Ndfip1 protected dopaminergic neurons via regulating mitochondrial function and ferroptosis in Parkinson's disease

Increasing evidence has shown that mitochondrial dysfunction and iron accumulation contribute to the pathogenesis of Parkinson's disease (PD). Nedd4 family interacting protein 1 (Ndfip1) is an adaptor protein of the Nedd4 E3 ubiquitin ligases. We have previously reported that Ndfip1 showed a neuroprotective effect in cell models of PD. However, whether Ndfip1 could protect dopaminergic neurons in PD animal models in vivo and the possible mechanisms are not known. Here, our results showed that the expression of Ndfip1 decreased in the substantia nigra (SN) of 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced PD mouse model. Overexpression of Ndfip1 could improve MPTP-induced motor dysfunction significantly and antagonize the loss of dopaminergic neurons in the SN of MPTP-induced mice. Further study showed that overexpression of Ndfip1 might protect against MPTP-induced neurotoxicity through regulation of voltage-dependent anion-selective channel (VDAC). In addition, we observed the downregulation of Ndfip1 and upregulation of VDAC1/2 in 1-methyl-4-phenylpyridinium ion (MPP+)-induced SH-SY5Y cells. Furthermore, high expression of Ndfip1 in SH-SY5Y cells inhibited MPP+-induced increase of VDAC1/2 and restored MPP+-induced mitochondrial dysfunction. Furthermore, Ndfip1 prevented MPP+-induced increase in the expression of long-chain acyl-CoA synthetase 4 (ACSL4), suggesting the possible role of Ndfip1 in regulating ferroptosis. Our results provide new evidence for the neuroprotective effect of Ndfip1 on dopaminergic neurons in PD animal models and provide promising targets for the treatment of iron-related diseases, including PD.

The specific NQO2 inhibitor, S29434, only marginally improves the survival of dopamine neurons in MPTP-intoxicated mice

Over the years, evidence has accumulated on a possible contributive role of the cytosolic quinone reductase NQO2 in models of dopamine neuron degeneration induced by parkinsonian toxin, but most of the data have been obtained in vitro. For this reason, we asked the question whether NQO2 is involved in the in vivo toxicity of MPTP, a neurotoxin classically used to model Parkinson disease-induced neurodegeneration. First, we show that NQO2 is expressed in mouse substantia nigra dopaminergic cell bodies and in human dopaminergic SH-SY5Y cells as well. A highly specific NQO2 inhibitor, S29434, was able to reduce MPTP-induced cell death in a co-culture system of SH-SY5Y cells with astrocytoma U373 cells but was inactive in SH-SY5Y monocultures. We found that S29434 only marginally prevents substantia nigra tyrosine hydroxylase+ cell loss after MPTP intoxication in vivo. The compound produced a slight increase of dopaminergic cell survival at day 7 and 21 following MPTP treatment, especially with 1.5 and 3 mg/kg dosage regimen. The rescue effect did not reach statistical significance (except for one experiment at day 7) and tended to decrease with the 4.5 mg/kg dose, at the latest time point. Despite the lack of robust protective activity of the inhibitor of NQO2 in the mouse MPTP model, we cannot rule out a possible role of the enzyme in parkinsonian degeneration, particularly because it is substantially expressed in dopaminergic neurons.

Oral Administration of Silybin Protects Against MPTP-Induced Neurotoxicity by Reducing Pro-inflammatory Cytokines and Preserving BDNF Levels in Mice

Parkinson's disease (PD) is the second most frequent neurodegenerative disease associated with motor dysfunction secondary to the loss of dopaminergic neurons in the nigrostriatal axis. Actual therapy consists mainly of levodopa; however, its long-term use promotes secondary effects. Consequently, finding new therapeutic alternatives, such as neuroprotective molecules, is necessary. Among these alternatives is silybin (Sb), the major bioactive flavonolignan in silymarin. Both exert neuroprotective effects, preserving dopamine levels and dopaminergic neurons when administered in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse PD model, being probably Sb the potential therapeutic molecule behind this effect. To elucidate the role of Sb in the PD model, we determined the dose-dependent conservation of striatal dopamine content following Sb oral administration. Then, we evaluated motor deficit tests using the best dopamine conservative dose of Sb and determined a cytokine-dependent inflammatory profile status, malondialdehyde as an oxidative stress product, and neurotrophic factors content in the MPTP-induced mouse PD model. Our results show that oral Sb at 100 mg/kg dose conserved about 60% dopamine levels. Also, Sb improved motor deficits, preserved neurotrophic factors content and mitochondrial function, reduced lipid peroxidation, diminished proinflammatory cytokines to basal levels, enhanced fractalkine production in the striatum and substantia nigra, and increased IL-10 and IL-4 levels in the substantia nigra in the MPTP mice. Thus, oral Sb may be a potential pharmacological PD treatment alternative.

Metabolic Disturbances in the Gut-brain Axis of a Mouse Model of MPTP-induced Parkinsonism Evaluated by Nuclear Magnetic Resonance

Parkinson's Disease is a synucleinopathy that primarily affects the dopaminergic cells of the central nervous system, leading to motor and gastrointestinal disturbances. However, intestinal peripheral neurons undergo a similar neurodegeneration process, marked by α-synuclein (αSyn) accumulation and loss of mitochondrial homeostasis. We investigated the metabolic alterations in different biometrics that compose the gut-brain axis (blood, brain, large intestine, and feces) in an MPTP-induced mouse model of sporadic Parkinson's Disease. Animals received escalating administration of MPTP. Tissues and fecal pellets were collected, and the metabolites were identified through the untargeted Nuclear Magnetic Resonance spectroscopic (1H NMR) technique. We found differences in many metabolites from all the tissues evaluated. The differential expression of metabolites in these samples mainly reflects inflammatory aspects, cytotoxicity, and mitochondrial impairment (oxidative stress and energy metabolism) in the animal model used. The direct evaluation of fecal metabolites revealed changes in several classes of metabolites. This data reinforces previous studies showing that Parkinson's disease is associated with metabolic perturbation not only in brain-related tissues, but also in periphery structures such as the gut. In addition, the evaluation of the microbiome and metabolites from gut and feces emerge as promising sources of information for understanding the evolution and progression of sporadic Parkinson's Disease.

Gastric Enteric Glial Cells: A New Contributor to the Synucleinopathies in the MPTP-Induced Parkinsonism Mouse

Accumulating evidence has shown that Parkinson's disease (PD) is a systemic disease other than a mere central nervous system (CNS) disorder. One of the most important peripheral symptoms is gastrointestinal dysfunction. The enteric nervous system (ENS) is regarded as an essential gateway to the environment. The discovery of the prion-like behavior of α-synuclein makes it possible for the neurodegenerative process to start in the ENS and spread via the gut-brain axis to the CNS. We first confirmed that synucleinopathies existed in the stomachs of chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)/probenecid (MPTP/p)-induced PD mice, as indicated by the significant increase in abnormal aggregated and nitrated α-synuclein in the TH-positive neurons and enteric glial cells (EGCs) of the gastric myenteric plexus. Next, we attempted to clarify the mechanisms in single MPTP-injected mice. The stomach naturally possesses high monoamine oxidase-B (MAO-B) activity and low superoxide dismutase (SOD) activity, making the stomach susceptible to MPTP-induced oxidative stress, as indicated by the significant increase in reactive oxygen species (ROS) in the stomach and elevated 4-hydroxynonenal (4-HNE) in the EGCs after MPTP exposure for 3 h. Additionally, stomach synucleinopathies appear before those of the nigrostriatal system, as determined by Western blotting 12 h after MPTP injection. Notably, nitrated α-synuclein was considerably increased in the EGCs after 3 h and 12 h of MPTP exposure. Taken together, our work demonstrated that the EGCs could be new contributors to synucleinopathies in the stomach. The early-initiated synucleinopathies might further influence neighboring neurons in the myenteric plexus and the CNS. Our results offer a new experimental clue for interpreting the etiology of PD.

Simvastatin Prevents Neurodegeneration in the MPTP Mouse Model of Parkinson's Disease via Inhibition of A1 Reactive Astrocytes

Emerging evidence indicates that A1 reactive astrocytes play crucial roles in the pathogenesis of Parkinson's disease (PD). Thus, development of agents that could inhibit the formation of A1 reactive astrocytes could be used to treat PD. Simvastatin has been touted as a potential neuroprotective agent for neurologic disorders such as PD, but the specific underlying mechanism remains unclear. The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD and primary astrocytes/neurons were prepared to investigate the effects of simvastatin on PD and its underlying mechanisms in vitro and in vivo. We show that simvastatin protects against the loss of dopamine neurons and behavioral deficits in the MPTP mouse model of PD. We also found that simvastatin suppressed the expression of A1 astrocytic specific markers in vivo and in vitro. In addition, simvastatin alleviated neuron death induced by A1 astrocytes. Our findings reveal that simvastatin is neuroprotective via the prevention of conversion of astrocytes to an A1 neurotoxic phenotype. In light of simvastatin favorable properties, it should be evaluated in the treatment of PD and related neurologic disorders characterized by A1 reactive astrocytes.

Beneficial effects of PGC-1α in the substantia nigra of a mouse model of MPTP-induced dopaminergic neurotoxicity

BACKGROUND

Mitochondrial dysfunction and oxidative stress are closely associated with the pathogenesis of Parkinson's disease. Peroxisome proliferator-activated receptor γ coactivator 1 alpha (PGC-1α) is thought to play multiple roles in the regulation of mitochondrial biogenesis and cellular energy metabolism. We recently reported that altering PGC-1α gene expression modulates mitochondrial functions in N-methyl-4-phenylpyridinium ion (MPP⁺) treated human SH-SY5Y neuroblastoma cells, possibly via the regulation of Estrogen-related receptor α (ERRα), nuclear respiratory factor 1 (NRF-1), nuclear respiratory factor 2 (NRF-2) and peroxisome proliferator-activated receptor γ (PPARγ) expression. In the present study, we aimed to further investigate the potential beneficial effects of PGC-1α in the substantia nigra of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treated C57BL mice.

METHODS

The overexpression or knockdown of the PGC-1α gene in the mouse model of dopaminergic neurotoxicity was performed using a stereotactic injection of lentivirus in MPTP-treated male C57BL/6 mice. Mice were randomly assigned to one of 6 groups (n=24 per group): normal saline (NS) intraperitoneal injection (i.p.) (con); MPTP i.p. (M); solvent of the lentivirus striatal injection (lentivirus control) + MPTP i.p. (LVcon+M); lentivirus striatal injection + MPTP i.p. (LV+M); LV-PGC-1α striatum injection + MPTP i.p. (LVPGC+M); and LV-PGC-1α-siRNA striatal injection + MPTP i.p. (LVsiRNA+M). Intraperitoneal injections of MPTP/NS were conducted two weeks after lentivirus injection.

RESULTS

We found significant improvement in motor behavior and increases in tyrosine hydroxylase expression in the substantia nigra (SN) in the brains of mice in the LVPGC+M group. The opposite tendency was observed in those in the LVsiRNA+M group. The expression of superoxide dismutase (SOD) in the SN region was also consistent with the changes in PGC-1α expression. Electron microscopy showed an increasing trend in the mitochondrial density in the LVPGC+M group and a decreasing trend in the M and LVsiRNA+M groups compared to that in the controls.

CONCLUSIONS

Our results indicated that PGC-1α rescues the effects of MPTP-induced mitochondrial dysfunction in C57BL mice.

NMDA receptor blockade ameliorates abnormalities of spike firing of subthalamic nucleus neurons in a parkinsonian nonhuman primate

N-methyl-D-aspartate receptors (NMDARs) are ion channels comprising tetrameric assemblies of GluN1 and GluN2 receptor subunits that mediate excitatory neurotransmission in the central nervous system. Of the four different GluN2 subunits, the GluN2D subunit-containing NMDARs have been suggested as a target for antiparkinsonian therapy because of their expression pattern in some of the basal ganglia nuclei that show abnormal firing patterns in the parkinsonian state, specifically the subthalamic nucleus (STN). In this study, we demonstrate that blockade of NMDARs altered spike firing in the STN in a male nonhuman primate that had been rendered parkinsonian by treatment with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. In accompanying experiments in male rodents, we found that GluN2D-NMDAR expression in the STN was reduced in acutely or chronically dopamine-depleted animals. Taken together, our data suggest that blockade of NMDARs in the STN may be a viable antiparkinsonian strategy, but that the ultimate success of this approach may be complicated by parkinsonism-associated changes in NMDAR expression in the STN.

Neuroprotective mechanisms of plant extracts against MPTP induced neurotoxicity: Future applications in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease, affecting about seven to 10 million patients worldwide. The major pathological features of PD are loss of dopaminergic neurons in the nigrostriatal pathway and accumulation of alpha-synuclein molecules, forming Lewy bodies. Until now, there is no effective cure for PD, and investigators are searching for neuroprotective strategies to stop or slow the disease progression. The MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) induced neurotoxicity of the nigrostriatal pathway has been used to initiate PD in animal models. Multiple experimental studies showed the ability of several plant extracts to protect against MPTP induced neurotoxicity through activation of catalase, superoxide dismutase, and glutathione reductase enzymes, which reduce the cellular concentration of free radicals, preventing intracellular Ca⁺⁺ release and subsequent apoptosis signaling. Other neuroprotective mechanisms of plant extracts include promoting autophagy of alpha-synuclein molecules and exerting an antiapoptotic activity via inhibition of proteolytic poly (ADP-ribose) polymerase and preventing caspase cleavage. The variety of neuroprotective mechanisms of natural plant extracts may allow researchers to target PD progression in different pathological stages and may be through multiple pathways. Further investigations are required to translate these neuroprotective mechanisms into safe and effective treatments for PD.

Closed-Loop Deep Brain Stimulation Effects on Parkinsonian Motor Symptoms in a Non-Human Primate - Is Beta Enough?

BACKGROUND

Incorporating feedback controls based on real-time measures of pathological brain activity may improve deep brain stimulation (DBS) approaches for the treatment of Parkinson's disease (PD). Excessive beta oscillations in subthalamic nucleus (STN) local field potentials (LFP) have been proposed as a potential biomarker for closed-loop DBS (CL-DBS).

OBJECTIVE

In a non-human primate PD model we compared CL-DBS, which delivered stimulation only when STN LFP beta activity was elevated, to traditional continuous DBS (tDBS).

METHODS

Therapeutic effects of CL-DBS and tDBS relative to the Off-DBS condition were evaluated via a clinical rating scale and objective measures of movement speed during a cued reaching task.

RESULTS

CL-DBS was comparable to tDBS at reducing rigidity, while reducing the amount of time DBS was on by ≈50%; however, only tDBS improved bradykinesia during the reaching behavior. This was likely due to reach-related reductions in beta amplitude that influence the timing and duration of stimulation in the CL-DBS condition.

CONCLUSION

These results illustrate the potential utility of closed-loop DBS devices for PD based on STN beta LFP levels. They also point to possible consequences in behavioral tasks when restricting real-time sensing to a single LFP frequency that itself is modulated during performance of such tasks. The present study provides data that suggest alternate algorithms or more than one physiological biomarker may be required to optimize the performance of behavioral tasks and demonstrates the value of using multiple objective measures when evaluating the efficacy of closed-loop DBS systems.

Medicinal plant Combretum leprosum mart ameliorates motor, biochemical and molecular alterations in a Parkinson's disease model induced by MPTP

ETHNOPHARMACOLOGICAL RELEVANCE

Combretum leprosum is a popular medicinal plant distributed in north and northeastern regions of Brazil. Many different parts of this plant are used in traditional medicine to treat several inflammatory diseases. Parkinson's disease (PD) is a disorder associated with inflammatory toxic factors and the treatments available provide merely a delay of the neurodegeneration.

AIM OF THE STUDY

We investigated the potential neuroprotective properties of the C. leprosum ethanolic extract (C.l.EE) in a murine model of PD using the toxin 1-methyl-4 phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP).

MATERIALS AND METHODS

The mice were split into four groups: V/S (vehicle/saline), E/S (extract/saline), V/M (vehicle/MPTP) and E/M (extract/ MPTP). Mice received MPTP (30mg/kg, i.p.) or vehicle (10ml/kg, i.p.) once a day for 5 consecutive days and vehicle (10ml/kg) or C.l.EE (100mg/kg) orally by intra-gastric gavage (i.g.) during a 14-d period, starting 3 days before the first MPTP injection. All groups were assessed for behavioural impairments (amphetamine-induced locomotor activity and muscle strength), dopamine content in striatum using high performance liquid chromatography (HPLC), tyrosine hydroxylase (TH) and dopamine transporter (DAT) gene expressions using qPCR.

RESULTS

Animals were injected with d-amphetamine (2mg/kg) and the activity was recorded. Amphetamine-induced hyperlocomotion was observed in all groups; however animals treated with MPTP showed exacerbated hyperlocomotion (approximately 3 fold increase compared to control groups). By contrast, mice treated with MPTP that received C.l.EE exhibited attenuation of the hyperlocomotion and did not differ from control groups. Muscle strength test pointed that C.l.EE strongly avoided muscular deficits caused by MPTP (approximately 2 fold increase compared to V/M group). Dopamine and its metabolites were measured in the striatum. The V/M group presented a dopamine reduction of 80%. On the other hand, the E/M group exhibited an increase in dopamine and its metabolites levels (approximately 3 fold increase compared to V/M group). Tyrosine hydroxylase (TH) and dopamine transporter (DAT) gene expressions were significantly reduced in the V/M group (60%). Conversely, C.l.EE treatment was able to increase the mRNA levels of those genes in the E/M group (approximately 2 fold for TH and DAT).

CONCLUSIONS

These data show, for the first time, that C. leprosum ethanolic extract prevented motor and molecular changes induced by MPTP, and partially reverted dopamine deficit. Thus, our results demonstrate that C.l.EE has potential for the treatment and prevention of PD.

The role of TWEAK/Fn14 signaling in the MPTP-model of Parkinson's disease

The tumor necrosis factor like weak inducer of apoptosis (TWEAK) and its receptor, fibroblast growth factor-inducible 14 (Fn14), mediate inflammation and neuronal apoptosis in cerebral edema, ischemic stroke and multiple sclerosis. The downstream effectors and pathways linked to TWEAK-Fn14 signaling are strongly implicated in the pathology of Parkinson's disease (PD), thus indicating a putative role for TWEAK/Fn14 signaling in PD neurodegeneration. Using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model, we aimed to determine whether genetic ablation or pharmacologic mitigation of the TWEAK protein and its Fn14 receptor affected substantia nigra and striatum Parkinsonian pathology. Changes in endogenous TWEAK protein expression were also quantified in tissue from both MPTP-treated mice and PD human samples. TWEAK protein expression was transiently increased in the striatal tissue but remained unaltered in substantia nigra tissue of MPTP-treated mice. There was also no change of TWEAK protein levels in the substantia nigra or the striatum of human PD patients as compared to matched control subjects. Mitigating the effects of endogenous TWEAK protein using neutralizing antibody did affect MPTP-mediated neurotoxicity in the substantia nigra using the sub-acute model of MPTP (30mg/kg i.p. over five consecutive days). Neither TWEAK nor Fn14 genetic ablation led to attenuation of MPTP-toxicity in the acute model. These findings suggest that TWEAK signaling might be an aspect of MPTP-mediated neuropathology and be involved in the overall neurodegenerative pathology of PD.

Neurotoxin mechanisms and processes relevant to Parkinson's disease: an update

The molecular mechanism responsible for degenerative process in the nigrostriatal dopaminergic system in Parkinson's disease (PD) remains unknown. One major advance in this field has been the discovery of several genes associated to familial PD, including alpha synuclein, parkin, LRRK2, etc., thereby providing important insight toward basic research approaches. There is an consensus in neurodegenerative research that mitochon dria dysfunction, protein degradation dysfunction, aggregation of alpha synuclein to neurotoxic oligomers, oxidative and endoplasmic reticulum stress, and neuroinflammation are involved in degeneration of the neuromelanin-containing dopaminergic neurons that are lost in the disease. An update of the mechanisms relating to neurotoxins that are used to produce preclinical models of Parkinson´s disease is presented. 6-Hydroxydopamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and rotenone have been the most wisely used neurotoxins to delve into mechanisms involved in the loss of dopaminergic neurons containing neuromelanin. Neurotoxins generated from dopamine oxidation during neuromelanin formation are likewise reviewed, as this pathway replicates neurotoxin-induced cellular oxidative stress, inactivation of key proteins related to mitochondria and protein degradation dysfunction, and formation of neurotoxic aggregates of alpha synuclein. This survey of neurotoxin modeling-highlighting newer technologies and implicating a variety of processes and pathways related to mechanisms attending PD-is focused on research studies from 2012 to 2014.

REM sleep behavior disorder in the marmoset MPTP model of early Parkinson disease

STUDY OBJECTIVES

Sleep problems are a common phenomenon in most neurological and psychiatric diseases. In Parkinson disease (PD), for instance, sleep problems may be the most common and burdensome non-motor symptoms in addition to the well-described classical motor symptoms. Since sleep disturbances generally become apparent in the disease before motor symptoms emerge, they may represent early diagnostic tools and a means to investigate early mechanisms in PD onset. The sleep disturbance, REM sleep behavior disorder (RBD), precedes PD in one-third of patients. We therefore investigated sleep changes in marmoset monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP), the non-human primate model for idiopathic PD.

DESIGN

Mild parkinsonism was induced in 5 marmoset monkeys (3M/2F) over a 2-week period of subchronic MPTP treatment. Electroencephalograms (EEGs) and electromyograms (EMGs) were recorded weekly. Motor activity and hand-eye coordination were also measured weekly, and any signs of parkinsonism were noted each day. Sleep parameters, motor activity, and performance data before and after MPTP treatment were compared between MPTP-treated marmosets and 4 control marmosets (1M/3F).

RESULTS

MPTP increased the number of sleep epochs with high-amplitude EMG bouts during REM sleep relative to control animals (mean ± SEM percentage of REM 58.2 ± 9.3 vs. 29.6 ± 7.7; P < 0.05). Of all sleep parameters measured, RBD-like measures discriminated best between MPTP-treated and control animals. On the other hand, functional motor behavior, as measured by hand-eye coordination, was not affected by MPTP treatment (correct trials MPTP: 23.40 ± 3.56 vs. control: 36.13 ± 5.88 correct trials; P = 0.32).

CONCLUSIONS

This REM sleep-specific change, in the absence of profound changes in wake motor behaviors, suggests that the MPTP marmoset model of PD could be used for further studies into the mechanisms and treatment of RBD and other sleep disorders in premotor symptom PD.

The antioxidative effect of electro-acupuncture in a mouse model of Parkinson's disease

Accumulating evidence indicates that oxidative stress plays a critical role in Parkinson's disease (PD). Our previous work has shown that 100 Hz electro-acupuncture (EA) stimulation at ZUSANLI (ST36) and SANYINJIAO (SP6) protects neurons in the substantia nigra pars compacta from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity in male C57BL/6 mice, a model of PD. In the present study we administered 100 Hz EA stimulation at the two acupoints to MPTP-lesioned mice for 12 sessions starting from the day prior to the first MPTP injection. We found that in the striatum of MPTP treated mice 100 Hz EA stimulation effectively inhibited the production of hydrogen peroxide and malonaldehyde, and increased glutathione concentration and total superoxide dismutase activity through biochemical methods. However, it decreased glutathione peroxidase activity via biochemical analysis and did not affect the level of 1-methyl-4-phenylpyridinium in the striatum revealed by high performance liquid chromatography with ultraviolet detection. These data suggest that 100 Hz EA stimulation at ST36 and SP6 has antioxidative effects in the MPTP model of PD. This data, along with our previous work, indicates that 100 Hz EA stimulation at ST36 and SP6 protects the nigrostriatal system by multiple mechanisms including antioxidation and antiapoptosis, and suggests that EA stimulation is a promising therapy for treating PD.

The MPTP marmoset model of parkinsonism: a multi-purpose non-human primate model for neurodegenerative diseases

Aging societies face an increasing prevalence of neurodegenerative disorders for which no cure exists. The paucity of relevant animal models that faithfully reproduce clinical and pathogenic features of neurodegenerative diseases is a major cause for the lack of effective therapies. Clinically distinct disorders, such as Alzheimer's and Parkinson's disease, are driven by overlapping pathogenic mechanisms that converge onto vulnerable neurons to ultimately cause abnormal clinical outcomes. These similarities, particularly in the early phases of neurodegeneration, might help identify appropriate animal model systems for studying of cell pathology. While reviewing some of the cellular mechanisms of disease progression, we discuss the MPTP-induced model of Parkinsonism in marmoset monkeys as a model system for construct, face and predictive validity in neurodegenerative studies.

Tyrosine hydroxylase-positive amacrine interneurons in the mouse retina are resistant against the application of various parkinsonian toxins

Toxins such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 6-hydroxydopamine (6-OHDA), or rotenone have been used to induce degeneration of dopaminergic (DA) neurons in the nigrostriatal pathway and to reproduce pathological characteristics of Parkinson's disease (PD). DA neurons are also present in the retina, and visual impairments in PD patients have been reported. We examined the vulnerability of TH-positive (TH(+)) amacrine interneurons in the retina against MPTP, 6-OHDA, or rotenone-induced cell death. We intraperitoneally (i.p.) injected mice with MPTP, which induced degeneration of DA neurons in the midbrain. However, no death of TH(+) amacrine cells was detectable in the same mice. HPLC analysis revealed a 9 times lower level of the toxic metabolite of MPTP, MPP(+), in the eye compared with the striatum. Another membrane-permeable compound (Tat-Hsp70) could be delivered into the retina after i.p. application, suggesting that the blood-retina barrier (BRB) could be overcome after systemic application. Possible reason for the survival of retinal amacrine cells after systemic MPTP application was a less efficient conversion into toxic MPP(+) in the retina or a general higher resistance against toxic insults of retinal DA neurons compared with DA neurons in the substantia nigra pars compacta (SNpc). Therefore, we directly injected high doses of MPP(+), 6-OHDA, or rotenone into the eye. No loss of TH(+) amacrine cells in the retina was observed, suggesting different properties and less vulnerability of amacrine neurons compared with DA neurons in the midbrain.

[The experimental models of Parkinson's disease in animals]

The current review describes the modem Parkinson's disease models in animals, their advantages, limitations and disadvantages. It was noted that the most widespread up-to-date models based on etiology of the Parkinson's disease. Although toxins mostly produce the Parkinson's disease, a study of involved genes allows investigating not only inherited but also sporadic (not inherited) forms of disease since the same genes are involved in both cases. Mutations of genes lead to formation of "mutant" toxic proteins, which produce a death of the specialized neurons of the nigrostriatal dopaminergic system and the development of Parkinson's disease. A significant place in the review takes adescription of characteristics of the toxic models produced by 6-OHDA, MPTP and rotenone, their similarities and differences in pathogenetic mechanisms of the Parkinson's disease development. On the basis of the considered experimental models of Parkinson's disease a conclusion has been done that none of these models may in full and adequate scale imitate the entire clinical, pathophysiological, morphological, biochemical and other aspects of the Parkinson's disease development.

Neuroprotective activities of CD4+CD25+ regulatory T cells in an animal model of Parkinson's disease

Progressive loss of dopaminergic neurons in the substantia nigra pars compacta and their terminal connections in the striatum are central features in Parkinson's disease (PD). Emerging evidence supports the notion that microglia neuroinflammatory responses speed neurodegenerative events. We demonstrated previously that this can be slowed by adoptive transfer of T cells from Copolymer-1-immunized mice administered to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) recipients. The cellular basis for this neuroprotective response was the CD4+ T cell population, suggesting involvement of CD4+CD25+ regulatory T cells (Tregs), cells known to suppress immune activation and maintain immune homeostasis and tolerance. We show for the first time that adoptive transfer of CD3-activated Tregs to MPTP-intoxicated mice provides greater than 90% protection of the nigrostriatal system. The response was dose-dependent and paralleled modulation of microglial responses and up-regulation of glial cell-derived neurotrophic factor (CDNF) and TGF-beta. Interestingly, that adoptive transfer of effector T cells showed no significant neuroprotective activities. Tregs were found to mediate neuroprotection through suppression of microglial responses to stimuli, including aggregated, nitrated alpha-synuclein. Moreover, Treg-mediated suppression was also operative following removal of Tregs from culture prior to stimulation. This neuroprotection was achieved through modulation of microglial oxidative stress and inflammation. As Tregs can be modulated in vivo, these data strongly support the use of such immunomodulatory strategies to treat PD.

Antioxidative and anti-inflammatory effects of four cysteine-containing agents in striatum of MPTP-treated mice

OBJECTIVES

Mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were used to examine the neuroprotective effects of n-acetyl cysteine (NAC), s-ethyl cysteine (SEC), s-methyl cysteine (SMC), and s-propyl cysteine (SPC).

METHODS

Each agent at 1 g/L was directly added to the drinking water for 3 wk. Mice were treated by subcutaneous injection of MPTP (24 mg/kg body weight) for 6 consecutive days. The brain from each mouse was quickly removed and the striatum was collected for analyses.

RESULTS

The MPTP treatment significantly depleted striatal glutathione content, reduced the activity of glutathione peroxidase (GPX), superoxide dismutase (SOD), and catalase, increased malondialdehyde level, and elevated interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) levels in striatum (P < 0.05). The pre-intake of NAC, SEC, SMC, and SPC significantly attenuated MPTP-induced glutathione loss, retained the activity of GPX and SOD, diminished oxidative stress, and suppressed MPTP-induced elevation of IL-6 and TNF-alpha (P < 0.05). MPTP treatment significantly suppressed GPX mRNA expression and enhanced TNF-alpha mRNA expression (P < 0.05). Compared with MPTP treatment alone, the pre-intake of NAC, SEC, SMC, and SPC significantly elevated GPX mRNA expression and diminished TNF-alpha mRNA expression (P < 0.05), in which SPC showed the greatest suppressive effect against MPTP-induced TNF-alpha mRNA expression (P < 0.05). Dopamine and 3,4-dihydroxyphenylacetic acid contents in the striatum were significantly decreased by MPTP treatment (P < 0.05). The pre-intake of four test agents significantly improved MPTP-induced dopamine depletion and increased dopamine/3,4-dihydroxyphenylacetic acid content (P < 0.05).

CONCLUSION

These results suggest that these cysteine-containing compounds could provide antioxidative and anti-inflammatory protection for the striatum against the development of Parkinson's disease.

Increased vulnerability of nigrostriatal terminals in DJ-1-deficient mice is mediated by the dopamine transporter

Mutations in the gene for DJ-1 have been associated with early-onset autosomal recessive parkinsonism. Previous studies of null DJ-1 mice have shown alterations in striatal dopamine (DA) transmission with no DAergic cell loss. Here we characterize a new line of DJ-1-deficient mice. A subtle locomotor deficit was present in the absence of a change in striatal DA levels. However, increased [(3)H]-DA synaptosomal uptake and [(125)I]-RTI-121 binding were measured in null DJ-1 vs. wild-type mice. Western analyses of synaptosomes revealed significantly higher dopamine transporter (DAT) levels in pre-synaptic membrane fractions. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exposure exacerbated striatal DA depletion in null DJ-1 mice with no difference in DAergic nigral cell loss. Furthermore, increased 1-methyl-4-phenylpyridinium (MPP(+)) synaptosomal uptake and enhanced MPP(+) accumulation were measured in DJ-1-deficient vs. control striatum. Thus, under null DJ-1 conditions, DAT changes likely contribute to altered DA neurotransmission and enhanced sensitivity to toxins that utilize DAT for nigrostriatal entry.

Synthetic bovine proline-rich-polypeptides generate hydroxyl radicals and fail to protect dopaminergic neurons against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic neurotoxicity in mice

Proline-rich-polypeptides (PRPs) isolated from bovine hypothalamus have been shown to render protection against neuronal injury of the brain and spinal cord. We examined two PRPs containing 15 and 10 amino acid residues (PRP-1 and PRP-4 synthetic polypeptide) for their effect, if any, on dopaminergic neuronal damage caused by the parkinsonian neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Effects of these PRPs on hydroxyl radical ((*)OH) generation in a Fenton-like reaction as well as from isolated mitochondria were monitored, employing a sensitive salicylate hydroxylation procedure. Balb/c mice treated (i.p., twice, 16 h apart) with MPTP (30 mg/kg) or PRP-1 (1.6 mg/kg), but not PRP-4 (1.6 mg/kg) showed significant loss of striatal dopamine and norepinephrine as assayed by an HPLC-electrochemical procedure. Pretreatment with the PRPs, 30 min prior to the neurotoxin administration failed to attenuate MPTP-induced striatal dopamine or norepinephrine depletion, but significantly attenuated the MPTP-induced decrease in dopamine turnover. A significant increase in the generation of (*)OH by the PRPs in a Fenton-like reaction or from isolated mitochondria suggests their pro-oxidant action, and explains their failure to protect against MPTP-induced parkinsonism in mice.

Different parkinsonism models produce a time-dependent induction of COX-2 in the substantia nigra of rats

The present study investigated the effects on general activity, COX-2 and TH protein expression of intranigral neurotoxins LPS, MPTP or 6-OHDA infusion in rats. Results indicate that LPS produced an increase in locomotion frequency (3 and 7 days after surgery) and a strong up-regulation of COX-2 protein 16 and 24 h after surgery, as observed in the substantia nigra (SN). The MPTP model generated impairment in locomotion frequency 24 h after surgery. Besides, MPTP caused a marked up-regulation in COX-2 protein observed in the SN 16 h after surgery. Moreover, the 6-OHDA model produced severe motor impairment indicated by the decrease in locomotion (24 h) and rearing (24 h, 3 and 7 days) frequencies and also an increase in latency (24 h, 3 and 7 days) and immobility (24 h and 3 days) times. We also demonstrated an up-regulation of COX-2, which occurred in the SN 4-24 h after surgery. TH protein did not appear to be reduced in the striatum in the groups lesioned with the neurotoxins. In contrast, the TH content of SN was significantly reduced in the groups lesioned with the very same neurotoxins. For all the models analyzed, we observed no statistical differences in the expression of COX-2 in the striatum along the time-points. The results of the present study suggest that COX-2 induction patterns differ in function of the neurotoxin tested. Such time-dependent induction has been found to be relatively constant, a fact of great significance considering the importance of the neuroinflammatory process in Parkinson's disease.

The copper chelator, D-penicillamine, does not attenuate MPTP induced dopamine depletion in mice

In MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and 6-hydroxydopamine induced dopaminergic neurotoxicity and Parkinson's disease iron accumulates in substantia nigra pars compacta which has been suggested to participate in oxidative stress induced neurodegeneration. Pretreatment with iron chelators desferal, clioquinol, VK-28 and M30 are neuroprotective in both models. To determine the specificity of chelation neuroprotective activity we have examined the effect of D-penicillamine, a relatively specific copper chelator, in the mice model of MPTP-induced dopamine depletion. Our studies show that D-penicillamine, employed for removal of copper in Wilson disease is relatively weak in preventing dopaminergic neurotoxicity induced by MPTP, as compared to iron chelators previously studied. The results indicate that for prevention of MPTP-induced dopamine depletion and dopamine neurodegeneration, iron rather than copper chelation may be more effective and specific.

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.

Epigallocatechin gallate protects dopaminergic neurons against 1-methyl-4- phenyl-1,2,3,6-tetrahydropyridine-induced neurotoxicity by inhibiting microglial cell activation

OBJECTIVE

To observe whether the dopaminergic neuroprotective effect of (-)-epigallocatechin gallate (EGCG) is associated with its inhibition of microglial cell activation in vivo.

METHODS

The effects of EGCG at different doses on dopaminergic neuronal survival were tested in a methyl-4-phenyl-pyridinium (MPP+)-induced dopaminergic neuronal injury model in the primary mesencephalic cell cultures. With unbiased stereological method, tyrosine hydroxylase-immunoreactive (TH-ir) cells were counted in the A8, A9 and A10 regions of the substantia nigra (SN) in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57BL/6 mice. The effect of EGCG on microglial activation in the SN was also investigated.

RESULTS

Pretreatment with EGCG (1 to 100 micromol/L) significantly attenuated MPP+-induced TH-ir cell loss by 22.2% to 80.5% in the mesencephalic cell cultures. In MPTP-treated C57BL/6 mice, EGCG at a low concentration (1 mg/kg) provided significant protection against MPTP-induced TH-ir cell loss by 50.9% in the whole nigral area and by 71.7% in the A9 region. EGCG at 5 mg/kg showed more prominent protective effect than at 1 or 10 mg/kg. EGCG pretreatment significantly inhibited microglial activation and CD11b expression induced by MPTP.

CONCLUSION

EGCG exerts potent dopaminergic neuroprotective activity by means of microglial inhibition, which shed light on the potential use of EGCG in treatment of Parkinson's disease.

JNK inhibition as a potential strategy in treating Parkinson's disease

Parkinson's disease is characterized by the pathological loss of dopaminergic neurons in the substantia nigra. The current therapy for Parkinson's disease is aimed to replace the lost transmitter. But the ultimate objective in the neurodegenerative therapy is the functional restoration and/or cessation of progression of neuronal loss. Given the critical role that the c-Jun N-terminal kinase (JNK) pathway plays in regulating the cellular processes that are involved in Parkinson's disease, the importance of JNK in this disease's pathogenesis is being increasingly recognized. Much evidence suggests that JNK plays an important role in mediating 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)/1-methyl-4-phenylpyridnium ion (MPP(+))-induced neurotoxicity. Therefore, direct blockade of JNK may prevent or effectively slow the progression of Parkinson's disease. Studies including our own showed that the inhibition of JNK with SP-600125, a specific inhibitor of JNK, protects dopaminergic neurons both from MPP(+)-induced neuronal apoptosis in vitro and in MPTP Parkinson's disease model. These results support JNK inhibition as a potential strategy in treating Parkinson's disease.

Interleukine-1beta and interleukine-6 levels in striatum and other brain structures after MPTP treatment: influence of behavioral lateralization

MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) induces diminution of the dopamine in nigrostriatal pathway and cognitive deficits in mice. MPTP treatment also increases pro-inflammatory cytokine production in substantia nigra and striatum. Since, pro-inflammatory cytokines influence striatal dopamine content and provoke cognitive impairments, the cognitive defects induced by MPTP may be partly due to brain cytokine induction in other structures than nigrostriatal pathway. Furthermore, behavioral lateralization, as assessed by paw preference, influences cytokine production at the periphery and in the central nervous system. Behavioral lateralization may thus influence brain cytokine levels after MPTP. In order to address these issues, mice selected for paw preference were injected with 25 mg/kg MPTP i.p. for five consecutive days after which striatal dopamine and DOPAC contents were measured by HPLC and IL-1beta and IL-6 quantified by ELISA in the striatum, cerebral cortex, hippocampus and hypothalamus. The results showed that MPTP treatment induced dramatic loss of DA in striatum, simultaneously, IL-6 levels decreased in the striatum and increased in hippocampus and hypothalamus, while IL-1beta levels decreased in the striatum, cerebral cortex and hippocampus. Interestingly, striatal dopamine turnover under basal conditions as well as striatal IL-1beta and IL-6 levels under basal conditions and after MPTP depended on behavioral lateralization. Left pawed mice showed a higher decrease in dopamine turnover and lower cytokine levels as compared to right pawed animals. Behavioral lateralization also influenced IL-6 hippocampal levels under basal conditions and IL-1beta cortical levels after MPTP. From these results, it can be concluded that MPTP-induced cognitive defects are accompanied by an alteration of pro-inflammatory cytokine levels in brain structures other than those involved in the nigrostriatal pathway. In addition, MPTP-induced dopamine decrease is influenced by behavioral lateralization, possibly through an effect on brain cytokine levels.

L-3-hydroxyacyl-CoA dehydrogenase II protects in a model of Parkinson's disease

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) impairs mitochondrial respiration and damages dopaminergic neurons as seen in Parkinson's disease (PD). Here, we report that L-3-hydroxyacyl-CoA dehydrogenase type II/amyloid binding alcohol dehydrogenase (HADH II/ABAD), a mitochondrial oxidoreductase enzyme involved in neuronal survival, is downregulated in PD patients and in MPTP-intoxicated mice. We also show that transgenic mice with increased expression of human HADH II/ABAD are significantly more resistant to MPTP than their wild-type littermates. This effect appears to be mediated by overexpression of HADH II/ABAD mitigating MPTP-induced impairment of oxidative phosphorylation and ATP production. This study demonstrates that HADH II/ABAD modulates MPTP neurotoxicity and suggests that HADH II/ABAD mimetics may provide protective benefit in the treatment of PD.

Heat shock protects PC12 cells against MPP+ toxicity

A mild heat shock preconditioning has been shown to induce thermotolerance and protection against a number of cytotoxic agents that may induce cell death by either apoptosis or necrosis. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin that selectively targets dopaminergic cells of the substantia nigra and, as such, it is often used to induce neuronal cell death in models of Parkinson's disease. PC12 cells were heat-shocked for 1 h at 41.5 degrees C. This led to a rapid induction of Hsp25 and Hsp70. Levels of these proteins remained elevated for at least 24 h post heat shock. Treatment of PC12 cells with 1-methyl-4-phenylpyridinium (MPP(+)), the active metabolite of MPTP, resulted in cell death. Morphological analysis and the lack of caspase activity suggested that cell death was by necrosis. Heat shocking the cells 6 h prior to addition of MPP(+) significantly inhibited the induction of cell death by MPP(+). These results indicated that heat shock is protective against MPP(+) neurotoxicity in PC12 cells.

Cerebral alterations in a MPTP-mouse model of Parkinson's disease--an immunocytochemical study

We investigated the immunohistochemical alterations of neuronal nitric oxide synthase (nNOS), endothelial NOS (eNOS), tyrosine hydroxylase (TH), microtubule-associated protein 2a,b (MAP 2), glial fibrillary acidic protein (GFAP), parvalbumin (PV), and dopamine transporter (DAT) in the striatum and substantia nigra following the application of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice. TH-, MAP 2- and DAT-immunoreactive cells were decreased gradually in the striatum and substantia nigra from 1 day up to 7 days after MPTP treatment, as well as the reduction of the striatal dopamine, DOPAC and HVA content. The number of GFAP-immunoreactive astrocytes increased gradually in the striatum and substantia nigra from 1 day up to 7 days after MPTP treatment. Striatal nNOS-immunoreactive cells were unchanged in MPTP-treated mice. In the substantia nigra, intense immunoreactivity of nNOS-positive cells increased 5 hr after MPTP treatment. Thereafter, the immunoreactivity of nNOS-positive cells decreased gradually from 1 day up to 7 days after MPTP treatment. eNOS-immunopositive cells were unchanged in the striatum and substantia nigra. These results demonstrate that nNOS may play a key role in the development of MPTP neurotoxicity. Our findings also indicate that MPTP can cause the functional damage of interneurons in the substantia nigra, but not in the striatum.

Role of alpha-synuclein in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism in mice

In humans, mutations in the alpha-synuclein gene or exposure to the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produce Parkinson's disease with loss of dopaminergic neurons and depletion of nigrostriatal dopamine. alpha-Synuclein is a vertebrate-specific component of presynaptic nerve terminals that may function in modulating synaptic transmission. To test whether MPTP toxicity involves alpha-synuclein, we generated alpha-synuclein-deficient mice by homologous recombination, and analyzed the effect of deleting alpha-synuclein on MPTP toxicity using these knockout mice. In addition, we examined commercially available mice that contain a spontaneous loss of the alpha-synuclein gene. As described previously, deletion of alpha-synuclein had no significant effects on brain structure or composition. In particular, the levels of synaptic proteins were not altered, and the concentrations of dopamine, dopamine metabolites, and dopaminergic proteins were unchanged. Upon acute MPTP challenge, alpha-synuclein knockout mice were partly protected from chronic depletion of nigrostriatal dopamine when compared with littermates of the same genetic background, whereas mice carrying the spontaneous deletion of the alpha-synuclein gene exhibited no protection. Furthermore, alpha-synuclein knockout mice but not the mice with the alpha-synuclein gene deletion were slightly more sensitive to methamphetamine than littermate control mice. These results demonstrate that alpha-synuclein is not obligatorily coupled to MPTP sensitivity, but can influence MPTP toxicity on some genetic backgrounds, and illustrate the need for extensive controls in studies aimed at describing the effects of mouse knockouts on MPTP sensitivity.

Differential declines in striatal nicotinic receptor subtype function after nigrostriatal damage in mice

Nigrostriatal damage leads to a reduction in striatal nicotinic acetylcholine receptors (nAChRs) in rodents, monkeys, and patients with Parkinson's disease. The present studies were undertaken to investigate whether these nAChR declines are associated with alterations in striatal nAChR function and, if so, to identify the receptor subtypes involved. To induce nigrostriatal damage, mice were injected with the selective dopaminergic toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We measured [(125)I]3 beta-(4-iodophenyl)tropane-2 beta-carboxylic acid isopropyl ester (RTI-121, dopamine transporter), (125)I-alpha-conotoxin MII (putative alpha 6-containing sites in the central nervous system), (125)I-epibatidine (multiple sites), 5-[(125)I]iodo-3-[2(S)-azetidinylmethoxy]pyridine-2HCl ([(125)I]A85380; beta2-containing sites), and (125)I-alpha-bungarotoxin (alpha 7-containing sites) binding in brains from control and MPTP-treated mice, as well as nAChR function by [(3)H]dopamine release, [(3)H]GABA release, and [(86)Rb(+)] efflux. After MPTP treatment, declines were observed in striatal dopamine transporter levels, both binding and functional measures of striatal alpha-conotoxin MII-sensitive nAChRs, and selected measures of striatal alpha-conotoxin MII-resistant nAChRs. In contrast, (125)I-alpha-bungarotoxin binding sites were not altered after nigrostriatal damage. The changes in striatal nAChRs were selective, with no declines in cortex, thalamus, or septum. Those striatal binding and functional measures of nAChRs that decreased with MPTP treatment correlated with dopamine transporter declines, an observation suggesting that the binding and functional changes in nAChRs are limited to dopaminergic terminals. The present results are the first to demonstrate differential alterations in nAChR subtype function after nigrostriatal damage, with a close correspondence between changes in receptor binding sites and function. These data suggest that the declines in nAChR sites observed in Parkinson's disease brains may be of functional significance.

The mouse MPTP model: gene expression changes in dopaminergic neurons

Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by the progressive loss of dopaminergic neurons in the substantia nigra. Although valuable animal models have been developed, our knowledge of the aetiology and pathogenic factors implicated in PD is still insufficient to develop causal therapeutic strategies aimed at halting its progression. The neurotoxicity induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is one of the most valuable models for analysing pathological aspects of PD. In this paper we studied the gene expression patterns underlying the pathogenesis of MPTP-induced neurodegeneration. We treated young and old C57BL/6 mice with different schedules of MPTP to induce degenerative processes that vary in intensity and time-course. During the first week after intoxication we used nonradioactive in situ-hybridization to investigate the expression patterns of genes associated with (i) dopamine metabolism and signalling; (ii) familial forms of PD; (iii) protein folding and (iv) energy metabolism. MPTP injections induced different severities of neuronal injury depending on the age of the animals and the schedule of administration as well as a significant degeneration in the striatum. In situ hybridization showed that MPTP intoxication initiated a number of gene expression changes that (i) were restricted to the neurons of the substantia nigra pars compacta; (ii) were correlated in intensity and number of changes with the age of the animals and the severity of histopathological disturbances; (iii) displayed in each a significant down-regulation by the end of one week after the last MPTP injection, but (iv) varied within one MPTP regimen in expression levels during the observation period. The subacute injection of MPTP into one-year-old mice induced the most severe changes in gene expression. All genes investigated were affected. However, alpha-synuclein was the only gene that was exclusively up-regulated in MPTP-treated animals displaying cell death.

Disruption of information processing in the supplementary motor area of the MPTP-treated monkey: a clue to the pathophysiology of akinesia?

It has been suggested that the underactivity of mesial frontal structures induced by dopamine depletion could constitute one of the main substrates underlying akinesia in Parkinson's disease. Functional imaging and movement-related potential recordings indicate an implication of the frontal lobes in this pathological process, but the question has not yet been investigated at a cellular level using single unit recording. We therefore compared neuronal activity in both the presupplementary motor area (pre-SMA) and the supplementary motor area proper (SMAp) of the Macaca mulatta monkey during a delayed motor task, before and after MPTP treatment. In the pre-SMA, which receives strong inputs from the prefrontal cortex, the baseline firing frequency and the percentage of neurons responding to visual instruction cues decreased in lesioned monkeys. In the SMAp, which sends direct outputs to the primary motor cortex, not only was the response to visual cues impaired, but the percentage of SMAp neurons responding to intracortical microstimulation fell and the threshold of response rose. Neuronal activity after the Go signal diminished sharply in both structures in the symptomatic animal and the discharge pattern became more irregular; in the SMAp neuronal activity remained modified longer. Most of these changes could already be observed in the presymptomatic animal presenting no clinical signs of parkinsonism. These data would indicate that, at the moment when dopamine depletion has impaired the ability of cortical neurons to operate the focused selection of incoming information giving instructions for movement, pre-SMA and SMAp neurons are also in a state of severe hypoactivity. The conjunction of these phenomena could play a critical role in the genesis of akinesia.

Zinc potentiates 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine induced dopamine depletion in caudate nucleus of mice brain

Present study describes the effect of zinc (Zn) on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced dopamine depletion in mice brain. MPTP is a known neurotoxicant primarily causing marked depletion of dopamine (DA) levels in nigrostriatal dopaminergic system. Adult Male C57-mice were intraperitonially injected with 25 mg/kg MPTP in the presence or absence of zinc acetate. Twenty-four hours after treatment animals were sacrificed and DA levels were determined by high performance liquid chromatography in caudate nucleus of control and treated mice. The results showed that there was a marked depletion of DA in MPTP treated mice, whereas no change was observed in DA levels in mice treated with Zn when compare to controls. Interestingly, mice receiving MPTP in conjunction with Zn showed significantly lower DA levels in brain when compare to animals receiving MPTP alone. In summary the data suggest that Zn treatment potentiates depletion of dopamine in MPTP treated mice.

[The role of substantia nigra in the cognitive activity in cats]

The role of substantia nigra (SN) in the cat cognitive activity of different complexity degree, was investigated by original technique. Neurosurgery or neurochemical SN switching off leads to reliable disturbances of condition, reflexes, generalization and abstraction. Rehabilitation was possible after pharmacological stimulation of dopaminergic, partly GABA-ergic, and cholinergic systems. Stimulation of serotonin system was ineffective.

Attenuation of 1-methyl-4-phenylpyridinium (MPP+) neurotoxicity by deprenyl in organotypic canine substantia nigra cultures

Systemic administration of MPTP to experimental animals induces neurodegeneration of dopaminergic neurons in the central nervous system. MPTP crosses the blood-brain barrier where it is taken up by astrocytes and converted to MPP+ by monamine oxidase-B (MAO-B). Subsequently, MPP+ is selectively taken up by dopaminergic neurons upon which it exerts intracellular neurotoxic effects. Systemic administration of the selective MAO-B inhibitor deprenyl prevents the conversion of MPTP to MPP+ and by this mechanism is able to protect against MPTP neurotoxicity. Deprenyl has also been reported to exert neuroprotective effects that are independent of its MAO-B inhibitory properties, but since MPP+ itself does not cross the blood-brain barrier it is difficult to directly study the MAO-B independent in vivo effects of MPP+ itself. One approach is to use organotypic tissue cultures of the canine substantia nigra (CSN) which permit administration of precise concentrations of pharmacological agents directly to mature, well-developed and metabolically active dopaminergic neurons. These neurons as well as other components of the cultures exhibit morphological and biochemical characteristics identical to their in vivo counterparts. This study was undertaken to evaluate the neuroprotective effects of deprenyl in MPP(+)-treated cultures by measuring changes in the levels of HVA as an indicator of dopamine release and metabolism by dopaminergic neurons and to correlate this indication of dopaminergic function with morphological evidence of survival or loss of dopaminergic neurons in mature CSN cultures. Mature CSN cultures, at 44 days in vitro (DIV), were exposed to either MPP+ alone, deprenyl alone or simultaneously to both deprenyl and MPP+ or to MPP+ following 4 day pretreatment with deprenyl. Exposure to MPP+ alone caused significant reduction in HVA levels, evidence of widespread injury and ultimate disappearance of large neurons in the cultures. These effects were attenuated by simultaneous exposure to MPP+ and deprenyl and the destructive effects of MPP+ appeared to be prevented by pretreatment with deprenyl. Thus the neuroprotective effects of deprenyl on MPP(+)-induced reduction of HVA levels in living cultures appears similar to the effects of deprenyl on dopamine levels and tyrosine hydroxylase activity reported by others in cultures previously exposed to deprenyl and MPP+. These studies also confirm that the neuroprotective effects of deprenyl against MPP+ in dopaminergic neurons are, at least in part, independent of deprenyl's inhibition of MAO-B.

Neurotoxicology of the brain barrier system: new implications

The concept of a barrier system in the brain has existed for nearly a century. The barrier that separates the blood from the cerebral interstitial fluid is defined as the blood-brain barrier, while the one that discontinues the circulation between the blood and cerebrospinal fluid is named the blood-cerebrospinal fluid barrier. Evidence in the past decades suggests that brain barriers are subject to toxic insults from neurotoxic chemicals circulating in blood. The aging process and some disease states render barriers more vulnerable to insults arising inside and outside the barriers. The implication of brain barriers in certain neurodegenerative diseases is compelling, although the contribution of chemical-induced barrier dysfunction in the etiology of any of these disorders remains poorly understood. This review examines what is currently understood about brain barrier systems in central nervous system disorders by focusing on chemical-induced neurotoxicities including those associated with nitrobenzenes, N-methyl-D-aspartate, cyclosporin A, pyridostigmine bromide, aluminum, lead, manganese, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and 3-nitropropionic acid. Contemporary research questions arising from this growing understanding show enormous promises for brain researchers, toxicologists, and clinicians.

Alpha-synuclein up-regulation in substantia nigra dopaminergic neurons following administration of the parkinsonian toxin MPTP

Mutations in alpha-synuclein cause a form of familial Parkinson's disease (PD), and wild-type alpha-synuclein is a major component of the intraneuronal inclusions called Lewy bodies, a pathological hallmark of PD. These observations suggest a pathogenic role for alpha-synuclein in PD. Thus far, however, little is known about the importance of alpha-synuclein in the nigral dopaminergic pathway in either normal or pathological situations. Herein, we studied this question by assessing the expression of synuclein-1, the rodent homologue of human alpha-synuclein, in both normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. In normal mice, detectable levels of synuclein mRNA and protein were seen in all brain regions studied and especially in ventral midbrain. In the latter, there was a dense synuclein-positive nerve fiber network, which predominated over the substantia nigra, and only few scattered synuclein-positive neurons. After a regimen of MPTP that kills dopaminergic neurons by apoptosis, synuclein mRNA and protein levels were increased significantly in midbrain extracts; the time course of these changes paralleled that of MPTP-induced dopaminergic neurodegeneration. In these MPTP-injected mice, there was also a dramatic increase in the number of synuclein-immunoreactive neurons exclusively in the substantia nigra pars compacta; all synuclein-positive neurons were tyrosine hydroxylase-positive, but none coexpressed apoptotic features. These data indicate that synuclein is highly expressed in the nigrostriatal pathway of normal mice and that it is up-regulated following MPTP-induced injury. In light of the synuclein alterations, it can be suggested that, by targeting this protein, one may modulate MPTP neurotoxicity and, consequently, open new therapeutic avenues for PD.

Differing effects of N-methyl-D-aspartate receptor subtype selective antagonists on dyskinesias in levodopa-treated 1-methyl-4-phenyl-tetrahydropyridine monkeys

The antiparkinsonian and antidyskinetic profile of two N-methyl-D-aspartate (NMDA) receptor antagonists, a competitive antagonist, (R)-4-oxo-5-phosphononorvaline (MDL 100,453), and a novel noncompetitive allosteric site antagonist, 4-hydroxy-N-[2-(4-hydroxyphenoxy)ethyl]-4-(4-methylbenzyl)piper idi ne (Co 101244/PD 174494), was assessed in six levodopa-treated 1-methyl-4-phenyl-tetrahydropyridine-lesioned parkinsonian monkeys. The effects on motor function of these two drugs, alone and in combination with levodopa, were then correlated with NMDA subtype selectivity and apparent affinity for four diheteromeric NMDA receptor subunit combinations expressed in Xenopus oocytes. MDL 100, 453 (300 mg/kg s.c.) by itself increased global motor activity (p =. 0005 versus vehicle) and administered 15 min after a low dose of levodopa/benserazide s.c., MDL 100,453 (50, 300 mg/kg s.c.) showed dose-dependent potentiation of antiparkinsonian responses and also produced dyskinesias. Following injection of a fully effective dose of levodopa, MDL 100,453 (300 mg/kg s.c.) also produced a 25% increase in mean dyskinesia score (p =.04). In contrast, Co 101244 did not change motor activity by itself and only showed a tendency to potentiate the antiparkinsonian response when given in combination with a low dose of levodopa, which did not attain statistical significance. However, with a high dose of levodopa, Co 101244 (0.1, 1 mg/kg s.c.) displayed antidyskinetic effects (67 and 71% reduction, respectively) while sparing levodopa motor benefit. In vitro, MDL 100,453 was an NMDA glutamate-site antagonist, with approximately 5- to 10-fold selectivity for the NR1A/NR2A subtype combination (K(b) = 0.6 microM) versus NR1A in combination with 2B, 2C, or 2D. In contrast, the allosteric site antagonist Co 101244 showed approximately 10,000-fold selectivity for the NR1A/NR2B (IC(50) = 0.026 microM) versus the other three subunit combinations tested. Taken together, the data suggest that the NR2 subunit selectivity profile of NMDA receptor antagonists can play an important role in predicting behavioral outcome and offer more evidence that NR2B-selective NMDA receptor antagonists may be useful agents in the treatment of Parkinson's disease.

Dietary restriction and 2-deoxyglucose administration improve behavioral outcome and reduce degeneration of dopaminergic neurons in models of Parkinson's disease

Parkinson's disease (PD) is an age-related disorder characterized by progressive degeneration of dopaminergic neurons in the substantia nigra (SN) and corresponding motor deficits. Oxidative stress and mitochondrial dysfunction are implicated in the neurodegenerative process in PD. Although dietary restriction (DR) extends lifespan and reduces levels of cellular oxidative stress in several different organ systems, the impact of DR on age-related neurodegenerative disorders is unknown. We report that DR in adult mice results in resistance of dopaminergic neurons in the SN to the toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP-induced loss of dopaminergic neurons and deficits in motor function were ameliorated in DR rats. To mimic the beneficial effect of DR on dopaminergic neurons, we administered 2-deoxy-D-glucose (2-DG; a nonmetabolizable analogue of glucose) to mice fed ad libitum. Mice receiving 2-DG exhibited reduced damage to dopaminergic neurons in the SN and improved behavioral outcome following MPTP treatment. The 2-DG treatment suppressed oxidative stress, preserved mitochondrial function, and attenuated cell death in cultured dopaminergic cells exposed to the complex I inhibitor rotenone or Fe2+. 2-DG and DR induced expression of the stress proteins heat-shock protein 70 and glucose-regulated protein 78 in dopaminergic cells, suggesting involvement of these cytoprotective proteins in the neuroprotective actions of 2-DG and DR. The striking beneficial effects of DR and 2-DG in models of PD, when considered in light of recent epidemiological data, suggest that DR may prove beneficial in reducing the incidence of PD in humans.

Dopamine transporter loss and clinical changes in MPTP-lesioned primates

Single photon emission computed tomography (SPECT) and the dopamine (DA) transporter tracer, 2 beta-carboxymethoxy-3 beta-(4-iodophenyl)tropane ([123I]beta-CIT), were used to determine DA transporter density in 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-lesioned monkeys with varying degrees of parkinsonism. The clinical stage of parkinsonism corresponded to SPECT measures of striatal DA transporter density suggesting that more severe parkinsonism was associated with a greater degree of dopaminergic terminal degeneration. These findings are similar to those reported earlier using positron emission tomography (PET) and the DA metabolism tracer, 6-[18F]fluoro-L-m-tyrosine (FMT), indicating that both are good methods for evaluating nigrostriatal degeneration in MPTP primate models.

Potent neuroprotective and antioxidant activity of apomorphine in MPTP and 6-hydroxydopamine induced neurotoxicity

Apomorphine is a potent radical scavenger and iron chelator. In vitro apomorphine acts as a potent iron chelator and radical scavenger with IC50 of 0.3 microM for iron (2.5 microM) induced lipid peroxidation in rat brain mitochondrial preparation, and it inhibits mice striatal MAO-A and MAO-B activities with IC50 values of 93 microM and 241 microM. Apomorphine (1-10 microM) protects rat pheochromocytoma (PC12) cells from 6-hydroxydopamine (150 microM) and H2O2 (0.6 mM) induced cytotoxicity and cell death. The neuroprotective property of (R)-apomorphine, a dopamine D1-D2 receptor agonist, has been studied in the MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) model of Parkinson's disease. (R)-apomorphine (5-10 mg/kg, s.c.) pretreatment in C57BL mice, protects against MPTP (24 mg/kg, i.p.) induced loss of nigro-striatal dopamine neurons, as indicated by striatal dopamine content, tyrosine hydroxylase content and tyrosine hydroxylase activity. It is suggested that the neuroprotective effect of (R)-apomorphine against MPTP neurotoxicity derives from its radical scavenging and MAO inhibitory actions and not from its agonistic activity, since the mechanism of MPTP dopaminergic neurotoxicity involves the generation of oxygen radical species induced-oxidative stress.

Differential strain susceptibility following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration acts in an autosomal dominant fashion: quantitative analysis in seven strains of Mus musculus

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been used as a potent neurotoxin to approximate, in animals, the pathology that is observed in human Parkinson's disease. In this study, we examine the toxicity of MPTP in seven strains of mice, spanning a genetic continuum of Mus musculus as a prelude to uncovering complex traits associated with MPTP toxicity. Seven days following injection of 80 mg/kg MPTP (4x20 mg/kg every 2 h), we find that the individual mouse strains exhibit dramatic differences in SNpc neuron survival, ranging from 63% cell loss in C57BL/6J mice to 14% cell loss in Swiss-Webster (SW) mice. In order to determine if the susceptibility trait was dominant, additive or recessive, we crossed C57Bl/6J mice with either SWR/J or AKR/J mice and examined the effect of MPTP on F1 C57BL/6JxSWR/J or F1 C57BL/6JxAKR/J animals. We find that all of the F1 animals were phenotypically identical to the C57BL/6J animals. In addition, no gender differences were noted in any of the MPTP-treated inbred mice or in the F1 animals. These results suggest that susceptibility to cell loss following MPTP is autosomal dominant and this polymorphism is carried on the C57BL/6J allele.

Reversal of experimental parkinsonism by using selective chemical ablation of the medial globus pallidus

OBJECT

Symptoms from Parkinson's disease improve after surgical ablation of the medial globus pallidus (GPm). Although, in theory, selective chemical ablation of neurons in the GPm could preserve vital structures jeopardized by surgery, the potential of this approach is limited when using traditional techniques of drug delivery. The authors examined the feasibility of convection-enhanced distribution of a neurotoxin by high-flow microinfusion to ablate the neurons of the GPm selectively and reverse experimental Parkinson's disease (akinesia, tremor, and rigidity).

METHODS

Initially, to test the feasibility of this approach, the GPms of two naive rhesus macaques were infused with kainic acid or ibotenic acid through two cannulas that had been placed using the magnetic resonance imaging-guided stereotactic technique. Two weeks later the animals were killed and their brains were examined histologically to determine the presence of neurons in the GPm and the integrity of the optic tract and the internal capsule. To examine the therapeutic potential of this paradigm, unilateral experimental Parkinson's disease was induced in six macaques by intracarotid infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and their behavior was studied for 12 weeks after chemopallidotomy was performed using kainic acid (three animals) or control infusion (three animals).

CONCLUSIONS

Chemopallidotomy using kainic acid permanently reversed the stigmata of MPTP-induced parkinsonism. By contrast, the control animals exhibited a transient recovery following intrapallidal infusion and then relapsed back to their baseline state. The use of high-flow microinfusion of selectively active toxins has the potential for treatment of Parkinson's disease and, by expanding the range of approachable targets to include large nuclei, for broad applications in clinical and experimental neuroscience.