after stimulation,and it declined 1h after.Overall,these results indicate a fundamental role for VN-VGlu T2+ neurons in balance and posturo-locomotor functions,but not for VN-GAD2+ neurons.This new optogenetic approach offers to better characterize the role of glutamatergic and gabaergic functions in vestibular compensation.According to existing studies,the VN,in addition to its role as a key nuclei for maintaining balance,it is often associated with vertigo,postural deficits,vestibular migraine,and neuro-degenerative diseases.These disease states are closely related,and the symptoms of the diseases mentioned above will also be accompanied by the activation of the locus coeruleus-norepinephrine(LC-NE)system.Therefore,in this part of the study,we combined the genetically modified mouse technology with the virus tracing technology.The results showed that there is a clear neural projection from the locus coeruleus(LC)to the vestibular nucleus(VN).Next,we used tyrosine hydroxylase(TH)antibodies to perform immune-histochemical experiments on mouse brain slices.The immune-fluorescence staining confirmed that the projection of LCVN was noradrenergic.Finally,the mice were subjected to a 24-hour sleep deprivation,higher c-Fos activation showed in the LC-NE neurons compared with the untreated control group,but the neurons in the VN were not significantly activated.This result suggests LC-NE may play an important role in stress-related VN malfunction.Our study reveals the connection between LC and VN to a certain extent,and provides anatomical basis for further neural circuity studies of LC-VN in balance and then its possible involvement in diseases.