Neuroprotection and Functional Recovery Associated with Decreased Microglial Activation Following Selective Activation of mGluR2/3 Receptors in a Rodent Model of Parkinson's Disease

Radiosynthesis and Evaluation of 11C-Labeled Isoindolone-Based Positive Allosteric Modulators for Positron Emission Tomography Imaging of Metabotropic Glutamate Receptor 2

The metabotropic glutamate receptor 2 (mGluR2) has emerged as a potential therapeutic target for the treatment of various neurological diseases, prompting substantial interest in the development of mGluR2-targeted drug candidates. As part of our medicinal chemistry program, we synthesized a series of isoindolone derivatives and assessed their potential as mGluR2 positive allosteric modulators (PAMs). Notably, AZ12559322 exhibited high affinity (K i mGluR2 = 1.31 nM) and an excellent in vitro binding specificity of 89% while demonstrating selectivity over other mGluR subtypes (>4000-fold). Autoradiography with the radiolabeled counterpart, [3H]AZ12559322, revealed a heterogeneous accumulation with the highest binding in mGluR2-rich brain regions. Radioligand binding was significantly reduced by pretreatment with nonradioactive mGluR2 PAMs in brains of rats and nonhuman primates. Although positron emission tomography imaging of [11C]AZ12559322 (6a) revealed low brain uptake in a nonhuman primate, this study provides valuable guidance to further design novel isoindolone-based mGluR2 PAMs with improved brain exposure.

Ion Channels and Metal Ions in Parkinson's Disease: Historical Perspective to the Current Scenario

Parkinson's disease (PD) is a neurodegenerative condition linked to the deterioration of motor and cognitive performance. It produces degeneration of the dopaminergic neurons along the nigrostriatal pathway in the central nervous system (CNS), which leads to symptoms such as bradykinesias, tremors, rigidity, and postural instability. There are several medications currently approved for the therapy of PD, but a permanent cure for it remains elusive. With the aging population set to increase, a number of PD cases are expected to shoot up in the coming times. Hence, there is a need to look for new molecular targets that could be investigated both preclinically and clinically for PD treatment. Among these, several ion channels and metal ions are being studied for their effects on PD pathology and the functioning of dopaminergic neurons. Ion channels such as N-methyl-D-aspartate (NMDA), γ-aminobutyric acid A (GABAA), voltage-gated calcium channels, potassium channels, HCN channels, Hv1 proton channels, and voltage-gated sodium channels and metal ions such as mercury, zinc, copper, iron, manganese, calcium, and lead showed prominent involvement in PD. Pharmacological agents have been used to target these ion channels and metal ions to prevent or treat PD. Hence, in the present review, we summarize the pathophysiological events linked to PD with an emphasis on the role of ions and ion channels in PD pathology, and pharmacological agents targeting these ion channels have also been listed.

G protein-coupled receptors in neurodegenerative diseases and psychiatric disorders

Neuropsychiatric disorders are multifactorial disorders with diverse aetiological factors. Identifying treatment targets is challenging because the diseases are resulting from heterogeneous biological, genetic, and environmental factors. Nevertheless, the increasing understanding of G protein-coupled receptor (GPCR) opens a new possibility in drug discovery. Harnessing our knowledge of molecular mechanisms and structural information of GPCRs will be advantageous for developing effective drugs. This review provides an overview of the role of GPCRs in various neurodegenerative and psychiatric diseases. Besides, we highlight the emerging opportunities of novel GPCR targets and address recent progress in GPCR drug development.

Promising biomarkers and therapeutic targets for the management of Parkinson's disease: recent advancements and contemporary research

Parkinson's disease (PD) is one of the progressive neurological diseases which affect around 10 million population worldwide. The clinical manifestation of motor symptoms in PD patients appears later when most dopaminergic neurons have degenerated. Thus, for better management of PD, the development of accurate biomarkers for the early prognosis of PD is imperative. The present work will discuss the potential biomarkers from various attributes covering biochemical, microRNA, and neuroimaging aspects (α-synuclein, DJ-1, UCH-L1, β-glucocerebrosidase, BDNF, etc.) for diagnosis, recent development in PD management, and major limitations with current and conventional anti-Parkinson therapy. This manuscript summarizes potential biomarkers and therapeutic targets, based on available preclinical and clinical evidence, for better management of PD.

Metabotropic glutamate receptors in Parkinson's disease

Parkinson's disease (PD) is a complex disorder that leads to alterations in multiple neurotransmitter systems, notably glutamate. As such, several drugs acting at glutamatergic receptors have been assessed to alleviate the manifestation of PD and treatment-related complications, culminating with the approval of the N-methyl-d-aspartate (NMDA) antagonist amantadine for l-3,4-dihydroxyphenylalanine (l-DOPA)-induced dyskinesia. Glutamate elicits its actions through several ionotropic and metabotropic (mGlu) receptors. There are 8 sub-types of mGlu receptors, with sub-types 4 (mGlu₄) and 5 (mGlu₅) modulators having been tested in the clinic for endpoints pertaining to PD, while sub-types 2 (mGlu₂) and 3 (mGlu₃) have been investigated in pre-clinical settings. In this book chapter, we provide an overview of mGlu receptors in PD, with a focus on mGlu₅, mGlu₄, mGlu₂ and mGlu₃ receptors. For each sub-type, we review, when applicable, their anatomical localization and possible mechanisms underlying their efficacy for specific disease manifestation or treatment-induced complications. We then summarize the findings of pre-clinical studies and clinical trials with pharmacological agents and discuss the potential strengths and limitations of each target. We conclude by offering some perspectives on the potential use of mGlu modulators in the treatment of PD.

Novel therapeutic interventions for combating Parkinson's disease and prospects of Nose-to-Brain drug delivery

Parkinson disease (PD) is a progressive neurodegenerative disorder prevalent mainly in geriatric population. While, L-DOPA remains one of the major choices for the therapeutic management of PD, various motor and non-motor manifestations complicate the management of PD. In the last two decades, exhaustive research has been carried out to explore novel therapeutic approaches for mitigating motor and non-motor symptoms of PD. These approaches majorly include receptor-based, anti-inflammatory, stem-cell and nucleic acid based. The major limitations of existing therapeutic interventions (of commonly oral route) are low efficacy due to low brain bioavailability and associated side effects. Nanotechnology has been exploited and has gained wide attention in the recent years as an approach for enhancement of bioavailability of various small molecule drugs in the brain. To address the challenges associated with PD therapy, nose-to-brain delivery utilizing nanomedicine-based approaches has been found to be encouraging in published evidence. Therefore, the present work summarises the major challenges and limitations with antiparkinsonian drugs, novel therapeutic interventions, and scope of nanomedicine-based nose-to-brain delivery in addressing the current challenges of antiparkinsonian therapy. The manuscript tries to sensitize the researchers for designing brain-targeted nanomedicine loaded with natural/synthetic scaffolds, biosimilars, and nucleic acids that can bypass the first-pass effect for the effective management of PD.

JM-20 protects against 6-hydroxydopamine-induced neurotoxicity in models of Parkinson's disease: Mitochondrial protection and antioxidant properties

We have previously shown that JM-20, a new chemical entity consisting of 1,5-benzodiazepine fused to a dihydropyridine moiety, protects against rotenone-induced neurotoxicity in an experimental model of Parkinson's disease (PD). The aim of this study was to investigate the effect of a novel hybrid molecule, named JM-20, in in vitro and in vivo models of PD induced by 6-hydroxydopamine (6-OHDA). PC-12 cells were exposed to 6-OHDA and treated with JM-20. Protection against mitochondrial damage induced by 6-OHDA was also investigated using isolated rat brain mitochondria. We found that JM-20 protected PC-12 cells against cytotoxicity induced by 6-OHDA and inhibited hydrogen peroxide generation, mitochondrial swelling and membrane potential dissipation. For in vivo experiments, adult male Wistar rats were lesioned in the substantia nigra pars compacta (SNpc) by 6-OHDA administration. JM-20 was orally administered (10, 20 or 40 mg/kg), intragastric via gavage, 24 h after surgery and daily for seven days. Treatment with JM-20 significantly reduced the percentage of motor asymmetry and increased vertical exploration. It improved the redox state of the SNpc and the striatal tissue of these animals. Also, JM-20 reduced glial fibrillary acidic protein overexpression and increased tyrosine hydroxylase-positive cell number, both in SNpc. Altogether, these results demonstrate that JM-20 is a potential neuroprotective agent against 6-OHDA-induced damage in both in vitro and in vivo models. The mechanism underlying JM-20 neuroprotection against 6-OHDA appears to be associated with the control of oxidative injury and mitochondrial impairment.

A Multi-Scale Computational Model of Excitotoxic Loss of Dopaminergic Cells in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder caused by loss of dopaminergic neurons in substantia nigra pars compacta (SNc). Although the exact cause of cell death is not clear, the hypothesis that metabolic deficiency is a key factor has been gaining attention in recent years. In the present study, we investigated this hypothesis using a multi-scale computational model of the subsystem of the basal ganglia comprising the subthalamic nucleus (STN), globus pallidus externa (GPe), and SNc. The proposed model is a multiscale model in that interaction among the three nuclei are simulated using more abstract Izhikevich neuron models, while the molecular pathways involved in cell death of SNc neurons are simulated in terms of detailed chemical kinetics. Simulation results obtained from the proposed model showed that energy deficiencies occurring at cellular and network levels could precipitate the excitotoxic loss of SNc neurons in PD. At the subcellular level, the models show how calcium elevation leads to apoptosis of SNc neurons. The therapeutic effects of several neuroprotective interventions are also simulated in the model. From neuroprotective studies, it was clear that glutamate inhibition and apoptotic signal blocker therapies were able to halt the progression of SNc cell loss when compared to other therapeutic interventions, which only slowed down the progression of SNc cell loss.

Identification and Development of a New Positron Emission Tomography Ligand 4-(2-Fluoro-4-[11C]methoxyphenyl)-5-((1-methyl-1H-pyrazol-3-yl)methoxy)picolinamide for Imaging Metabotropic Glutamate Receptor Subtype 2 (mGlu2)

Metabotropic glutamate receptor 2 (mGlu₂) is a known target for treating several central nervous system (CNS) disorders. To develop a viable positron emission tomography (PET) ligand for mGlu₂, we identified new candidates 5a-i that are potent negative allosteric modulators (NAMs) of mGlu₂. Among these candidates, 4-(2-fluoro-4-methoxyphenyl)-5-((1-methyl-1H-pyrazol-3-yl)methoxy)picolinamide (5i, also named as [¹¹C]MG2-1812) exhibited high potency, high subtype selectivity, and favorable lipophilicity. Compound 5i was labeled with positron-emitting carbon-11 (¹¹C) to obtain [¹¹C]5i in high radiochemical yield and high molar activity by O-[¹¹C]methylation of the phenol precursor 12 with [¹¹C]CH₃I. In vitro autoradiography with [¹¹C]5i showed heterogeneous radioactive accumulation in the brain tissue sections, ranked in the order: cortex > striatum > hippocampus > cerebellum ≫ thalamus > pons. PET study of [¹¹C]5i indicated in vivo specific binding of mGlu₂ in the rat brain. Based on the [¹¹C]5i scaffold, further optimization for new candidates is underway to identify a more suitable ligand for imaging mGlu₂.

Study on Effect of Striatal mGluR2/3 in Alleviating Motor Dysfunction in Rat PD Model Treated by Exercise Therapy

Background: Exercise therapy has been widely applied in clinical rehabilitation as an important practical and side effect-free adjuvant therapy, with a significant effect in alleviating motor dysfunction of patients with Parkinson's disease (PD) or animal PD models. This study focuses on the effect of exercise therapy in reducing the concentration of extracellular glutamate (Glu) in the striatum in a rat PD model by upregulating the expression of group II metabotropic Glu receptor (mGluR2/3), so as to alleviate motor dysfunction in the rat PD model. Methods: Neurotoxin 6-hydroxydopamine (6-OHDA) was injected into the right medial forebrain bundle (MFB) of the rats to establish the semi-lateral cerebral damage PD model. The sham-operated group was given an equal amount of normal saline at the same site and taken as the control group. The apomorphine (APO)-induced rotational behavior test combined with immunohistochemical staining with tyrosine hydroxylase (TH) in the substantia nigra (SNc) and striatum was performed to assess the reliability of the model. The exercise group was given treadmill exercise intervention for 4 weeks (11 m/min, 30 min/day, 5 days/week) 1 week after the operation. The open field test (OFT) was performed to assess the locomotor activity of the rats; the Western blot technique was used to detect SNc TH and striatal mGluR2/3 protein expressions; real-time polymerase chain reaction (RT-PCR) was applied to detect striatal mGluR2 and mGluR3 mRNA expressions; the microdialysis-high-performance liquid chromatography (HPLC) method was adopted to detect the concentration of extracellular Glu in striatal neurons. Results: Compared with the control group, the number of rotations of each model group at the first week was significantly increased (P < 0.01); compared with the PD group, the number of rotations of the PD + exercise group at the third week and the fifth week was significantly decreased (P < 0.05, P < 0.01). Compared with the control group, the total movement distance, the total movement time, and the mean velocity of each model group at the first week were significantly reduced (P < 0.05); compared with the PD group, the total movement distance, the total movement time, and the mean velocity of the PD + exercise group at the third week and the fifth week were significantly increased (P < 0.01). Compared with the control group, the count of immunopositive cells and protein expression of SNc TH, and the content of immunopositive fiber terminals in the striatal TH of each model group significantly declined (P < 0.01). Compared with the PD group, the striatal mGluR2/3 protein expression of the PD + exercise group significantly rose (P < 0.01). Compared with the control group, the concentration of extracellular Glu in striatal neurons of each model group at the first week significantly grew (P < 0.05); compared with the PD group, the concentration of extracellular Glu in striatal neurons of the PD + exercise group at the third week and the fifth week was significantly decreased (P < 0.01); compared with the PD + exercise group, the concentration of extracellular Glu in striatal neurons of the group injected with mGluR2/3 antagonist (RS)-1-amino-5-phosphonoindan-1-carboxylic acid (APICA) into the striatum at the third week and the fifth week was significantly increased (P < 0.05, P < 0.01). Compared with the control group, the striatal mGluR2/3 protein expression of the PD group was significantly downregulated (P < 0.01); compared with the PD group, the striatal mGluR2/3 protein expression of the PD + exercise group was significantly upregulated (P < 0.05); compared with the control group, the striatal mGluR3 mRNA expression of the PD group was significantly downregulated (P < 0.01); compared with the PD group, the striatal mGluR3 mRNA expression of the PD + exercise group was significantly upregulated (P < 0.01); 6-OHDA damage and exercise intervention had no significant effect on the striatal mGluR2 mRNA expression (P > 0.05). Compared with the PD + exercise group, the total movement distance, the total movement time, and the mean velocity of the PD + exercise + APICA group were significantly decreased (P < 0.05); compared with the PD group, the PD + exercise + APICA group had no significant change in the total movement distance, the total movement time, and the mean velocity (P > 0.05). Conclusion: These data collectively demonstrate that the mGluR2/3-mediated glutamatergic transmission in the striatum is sensitive to dopamine (DA) depletion and may serve as a target of exercise intervention for mediating the therapeutic effect of exercise intervention in a rat model of PD.

A Computational Model of Loss of Dopaminergic Cells in Parkinson's Disease Due to Glutamate-Induced Excitotoxicity

Parkinson's disease (PD) is a neurodegenerative disease associated with progressive and inexorable loss of dopaminergic cells in Substantia Nigra pars compacta (SNc). Although many mechanisms have been suggested, a decisive root cause of this cell loss is unknown. A couple of the proposed mechanisms, however, show potential for the development of a novel line of PD therapeutics. One of these mechanisms is the peculiar metabolic vulnerability of SNc cells compared to other dopaminergic clusters; the other is the SubThalamic Nucleus (STN)-induced excitotoxicity in SNc. To investigate the latter hypothesis computationally, we developed a spiking neuron network-model of SNc-STN-GPe system. In the model, prolonged stimulation of SNc cells by an overactive STN leads to an increase in ‘stress' variable; when the stress in a SNc neuron exceeds a stress threshold, the neuron dies. The model shows that the interaction between SNc and STN involves a positive-feedback due to which, an initial loss of SNc cells that crosses a threshold causes a runaway-effect, leading to an inexorable loss of SNc cells, strongly resembling the process of neurodegeneration. The model further suggests a link between the two aforementioned mechanisms of SNc cell loss. Our simulation results show that the excitotoxic cause of SNc cell loss might initiate by weak-excitotoxicity mediated by energy deficit, followed by strong-excitotoxicity, mediated by a disinhibited STN. A variety of conventional therapies were simulated to test their efficacy in slowing down SNc cell loss. Among them, glutamate inhibition, dopamine restoration, subthalamotomy and deep brain stimulation showed superior neuroprotective-effects in the proposed model.

KM-34, a Novel Antioxidant Compound, Protects against 6-Hydroxydopamine-Induced Mitochondrial Damage and Neurotoxicity

The etiology of Parkinson's disease is not completely understood and is believed to be multifactorial. Neuronal disorders associated to oxidative stress and mitochondrial dysfunction are widely considered major consequences. The aim of this study was to investigate the effect of the synthetic arylidenmalonate derivative 5-(3,4-dihydroxybenzylidene)-2,2-dimethyl-1,3-dioxane-4,6-dione (KM-34), in oxidative stress and mitochondrial dysfunction induced by 6-hydroxydopamine (6-OHDA). Pretreatment (2 h) with KM-34 (1 and 10 μM) markedly attenuated 6-OHDA-induced PC12 cell death in a concentration-dependent manner. KM-34 also inhibited H₂O₂ generation, mitochondrial swelling, and membrane potential dissipation after 6-OHDA-induced mitochondrial damage. In vivo, KM-34 treatment (1 and 2 mg/Kg) reduced percentage of asymmetry (cylinder test) and increased the vertical exploration (open field) with respect to untreated injured animals; KM-34 also reduced glial fibrillary acidic protein overexpression and increased tyrosine hydroxylase-positive cell number, both in substantia nigra pars compacta. These results demonstrate that KM-34 present biological effects associated to mitoprotection and neuroprotection in vitro, moreover, glial response and neuroprotection in SNpc in vivo. We suggest that KM-34 could be a putative neuroprotective agent for inhibiting the progressive neurodegenerative disease associated to oxidative stress and mitochondrial dysfunction.

Metabotropic glutamate receptors as therapeutic targets in Parkinson's disease: An update from the last 5 years of research

Disturbance of glutamate neurotransmission in Parkinson's disease (PD) and l-DOPA induced dyskinesia (LID) is well documented. This review focuses on advances during the past five years on pharmacological modulation of metabotropic glutamate (mGlu) receptors in relation to anti-parkinsonian activity, LID attenuation, and neuroprotection. Drug design and characterization have led to the development of orthosteric agonists binding the same site as glutamate and Positive and Negative Allosteric modulators (PAMs and NAMs) binding sites different from the orthosteric site and offering subtype selectivity. Inhibition of group I (mGlu1 and mGlu5) receptors with NAMs and activation of group II (mGlu2 and 3 receptors) and group III (mGlu 4, 7 and 8 receptors) with PAMs and orthosteric agonists have shown their potential to inhibit glutamate release and attenuate excitotoxicity. Earlier and recent studies have led to the development of mGlu5 receptors NAMs to reduce LID and for neuroprotection, mGlu3 receptor agonists for neuroprotection while mGlu4 receptor PAMs and agonists for antiparkinsonian effects and neuroprotection. Furthermore, homo- and heterodimers of mGlu receptors are documented and highlight the complexity of the functioning of these receptors. Research on partial allosteric modulators and biased mGlu receptor allosteric modulators offer new glutamatergic drugs with better therapeutic effects and less off target adverse activity. Thus these various mGlu receptor targets will enable the development of novel drugs with improved clinical effects for normalization of glutamate transmission, treat PD and LID relief. This article is part of the Special Issue entitled 'Metabotropic Glutamate Receptors, 5 years on'.

Granulocyte-colony stimulating factor improves Parkinson's disease associated with co-morbid depression: an experimental exploratory study

Introduction:

The present study was designed to evaluate the effect of granulocyte-colony stimulating factor (G-CSF) in the treatment of Parkinson's disease (PD), the second most common neurodegenerative disease characterized by muscle and movement disorder, often associated with depression. PD is very difficult to treat. Hence, the present study was aimed to evaluate the effect of G-CSF in PD associated with depression.

Materials and Methods:

Adult Wistar male rats weighing about 180-250 g were selected and divided into five groups in parallel designed method namely; control group (n = 5); sham operated group (n = 5); Vehicle group (n = 5); G-CSF group (70 μg/kg, s.c.) (n = 5) and L-DOPA group (n = 5). The rats were treated with 6-hydroxydopamine (6-OHDA) on day 0 and then treatment was continued for 14 day of L-DOPA/carbidopa, whereas G-CSF (70 μg/kg, s.c.) was given from day 1 to 6. Thereafter, adhesive removal and forced swim tests were conducted to evaluate the behavioral outcome of G-CSF treatment. The finding was correlated and analyzed with Nissl staining findings for the final conclusion.

Results:

The behavioral parameters were assessed and found to be ameliorate the symptoms of Parkinson's and reduced the depression like behavior in PD. The histological findings were supported the behavioral findings and showed pathological improvement.

Conclusion:

As a preliminary work, the present study first time suggested that G-CSF have a potential role in PD and associated depression.

Targeting glutamate receptors to tackle the pathogenesis, clinical symptoms and levodopa-induced dyskinesia associated with Parkinson's disease

The appearance of levodopa-induced dyskinesia (LID) and ongoing degeneration of nigrostriatal dopaminergic neurons are two key features of Parkinson's disease (PD) that current treatments fail to address. Increased glutamate transmission contributes to the motor symptoms in PD, to the striatal plasticity that underpins LID and to the progression of neurodegeneration through excitotoxic mechanisms. Glutamate receptors have therefore long been considered as potential targets for pharmacological intervention in PD, with emphasis on either blocking activation of 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid (AMPA), N-methyl-D-aspartate (NMDA) or excitatory metabotropic glutamate (mGlu) 5 receptors or promoting the activation of group II/III mGlu receptors. Following a brief summary of the role of glutamate in PD and LID, this article explores the current status of pharmacological studies in pre-clinical rodent and primate models through to clinical trials, where applicable, that support the potential of glutamate-based therapeutic interventions. To date, AMPA antagonists have shown good efficacy against LID in rat and primate models, but the failure of perampanel to lessen LID in clinical trials casts doubt on the translational potential of this approach. In contrast, antagonists selective for NR2B-containing NMDA receptors were effective against LID in animal models and in small-scale clinical trials, though observed adverse cognitive effects need addressing. So far, mGlu5 antagonists or negative allosteric modulators (NAMs) look set to become the first introduced for tackling LID, with AFQ-056 reported to exhibit good efficacy in phase II clinical trials. NR2B antagonists and mGlu5 NAMs may subsequently prove to also be effective disease-modifying agents if their protective effects in rat and primate models of PD, respectively, are replicated in the next stages of investigation. Finally, group III mGlu4 agonists or positive allosteric modulators (PAMs), although in the early pre-clinical stages of investigation, are showing good efficacy against motor symptoms, neurodegeneration and LID. It is anticipated that the recent development of mGlu4 PAMs with improved systemic bioavailability will facilitate progression of these agents into the primate model of PD where their potential can be further explored.

A guide to neurotoxic animal models of Parkinson's disease

Parkinson's disease (PD) is a neurological movement disorder primarily resulting from damage to the nigrostriatal dopaminergic pathway. To elucidate the pathogenesis, mechanisms of cell death, and to evaluate therapeutic strategies for PD, numerous animal models have been developed. Understanding the strengths and limitations of these models can significantly impact the choice of model, experimental design, and data interpretation. The primary objectives of this article are twofold: First, to assist new investigators who are contemplating embarking on PD research to navigate through the available animal models. Emphasis will be placed on common neurotoxic murine models in which toxic molecules are used to lesion the nigrostriatal dopaminergic system. And second, to provide an overview of basic technical requirements for assessing the pathology, structure, and function of the nigrostriatal pathway.

Neuroprotection by the selective iNOS inhibitor GW274150 in a model of Parkinson disease

Neuroinflammation and the activation of inducible nitric oxide synthase (iNOS) have been proposed to play a role in the pathogenesis of Parkinson disease (PD). In this study we investigated the effects of the selective iNOS inhibitor GW274150 in the 6-OHDA model of PD. 6-OHDA administration was associated with increased numbers of cells expressing iNOS. Administration of the iNOS inhibitor twice daily for 7 days, beginning 2 days after the 6-OHDA lesioning, led to a significant neuroprotection as shown by assessment of the integrity of the nigrostriatal system by tyrosine hydroxylase immunocytochemistry and HPLC assessment of striatal dopamine content. However, GW274150 displayed a bell-shaped neuroprotective profile, being ineffective at high doses. 6-OHDA lesioning was associated with an increase in microglial activation as assessed by the MHC II antigen OX-6 and the number of matrix metalloproteinase 9 (MMP-9)-immunopositive cells. NO is a known modulator of MMP-9, and iNOS inhibition was associated with decreased numbers of MMP-9-immunopositive cells, culminating in a reduction in the numbers of reactive microglia. Withdrawal of GW274150 for a further 7 days negated any neuroprotective effects of iNOS inhibition, suggesting that the damaging effects of inflammation last beyond 7 days in this model and the continued administration of the drug may be required.