The Correlation Between Iron And Alpha-synuclein In Different Brain Regions In Rotenone-treated Mice

Parkinson's disease(PD)is a common neurodegenerative disease characterized by the loss of dopaminergic(DA)neurons in the substantia nigra pars compacta(SNc)and the occurrence of Lewy-bodies(LBs),which is mainly composed of ?-synuclein(?-syn).PD is not only a regional disease referred to the SN,but a generalized disorder affecting peripheral and central nervous system(CNS).The typical motor symptoms include: resting tremor,rigidity,bradykinesia and postural reflex impairment and so on.Before the onset of motor symptoms,PD patients often have non-motor symptoms such as olfactory dysfunction,constipation,anxiety and orthostatic hypotension.Many studies based on PD patients and animals have found that iron levels in the SN are significantly increased,which is often accompanied with accumulation of ?-syn.Iron can promote the aggregation of ?-syn,as an iron metabolism-related protein,?-syn can also affect iron deposition.More than 90% of ?-syn in LBs is phosphorylated,and phosphorylated alpha-synuclein(phos-?-syn)may be more prone to accumulate.To investigate the distribution of iron and phos-?-syn deposition,12-month-old C57BL/6 male mice were given intragastric administration of rotenone for 1 week,2 weeks,3 weeks,1 month,2 months,and 3 months,and independent vehicle-treated control group was established.The changes of anxiety,function of autonomic nervous system,olfactory sensitivity,and motor coordination were measured by open field test(OFT),blood pressure measurement,olfactory test,and rotarod test.Perl's iron staining and immunohistochemical staining were used to detect changes in iron deposition and phos-?-syn positive cells in different brain regions of mice.The results are as follows: 1.The number of iron staining positive cells.The SN and Str of rotenone-treated mice significantly increased from 2 weeks to 3 months(P<0.05,n=6);the olfactory bu LBs (OB)of rotenone-treated mice significantly increased from 1month to 3 months (P<0.05,n=6);the locus coeruleus(LC)and the visual cortex(V)of rotenone-treated mice significantly increased from 2 months to 3 months(P<0.05,n=6);the dorsal motor nucleus of vagus(DMV),the raphe nucleus(RP),the frontal association cortex, (FrA)and the temporal association cortex(TeA)of rotenone-treated mice significantly increased only in 3 months(P<0.05,n=6);no changes were found in the ventral tegmental area(VTA)of rotenone-treated mice(P>0.05,n=5-6)compared to the vehicle-treated mice.2.The number of phos-?-syn positive cells.The SN,Str and OB of rotenone-treated mice significantly increased from 2 weeks to 3 months(P<0.05,n=6);the DMV,RP and LC of rotenone-treated mice significantly increased from 3 weeks to 3 months(P<0.05, n=6);the FrA,TeA and V of rotenone-treated mice significantly increased only in 3 months(P<0.05,n=6);no changes were found in the ventral tegmental area(VTA)of rotenone-treated mice(P>0.05,n=5-6)compared to the vehicle-treated mice.3.The weight of rotenone-treated mice were significantly decreased from 2 weeks to 6 weeks compared to vehicle-treated mice.(P<0.05,n=23).4.Higher anxiety level were observed in the rotenone-treated mice of 2 weeks group compared to vehicle-treated mice.(P<0.01,n=11-16).5.The systolic blood pressure(SBP)and diastolic blood pressure(DBP)were decreased inrotenone-treated mice of 2 weeks;the heart rate(HR)of mice were decreased in rotenone-treated mice of 1 month(SBP,P<0.01;DBP,P<0.05;MAP,P>0.05;HR, P<0.01;n=11-16)compared to the vehicle-treated mice.6.Impairment of olfactory function were observed in the rotenone-treated mice from 3 weeks to 3 months compared to vehicle-treated mice.(P<0.05,n=11-16).7.The motor coordination ability of rotenone-treated mice were significantly decreased from 2 months to 3 months compared to vehicle-treated mice.(P<0.05,n=11-15).In summary,the changes of iron caused by rotenone were chronologically performed: SN and Str;then OB;followed by LC and V;finally DMV,RP,FrA and TeA.The increase in the number of phos-?-syn positive cells in the mice brain was chronologically performed: SN,Str,OB;then DMV,RP,and LC;finally FrA,TeA,and V.The deposition of iron first appeared in the nigrostriatal system,not later than the increase of phos-?-syn.Rotenone can significantly decrease the body weight of mice from 2 weeks to 6 weeks,decrease SBP and DBP at 2 weeks,and induce olfactory injury from 3 weeks to 3 months.The ability of coordination in movement decreased from 2 months to 3 months.The non-motor symptoms caused by rotenone are earlier than the motor symptoms.The early non-motor symptoms of PD are lacking specificity in clinical.Therefore,developing a method for early detecting iron deposition in the brain will definitely promote the diagnosis and intervention of PD.