A Quantitative Study of Cell Death of nigral neurons in Rat Model of Parkinson's disease

초록

Background: The purpose of this study was first to make a rat model of Parkinson’s disease by complete transection of nigrostriatal pathway to investigate the degree and time course of retrograde neuronal death in substantia nigra pars compacta (SNpc). The second aim was to identify which subpopulation of these dopaminergic neurons may be more vulnerable or resistant to axotomy. Also, a preliminary study was conducted to observe whether a peripheral nerve graft implanted close to the transection could rescue these neurons. Methods: A retrograde tracer, DiI, was injected into striatum of both sides 7 days prior to the transection. A modified technique involving transection of medial forebrain bundle (MFB) at 1 mm rostral to tip of SN with a custom-designed wire knife was used. Animals were assigned to each time interval group (~16 weeks). Degree and location of cell death, and counting of survived neurons was done by tyrosine hydroxylase ( T H ) - i m m u n o h i s t o c h e m i s t r y, and computer image software (SigmaScan) was used for measurement and mapping. Results: DiI labelled SNpc neurons represented over 90% of TH(+) neurons in all groups including normal groups. Death of nigral neurons progressed over several weeks, but after 4 weeks, only 5.1%-7.0% of neurons remained when compared to the intact side. However, by double labeling, it was demonstrated that these remaining neurons most likely have contralateral projections. The size of the neurons also decreased significantly. Surviving neurons were located mostly within the medial half of SN close to ventral tegmental area (VTA). Completeness of lesion was correlated with the absence of TH-immunoreactivity in the striatum. When a tibial nerve is implanted (autograft, n=8) into MFB after its transection and examined after 16 weeks, there was a substantial number of surviving nigral neurons (~ 35%). Conclusions: With this modified technique, a complete cell death in SNpc is seen by 4 weeks after transection of MFB. Neurons in the medial region survived longer than those in lateral group. A substantial regeneration of SN neurons after peripheral nerve graft implantation indicates that it should be possible to implant a graft between the SN or MFB and denervated striatum in order to determine whether dopaminergic reinnervation and functional improvement occurs.