Electrochemical And Histochemical Study On Relationship Between Iron Concentration And Degeneration Of Dopaminergic Neurons In Substantia Nigra Of Rat

Parkinson's disease is a progressive neurodegenerative disorder associated with the loss of dopamine neurons originating in the zona compacta of the substantia nigra (SNc) and terminating in the caudate and putamen (CPu). This disorder is characterized symptomatically by akinesia, tremor and rigidity. Extensive studies have indicated that iron levels increased in the SN of parkinsonian patients, and this metal catalyzes the fomation of free radicals which participate in the cascade of events ending in cell death. The increase of iron content may be involved in the etiology of PD. 6-OHDA unilaterally lesioned rat is believed to be a classic model of PD. Typically, rats develop unilateral movement deficiencies coupled with apomorphine-induced rotation behavior at least one week after an ipsilateral 6-OHDA lesion of the nigrostriatal dopamine (DA) system. So, most studies have concentrated on long-term behavioral and morphological effects that occur one week following the administration of 6-OHDA, or when dopamine (DA) loss exceeds 90% of total dopamine in the CPu. However, neuroanatomical and biochemical changes likely appear almost immediately upon administration and uptake of 6-OHDA. Thus we utilized the 6-OHDA unilaterally lesioned rats in the present study to investigate the acute time course of changes of histochemistry,neurochemistry and electrochemistry in SN and CPu. Using fastcyclic Voltammetry (FCV), we monitored DA release from caudate putamen (CPu) of 6-OHDA unilaterally lesioned rats. DA release was evoked by electrical stimulation of medial forbrain bundle (MFB). Additionally, the changes of iron in SN was measured by Atomic Absorption/Flame Emission Spectrophotometer and iron staining. Using tyrosine hydroxylase (TH) immunochemistry , we examined cell death in the SN. The results are as follows:1. One day after a unilateral 6-OHDA injected into MFB, there was a 45% reduction in the density of TH immunoreactive cells on the lesioned side. Three days after the 6-OHDA injection, 66% reduction was observed.2. One day after a unilateral 6-OHDA injected into MFB, the SN of lesioned side showed an increase in iron staining intensity in comparision with the contralateral unlesioned side and normal rats. There was no difference in iron staining of lesioned side between groups of one day postlesioning and three days postlesioning.3. One day after a unilateral 6-OHDA injected into MFB, iron concentration increased in ipsilateral SN compared with contralateral unlesioned side and normal rats.There was no difference in iron concentration of lesioned side between one day postlesioning and three days postlesioning.4. One day or three days after a unilateral 6-OHDA injected into MFB, the DA release in CPu of lesioned side did not change,Abstract Electrochemical and Hisochemical Study on Relationship... compared with the normal and nonlesioned side.Taking these together, it suggests that one day after 6-OHDA(19.8ug/5.5ul) injected into MFB, there is a 45% reduction in the density of TH immunoreactive cells on the lesioned side, and nigral iron increases while DA release in CPu does not change.It has been confirmed that gross behavial deficits do not occur unless more than 90% of dopaminergic neurons have degenerated. That means, immence compensatory mechanism of DA system have covered the process of PD. So with the 6-OHDA unilaterally lesioned rat to examine the acute time course of changes of histochemistry, neurochemistry and electrochemistry in SN and CPu, our study provides experimental evidence for the relationship between iron and PD, and suggests using chelator in the early stage of the disease to reduce high brain iron might be a strategy for the prevention and treatment of PD.