Neuroglial responses to the dopaminergic neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mouse striatum

Neuroprotective effects of 2,4-dinitrophenol in an acute model of Parkinson's disease

Neurons depend on mitochondria for homeostasis and survival, and thus, mitochondrial dysfunction has been implicated in neurodegenerative diseases, including Parkinson's disease (PD). Increasing evidence indicates the mitochondrial uncoupler, 2,4-dinitrophenol (DNP), protects neurons against neurodegeneration and enhances neural plasticity. Here, the authors evaluated the protective effects of intraperitoneally (i.p.) administered low dose DNP in an acute mouse model of PD. Mice were administered DNP (1 or 5mg/kg) for 12 consecutive days, and then on day 13, MPTP (20mg/kg, i.p.) was administered four times (with 2h intervals between injections) to induce PD. It was found that MPTP-induced motor dysfunction was ameliorated in the DNP-treated mice versus vehicle-treated controls. Additionally, DNP effectively attenuated dopaminergic neuronal loss observed in MPTP treated mice. Moreover, in primary cultured neurons, DNP at 10μM, but not at 100μM, prevented MPP⁺-induced cell death and mitochondrial membrane potential (MMP) reduction. In addition, DNP was observed to cause the nuclear translocation of Nrf2 in primary neurons. Taken together, these findings of the present study suggest that DNP protects dopaminergic neurons against neurodegeneration and maintains MMP integrity in PD by activating adaptive stress responses.

Immunohistochemical Changes in the Mouse Striatum Induced by the Pyrethroid Insecticide Permethrin

Epidemiological studies have linked insecticide exposure and Parkinson's disease. In addition, some insecticides produce damage or physiological disruption within the dopaminergic nigrostriatal pathway of non-humans. This study employed immunohistochemical analysis in striatum of the C57BL/6 mouse to clarify tissue changes suggested by previous pharmacological studies of the pyrethroid insecticide permethrin. Dopamine transporter, tyrosine hydroxylase, and glial fibrillary acidic protein immunoreactivities were examined in caudate-putamen to distinguish changes in amount of dopamine transporter immunoreactive protein from degeneration or other damage to dopaminergic neuropil. Weight-matched pairs of pesticide-treated and vehicle-control mice were dosed and sacrificed on the same days. Permethrin at 0.8, 1.5 and 3.0 mg/kg were the low doses and at 200 mg/kg the high dose. Brains from matched pairs of mice were processed on the same slides using the avidin-biotin technique. Four fields were morphometrically located in each of the serial sections of caudateputamen, digitally photographed, and immunopositive image pixels were counted and compared between members of matched pairs of permethrin-treated and vehicle-control mice. For low doses, only 3.0 mg/kg produced a significant decrease in dopamine transporter immunostaining. The high dose of permethrin did not produce a significant change in dopamine transporter or tyrosine hydroxylase immunostaining, but resulted in a significant increase in glial fibrillary acidic protein immunostaining. These data suggest that a low dose of permethrin can reduce the amount of dopamine transporter immunoreactive protein in the caudate-putamen. They also suggest that previously reported reductions in dopamine uptake of striatal synaptosomes of high-dose mice may be due to nondegenerative tissue damage within this region as opposed to reductions of dopamine transporter protein or death of nigrostriatal terminals. These data provide further evidence that insecticides can affect the primary neurodegenerative substrate of Parkinson's disease.

Near-infrared light treatment reduces astrogliosis in MPTP-treated monkeys

We have reported previously that intracranial application of near-infrared light (NIr) reduces clinical signs and offers neuroprotection in a subacute MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) monkey model of Parkinson's disease. In this study, we explored whether NIr reduces the gliosis in this animal model. Sections of midbrain (containing the substantia nigra pars compacta; SNc) and striatum were processed for glial fibrillary acidic protein (to label astrocytes; GFAP) and ionised calcium-binding adaptor molecule 1 (to label microglia; IBA1) immunohistochemistry. Cell counts were undertaken using stereology, and cell body sizes were measured using ImageJ. Our results showed that NIr treatment reduced dramatically (~75 %) MPTP-induced astrogliosis in both the SNc and striatum. Among microglia, however, NIr had a more limited impact in both nuclei; although there was a reduction in overall cell size, there were no changes in the number of microglia in the MPTP-treated monkeys after NIr treatment. In summary, we showed that NIr treatment influenced the glial response, particularly that of the astrocytes, in our monkey MPTP model of Parkinson's disease. Our findings raise the possibility of glial cells as a future therapeutic target using NIr.

Friends or Foes: Matrix Metalloproteinases and Their Multifaceted Roles in Neurodegenerative Diseases

Neurodegeneration is a chronic progressive loss of neuronal cells leading to deterioration of central nervous system (CNS) functionality. It has been shown that neuroinflammation precedes neurodegeneration in various neurodegenerative diseases. Matrix metalloproteinases (MMPs), a protein family of zinc-containing endopeptidases, are essential in (neuro)inflammation and might be involved in neurodegeneration. Although MMPs are indispensable for physiological development and functioning of the organism, they are often referred to as double-edged swords due to their ability to also inflict substantial damage in various pathological conditions. MMP activity is strictly controlled, and its dysregulation leads to a variety of pathologies. Investigation of their potential use as therapeutic targets requires a better understanding of their contributions to the development of neurodegenerative diseases. Here, we review MMPs and their roles in neurodegenerative diseases: Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and multiple sclerosis (MS). We also discuss MMP inhibition as a possible therapeutic strategy to treat neurodegenerative diseases.

Dietary curcumin supplementation attenuates 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in C57BL mice

Studies in vivo and in vitro suggest that curcumin is a neuroprotective agent. Experiments were conducted to determine whether dietary supplementation with curcumin has neuroprotective effects in a mouse model of Parkinson’s disease (PD). Treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) significantly induced the loss of dopaminergic cells in the substantia nigra and deletion of dopamine in the striatum, which was attenuated by long-term (7 weeks) dietary supplementation with curcumin at a concentration of 0.5% or 2.0% (w/w). Although curcumin did not prevent the MPTP-induced apoptosis of neuroblasts in the subventricular zone (SVZ), it promoted the regeneration of neuroblasts in the anterior part of the SVZ (SVZa) at 3 days after MPTP treatment. Furthermore, curcumin enhanced the MPTP-induced activation of microglia and astrocytes in the striatum and increased the expression of glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor-β1 (TGFβ1) in the striatum and SVZ. GDNF and TGFβ1 are thought to play an important role in protecting neurons from injury in the central and peripheral nervous systems. These results suggest that long-term administration of curcumin blocks the neurotoxicity of MPTP in the nigrostriatal dopaminergic system of the mouse and that the neuroprotective effect might be correlated with the increased expression of GDNF and TGFβ1. Curcumin may be effective in preventing or slowing the progression of PD.

Microglia-Induced Maladaptive Plasticity Can Be Modulated by Neuropeptides In Vivo

Microglia-induced maladaptive plasticity is being recognized as a major cause of deleterious self-sustaining pathological processes that occur in neurodegenerative and neuroinflammatory diseases. Microglia, the primary homeostatic guardian of the central nervous system, exert critical functions both during development, in neural circuit reshaping, and during adult life, in the brain physiological and pathological surveillance. This delicate critical role can be disrupted by neural, but also peripheral, noxious stimuli that can prime microglia to become overreactive to a second noxious stimulus or worsen underlying pathological processes. Among regulators of microglia, neuropeptides can play a major role. Their receptors are widely expressed in microglial cells and neuropeptide challenge can potently influence microglial activity in vitro. More relevantly, this regulator activity has been assessed also in vivo, in experimental models of brain diseases. Neuropeptide action in the central nervous system has been associated with beneficial effects in neurodegenerative and neuroinflammatory pathological experimental models. This review describes some of the mechanisms of the microglia maladaptive plasticity in vivo and how neuropeptide activity can represent a useful therapeutical target in a variety of human brain pathologies.

The effect of different doses of near infrared light on dopaminergic cell survival and gliosis in MPTP-treated mice

We have used the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mouse model to explore whether (i) the neuroprotective effect of near infrared light (NIr) treatment in the SNc is dose-dependent and (ii) the relationship between tyrosine hydroxylase (TH)+ terminal density and glial cells in the caudate-putamen complex (CPu). Mice received MPTP injections (50 mg/kg) and 2 J/cm2 NIr dose with either 2 d or 7 d survival period. In another series, with a longer 14 d survival period, mice had a stronger MPTP regime (100 mg/kg) and either 2 J/cm2 or 4 J/cm2 NIr dose. Brains were processed for routine immunohistochemistry and cell counts were made using stereology. Our findings were that in the 2 d series, no change in SNc TH+ cell number was evident after any treatment. In the 7 d series however, MPTP insult resulted in ∼45% reduction in TH+ cell number; after NIr (2 J/cm2) treatment, many cells were protected from the toxic insult. In the 14 d series, MPTP induced a similar reduction in TH+ cell number. NIr mitigated the loss of TH+ cells, but only at the higher dose of 4 J/cm2; the lower dose of 2 J/cm2 had no neuroprotective effect in this series. The higher dose of NIr, unlike the lower dose, also mitigated the MPTP- induced increase in CPu astrocytes after 14 d; these changes were independent of TH+ terminal density, of which, did not vary across the different experimental groups. In summary, we showed that neuroprotection by NIr irradiation in MPTP-treated mice was dose-dependent; with increasing MPTP toxicity, higher doses of NIr were required to protect cells and reduce astrogliosis.

Ceftriaxone prevents and reverses behavioral and neuronal deficits in an MPTP-induced animal model of Parkinson's disease dementia

Glutamatergic hyperactivity plays an important role in the pathophysiology of Parkinson's disease (PD). Ceftriaxone increases expression of glutamate transporter 1 (GLT-1) and affords neuroprotection. This study was aimed at clarifying whether ceftriaxone prevented, or reversed, behavioral and neuronal deficits in an 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD rat model. Male Wistar rats were injected daily with either ceftriaxone starting 5 days before or 3 days after MPTP lesioning (day 0) or saline and underwent a bar-test on days 1-7, a T-maze test on days 9-11, and an object recognition test on days 12-14, then the brains were taken for histological evaluation on day 15. Dopaminergic degeneration in the substantia nigra pars compacta and striatum was observed on days 3 and 15. Motor dysfunction in the bar test was observed on day 1, but disappeared by day 7. In addition, lesioning resulted in deficits in working memory in the T-maze test and in object recognition in the object recognition task, but these were not observed in rats treated pre- or post-lesioning with ceftriaxone. Lesioning also caused neurodegeneration in the hippocampal CA1 area and induced glutamatergic hyperactivity in the subthalamic nucleus, and both changes were suppressed by ceftriaxone. Increased GLT-1 expression and its co-localization with astrocytes were observed in the striatum and hippocampus in the ceftriaxone-treated animals. To our knowledge, this is the first study showing a relationship between ceftriaxone-induced GLT-1 expression, neuroprotection, and improved cognition in a PD rat model. Ceftriaxone may have clinical potential for the prevention and treatment of dementia associated with PD.

Asiaticoside, a trisaccaride triterpene induces biochemical and molecular variations in brain of mice with parkinsonism

BACKGROUND

Parkinson's disease characterized by oxidative stress and mitochondrial damage in the pars compacta of substantia nigra remains a challenge to manage with an added disadvantage of side effects of L-levo dopa, the standard drug used for therapy. Thus, an alternative approach of utilizing natural components would be beneficial in the management of the disease. The present study was aimed to investigate the potential role of asiaticoside (As), a trisaccaride triterpene against1 - methyl 4 - phenyl 1,2,3,6 tetrahydropyridine (MPTP)-induced neurotoxicity in experimental mice.

METHODS

Mice were divided into 4 groups: Group I received vehicle saline, group II was treated with 20 mg/kg of body weight of MPTP (2 doses with 2 h intervals), group III received MPTP along with 50 mg/kg body weight of As for the 21 consecutive days starting from the day of MPTP intoxication. Group IV received 50 mg/kg body weight of asiaticoside for the same period serving as drug control. Animals were sacrificed at the end of experimental period and the striatum and midbrain samples were analyzed for enzyme assays, transmission electron microscopic (TEM) analysis. Immunofluorescent assay was performed to study the expression of GFAP to detect astrocyte, which are activated due to neuronal damage. Imunohistochemical studies were carried out to quantify the expression of Bax and Bcl2, the molecular signatures that would provide clues of the extent of neurodegeneration.

RESULTS

The activities of enzymes were increased on As administration when compared with those of group II animals. Expressions of Bax and Bcl2 along with GFAP did show significant variations (p < 0.05) on MPTP treatment when compared to control animals and the changes were found to be reversed significantly (p < 0.05) after treatment with asiaticoside. TEM analysis also showed attenuated degenerative architecture on As administration. The mice which received As alone (drug control IV) did not show significant variation from that of the control mice.

CONCLUSION

The observations suggest that asiaticoside may be efficacious in protecting neurons from the oxidative damage caused by the insult of MPTP.

Neural and immune mechanisms in the pathogenesis of Parkinson's disease

Although almost 50 years have passed since impaired dopaminergic transmission was identified as the main neurochemical defect in Parkinson's disease (PD), the cause of the disease remains unknown. A restricted number of biological mechanisms are likely to contribute to the process of cell death in the nigrostriatal pathway. These mechanisms include mitochondrial defects and enhanced formation of reactive oxygen species--leading to oxidative damage--and abnormal protein aggregation. In addition to or, possibly, intermingled with these mechanisms of neuronal damage there is another crucial factor: neuroinflammation. The inflammatory response associated with cell loss in the dopaminergic nigrostriatal tract and, more in general, the role of immune mechanisms are increasingly recognized in PD pathogenesis. Neuroinflammatory changes have been repeatedly demonstrated, in both neurotoxic and transgenic animal models of PD, as well as in PD patients. Transgenic models based on α-synuclein overexpression, in particular, have provided crucial insights into the correlation between this protein and the dichotomous response that microglia can activate, with the polarization toward a cytotoxic (M1) or cytoprotective (M2) phenotype. Full understanding of such mechanisms may set the ground for a fine tuning of the neuroinflammatory process that accompanies and sustains neurodegeneration, thereby opening new therapeutic perspectives for PD.

The MPTP neurotoxic lesion model of Parkinson's disease activates the apolipoprotein E cascade in the mouse brain

Apolipoprotein E (apoE) is recognized as a key actor in brain remodeling. It has been shown to increase after peripheral and central injury, to modulate reparative capacity in neurodegenerative conditions like Alzheimer's disease (AD) and to be associated with a number of other neurodegenerative diseases. This particular function of apoE has been postulated to underlie the robust association with risk and age at onset of AD. ApoE associations studies with Parkinson's disease (PD), the second most prevalent neurodegenerative disease, have generated contradictory results but associations with age at onset and dementia in PD stand out. We investigate here whether apoE is involved in response to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced degeneration that models PD-like deafferentation of the striatum in the mouse and participates in compensatory reinnervation mechanisms. We examined the modifications in gene expression and protein levels of apoE and its key receptors, the low density lipoprotein receptor (LDLR) and the LDLR-related protein (LRP), as well as the reactive astrocyte marker glial fibrillary acidic protein (GFAP) in different brain structures throughout the degenerative and reactive regenerative period. In the striatum, upregulations of GFAP, apoE and LRP mRNAs at 1 day post-treatment were associated with marked decreases in dopamine (DA) levels, loss in tyrosine hydroxylase protein content, as well as to a compensatory increase in dopaminergic metabolism. Subsequent return to near control levels coincided with indications of reinnervation in the striatum: all consistent with a role of apoE during the degenerative process and regenerative period. We also found that this cascade was activated in the hippocampus and more so than in the striatum, with a particular contribution of LDLR expression. The hippocampal activation did not correlate with substantial neurochemical reductions but appears to reflect local subtle alteration of DA metabolism and the regulation of plasticity-related event in this structure. This study provides first evidence of an activation of the apoE/apoE receptors cascade in a mouse model of PD, specifically in the MPTP-induced deafferentation of the striatum. Results are also quite consistent with the postulated role of apoE in brain repair but, raise the issue of possible lesion- and region-specific alterations in gene expression.

Dose-related immunohistochemical and ultrastructural changes after oral methylphenidate administration in cerebrum and cerebellum of the rat

Methylphenidate is a piperidine derivative and is the drug most often used to treat attention deficit/hyperactivity disorder of children and young adults. Our aim is to investigate dose-dependent dopamine-2 receptor and glial fibrillary acidic protein expression and ultrastructural changes of the rat brain, to demonstrate possible toxicity of the long-term and high dose use of the methylphenidate. In this study, 27 female prepubertal Wistar albino rats, divided into three different dose groups (5, 10 and 20 mg/kg) were treated orally with methylphenidate dissolved in saline solution for 5 days per week during 3 months. At the end of the third month, tissues were removed and sections were collected for immunohistochemical and ultrastructural studies. We believe that methylphenidate causes dose-related activation of the dopaminergic system in several brain regions especially in ventral tegmental area and also causing neuronal degeneration and capillary wall structural changes such as basal membrane thickness and augmentation of the pinostatic vesicle in the endothelial cells. Also, increased dose of Ritalin is inducing astrocytes hypertrophy especially astrogliosis in pia-glial membrane and this is the result of the degenerative changes in prefrontal cortex region due to high dose methylphenidate administration. The dose-related accumulation of the astrocytes in capillary wall might well be a consequence of the need for nutrition of the neuronal tissue, due to transport mechanism deficiency related to neuronal and vascular degeneration. Thus, we believe that the therapeutic dose of methylphenidate must be kept in minimum level to prevent ultrastructural changes.

Defining "neuroinflammation"

Neuroinflammation is a hot topic in contemporary neuroscience. A relatively new open-access journal, the Journal of Neuroinflammation, focuses on this field. As another example, abstracts to the 2007 Annual Meeting of the Society for Neuroscience could be submitted in several subcategories of neuroinflammation, a strong signal of growth in this research area. While it is becoming clear that activation of microglia and astroglia and the attendant expression of proinflammatory cytokines and chemokines often are associated with disease-, trauma-, and toxicant-induced damage to the CNS, it is by no means clear that a cause-and-effect relationship exists between the presence of a neuroinflammatory process and neural damage. We have explored this issue with two models of dopaminergic neurotoxicity. We used a single low-dose regimen of MPTP or METH, a paradigm that causes selective degeneration of striatal dopaminergic nerve terminals without affecting the cell body in the substantia nigra. Both compounds increased the expression of the microglia-associated factors, Il-1alpha, Il6, Ccl2, and Tnf-alpha, and also elicited morphologic evidence of microglial activation prior to induction of astrogliosis. Pharmacologic antagonism of MPTP and METH neurotoxicity prevented these proinflammatory responses, findings suggestive of a link between neuroinflammation and the observed neurotoxic outcomes. Nevertheless, when we used minocycline to suppress the expression of all these mediators, with the exception of Tnf-alpha, we failed to see neuroprotection. Likewise, when we examined the effects of MPTP or METH in transgenic mice lacking Il6, Ccl2, or Tnfr1/2 genes, deficiency of either Il6 or Ccl2 did not alter neurotoxicity, whereas deficiency in Tnfr1/2 was neuroprotective. Although these observations pointed to a role of the proinflammatory cytokine, TNF-alpha, in the neurotoxic effects of MPTP and METH, other observations did not support this supposition. For example, activation of NF-kappaB or induction of iNOS, known components of inflammatory responses and free radical formation, were not observed. Moreover, immunosuppressive regimens of glucocorticoids failed to suppress TNF-alpha or attenuate neurotoxicity. Taken together, our observations suggest that MPTP and METH neurotoxicity are associated with the elaboration of a "neuroinflammatory" response, yet this response lacks key features of inflammation and, with the exception of TNF-alpha, neurotoxicity appears to be the cause rather than the consequence of proinflammatory signals.

Minocycline restores striatal tyrosine hydroxylase in GDNF heterozygous mice but not in methamphetamine-treated mice

Inflammation, phospho-p38 MAPK activation, and a reduction in glial cell line-derived neurotrophic factor (GDNF) occur in Parkinson's disease. Microglial activation in the substantia nigra and a tyrosine hydroxylase deficit in the striatum of 3-month-old GDNF heterozygous (GDNF(+/-)) mice were previously reported and both were exacerbated by a toxic methamphetamine binge. The current study assessed the effects of minocycline on these methamphetamine-induced effects. Minocycline (45 mg/kg, i.p.x 14 days post-methamphetamine or saline injections) reduced microglial activation and phospho-p38 MAPK in the substantia nigra of saline-treated GDNF(+/-) mice and in methamphetamine-treated wildtype and GDNF(+/-) mice. Although minocycline increased tyrosine hydroxylase-immunoreactivity in GDNF(+/-) mice, it did not attenuate the methamphetamine-induced reduction of tyrosine hydroxylase. The results suggest that neuroinflammation is deleterious to the dopamine system of GDNF(+/-) mice but is not the primary cause of methamphetamine-induced damage to the dopamine system in either GDNF(+/-) or wildtype mice.

Caffeine protects against MPTP-induced blood-brain barrier dysfunction in mouse striatum

The blood-brain barrier (BBB) is important physiologically. Pathologically, BBB disruption has been implicated in a wide spectrum of neurological disorders including Parkinson's disease (PD). Recent studies indicate that caffeine is protective against PD, but by poorly understood mechanisms. Using a MPTP neurotoxin model of PD we tested the hypothesis that the protective actions of caffeine were because of, at least in part, preventing MPTP-induced BBB dysfunction. FVB mice were pre-treated with caffeine (10 mg/kg, i.p.) or saline for 7 days prior to initiation of neurotoxin treatments; during the 7 days of neurotoxin treatment, caffeine or saline continued to be administered 10 min before each dose of MPTP (20 mg/kg, i.p.). Striatum (and for some studies hippocampus and cerebral cortex as well) were evaluated for BBB leakage, tight junction protein expression levels, integrity of dopaminergic neurons, and activation of astrocytes and microglia using immunostaining, immunoblotting and real-time PCR techniques. We found that caffeine blocked MPTP-induced decreases in numbers of tyrosine hydroxylase-positive dopaminergic neurons, increases in leakage of Evan's blue dye and FITC-albumin in striatum but not in cerebral cortex or hippocampus, decreases in levels of the tight junction proteins occludin and ZO-1, and increases in reactive gliosis. Our results suggest that caffeine might protect against PD and PD-like features in animal models, in part, by stabilizing the BBB.

Differential effects of the dopamine neurotoxin MPTP in animals with a partial deletion of the GDNF receptor, GFR alpha1, gene

Glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor beta (TGFbeta) superfamily, is a potent neurotrophic protein promoting the survival and maintenance of dopaminergic (DA) neurons in the substantia nigra during development and adulthood. DA neurons that project to the striatum in the nigrostriatal pathway express GDNF receptors, GFR alpha1. The purpose of this study was to determine whether these neurons are especially sensitive to neurotoxic insults. Therefore, we examined effects of the dopaminergic toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on locomotion and DA neurons in 26-month-old male GFR alpha1 heterozygous (GFR alpha1(+/-)) mice compared to aged-matched wild-type (WT) littermates. MPTP gave rise to increased locomotion, regardless of genotype, while GFR alpha1(+/-) mice treated with saline exhibited lower spontaneous locomotion, compared to WT mice. Moreover, GFR alpha1(+/-) saline mice had fewer TH-positive neurons, greater expression of inflammatory markers (CD45 immunostaining and phosphorylated p38 MAPK) in the nigra, and reduced striatal TH staining. MPTP exacerbated these effects, with the lowest density of striatal TH and highest density of nigral CD45 and phospho-p38 MAPK immunoreactivity observed in GFR alpha1(+/-) mice. The findings point to increased sensitivity of the DAergic system with age and neurotoxic exposure as a result of a genetic reduction of GFR alpha1.

Distinct mechanisms of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine resistance revealed by transcriptome mapping in mouse striatum

The etiology of idiopathic Parkinson's disease is thought to involve interplay between environmental factors and predisposing genetic traits, although the identification of genetic risk factors remain elusive. The neurotoxicant, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine (MPTP) produces parkinsonian-like symptoms and pathology in mice and humans. As sensitivity to MPTP is genetically determined in mice this provides an opportunity to identify genes and biological mechanisms that modify the response to an exogenous agent that produces a Parkinson's disease-like condition. MPTP primarily targets dopaminergic nerve terminals in the striatum and elicits changes in striatal gene expression. Therefore, we used Affymetrix and qRT-PCR technology to characterize temporal mRNA changes in striatum in response to MPTP in genetically MPTP-sensitive, C57BL/6J, and MPTP-resistant Swiss Webster and BCL2-associated X protein (Bax)-/- mice. We identified three phases of mRNA expression changes composed of largely distinct gene sets. An early response (5 h) occurred in all strains of mice and multiple brain regions. In contrast, intermediate (24 h) and late (72 h) phases were striatum specific and much reduced in Swiss Webster, indicating these genes contribute and/or are responsive to MPTP-induced pathology. However, Bax-/- mice have robust intermediate responses. We propose a model in which the acute entry of MPP+ into dopaminergic nerve terminals damages them but is insufficient per se to kill the neurons. Rather, we suggest that the compromised nerve terminals elicit longer lasting transcriptional responses in surrounding cells involving production of molecules that feedback on the terminals to cause additional damage that results in cell death. In Swiss Webster, resistance lies upstream in the cascade of events triggered by MPTP and uncouples the acute events elicited by MPTP from the damaging secondary responses. In contrast, in Bax-/- mice resistance lies downstream in the cascade and suggests enhanced tolerance to the secondary insult rather than its attenuation.

IGF-1 signaling reduces neuro-inflammatory response and sensitivity of neurons to MPTP

Reduced expression of IGF-1R increases lifespan and resistance to oxidative stress in the mouse, raising the possibility that this also confers relative protection against the pro-parkinsonian neurotoxin MPTP, known to involve an oxidative stress component. We used heterozygous IGF-1R(+/-) mice and challenged them with MPTP. Interestingly, MPTP induced more severe lesions of dopaminergic neurons of the substantia nigra, in IGF-1R(+/-) mice than in wild-type animals. Using electron spin resonance, we found that free radicals were decreased in IGF-1R(+/-) mice in comparison with controls, both before and after MPTP exposure, suggesting that the increased vulnerability of dopamine neurons is not caused by oxidative stress. Importantly, we showed that IGF-1R(+/-) mice display a dramatically increased neuro-inflammatory response to MPTP that may ground the observed increase in neuronal death. Microarray analysis revealed that oxidative stress-associated genes, but also several anti-inflammatory signaling pathways were downregulated under control conditions in IGF-1R(+/-) mice compared to WT. Collectively, these data indicate that IGF signaling can reduce neuro-inflammation dependent sensitivity of neurons to MPTP.

Long-term consequences of methamphetamine exposure in young adults are exacerbated in glial cell line-derived neurotrophic factor heterozygous mice

Methamphetamine abuse in young adults has long-term deleterious effects on brain function that are associated with damage to monoaminergic neurons. Administration of glial cell line-derived neurotrophic factor (GDNF) protects dopamine neurons from the toxic effects of methamphetamine in animal models. Therefore, we hypothesized that a partial GDNF gene deletion would increase the susceptibility of mice to methamphetamine neurotoxicity during young adulthood and possibly increase age-related deterioration of behavior and dopamine function. Two weeks after a methamphetamine binge (4 x 10 mg/kg, i.p., at 2 h intervals), GDNF(+/-) mice had a significantly greater reduction of tyrosine hydroxylase immunoreactivity in the medial striatum, a proportionally greater depletion of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the striatum, and a greater increase in activated microglia in the substantia nigra than wild-type mice. At 12 months of age, methamphetamine-treated GDNF(+/-) mice exhibited less motor activity and lower levels of tyrosine hydroxylase-immunoreactivity, dopamine, DOPAC, and serotonin than wild-type mice. Greater striatal dopamine transporter activity in GDNF(+/-) mice may underlie their differential response to methamphetamine. These data suggest the possibility that methamphetamine use in young adults, when combined with lower levels of GDNF throughout life, may precipitate the appearance of parkinsonian-like behaviors during aging.

Exacerbation of Dopaminergic Terminal Damage in a Mouse Model of Parkinson's Disease by the G-Protein-Coupled Receptor Protease-Activated Receptor 1

Protease-activated receptor 1 (PAR1) is a G-protein-coupled receptor activated by serine proteases and expressed in astrocytes, microglia, and specific neuronal populations. We examined the effects of genetic deletion and pharmacologic blockade of PAR1 in the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson's disease, a neurodegenerative disease characterized by nigrostriatal dopamine damage and gliosis. After MPTP injection, PAR1-/- mice showed significantly higher residual levels of dopamine, dopamine transporter, and tyrosine hydroxylase and diminished microgliosis compared with wild-type mice. Comparable levels of dopaminergic neuroprotection from MPTP-induced toxicity were obtained by infusion of the PAR1 antagonist, BMS-200261 into the right lateral cerebral ventricle. MPTP administration caused changes in the brain protease system, including increased levels of mRNA for two PAR1 activators, matrix metalloprotease-1 and Factor Xa, suggesting a mechanism by which MPTP administration could lead to overactivation of PAR1. We also report that PAR1 is expressed in human substantia nigra pars compacta glia as well as tyrosine hydroxylase-positive neurons. Together, these data suggest that PAR1 might be a target for therapeutic intervention in Parkinson's disease.

Divergent roles for tumor necrosis factor-alpha in the brain

Proinflammatory cytokines and chemokines have been implicated in the pathogenesis of several neurological and neurodegenerative disorders. Prominent among such factors is the pleiotropic cytokine, tumor necrosis factor (TNF)-alpha. Under normal physiological conditions, TNF-alpha orchestrates a diverse array of functions involved in immune surveillance and defense, cellular homeostasis, and protection against certain neurological insults. However, paradoxical effects of this cytokine have been observed. TNF-alpha is elicited in the brain following injury (ischemia, trauma), infection (HIV, meningitis), neurodegeneration (Alzheimer's, Parkinson's), and chemically induced neurotoxicity. The multifarious identity for this cytokine appears to be influenced by several mechanisms. Among the most prominent are the regulation of TNFalpha-induced NF-kappaB activation by adapter proteins such as TRADD and TRAF, and second, the heterogeneity of microglia and their distribution pattern across brain regions. Here, we review the differential role of TNF-alpha in response to brain injury, with emphasis on neurodegeneration, and discuss the possible mechanisms for such diverse and region-specific effects.

Temporal mRNA profiles of inflammatory mediators in the murine 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). With the exception of a few rare familial forms of the disease, the precise molecular mechanisms underlying PD are unknown. Inflammation is a common finding in the PD brain, but due to the limitation of postmortem analysis its relationship to disease progression cannot be established. However, studies using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD have also identified inflammatory responses in the nigrostriatal pathway that precede neuronal degeneration in the SNpc. To assess the pathological relevance of these inflammatory responses and to identify candidate genes that might contribute to neuronal vulnerability, we used quantitative reverse-transcription polymerase chain reaction (qRT-PCR) to measure mRNA levels of 11 cytokine and chemokine encoding genes in the striatum of MPTP-sensitive (C57BL/6J) and MPTP-insensitive (Swiss Webster, SWR) mice following administration of MPTP. The mRNA levels of all 11 genes changed following MPTP treatment, indicating the presence of inflammatory responses in both strains. Furthermore, of the 11 genes examined only 3, interleukin 6 (Il-6), macrophage inflammatory protein 1 alpha/CC chemokine ligand 3 (Mip-1alpha/Ccl3) and macrophage inflammatory protein 1 beta/CC chemokine ligand 4 (Mip-1beta/Ccl4), were differentially regulated between C57BL/6J and SWR mice. In both mouse strains, the level of monocyte chemoattractant protein 1/CC chemokine ligand 2 (Mcp-1/Ccl2) mRNA was the first to increase following MPTP administration, and might represent a key initiating component of the inflammatory response. Using Mcp-1/Ccl2 knockout mice backcrossed onto a C57BL/6J background we found that MPTP-stimulated Mip-1alpha/Ccl3 and Mip-1beta/Ccl4 mRNA expression was significantly lower in the knockout mice; suggesting that Mcp-1/Ccl2 contributes to MPTP-enhanced expression of Mip-1alpha/Ccl3 and Mip-1beta/Ccl4. However, stereological analysis of SNpc neuronal loss in Mcp-1/Ccl2 knockout and wild-type mice showed no differences. These findings suggest that it is the ability of dopaminergic SNpc neurons to survive an inflammatory insult, rather than genetically determined differences in the inflammatory response itself, that underlie the molecular basis of MPTP resistance.

Paeoniflorin attenuates neuroinflammation and dopaminergic neurodegeneration in the MPTP model of Parkinson's disease by activation of adenosine A1 receptor

1. This study examined whether Paeoniflorin (PF), the major active components of Chinese herb Paeoniae alba Radix, has neuroprotective effect in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease (PD). 2. Subcutaneous administration of PF (2.5 and 5 mg kg(-1)) for 11 days could protect tyrosine hydroxylase (TH)-positive substantia nigra neurons and striatal nerve fibers from death and bradykinesia induced by four-dose injection of MPTP (20 mg kg(-1)) on day 8. 3. When given at 1 h after the last dose of MPTP, and then administered once a day for the following 3 days, PF (2.5 and 5 mg kg(-1)) also significantly attenuated the dopaminergic neurodegeneration in a dose-dependent manner. Post-treatment with PF (5 mg kg(-1)) significantly attenuated MPTP-induced proinflammatory gene upregulation and microglial and astrocytic activation. 4. Pretreatment with 0.3 mg kg(-1) 8-cyclopentyl-1,3-dipropylxanthine, an adenosine A1 receptor (A1AR) antagonist, 15 min before each dose of PF, reversed the neuroprotective and antineuroinflammatory effects of PF. 5. In conclusion, this study demonstrated that PF could reduce the MPTP-induced toxicity by inhibition of neuroinflammation by activation of the A1AR, and suggested that PF might be a valuable neuroprotective agent for the treatment of PD.

Obligatory Role for Complex I Inhibition in the Dopaminergic Neurotoxicity of 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to mice and nonhuman primates causes a parkinsonian disorder characterized by a loss of dopamine-producing neurons in the substantia nigra and corresponding motor deficits. MPTP has been proposed to exert its neurotoxic effects through a variety of mechanisms, including inhibition of complex I of the mitochondrial respiratory chain, displacement of dopamine from vesicular stores, and formation of reactive oxygen species from mitochondrial or cytosolic sources. However, the mechanism of MPTP-induced neurotoxicity is still a matter of debate. Recently, we reported that the yeast single-subunit nicotinamide adenine dinucleotide (reduced) dehydrogenase (NDI1) is resistant to rotenone, a complex I inhibitor that produces a parkinsonian syndrome in rats, and that overexpression of NDI1 in SK-N-MC cells prevents the toxicity of rotenone. In this study, we used viral-mediated overexpression of NDI1 in SK-N-MC cells and animals to determine the relative contribution of complex I inhibition in the toxicity of MPTP. In cell culture, NDI1 overexpression abolished the toxicity of 1-methyl-4-phenylpyridinium, the active metabolite of MPTP. Overexpression of NDI1 through stereotactic administration of a viral vector harboring the NDI1 gene into the substantia nigra protected mice from both the neurochemical and behavioral deficits elicited by MPTP. These data identify inhibition of complex I as a requirement for dopaminergic neurodegeneration and subsequent behavioral deficits produced by MPTP. Furthermore, combined with reports of a complex I defect in Parkinson's disease (PD) patients, the present study affirms the utility of MPTP in understanding the molecular mechanisms underlying dopaminergic neurodegeneration in PD.

Modulation of microglial pro-inflammatory and neurotoxic activity for the treatment of Parkinson's disease

Parkinson's disease (PD) is a debilitating movement disorder resulting from a progressive degeneration of the nigrostriatal dopaminergic pathway and depletion of neurotransmitter dopamine in the striatum. Molecular cloning studies have identified nearly a dozen genes or loci that are associated with small clusters of mostly early onset and genetic forms of PD. The etiology of the vast majority of PD cases remains unknown, and the precise molecular and biochemical processes governing the selective and progressive degeneration of the nigrostriatal dopaminergic pathway are poorly understood. Current drug therapies for PD are symptomatic and appear to bear little effect on the progressive neurodegenerative process. Studies of postmortem PD brains and various cellular and animal models of PD in the last 2 decades strongly suggest that the generation of pro-inflammatory and neurotoxic factors by the resident brain immune cells, microglia, plays a prominent role in mediating the progressive neurodegenerative process. This review discusses literature supporting the possibility of modulating the activity of microglia as a neuroprotective strategy for the treatment of PD.

Temporal effects of paraquat/maneb on microglial activation and dopamine neuronal loss in older rats

We investigated the effects of combined systemic exposure to the herbicide paraquat (PQ) and the fungicide maneb (MB) in 6-month-old rats, an animal model of Parkinson's disease resulting from environmental toxin exposure. Following two doses of PQ (10 mg/kg) and MB (30 mg/kg), 52% of animals developed fatal lung injury. Examination of the remaining animals showed degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta 6 weeks, but not 4 weeks, following PQ/MB. In contrast, microglial activation was observed at 4 weeks, but had abated by 6 weeks. Compared with our previous findings in younger rats, these results suggest increased susceptibility of older animals to lung and brain toxicity from PQ/MB exposure. Microglial activation preceded, and therefore likely contributed to, DA neurodegeneration. Further, electron microscopy revealed an abnormal appearance of the Golgi apparatus at 4 weeks that was confirmed using double immunostaining for tyrosine hydroxylase and Golgi. This suggests that PQ/MB causes protein processing dysfunction in nigral DA neurons that may be either a direct effect of PQ/MB or the result of microglial activation.

Deficiency of TNF receptors suppresses microglial activation and alters the susceptibility of brain regions to MPTP-induced neurotoxicity: role of TNF-alpha

Enhanced expression of tumor necrosis factor (TNF) -alpha, is associated with the neuropathological effects underlying disease-, trauma- and chemically induced neurodegeneration. Previously, we have shown that deficiency of TNF receptors protects against MPTP-induced striatal dopaminergic neurotoxicity, findings suggestive of a role for TNF-alpha in neurodegeneration. Here, we demonstrate that deficiency of TNF receptors suppresses microglial activation and alters the susceptibility of brain regions to MPTP. MPTP-induced expression of microglia-derived factors, TNF-alpha, MCP-1, and IL-1alpha, preceded the degeneration of striatal dopaminergic nerve terminals and astrogliosis, as assessed by loss of striatal dopamine and TH, and an increase in striatal GFAP. Pharmacological neuroprotection with the dopamine reuptake inhibitor, nomifensine, abolished striatal dopaminergic neurotoxicity and associated microglial activation. Similarly, in mice lacking TNF receptors, microglial activation was suppressed, findings consistent with a role for TNF-alpha in striatal MPTP neurotoxicity. In the hippocampus, however, TNF receptor-deficient mice showed exacerbated neuronal damage after MPTP, as evidenced by Fluoro Jade-B staining (to identify degenerating neurons) and decreased microtubule-associated protein-2 (MAP-2) immunoreactivity. These effects were not accompanied by microglial activation, but were associated with increased oxidative stress (nitrosylation of tyrosine residues). These findings suggest that TNF-alpha exerts a neurotrophic/neuroprotective effect in hippocampus. The marked differences we observed in the regional density, distribution and/or activity of microglia and microglia-derived factors may influence the region-specific role for this cell type. Taken together, our results are indicative of a region-specific and dual role for TNF-alpha in the brain: a promoter of neurodegeneration in striatum and a protector against neurodegeneration in hippocampus.

Minocycline attenuates microglial activation but fails to mitigate striatal dopaminergic neurotoxicity: role of tumor necrosis factor-alpha

Activated microglia are implicated in the pathogenesis of disease-, trauma- and toxicant-induced damage to the CNS, and strategies to modulate microglial activation are gaining impetus. A novel action of the tetracycline derivative minocycline is the ability to inhibit inflammation and free radical formation, factors that influence microglial activation. Minocycline is therefore being tested as a neuroprotective agent to alleviate CNS damage, although findings so far have yielded mixed results. Here, we showed that administration of a single low dose of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or methamphetamine (METH), a paradigm that causes selective degeneration of striatal dopaminergic nerve terminals without affecting the cell body in substantia nigra, increased the expression of mRNAs encoding microglia-associated factors F4/80, interleukin (IL)-1alpha, IL-6, monocyte chemoattractant protein-1 (MCP-1, CCL2) and tumor necrosis factor (TNF)-alpha. Minocycline treatment attenuated MPTP- or METH-mediated microglial activation, but failed to afford neuroprotection. Lack of neuroprotection was shown to be due to the inability of minocycline to abolish the induction of TNF-alpha and its receptors, thereby failing to modulate TNF signaling. Thus, TNF-alpha appeared to be an obligatory component of dopaminergic neurotoxicity. To address this possibility, we examined the effects of MPTP or METH in mice lacking genes encoding IL-6, CCL2 or TNF receptor (TNFR)1/2. Deficiency of either IL-6 or CCL2 did not alter MPTP neurotoxicity. However, deficiency of both TNFRs protected against the dopaminergic neurotoxicity of MPTP. Taken together, our findings suggest that attenuation of microglial activation is insufficient to modulate neurotoxicity as transient activation of microglia may suffice to initiate neurodegeneration. These findings support the hypothesis that TNF-alpha may play a role in the selective vulnerability of the nigrostriatal pathway associated with dopaminergic neurotoxicity and perhaps Parkinson's disease.

Cellular distribution of interleukin-1α-immunoreactivity after MPTP intoxication in mice

In young rodents, peripheral injection of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) results in a dopaminergic nigrostriatal denervation (during the first week after injection), followed by a spontaneous dopaminergic reinnervation. Sprouting from residual neurons has been proposed to account for this event. It has been shown that an inflammatory process takes place during striatal dopaminergic denervation but its consequences remain controversial. Some clues notably indicate that interleukin (IL)-1alpha may participate in MPTP-induced inflammation and promote recovery. We therefore studied the immunohistochemical localization of IL-1alpha expression in the striatum and ventral mesencephalon at different times (1, 3, 6, 16, and 30 days) after MPTP injection in mice. IL-1alpha-immunoreactivity (ir) was observed in striatum, substantia nigra pars compacta, and ventral tegmental area. Apart from a few localization in mesencephalic activated microglia, IL-1alpha was almost exclusively found in activated astrocytes. However, in the striatal parenchyma, another component of IL-1alpha-ir colocalized with tyrosine hydroxylase (TH)-ir, a marker for dopaminergic neurons. Moreover, some parenchymal TH-positive axons were also found to express the growth cone-associated protein (GAP)-43, a marker for axonal growth cones. In the striatum, IL-1alpha-ir was also detected in a non-astrocytic perivascular component, with a distribution similar to GAP-43-ir. IL-1alpha could thus directly or indirectly influence striatal reorganization after MPTP.

Apoptosis and nestin expression in the cortex and cultured astrocytes following 6-OHDA administration

We used the dopaminergic neurotoxicant, 6-hydroxydopamine (6-OHDA), as a tool to characterize the origins of the astrocytic response to injury. Reactive astrocytes were examined by immunocyto- and histo-chemical visualization of nestin protein in the brain and cultivated cells. Following 6-OHDA (dose-dependent) treatment, the expression of nestin-like immunoreactive cells in the corpus callosum and cerebral cortex was increased compared with that of the control animals, indicating that a significant up-regulation of nestin protein occurred in these regions. In the corpus callosum and cerebral cortex, the majority of the nestin-like immunoreactive cells showed a distribution and pattern similar to those of the glial fibrillary acid protein (GFAP)-immunoreactive cells. Double immunofluorescence measurements showed that 100% of the nestin-like immunoreactive cells expressed GFAP-immunoreactive cells, indicating that these nestin-like immunoreactive cells belong to a reactive population of the astrocytes. In this study, we observed the morphological changes in the astrocytes following 6-OHDA administration, demonstrating that 6-OHDA induced injury leads to a rapid and transient up-regulation of nestin-like immunoreactivity in activated astrocytes.

Differential inflammatory activation of IL-6 (−/−) astrocytes

IL-6 is a major immunomodulatory cytokine with neuroprotective activity. The absence of interleukin-6 (IL-6) results in increased vulnerability of dopaminergic neurons to the neurotoxicant, MPTP, and a compromised reactive microgliosis. To determine how astrogliosis may contribute to nigrostriatal degeneration in IL-6 (-/-) mice, the inflammatory profiles of astrocytes of IL-6 genotype were compared. Fourteen cytokines and four chemokines were simultaneously assayed in the supernatants of LPS-stimulated primary astrocyte cultures. In a time course of 6, 18 and 48 h and LPS stimulations of 0, 0.1, 1, 10 and 100 ng/ml, IL-6 (-/-) astrocytes secreted significantly greater amounts of the pro-inflammatory cytokines IL-1alpha, IL-1beta and TNFalpha than did IL-6 (+/+) cells. Elevated levels of IL-10 and IL-12p40 were only detected at 48 h post-stimulation with greater IL-10 in IL-6 (-/-) supernatants and greater IL-12p40 in IL-6 (+/+) supernatants. IL-6 (+/+) astrocytes produced more G-CSF and GM-CSF when compared with IL-6 (-/-) astrocytes. Chemokine levels were greater in supernatants of IL-6 (+/+) astrocytes than IL-6 (-/-) cells prior to 48 h post-stimulation. At that time, higher levels of MIP-1alpha were maintained in IL-6 (+/+) supernatant, while similar levels of MCP-1 in supernatants of both IL-6 (+/+) and IL-6 (-/-) cells were measured. Additionally, LPS (100 ng/ml) resulted in greater levels of KC and Rantes in IL-6 (-/-) astrocyte supernatants compared with IL-6 (+/+) supernatants at that time. These results suggest that the autocrine modulatory activities of IL-6 affect multiple cytokine secretory pathways, which could participate in neurodegenerative processes.

Genetic and genomic studies of Drosophila parkin mutants implicate oxidative stress and innate immune responses in pathogenesis

Loss-of-function mutations of the parkin gene, which encodes a ubiquitin-protein ligase, are a common cause of autosomal recessive juvenile parkinsonism (ARJP). Previous work has led to the identification of a number of Parkin substrates that implicate specific pathways in ARJP pathogenesis, including endoplasmic reticulum (ER) stress and cell cycle activation. To test the involvement of previously implicated pathways, as well as to identify novel pathways in ARJP pathogenesis, we are using genetic and genomic approaches to study Parkin function in the fruit fly Drosophila melanogaster. In previous work, we demonstrated that Drosophila parkin null mutants exhibit mitochondrial pathology and flight muscle degeneration. To further explore the mechanisms responsible for pathology in parkin mutants, we analyzed the transcriptional alterations that occur during muscle degeneration and performed a genetic screen for parkin modifiers. Results of these studies indicate that oxidative stress response components are induced in parkin mutants and that loss-of-function mutations in oxidative stress components enhance the parkin mutant phenotypes. Genes involved in the innate immune response are also induced in parkin mutants. In contrast, our studies did not reveal evidence for cell cycle or ER stress pathway induction in parkin mutants. These results suggest that oxidative stress and/or inflammation may play a fundamental role in the etiology of ARJP.

Pathological dynamics of activated microglia following medial forebrain bundle transection

To elucidate the role and pathological dynamics of activated microglia, this study assessed the phagocytic, immunophenotypic, morphological, and migratory properties of activated microglia in the medial forebrain bundle (MFB) axotomized rat brain. Activated microglia were identified using two different monoclonal antibodies: ED1 for phagocytic activity and OX6 for major histocompatibility complex (MHC) class II. Phagocytic microglia, characterized by ED1-immunoreactivity or ED1- and OX6-immunoreactivity, appeared in the MFB and substantia nigra (SN) as early as 1-3 days post-lesion (dpl), when there was no apparent loss of SN dopamine (DA) neurons. Thereafter, a great number of activated microglia selectively adhered to degenerating axons, dendrites and DA neuronal somas of the SN. This was followed by significant loss of these fibers and nigral DA neurons. Activation of microglia into phagocytic stage was most pronounced between 14 approximately 28 dpl and gradually subsided, but phagocytic microglia persisted until 70 dpl, the last time point examined. ED1 expression preceded MHC II expression in phagocytic microglia. All phagocytic microglia sticking to DA neurons showed activated but ramified form with enlarged somas and thickened processes. They were recruited to the SNc from cranial, dorsal and ventral aspects along various structures and finally stuck to DA neurons of the SNc. Characteristic rod-shaped microglia in the white matter were thought to migrate a long distance. The present study strongly suggests that neurons undergoing delayed neurodegeneration may be phagocytosed by numerous phagocytic, ramified microglia at various sites where specific surface signals are exposed or diffusible molecules are released.

Arundic acid, an astrocyte-modulating agent, protects dopaminergic neurons against MPTP neurotoxicity in mice

We examined the neuroprotective effects of a novel astrocyte-modulating agent, arundic acid (ONO-2506), in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease. Male C57BL/6 mice received four intraperitoneal injections of MPTP (20 mg/kg) at 2 h intervals. Dopamine content in the striatum was reduced to 21% of the normal control after 7 days. Treatment with arundic acid (30 mg/kg, i.p.) administered 1 min, 6 h, 24 h, 48 h, and 72 h after the last MPTP injection prevented the dopamine depletion (52% of the control, p<0.01). In addition, this treatment resulted in behavioral benefits. Behavioral testing showed that MPTP-injected mice exhibited motor deficits in the pole test and catalepsy test after 7 days, but arundic acid prevented the appearance of motor abnormalities in these tests. The MPTP-injected animals exhibited an 87% loss of tyrosine hydroxylase-containing dopaminergic neurons in the substantia nigra after 7 days, but the arundic acid-treated mice showed only a 56% reduction (p<0.01). GFAP-positive reactive astrocytes were accumulated in the striatum and substantia nigra 7 days after the MPTP injection, whereas arundic acid treatment induced an earlier appearance of reactive astrocytes by 3 days. The reactive astrocytes increased the production of S-100 protein, which is thought to promote neuronal damage, but arundic acid suppressed the expression of S-100. Thus, arundic acid protected dopaminergic neurons against MPTP neurotoxicity in mice and ameliorated neurological deficits. The results suggest that the neuroprotection is mediated through the modulation of astrocytic activation, including the inhibition of S-100 protein synthesis.

Genetic ablation of tumor necrosis factor-alpha (TNF-alpha) and pharmacological inhibition of TNF-synthesis attenuates MPTP toxicity in mouse striatum

The impact of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) in the pathology of Parkinson's disease (PD) and in MPTP neurotoxicity remains unclear. Here, male TNF-alpha (-/-) deficient mice and C57bL/6 mice were treated with MPTP (4 x 15 mg/kg, 24 h intervals) and in one series, thalidomide was administered to inhibit TNF-alpha synthesis. Real-time RT-PCR revealed that the striatal mRNA levels of TNF-alpha, of the astrocytic marker glial fibrillary acidic protein (GFAP) and of the marker for activated microglia, macrophage antigen complex-1 (MAC-1), were significantly enhanced after MPTP administration. Thalidomide (50 mg/kg, p.o.) partly protected against the MPTP-induced dopamine (DA) depletion, and TNF-alpha (-/-) mice showed a significant attenuation of striatal DA and DA metabolite loss as well as striatal tyrosine hydroxylase (TH) fiber density, but no difference in nigral TH and DA transporter immunoreactivity. TNF-alpha deficient mice suffered a lower mortality (10%) compared to the high mortality (75%) seen in wild-type mice after acute MPTP treatment (4 x 20 mg/kg, 2 h interval). HPLC measurement of MPP(+) levels revealed no differences in TNF-alpha (-/-), wild-type and thalidomide treated mice. This study demonstrates that TNF-alpha is involved in MPTP toxicity and that inhibition of TNF-alpha response may be a promising target for extending beyond symptomatic treatment and developing anti-parkinsonian drugs for the treatment of the inflammatory processes in PD.

Induction of gp130-related Cytokines and Activation of JAK2/STAT3 Pathway in Astrocytes Precedes Up-regulation of Glial Fibrillary Acidic Protein in the 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine Model of Neurodegeneration

Reactive gliosis is a hallmark of disease-, trauma-, and chemical-induced damage to the central nervous system. The signaling pathways associated with this response to neural injury remain to be elucidated, but recent evidence implicates the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway. Here, we used the known dopaminergic neurotoxicant, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), to selectively damage striatal dopaminergic nerve terminals and elicit a glial response. We then analyzed changes in gene expression and protein phosphorylation, in vivo, to identify ligands and mediators of the JAK-STAT pathway that accompany glial activation. Administration of MPTP caused rapid tyrosine (Tyr-705) phosphorylation and nuclear translocation of STAT3 in striatal astrocytes, prior to the induction of glial fibrillary acidic protein mRNA and protein. Pharmacological protection of dopaminergic nerve terminals with nomifensine abolished MPTP-mediated phosphorylation and translocation of STAT3 and prevented induction of astrogliosis. Among the Janus kinase family of tyrosine kinases, only JAK2 was associated with the phosphorylation of STAT3 after MPTP and, inhibition of JAK2 by AG490, in vivo, attenuated both the phosphorylation of STAT3 and induction of GFAP. The p44/42 mitogen-activated protein kinase (MAPK; ERK1/2) also was activated by MPTP, but was not associated with activation of STAT3, because serine (Ser-727) was not phosphorylated. The mRNA for ligands of the gp130-JAK/STAT3 signaling pathway, interleukin-6, leukemia inhibitory factor, and oncostatin M were elevated prior to activation of STAT3 and induction of astrogliosis; neuroprotection with nomifensine blocked these effects of MPTP. Taken together, our results suggest that the gp130-mediated activation of JAK2/STAT3 signaling pathway may play a key role in the induction of astrogliosis.

Microglial response is poorly correlated with neurodegeneration following chronic, low-dose MPTP administration in monkeys

Many investigators have reported extensive microglial activation in the mouse substantia nigra and striatum following acute, high-dose 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration. Our previous work demonstrated tyrosine hydroxylase (TH)-positive fiber sprouting in the striatum in monkeys that had received a partial dopaminergic lesion using a low-dose, chronic MPTP administration paradigm. To characterize the microglial response, we utilized HLA-DR (LN3) to immunolabel the class II major histocompatibility complex (MHC II). In MPTP-treated monkeys, there was an intense microglial response in the substantia nigra, nigrostriatal tract, and in both segments of the globus pallidus. This response was morphologically heterogeneous, with commingled ramified, activated, and multicellular morphologies throughout the extent of these basal ganglia structures. Surprisingly, there was little evidence of microglial reactivity in the striatum despite evidence of neurodegeneration-by silver labeling and by loss of TH immunolabeling. Moreover, this pattern of microglial reactivity was the same in all animals that had received MPTP and seemed to be independent of the degree of neurotoxin-induced neurodegeneration. Thus, we conclude that microglial reactivity, per se, is not consistently associated with neurodegeneration, but depends on regional differences.

Protective effects of neuronal nitric oxide synthase inhibitor in mouse brain against MPTP neurotoxicity: an immunohistological study

We recently reported that neuronal nitric oxide synthase (nNOS) inhibitor, 7-nitroindazole, can protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in mice. It protected against both dopamine depletions and tyrosine hydroxylase (TH) positive neuron decreases in the mouse brain. In the present study, we further examined whether 7-nitroindazole can also protect against the alterations of TH-, microtubule-associated protein 2a,b (MAP2)-, glial fibrillary acidic protein (GFAP)-, parvalbumin (PV)-, dopamine transporter (DAT)-, nNOS- or endothelial NOS (eNOS)-positive cells, in comparison with pargyline as a relatively selective inhibitor of the monoamine oxidase-B (MAO-B). The present study showed that nNOS inhibitor as well as MAO-B inhibitor has a dose-dependent protective effect against MPTP-induced striatal dopamine and DOPAC depletion in mice. Furthermore, the present study revealed that 7-nitroindazole and pargyline can protect the alterations of immunohistochemical changes in the striatum and substantia nigra after MPTP treatment. These protective effects may be, at least in part, produced by the reduction of neuronally derived NO and peroxynitrite caused by MPTP. Our results also demonstrate that MPTP can cause functional damage of interneurons in the substantia nigra. These results suggest the possibility that nNOS inhibitors as well as MAO-B inhibitors may be therapeutically useful in neurodegenerative diseases such as Parkinson's disease. Thus our present results provide valuable information for the pathogenesis of degeneration of the nigrostriatal dopaminergic neuronal pathway.

MPTP potentiates 3-nitropropionic acid-induced striatal damage in mice: reference to striatonigral degeneration

Striatonigral degeneration (SND) is a parkinsonian disorder due to the combined degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc) and striatal output neurons. The aims of this study were to explore (1) the behavioral and histopathological consequences of combined MPTP plus 3-nitropropionic acid (3-NP) intoxication in C57/Bl6 mice and (2) its ability to reproduce the neuropathological hallmarks of SND. 3-NP was administered i.p. every 12 h (total dose=450 mg/kg in 9 days) and MPTP i.p. at 10 mg/(kg day) (total dose=90 mg/kg in 9 days). Four groups of mice (n=10) were compared: control, 3-NP alone, MPTP alone, MPTP + 3-NP. Mice intoxicated with 3-NP and MPTP + 3-NP developed motor symptoms, including hindlimb dystonia and clasping, truncal dystonia and impaired balance adjustments. The severity of motor disorder was worse and lasted longer in MPTP + 3-NP-treated mice compared to 3-NP alone, MPTP alone and controls. 3-NP and MPTP + 3-NP-treated mice also displayed altered gait patterns, impaired motor performance on the pole test, rotarod and traversing a beam tasks and activity parameters. Several of these sensorimotor deficits were also more severe and lasted longer in MPTP + 3-NP-treated mice. Histology demonstrated increased neuronal loss along with astrocytic activation (glial fibrillary acid protein, GFAP) and a higher incidence of circumscribed striatal lateral lesions in MPTP + 3-NP-treated mice compared to 3-NP. Neuronal loss and astrocytic activation were increased in the lateral part of the striatum in 3-NP-intoxicated mice while observed both in the medial and lateral part in MPTP + 3-NP-intoxicated mice. There was also a significant loss of SNc dopaminergic neurons and striatal terminals, similar to that in MPTP-treated mice. Altogether, these results suggest that MPTP potentiates striatal damage and behavioral impairments induced by 3-NP intoxication in mice and constitutes a useful model of the motor disorder and its histopathological correlates in SND.

Identification of brain-derived neurotrophic factor in nestin-expressing astroglial cells in the neostriatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice

Up-regulation of nestin expression was significantly induced in the caudate-putamen of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice in our previous observation [Brain Res 925 (2002) 9]. We hypothesized that the nestin-expressing cells might play an important role in the pathogenesis of parkinsonian model, and characterization of these nestin-expressing cells was studied by RT-PCR, immunohistochemistry and semi-quantitative analysis for various markers of glial fibrillary acid protein (GFAP), S-100, neuronal nuclear specific protein (NeuN), beta-tubulin, Ki-67 and brain-derived neurotrophic factor (BDNF) expression in MPTP-treated C57/BL mice. Firstly, significant increasing in both nestin protein and mRNA was found in MPTP-treated mice. Up-regulation of nestin expression started at day 1, peaked at day 3, and gradually went down at days 7-21 in the neostriatum after MPTP treatment. Secondly, double immunofluorescence indicated that almost all of nestin-positive cells exhibited GFAP (98%) or S-100 (96%)-immunoreactivity, whereas NeuN or beta-tubulin was hardly detected in these nestin-positive cells. Thirdly, a minor population (7.0%) of nestin-positive cells showed Ki-67 (cell proliferation marker)-immunoreactivity, showing some of them went into cell mitotic state. Finally but more interestingly, a major population (86%) of nestin-expressing cells also exhibited immunoreactivity for BDNF, one neurotrophic factor. These results present time-dependent up-regulation of nestin expression in neostriatum, the proliferative and neurotrophic properties of nestin-expressing astroglial cells in MPTP-treated C57/BL mice. Taken together with previous observations, this study suggests that nestin-expressing activated astroglial cells, possibly partially through synthesizing and releasing neurotrophic factors such as BDNF in the basal ganglia, may play important roles in protection of nigrostriatal dopamine neurons and in the pathogenesis of Parkinson's disease in mammals.

Compromised reactive microgliosis in MPTP-lesioned IL-6 KO mice

Reactive gliosis, the cellular manifestation of neuroinflammation, is a pathological hallmark of neurodegenerative diseases including Parkinson's disease. The persistent gliosis observed in the Parkinson's disease substantia nigra (SN) and in humans and animals exposed to the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) may represent a chronic inflammatory response that contributes to pathology. We have previously shown that in the absence of interleukin-6 (IL-6) dopaminergic neurons are more vulnerable to MPTP. Since IL-6 is both an autocrine and paracrine proliferation factor for CNS glia, we investigated reactive gliosis in MPTP-lesioned IL-6 (-/-) mice. While astrogliosis was similar in injured IL-6 (+/+) and IL-6 (-/-) SN pars compacta (pc), microgliosis was severely compromised in IL-6 (-/-) mice. In the absence of IL-6, an acute reactive microgliosis was transient with a complete absence of reactive microglia at day 7 post-lesion. Extensive reactive microgliosis was observed in the SNpc of MPTP-lesioned IL-6 (+/+) mice. Because glial derived inducible nitric oxide synthase (iNOS) has been implicated in dopaminergic cell death, we examined glial iNOS expression in the IL-6 genotypes to determine if it correlated with the greater vulnerability and reduced microgliosis observed in the MPTP-lesioned IL-6 (-/-) nigrostriatal system. Both reactive microglia and astrocytes expressed iNOS in the lesioned SNpc. In the IL-6 (-/-) mice, microglial iNOS expression diminished as reactive microgliosis declined. The data suggest IL-6 regulation of microglia activation, while iNOS expression appears to be secondary to cell activation.

Increased vulnerability of dopaminergic neurons in MPTP-lesioned interleukin-6 deficient mice

To test the hypothesis that neuroinflammation contributes to dopaminergic neuron death in the MPTP-lesioned mouse, we compared nigrostriatal degeneration in interleukin (IL)-6 (+/+) with IL-6 (-/-) mice. In the absence of IL-6, a single injection of MPTP (30 mg/kg) resulted in significantly greater striatal dopamine depletion than that measured in IL-6 (+/+) mice. The observed dopamine depletion was MPTP dose dependent. This loss of striatal dopamine and a significantly greater loss of TH+ cells in the substantia nigra pars compacta in IL-6 (-/-) mice as compared with control IL-6 (+/+) mice, suggest that IL-6 is neuroprotective in the MPTP-lesioned nigrostriatal system. Co-localization experiments identified striatal astrocytes as the source of IL-6 in IL-6 (+/+) mice at 1 and 7 days postinjection of MPTP. The increased sensitivity of dopaminergic neurons to neurotoxicant in the absence of IL-6, is compatible with a neuroprotective activity of IL-6 in the injured nigrostriatal system.

Mice deficient in TNF receptors are protected against dopaminergic neurotoxicity: implications for Parkinson's disease

The pathogenic mechanisms underlying idiopathic Parkinson's disease (PD) remain enigmatic. Recent findings suggest that inflammatory processes are associated with several neurodegenerative disorders, including PD. Enhanced expression of the proinflammatory cytokine, tumor necrosis factor (TNF)-alpha, has been found in association with glial cells in the substantia nigra of patients with PD. To determine the potential role for TNF-alpha in PD, we examined the effects of the 1-methyl-4-phenyl-1,2,3,4-tetrahydropyridine (MPTP), a dopaminergic neurotoxin that mimics some of the key features associated with PD, using transgenic mice lacking TNF receptors. Administration of MPTP to wild-type (+/+) mice resulted in a time-dependent expression of TNF-alpha in striatum, which preceded the loss of dopaminergic markers and reactive gliosis. In contrast, transgenic mice carrying homozygous mutant alleles for both the TNF receptors (TNFR-DKO), but not the individual receptors, were completely protected against the dopaminergic neurotoxicity of MPTP. The data indicate that the proinflammatory cytokine TNF-alpha is an obligatory component of dopaminergic neurodegeneration. Moreover, because TNF-alpha is synthesized predominantly by microglia and astrocytes, our findings implicate the participation of glial cells in MPTP-induced neurotoxicity. Similar mechanisms may underlie the etiopathogenesis of PD.

Lentivirally delivered glial cell line-derived neurotrophic factor increases the number of striatal dopaminergic neurons in primate models of nigrostriatal degeneration

The primate striatum contains tyrosine hydroxylase (TH)-immunoreactive (ir) neurons, the numbers of which are augmented after dopamine depletion. Glial cell line-derived neurotrophic factor (GDNF) strongly modulates the viability and phenotypic expression of dopamine ventral mesencephalic neurons. The effect of GDNF on TH-ir neurons intrinsic to the striatum has yet to be investigated. In the present study, stereological counts of TH-ir striatal neurons in aged and parkinsonian nonhuman primates revealed that GDNF delivered via a lentiviral vector (lenti-) further increased the number of these cells. Aged monkeys treated with lenti-GDNF displayed an eightfold increase in TH-ir neurons relative to lenti-beta-galactosidase-treated monkeys. Unilateral 1-methyl-4-phenyl- 1,2,3,6-tetrahydropyridine treatment alone in young monkeys resulted in a bilateral eightfold increase in TH-ir striatal cells. This effect was further magnified sevenfold on the side of lenti-GDNF treatment. These cells colocalized with the neuronal marker neuronal-specific nuclear protein. Some of these cells colocalized with GDNF-ir, indicating that an alteration in phenotype may occur by the direct actions of this trophic factor. Thus, GDNF may mediate plasticity in the dopamine-depleted primate brain, which may serve to compensate for cell loss by converting striatal neurons to a dopaminergic phenotype.

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine induces apoptosis in mouse nigrostriatal glia. Relevance to nigral neuronal death and striatal neurochemical changes

Swiss mice were given 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 25 mg/kg/day, for 5 consecutive days and killed at different days after MPTP discontinuance. Decreases in striatal tyrosine hydroxylase activity and levels of dopamine and its metabolites were observed 1 day after MPTP discontinuance. Ascorbic acid and glutamate levels had increased, dehydroascorbic acid and GSH decreased, whereas catabolites of high-energy phosphates (inosine, hypoxanthine, xanthine, and uric acid) were unchanged. In addition, gliosis was observed in both striatum and substantia nigra compacta (SNc). Sections of SNc showed some terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate nick end labeling (TUNEL)-positive cells. Neurochemical parameters of dopaminergic activity showed a trend toward recovery 3 days after MPTP discontinuance. At this time point, TUNEL-positive cells were detected in SNc; some of them showed nuclei with neuronal morphology. A late (days 6-11) increase in striatal dopamine oxidative metabolism, ascorbic acid oxidative status, and catabolites of high-energy phosphates were observed concomitant with nigral neuron and nigrostriatal glial cell apoptotic death, as revealed by TUNEL, acridine orange, and Hoechst staining, and transmission electron microscopy. These data suggest that MPTP-induced activation/apoptotic death of glial cells plays a key role in the sequential linkage of neurochemical and cellular events leading to dopaminergic nigral neuron apoptotic death.

Neuronal ectopic expression of tyrosine hydroxylase in the mouse striatum by combined administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and 3-nitropropionic acid

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a dopaminergic neurotoxin which inhibits mitochondrial complex I. 3-Nitropropionic acid (3-NPA) inhibits mitochondrial complex II and produces specific striatal lesions. In order to produce a combined striatal neuronal and dopaminergic afferent lesion, we administered both toxins simultaneously to the mouse. The combination brought about a lesion in the striatum that was not simply additive of the two combined toxins. Intriguingly, a group of striatal neurons became immunoreactive to tyrosine hydroxylase after day 1. Some of them were clearly visible up to the dendritic details. Immuno-electron microscopy indicated that the tyrosine hydroxylase-positive striatal neurons contained densely immunoreactive polyribosomes. Reverse transcriptase-polymerase chain reaction analysis indicated the up-regulation of tyrosine hydroxylase mRNA in the treated striatum. These neurons were also immunoreactive to aromatic L-amino acid decarboxylase.We conclude that the combined administration of MPTP and 3-NPA caused a more profound damage to the nigro-striatal dopaminergic system, and thus some striatal neurons capable of up-regulating tyrosine hydroxylase were induced to produce dopamine, probably to compensate for the dopamine depletion.

Significant up-regulation of nestin protein in the neostriatum of MPTP-treated mice. Are the striatal astrocytes regionally activated after systemic MPTP administration?

We are interested in the possible role of central glial cells in pathogenesis of Parkinson's disease of mammals. Parkinsonism model was induced by systemic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration, and the reactive glial cells were examined by immunocytochemical visualization of nestin protein in the brains and spinal cords of C57 mice. Abundant nestin-like immunoreactivity was predominately found in the caudate putamen of MPTP-treated mice and about 481-fold of nestin-like immunoreactive cells increased compared with that of control animals, indicating that significant up-regulation of nestin protein occurred in these regions. Majority of nestin-like immunoreactive cells characterized with astrocytic profiles of multiple, radical and hypotrophic processes, and showed a distribution and dynamic patterns similar to that of glial fibrillary acid protein (GFAP)-immunoreactive cells in the caudate putamen. Double immunofluorescence confirmed that 100% of nestin-like immunoreactive cells exhibited GFAP-immunoreactivity while nestin/GFAP double-labeled cells constituted about 84% of total GFAP-immunoreactive cells in the caudate putamen, indicating these nestin-like immunoreactive cells belong to a reactive population of the astrocytes. On the other hand, no obvious changes of nestin- or GFAP-like immunoreactivities were detected in the globus pallidus, the substantia nigra and the ventral tegmental area after MPTP-treatment. The results have provided morphological evidence for the regional activation of astrocytic glial cells following systemic MPTP administration, suggesting that a large population of reactive striatal astrocytes might play an important role in initial pathogenesis or acute stage of Parkinson's disease in mammals.

Biochemical and immunohistological changes in the brain of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse

We investigated neurochemically and neuropathologically the utility of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice as a model of Parkinson's disease. The changes in dopamine D1 and D2 receptors and dopamine uptake sites were determined by quantitative autoradiography using [3H]SCH23390, [3H]raclopride and [3H]mazindol, respectively. Dopamine and 3,4-dihydroxyphenyl acetic acid (DOPAC) contents in the striatum were measured by high-performance liquid chromatography. The distribution of nigral neurons and reactive astrocytes was determined by immunohistochemical staining with antibody against tyrosine hydroxylase (TH) and glial fibrillary acidic protein (GFAP). The mice received four intraperitoneal injections of MPTP (10 mg/kg) at 1-h intervals and then the brains were analyzed at 3 and 7 days after the treatments. No significant change in dopamine D1 receptors was observed in the striatum and substantia nigra after acute treatment with MPTP. Dopamine D2 receptors were reduced significantly in the substantia nigra only 7 days after the MPTP treatment, whereas striatum showed no significant change in the binding throughout the experiments. In contrast, dopamine uptake sites were reduced markedly in the striatum and substantia nigra 3 and 7 days after the MPTP treatment. Dopamine and DOPAC content were also reduced in the striatum 3 and 7 days after the MPTP treatment. An immunohistochemical study indicated a loss of the number of TH-positive neurons in the substantia nigra 7 days after the MPTP treatment. In contrast, numerous GFAP-positive astrocytes were evident in the striatum 7 days after the MPTP treatment. These results provide valuable information for the pathogenesis of acute stage of Parkinson's disease.