Experimental Studies Of 7,8-DHF,A Trkb Agonist,Treatment On L-DOPA-induced Dyskinesia In A Rat Model Of Parkinson's Disease

Part 1 Study of 7,8-DHF,a TrkB agonist,on behaviour of L-DOPA-induced dyskinesia in a rat model of Parkinson's diseaseObjective:To study the effects of 7,8-dihydroxyflavone(7,8-DHF),a Tyrosine kinase B(TrkB)agonist,on behaviour of L-DOPA-induced dyskinesia(LID)in a rat model of Parkinson' s disease(PD).Methods:We established Parkinson' s disease rat model by destroying the right medial forebrain with 6-hydroxydopamine(6-OHDA)in SD rats.Next,60 successful PD rats were randomly separated into 6 groups:Nacl solution(NS),L-DOPA,L-DOPA+7,8-DHF(5mg/kg),L-DOPA+7,8-DHF(10mg/kg),L-DOPA+7,8-DHF(20mg/kg)and 7,8-DHF(20mg/kg).Rats were injected intraperitoneally with L-DOPA or NS twice daily for 21 days,30 mins before that 5mg/kg,10mg/kg,20mg/kg 7,8-DHF or vehicle was treated everyday.Behavioral tests of abnormal involuntary movement(AIM),forepaw adjusting steps and rotational response duration were recorded on day 2,9,11,18 and 21.Results:1.Compared with L-DOPA group,axial AIM scores of L-DOPA+7,8-DHF(10mg/kg)group were decreased on day 9,11 and 18(P<0.05);Compared with L-DOPA group,limb,orolingual and total AIM scores of L-DOPA+7,8-DHF(10mg/kg)group were decreased on day 9,11,18 and 21(P<0.05);Axial,limb,orolingual and total(axial,limb and orolingual)AIM scores of L-DOPA+7,8-DHF(20mg/kg)group were decreased on day 9,11,18 and 21,compared with L-DOPA group(P<0.05).But,7,8-DHF of 5mg/kg failed to improve L-DOPA-induced dyskinesia in PD rats(P>0.05).2.L-DOPA+7,8-DHF group had no significant difference between L-DOPA group on forepaw adjusting steps and rotational response duration(P>0.05).Conclusion:7,8-DHF,as a TrkB agonist,markedly ameliorated behavior of L-DOPA-induced dyskinesia in PD rats,without diminishing anti-parkinsonian effect of L-DOPA.Part 2 Study of the role of 7,8-DHF,a TrkB agonist,in transcriptional level of TrkB receptor in striatum of L-DOPA-induced dyskinesia in a rat model of Parkinson's diseaseObjective:To explore level of tyrosine hydroxylase(TH)in substantia nigra,transcriptional level of brain-derived neurotrophic factor(Bdnf)and level of TrkB,pTrkB,cAMP-response element binding protein(CREB)and pCREB in striatum effected by injecting with 7,8-DHF intraperitoneally.Methods:The striatum and substantia nigra of rats in four groups(NS,L-DOPA,L-DOPA+7,8-DHF(20mg/kg)and 7,8-DHF(20mg/kg))were dissected after behavioral tests on day 21.Western blot was used to detect level of TH in substantia nigra and phosphorylation of TrkB and CREB in striatum.Quantitative RT-PCR was used to detect BDNF mRNA in the striatum.Immunohistochemistry staining was used to count TH neurons i.n substantia nigra.Results:1.7,8-DHF group had no significant difference between L-DOPA group on level of TH in lesioned substantia nigra(P>0.05).2.Compared to L-DOPA group,level of pTrkB markedly increased in bilateral striatum of L-DOPA+7,8-DHF(20mg/kg)group(P<0.01).Compared to NS group,Level of pTrkB increased in bilateral striatum of 7,8-DHF group(P<0.001).3.Compared to L-DOPA group,transcriptional level of Bdnf and level of pCREB markedly increased in lesioned striatum of L-DOPA+7,8-DHF(20mg/kg)group(P<0.05).Conclusion:7,8-DHF activated TrkB receptor,and then phosphorylation of TrkB receptor initiates CREB activation,subsequently upregulates expression of its downstream gene Bdnf.