The Role Of Lateral Parabrachial Nucleus-Hypothalamic Paraventricular Nucleus Excitatory Glutaminergic Pathway In The Pathogenesis Of Motion Sickness

Motion sickness(MS)is a multi-system physiological reaction caused by exposure to abnormal acceleration.The early symptoms of motion sickness mainly include loss of appetite,pallor,drowsiness,cold sweat,etc.With the extension of stimulation time,there will also be nausea,salivation,vomiting,lower core body temperature,increased body surface heat dissipation and other autonomic nervous reactions.In animal studies,motion sickness induced decreased feeding,gastrointestinal reactions(conditioned mouth opening and defecation responses),decreased spontaneous activity,and decreased body temperature in rats.It has been reported in a large number of literatures that motion sickness stimulation activates several important neural nucleus in the hypothalamus,brainstem and limbic system,which are collectively referred to as motion sickness related nucleus,including: Lateral parabrachial nucleus(LPBN),Paraventricular hypothalamic nucleus(PVN),Median preoptic nucleus(Mn PO),Dorsomedial hypothalamic nucleus(DMH),Ventromedial hypothalamic nucleus(VMH),Medial amygdala(MEA),Central amygdaloid nucleus(CEA),Premammillary nucleus,(PMV),Posterior subthalamic nucleus(PSTh),Locus coeruleus(LC),Vestibular spinal tract nucleus,Sp Ve),Medial vestibular nucleus(MVe),Solitary tract(NTS).In previous studies,we found that the medial vestibular nucleus(MVe)and vestibular spinal tract nucleus(Sp Ve)can receive motion sickness stimulation signals and transmit the signals to the lateral parbrachial nucleus(LPBN)to produce motion sickness symptoms.However,LPBN is an important relay nucleus group,and the downstream nucleus group regulated by LPBN remains unclear.The neurons mediating motion sickness in LPBN are mainly glutaminergic neurons,and it is not clear whether they regulate the downstream nucleus through glutaminergic neural pathway.In order to clarify the role of LPBN glutaminergic neural pathway in the occurrence of motion sickness,the following studies were carried out in this subject.First,recombinant adeno-associated virus(AAV2/1-Ca MKII-EGFP),which uses Calcium/Calmodulin dependent protein kinase II(Ca MKII)as a specific promoter,was injected into LPBN.Enhanced Green Fluorescent Protein(EGFP)can be expressed within glutaminergic neurons to display anteriorly-labeled glutaminergic nerve fibers.The projection intensity of LPBN glutaminergic nerve fibers in each nucleus was determined according to the projection morphology and quantitative immunofluorescence analysis results.Secondly,the expression amount of early gene Fos protein and the proportion of EGFP/Fos co-expressing neurons after motion sickness stimulation were observed to determine the downstream nucleus regulated by LPBN.Further,immunofluorescence method was used to observe the co-labeling of the 3 vesglutamate transporter 1-3,(VGLUT1-3)in LPBN and PVN with Fos protein expressed after motion sickness stimulation.To clarify the activation of LPBN-PVN glutaminergic neural pathway in the occurrence of motion sickness.Third,optogenetic specific activation of this pathway was used to observe the behavioral changes associated with motion sickness in rats,in order to verify the role of this pathway in inducing behavioral manifestations of motion sickness.Finally,immunofluorescence was used to observe the relationship between Fos protein and key neuropeptides [Arginine vasopressin(AVP),Oxytocin,(OXT),Corticotropin Releasing hormone(CRH)],Acetylcholine transferase(Ch AT),a neuron-specific marker of cholinergic activity and Reelin to investigate the main types of neurons regulated by motion sickness in PVN.Research content:1.Observation of glutaminergic neural pathways between nucleus associated with motion sickness and LPBN.SD rats were injected with AAV2/1-CaMKII-EGFP with unilateral(right)LPBN,and appropriate slices of LPBN injection area and motion sickness associated nucleus were cut.The projection distribution of LPBN glutaminergic projecting nerve fibers in different motion sickness associated nucleus and the green fluorescence expression in each nucleus were observed under fluorescence microscope.The projection intensity of LPBN glutaminergic nerve fibers in nucleus associated with motion sickness was determined according to the projection morphology of nerve fibers in nucleus and the quantitative analysis results of green fluorescence in nucleus.2.The coexistence of LPBN anterograde projective fibers and Fos protein-expressing neurons after rotation stimulation.SD rats were injected with the above virus AAV2/1-Ca MKII-EGFP by unilateral(right)LPBN.After 3 weeks of normal feeding,the rats were stimulated with motion sickness for 2h.The brains were immediately taken by cardiac perfusion and fixed with paraformaldehyde.Immunofluorescence co-labeling was used to observe the co-expression of Fos protein and virus projection fibers in motion sickness associated nucleus.3.Colabeling of glutamic acid vesicle-type transporters with Fos protein induced by halo stimulation in LPBN and PVN was observed.The experiment was conducted in three batches.The brain was taken by cardiac perfusion immediately after 2h of motion sickness stimulation,and appropriate slices of LPBN and PVN were selected to carry out immunofluorescence co-labeling of glutamic vesicular transporters(VGLUT1,VGLUT2,VGLUT3)and Fos protein,respectively.4.The LPBN-PVN glutaminergic neural pathway was activated by optogenetic,and behavioral changes related to motion sickness were observed.LPBN of SD rats were injected with virus(AAV2/1-CaMKII-Ch R2-EGFP,which transfected neurons to express the light-sensitive protein Ch R2 and was activated by473 nm blue light).After three weeks of normal feeding,optical fiber was embedded0.3mm above the PVN nucleus,and 50 Hz and 473 nm blue light was irradiated for 2 hours.Spontaneous activity,fecal particle number,body temperature and 24 h food intake of rats were observed.5.Immunofluorescence co-labeling of Fos protein expressed after motion sickness stimulation with PVN neuropeptides were observed.After 2h of motion sickness stimulation,the brains of SD rats were immediately taken by cardiac perfusion,and appropriate sections of PVN nucleus were selected.The co-expression of Fos protein with AVP,OXT,CRH,Ch AT and Reelin in different subregions of PVN was observed by immunofluorescence co-labeling method,so as to preliminatively explore the types of peptidenergic neurons regulated by motion sickness stimulation in PVN.Research results:1.The projection strength of LPBN nerve fibers in motion sickness associated nucleus was different.According to the projection morphology of nucleus and quantitative immunofluorescence analysis results,the nucleus with high intensity projection association with LPBN were: Mn PO,CEA,VMH,PSTh;the nucleus associated with medium intensity projection were PVN,DMH,MEA and Sp Ve.the low intensity projective associated nucleus are PMV,LC,MVe and NTS.2.EGFP-positive LPBN anterograde projection fibers co-existed with Fos protein in motion sickness associated nucleus.There was a difference in the proportion of EGFP/Fos co-labeled neurons to Fos positive neurons in motion sickness related nucleus.The nucleus with more than 50% of EGFP/ Fos co-labeled neurons were PVN.30%～50% are: Sp Ve,CEA,MEA;5%-30% of the nucleus were Mn PO,DMH,PSTh,VMH;< 5% are: MVe,LC,PMV,NTS.The proportion of EGFP/Fos colabeled neurons in PVN was the highest(66.9%).3.Glutamic acid vesicular transporters in LPBN and PVN coexisted with Fos protein.VGLUT1-3 and Fos protein were co-expressed by immunofluorescence in LPBN and PVN after motion sickness stimulation.In LPBN,VGLUT1/Fos,VGLUT2/Fos and VGLUT3/Fos co-labeled neurons accounted for 92.8%,95.4% and 89.3% of Fos positive neurons.The proportion of VGLUT2/Fos and VGLUT3/Fos co-labeled neurons in PVN was significantly higher than that of VGLUT1/Fos(85.4%,83.1% vs.1.7%).4.Optogenetic activates the LPBN-PVN glutaminergic neural pathway and induces behavioral changes associated with motion sickness.Compared with the control group without light and empty virus,the expression of EGFP fluorescent protein and Fos protein in PVN was significantly increased by optogenetic stimulation.Food intake,fecal particle number and spontaneous activity decreased significantly,but tail temperature did not change significantly.5.There were differences in the co-expression relationship between Fos protein and important neuropeptides after motion sickness stimulation in PVN.ChAT/Fos and Reelin/Fos co-labeled neurons accounted for more than 90% of Fos positive neurons,CRH/Fos co-labeled neurons accounted for about 40%,mainly distributed in the inner small cells of PVN,and AVP/Fos and OXT/Fos co-labeled neurons accounted for less than 5%.Research conclusion:1.The projective fiber distribution of LPBN glutaminergic neurons in motion sickness related nucleus was significantly different;There were strong glutaminergic fiber projection between LPBN and MnPO,CEA,VMH,PSTh,PVN,DMH,MEA and Sp Ve.2.In motion sickness related nucleus,LPBN glutamate-projecting fibers coexisted with Fos protein expressed after motion sickness stimulation.The number of neurons that received glutamic ergic projection of LPBN and were activated by motion sickness was significantly different.The main nucleus activated by motion sickness stimulus included PVN,Sp Ve,CEA and MEA.3.Optogenetic specific activation of the LPBN-PVN glutaminergic neural pathway induced motion sickness related behavioral changes in rats,including reduced food intake,decreased spontaneous activity,and increased fecal particle count.However,there was no increase in tail heat dissipation similar to that after motion sickness stimulation.4.The glutamic acid projective fiber of LPBN-PVN coexisted with glutamic acid vesicular transporters VGLUT2 and 3.Ch AT,Reelin and CRH positive neurons in PVN were significantly activated by motion sickness stimulation.