| Parkinson’s disease(PD)is a common neurodegenerative disease in the elderly characterized by the progressive loss of dopaminergic neurons in the substantia nigra(SN)of the midbrain.The prevalence of PD increases with age.The significant clinical symptoms of PD include resting tremor,bradykinesia and rigidity.Non-motor symptoms of PD appear before motor symptoms,including depression,anxiety,olfactory dysfunction,sleep disorders and gastrointestinal(GI)dysfunction,among which the incidence of GI dysfunction is up to 80%.Actually,the dopaminergic neurons in the SN have already been impaired when the non-motor symptoms appear and about50%～60% dopaminergic neurons have been lost when PD patients show motor symptoms.Braak et al.proposed the 6 stages hypothesis of PD pathology in 2003.The hypothesis considered that the pathogens or toxins exposure may trigger the accumulation of α-syn in the GI tract which was transmitted to DMV and SN in turn through neural pathways,and resulted in PD.Braak et al.also assumed that some pathogens infected in the stomach and nasal cavity due to the olfactory and autonomic dysfunctions in PD,termed as the "double-hit theory",which indicated that α-synuclein(α-syn)could accumulated in these sites,and spread the central nervous system(CNS)from the periphery.The vagus nerve might serve as a bridge between GI tract and CNS since the risk of PD decreased in patients with vagotomy,and animal studies also showed that vagotomy delay the progress of PD.Vagus is a mixed nerve composed of both afferent and efferent fibers.As the efferent fibers are emitted from DMV in whichα-syn is accumulated significantly,the efferent fibers of the vagus nerve are considered as the major pathway for the spread of PD from the GI tract to the CNS.However,the afferent fibers account for the majority of the vagus,and the aggregation of α-syn is detected in the nucleus of solitary tract(NTS)which is connected to the vagal afferent.So far,it has not been reported that the role of vagal afferent nerve in the spread of aggregated α-syn from the periphery to the CNS and in the progression of PD.The clarification of this problem will further reveal the pathogenesis of PD and provide an important experimental basis for the prevention and treatment of PD.To explore the role of the vagal afferent nerve in the progression of PD,after impairing the vagal afferent,the mice were treated with intragastric administration of rotenone.Using the behavioral test,immunofluorescence technology and western blot,we observed the motor behaviors and α-syn expression in ENS,DMV and SN.In addition,the expression of dopaminergic neurons,tyrosine hydroxylase(TH)expression and inflammation alteration were detected in the SN.The results were as follows:1.The body weight of mice in the rotenone-treated 1 month group was decreased significantly in the second(P<0.001),third(P<0.0001)and fourth(P<0.0001)week compared with the control group.The body weight of mice in the capsaicinrotenone treated 1 month group was decreased slower compared with the rotenonetreated 1 month group at the fourth week(P<0.05).The body weight of mice in rotenone-treated 3 month group was decreased compared with the control group in the first,third,fourth,eighth and twelfth week(P<0.001).The body weight of mice in the capsaicin-rotenone treated 3 month group was decreased slower at the fourth and twelfth week than rotenone-treated 3 month group(P<0.01).2.In the pole climbing test,turnaround and arrival time were prolonged in the rotenone-treated 1 month and 3 month group compared with that of the control.The arrival time of capsaicin-rotenone treated 3 month group was reduced by 36.9%compared with that of the control(P<0.001).3.In the open field test,the distance travelled,mean of velocity and the fraction of time exploring in center were decreased,and the time of immobility was increased in the rotenone-treated 1 month and 3 month group compared with the control group.In the capsaicin-rotenone treated 1 month group,the distance travelled was increased by 107.9%(P<0.0001),the time of immobility(P<0.0001)also was increased by 107.9%,and the mean of velocity was improved 21.4%(P<0.0001)compared with the rotenone-treated 1 month group.In the capsaicin-rotenone treated 3 month group,the distance travelled was increased by 56.9%(P<0.001),the mean of velocity was increased by 36.1%(P<0.05),and the fraction of time exploring in center was increased by 62.7%(P<0.05),and the time of immobility was decreased by 22.7%(P<0.001)compared with the rotenone-treated 3 month group.4.In the rotating test,the time of latency fall was reduced in rotenone-treated 1 month and 3 month group compared with that of the control.The latency time was increased by 51.1% in capsaicin-rotenone treated 1 month group compared with rotenone-treated 1 month group(P<0.05).The latency time was increased by 102.9%in capsaicin-rotenone treated 3 month group compared with rotenone-treated 3month group(P<0.001).5.The immunofluorescence staining and western blot showed the α-syn were no significant alterations in ENS between control,rotenone-treated and capsaicinrotenone treated groups.6.The immunofluorescence staining results showed that the expression of α-syn in DMV was increased in the rotenone-treated 1 month and 3 month group compared with the control.The expression of α-syn in DMV was decreased in the capsaicinrotenone treated 1 month and 3 month group compared with rotenone-treated 1month and 3 month group.7.Immunofluorescence staining showed the expression of TH in the SN was decreased in the rotenone-treated 1 month and 3 month group,while increased in capsaicin-rotenone 1 month and 3 month group.TH protein levels were increased by 54.0%(P<0.001)in the capsaicin-rotenone treated 1 month group than rotenonetreated 1 month group.TH protein levels were increased by 49.40%(P<0.05)in the capsaicin-rotenone treated 3 month group than rotenone-treated 3 month group.8.α-Syn levels in the SN were reduced by 32.3% in capsaicin-rotenone treated 3month group than rotenone-treated 3 month group(P<0.05).9.The activation of microglia in the SN had no significant change in the rotenonetreated 1 month and capsaicin-rotenone treated 1 month group.The activation of microglia was increased in the rotenone-treated 3 month group,and was decreased in the capsaicin-rotenone treated 3 month group.IL-6 protein levels in the SN were increased in the rotenone-treated 1 month and 3 month group and decreased capsaicin-rotenone treated 1 month and 3 month group.In summary,after intragastric administration of rotenone in mice,motor behavior was impaired,α-syn expression in the DMV and SN was increased and the microglia were activated in the SN.The above symptoms could be alleviated after the vagal afferent nerve was lesioned by capsaicin.This study showed the direct evidence that the vagal afferent nerve participated in the progression of PD and play an important role in PD pathophysiology.The impairment of vagal afferent nerve delays the progession of PD,which provide new strategies for the prevention of PD. |
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