Differential vulnerability of dopamine receptors in the mouse brain treated with MPTP

We investigated the chronological changes of dopamine D1 and D2 receptors and dopamine uptake sites in the striatum and substantia nigra of mouse brain treated with 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP) by quantitative autoradiography using [3H]SCH23390, [3H]raclopride and [3H]mazindol, respectively. The mice received i.p. injections of MPTP (10 mg/kg) four times at intervals of 60 min, the brains were analyzed at 6 h and 1, 3, 7 and 21 days after the last the injection. Dopamine D2 receptor binding activity was significantly decreased in the substantia nigra from 7 to 21 days after MPTP administration, whereas such binding activity was significantly increased in the medial part of the striatum at 21 days. There was no alteration of dopamine D1 receptor binding activity in either the striatum or the substantia nigra for the 21 days. The number of dopamine uptake sites gradually decreased in the striatum and the substantia nigra, starting at 6 h after MPTP administration, and the lowest levels of binding activity were observed at 3 and 7 days in the striatum (18% of the control values in the medial part and 30% in the lateral part) and at 1 day in the substantia nigra (20% of the control values). These results indicate that severe functional damage to the dopamine uptake sites occurs in the striatum and the substantia nigra, starting at an early stage after MPTP treatment. Our findings also demonstrate the compensatory up-regulation in dopamine D2 receptors, but not dopamine D1 receptors, in the striatum after MPTP treatment. Furthermore, our results support the existence of dopamine D2 receptors, but not dopamine D1 receptors, on the nigral neurons. The present findings suggest that there are differential vulnerabilities to MPTP toxicity in the nigrostriatal dopaminergic receptor systems of mouse brain.     

Paraquat elicited neurobehavioral syndrome caused by dopaminergic neuron loss

The herbicide paraquat, bearing structural similarity to the known dopaminergic neurotoxicant MPTP, has been suggested as a potential etiologic factor in Parkinson's disease. Consideration of paraquat as a candidate neurotoxicant requires demonstration that systemic delivery produces substantia nigra dopaminergic neuron loss and the attendant neurobehavioral syndrome reflecting depletion of dopamine terminals within the striatum. To address these issues paraquat was administered systemically into adult C57 bl/6 mice, ambulatory behavior monitored, substantia nigra dopamine neuron number and striatal dopamine terminal density quantified. The data indicate that paraquat like MPTP elicits a dose-dependent decrease in substantia nigra dopaminergic neurons assessed by a Fluoro-gold prelabeling method, a decline in striatal dopamine nerve terminal density assessed by measurement of tyrosine hydroxylase immunoreactivity; and neurobehavioral syndrome characterized by reduced ambulatory activity. Taken together, these data suggest that systemically absorbed paraquat crosses the blood-brain barrier to cause destruction of dopamine neurons in the substantia nigra, consequent reduction of dopaminergic innervation of the striatum and a neurobehavioral syndrome similar to the well characterized and bona fide dopaminergic toxin MPTP.     

Time course of MPTP-induced degeneration of the nigrostriatal dopamine system in C57 BL/6 mice

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) is a parkinsonism-inducing dopamine (DA) neurotoxin most effective in primates. MPTP also causes a degeneration of both perikarya and axon terminals of the nigrostriatal DA neurons in C57 BL/6 mice. The time courses of the changes in tyrosine hydroxylase immunoreactive objects, endogenous DA concentrations and specifically bound 3H-mazindol as markers of the integrity of DA neurons were studied in substantia nigra and striatum of adult C57 BL/6 mice, after systemic treatment with MPTP or intranigral injections of the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA). A rapid decrease in the three parameters studied was found in the substantia nigra during the first 2 days after MPTP-treatment while the MPTP-induced effects in the striatum were more protracted and maximal reduction was observed 7 days after MPTP. A basically similar pattern was found when studying the 6-OHDA-induced anterograde degeneration of the nigrostriatal system. These results indicate that in C57 BL/6 mice, MPTP primarily destroys the DAergic perikarya with a subsequent anterograde degeneration of the striatal axon terminals, although a limited rapid destruction of some striatal terminals cannot be excluded.     

C57BL小鼠帕金森病模型多巴胺转运蛋白99mTc-TRODAT-1放射自显影研究

目的　评价不同损毁程度 Ｃ５７ Ｂ Ｌ 小鼠帕金森病（ Ｐ Ｄ）模型纹状体多巴胺转运蛋白（ Ｄ Ａ Ｔ）的变化。方法　根据腹腔注射 Ｍ Ｐ Ｔ Ｐ 的天数将小鼠分为 １、３、５ 和 ７ｄ 模型组以及对照组,静脉注射９９ｍ Ｔｃ Ｔ Ｒ Ｏ Ｄ Ａ Ｔ１６ｍ Ｃｉ,１ｈ 后处死行脑纹状体放射自显影,同时行免疫组化酪氨酸羟化酶（ Ｔ Ｈ）染色。结果　对照组的放射自显影可见９９ｍ Ｔｃ Ｔ Ｒ Ｏ Ｄ Ａ Ｔ１ 于纹状体部位有高度放射性聚集,且两侧纹状体基本相同。注射 Ｍ Ｐ Ｔ Ｐ １ｄ 者,其纹状体的放射性浓集比对照组有所下降。注射 Ｍ Ｐ Ｔ Ｐ ３、５ 及 ７ｄ 者,两侧纹状体的放射性浓集逐日降低,第 ７ｄ 者几乎消失。 Ｔ Ｈ 染色发现黑质 Ｔ Ｈ 阳性神经元亦随注射 Ｍ Ｐ Ｔ Ｐ 天数的增加而数量减少。结论　不同程度损毁的 Ｃ５７ Ｂ Ｌ 小鼠 Ｐ Ｄ 模型可模拟 Ｐ Ｄ 的发展过程,９９ｍ Ｔｃ Ｔ Ｒ Ｏ Ｄ Ａ Ｔ１ 作为 Ｄ Ａ Ｔ 的显影剂可用于早期诊断的神经显像学研究。     

The acute histopathology of MPTP in the mouse CNS

We found that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) rapidly induced cytopathological changes in the brain, involving some neurons selectively, as well as astrocytes and blood vessels. Dopaminergic neurons in the midbrain, as identified by immunostaining for tyrosine hydroxylase, were damaged as early as 2.5 hr after MPTP administration. Ultrastructurally, there was disruption of the endoplasmic reticulum and cytoplasmic condensation and vacuolation of the tyrosine hydroxylase reactive neurons in the substantia nigra as well as their axon terminals in the striatum. Perivascular edema was associated with vacuolation and swelling of astrocytic cytoplasm and rupture of perivascular foot processes. There was also capillary and arteriolar endothelial damage. Surprisingly, there was no clear correlation of MPTP-induced pathology with mitochondrial damage in any cell type. Biochemically, dopamine was depleted in the substantia nigra and the striatum within a few hours following MPTP administration. However, in the substantia nigra, homovanillic acid (HVA), one of the metabolites of dopamine, showed relatively less depletion than did dopamine by MPTP. These results may indicate that the turnover of dopamine was stimulated in the brain as a homeostatic mechanism.     

Neuroprotective properties of 17beta-estradiol, progesterone, and raloxifene in MPTP C57Bl/6 mice

Previous work from our laboratory showed prevention of 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) induced dopamine depletion in striatum of C57Bl/6 mice by 17beta-estradiol, progesterone, and raloxifene, whereas 17alpha-estradiol had no effect. The present study investigated the mechanism by which these compounds exert their neuroprotective activity. The hormonal effect on the dopamine transporter (DAT) was examined to probe the integrity of dopamine neurons and glutamate receptors in order to find a possible excitotoxic mechanism. Drugs were injected daily for 5 days before MPTP (four injections, 15 mg/kg ip at 2-h intervals) and drug treatment continued for 5 more days. MPTP induced a decrease of striatal DAT-specific binding (50% of control) and DAT mRNA in the substantia nigra (20% of control), suggesting that loss of neuronal nerve terminals was more extensive than cell bodies. This MPTP-induced decrease of striatal [(125)I]RTI-121 specific binding was prevented by 17beta-estradiol (2 microg/day), progesterone (2 microg/day), or raloxifene (5 mg/kg/day) but not by 17alpha-estradiol (2 microg/day) or raloxifene (1 mg/kg/day). No treatment completely reversed the decreased levels of DAT mRNA in the substantia nigra. Striatal [(125)I]RTI-121 specific binding was positively correlated with dopamine concentrations in intact, saline, or hormone-treated MPTP mice. Striatal NMDA-sensitive [(3)H]glutamate or [(3)H]AMPA specific binding remained unchanged in intact, saline, or hormone-treated MPTP mice, suggesting the unlikely implication of changes of glutamate receptors in an excitotoxic mechanism. These results show a stereospecific neuroprotection by 17beta-estradiol of MPTP neurotoxicity, which is also observed with progesterone or raloxifene treatment. The present paradigm modeled early DA nerve cell damage and was responsive to hormones.     

Role of reactive nitrogen and reactive oxygen species against MPTP neurotoxicity in mice

There is growing evidence indicating that reactive nitrogen species (RNS) and reactive oxygen species (ROS) are a major contributor to the pathogenesis and progression of Parkinson's disease. Here we investigated whether edaravone (free radical scavenger), minocycline (inducible nitric oxide synthase, iNOS inhibitor), 7-nitroindazole (neuronal NOS, nNOS inhibitor), fluvastatin (endothelial NOS, eNOS activator) and pitavastatin (eNOS activator) can protect against MPTP neurotoxicity in mice under the same condition. The present study showed that 7-nitroindazole could protect dose-dependently against the striatal dopamine depletions in mice 5 days after MPTP treatment. In contrast, edaravone, minocycline, fluvastatin and pitavastatin did not show the neuroprotective effect on MPTP-induced striatal dopamine depletion. Our immunohistochemical study showed that TH (tyrosine hydroxylase) and DAT (dopamine transporter) immunoreactivity was decreased significantly in the striatum and substantia nigra 5 days after MPTP treatment. The administration of 7-nitroindazole showed a protective effect against the severe reductions in levels of TH and DAT immunoreactivity in the striatum and substantia nigra 5 days after MPTP treatment. Furthermore, our Western blot analyses study showed the remarkable loss of TH protein levels in the striatum 5 days after MPTP treatment. In contrast, 7-nitroindazole prevented a significant loss in TH protein levels in the striatum 5 days after MPTP treatment. On the other hand, GFAP (glial fibrillary acidic protein) immunoreactivity increased significantly in the striatum and substantia nigra, 5 days after MPTP treatment. 7-Nitroindazole ameliorated severe increases in number of GFAP immunoreactive astrocytes in the striatum and substantia nigra 5 days after MPTP treatment. Furthermore, our Western blot analyses study showed the increase of GFAP protein levels in the striatum 5 days after MPTP treatment. 7-Nitroindazole prevented a significant increase in the GFAP protein levels in the striatum 5 days after MPTP treatment. The present results indicate that 7-nitroindazole can protect dose-dependently against the striatal dopamine depletions in mice 5 days after MPTP treatment. In contrast, edaravone, minocycline, fluvastatin and pitavastatin did not show the neuroprotective effect on MPTP-induced striatal dopamine depletions. These findings demonstrate that the overexpression of nNOS may play a major role in the neurotoxic processes of MPTP, as compared to the production of ROS, the overexpression of iNOS and the modulation of eNOS. Thus, our findings provide strong evidence for neuroprotective properties of nNOS inhibitor in this animal model of Parkinson's disease.     

GM1 ganglioside-induced recovery of nigrostriatal dopaminergic neurons after MPTP: an immunohistochemical study

The administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to mice results in the loss of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) from the mouse striatum and a loss of cells containing tyrosine hydroxylase (TH)-immunoreactivity from the substantia nigra. The cells that remained in the nigra after MPTP treatment were smaller in diameter than normal cells. Treatment with GM1 ganglioside beginning 24 h after establishing the MPTP lesion resulted in partial restoration of DA and DOPAC content in the striatum and an increase in the diameter of the TH-immunoreactive nigra cells. It appears, therefore, that treatment of MPTP-intoxicated mice with GM1 ganglioside results in the partial restoration of both the biochemistry and morphology of dopaminergic neurons.     

Diethyldithiocarbamate causes nigral cell loss and dopamine depletion with nontoxic doses of MPTP

Although nontoxic when administered alone, diethyldithiocarbamate (DDC) is known to enhance the dopamine-depleting effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the mouse striatum. The purpose of the present study was twofold: (i) to carefully characterize the effects of DDC on MPTP-induced degeneration of dopaminergic neurons in substantia nigra pars compacta using unbiased, stereological cell counting techniques and (ii) to determine whether or not DDC can convert a nontoxic dose of MPTP into one which is clearly toxic on dopaminergic neurons in the substantia nigra. A single low dose of MPTP (15 mg/kg intraperitoneally (ip)) was used for these studies, which failed to induce any neurochemical or histological effects on the nigrostriatal system of C57BL/6 mice when administered alone. However, when animals were pretreated with DDC (400 mg/kg ip), the same dose of MPTP resulted in a 50% loss of neurons in the substantia nigra pars compacta, as well as a 70% reduction in striatal dopamine (DA). A 31% reduction of DA in the ventral mesencephalon was also seen. This combined regimen of DDC and MPTP was not significantly different from a maximally tolerated "toxic" dose of MPTP alone (15 mg/kg x 4, 1 h apart, ip). As expected, animals receiving DDC alone did not show any dopamine depletion nor nigral neuronal loss. The present study confirms previous work suggesting that DDC enhances MPTP-induced nigral cell loss and shows for the first time that DDC can "unmask" MPTP toxicity. These observations could have implications for theories on the cause of Parkinson's disease.     

Protection of dopaminergic neurons with a novel astrocyte modulating agent (R)-(-)-2-propyloctanoic acid (ONO-2506) in an MPTP-mouse model of Parkinson's disease

We examined the neuroprotective effects of a novel astrocyte-modulating agent, (R)-(-)-2-propyloctanoic acid (ONO-2506), in a mouse model of Parkinson's disease. Male C57BL/6 mice received four intraperitoneal injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (10 mg/kg) at 1-h intervals. Dopamine content in the striatum, measured with HPLC 3 days after MPTP injection, was reduced to 23% of control. But this dopamine depletion was dose-dependently prevented by repeated treatments with ONO-2506 (3, 10 and 30 mg/kg, i.p.) administered 1, 6, 24 and 48 h after MPTP injection (51% of control in 30 mg/kg group, p<0.01). ONO-2506 treatment (30 mg/kg) started after 6 h, followed by treatments at 24 and 48 h, also prevented the reduction of dopamine content (42% of control vs. 11% of control in the saline-treated group, p<0.01). We also performed immunohistochemistry for tyrosine hydroxylase (TH) and glial fibrillary acidic protein (GFAP). The MPTP injection resulted in a loss of TH-positive dopaminergic neurons (42% of control, p<0.01) in the substantia nigra after 7 days, but ONO-2506 treatment prevented this neuronal loss (70% of control, p<0.01). The MPTP injection led to reactive astrocytosis in the striatum after 7 days, but ONO-2506 induced earlier, moderate astrocytic activation after 3-7 days. These findings show that ONO-2506 protects dopaminergic neurons against MPTP neurotoxicity probably through facilitating astrocytic support for neuronal recovery from injury. Pharmacological modulation of astrocytes may offer a novel therapeutic strategy for Parkinson's disease.     

Matrix metalloproteinase-9 is elevated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism in mice

Matrix metalloproteinases (MMPs) are proteolytic enzymes capable of degrading components of the extracellular matrix. Recent evidence has implicated MMPs in the pathogenesis of neurodegenerative diseases as Alzheimer’s disease and amyotrophic lateral sclerosis. In this study, we investigated the involvement of MMP-9 (gelatinase B) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson’s disease using zymography, immunohistochemistry, and Western blot analysis. The activity of MMP-9 was upregulated at 3 h after MPTP injection in the striatum and after 24 h in the substantia nigra. Although MMP-9 expression decreased in the striatum by 72 h, it remained elevated in the substantia nigra compared to controls up to 7 d after MPTP administration. Immunohistochemistry showed that neurons and microglia are the source of MMP-9 expression after MPTP administration to mice. Treatment with a hydroxamate-based MMP inhibitor, Ro 28-2653 significantly reduced dopamine depletion and loss of tyrosine hydroxylase immunoreactive neurons in the substantia nigra pars compacta. MMP-9 expression as measured via zymography in the substantia nigra was reduced by the MMP inhibitor. These results indicate that MMP-9 is induced after MPTP application in mice and that pharmacologic inhibition of MMPs protects against MPTP neurotoxicity.     

Evaluation of a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57 black mouse model for parkinsonism

We evaluated neurochemically, behaviorally, and neuropathologically the availability of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57 black (BL) mice as a model for Parkinson's disease. The dopamine and 3,4-dihydroxyphenyl acetic acid content in the striatum, measured by high-performance liquid chromatography with an alectrochemical detector, decreased by 70% at 10 and 20 days after the withdrawal of MPTP (30 mg/kg, i.p. twice daily for 5 days). During these days, the mice showed a decrease in locomotor activity and exhibited akinesia in both pole and traction tests. Light microscopically, 44% of the MPTP-treated mice showed neuronal degeneration in the substantia nigra 1 month after the withdrawal (damaged group), and 56% showed no change (undamaged group). Morphometric analysis revealed that the number of neurons in the substantia nigra decreased by 33% on the average in both groups. Electron microscopically, an electron-dense degeneration of most neurons was seen in the substantia nigra of the damaged group, and even in the undamaged group, loss of rough endoplasmic reticulum and mitochondrial deformity were seen in 50–70% of the neurons. Electron-dense bodies were seen in the striatum of both groups. These results show the validity of the MPTP-treated C57 BL mice as a suitable model fro parkinsonism, including Parkinson's disease.     

Plasticity of the nigrostriatal system in MPTP-treated mice

In order to compare the recovery capacity of the nigrostriatal system between adult and old mice, MPTP hydrochloride was administered to 48 BL/C57 male mice, which were sacrificed 24 h or 10 d after the second dose. The animals were divided into four groups, based on age (adult or old) and moment of sacrifice (24 h or 10 d). The detailed morphology of the neurons and the cellular processes of the substantia nigra pars compacta and the striatum were studied using the Golgi method. Immunostaining with a polyclonal glial fibrillary acidic protein antiserum using the peroxidase-antiperoxidase technique was performed to study the glial response. Striatal catecholamines were determined to correlate the biochemical data with the morphological changes. Significant neuronal changes of cellular processes were observed in substantia nigra pars compacta from all MPTP-treated mice, consisting of swelling and distortion of cellular bodies, discontinuous thickness, and nodulations of dendrites with baded aspect. Axons showing focal swelling and nodulations were also found in the neuropil of silver impregnated striata. Marked gliosis with reactive astrocytes in substantia nigra and striatum from all the old treated mice was found. Recovery was only observed in adult mice sacrificed 10 d after withdrawal. At this time, all the old MPTP-treated mice showed marked neuronal changes and a persistent marked gliosis. As expected, 24 h after the MPTP treatment, a marked depletion of dopamine and its metabolites was found in all the animals; at 10 d, the depletion was partially reversed in the adult group. These data correlate well with the observed morphological changes. Our results suggest that, in mice, deterioration of dendritic and axonal neuropil constitutes a significant causal factor of the MPTP neurotoxicity. These features are related to the age of the animals and the integrity of the plasticity phenomena, which appear to be altered in old mice.     

Mice lacking alpha-synuclein are resistant to mitochondrial toxins

Abnormalities in the function of alpha-synuclein are implicated in the pathogenesis of Parkinson's disease (PD). We found that alpha-synuclein-deficient mice are resistant to MPTP-induced degeneration of dopaminergic neurons. There was dose-dependent protection against loss of both dopamine in the striatum and dopamine transporter (DAT) immunoreactive neurons in the substantia nigra. These effects were not due to alterations in MPTP processing. We found that alpha-synuclein-deficient mice are also resistant to both malonate and 3-nitropropionic acid (3-NP) neurotoxicity. There was reduced generation of reactive oxygen species in alpha-synuclein-deficient mice following administration of 3-NP. These findings implicate alpha-synuclein as a modulator of oxidative damage, which has been implicated in neuronal death produced by MPTP and other mitochondrial toxins.     

Oestrogens prevent loss of dopamine transporter (DAT) and vesicular monoamine transporter (VMAT2) in substantia nigra of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mice

Previous results from our laboratory have shown that 17beta-oestradiol prevents 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) striatal dopamine depletion. 17beta-oestradiol, oestriol and oestrone are the naturally occurring oestogens in humans. Using various dopamine markers, the present study investigated whether oestrone and oestriol such as 17beta-oestradiol have neuroprotective activity in MPTP-treated mice. Male mice were treated with 17beta-oestradiol, oestriol or oestrone for 5 days before and after MPTP administration, and were compared with nonlesioned mice receiving the same treatment. Striatal concentrations of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), were assayed by high-performance liquid chromatography. Dopamine transporter (DAT) and vesicular monoamine transporter (VMAT2) specific binding were measured by autoradiography. DAT, VMAT2 and tyrosine hydroxylase mRNA levels were measured by in situ hybridisation. MPTP induced a loss of DAT and VMAT2 specific binding in the striatum and substantia nigra, as well as a decrease of VMAT2 mRNA in the substantia nigra. 17beta-oestradiol treatment prevented the loss of these dopaminergic markers, as well as striatal concentrations of dopamine, DOPAC and HVA. Mice receiving oestriol and oestrone showed catecholamine concentrations comparable to MPTP mice. Oestriol treatment had no effect on dopaminergic markers in MPTP mice whereas oestrone prevented striatal DAT loss and the decrease of VMAT2 mRNA in the substantia nigra. In nonlesioned mice, 17beta-oestradiol, oestriol or oestrone had no effect on all the dopaminergic markers investigated. In conclusion, a weak or a lack of effect of oestriol and oestrone was observed compared to 17beta-oestradiol in MPTP mice and none of these steroids had an effect in nonlesioned mice. A DAT and VMAT2 specific binding decrease after MPTP in the striatum and substantia nigra, as well as a decrease of substantia nigra VMAT2 mRNA, was observed and could be prevented by oestradiol.     

Estrogen down-regulates glial activation in male mice following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine intoxication

Emerging evidence suggests beneficial effect of estrogen for Parkinson's disease (PD), yet the exact mechanisms implicated remain obscured. Activated glia observed in MPTP mouse model and in PD may participate in the cascade of deleterious events that ultimately leads to dopaminergic nigral neuronal death. In vitro studies demonstrate that estrogen can modify the microglial and astroglial expression of inflammatory mediator, such as cytokines and chemokines implicated in neuroinflammation and neurodegeneration. To determine whether estrogen-elicited neuroprotection in PD is mediated through glia, adult male C57Bl/6 mice were treated with 17beta-estradiol (E2) for a total of 11 days. Following 5 days of pretreatment with E2, they were injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on the sixth day. The brains were collected on day 11. Immunohistochemistry and quantitative study were used to assess the number of tyrosine hydroxylase-immunoreactive (TH-IR) neurons in the substantia nigra pars compacta (SNpc) and that of activated astrocytes and activated microglia in the SNpc and the striatum. Pretreatment with E2 decreased the loss of TH-IR nigral neurons and diminished the deficit of TH-IR striatal fibers triggered by MPTP. The neuroprotective effect of E2 was coincident with an attenuation of a glial response within the nigra and the striatum. These findings suggest that the neuroprotective effects of E2 evidenced in MPTP mouse model might mediate through an inhibition of reactive glia. However, direct neuroprotective effects of E2 upon TH-IR neurons cannot be excluded.     

The Neurotoxin MPTP Causes Degeneration of Specific Nucleus A8, A9 and A10 Dopaminergic Neurons in the Mouse

The neurotoxin MPTP has been used to create an animal model of Parkinson's disease in the mouse, in part, because it causes a significant loss of dopaminergic neurons in the substantia nigra (nucleus A9). The purpose of the present study was to determine whether MPTP also causes degeneration of midbrain dopaminergic neurons in nuclei A8 and A10 in the mouse, as occurs in humans with Parkinson's disease. Two commonly used strains of mice were used: FVB/N and C57BL/6. MPTP was administered in cumulative doses of 50—300 mg/kg. Seven days later, dopamine concentrations were measured in the striatum using high performance liquid chromatography, and midbrain dopaminergic neurons were identified using an antibody against tyrosine hydroxylase. The cell locations were mapped with a computer imaging system. In the FVB/N strain, there was a dose-dependent decrease in striatal dopamine concentrations. Although the highest dose (300 mg/kg) caused an 86% reduction in striatal dopamine concentrations, there was only a moderate and non-significant loss of midbrain dopaminergic neurons. In the C57BL/6 strain, however, a high dose of MPTP (240 mg/kg) caused a significant reduction in both striatal dopamine concentrations (95%), and midbrain dopaminergic cells; 69% loss of nucleus A8 cells, 75% loss of nucleus A9 cells, and in nucleus A10 subnuclei there was 42% loss of ventral tegmental area cells, 55% loss of interfascicular nucleus cells, and no loss of cells in the central linear nucleus. These data (1) provide further evidence for differential susceptibility to MPTP toxicity among different mouse strains, (2) indicate that a significant depletion of striatal dopamine is not necessarily due to degeneration of midbrain dopaminergic neurons, (3) provide the precise locations of midbrain dopaminergic cells that are vulnerable to MPTP, which will aid future studies that seek to determine the mechanism/s by which MPTP selectively destroys only certain midbrain dopaminergic neurons, and (4) indicate that MPTP produces midbrain dopaminergic neuronal degeneration in the same nuclei in the C57BL16 mouse that degenerate in humans with Parkinson's disease..     

重复经颅磁刺激治疗MPTP帕金森病模型小鼠的疗效观察

目的观察重复经颅磁刺激对MPTP帕金森病模型小鼠的治疗效果。方法于雄性C57BL/6J小鼠皮下注射MPTP制备帕金森病动物模型,24 h后进行重复经颅磁刺激(刺激频率1.00 Hz、刺激强度1.00 T、刺激时间25 s/次,共刺激5个序列,1次/d)。Rotarod实验评价小鼠身体协调能力和连续运动能力,免疫组织化学染色观察重复经颅磁刺激前后黑质区酪氨酸羟化酶阳性神经元数目和纹状体区酪氨酸羟化酶阳性神经纤维变化,高效液相色谱-电化学法检测重复经颅磁刺激对帕金森病小鼠纹状体多巴胺表达水平的影响。结果重复经颅磁刺激组小鼠停留于旋转杆上的圈数(85.89±3.74)、黑质区酪氨酸羟化酶阳性神经元数目(36.67±3.82)和纹状体多巴胺表达水平(258.70±1.06)均高于单纯帕金森病模型组(59.71±8.33,31.67±3.35,152.35±1.64;均P=0.000)。结论重复经颅磁刺激可改善帕金森病小鼠运动协调能力,保护受损黑质区酪氨酸羟化酶阳性神经元及纹状体区酪氨酸羟化酶阳性神经纤维,提高纹状体多巴胺及其代谢产物水平。     

The effect of MPTP on uridine uptake in murine nerve cells

Sixty, 3-month-old, male Theiler mice were injected with 1 mg 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) each i.p. Six groups of 5 animals each were then injected with 0.25 mCi [5-H3]uridine i.v. at intervals of 6h, 1,2,5,7 and 9 weeks after MPTP injection and each group was killed 1 h after uridine injection. Microautoradiograms were performed and the grain number determined in nerve cell nuclei in the striatum, substantia nigra and cerebral cortex. An initial increase in uridine uptake was found in substantia nigra, followed by a decrease during the following 9 weeks. A decrease in uptake occurred in the striatum from weeks 5-9, but without any initial increase. An increase in uptake was observed in the cortex 2 weeks after MPTP injection. Thus, in mice, a single injection of MPTP has a significantly prolonged effect upon the basic metabolic process (RNA synthesis) in substantia nigra and striatum. Selegiline, which causes a significant decrease in uridine uptake, also protects nerve cells from the effect of MPTP. The amount of dopamine in striatum and substantia nigra following MPTP did not change significantly during the 9 weeks. However, the amount of dihydroxyphenylalanine (DOPA) increased in both these areas during this period.     

GM1 ganglioside treatment promotes recovery of striatal dopamine concentrations in the mouse model of MPTP-induced parkinsonism

GM1 ganglioside (GM1) has in the past been reported to promote regenerative sprouting and functional recovery in both central and peripheral nervous systems. The present experiments were performed in order to investigate whether GM1 might have any therapeutic effect on young mice who had been exposed to the Parkinson-producing neurotoxin MPTP. GM1 caused moderate to dramatic increases in striatal dopamine levels, depending upon duration of exposure to GM1, in animals previously exposed to MPTP. Furthermore, the effects of GM1 on enhancing striatal dopamine levels were apparent when GM1 administration was delayed until 3 days after the last MPTP injection was given and these effects were not reversed when GM1 was withdrawn. Tyrosine hydroxylase (TH) immunohistochemistry of the striatum demonstrated increased numbers of TH-positive fibers and TH-positive terminal fields in GM1-treated animals as compared to animals that received only MPTP. TH immunohistochemistry of the substantia nigra revealed little or no loss of parts compacta neurons in the MPTP-treated mice. On the basis of these observations, GM1 appears to increase the dopamine content of the striatum by promoting or stimulating regenerative sprouting of dopaminergic terminals and perhaps collateral sprouting from remaining intact fibers in the MPTP model of Parkinsonism in the young mouse. We suggest that GM1 ganglioside may hold some promise as a potential adjunct in the treatment of Parkinson's Disease.