ABSTRACT
Objective To explore the relationship between the genesis of dyskinesia and the degree of substantia nigra lesion in Parkinson disease(PD).Methods The hemi-parkinsonian rat model was established by injecting 6-OHDA stereotaxically to right medial forebrain bundle(MFB). Then the hemi-parkinsonian rat was injected intraperitoneally with levodopa methylester(25 mg?kg~(-1)?d~(-1),twice a day)for 21 days,the abnormal involuntary movements were estimated.After being sacrificed,the midbrain was removed,and the injured degree of dopaminergic neurons at substantia nigra was observed by tyrosine hydroxylase immunohistochemistry staining.The relationship between the abnormal involuntary movement scores and dopaminergic neurons loss at substantia nigra was evaluated by sigmoid equation analysis by using Excel software.Results The apomorphine-induced rotation rate above 7 r/min was found in 10 of 25 rats,those rats were regarded as successful hemi-parkinsonian model rats.After the treatment with levodopa methylester,8 of 10 rats displayed abnormal involuntary movements,including stereotype and contralateral rotation,the types of movements varied.Abnormal involuntary movements were appeared in the rats with dopaminergic neurons loss above 90%.The positive relationship was observed between the degree of lesion in substantia nigra and the severity of abnormal involuntary movements.Conclusions The severe loss of dopaminergic neurons at substantia nigra probably plays a role in the development of levodopa-induced dyskinesia in patient with Parkinson disease.
ABSTRACT
Objective To investigate cellular and behavioural effects of 5-HT1A receptor agonist 8- OH-DPAT in a rat model of levodopa-induced motor complications.Methods The hemi-parkinsonian rat model was produced by stereotaxically injecting 6-OHDA to right medial forebrain bundle(MFB).Two sets of experiments were performed.First,rats were intrapefitoneally treated with levodopa 50 mg/kg plus benserazide 12.5 mg/kg twice a day for 22 days.On day 23,rats intraperitoneally received either 8-OH- DPAT(1 mg/kg)or 8-OH-DPAT plus WAY-100635(0.1 mg/kg)or dissolvent with each levodopa dose as controls.In the second set,rats were intraperitoneally treated either with levodopa(50 mg/kg)plus 8-OH- DPAT(1 mg/kg)or levodopa 50 mg/kg plus dissolvent,administered twice daily for 22 consecutive days. Rotational duration and frequency of off period were estimated.After sacrificed,subcellualr distribution of GluR1 and GluR1Ser845 phosphorylation was observed by Western blot.Results 8-OH-DPAT,reversing the shortened rotational duration induced by levodopa,prolonged the rotational duration by 27.8%?6.1% and reduced the frequency of failures to levodopa by 7.2%?1.7%.Co-administration of WAY-100635,a 5-HT1A receptor antagonist,with 8-OH-DPAT eliminated the effect of 8-OH-DPAT on motor complications, indicating that the observed 8-OH-DPAT responses were probably mediated via the 5-HT1A autoreceptor. Moreover,8-OH-DPAT could regulate subcellular distribution of GluR1 and reduce hyperphosphorylation of GluR1 Ser845 by 22.1%?3.5%,which was closely associated with levodopa-induced motor complications. Conclusions These results suggest that pharmaceuticals stimulating 5-HT1A receptors could be useful in the treatment and prevention of the motor complications in parkinsonian patients.