Vagal Nerve Stimulation Attenuates Ischemia-reperfusion Induced By Acute Ocular Hypertension Model And The Neuroprotection In Retina

Part 1.Necroptosis in Acute Ocular Hypertension Induced Retina Ischemia Reperfusion InjuryPurpose: The present study aimed to investigate the mechanisms of acute ocular hypertension model induced retina Ischemia-Reperfusion.Methods: Mature C57 mouse were randomly divided into sham group,retina ischemia-reperfusion group(pressure-induced retina ischemia for 1h and reperfusion for 1h in the right eye)and I/R+TAK-632 group.Retina was collected at 6h,12 h,24h,and 72 h after retina I/R.The number of retina ganglion cells(RGCs)of each time point was counted.The function of mice’s retina in eaach time point of retina I/R model was detected by flash Electroretinagram(f-ERG).We analyzed the expression of caspase-3;caspase-8;mixed lineage kinase domain-like(MLKL)and phosphorylated mixed lineage kinase domain-like(p-MLKL)in retina,which protien represented the necroptosis and apoptosis sigaling pathway,by western blot.Finally,TAK-632,a kind of inhibitor of RIPK1/3,was used to block necroptosis pathway in retina and study the function of necroptosis in the early time and the late time in retina I/R model.Result: Compared with control group,the number of RGCs in C57 retina were decreased in 24-hours group(P < 0.05,n = 8).In 72 hours of ganglion cells appear obvious difference(P < 0.01;n = 8).At 6 hours and 12 hours retina I/R group,the number of ganglion cells did not change.The function of retina was detected by f-ERG.It was shown that amplitude of b wave was decreased 12-hour,24-hour,and72-hour after reina I/R model(P < 0.05,n = 4).The amplitude of a wave started to decrease in 12-hours.In western blot,the caspase-8 appeared in 24-hours group and72-hours group.MLKL in 24-hours group and 72-hours group decreased(P < 0.05,n= 8).P-MLKL in the model groups is higher than the control group.The highest peak appeared in 24-hours group,and then fell in 72-hours group(p < 0.05,n = 8).The activity of caspase-3,at time of 24-hour retina after I/R,didn’t increase.On the contrary,it was activated into c-caspase-3 at time of 7-day in retina I/R.Conclusion: The decreasing and disfunction of retinal ganglion cells appeared in the early time of acute ocular hypertension induced the retinal ischemia reperfusion damage attribute to necroptosis pathway.Blocking necroptosis can partly protectRGCs in early time,but not that in late time,which was decreased via apoptosis.Part 2.Vagal Nerve Stimulation Attenuates Ischemia-Reperfusion Induced Retina Dysfunction in Acute Ocular HypertensionPurpose: The present study aimed to investigate whether cervical vagal nerve stimulation(VNS)could prevent retinal ganglion cell(RGC)loss and retinal dysfunction after ischemia/reperfusion(I/R)injury.Methods: First,rats were randomly divided into sham group(n = 4)and VNS group(n = 12).Activation of the nodose ganglia(NOG),nucleus of the solitary tract(NTS),superior salivatory nucleus(SSN),and pterygopalatine ganglion(PPG)neural circuit were evaluated by c-fos expression at 0 h after sham VNS and at 0 h(n = 4),6h(n = 4),72 h(n = 4)after VNS.Secondly,rats were randomly assigned to I/R group(pressure-induced retinal ischemia for 1 h and reperfusion for 1 h in the right eye,n =16)and I/R+VNS group(right cervical VNS for 2 h during the I/R period,n = 16).The left eye of each rat served as a control.Electroretinogram(ERG),RGC numbers,tumor necrosis factor-α(TNF-α)and vasoactive intestinal polypeptide(VIP)levels in retina were determined.Additionally,the level of VIP in PPG was evaluated.Results: In the first part of the study,compared with the sham group,the VNS group exhibited significantly increased expression of c-fos in NOG,NTS,SSN,and PPG tissues at 0,6,and 72 h.In the second part of the study,compared with left eyes,retinal function in right eyes(as assessed by the a-wave,b-wave and the oscillatory potential amplitudes of ERG and RGC data)was significantly decreased by I/R.The decreased retinal function was attenuated by VNS.In addition,I/R induced an increase in inflammation,which was reflected by elevated TNF-α expression in the retina.VNS significantly attenuated the increase in I/R-induced inflammation.Moreover,VIP expression in the retina and PPG,which may contribute to the inhibition of the inflammatory response,was significantly increased after VNS.Conclusion: VNS could protect against retinal I/R injury by downregulating TNF-α.Upregulation of VIP expression due to activation of the NOG-NTS-SSN-PPG neural circuit may underlie to the protective effects of VNS.