The protective effect of repetitive transcranial magnetic stimulation on the nigrostriatal system in Parkinson's disease

Objective To investigate the effect of repetitive transcranial magnetic stimulation (rTMS) on dopaminergic neurons in substantia nigra and nigrostriate fibers in the striatum in cases of Parkinson's disease (PD).Methods Forty male C57BL/6J mice were randomly divided into a control group,a PD model group,a sham-rTMS (srTMS) group and an rTMS group with 10 mice in each group.A PD model was established by subcutaneous injection of a solution of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP),and the mice were treated with rTMS or sham rTMS for 14 days.Tyrosine hydroxylase (TH) expression in the substantia and striatum were detected using an immunohistochemical technique,and the corrected optical densities (CODs) of TH in the striatum were analysed using an image analysis system.The Nissl bodies were detected by Nissl staining.The morphological disposition of nerve fibers in the striatum was detected using Warthin-Starry staining.Results The fraction of neurons expressing TH decreased significantly more in the substantia nigras of mice in the rTMS group than in the control group,the PD group and the srTMS group.In the control group the neural plasm of dopaminergic neurons was full of dark blue and granular Nissl bodies.Many Nissl bodies were lost in the PD and srTMS groups,and the remaining Nissl bodies were colored lightly.Few Nissl bodies were lost in the rTMS group.Positive TH reactions in the striatum were significantly decreased in the rTMS group compared to the control group.The average COD was also significantly lower.But positive TH reactions in the striata of the rTMS group mice were significantly greater than in the PD and srTMS groups,and the average COD was significantly higher.In the control group,the disposition of nerve fibers in the striatum was typically fasciculated,concentrated and ordered; in PD and srTMS groups,many fibers were lost,and the remaining nerve fibers were rare,ruptured and scattered ; in the rTMS group fewer nerve fibers were lost and the disposition of the remaining fibers was more fasciculated,concentrated and ordered than in the PD and srTMS groups.Conclusion rTMS may play a role in treating Parkinson's disease by protecting dopaminergic neurons as well as nigrostriate fibers and by improving the synthesis and transport of dopamine. Key words: Transcranial magnetic stimulation; Substantia nigra; Corpus striatum; Parkinson's disease