Decreased susceptibility to oxidative stress underlies the resistance of specific dopaminergic cell populations to paraquat-induced degeneration

Applying the area fraction fractionator (AFF) probe for total volume estimations of somatic, dendritic and axonal domains of the nigrostriatal dopaminergic system in a murine model

BACKGROUND

The Cavalieri estimator is used for volume measurement of brain and brain regions. Derived from this estimator is the Area Fraction Fractionator (AFF), used for efficient area and number estimations of small 2D elements, such as axons in cross-sectioned nerves. However, to our knowledge, the AFF has not been combined with serial sectioning analysis to measure the volume of small-size nervous structures.

NEW METHOD

Using the nigrostriatal dopaminergic system as an illustrative case, we describe a protocol based on Cavalieri's principle and AFF to estimate the volume of its somatic, nuclear, dendritic, axonal and axon terminal cellular compartments in the adult mouse. The protocol consists of (1) systematic random sampling of sites within and across sections in regions of interest (substantia nigra, the nigrostriatal tract, caudate-putamen), (2) confocal image acquisition of sites, (3) marking of cellular domains using Cavalieri's 2D point-counting grids, and 4) determination of compartments' total volume using the estimated area of each compartment, and between-sections distance.

RESULTS

The volume of the nigrostriatal system per hemisphere is ∼0.38 mm3, with ∼5 % corresponding to perikarya and cell nuclei, ∼10 % to neuropil/dendrites, and ∼85 % to axons and varicosities.

COMPARISON WITH EXISTING METHODS

In contrast to other methods to measure volume of discrete objects, such as the optical nucleator or 3D reconstructions, it stands out for its versatility and ease of use.

CONCLUSIONS

The use of a simple quantitative, unbiased approach to assess the global state of a system may allow quantification of compartment-specific changes that may accompany neurodegenerative processes.

Neurotoxicity of Some Environmental Pollutants to Zebrafish

The aquatic environment encompasses a wide variety of pollutants, from plastics to drug residues, pesticides, food compounds, and other food by-products, and improper disposal of waste is the main cause of the accumulation of toxic substances in water. Monitoring, assessing, and attempting to control the effects of contaminants in the aquatic environment are necessary and essential to protect the environment and thus human and animal health, and the study of aquatic ecotoxicology has become topical. In this respect, zebrafish are used as model organisms to study the bioaccumulation, toxicity, and influence of environmental pollutants due to their structural, functional, and material advantages. There are many similarities between the metabolism and physiological structures of zebrafish and humans, and the nervous system structure, blood-brain barrier function, and social behavior of zebrafish are characteristics that make them an ideal animal model for studying neurotoxicity. The aim of the study was to highlight the neurotoxicity of nanoplastics, microplastics, fipronil, deltamethrin, and rotenone and to highlight the main behavioral, histological, and oxidative status changes produced in zebrafish exposed to them.

Transcriptome and Metabolome Analysis Reveals the Importance of Amino-Acid Metabolism in Spodoptera Frugiperda Exposed to Spinetoram

Pests are inevitably exposed to sublethal and lethal doses in the agroecosystem following the application of pesticides indispensable to protect food sources. The effect of spinetoram on amino-acid metabolism of fall armyworm, Spodoptera frugiperda (J.E. Smith), was investigated, at the dose of LC10 and LC90, by transcriptome and LC-MS/MS analysis. Using statistics-based analysis of both POS and NEG mode, a total of 715,501 metabolites in S. frugiperda were significantly changed after spinetoram treatment. The enhancement of glucose metabolism provides energy support for detoxification in larvae. The decrease in valine and isoleucine is associated with an increase in leucine, without maintaining the conservation of citric acid in the larvae. The down-regulation of phenylalanine may retard the tricarboxylic acid cycle to produce GTP. The abundance of lysine was decreased in response to spinetoram exposure, which damages the nervous system of the larvae. The abundance of arginine increases and causes non-functional contraction of the insect's muscles, causing the larva to expend excess energy. Tryptophan provides an important substrate for eliminating ROS. The changes in glutamic acid, aspartic acid, and lysine cause damage to the nerve centers of the larvae. The results of transcriptome and LC-MS/MS analysis revealed the effects of pesticide exposure on amino-acid metabolism of S. frugiperda successfully and provide a new overview of the response of insect physio-biochemistry against pesticides.

Impact of Environmental Risk Factors on Mitochondrial Dysfunction, Neuroinflammation, Protein Misfolding, and Oxidative Stress in the Etiopathogenesis of Parkinson's Disease

As a prevalent progressive neurodegenerative disorder, Parkinson's disease (PD) is characterized by the neuropathological hallmark of the loss of nigrostriatal dopaminergic (DAergic) innervation and the appearance of Lewy bodies with aggregated α-synuclein. Although several familial forms of PD have been reported to be associated with several gene variants, most cases in nature are sporadic, triggered by a complex interplay of genetic and environmental risk factors. Numerous epidemiological studies during the past two decades have shown positive associations between PD and several environmental factors, including exposure to neurotoxic pesticides/herbicides and heavy metals as well as traumatic brain injury. Other environmental factors that have been implicated as potential risk factors for PD include industrial chemicals, wood pulp mills, farming, well-water consumption, and rural residence. In this review, we summarize the environmental toxicology of PD with the focus on the elaboration of chemical toxicity and the underlying pathogenic mechanisms associated with exposure to several neurotoxic chemicals, specifically 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, paraquat (PQ), dichloro-diphenyl-trichloroethane (DDT), dieldrin, manganese (Mn), and vanadium (V). Our overview of the current findings from cellular, animal, and human studies of PD provides information for possible intervention strategies aimed at halting the initiation and exacerbation of environmentally linked PD.

A Critical Review of Zebrafish Models of Parkinson's Disease

A wide variety of human diseases have been modelled in zebrafish, including various types of cancer, cardiovascular diseases and neurodegenerative diseases like Alzheimer’s and Parkinson’s. Recent reviews have summarized the currently available zebrafish models of Parkinson’s Disease, which include gene-based, chemically induced and chemogenetic ablation models. The present review updates the literature, critically evaluates each of the available models of Parkinson’s Disease in zebrafish and compares them with similar models in invertebrates and mammals to determine their advantages and disadvantages. We examine gene-based models, including ones linked to Early-Onset Parkinson’s Disease: PARKIN, PINK1, DJ-1, and SNCA; but we also examine LRRK2, which is linked to Late-Onset Parkinson’s Disease. We evaluate chemically induced models like MPTP, 6-OHDA, rotenone and paraquat, as well as chemogenetic ablation models like metronidazole-nitroreductase. The article also reviews the unique advantages of zebrafish, including the abundance of behavioural assays available to researchers and the efficiency of high-throughput screens. This offers a rare opportunity for assessing the potential therapeutic efficacy of pharmacological interventions. Zebrafish also are very amenable to genetic manipulation using a wide variety of techniques, which can be combined with an array of advanced microscopic imaging methods to enable in vivo visualization of cells and tissue. Taken together, these factors place zebrafish on the forefront of research as a versatile model for investigating disease states. The end goal of this review is to determine the benefits of using zebrafish in comparison to utilising other animals and to consider the limitations of zebrafish for investigating human disease.

Application of neurotoxin- and pesticide-induced animal models of Parkinson's disease in the evaluation of new drug delivery systems

Parkinson's disease (PD) is the second most prevalent neuro-degenerative disease after Alzheimer´s disease. It is characterized by motor symptoms such as akinesia, bradykinesia, tremor, rigidity, and postural abnormalities, due to the loss of nigral dopaminergic neurons and a decrease in the dopa-mine contents of the caudate-putamen structures. To this date, there is no cure for the disease and available treatments are aimed at controlling the symptoms. Therefore, there is an unmet need for new treatments for PD. In the past decades, animal models of PD have been proven to be valuable tools in elucidating the nature of the pathogenic processes involved in the disease, and in designing new pharmacological approaches. Here, we review the use of neurotoxin-induced and pesticide-induced animal models of PD, specifically those induced by rotenone, paraquat, maneb, MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and 6-OHDA (6-hydroxydopamine), and their application in the development of new drug delivery systems for PD.

Association of Oxidative Stress with Neurological Disorders

BACKGORUND

Oxidative stress is one of the main contributing factors involved in cerebral biochemical impairment. The higher susceptibility of the central nervous system to reactive oxygen species mediated damage could be attributed to several factors. For example, neurons use a greater quantity of oxygen, many parts of the brain have higher concentraton of iron, and neuronal mitochondria produce huge content of hydrogen peroxide. In addition, neuronal membranes have polyunsaturated fatty acids, which are predominantly vulnerable to oxidative stress (OS). OS is the imbalance between reactive oxygen species generation and cellular antioxidant potential. This may lead to various pathological conditions and diseases, especially neurodegenerative diseases such as, Parkinson's, Alzheimer's, and Huntington's diseases.

OBJECTIVES

In this study, we explored the involvement of OS in neurodegenerative diseases.

METHODS

We used different search terms like "oxidative stress and neurological disorders" "free radicals and neurodegenerative disorders" "oxidative stress, free radicals, and neurological disorders" and "association of oxidative stress with the name of disorders taken from the list of neurological disorders. We tried to summarize the source, biological effects, and physiologic functions of ROS.

RESULTS

Finally, it was noted that more than 190 neurological disorders are associated with oxidative stress.

CONCLUSION

More elaborated studies in the future will certainly help in understanding the exact mechanism involved in neurological diseases and provide insight into revelation of therapeutic targets.

Paraquat-induced oxidative stress regulates N6-methyladenosine (m6A) modification of circular RNAs

Paraquat (PQ), a widely used herbicide and well-known oxidative stress inducer, has been linked to numerous neurodegenerative diseases, but the underlying mechanism(s) remains unknown. Circular RNAs (circRNAs) have recently been reported to be associated with oxidative stress in Parkinson's disease. Herein, we performed methylated RNA immunoprecipitation and RNA sequencing assays for mouse neuroblastoma (Neuro-2a) cells and successfully established a positive link between the alteration of circRNAs driven by m⁶A modification and PQ-induced oxidative stress. We observed oxidative stress and antioxidative stress present distinct m⁶A modification pattern of circRNAs as well as biological effect. Gene ontology and pathway analysis predicted that differentially m⁶A-methylated and expressed circRNAs are highly clustered in pathways associated with function and development of nervous system, including axon cargo transport, nervous system development, long-term potentiation, and neurotrophic signaling pathways. Moreover, we demonstrated that the alteration of m⁶A-methylated circRNAs upon PQ exposure could be partially reversed by N-acetylcysteine pretreatment. The mechanistic analysis further demonstrated that N-acetylcysteine pretreatment attenuated the decreased expression of target genes (UBC and PPP2CA) induced by PQ. These findings revealed distinct patterns of differentially m⁶A-modified circRNAs, indicating that m⁶A could participate in a specific regulatory network of circRNAs to modulate the expression of downstream genes in response to PQ-induced oxidative stress. In conclusion, our work established a link between m⁶A modification of circRNAs and PQ-induced oxidative stress, and further studies are required to explore the underlying molecular mechanisms associated with PQ-induced neurotoxicity.

Selective neuronal vulnerability in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, disabling millions worldwide. Despite the imperative PD poses, at present, there is no cure or means of slowing progression. This gap is attributable to our incomplete understanding of the factors driving pathogenesis. Research over the past several decades suggests that both cell-autonomous and non-cell autonomous processes contribute to the neuronal dysfunction underlying PD symptoms. The thesis of this review is that an intersection of these processes governs the pattern of pathology in PD. Studies of substantia nigra pars compacta (SNc) dopaminergic neurons, whose loss is responsible for the core motor symptoms of PD, suggest that they have a combination of traits-a long, highly branched axon, autonomous activity, and elevated mitochondrial oxidant stress-that predispose them to non-cell autonomous drivers of pathogenesis, like misfolded forms of alpha-synuclein (α-SYN) and inflammation. The literature surrounding these issues will be briefly summarized, and the translational implications of an intersectional hypothesis of PD pathogenesis discussed.

Nrf2-regulated miR-380-3p Blocks the Translation of Sp3 Protein and Its Mediation of Paraquat-Induced Toxicity in Mouse Neuroblastoma N2a Cells

Laboratorial and epidemiological research has established a relationship between paraquat (PQ) exposure and a risk for Parkinson's disease. Previously, we have investigated the effects of nuclear factor erythroid 2 related factor 2 (Nrf2) and microRNAs in PQ-induced neurotoxicity, addressing the function of miR-380-3p, a microRNA dysregulated by PQ, as well as Nrf2 deficiency. Nrf2 is known to mediate the expression of a variety of genes, including noncoding genes. By chromatin immunoprecipitation, we identified the relationship between Nrf2 and miR-380-3p in transcriptional regulation. qRT-PCR, Western blots, and dual-luciferase reporter gene assay showed that miR-380-3p blocked the translation of the transcription factor specificity protein-3 (Sp3) in the absence of degradation of Sp3 mRNA. Results based on cell counting analysis, annexin v-fluorescein isothiocyanate/propidium iodide double-staining assay, and propidium iodide staining showed that overexpression of miR-380-3p inhibited cell proliferation, increased the apoptotic rate, induced cell cycle arrest, and intensified the toxicity of PQ in mouse neuroblastoma (N2a [Neuro2a]) cells. Knockdown of Sp3 inhibited cell proliferation and eclipsed the alterations induced by miR-380-3p in cell proliferation. Two mediators of apoptosis and cell cycle identified in previous studies as Sp3-regulated, namely cyclin-dependent kinase inhibitor 1 (p21) and calmodulin (CaM), were dysregulated by PQ, but not Sp3 deficiency. In conclusion, Nrf2-regulated miR-380-3p inhibited cell proliferation and enhanced the PQ-induced toxicity in N2a cells potentially by blocking the translation Sp3 mRNA. We conclude that CaM and p21 were involved in PQ-induced toxicity.

Early Postnatal Exposure to Paraquat and Maneb in Mice Increases Nigrostriatal Dopaminergic Susceptibility to a Re-challenge with the Same Pesticides at Adulthood: Implications for Parkinson's Disease

Exposure to environmental contaminants represents an important etiological factor in sporadic Parkinson's disease (PD). It has been reported that PD could arise from events that occur early in development and that lead to delayed adverse consequences in the nigrostriatal dopaminergic system at adult life. We investigated the occurrence of late nigrostriatal dopaminergic neurotoxicity induced by exposures to the pesticides paraquat (PQ) and maneb (MB) during the early postnatal period in mice, as well as whether the exposure to pesticides during development could enhance mice vulnerability to subsequent challenges. Male Swiss mice were exposed to a combination of 0.3 mg/kg PQ and 1.0 mg/kg MB (PQ + MB) from postnatal (PN) day 5 to 19. PN exposure to pesticides neither induced mortally nor modified motor-related parameters. However, PN pesticides exposure decreased the number of tyrosine hydroxylase (TH)- and dopamine transporter (DAT)-positive neurons in the substantia nigra pars compacta (SNpc), as well as reduced TH and DAT immunoreactivity in the striatum. A parallel group of animals developmentally exposed to the pesticides was re-challenged at 3 months of age with 10 mg/kg PQ plus 30 mg/kg MB (twice a week, 6 weeks). Mice exposed to pesticides at both periods (PN + adulthood) presented motor deficits and reductions in the number of TH- and DAT-positive neurons in the SNpc. These findings indicate that the exposure to PQ + MB during the early PN period can cause neurotoxicity in the mouse nigrostriatal dopaminergic system, rendering it more susceptible to a subsequent adult re-challenge with the same pesticides.

Oxidative stress in vagal neurons promotes parkinsonian pathology and intercellular α-synuclein transfer

Specific neuronal populations display high vulnerability to pathological processes in Parkinson's disease (PD). The dorsal motor nucleus of the vagus nerve (DMnX) is a primary site of pathological α-synuclein deposition and may play a key role in the spreading of α-synuclein lesions within and outside the CNS. Using in vivo models, we show that cholinergic neurons forming this nucleus are particularly susceptible to oxidative challenges and accumulation of reactive oxidative species (ROS). Targeted α-synuclein overexpression within these neurons triggered an oxidative stress that became significantly more pronounced after exposure to the ROS-generating agent paraquat. A more severe oxidative stress resulted in enhanced production of oxidatively modified forms of α-synuclein, increased α-synuclein aggregation into oligomeric species and marked degeneration of DMnX neurons. Enhanced oxidative stress also affected neuron-to-neuron protein transfer, causing an increased spreading of α-synuclein from the DMnX toward more rostral brain regions. In vitro experiments confirmed a greater propensity of α-synuclein to pass from cell to cell under pro-oxidant conditions, and identified nitrated α-synuclein forms as highly transferable protein species. These findings substantiate the relevance of oxidative injury in PD pathogenetic processes, establish a relationship between oxidative stress and vulnerability to α-synuclein pathology and define a new mechanism, enhanced cell-to-cell α-synuclein transmission, by which oxidative stress could promote PD development and progression.

Peripubertal exposure to the neonicotinoid pesticide dinotefuran affects dopaminergic neurons and causes hyperactivity in male mice

Although neonicotinoid pesticides are expected to have harmful influence on mammals, there is little animal experimental data to support the effect and mechanisms. Since acetylcholine causes the release of dopamine, neonicotinoids may confer a risk of developmental disorders via a disturbance in the monoamine systems. Male mice were peripubertally administered dinotefuran (DIN) referring to no observed effect level (NOEL) and performed behavioral and immunohistological analyses. In an open field test, the total locomotor activity was increased in a dose-dependent manner. The immunoreactivity of tyrosine hydroxylase in the substantia nigra was increased in DIN-exposed mice. These results suggest that exposure to DIN in peripubertal male mice causes hyperactivity and a disturbance of dopaminergic signaling.

A Single Neonatal Exposure to BMAA in a Rat Model Produces Neuropathology Consistent with Neurodegenerative Diseases

Although cyanobacterial β-N-methylamino-l-alanine (BMAA) has been implicated in the development of Alzheimer's Disease (AD), Parkinson's Disease (PD) and Amyotrophic Lateral Sclerosis (ALS), no BMAA animal model has reproduced all the neuropathology typically associated with these neurodegenerative diseases. We present here a neonatal BMAA model that causes β-amyloid deposition, neurofibrillary tangles of hyper-phosphorylated tau, TDP-43 inclusions, Lewy bodies, microbleeds and microgliosis as well as severe neuronal loss in the hippocampus, striatum, substantia nigra pars compacta, and ventral horn of the spinal cord in rats following a single BMAA exposure. We also report here that BMAA exposure on particularly PND3, but also PND4 and 5, the critical period of neurogenesis in the rodent brain, is substantially more toxic than exposure to BMAA on G14, PND6, 7 and 10 which suggests that BMAA could potentially interfere with neonatal neurogenesis in rats. The observed selective toxicity of BMAA during neurogenesis and, in particular, the observed pattern of neuronal loss observed in BMAA-exposed rats suggest that BMAA elicits its effect by altering dopamine and/or serotonin signaling in rats.

Alpha-synuclein, epigenetics, mitochondria, metabolism, calcium traffic, & circadian dysfunction in Parkinson's disease. An integrated strategy for management

The motor deficits which characterise the sporadic form of Parkinson's disease arise from age-related loss of a subset of dopamine neurons in the substantia nigra. Although motor symptoms respond to dopamine replacement therapies, the underlying disease process remains. This review details some features of the progressive molecular pathology and proposes deployment of a combination of nutrients: R-lipoic acid, acetyl-l-carnitine, ubiquinol, melatonin (or receptor agonists) and vitamin D3, with the collective potential to slow progression of these features. The main nutrient targets include impaired mitochondria and the associated oxidative/nitrosative stress, calcium stress and impaired gene transcription induced by pathogenic forms of alpha- synuclein. Benefits may be achieved via nutrient influence on epigenetic signaling pathways governing transcription factors for mitochondrial biogenesis, antioxidant defences and the autophagy-lysosomal pathway, via regulation of the metabolic energy sensor AMP activated protein kinase (AMPK) and the mammalian target of rapamycin mTOR. Nutrients also benefit expression of the transcription factor for neuronal survival (NR4A2), trophic factors GDNF and BDNF, and age-related calcium signals. In addition a number of non-motor related dysfunctions in circadian control, clock genes and associated metabolic, endocrine and sleep-wake activity are briefly addressed, as are late-stage complications in respect of cognitive decline and osteoporosis. Analysis of the network of nutrient effects reveals how beneficial synergies may counter the accumulation and promote clearance of pathogenic alpha-synuclein.

Age and Chronicity of Administration Dramatically Influenced the Impact of Low Dose Paraquat Exposure on Behavior and Hypothalamic-Pituitary-Adrenal Activity

Little is known of the age-dependent and long-term consequences of low exposure levels of the herbicide and dopaminergic toxicant, paraquat. Thus, we assessed the dose-dependent effects of paraquat using a typical short-term (3 week) exposure procedure, followed by an assessment of the effects of chronic (16 weeks) exposure to a very low dose (1/10th of what previously induced dopaminergic neuronal damage). Short term paraquat treatment dose-dependently induced deficits in locomotion, sucrose preference and Y-maze performance. Chronic low dose paraquat treatment had a very different pattern of effects that were also dependent upon the age of the animal: in direct contrast to the short-term effects, chronic low dose paraquat increased sucrose consumption and reduced forced swim test (FST) immobility. Yet these effects were age-dependent, only emerging in mice older than 13 months. Likewise, Y-maze spontaneous alternations and home cage activity were dramatically altered as a function of age and paraquat chronicity. In both the short and long-term exposure studies, increased corticosterone and altered hippocampal glucocorticoid receptor (GR) levels were induced by paraquat, but surprisingly these effects were blunted in the older mice. Thus, paraquat clearly acts as a systemic stressor in terms of corticoid signaling and behavioral outcomes, but that paradoxical effects may occur with: (a) repeated exposure at; (b) very low doses; and (c) older age. Collectively, these data raise the possibility that repeated “hits” with low doses of paraquat in combination with aging processes might have promoted compensatory outcomes.

Selective neuronal vulnerability in Parkinson disease

Intracellular α-synuclein (α-syn)-rich protein aggregates called Lewy pathology (LP) and neuronal death are commonly found in the brains of patients with clinical Parkinson disease (cPD). It is widely believed that LP appears early in the disease and spreads in synaptically coupled brain networks, driving neuronal dysfunction and death. However, post-mortem analysis of human brains and connectome-mapping studies show that the pattern of LP in cPD is not consistent with this simple model, arguing that, if LP propagates in cPD, it must be gated by cell- or region-autonomous mechanisms. Moreover, the correlation between LP and neuronal death is weak. In this Review, we briefly discuss the evidence for and against the spreading LP model, as well as evidence that cell-autonomous factors govern both α-syn pathology and neuronal death.

Sodium Selenite Prevents Paraquat-Induced Neurotoxicity in Zebrafish

Considering the antioxidant properties of sodium selenite (Na₂SeO₃) and the involvement of oxidative stress events in paraquat-induced neurotoxicity, this study investigated the protective effect of dietary Na₂SeO₃ on biochemical and behavioral parameters of zebrafish exposed to paraquat (PQ). Fish were pretreated with a Na₂SeO₃ diet for 21 days and then PQ (20 mg/kg) was administered intraperitoneally with six injections for 16 days. In the novel tank test, the Na₂SeO₃ diet prevented the locomotor impairments, as well as the increase in the time spent in the top area of the tank, and the exacerbation of freezing episodes. In the preference for conspecifics and in the mirror-induced aggression (MIA) tasks, Na₂SeO₃ prevented the increase in the latency to enter the area closer to conspecifics and the agonistic behavior of PQ-treated animals, respectively. Na₂SeO₃ prevented the increase of carbonylated protein (CP), reactive oxygen species (ROS), and nitrite/nitrate (NOx) levels, as well as the decrease in non-protein thiols (NPSH) levels. Regarding the antioxidant enzymatic defenses, Na₂SeO₃ prevented the increase in catalase (CAT) and glutathione peroxidase (GPx) activities caused by PQ. Altogether, dietary Na₂SeO₃ improves behavioral and biochemical function impaired by PQ treatment in zebrafish, by modulating not only redox parameters, but also anxiety- and aggressive-like phenotypes in zebrafish.

Chronic Treatment with Paraquat Induces Brain Injury, Changes in Antioxidant Defenses System, and Modulates Behavioral Functions in Zebrafish

Paraquat (PQ) administration consists in a chemical model that mimics phenotypes observed in Parkinson's disease (PD), due to its ability to induce changes in dopaminergic system and oxidative stress. The aim of this study was to evaluate the actions of PQ in behavioral functions of adult zebrafish and its influence on oxidative stress biomarkers in brain samples. PQ (20 mg/kg) was administered intraperitoneally with six injections for 16 days (one injection every 3 days). PQ-treated group showed a significant decrease in the time spent in the bottom section and a shorter latency to enter the top area in the novel tank test. Moreover, PQ-exposed fish showed a significant decrease in the number and duration of risk assessment episodes in the light-dark test, as well as an increase in the agonistic behavior in the mirror-induced aggression (MIA) test. PQ induced brain damage by decreasing mitochondrial viability. Concerning the antioxidant defense system, PQ increased catalase (CAT) and glutathione peroxidase (GPx) activities, as well as the non-protein sulfhydryl content (NPSH), but did not change ROS formation and decreased lipid peroxidation. We demonstrate, for the first time, that PQ induces an increase in aggressive behavior, alters non-motor patterns associated to defensive behaviors, and changes redox parameters in zebrafish brain. Overall, our findings may serve as useful tools to investigate the interaction between behavioral and neurochemical impairments triggered by PQ administration in zebrafish.

Estrogen modulation of calretinin and BDNF expression in midbrain dopaminergic neurons of ovariectomised mice

Estrogen attenuates the loss of dopamine neurons from the substantia nigra in animal models of Parkinson's disease (PD) and excitatory amino-acid induced neurotoxicity by interactions with brain-derived neurotrophic factor (BDNF), and calretinin (CR) containing dopaminergic (DA) neurons. To examine this interaction more closely, we treated the ovariectomised (OVX) mice with estrodial for 10days, and compared these mice to those OVX mice injected with the vehicle or control mice. Estrogen treatment in OVX mice had significantly more tyrosine hydroxylase (TH) positive neurons in the substantia nigra pars compacta (SNpc). Dopamine transporter (DAT) mRNA and BDNF mRNA levels in the midbrain were also significantly increased by estrogen treatment (P<0.05). OVX markedly decreased the number of TH/CR double stained cells in the SNpc (P<0.05), a trend which could be reversed by estrogen treatment. However, the number of GFAP positive cells in the substantia nigra did not show significant changes (P >0.05) after vehicle or estrodial treatment. Furthermore, we found that estrogen treatment abrogated the OVX-induced decrease in the phosphorylated AKT (p-AKT), but not p-ERK. We hypothesize that short-term treatment with estrogen confers neuroprotection to DA neurons by increasing CR in the DA neurons and BDNF in the midbrain, which possibly related to activation of the PI3K/Akt signaling pathway.

Diquat causes caspase-independent cell death in SH-SY5Y cells by production of ROS independently of mitochondria

Evidence indicates that Parkinson's disease (PD), in addition to having a genetic aetiology, has an environmental component that contributes to disease onset and progression. The exact nature of any environmental agent contributing to PD is unknown in most cases. Given its similarity to paraquat, an agrochemical removed from registration in the EU for its suspected potential to cause PD, we have investigated the in vitro capacity of the related herbicide Diquat to cause PD-like cell death. Diquat showed greater toxicity towards SH-SY5Y neuroblastoma cells and human midbrain neural cells than paraquat and also MPTP, which was independent of dopamine transporter-mediated uptake. Diquat caused cell death independently of caspase activation, potentially via RIP1 kinase, with only a minor contribution from apoptosis, which was accompanied by enhanced reactive oxygen species production in the absence of major inhibition of complex I of the mitochondrial respiratory chain. No changes in α-synuclein expression were observed following 24-h or 4-week exposure. Diquat may, therefore, kill neural tissue by programmed necrosis rather than apoptosis, reflecting the pathological changes seen following high-level exposure, although its ability to promote PD is unclear.

A dopamine receptor contributes to paraquat-induced neurotoxicity in Drosophila

Long-term exposure to environmental oxidative stressors, like the herbicide paraquat (PQ), has been linked to the development of Parkinson's disease (PD), the most frequent neurodegenerative movement disorder. Paraquat is thus frequently used in the fruit fly Drosophila melanogaster and other animal models to study PD and the degeneration of dopaminergic neurons (DNs) that characterizes this disease. Here, we show that a D1-like dopamine (DA) receptor, DAMB, actively contributes to the fast central nervous system (CNS) failure induced by PQ in the fly. First, we found that a long-term increase in neuronal DA synthesis reduced DAMB expression and protected against PQ neurotoxicity. Secondly, a striking age-related decrease in PQ resistance in young adult flies correlated with an augmentation of DAMB expression. This aging-associated increase in oxidative stress vulnerability was not observed in a DAMB-deficient mutant. Thirdly, targeted inactivation of this receptor in glutamatergic neurons (GNs) markedly enhanced the survival of Drosophila exposed to either PQ or neurotoxic levels of DA, whereas, conversely, DAMB overexpression in these cells made the flies more vulnerable to both compounds. Fourthly, a mutation in the Drosophila ryanodine receptor (RyR), which inhibits activity-induced increase in cytosolic Ca(2+), also strongly enhanced PQ resistance. Finally, we found that DAMB overexpression in specific neuronal populations arrested development of the fly and that in vivo stimulation of either DNs or GNs increased PQ susceptibility. This suggests a model for DA receptor-mediated potentiation of PQ-induced neurotoxicity. Further studies of DAMB signaling in Drosophila could have implications for better understanding DA-related neurodegenerative disorders in humans.

Death in the substantia nigra: a motor tragedy

It is well known that the death of dopaminergic neurons of the substantia nigra pars compacta (SNc) is the pathological hallmark of Parkinson's disease (PD), the second most common and disabling condition in the expanding elderly population. Nevertheless, the intracellular cascade of events leading to dopamine cell death is still unknown and, consequently, treatment is largely symptomatic rather than preventive. Moreover, the mechanisms whereby nigral dopaminergic neurons may degenerate still remain controversial. Hitherto, several data have shown that the earlier cellular disturbances occurring in dopaminergic neurons include oxidative stress, excitotoxicity, inflammation, mitochondrial dysfunction and altered proteolysis. These alterations, rather than killing neurons, trigger subsequent death-related molecular pathways, including elements of apoptosis. In rare incidences, PD may be inherited; this evidence has opened a new and exciting area of research, attempting to shed light on the nature of the more common idiopathic PD form. In this review, the characteristics of the SNc dopaminergic neurons and their lifecycle from birth to death are reviewed. In addition, of the mechanisms by which the aforementioned alterations cause neuronal dopaminergic death, particular emphasis will be given to the role played by inflammation, and the relevance of the possible use of anti-inflammatory drugs in the treatment of PD. Finally, new evidence of a possible de novo neurogenesis in the SNc of adult animals and in PD patients will also be examined.

Exercise does not protect against MPTP-induced neurotoxicity in BDNF haploinsufficient mice

Exercise has been demonstrated to potently protect substantia nigra pars compacta (SN) dopaminergic neurons from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity. One mechanism proposed to account for this neuroprotection is the upregulation of neurotrophic factors. Several neurotrophic factors, including Brain Derived Neurotrophic Factor (BDNF), have been shown to upregulate in response to exercise. In order to determine if exercise-induced neuroprotection is dependent upon BDNF, we compared the neuroprotective effects of voluntary exercise in mice heterozygous for the BDNF gene (BDNF+/-) with strain-matched wild-type (WT) mice. Stereological estimates of SNpc DA neurons from WT mice allowed 90 days exercise via unrestricted running demonstrated complete protection against the MPTP-induced neurotoxicity. However, BDNF+/- mice allowed 90 days of unrestricted exercise were not protected from MPTP-induced SNpc DA neuron loss. Proteomic analysis comparing SN and striatum from 90 day exercised WT and BDNF+/- mice showed differential expression of proteins related to energy regulation, intracellular signaling and trafficking. These results suggest that a full genetic complement of BDNF is critical for the exercise-induced neuroprotection of SNpc DA neurons.

A synopsis on the role of tyrosine hydroxylase in Parkinson's disease

Parkinson's disease (PD) is a common chronic progressive neurodegenerative disorder in elderly people. A consistent neurochemical abnormality in PD is degeneration of dopaminergic neurons in substantia nigra pars compacta, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-dihydroxyphenylalanine (L-DOPA), the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Problems related to PD usually build up when vesicular storage of DA is altered by the presence of either α-synuclein protofibrils or oxidative stress. Phosphorylation of three physiologically-regulated specific sites of N-terminal domain of TH is vital in regulating its kinetic and protein interaction. The concept of physiological significance of TH isoforms is another interesting aspect to be explored further for a comprehensive understanding of its role in PD. Thus, a logical and efficient strategy for PD treatment is based on correcting or bypassing the enzyme deficiency by the treatment with L-DOPA, DA agonists, inhibitors of DA metabolism or brain grafts with cells expressing a high level of TH. Neurotrophic factors are also attracting the attention of neuroscientists because they provide the essential neuroprotective and neurorestorative properties to the nigrostriatal DA system. PPAR-γ, a key regulator of immune responses, is likewise a promising target for the treatment of PD, which can be achieved by the use of agonists with the potential to impact the expression of pro- and anti-inflammatory cytokines at the transcriptional level in immune cells via expression of TH. Herein, we review the primary biochemical and pathological features of PD, and describe both classical and developing approaches aimed to ameliorate disease symptoms and its progression.

Systematic review of parkinsonian syndromes in short- and long-term survivors of paraquat poisoning

OBJECTIVE

The objective of this study was to assess whether high-dose paraquat exposure was associated with the development of parkinsonism.

METHODS

We carried out a systematic review of all published cases of paraquat toxicity meeting a case-definition of paraquat poisoning and who either recovered or lived for at least 30 days (primary analysis) or lived for 15 to 30 days (secondary analysis). Cases were included if they contained sufficient information to determine whether they had signs of parkinsonism.

RESULTS

Our search yielded 818 publications containing 83 cases. The primary analysis yielded 70 cases. None manifested signs of parkinsonism. An additional 13 were in the secondary analysis and none exhibited signs of parkinsonism.

CONCLUSION

An analysis the world's entire published experience found no connection between high-dose paraquat exposure in humans and the development of parkinsonism.

Paraquat neurotoxicity is mediated by the dopamine transporter and organic cation transporter-3

The herbicide paraquat (PQ) has increasingly been reported in epidemiological studies to enhance the risk of developing Parkinson's disease (PD). Furthermore, case-control studies report that individuals with genetic variants in the dopamine transporter (DAT, SLC6A) have a higher PD risk when exposed to PQ. However, it remains a topic of debate whether PQ can enter dopamine (DA) neurons through DAT. We report here a mechanism by which PQ is transported by DAT: In its native divalent cation state, PQ(2+) is not a substrate for DAT; however, when converted to the monovalent cation PQ(+) by either a reducing agent or NADPH oxidase on microglia, it becomes a substrate for DAT and is accumulated in DA neurons, where it induces oxidative stress and cytotoxicity. Impaired DAT function in cultured cells and mutant mice significantly attenuated neurotoxicity induced by PQ(+). In addition to DAT, PQ(+) is also a substrate for the organic cation transporter 3 (Oct3, Slc22a3), which is abundantly expressed in non-DA cells in the nigrostriatal regions. In mice with Oct3 deficiency, enhanced striatal damage was detected after PQ treatment. This increased sensitivity likely results from reduced buffering capacity by non-DA cells, leading to more PQ(+) being available for uptake by DA neurons. This study provides a mechanism by which DAT and Oct3 modulate nigrostriatal damage induced by PQ(2+)/PQ(+) redox cycling.

Differential regional expression patterns of α-synuclein, TNF-α, and IL-1β; and variable status of dopaminergic neurotoxicity in mouse brain after Paraquat treatment

Background

Paraquat (1, 1-dimethyl-4, 4-bipyridium dichloride; PQ) causes neurotoxicity, especially dopaminergic neurotoxicity, and is a supposed risk factor for Parkinson's disease (PD). However, the cellular and molecular mechanisms of PQ-induced neurodegeneration are far from clear. Previous studies have shown that PQ induces neuroinflammation and dopaminergic cell loss, but the prime cause of those events is still in debate.

Methods

We examined the neuropathological effects of PQ not only in substantia nigra (SN) but also in frontal cortex (FC) and hippocampus of the progressive mouse (adult Swiss albino) model of PD-like neurodegeneration, using immunohistochemistry, western blots, and histological and biochemical analyses.

Results

PQ caused differential patterns of changes in cellular morphology and expression of proteins related to PD and neuroinflammation in the three regions examined (SN, FC and hippocampus). Coincident with behavioral impairment and brain-specific ROS generation, there was differential immunolocalization and decreased expression levels of tyrosine hydroxylase (TH) in the three regions, whereas α-synuclein immunopositivity increased in hippocampus, increased in FC and decreased in SN. PQ-induced neuroinflammation was characterized by area-specific changes in localization and appearances of microglial cells with or without activation and increment in expression patterns of tumor necrosis factor-α in the three regions of mouse brain. Expression of interleukin-1β was increased in FC and hippocampus but not significantly changed in SN.

Conclusion

The present study demonstrates that PQ induces ROS production and differential α-synuclein expression that promotes neuroinflammation in microglia-dependent or -independent manners, and produces different patterns of dopaminergic neurotoxicity in three different regions of mouse brain.

Selective responses of myenteric neurons to oxidative stress and diabetic stimuli

BACKGROUND

Diabetes has a differential effect on different subpopulations of myenteric neurons. Our aim was to investigate an in vitro model to examine the pathways underlying the development of nerve changes in diabetes.

METHODS

The proportions of neuronal cell bodies containing vasoactive intestinal polypeptide (VIP), neuronal nitric oxide synthase (nNOS) and calbindin relative to the pan-neuronal marker HuC/D were quantified in wholemount preparations of the myenteric plexus of adult rat ileum using double labeling immunohistochemistry. Preparations were maintained in culture for 24 h in the presence and absence of stimuli mimicking the diabetic environment including oxidative stress, carbonyl stress, high glucose and advanced glycation end products (AGEs). Data were compared with the effect of streptozotocin-induced diabetes in vivo. KEY RESULTS Only oxidative stress in vitro produced the same pattern as observed in diabetes with an increase in VIP-, decrease in nNOS-, and no change in calbindin-positive neurons. Carbonyl stress and high glucose caused an increase in VIP-containing neurons without affecting nNOS expression. In contrast, exposure to AGEs only caused a decrease in nNOS-positive neurons. Calbindin expression was unaffected by any of the stimuli. The effects of the stimuli were prevented by the antioxidant, α-lipoic acid, or the carbonyl scavenger, aminoguanidine.

CONCLUSIONS & INFERENCES

The results provide evidence that oxidative stress is the common factor in the development of neuronal changes in diabetes; however, the mechanism by which oxidative stress occurs depends on the individual subpopulation of myenteric neurons examined. The presence of calbindin appears to protect myenteric neurons against harmful stimuli.

Dopamine and paraquat enhance α-synuclein-induced alterations in membrane conductance

We have previously demonstrated that α-synuclein overexpression increases the membrane conductance of dopaminergic-like cells. Although α-synuclein is thought to play a central role in the pathogenesis of several neurodegenerative diseases including Parkinson's disease, multiple system atrophy, and diffuse Lewy body disease, the mechanism of action is not completely understood. In this study, we sought to determine whether multiple factors act together with α-synuclein to engender cell vulnerability through an augmentation of membrane conductance. In this article, we employed a cell model that mimics dopaminergic neurons coupled with α-synuclein overexpression and oxidative stressors. We demonstrate an enhancement of α-synuclein-induced toxicity in the presence of combined treatment with dopamine and paraquat, two molecules known to incite oxidative stress. In addition, we show that combined dopamine and paraquat treatment increases the expression of heme oxygenase-1, an antioxidant response protein. Finally, we demonstrate for the first time that combined treatment of dopaminergic cells with paraquat and dopamine enhances α-synuclein-induced leak channel properties resulting in increased membrane conductance. Importantly, these increases are most robust when both paraquat and dopamine are present suggesting the need for multiple oxidative insults to augment α-synuclein-induced disruption of membrane integrity.

The inhibitory influence of the lateral habenula on midbrain dopamine cells: ultrastructural evidence for indirect mediation via the rostromedial mesopontine tegmental nucleus

The lateral habenula (LHb) provides an important source of negative reinforcement signals to midbrain dopamine (DA) cells in the substantia nigra and ventral tegmental area (VTA). This profound and consistent inhibitory influence involves a disynaptic connection from glutamate neurons in the LHb to some population of γ-aminobutyric acid (GABA) cells that, in turn, innervates DA neurons. Previous studies demonstrated that the GABA cells intrinsic to the VTA receive insufficient synaptic input from the LHb to serve as the primary source of this intermediate connection. In this investigation, we sought ultrastructural evidence supporting the hypothesis that a newly identified region of the brainstem, the rostromedial mesopontine tegmental nucleus (RMTg), is a more likely candidate for inhibiting midbrain DA cells in response to LHb activation. Electron microscopic examination of rat brain sections containing dual immunoreactivity for an anterograde tracing agent and a phenotypic marker revealed that: 1) more than 55% of the synapses formed by LHb axons in the RMTg were onto GABA-labeled dendrites; 2) more than 80% of the synapses formed by RMTg axons in the VTA contacted dendrites immunoreactive for the DA synthetic enzyme tyrosine hydroxylase; and 3) nearly all RMTg axons formed symmetric synapses and contained postembedding immunoreactivity for GABA. These findings indicate that the newly identified RMTg region is an intermediate structure in a disynaptic pathway that connects the LHb to VTA DA neurons. The results have important implications for understanding mental disorders characterized by a dysregulation of reward circuitry involving LHb and DA cell populations.

The neurotoxicity of DOPAL: behavioral and stereological evidence for its role in Parkinson disease pathogenesis

BACKGROUND

The etiology of Parkinson disease (PD) has yet to be fully elucidated. We examined the consequences of injections of 3,4-dihydroxyphenylacetaldehyde (DOPAL), a toxic metabolite of dopamine, into the substantia nigra of rats on motor behavior and neuronal survival.

METHODS/PRINCIPAL FINDINGS

A total of 800 nl/rat of DOPAL (1 µg/200 nl) was injected stereotaxically into the substantia nigra over three sites while control animals received similar injections of phosphate buffered saline. Rotational behavior of these rats was analyzed, optical density of striatal tyrosine hydroxylase was calculated, and unbiased stereological counts of the substantia nigra were made. The rats showed significant rotational asymmetry ipsilateral to the lesion, supporting disruption of dopaminergic nigrostriatal projections. Such disruption was verified since the density of striatal tyrosine hydroxylase decreased significantly (p<0.001) on the side ipsilateral to the DOPAL injections when compared to the non-injected side. Stereological counts of neurons stained for Nissl in pars compacta of the substantia nigra significantly decreased (p<0.001) from control values, while counts of those in pars reticulata were unchanged after DOPAL injections. Counts of neurons immunostained for tyrosine hydroxylase also showed a significant (p=0.032) loss of dopaminergic neurons. In spite of significant loss of dopaminergic neurons, DOPAL injections did not induce significant glial reaction in the substantia nigra.

CONCLUSIONS

The present study provides the first in vivo quantification of substantia nigra pars compacta neuronal loss after injection of the endogenous toxin DOPAL. The results demonstrate that injections of DOPAL selectively kills SN DA neurons, suggests loss of striatal DA terminals, spares non-dopaminergic neurons of the pars reticulata, and triggers a behavioral phenotype (rotational asymmetry) consistent with other PD animal models. This study supports the "catecholaldehyde hypothesis" as an important link for the etiology of sporadic PD.

Selective neuronal vulnerability to oxidative stress in the brain

Oxidative stress (OS), caused by the imbalance between the generation and detoxification of reactive oxygen and nitrogen species (ROS/RNS), plays an important role in brain aging, neurodegenerative diseases, and other related adverse conditions, such as ischemia. While ROS/RNS serve as signaling molecules at physiological levels, an excessive amount of these molecules leads to oxidative modification and, therefore, dysfunction of proteins, nucleic acids, and lipids. The response of neurons to this pervasive stress, however, is not uniform in the brain. While many brain neurons can cope with a rise in OS, there are select populations of neurons in the brain that are vulnerable. Because of their selective vulnerability, these neurons are usually the first to exhibit functional decline and cell death during normal aging, or in age-associated neurodegenerative diseases, such as Alzheimer's disease. Understanding the molecular and cellular mechanisms of selective neuronal vulnerability (SNV) to OS is important in the development of future intervention approaches to protect such vulnerable neurons from the stresses of the aging process and the pathological states that lead to neurodegeneration. In this review, the currently known molecular and cellular factors that contribute to SNV to OS are summarized. Included among the major underlying factors are high intrinsic OS, high demand for ROS/RNS-based signaling, low ATP production, mitochondrial dysfunction, and high inflammatory response in vulnerable neurons. The contribution to the selective vulnerability of neurons to OS by other intrinsic or extrinsic factors, such as deficient DNA damage repair, low calcium-buffering capacity, and glutamate excitotoxicity, are also discussed.

Lysosomal degradation of alpha-synuclein in vivo

Pathologic accumulation of alpha-synuclein is a feature of human parkinsonism and other neurodegenerative diseases. This accumulation may be counteracted by mechanisms of protein degradation that have been investigated in vitro but remain to be elucidated in animal models. In this study, lysosomal clearance of alpha-synuclein in vivo was indicated by the detection of alpha-synuclein in the lumen of lysosomes isolated from the mouse midbrain. When neuronal alpha-synuclein expression was enhanced as a result of toxic injury (i.e. treatment of mice with the herbicide paraquat) or transgenic protein overexpression, the intralysosomal content of alpha-synuclein was also significantly increased. This effect was paralleled by a marked elevation of the lysosome-associated membrane protein type 2A (LAMP-2A) and the lysosomal heat shock cognate protein of 70 kDa (hsc70), two essential components of chaperone-mediated autophagy (CMA). Immunofluorescence microscopy revealed an increase in punctate (lysosomal) LAMP-2A staining that co-localized with alpha-synuclein within nigral dopaminergic neurons of paraquat-treated and alpha-synuclein-overexpressing animals. The data provide in vivo evidence of lysosomal degradation of alpha-synuclein under normal conditions and, quite importantly, under conditions of enhanced protein burden. In the latter, increased lysosomal clearance of alpha-synuclein was mediated, at least in part, by CMA induction. It is conceivable that these neuronal mechanisms of protein clearance play an important role in neurodegenerative processes characterized by abnormal alpha-synuclein buildup.

Mitochondrial ferritin in the substantia nigra in restless legs syndrome

Restless legs syndrome (RLS) is a neurological disorder that is thought to involve decreased iron availability in the brain. Iron is required for oxidative metabolism and plays a critical role in redox reactions in mitochondria. The recent discovery of mitochondrial ferritin (FtMt) provided the opportunity to identify a potential correlation between iron and mitochondrial function in RLS. Human substantia nigra (SN) and putamen autopsy samples from 8 RLS cases and 8 controls were analyzed. Mitochondrial ferritin levels in RLS SN tissue homogenate samples assessed by immunoblots had more FtMt than control samples (p < 0.01), whereas there were no significant differences in FtMt in the putamen samples. By immunohistochemistry, neuromelanin-containing neurons in the SN were the predominant cell type expressing FtMt. Staining in neurons in RLS samples was consistently greater than that in controls. Cytochrome c oxidase staining, which reflects numbers of mitochondria, showed a similar staining pattern to that of FtMt, whereas there was less immunostaining in the RLS cases for cytosolic H-ferritin. These results suggest that increased numbers of mitochondria in neurons in RLS and increased FtMt might contribute to insufficient cytosolic iron levels in RLS SN neurons; they are consistent with the hypothesis that energy insufficiency in these neurons may be involved in the pathogenesis of RLS.

Calbindin-1 association and Parkinson's disease

BACKGROUND AND PURPOSE

Calcium levels have been proposed to play an important role in the selective vulnerability of nigrostriatal dopaminergic neurons in Parkinson's disease (PD). Recently, an association was reported between the calcium buffer, calbindin (rs1805874) and risk of PD in a Japanese patient-control series.

METHODS

We genotyped rs1805874 in four independent Caucasian patient-control series (1543 PD patients, 1771 controls).

RESULTS

There was no evidence of an association between rs1805874 and disease risk in individual populations or in the combined series (odds ratio: 1.04, 95% CI: 0.82-1.31, P = 0.74).

DISCUSSION

Our study shows there is no association between rs1805874 and risk for PD in four Caucasian populations. This suggests the effect of calbindin on PD risk displays population specificity.

A comparison of model-based (2D) and design-based (3D) stereological methods for estimating cell number in the substantia nigra pars compacta (SNpc) of the C57BL/6J mouse

The substantia nigra pars compacta (SNpc) is a compact brain structure that contains a variable distribution of cells in both medial to lateral and rostral to caudal dimensions. The SNpc is the primary brain structure affected in Parkinson's disease, where loss of dopaminergic neurons is one of the major hallmarks of the disorder. Neurotoxic and genetic models of Parkinson's disease, as well as mechanisms to treat this disorder, are modeled in the mouse. To accurately assess the validity of a model, one needs to be assured that the method(s) of analysis is accurate. Here, we determined the total number of dopaminergic neurons in the SNpc of the C57BL/6J mouse by serial reconstruction then compared that value to estimates derived using model-based stereology and design-based stereology. Serial reconstruction of the SNpc revealed the total number of SNpc dopaminergic neurons to be 8305+/-540 (+/-SEM). We compared this empirically derived neuron number to model based and design-based stereological estimates. We found that model based estimates gave a value of 8002+/-91 (+/-SEM) while design-based estimates were 8716+/-338 (+/-SEM). Statistical analysis showed no significant difference between estimates generated using model- or design-based stereological methods compared to empirically-derived counts using serial reconstruction.

Parkin deficiency increases vulnerability to inflammation-related nigral degeneration

The loss of nigral dopaminergic (DA) neurons in idiopathic Parkinson's disease (PD) is believed to result from interactions between genetic susceptibility and environmental factors. Evidence that inflammatory processes modulate PD risk comes from prospective studies that suggest that higher plasma concentrations of a number of proinflammatory cytokines correlate with an increased risk of developing PD and chronic nonsteroidal anti-inflammatory drug regimens reduce the incidence of PD. Although loss-of-function mutations in the parkin gene cause early-onset familial PD, Parkin-deficient (parkin-/-) mice do not display nigrostriatal pathway degeneration, suggesting that a genetic factor is not sufficient, and an environmental trigger may be needed to cause nigral DA neuron loss. To test the hypothesis that parkin-/- mice require an inflammatory stimulus to develop nigral DA neuron loss, low-dose lipopolysaccaride (LPS) was administered intraperitoneally for prolonged periods. Quantitative real-time PCR and immunofluorescence labeling of inflammatory markers indicated that this systemic LPS treatment regimen triggered persistent neuroinflammation in wild-type and parkin-/- mice. Although inflammatory and oxidative stress responses to the inflammation regimen did not differ significantly between the two genotypes, only parkin-/- mice displayed subtle fine-motor deficits and selective loss of DA neurons in substantia nigra. Therefore, our studies suggest that loss of Parkin function increases the vulnerability of nigral DA neurons to inflammation-related degeneration. This new model of nigral DA neuron loss may enable identification of early biomarkers of degeneration and aid in preclinical screening efforts to identify compounds that can halt or delay the progressive degeneration of the nigrostriatal pathway.

Mitochondrial complex I inhibition is not required for dopaminergic neuron death induced by rotenone, MPP+, or paraquat

Inhibition of mitochondrial complex I is one of the leading hypotheses for dopaminergic neuron death associated with Parkinson's disease (PD). To test this hypothesis genetically, we used a mouse strain lacking functional Ndufs4, a gene encoding a subunit required for complete assembly and function of complex I. Deletion of the Ndufs4 gene abolished complex I activity in midbrain mesencephalic neurons cultured from embryonic day (E) 14 mice, but did not affect the survival of dopaminergic neurons in culture. Although dopaminergic neurons were more sensitive than other neurons in these cultures to cell death induced by rotenone, MPP(+), or paraquat treatments, the absence of complex I activity did not protect the dopaminergic neurons, as would be expected if these compounds act by inhibiting complex 1. In fact, the dopaminergic neurons were more sensitive to rotenone. These data suggest that dopaminergic neuron death induced by treatment with rotenone, MPP(+), or paraquat is independent of complex I inhibition.

Fas-associated factor 1 and Parkinson's disease

Fas-associated factor 1 or FAF1 is a Fas-binding protein implicated in apoptosis. FAF1 is the product of a gene at PARK 10 locus on chromosome 1p32, a locus associated with late-onset PD [Hicks, A.A., Petursson, H., Jonsson, T., Stefansson, H., Johannsdottir, H.S., Sainz, J., Frigge, M.L.et al., 2002. A susceptibility gene for late-onset idiopathic Parkinson's disease. Ann Neurol. 52, 549-555.]. In the present study we investigated the role of FAF1 in cell death and in Parkinson's disease (PD) pathogenesis. FAF1 levels were significantly increased in frontal cortex of PD as well as in PD cases with Alzheimer's disease (AD) pathology compared to control cases. Changes in FAF1 expression were specific to PD-related alpha-synuclein pathology and nigral cell loss. In addition, PD-related insults including, mitochondrial complex I inhibition, oxidative stress, and increased alpha-synuclein expression specifically increased endogenous FAF1 expression in vitro. Increased FAF1 levels induced cell death and significantly potentiated toxic effects of PD-related stressors including, oxidative stress, mitochondrial complex I inhibition and proteasomal inhibition. These studies, together with previous genetic linkage studies, highlight the potential significance of FAF1 in pathogenesis of idiopathic PD.

Behavioral and histopathological consequences of paraquat intoxication in mice: effects of alpha-synuclein over-expression

Genetic variability in the alpha-synuclein gene and long-term exposure to the pesticide paraquat constitute possible risk factors for sporadic Parkinson's disease. The goal of the present study was to further characterize the effects of paraquat in mice as a model of Parkinson's disease and to determine whether it acted synergistically with alpha-synuclein over-expression to cause nigrostriatal cell death or dysfunction. Paraquat (10 mg/kg i.p.) was administered once a week for 3 weeks to mice over-expressing human alpha-synuclein under the Thy1 promoter and their wild-type littermates. The effect of paraquat on catecholaminergic neurons was reminiscent of that of Parkinson's disease, with preferential loss of dopaminergic neurons in the ventral tier of the substantia nigra pars compacta and loss of tyrosine hydroxylase staining in the locus coeruleus. alpha-Synuclein over-expression did not increase paraquat-induced cell loss, and paraquat did not worsen the behavioral deficits observed in the transgenic mice. However, paraquat markedly increased proteinase-K-resistant alpha-synuclein aggregates in substantia nigra of the transgenic mice. The data further validate the use of paraquat to model Parkinson's disease in mice and show that although paraquat and alpha-synuclein over-expression act synergistically to increase protein aggregation in vivo, this interaction does not result in short-term neuroprotection or increased vulnerability of nigrostriatal neurons.

Pharmacological inhibition of neuronal NADPH oxidase protects against 1-methyl-4-phenylpyridinium (MPP+)-induced oxidative stress and apoptosis in mesencephalic dopaminergic neuronal cells

Oxidative stress is widely recognized as a key mediator of degenerative processes in Parkinson's disease (PD). Recently, we demonstrated that the dopaminergic toxin MPP+ initiates oxidative stress to cause caspase-3-dependent apoptotic cell death in mesencephalic dopaminergic neuronal (N27) cells. In this study, we determined the source of reactive oxygen species (ROS) produced during MPP+-induced apoptotic cell death. In addition to mitochondria, plasma membrane NADPH oxidase is considered a major producer of ROS inside the cell. Here, we show that N27 neuronal cells express key NADPH oxidase subunits gp91phox and p67phox. We used structurally diverse NADPH oxidase inhibitors, aminoethyl-benzenesulfonylfluoride (AEBSF, 100-1000microM), apocynin (100-1000microM), and diphenylene iodonium (DPI, 3-30microM), to inhibit intrinsic NADPH oxidase activity in N27 cells. Flow cytometric analysis using the ROS-sensitive dye hydroethidine revealed that AEBSF blocked 300microM MPP+-induced ROS production for over 45min in N27 cells, in a dose-dependent manner. Further treatment with DPI, apocynin, and SOD also blocked MPP+-induced ROS production. In Sytox cell death assays, co-treatment with AEBSF, apocynin, or DPI for 24h significantly suppressed MPP+-induced cytotoxic cell death. Similarly, co-treatment with these inhibitors also significantly attenuated MPP+-induced increases in caspase-3 enzymatic activity. Furthermore, quantitative DNA fragmentation ELISA assays revealed that AEBSF, DPI, and apocynin rescue N27 cells from MPP+-induced apoptotic cell death. Together, these results indicate for the first time that intracellular ROS generated by NAPDH oxidase are present within the mesencephalic neuronal cells, and are a key determinant of MPP+-mediated dopaminergic degeneration in in vitro models of dopaminergic degeneration. This study supports a critical role of NADPH oxidase in the oxidative damage in PD; targeting this enzyme may lead to novel therapies for PD.

Generation and survival of midbrain dopaminergic neurons in weaver mice

Generation and survival of midbrain dopaminergic (DA) neurons were investigated using tyrosine hydroxylase (TH) immunocytochemistry combined with tritiated thymidine autoradiography at appropriate anatomical levels throughout the anteroposterior (A/P) axes of the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA). The wild-type (+/+) and homozygous weaver (wv/wv) mice used here were the offspring of pregnant dams injected with the radioactive precursor when the mesencephalic neurons were being produced (gestational days 11-15). Data reveal that, at postnatal day 90, depletion of TH-stained cells in the wv/wv presented an A/P pattern of increasing severity and, therefore, the DA cells located in posterior parts of the SNc or the VTA appear to be more vulnerable than the settled anterior neurons. When the time of neuron origin is inferred for each level of these cell groups, it is found that the neurogenesis span is similar for both experimental groups, although significant deficits in the frequency of wv/wv late-generated neurons were observed in any level considered. On the other hand, it has been found that TH-positive neurons were settled along the extent of the SNc and the VTA following precise and differential neurogenetic gradients. Thus, the acute rostrocaudal increase in the proportion of late-generated neurons detected in both+/+DA-cell groups is disturbed in the weaver homozygotes due to the indicated A/P depletion.