Study On The Effect Of Peripheral Inflammation On Lipopolysaccharide-induced Dopaminergic Neuron Damage In Midbrain

Objective:This study aims to explore the effects of peripheral inflammation on lipopolysaccharide（LPS）-induced dopaminergic（DA）neuron damage in rat midbrain substantia nigra pars compacta（SNc）and its possible mechanisms.Methods:Male SD rats were randomly divided into five groups:1)Control group;2)Intraperitoneal injection of LPS group[LPS_（i.p.）0.5 mg/kg];3)LPS injection in midbrain SNc group[LPS_（SN）];4)Intraperitoneal injection of LPS（0.5 mg/kg）+LPS injection in midbrain SNc group[LPS_（i.p.）0.5mg/kg+LPS_（SN）];5)Intraperitoneal injection of LPS（1.0mg/kg）+LPS injection in midbrain SNc group[LPS_（i.p.）1.0 mg/kg+LPS_（SN）].Rats were intraperitoneally injected with LPS（0.5 mg/kg and 1.0 mg/kg）once a day for 4consecutive days to induce peripheral inflammation,and then rats received LPS（8μg）injection to midbrain SNc to induce DA neuronal damage 0,30 and 90 days after LPS_（i.p.）administration.First,behavior change of rats was detected by rotarod and open field tests.Then,the expressions of TH（DA neurons marker）,IBA-1（microglia marker）and GFAP（astroglia marker）in midbrain were detected by immunohistochemistry and western blot assays.In addition,the expressions of DAT（DA neuron terminal maker）,tumor necrosis factor-α（TNF-α）and interleukin-1β（IL-1β）in midbrain were determined by western blot.The concentration of inflammatory factors,such as TNF-αand IL-1β,in peripheral blood was measured by ELISA kit.The expressions of micglia M1 type marker（i NOS and IL-6）,M2 type marker（IL-10 and Arg-1）,T cells marker（CD8αand CD4）,B cells marker（CD19and BCL2）and monocytes marker（MPO and CCL2）in midbrain were detected by real time RT-PCR.The expressions of CD8α,IBA-1,i NOS,Arg-1 and TH in midbrain were analyzed by immunofluorescence assay.Results:（1）LPS_（i.p.）caused inflammatory factors increased in peripheral blood of rats,and intraperitoneal injection of LPS caused peripheral inflammation in rats.（2）Peripheral inflammation improved LPS_（SN）-induced behavior disorder,peripheral inflammation increased the expression of TH and DAT in the midbrain induced by LPS_（SN）,LPS-induced peripheral inflammation could protect LPS_（SN）-induced DA neuronal damage in midbrain.（3）Peripheral inflammation reduced the expression of IBA-1 and GFAP in the midbrain induced by LPS_（SN）,peripheral inflammation suppressed LPS_（SN）-induced microglia activation.（4）Peripheral inflammation reduced the inflammatory factors TNF-αand IL-1βrelease in the midbrain induced by LPS_（SN）.（5）Peripheral inflammation suppressed M1type microglia activation in midbrain induced by LPS_（SN）.（6）Via the detection of the expressions of T cells,B cells and monocytes in midbrain,results suggested that peripheral inflammation increased the expressions of CD8αand CD4 of T cell markers in midbrain.In addition,further investigation suggested that peripheral inflammation recruited T cells into brain to regulate the activation of M1 type microglia and then effected DA neuronal survival.Conclusion:This study suggested that peripheral inflammation could inhibit the development of LPS-induce DA neuronal damage in SNc,and the mechanisms might be associated with the recruitment of T cells to regualate M1 microglial activation and the subsequent pro-inflammatory factors release.