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Marketed drugs for Parkinson’s disease (PD) treat disease motor symptoms but are ineffective in stopping or slowing disease progression. In the quest of novel pharmacological approaches that may target disease progression, drug-repurposing provides a strategy to accelerate the preclinical and clinical testing of drugs already approved for other medical indications. Here, we targeted the inflammatory component of PD pathology, by testing for the first time the disease-modifying properties of the immunomodulatory imide drug (IMiD) pomalidomide in a translational rat model of PD neuropathology based on the intranigral bilateral infusion of toxic preformed oligomers of human α-synuclein (H-αSynOs). The neuroprotective effect of pomalidomide (20 mg/kg; i.p. three times/week 48 h apart) was tested in the first stage of disease progression by means of a chronic two-month administration, starting 1 month after H-αSynOs infusion, when an already ongoing neuroinflammation is observed. The intracerebral infusion of H-αSynOs induced an impairment in motor and coordination performance that was fully rescued by pomalidomide, as assessed via a battery of motor tests three months after infusion. Moreover, H-αSynOs-infused rats displayed a 40–45% cell loss within the bilateral substantia nigra, as measured by stereological counting of TH + and Nissl-stained neurons, that was largely abolished by pomalidomide. The inflammatory response to H-αSynOs infusion and the pomalidomide treatment was evaluated both in CNS affected areas and peripherally in the serum. A reactive microgliosis, measured as the volume occupied by the microglial marker Iba-1, was present in the substantia nigra three months after H-αSynOs infusion as well as after H-αSynOs plus pomalidomide treatment. However, microglia differed for their phenotype among experimental groups. After H-αSynOs infusion, microglia displayed a proinflammatory profile, producing a large amount of the proinflammatory cytokine TNF-α. In contrast, pomalidomide inhibited the TNF-α overproduction and elevated the anti-inflammatory cytokine IL-10. Moreover, the H-αSynOs infusion induced a systemic inflammation with overproduction of serum proinflammatory cytokines and chemokines, that was largely mitigated by pomalidomide. Results provide evidence of the disease modifying potential of pomalidomide in a neuropathological rodent model of PD and support the repurposing of this drug for clinical testing in PD patients.

Major depressive disorder is one of the primary causes of disability and disease worldwide. The therapy of depression is prevalently based on monoamine reuptake blockers; consequently, investigations aimed to clarify the aetiology of depression have mostly looked at brain areas innervated by monamines and brain circuitry involved in inputs and outputs of these areas. The recent approval of esketamine as a rapid-acting antidepressant drug in treatment-resistant depression, has definitively projected glutamatergic transmission as a key constituent in the use of new drugs in antidepressant therapy. In this review we have examined the role of several brain areas: namely, the hippocampus, the medial Prefrontal Cortex (mPFC), the nucleus accumbens (NAc), the Lateral Habenula (LHb), the amygdala and the Bed Nucleus of Stria Terminalis (BNST). The reason for undertaking an in-depth review is due to their significant role in animal models of depression, which highlight their inter-connections as well as their inputs and outputs. In particular, we examined the modification of the expression and release of the brain derived neurotrophic factor (BDNF) and associated changes in dendritic density induced by chronic stress in the above areas of animal models of depression (AnMD). We also examined the effectiveness of ketamine and standard antidepressants in reversing these alterations, with the aim of identifying a brain circuit where pathological alteration might trigger the appearance of depression symptoms. Based on the role that these brain areas play in the generation of the symptoms of depression, we assumed that the mPFC, the NAc/Ventral Tegmental Area (VTA) and the hippocampus form a primary circuit of depression, where regular performance can endure resilience to stress. We have also examined how this circuit is affected by environmental challenges and how the activation of one or more areas, including amygdala, LHb or BNST can produce local detrimental effects that spread over specific circuits and generate depression symptoms. Furthermore, we also examined how, through their outputs, these three areas can negatively influence the NAc/VTA-PFC circuit directly or through the BNST, to generate anhedonia, one of the most devastating symptoms of depression.

BACKGROUND Thalidomide and closely related analogues are used clinically for their immunomodulatory and antiangiogenic properties mediated by the inhibition of the proinflammatory cytokine tumor necrosis factor α. Neuroinflammation and angiogenesis contribute to classical neuronal mechanisms underpinning the pathophysiology of l-dopa-induced dyskinesia, a motor complication associated with l-dopa therapy in Parkinson's disease. The efficacy of thalidomide and the more potent derivative 3,6'-dithiothalidomide on dyskinesia was tested in the 6-hydroxydopamine Parkinson's disease model. METHODS Three weeks after 6-hydroxydopamine infusion, rats received 10 days of treatment with l-dopa plus benserazide (6 mg/kg each) and thalidomide (70 mg/kg) or 3,6'-dithiothalidomide (56 mg/kg), and dyskinesia and contralateral turning were recorded daily. Rats were euthanized 1 hour after the last l-dopa injection, and levels of tumor necrosis factor-α, interleukin-10, OX-42, vimentin, and vascular endothelial growth factor immunoreactivity were measured in their striatum and substantia nigra reticulata to evaluate neuroinflammation and angiogenesis. Striatal levels of GLUR1 were measured as a l-dopa-induced postsynaptic change that is under tumor necrosis factor-α control. RESULTS Thalidomide and 3,6'-dithiothalidomide significantly attenuated the severity of l-dopa-induced dyskinesia while not affecting contralateral turning. Moreover, both compounds inhibited the l-dopa-induced microgliosis and excessive tumor necrosis factor-α in the striatum and substantia nigra reticulata, while restoring physiological levels of the anti-inflammatory cytokine interleukin-10. l-Dopa-induced angiogenesis was inhibited in both basal ganglia nuclei, and l-dopa-induced GLUR1 overexpression in the dorsolateral striatum was restored to normal levels. CONCLUSIONS These data suggest that decreasing tumor necrosis factor-α levels may be useful to reduce the appearance of dyskinesia, and thalidomide, and more potent derivatives may provide an effective therapeutic approach to dyskinesia. © 2019 International Parkinson and Movement Disorder Society.

The accumulation of aggregated &alpha, synuclein (&alpha, Syn) is a hallmark of Parkinson&rsquo, s disease (PD). Current evidence indicates that small soluble &alpha, Syn oligomers (&alpha, SynOs) are the most toxic species among the forms of &alpha, Syn aggregates, and that size and topological structural properties are crucial factors for &alpha, SynOs-mediated toxicity, involving the interaction with either neurons or glial cells. We previously characterized a human &alpha, SynO (H-&alpha, SynO) with specific structural properties promoting toxicity against neuronal membranes. Here, we tested the neurotoxic potential of these H-&alpha, SynOs in vivo, in relation to the neuropathological and symptomatic features of PD. The H-&alpha, SynOs were unilaterally infused into the rat substantia nigra pars compacta (SNpc). Phosphorylated &alpha, Syn (p129-&alpha, Syn), reactive microglia, and cytokine levels were measured at progressive time points. Additionally, a phagocytosis assay in vitro was performed after microglia pre-exposure to &alpha, synOs. Dopaminergic loss, motor, and cognitive performances were assessed. H-&alpha, SynOs triggered p129-&alpha, Syn deposition in SNpc neurons and microglia and spread to the striatum. Early and persistent neuroinflammatory responses were induced in the SNpc. In vitro, H-&alpha, SynOs inhibited the phagocytic function of microglia. H-&alpha, synOs-infused rats displayed early mitochondrial loss and abnormalities in SNpc neurons, followed by a gradual nigrostriatal dopaminergic loss, associated with motor and cognitive impairment. The intracerebral inoculation of structurally characterized H-&alpha, SynOs provides a model of progressive PD neuropathology in rats, which will be helpful for testing neuroprotective therapies.

Originally believed to primarily affect neurons, Parkinson's disease (PD) has recently been recognized to also affect the functions and integrity of microglia and astroglia, two cell categories of fundamental importance to brain tissue homeostasis, defense, and repair. Both a loss of glial supportive-defensive functions and a toxic gain of glial functions are implicated in the neurodegenerative process. Moreover, the chronic treatment with L-DOPA may cause maladaptive glial plasticity favoring a development of therapy complications. This chapter focuses on the pathophysiology of PD from a glial point of view, presenting this rapidly growing field from the first discoveries made to the most recent developments. We report and compare histopathological and molecular findings from experimental models of PD and human studies. We moreover discuss the important role played by astrocytes in compensatory adaptations taking place during presymptomatic disease stages. We finally describe examples of potential therapeutic applications stemming from an increased understanding of the important roles of glia in PD.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a pandemic disease (COVID-19) that has spread globally causing more than 30,000 deaths. Despite the immense and ongoing global effort, no efficacious drugs to fight this plague have been identified and patients admitted to the intensive care units (ICU), for respiratory distress, are managed mostly by means of supportive care based on oxygen maintenance. Several authors have reported that the prevalence of hypertension, diabetes, cardiovascular and cerebrovascular diseases comorbidities were indeed frequent among patients with COVID-19, which suggests that these conditions are likely to aggravate and complicate the prognosis. What the aforementioned diseases have in common is a latent chronic inflammatory state that may be associated with the alteration of laboratory parameters that are typical of the metabolic syndrome and insulin resistance. In severe COVID-19 patients laboratory markers of inflammation such as C-reactive protein, IL-6, D-dimer, serum ferritin and lactate dehydrogenase are elevated in many patients; assessed since the 4th-6th day of illness onset, such increases seem to be predictive of an adverse prognosis. Our hypothesis is that drugs belonging to the family of thiazolidinediones (TZD) such as pioglitazone or rosiglitazone, approved for treating the condition of insulin resistance and the accompanying inflammation, could ameliorate the prognosis of those COVID-19 patients with diabetes, hypertension and cardiovascular disorders comorbidities. TZD are PPARγ agonists that act on nuclear receptors, thereby triggering certain transcription factors. TZD were widely used for type-2 diabetes in the first decade of this century and although concerns have been raised for possible side effects associated with long-term treatment, their use has been recently revaluated for their anti-inflammatory properties in numerous medical conditions.

Originally believed to primarily affect neurons, Parkinson's disease (PD) has recently been recognized to also affect the functions and integrity of microglia and astroglia, two cell categories of fundamental importance to brain tissue homeostasis, defense, and repair. Both a loss of glial supportive-defensive functions and a toxic gain of glial functions are implicated in the neurodegenerative process. Moreover, the chronic treatment with L-DOPA may cause maladaptive glial plasticity favoring a development of therapy complications. This chapter focuses on the pathophysiology of PD from a glial point of view, presenting this rapidly growing field from the first discoveries made to the most recent developments. We report and compare histopathological and molecular findings from experimental models of PD and human studies. We moreover discuss the important role played by astrocytes in compensatory adaptations taking place during presymptomatic disease stages. We finally describe examples of potential therapeutic applications stemming from an increased understanding of the important roles of glia in PD.

Background and purpose Microglial phenotype and phagocytic activity are deregulated in Parkinson's disease (PD). PPARγ agonists are neuroprotective in experimental PD, but their role in regulating microglial phenotype and phagocytosis has been poorly investigated. We addressed it by using the PPARγ agonist MDG548. Experimental approach Murine microglial cell line MMGT12 was stimulated with LPS and/or MDG548, and their effect on phagocytosis of fluorescent microspheres or necrotic neurons was investigated by flow cytometry. Cytokines and markers of microglia phenotype, such as mannose receptor C type 1; MRC1), Ym1 and CD68 were measured by elisa and fluorescent immunohistochemistry. Levels of Beclin-1, which plays a role in microglial phagocytosis, were measured by Western blotting. In the in vivo MPTP-probenecid (MPTPp) model of PD in mice, MDG548 was tested on motor impairment, nigral neurodegeneration, microglial activation and phenotype. Key results In LPS-stimulated microglia, MDG548 increased phagocytosis of both latex beads and necrotic cells, up-regulated the expression of MRC1, CD68 and to a lesser extent IL-10, while blocking the LPS-induced increase of TNF-α and iNOS. MDG548 also induced Beclin-1. Chronic MPTPp treatment in mice down-regulated MRC1 and TGF-β and up-regulated TNF-α and IL-1β immunoreactivity in activated CD11b-positive microglia, causing the death of nigral dopaminergic neurons. MDG548 arrested MPTPp-induced cell death, enhanced MRC1 and restored cytokine levels. Conclusions and implications This study adds a novel mechanism for PPARγ-mediated neuroprotection in PD and suggests that increasing phagocytic activity and anti-inflammatory markers may represent an effective disease-modifying approach.

Aggregates of alpha-synuclein (αSyn) have been described in Parkinson's disease (PD) patients, and recent evidence has suggested that the most toxic αSyn species in PD are small soluble aggregates including oligomers, prefibrils, protofibrils. The physiological function of αSyn is still highly debated, with a possible role in synaptic vesicle trafficking and release at the presynaptic compartment, and in the regulation of gene expression in the nucleus. Emerging evidence indicate that most of αSyn functions are related with the crucial ability to bind biological membranes, which is associated with structural conversion from a disordered monomer to an α-helical enriched structure. Conformational properties of αSyn can be modulated by a number of factors including post-translational modifications, gene duplication and triplication-driven overexpression, single point mutations, environmental changes, which affect membrane binding and the protein propensity to aggregate in toxic species. The recognized toxic role of αSyn in PD has laid the rational for purposing of αSyn-based, neuropathologically relevant preclinical models of PD. Different approaches have led to the establishment of transgenic models, viral vector-based models, and more recently models based on the intracerebral inoculation of exogenous αSyn preformed fibrils/oligomers. Here, we overview and compare viral vector-based models of αSyn overexpression and models obtained by direct intracerebral infusion of in vitro preformed αSyn species. The advantages and pitfalls associated with these different approaches are discussed.

The search for new disease-modifying drugs for Parkinson’s disease (PD) is a slow and highly expensive process, and the repurposing of drugs already approved for different medical indications is becoming a compelling alternative option for researchers. Genetic variables represent a predisposing factor to the disease and mutations in leucine-rich repeat kinase 2 (LRRK2) locus have been correlated to late-onset autosomal-dominant PD. The common fruit fly Drosophila melanogaster carrying the mutation LRRK2 loss-of-function in the WD40 domain (LRRK2WD40), is a simple in vivo model of PD and is a valid tool to first evaluate novel therapeutic approaches to the disease. Recent studies have suggested a neuroprotective activity of immunomodulatory agents in PD models. Here the immunomodulatory drug Pomalidomide (POM), a Thalidomide derivative, was examined in the Drosophila LRRK2WD40 genetic model of PD. Mutant and wild type flies received increasing POM doses (1, 0.5, 0.25 mM) through their diet from day 1 post eclosion, until postnatal day (PN) 7 or 14, when POM’s actions were evaluated by quantifying changes in climbing behavior as a measure of motor performance, the number of brain dopaminergic neurons and T-bars, mitochondria integrity. LRRK2WD40 flies displayed a spontaneous age-related impairment of climbing activity, and POM significantly and dose-dependently improved climbing performance both at PN 7 and PN 14. LRRK2WD40 fly motor disability was underpinned by a progressive loss of dopaminergic neurons in posterior clusters of the protocerebrum, which are involved in the control of locomotion, by a low number of T-bars density in the presynaptic bouton active zones. POM treatment fully rescued the cell loss in all posterior clusters at PN 7 and PN 14 and significantly increased the T-bars density. Moreover, several damaged mitochondria with dilated cristae were observed in LRRK2WD40 flies treated with vehicle but not following POM. This study demonstrates the neuroprotective activity of the immunomodulatory agent POM in a genetic model of PD. POM is an FDA-approved clinically available and well-tolerated drug used for the treatment of multiple myeloma. If further validated in mammalian models of PD, POM could rapidly be clinically tested in humans.

Background Currently, there are no effective therapeutic options for Alzheimer’s disease, the most common, multifactorial form of dementia, characterized by anomalous amyloid accumulation in the brain. Growing evidence points to neuroinflammation as a major promoter of AD. We have previously shown that the proinflammatory cytokine TNFSF10 fuels AD neuroinflammation, and that its immunoneutralization results in improved cognition in the 3xTg-AD mouse. Methods Here, we hypothesize that inflammatory hallmarks of AD might parallel with central and peripheral immune response dysfunction. To verify such hypothesis, we used a triple transgenic mouse model of AD. 3xTg-AD mice were treated for 12 months with an anti-TNFSF10 antibody, and thereafter immune/inflammatory markers including COX2, iNOS, IL-1β and TNF-α, CD3, GITR, and FoxP3 (markers of regulatory T cells) were measured in the spleen as well as in the hippocampus. Results Spleens displayed accumulation of amyloid-β1–42 (Aβ1-42), as well as high expression of Treg cell markers FoxP3 and GITR, in parallel with the increased levels of inflammatory markers COX2, iNOS, IL-1β and TNF-α, and blunted IL-10 expression. Moreover, CD3 expression was increased in the hippocampus, consistently with FoxP3 and GITR. After chronic treatment of 3xTg-AD mice with an anti-TNFSF10 antibody, splenic FoxP3, GITR, and the above-mentioned inflammatory markers expression was restored to basal levels, while expression of IL-10 was increased. A similar picture was observed in the hippocampus. Such improvement of peripheral and CNS inflammatory/immune response was associated with decreased microglial activity in terms of TNFα production, as well as decreased expression of both amyloid and phosphorylated tau protein in the hippocampus of treated 3xTg-AD mice. Interestingly, we also reported an increased expression of both CD3 and FoxP3, in sections from human AD brain. Conclusions We suggest that neuroinflammation in the brain of 3xTg-AD mice triggered by TNFSF10 might result in a more general overshooting of the immune response. Treatment with an anti-TNFSF10 antibody blunted inflammatory processes both in the spleen and hippocampus. These data confirm the detrimental role of TNFSF10 in neurodegeneration, and corroborate the hypothesis of the anti-TNFSF10 strategy as a potential treatment to improve outcomes in AD. Electronic supplementary material The online version of this article (10.1186/s12974-019-1554-9) contains supplementary material, which is available to authorized users.

The bed nucleus of stria terminalis (BNST) is a complex limbic area involved in neuroendocrine and behavioural responses and, in particular, in the modulation of the stress response. BNST is innervated by dopamine and norepinephrine, which are known to be involved in drug addiction. It is also known that several drugs of abuse increase dopamine transmission in the BNST, but there has been less research regarding the effect on norepinephrine transmission. Here, we have used the microdialysis technique to investigate the effect of several drugs of abuse on norepinephrine transmission in the BNST of freely moving rats. We observed that nicotine (0.2-0.4 mg/kg), cocaine (2.5-5 mg/kg), amphetamine (0.25-0.5 mg/kg), and ethanol (0.5-1.0 g/kg), dose-dependently increased norepinephrine output while the effect of morphine at 3.0 was lower than that of 1.0 mg/kg. These results suggest that many drugs of abuse, though possessing diverse mechanisms of action, share the property of increasing norepinephrine transmission in the BNST. Furthermore, we suggest that the recurring activation of NE transmission in the BNST, due to drug administration, contributes to the alteration of the function that BNST assumes in how the behavioural response to stress manifests, favouring the establishment of the stress-induced drug seeking.

In Parkinson's disease (PD), l-DOPA therapy leads to the emergence of motor complications including l-DOPA-induced dyskinesia (LID). LID relies on a sequence of pre- and postsynaptic neuronal events, leading to abnormal corticostriatal neurotransmission and maladaptive changes in striatal projection neurons. In recent years, additional non-neuronal mechanisms have been proposed to contribute to LID. Among these mechanisms, considerable attention has been focused on l-DOPA-induced inflammatory responses. Microglia and astrocytes are the main actors in neuroinflammatory responses, and their double role at the interface between immune and neurophysiological responses is starting to be elucidated. Both microglia and astrocytes express a multitude of neurotransmitter receptors and via the release of several soluble molecules modulate synaptic function in neuronal networks. Here we review preclinical and clinical evidence of glial overactivation by l-DOPA, supporting a role of microglia and astrocytes in the development of LID. We propose that in PD, chronically and abnormally activated microglia and astrocytes lead to an aberrant neuron-glia communication, which affect synaptic activity and neuroplasticity contributing to the development of LID.

Parkinson&rsquo, s disease (PD) is considered a synucleinopathy because of the intraneuronal accumulation of aggregated &alpha, synuclein (&alpha, Syn). Recent evidence points to soluble &alpha, Syn-oligomers (&alpha, SynO) as the main cytotoxic species responsible for cell death. Given the pivotal role of &alpha, Syn in PD, &alpha, Syn-based models are crucial for the investigation of toxic mechanisms and the identification of new therapeutic targets in PD. By using a metabolomics approach, we evaluated the metabolic profile of brain and serum samples of rats infused unilaterally with preformed human &alpha, SynOs (H&alpha, SynOs), or vehicle, into the substantia nigra pars compacta (SNpc). Three months postinfusion, the striatum was dissected for striatal dopamine (DA) measurements via High Pressure Liquid Chromatography (HPLC) analysis and mesencephalon and serum samples were collected for the evaluation of metabolite content via gas chromatography mass spectrometry analysis. Multivariate, univariate and correlation statistics were applied. A 40% decrease of DA content was measured in the H&alpha, SynO-infused striatum as compared to the contralateral and the vehicle-infused striata. Decreased levels of dehydroascorbic acid, myo-inositol, and glycine, and increased levels of threonine, were found in the mesencephalon, while increased contents of fructose and mannose, and a decrease in glycine and urea, were found in the serum of H&alpha, SynO-infused rats. The significant correlation between DA and metabolite content indicated that metabolic variations reflected the nigrostriatal degeneration. Collectively, the metabolomic fingerprint of H&alpha, SynO-infused rats points to an increase of oxidative stress markers, in line with PD neuropathology, and provides hints for potential biomarkers of PD.

Cell signalling mechanisms are central to neuronal activity and their dysregulation may lead to neurodegenerative processes and associated cognitive decline. So far, a major effort has been directed toward the dissection of disease specific pathways with the still unmet promise to develop precision medicine strategies. With a different approach, here we show that a selective genetic potentiation of neuronal ERK signalling prevents cell death in vitro and in vivo in the mouse brain while ERK attenuation does the opposite. This neuroprotective effect can also be induced pharmacologically by a cell permeable peptide mimicking the loss of ERK1 MAP kinase, leading to a selective enhancement of ERK2 mediated nuclear cell signalling. The drug treatment prevents neurodegeneration in mouse models of Huntington's (HD), Alzheimer's (AD), and Parkinson's disease (PD). Importantly, the selective potentiation of ERK2 signalling facilitates both structural and synaptic plasticity, enhances cognition in healthy mice and rescues mild cognitive impairments in both models of AD and HD. Altogether, our observation truly represents a remarkable example of a shared molecular mechanism across multiple neurodegenerative disorders and a potentially valuable therapeutic target for neuro-enhancement.

The role of phagocytosis in the neuroprotective function of microglia has been appreciated for a long time, but only more recently a dysregulation of this process has been recognized in Parkinson's disease (PD). Indeed, microglia play several critical roles in central nervous system (CNS), such as clearance of dying neurons and pathogens as well as immunomodulation, and to fulfill these complex tasks they engage distinct phenotypes. Regulation of phenotypic plasticity and phagocytosis in microglia can be impaired by defects in molecular machinery regulating critical homeostatic mechanisms, including autophagy. Here, we briefly summarize current knowledge on molecular mechanisms of microglia phagocytosis, and the neuro-pathological role of microglia in PD. Then we focus more in detail on the possible functional role of microglial phagocytosis in the pathogenesis and progression of PD. Evidence in support of either a beneficial or deleterious role of phagocytosis in dopaminergic degeneration is reported. Altered expression of target-recognizing receptors and lysosomal receptor CD68, as well as the emerging determinant role of α-synuclein (α-SYN) in phagocytic function is discussed. We finally discuss the rationale to consider phagocytic processes as a therapeutic target to prevent or slow down dopaminergic degeneration.

Long-term administration of l-3,4-dihydroxyphenylalanine (levodopa), the mainstay treatment for Parkinson's disease (PD), is accompanied by fluctuations in its duration of action and motor complications (dyskinesia) that dramatically affect the quality of life of patients. Levodopa-induced dyskinesias (LID) can be modeled in rats with unilateral 6-OHDA lesions via chronic administration of levodopa, which causes increasingly severe axial, limb, and orofacial abnormal involuntary movements (AIMs) over time. In previous studies, we showed that the direct activation of CB1 cannabinoid receptors alleviated rat AIMs. Interestingly, elevation of the endocannabinoid anandamide by URB597 (URB), an inhibitor of endocannabinoid catabolism, produced an anti-dyskinetic response that was only partially mediated via CB1 receptors and required the concomitant blockade of transient receptor potential vanilloid type-1 (TRPV1) channels by capsazepine (CPZ) (Morgese et al., 2007). In this study, we showed that the stimulation of peroxisome proliferator-activated receptors (PPAR), a family of transcription factors activated by anandamide, contributes to the anti-dyskinetic effects of URB + CPZ, and that the direct activation of the PPARγ subtype by rosiglitazone (RGZ) alleviates levodopa-induced AIMs in 6-OHDA rats. AIM reduction was associated with an attenuation of levodopa-induced increase of dynorphin, zif-268, and of ERK phosphorylation in the denervated striatum. RGZ treatment did not decrease striatal levodopa and dopamine bioavailability, nor did it affect levodopa anti-parkinsonian activity. Collectively, these data indicate that PPARγ may represent a new pharmacological target for the treatment of LID.

Neuroinflammation is a main component of Parkinson’s disease (PD) neuropathology, where unremitting reactive microglia and microglia-secreted soluble molecules such as cytokines, contribute to the neurodegenerative process as part of an aberrant immune reaction. Besides, pro-inflammatory cytokines, predominantly TNF-α, play an important neuromodulatory role in the healthy and diseased brain, being involved in neurotransmitter metabolism, synaptic scaling and brain plasticity. Recent preclinical studies have evidenced an exacerbated neuroinflammatory reaction in the striatum of parkinsonian rats that developed dyskinetic responses following l-DOPA administration. These findings prompted investigation of non-neuronal mechanisms of l-DOPA-induced dyskinesia (LID) involving glial cells and glial-secreted soluble molecules. Hence, besides the classical mechanisms of LID that include abnormal corticostriatal neurotransmission and maladaptive changes in striatal medium spiny neurons (MSNs), here we review studies supporting a role of striatal neuroinflammation in the development of LID, with a focus on microglia and the pro-inflammatory cytokine TNF-α. Moreover, we discuss several mechanisms that have been involved in the development of LID, which are directly or indirectly under the control of TNF-α, and might be abnormally affected by its chronic overproduction and release by microglia in PD. It is proposed that TNF-α may contribute to the altered neuronal responses occurring in LID by targeting receptor trafficking and function in MSNs, but also dopamine synthesis in preserved dopaminergic terminals and serotonin metabolism in serotonergic neurons. Therapeutic approaches specifically targeting glial-secreted cytokines may represent a novel target for preventing or treating LID.

Over the last decade the important concept has emerged that microglia, similar to other tissue macrophages, assume different phenotypes and serve several effector functions, generating the theory that activated microglia can be organized by their pro-inflammatory or anti-inflammatory and repairing functions. Importantly, microglia exist in a heterogenous population and their phenotypes are not permanently polarized into two categories; they exist along a continuum where they acquire different profiles based on their local environment. In Parkinson's disease (PD), neuroinflammation and microglia activation are considered neuropathological hallmarks, however their precise role in relation to disease progression is not clear, yet represent a critical challenge in the search of disease-modifying strategies. This review will critically address current knowledge on the activation states of microglia as well as microglial phenotypes found in PD and in animal models of PD, focusing on the expression of surface molecules as well as pro-inflammatory and anti-inflammatory cytokine production during the disease process. While human studies have reported an elevation of both pro- or anti-inflammatory markers in the serum and CSF of PD patients, animal models have provided insights on dynamic changes of microglia phenotypes in relation to disease progression especially prior to the development of motor deficits. We also review recent evidence of malfunction at multiple steps of NFκB signaling that may have a causal interrelationship with pathological microglia activation in animal models of PD. Finally, we discuss the immune-modifying strategies that have been explored regarding mechanisms of chronic microglial activation.

Adenosine A(2A) receptors antagonists produce neuroprotective effects in animal models of Parkinson's disease (PD). As neuroinflammation is involved in PD pathogenesis, both neuronal and glial A(2A) receptors might participate to neuroprotection. We employed complementary pharmacologic and genetic approaches to A(2A) receptor inactivation, in a multiple MPTP mouse model of PD, to investigate the cellular basis of neuroprotection by A(2A) antagonism. MPTP.HCl (20 mg/kg daily for 4 days) was administered in mice treated with the A(2A) antagonist SCH58261, or in conditional knockout mice lacking A(2A) receptors on forebrain neurons (fbnA(2A)KO mice). MPTP-induced partial loss of dopamine neurons in substantia nigra pars compacta (SNc) and striatum (Str), associated with increased astroglial and microglial immunoreactivity in these areas. Astroglia was similarly activated 1, 3, and 7 days after MPTP administration, whereas maximal microglial reactivity was detected on day 1, returning to baseline 7 days after MPTP administration. SCH58261 attenuated dopamine cell loss and gliosis in SNc and Str. Selective depletion of A(2A) receptors in fbnA(2A)KO mice completely prevented MPTP-induced dopamine neuron degeneration and gliosis in SNc, and partially counteracted gliosis in Str. Results provide evidence of a primary role played by neuronal A(2A) receptors in neuroprotective effects of A(2A) antagonists in a multiple MPTP injections model of PD. With the symptomatic antiparkinsonian potential of several A(2A) receptor antagonists being pursued in clinical trials, this study adds to the rationale for broader clinical benefit and use of these drugs early in the treatment of PD.

Rosiglitazone is a commonly prescribed insulin-sensitizing drug with a selective agonistic activity on the peroxisome proliferator-activated receptor-gamma (PPAR-gamma). PPAR-gamma can modulate inflammatory responses in the brain, and agonists might be beneficial in neurodegenerative diseases. In the present study we used a chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine plus probenecid (MPTPp) mouse model of progressive Parkinson's disease (PD) to assess the therapeutic efficacy of rosiglitazone on behavioural impairment, neurodegeneration and inflammation. Mice chronically treated with MPTPp displayed typical features of PD, including impairment of motor and olfactory functions associated with partial loss of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNc), decrease of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) content and dynorphin (Dyn) mRNA levels in the caudate-putamen (CPu), intense microglial and astroglial response in the SNc and CPu. Chronic rosiglitazone, administered in association with MPTPp, completely prevented motor and olfactory dysfunctions and loss of TH-positive cells in the SNc. In the CPu, loss of striatal DA was partially prevented, whereas decreases in DOPAC content and Dyn were fully counteracted. Moreover, rosiglitazone completely inhibited microglia reactivity in SNc and CPu, as measured by CD11b immunostaining, and partially inhibited astroglial response assessed by glial fibrillary acidic protein immunoreactivity. Measurement of striatal MPP+ levels 2, 4, 6 h and 3 days after chronic treatment indicated that MPTP metabolism was not altered by rosiglitazone. The results support the use of PPAR-gamma agonists as a putative anti-inflammatory therapy aimed at arresting PD progression, and suggest that assessment in PD clinical trials is warranted.

Prolonged treatment with L-DOPA induces highly disabling dyskinesia in Parkinson's disease (PD) patients. In contrast, dopaminergic agonists display variably dyskinetic outcome, depending on pharmacokinetic/pharmacodynamic profile. The present study was aimed at assessing behavioral and biochemical correlates of intense or mild dyskinesia displayed by the different dopamine (DA) receptors stimulation in a rat model of PD. The effect of subchronic stimulation of the D(1) receptor by SKF38393, and the D(2)/D(3) receptor by ropinirole was evaluated in unilaterally 6-hydroxyDA-lesioned rats. Sensitization of contralateral turning (SCT) behavior and abnormal involuntary movements (AIMs) were assessed as behavioral correlates of dyskinetic responses. Opioid peptides mRNA in the dorsolateral striatum (dlStr) and glutamic acid decarboxylase (GAD67) mRNA content in globus pallidus (GP), were evaluated as an index of neuroadaptive changes occurring in the direct and indirect basal ganglia pathways. Subchronic SKF38393 caused AIMs and SCT whereas ropinirole elicited SCT only, indicating that both drugs induced some dyskinetic response, albeit of different type. Peptides mRNA evaluation in dlStr, showed that SKF38393 subchronic treatment was associated to an overexpression of both dynorphin (DYN) and enkephalin (ENK) mRNAs, in the direct and indirect striatal pathway respectively. In contrast, a decrease in DYN mRNA levels only was observed after treatment with ropinirole. Analysis of GAD67 mRNA levels in the GP showed an increase after both D(1) and D(2)/D(3) agonist treatments. Results suggest that presence of SCT alone or SCT plus AIMs might represent correlates of the differential severity of dyskinetic movements induced by treatment with low (ropinirole) or high (SKF38393) dyskinetic potential. Neuroadaptive increases in opioid peptide expression in both direct and indirect striatal pathways were associated to the appearance of AIMs alone. In contrast, increase of GAD67 mRNA in the GP was associated to both behavioral responses (SCT and AIMs), suggesting that neuroadaptive changes in this area were unrelated to the difference in dyskinetic potential of drugs.

The neurotoxin 6-hydroxydopamine (6-OHDA) continues to constitute a valuable topical tool used chiefly in modeling Parkinson's disease in the rat. The classical method of intracerebral infusion of 6-OHDA involving a massive destruction of nigrostriatal dopaminergic neurons, is largely used to investigate motor and biochemical dysfunctions in Parkinson's disease. Subsequently, more subtle models of partial dopaminergic degeneration have been developed with the aim of revealing finer motor deficits. The present review will examine the main features of 6-OHDA models, namely the mechanisms of neurotoxin-induced neurodegeneration as well as several behavioural deficits and motor dysfunctions, including the priming model, modeled by this means. An overview of the most recent morphological and biochemical findings obtained with the 6-OHDA model will also be provided, particular attention being focused on the newly investigated intracellular mechanisms at the striatal level (e.g., A(2A) and NMDA receptors, PKA, CaMKII, ERK kinases, as well as immediate early genes, GAD67 and peptides). Thanks to studies performed in the 6-OHDA model, all these mechanisms have now been hypothesised to represent the site of pathological dysfunction at cellular level in Parkinson's disease.

In spite of the current availability of several pharmacological therapies for the treatment of Parkinson's disease, side effects are invariably manifested during long-term treatment. Dyskinesia, wearing-off and on-off are among the most disabling side effects produced by the dopamine precursor L-dihydroxyphenylalanine and, to a lesser degree, by other pharmacological treatments based on dopamine receptor agonism. Evaluation of the side effects, in particular dyskinesia, produced by antiparkinsonian drug treatments, therefore represents a critical issue in drug validation prior to a clinical trial. Moreover, a reliable model of dyskinesia is a fundamental requirement for the study of the as yet unknown mechanisms at the basis of this severely disabling side effect. The present review aims to provide a critical evaluation of the validity, reliability and utility of animal models of dyskinesia. In the first part of this review, we present a brief overview of the different models of Parkinson's disease focusing on those utilized for the evaluation of dyskinetic movements, then proceed to critically examine the turning behaviour model in an attempt to assess the way in which it has influenced the evaluation of drugs utilized in the treatment of Parkinson's disease. Subsequently, the various models of dyskinesia are reviewed and conclusions are drawn as to how the environment in which experiments are performed can influence the behaviour observed.

Although the role of orexins in sleep/wake cycle and feeding behavior is well established, underlying mechanisms have not been fully understood. An attempt has been made to investigate the role of GABAA receptors and their benzodiazepine site on the orexinA induced response to feeding. Different groups of rats were food deprived overnight and next day injected intracerebroventricularly (icv) with vehicle (artificial CSF; 5 ml/rat) or orexin-A (20e50 nM/rat) and the animals were given free access to food. Cumulative food intake was measured during light phase of light/dark cycle at 1-, 2-, 4- and 6-h post-injection time points. Orexin-A (30e 50 nM/rat, icv) stimulated food intake at all the time points (P ! 0.05). Prior administration of GABAA receptor agonists muscimol (25 ng/rat, icv) and diazepam (0.5 mg/kg, ip) at subeffective doses significantly potentiated the hyperphagic effect of orexin-A (30 nM/rat, icv). However, the effect was negated by the GABAA receptor antagonist bicuculline (1 mg/kg, ip). Interestingly, benzodiazepine receptor antagonist flumazenil (5 ng/rat, icv), augmented the orexin-A (30 nM/rat, icv) induced hyperphagia; the effect may be attributed to the intrinsic activity of the agent. The results suggest that the hyperphagic effect of orexin-A, at least in part, is mediated by enhanced GABAA receptor activity. 2005 Elsevier Ltd. All rights reserved.

In the unilateral 6-hydroxydopamine-lesioned rat model of Parkinson’s disease, blockade of A 2A receptors facilitates l-dopa-induced turning behavior by antagonism of A 2A transmission, which is increased after dopamine depletion. After long-term intermittent administration of doses that produced the same effect on turning behavior, SCH 58261 (5 mg/kg) + l-dopa (3 mg/kg) induced a stable turning behavior, whereas l-dopa (6 mg/kg) alone induced a sensitized turning behavior. Behavioral studies were correlated to changes in dynorphin and enkephalin mRNAs in the striatum and in glutamic acid decarboxylase 67 (GAD67) mRNA in the striatum, globus pallidus, and substantia nigra. The expression of dynorphin and, to a lesser extent, enkephalin mRNAs was increased in the lesioned striatum of rats that received long-term l-dopa treatment but not in rats that received long-term SCH 58261 + l-dopa treatment. Similarly, GAD67 mRNA was increased in the striatum and globus pallidus by long-term l-dopa administration but not by long-term SCH 58261 + l-dopa administration. GAD67 mRNA was strongly reduced in the lesioned substantia nigra after long-term l-dopa treatment, whereas the reduction of GAD67 mRNA was less marked after SCH 58261 + l-dopa treatment. By increasing l-dopa turning behavior, A 2A receptor antagonism allows the utilization of doses of l-dopa that do not produce sensitization of turning behavior, an effect correlated with the dyskinetic potential of dopamine agonist drugs. Moreover, the combination of SCH 58261 + l-dopa produces little or no change in the striatal, pallidal, and nigral expression of markers correlated with dopamine agonist dyskinetic potential.

There are still many controversies about the role of leptin in reproductive function and sexual development. We recently demonstrated that leptin receptors are expressed in rodent Leydig cells and that leptin has inhibitory effects on hCG-stimulated testosterone production by adult rat Leydig cells in culture. In this study, we evaluated the expression of leptin receptor (Ob-R) in rat testes from gestational to adult age in comparison with the pattern of expression of relaxin-like factor (RLF), a specific marker of Leydig cell differentiation status. Immunohistochemical analysis showed that, in prenatal life, Ob-R immunoreactivity was absent at early embryonic ages (E14.5) and appeared at a late embryonic age (E19.5); in postnatal life, immunoreactivity was evident only after sexual maturation (35-, 60-, and 90-days old), whereas it was absent in testes from sexually immature rats (7-, 14-, and 21-days old). Immunoreaction was always confined to Leydig cells and no signal of Ob-R was detected within the tubules. The pattern of expression of Ob-R during testicular development was similar with that of RLF immunoreactivity, which was present in mature fetal as well as adult-type Leydig cells. In contrast with the findings in the testis, in the hypothalamus, the immunohistochemical pattern of Ob-R was very similar between pre- and postpubertal life. Reverse transcription-polymerase chain reaction studies showed that Ob-R expression was present in embryonic, prepubertal, and adult rat testes; semiquantitative analysis showed that mRNA levels were much higher in late versus early embryonic testes, as well as in mature adults versus sexually immature testes, with a gradual increase from younger to older ages. Functional studies showed that, while leptin (150 ng/ml) significantly inhibited hCG-stimulated testosterone production in adult rat Leydig cells (46% reduction; P > 0.01), it did not modify prepubertal rat Leydig cells steroidogenic function in vitro. In conclusion, we showed that, in rat testis, Ob-R expression is characteristic of mature Leydig cells (fetal and adult type) and it is functional in adult but not prepubertal life.

Current treatment of Parkinson's disease (PD) is limited to symptomatic dopaminergic therapy, while no interventions have been shown to slow down disease progression.The following article highlights a group of PPAR-γ agonists called thiazolidinediones (TZDs), which are currently being tested for a putative disease-modifying benefit in PD, using pioglitazone as a prototypic compound. PPAR-γ is highly expressed in neurons of the substantia nigra and CNS immune cells. Preclinical data in rodent and primate support an effect of TZDs in preventing and/or arresting neurodegeneration and development of motor symptoms. Although no data on the neuroprotective effect of TZDs is currently available, a clinical trial is ongoing where the primary objective is to assess pioglitazone's impact on the progression of PD. The trial is also evaluating the drug's safety concerns.The efficacy data from clinical trials must be carefully weighed against the safety concerns. However, given the solid preclinical data, and since the safety data are not yet fully conclusive and limited to the diabetic population, PPAR-γ research in PD can continue with caution. Ideally, drug discovery and development efforts will lead to the identification of new compounds with reduced risk of peripheral side effects.

Central effects of psychostimulants such as cocaine are predominantly mediated by dopamine receptors. We have used mice with a targeted deletion of the D3 dopamine receptor subtype to investigate the role of this receptor in the regulation of gene expression in striatal neurons and behavior by acute and repeated treatment with cocaine (25 mg/kg). In mice lacking D3 receptors, acute administration of cocaine has more pronounced stimulatory effects on c-fos and dynorphin expression in the dorsal and ventral striatum. The behavioral response to cocaine is also increased in these mice. These findings indicate that the D3 receptor plays an inhibitory role in the action of cocaine on behavior and gene regulation in the striatum.

Several studies indicate that the size of body fat stores and the circulating levels of the adipocyte-derived hormone leptin are able to influence the activity of the hypothalamic-pituitary-gonadal axis. The leptin-hypothalamic-pituitary-gonadal interactions have been mainly studied at the level of the central nervous system. In this study, we investigated the possibility that leptin may have direct effects on the rodent Leydig cell function. To probe this hypothesis, we first analyzed the expression of leptin receptors (OB-R) in rodent Leydig cells in culture. RT-PCR studies showed that rat Leydig cells express both the long (OB-Rb) and short isoform (OB-Ra) of leptin receptor, whereas MLTC-1 cells (a murine Leydig tumor cell line) express only the long isoform. Short-term (30 ‐90 min) incubation of rat Leydig cells with increasing concentrations of leptin (2‐500 ng/ml) led to a significant and dose-dependent inhibition of human (h)CGstimulated testosterone (T) production (;60% reduction, IC50 5 20 ng/ml) but no change in basal androgen release. Also, leptin (150 ng/ml) amplified hCG-induced intracellular cAMP formation (1- to 2-fold) without modifying basal cAMP levels. Subsequent experiments showed that leptin inhibited 8Br-cAMP-stimulated T production, indicating that leptin’s effect is exerted beyond cAMP. The inhibitory effect of leptin on hCG-induced T secretion was accompanied by a significant reduction of androstenedione and a concomitant rise of the precursor metabolites pregnenolone, progesterone, and 17-OHprogesterone, conceivable with a leptin-induced lesion of 17,20 lyase activity. Separate experiments performed with the MLTC-1 cells (not expressing cytochrome P450 ‐17a) showed that leptin, though amplifying hCG-stimulated cAMP production, did not modify hCG-stimulated pregnenolone and progesterone release. These results further indicate that leptin action on steroidogenesis occurs downstream of progesterone synthesis. Northern Blot experiments showed no acute effect of leptin on cytochrome P450 ‐17a messenger RNA accumulation in rat Leydig cells in basal and hCG-stimulated conditions, excluding that the rapid changes observed were caused by messenger RNA degradation. In conclusion, these findings, for the first time, show that leptin has direct, receptor-mediated actions on rodent Leydig cells in culture, at concentrations within the range of obese men. (Endocrinology 140: 4939 ‐ 4947, 1999)

The role of the D 3 dopamine receptor in mediating the effects of clozapine was analysed using in situ hybridization histochemistry to measure the induction of the immediate early gene c-fos in different brain areas of mice lacking a functional D 3 dopamine receptor compared to wild type mice. Clozapine treatment (15 and 30 mg/kg, s.c.) resulted in a dose-dependent pattern of induction of c-fos messenger RNA in the striatum, accumbens and septal area, with a non-significant increase in the prefrontal cortex. There was no difference detected in any of these areas in the level of induction between mice lacking the D 3 receptor (D 3 −/−) and wild type (D 3 +/+). To determine which types of neurons in the striatum and accumbens displayed clozapine (30 mg/kg) induction of c-fos messenger RNA, a double-labeling experiment was performed using a radioactive c-fos messenger RNA probe and a digoxigenin-labeled enkephalin messenger RNA probe, the latter used as a marker of D 2 -containing neurons. Clozapine-induced c-fos was detected in 20% of enkephalin-positive striatal neurons and 15% of enkephalin-positive accumbens neurons, and in both areas in about 10% of enkephalin-negative, putative D 1 neurons, in both D 3 +/+ and D 3 −/− mice. These results demonstrate that clozapine induction of c-fos messenger RNA is not dependent on the D 3 dopamine receptor subtype in the striatum or nucleus accumbens.

In rats with a unilateral 6-hydroxydopamine lesion of the ascending dopamine neurons, we investigated the relationship between the expression of Fos-like immunoreactivity in the caudate-putamen and contralateral turning behavior in response to dopamine agonists during the induction and expression of sensitization (priming) to D1-dependent turning behavior. Priming was induced by apomorphine (0.1 mg/kg s.c.) or by SKF 38393 (10 mg/kg s.c.) 14 days after 6-hydroxydopamine lesions and was expressed by challenge with SKF 38393 (3 mg/kg s.c.). In the induction phase of priming, administration of MK 801 (0.1 mg/kg s.c.) potentiated contralateral turning but differentially influenced stimulation of Fos expression in the caudate-putamen by apomorphine and by SKF 38393. Thus, MK 801 reduced in the expression phase of priming the stimulation of Fos expression by apomorphine in the dorsolateral caudate-putamen, but did not affect that by SKF 38393. MK 801, while preventing priming of SKF 38393-induced turning by apomorphine, failed to affect priming by SKF 38393. MK 801, given with apomorphine in the induction phase, reduced the stimulation of Fos expression in the dorsolateral caudate-putamen by SKF 38393. No such inhibitory effect of MK 801 on SKF 38393-stimulated Fos expression was observed in rats primed with SKF 38393. These results are consistent with the possibility that MK 801 disrupts sensitization of D1 transduction by reducing the activation of c-fos by the DA agonist during the induction phase of priming.

Parkinson's disease (PD) is amongst the most frequent neurodegenerative disorders, the main pathologic hallmark of which is the degeneration of the substantia nigra pars compacta. Damage to multiple cellular components, such as mitochondrial dysfunction, oxidative stress, neuroinflammation, and proteasomal dysfunction, contribute to the progression of the neurodegenerative process. Peroxisome proliferator-activated receptor gamma (PPAR-γ) agonists, mainly thiazolidinediones, pioglitazone and rosiglitazone, have been successfully tested for their neuroprotective potential in PD experimental models, although the cellular target and underlying mechanism are currently a matter of debate. While the anti-inflammatory activity and attenuation of microgliosis have been proposed as a main mechanism of neuroprotection, other cellular targets might be involved, such as mitochondrial proteins controlling cellular bioenergetic and oxidative stress. Here, the current evidence of neuroprotection by PPAR-γ agonists in in vitro and in vivo experimental PD models is reported. Moreover, cellular pathways which have been investigated as potential targets of neuroprotection are reviewed. Taken together, the available data suggest that simultaneous targeting of multiple dysfunctional pathways may underlie the potent neuroprotective activity displayed by PPAR-γ agonists.

In rats with a unilateral 6-hydroxydopamine lesion of the dopaminergic nigro-striatal pathway, striatal Dl-receptor-stimulated c-fos expression and turning behavior are positively modulated by D2 receptor stimulation and by blockade of N-methyl-D-aspartate (NMDA) or muscarinic receptors. Combined D1/D2 receptor stimulation by L-dopa activates c-fos in a manner not additive with muscarinic receptor blockade by scopolamine. On the other hand, blockade of NMDA receptors by MK 801 reduced c-fos expression induced by L-dopa while, depending on the dose of L-dopa, differentially affecting contralateral turning behavior. The results are interpreted to suggest that D2 receptor stimulation amplifies D1-receptor-mediated c-fos expression by two mechanisms differentially related to muscarinic and NMDA receptors. ©1994 Wilev-Lisa. Inc.

In the dopamine-depleted striatum, an altered post-synaptic signalling of efferent neurons might underline the onset of variable dyskinetic responses to dopaminergic agonists. We have previously shown that a subchronic treatment with the D1 agonist SKF-38393 and the D2 agonist ropinirole induces a dyskinetic response of high and low intensities respectively, in 6-hydroxydopamine-lesioned rats. Here, zif-268 mRNA expression was evaluated in striatonigral and striatopallidal neurons to assess a neurochemical marker of these different dyskinetic responses upon drug administration. Acute and subchronic SKF-38393 (3mg/kg) increased zif-268 expression per neuron in the striatonigral pathway, albeit the number of neurons displaying high early-gene levels was reduced by the subchronic treatment. Zif-268 mRNA in striatopallidal neurons was not affected by SKF-38393 treatments. In contrast, ropinirole (5mg/kg) did not alter zif-268 mRNA in striatonigral neurons acutely, whereas ropinirole decreased zif-268 mRNA subchronically. Both acute and subchronic ropinirole decreased zif-268 levels in the striatopallidal pathway. The differential expression of zif-268 in striatonigral and striatopallidal neurons might provide a biochemical correlate of the dyskinetic outcome displayed by SKF-38393 and ropinirole treatments, suggesting that evaluation of neuronal responses upon drug administration provides a tool for the preclinical characterization of dyskinetic potential beyond behavioural tests.

The motor symptoms of Parkinson's disease (PD) are primarily due to the degeneration of the dopaminergic neurons in the nigrostriatal pathway. However, several other brain areas and neurotransmitters other than dopamine such as noradrenaline, 5-hydroxytryptamine and acetylcholine are affected in the disease. Moreover, adenosine because of the extensive interaction of its receptors with the dopaminergic system has been implicated in the pathophysiology of the disease. Based on the involvement of these non-dopaminergic neurotransmitters in PD and the sometimes severe adverse effects that limit the mainstay use of dopamine-based anti-parkinsonian treatments, recent assessments have called for a broadening of therapeutic options beyond the traditional dopaminergic drug arsenal. In this review we describe the interactions between dopamine and adenosine receptors that underpin the pre-clinical and clinical rationale for pursuing adenosine A(2A) receptor antagonists as symptomatic and potentially neuroprotective treatment of PD. The review will pay particular attention to recent results regarding specific A(2A) receptor-receptor interactions and recent findings identifying urate, the end product of purine metabolism, as a novel prognostic biomarker and candidate neuroprotectant in PD.

Publisher Summary This chapter explores that adenosine is a nucleoside composed of the purine base adenine and ribose. Adenosine receptors affect basal ganglia (BG) functions is explained by the role of adenosine as a signaling molecule in the nervous system. This type of modulation forms a new concept for how BG function is controlled in normal physiological circumstances and in pathological conditions. The selective localization of A 2A receptors to the BG and specifically to the indirect output pathway, offers a unique opportunity to modulate the dopamine output from the striatum that is believed critical to the occurrence of motor behavior. The ability of A 2A receptor antagonists to modulate neurotransmission, gamma-aminobutyric-acid (GABA)-ergic and glutamatergic transmission places adenosine signaling in a prime position to influence motor function. Another field of potential utilisation of compounds binding adenosine receptors is neuroprotection. The chapter also discusses that the current preclinical data strongly support a role for drugs binding A 2A receptors in protecting neurons from the type of pathogenic processes believed to occur in Parkinson's disease (PD) and some stages of Huntington's disease (HD). Finally the action of adenosine receptors in brain areas directly connected to the BG might play important roles in cognitive functions opening new therapeutic possibilities for drugs acting at this level.