Simvastatin reverses the downregulation of dopamine D1 and D2 receptor expression in the prefrontal cortex of 6-hydroxydopamine-induced Parkinsonian rats

An update on drug repurposing in Parkinson's disease: Preclinical and clinical considerations

The strategy of drug repositioning has historically played a significant role in the identification of new treatments for Parkinson's disease. Still today, numerous clinical and preclinical studies are investigating drug classes, already marketed for the treatment of metabolic disorders, for their potential use in Parkinson's disease patients. While drug repurposing offers a promising, fast, and cost-effective path to new treatments, these drugs still require thorough preclinical evaluation to assess their efficacy, addressing the specific neurodegenerative mechanisms of the disease. This review explores the state-of-the-art approaches to drug repurposing for Parkinson's disease, highlighting particularly relevant aspects. Preclinical studies still predominantly rely on traditional neurotoxin-based animal models, which fail to effectively replicate disease progression and are characterized by significant variability in model severity and timing of drug treatment. Importantly, for almost all the drugs analyzed here, there is insufficient data regarding the mechanism of action responsible for the therapeutic effect. Regarding drug efficacy, these factors may obviously render results less reliable or comparable. Accordingly, future preclinical drug repurposing studies in the Parkinson's disease field should be carried out using next-generation animal models like α-synuclein-based models that, unfortunately, have to date been used mostly for studies of disease pathogenesis and only rarely in pharmacological studies.

Statins in Parkinson's Disease: Influence on Motor Progression

BACKGROUND

It has been speculated that stains are neuroprotective and are associated with a reduced risk of Parkinson's disease (PD), but only a few studies have investigated the influence of statins on the progression of PD.

OBJECTIVE

To evaluate whether long-term statin use may affect motor progression in a large cohort of de novo patients with PD.

METHODS

We conducted a 4-year retrospective observational cohort study to assess patients with PD. The patients were consecutively recruited from a single tertiary center between January 2015 and January 2017. Information on motor function was obtained using the MDS-Unified Parkinson Disease Rating Scale (UPDRS)-III and all subjects were extensively characterized, including information about lifestyle habits, cardiovascular risk factors and cholesterol blood levels.

RESULTS

Of the 181 participants included in the study, 104 patients were evaluated for eligibility (42 patients were exposed to statin therapies and 62 were not treated with statins). They presented similar scores in UPDRS III at baseline but the statin users had a lower motor impairment at 4 years compared to non-user PD patients. Additionally, statin treatment resulted in slower progression of the rigidity score of UPDRS over 4 years. No other significant differences were observed between PD patients with and without statins.

CONCLUSION

Early PD patients with long-term statin usage showed lower motor deterioration after 4 years of disease duration compared with patients not taking statins at diagnosis, suggesting a possible influence of statins on disease progression in PD. Further investigation is warranted to understand the potential beneficial effects of statin treatment on clinical symptoms in PD.

Lesions of mediodorsal thalamic nucleus reverse abnormal firing of the medial prefrontal cortex neurons in parkinsonian rats

The dysfunction of the medial prefrontal cortex is associated with affective disorders and non-motor features in Parkinson’s disease. However, the exact role of the mediodorsal thalamic nucleus in the function of the prefrontal cortex remains unclear. To study the possible effects of the mediodorsal thalamic nucleus on the neurological function of the medial prefrontal cortex, a model of Parkinson’s disease was established by injecting 8 µg 6-hydroxydopamine into the substantia nigra compacta of rats. After 1 or 3 weeks, 0.3 µg ibotenic acid was injected into the mediodorsal thalamic nucleus of the midbrain. At 3 or 5 weeks after the initial injury, neuronal discharge in medial prefrontal cortex of rat brain was determined electrophysiologically. The numbers of dopamine-positive neurons and tyrosine hydroxylase immunoreactivity in substantia nigra compacta and ventral tegmental area were detected by immunohistochemical staining. Results demonstrated that after injury, the immunoreactivity of dopamine neurons and tyrosine hydroxylase decreased in the substantia nigra compacta and ventral tegmental areas of rats. Compared with normal medial prefrontal cortical neurons, at 3 and 5 weeks after substantia nigra compacta injury, the discharge frequency of pyramidal neurons increased and the discharge pattern of these neurons tended to be a burst-discharge, with an increased discharge interval. The discharge frequency of interneurons decreased and the discharge pattern also tended to be a burst-discharge, but the discharge interval was only higher at 3 weeks. At 3 weeks after the combined lesions, the discharge frequency, discharge pattern and discharge interval were restored to a normal level in pyramidal neurons and interneurons in medial prefrontal cortex. These findings have confirmed that mediodorsal thalamic nucleus is involved in regulating neuronal activities of the medial prefrontal cortex. The changes in the function of the mediodorsal thalamic nucleus may be associated with the abnormal discharge activity of the medial prefrontal cortex neurons after substantia nigra compacta injury. All experimental procedures were approved by the Institutional Animal Care and Use Committee of Xi’an Jiaotong University, China (approval No. XJTULAC2017-067) on August 26, 2017.

The beneficial effects of HMG-CoA reductase inhibitors in the processes of neurodegeneration

Statins, cholesterol lowering drugs, have been demonstrated to exert beneficial effects in other conditions such as primary and progressing neurodegenerative diseases beyond their original role. Observation that statins ameliorate the neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), multiple sclerosis (MS) and cerebral ischemic stroke, the neuroprotective effects of these drugs are thought to be linked to their anti-inflammatory, anti-oxidative, and anti-excitotoxic properties. Despite the voluminous literature on the clinical advantages of 3-hydroxy-3-methylglutaryl Co-enzyme A reductase (HMGCR) inhibitors (statins) in cardiovascular system, the neuroprotective effects and the underlying mechanisms are little understood. Hence, the present review tries to provide a critical overview on the statin-induced neuroprotection, which are presumed to be associated with the ability to reduce cholesterol, Amyloid-β and apolipoprotein E (ApoE) levels, decrease reactive oxygen and nitrogen species (ROS and RNS) formation, inhibit excitotoxicity, modulate matrix metalloproteinases (MMPs), stimulate endothelial nitric oxide synthase (eNOS), and increase cerebral blood perfusion. This review is also aimed to illustrate that statins protect neurons against the neuro-inflammatory processes through balancing pro-inflammatory/anti-inflammatory cytokines. Ultimately, the beneficial role of statins in ameliorating the development of PD, AD, MS and cerebral ischemic stroke has been separately reviewed.

Current insights into pathogenesis of Parkinson's disease: Approach to mevalonate pathway and protective role of statins

Although Parkinson's disease (PD) is considered as the second most common life threatening age-related neurodegenerative disorder, but the underlying mechanisms for pathogenesis of PD are remained to be fully found. However, a complex relationship between genetic and environmental predisposing factors are involved in progression of PD. Dopaminergic neuronal cell death caused by mutations and accumulation of α-synuclein in Lewy bodies and neurites was suggested as the main strategy for PD, but current studies have paid attention to the role of mevalonate pathway in incidence of neurodegenerative diseases including PD. The discovery may change the therapeutic protocols from symptomatic treatment by dopamine precursors and agonists to neurodegenerative process halting drugs. Moreover, the downstream metabolites of mevalonate pathway may be used as diagnostic biomarkers for early diagnosis of PD. Statins, as cholesterol lowering drugs, may ameliorate the enzyme complex dysfunction, a key step in the progression of the neurodegenerative disorders, oxidative stress-induced damage and neuro-inflammation. Statins exert the neuroprotective effects on striatal dopaminergic neurons through blocking the mevalonate pathway. In the present review, we have focused on the new approaches to pathogenesis of PD regarding to mevalonate pathway, in addition to the previous understood mechanisms for the disease. It tries to elucidate the novel findings about PD for the development of future diagnostic and therapeutic strategies. Moreover, we explain the controversial role of statins in improvement or progression of PD and the position of these drugs in neuroprotection in PD patients.

Simultaneous administration of fluoxetine and simvastatin ameliorates lipid profile, improves brain level of neurotransmitters, and increases bioavailability of simvastatin

Simvastatin (STT), a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, is widely prescribed for dyslipidemia, whereas fluoxetine (FLX) is the first-choice drug for the treatment of depression and anxiety. A recent report suggests that selective serotonin reuptake inhibitors can interact with the cytochrome P450 3A4 substrate, and another one suggests that STT enhances the antidepressant activity of FLX. However, the data are inconclusive. The present study was designed to explore the pharmacokinetic and pharmacodynamic consequences of coadministration of STT and FLX in experimental animals. For this, Wistar rats weighing 250±10 g were divided into four groups, including control, STT (40 mg/kg/day), FLX (20 mg/kg/day), and STT+FLX group, respectively. After the dosing period of 4 weeks, the animals were sacrificed, and the blood and brain samples were collected for the analysis of STT, simvastatin acid (STA), FLX, total cholesterol, triglyceride, high-density lipoprotein (HDL), 5-hydroxytryptamine, dopamine, and hydroxy indole acetic acid. It was found that the coadministration resulted in a significant increase in the bioavailability of STT in the plasma (41.8%) and brain (68.7%) compared to administration of STT alone (p<0.05). The maximum drug concentration (C_max) of STT was also found to be increased significantly in the plasma and brain compared to that achieved after monotherapy (p<0.05). However, STT failed to improve the pharmacokinetics of FLX up to a significant level. The results of this study showed that the combined regimen significantly reduced the level of cholesterol and triglyceride and increased the level of HDL when compared to STT monotherapy. Furthermore, the coadministration of STT with FLX led to an elevated level of neurotransmitters in the brain (p<0.05). FLX increased the concentration of STT in the plasma and brain. The coadministration of these drugs also led to an improved lipid profile. However, in the long-term, this interaction may have a vital clinical importance because the increase in STT level may lead to life-threatening side effects associated with statins.

Acetyl-L-Carnitine via Upegulating Dopamine D1 Receptor and Attenuating Microglial Activation Prevents Neuronal Loss and Improves Memory Functions in Parkinsonian Rats

Parkinson's disease is accompanied by nonmotor symptoms including cognitive impairment, which precede the onset of motor symptoms in patients and are regulated by dopamine (DA) receptors and the mesocorticolimbic pathway. The relative contribution of DA receptors and astrocytic glutamate transporter (GLT-1) in cognitive functions is largely unexplored. Similarly, whether microglia-derived increased immune response affects cognitive functions and neuronal survival is not yet understood. We have investigated the effect of acetyl-L-carnitine (ALCAR) on cognitive functions and its possible underlying mechanism of action in 6-hydroxydopamine (6-OHDA)-induced hemiparkinsonian rats. ALCAR treatment in 6-OHDA-lesioned rats improved memory functions as confirmed by decreased latency time and path length in the Morris water maze test. ALCAR further enhanced D1 receptor levels without altering D2 receptor levels in the hippocampus and prefrontal cortex (PFC) regions, suggesting that the D1 receptor is preferentially involved in the regulation of cognitive functions. ALCAR attenuated microglial activation and release of inflammatory mediators through balancing proinflammatory and anti-inflammatory cytokines, which subsequently enhanced the survival of mature neurons in the CA1, CA3, and PFC regions and improved cognitive functions in hemiparkinsonian rats. ALCAR treatment also improved glutathione (GSH) content, while decreasing oxidative stress indices, inducible nitrogen oxide synthase (iNOS) levels, and astrogliosis resulting in the upregulation of GLT-1 levels. Additionally, ALCAR prevented the loss of dopaminergic (DAergic) neurons in ventral tagmental area (VTA)/substantia nigra pars compacta (SNpc) regions of 6-OHDA-lesioned rats, thus maintaining the integrity of the nigrostriatal pathway. Together, these results demonstrate that ALCAR treatment in hemiparkinsonian rats ameliorates neurodegeneration and cognitive deficits, hence suggesting its therapeutic potential in neurodegenerative diseases.

In vitro 6-hydroxydopamine-induced toxicity in striatal, cerebrocortical and hippocampal slices is attenuated by atorvastatin and MK-801

Parkinson's disease (PD) involves the loss of striatal dopaminergic neurons, although other neurotransmitters and brain areas are also involved in its pathophysiology. In rodent models to PD it has been shown statins improve cognitive and motor deficits and attenuate inflammatory responses evoked by PD-related toxins. Statins are the drugs most prescribed to hypercholesterolemia, but neuroprotective effects have also been attributed to statins treatment in humans and in animal models. This study aimed to establish an in vitro model of 6-hydroxydopamine (6-OHDA)-induced toxicity, used as an initial screening test to identify effective drugs against neural degeneration related to PD. The putative neuroprotective effect of atorvastatin against 6-OHDA-induced toxicity in rat striatal, cerebrocortical and hippocampal slices was also evaluated. 6-OHDA (100μM) decreased cellular viability in slices obtained from rat cerebral cortex, hippocampus and striatum. 6-OHDA also induced an increased reactive oxygen species (ROS) production and mitochondrial dysfunction. Co-incubation of 6-OHDA with atorvastatin (10μM) or MK-801 (50μM) an N-methyl-d-aspartate (NMDA) receptor antagonist, partially attenuated the cellular damage evoked by 6-OHDA in the three brain areas. Atorvastatin partially reduced ROS production in the hippocampus and striatum and disturbances of mitochondria membrane potential in cortex and striatum. 6-OHDA-induced toxicity in vitro displays differences among the brain structures, but it is also observed in cerebrocortical and hippocampal slices, besides striatum.

Cholesterol - A putative endogenous contributor towards Parkinson's disease

Elevated levels of cholesterol and its metabolites (oxysterols) have been reported to be associated not only with several metabolic syndromes, but also become a prognostic risk factor of neurodegenerative diseases particularly Alzheimer's disease. The incidence and the prospect of Alzheimer's disease with respect to elevated levels of cholesterol have been studied extensively and reviewed earlier. Recently, several interesting findings have shown the occurrence of equivalent Parkinsonian pathologies in cellular neuronal models, mediated by oxysterols or excess exposure to cholesterol. In this regard, oxysterols are particular in causing alpha-synuclein aggregation and destruction of dopamine containing neurons in in vitro models, which is linked to their direct influence on oxidative stress provoking potency. Inspite of the significant in vitro reports, which suggest the relativeness of cholesterol or oxysterol towards Parkinsonism, several prospective clinical reports provided a negative or no correlation. However, few prospective clinical studies showed a positive correlation between plasma cholesterol and incidence of Parkinson's disease (PD). Also, few significant studies have convincingly demonstrated that high fat diet exacerbates parkinsonian pathologies, including loss of dopaminergic neurons and oxidative stress parameters in animal models of PD. The present review brings together all the neuropathological proceedings mediated by excess cholesterol or its metabolites in brain in the light of their contribution towards the onset of PD. Also we have reviewed the possibilities of cholesterol lowering efficacy of statin therapy, in reducing the occurrence of PD.

The ongoing pursuit of neuroprotective therapies in Parkinson disease

Many agents developed for neuroprotective treatment of Parkinson disease (PD) have shown great promise in the laboratory, but none have translated to positive results in patients with PD. Potential neuroprotective drugs, such as ubiquinone, creatine and PYM50028, have failed to show any clinical benefits in recent high-profile clinical trials. This 'failure to translate' is likely to be related primarily to our incomplete understanding of the pathogenic mechanisms underlying PD, and excessive reliance on data from toxin-based animal models to judge which agents should be selected for clinical trials. Restricted resources inevitably mean that difficult compromises must be made in terms of trial design, and reliable estimation of efficacy is further hampered by the absence of validated biomarkers of disease progression. Drug development in PD dementia has been mostly unsuccessful; however, emerging biochemical, genetic and pathological evidence suggests a link between tau and amyloid-β deposition and cognitive decline in PD, potentially opening up new possibilities for therapeutic intervention. This Review discusses the most important 'druggable' disease mechanisms in PD, as well as the most-promising drugs that are being evaluated for their potential efficiency in treatment of motor and cognitive impairments in PD.

Alteration in the expression of exon IIC transcripts of brain-derived neurotrophic factor gene by simvastatin [correction of simvastain] in chronic mild stress in mice: a possible link with dopaminergic pathway

We have investigated the influence of dopaminergic agents on the expression of brain-derived neurotrophic factor (BDNF) gene in relation with lipid levels in chronic mild stress (CMS). Mice subjected to CMS were treated with simvastatin (10 mg/kg, per os (orally)) along with bromocriptine (2 mg/kg, intraperitoneally (ip)), levodopa (200 mg/kg, ip), or haloperidol (0.1 mg/kg, ip) for 14 days. CMS produced a decrease in sucrose intake and an increase in serum cholesterol and triglycerides levels with a decrease in high-density lipoprotein cholesterol, which were prevented by simvastatin. This was greater when it was combined with bromocriptine or levodopa. Haloperidol significantly prevented the simvastatin-induced increase in sucrose intake but not the alterations in lipids. There was an upregulation in the expression of BDNF exon-IIA and -IIB transcripts by CMS but not the exon-IIC transcripts. Simvastatin could increase expression of exon-IIC transcripts in stressed mice. This was partially increased by bromocriptine. Haloperidol significantly prevented simvastatin-induced increase in expression of BDNF exon-IIC transcripts. The results showed a positive correlation between expression of BDNF exon-IIC transcripts and sucrose intake. In conclusion, our data suggest the involvement of lipid levels and BDNF exon-IIC transcripts in CMS-induced behaviour in mice, possibly through the dopaminergic system.

The theta-related firing activity of parvalbumin-positive neurons in the medial septum-diagonal band of Broca complex and their response to 5-HT1A receptor stimulation in a rat model of Parkinson's disease

The parvalbumin (PV)-positive neurons in the medial septum-diagonal band of Broca complex (MS-DB) play an important role in the generation of hippocampal theta rhythm involved in cognitive functions. These neurons in this region express a high density of 5-HT1A receptors which regulate the neuronal activity and consequently affect the theta rhythm. In this study, we examined changes in the theta-related firing activity of PV-positive neurons in the MS-DB, their response to 5-HT1A receptor stimulation and the corresponding hippocampal theta rhythm, and the density of PV-positive neurons and their co-localization with 5-HT1A receptors in rats with 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc). The lesion of the SNc decreased the rhythmically bursting activity of PV-positive neurons and the peak frequency of hippocampal theta rhythm. Systemic administration of 5-HT1A receptor agonist 8-OH-DPAT (0.5-128 µg/kg, i.v.) inhibited the firing rate of PV-positive neurons and disrupted rhythmically bursting activity of the neurons and the theta rhythm in sham-operated and the lesioned rats, respectively. The cumulative doses producing inhibition and disruption in the lesioned rats were higher than that of sham-operated rats. Furthermore, local application of 8-OH-DPAT (0.005 μg) in the MS-DB also inhibited the firing rate of PV-positive neurons and disrupted their rhythmically bursting activity in sham-operated rats, while having no effect on PV-positive neurons in the lesioned rats. The lesion of the SNc decreased the density of PV-positive neurons in the MS-DB, and percentage of PV-positive neurons expressing 5-HT1A receptors. These results indicate that the lesion of the SNc leads to suppression of PV-positive neurons in the MS-DB and hippocampal theta rhythm. Furthermore, the lesion decreases the response of these neurons to 5-HT1A receptor stimulation, which attributes to dysfunction and/or down-regulation of 5-HT1A receptor expression on these neurons. These changes may be involved in cognitive impairments of Parkinson's disease.

Alterations of NMDA receptor binding in various brain regions among 6-hydroxydopamine-induced Parkinsonian rats

The N-methyl-d-aspartate (NMDA) system closely interacts with the dopaminergic system and is strongly implicated in the pathophysiological mechanisms and therapeutic paradigms of Parkinson's disease. This study aims to systematically investigate the changes of NMDA receptors in a wide range of brain structures 3 weeks after unilateral medial forebrain bundle lesion by 6-hydroxydopamine (6-OHDA). NMDA receptor distributions and alterations in the post-mortem rat brain were detected by [(3)H] MK-801 binding autoradiography. In the 6-OHDA-induced Parkinsonian rat model, nigrostriatal dopaminergic neuron loss significantly mediated the decreased [(3)H] MK-801 binding, predominantly in the hippocampus (-22.4%, p < 0.001), caudate putamen (-14.1%, p < 0.01), accumbens nucleus (-13.8%, p < 0.05), cingulate cortex (-13.4%, p < 0.001), posteromedial cortical amygdala (-14.5%, p < 0.01) and piriform cortex (-9%, p < 0.05) compared to the controls, while there was a profound reduction of tyrosine hydroxylase (TH) immunohistochemistry in the substantia nigra pars compacta. Alterations in [(3)H] MK-801 in the specific brain regions related to cognitive functions may indicate that cognitive dysfunctions caused by 6-OHDA lesion were via the NMDA system. The downregulation of NMDA receptor binding in the present study provides indirect evidence for plasticity in the NMDA system in the rat brain. The present study improves our understanding of the critical roles of the NMDA receptors in treating neurodegenerative disorders, and implicates NMDA receptors as a novel therapeutic target in the treatment of Parkinson's disease.

Neuroprotective potential of atorvastatin and simvastatin (HMG-CoA reductase inhibitors) against 6-hydroxydopamine (6-OHDA) induced Parkinson-like symptoms

Neuro-inflammation and oxidative stress plays a key role in the pathophysiology of Parkinson's disease (PD). Studies demonstrated that neuro-inflammation and associated infiltration of inflammatory cells into central nervous system are inhibited by 3-hydroxy-3-methyl glutaryl co-enzyme A (HMG-CoA) reductase inhibitors. Based on these experimental evidences, the present study has been designed to evaluate the neuroprotective effect of HMG-CoA reductase inhibitors (atorvastatin and simvastatin) against 6-hydroxydopamine (6-OHDA) induced unilateral lesion model of PD. In the present study, the animals were divided into nine groups (n=15 per group). Group I: Naive (without treatment); Group II: Sham (surgery performed, vehicle administered); Group III: Atorvastatin (20mg/kg); Group IV: Simvastatin (30 mg/kg); Group V: Control [Intrastriatal 6-OHDA (20 μg; single unilateral injection)]; Groups VI and VII: 6-OHDA (20 μg)+atorvastatin (10mg/kg and 20mg/kg) respectively; Groups VIII and IX: 6-OHDA (20 μg)+simvastatin (15 mg/kg and 30 mg/kg) respectively. Intrastriatal administration of 6-OHDA (20 μg; 4 μl of 5 μg/μl) significantly caused impairment in body weight, locomotor activity, rota-rod performance, oxidative defense and mitochondrial enzyme complex activity, and increase in the inflammatory cytokine levels (TNF-α and IL-6) as compared to naive animals. Atorvastatin (20mg/kg) and simvastatin (30 mg/kg) drug treatment significantly improved these behavioral and biochemical alterations restored mitochondrial enzyme complex activities and attenuated neuroinflammatory markers in 6-OHDA (20 μg) treated animals as compared to control group. The findings of the present study demonstrate the neuroprotective potential of statins in experimental model of 6-OHDA induced Parkinson like symptoms.

Neurotransmitter receptors and cognitive dysfunction in Alzheimer's disease and Parkinson's disease

Cognitive dysfunction is one of the most typical characteristics in various neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease (advanced stage). Although several mechanisms like neuronal apoptosis and inflammatory responses have been recognized to be involved in the pathogenesis of cognitive dysfunction in these diseases, recent studies on neurodegeneration and cognitive dysfunction have demonstrated a significant impact of receptor modulation on cognitive changes. The pathological alterations in various receptors appear to contribute to cognitive impairment and/or deterioration with correlation to diversified mechanisms. This article recapitulates the present understandings and concepts underlying the modulation of different receptors in human beings and various experimental models of Alzheimer's disease and Parkinson's disease as well as a conceptual update on the underlying mechanisms. Specific roles of serotonin, adrenaline, acetylcholine, dopamine receptors, and N-methyl-D-aspartate receptors in Alzheimer's disease and Parkinson's disease will be interactively discussed. Complex mechanisms involved in their signaling pathways in the cognitive dysfunction associated with the neurodegenerative diseases will also be addressed. Substantial evidence has suggested that those receptors are crucial neuroregulators contributing to cognitive pathology and complicated correlations exist between those receptors and the expression of cognitive capacities. The pathological alterations in the receptors would, therefore, contribute to cognitive impairments and/or deterioration in Alzheimer's disease and Parkinson's disease. Future research may shed light on new clues for the treatment of cognitive dysfunction in neurodegenerative diseases by targeting specific alterations in these receptors and their signal transduction pathways in the frontal-striatal, fronto-striato-thalamic, and mesolimbic circuitries.

Simvastatin prevents dopaminergic neurodegeneration in experimental parkinsonian models: the association with anti-inflammatory responses

BACKGROUND

In addition to their original applications to lowering cholesterol, statins display multiple neuroprotective effects. N-methyl-D-aspartate (NMDA) receptors interact closely with the dopaminergic system and are strongly implicated in therapeutic paradigms of Parkinson's disease (PD). This study aims to investigate how simvastatin impacts on experimental parkinsonian models via regulating NMDA receptors.

METHODOLOGY/PRINCIPAL FINDINGS

Regional changes in NMDA receptors in the rat brain and anxiolytic-like activity were examined after unilateral medial forebrain bundle lesion by 6-hydroxydopamine via a 3-week administration of simvastatin. NMDA receptor alterations in the post-mortem rat brain were detected by [³H]MK-801(Dizocilpine) binding autoradiography. 6-hydroxydopamine treated PC12 was applied to investigate the neuroprotection of simvastatin, the association with NMDA receptors, and the anti-inflammation. 6-hydroxydopamine induced anxiety and the downregulation of NMDA receptors in the hippocampus, CA1(Cornu Ammonis 1 Area), amygdala and caudate putamen was observed in 6-OHDA(6-hydroxydopamine) lesioned rats whereas simvastatin significantly ameliorated the anxiety-like activity and restored the expression of NMDA receptors in examined brain regions. Significant positive correlations were identified between anxiolytic-like activity and the restoration of expression of NMDA receptors in the hippocampus, amygdala and CA1 following simvastatin administration. Simvastatin exerted neuroprotection in 6-hydroxydopamine-lesioned rat brain and 6-hydroxydopamine treated PC12, partially by regulating NMDA receptors, MMP9 (matrix metalloproteinase-9), and TNF-a (tumour necrosis factor-alpha).

CONCLUSIONS/SIGNIFICANCE

Our results provide strong evidence that NMDA receptor modulation after simvastatin treatment could partially explain its anxiolytic-like activity and anti-inflammatory mechanisms in experimental parkinsonian models. These findings contribute to a better understanding of the critical roles of simvastatin in treating PD via NMDA receptors.

Unilateral lesion of the nigrostriatal pathway decreases the response of fast-spiking interneurons in the medial prefrontal cortex to 5-HT1A receptor agonist and expression of the receptor in parvalbumin-positive neurons in the rat

5-Hydroxytryptamine(1A) (5-HT(1A)) receptors are expressed in the prefrontal cortical interneurons. Among these interneurons, calcium-binding protein parvalbumin (PV)-positive fast spiking (FS) interneurons play an important role in regulatory function of the prefrontal cortex. In the present study, the response of medial prefrontal cortex (mPFC) FS interneurons to the selective 5-HT(1A) receptor agonist 8-OH-DPAT and change in expression of 5-HT(1A) receptor on PV-positive neurons were examined in rats with 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta (SNc) by using extracellular recording and double-labeling immunofluorescence histochemistry. Systemic administration of 8-OH-DPAT (1-243 μg/kg, i.v.) dose-dependently inhibited the mean firing rate of the FS interneurons in sham-operated and the lesioned rats, respectively. The cumulative doses producing inhibition in the lesioned rats (243 μg/kg) was significantly higher than that of sham-operated rats (27 μg/kg). Furthermore, the local application of 8-OH-DPAT (0.01 μg) in the mPFC inhibited the FS interneurons in sham-operated rats, while having no effect on firing rate of the FS interneurons in the lesioned rats. In contrast to sham-operated rats, the lesion of the SNc in rats did not cause the change of PV-positive neurons in the prelimbic prefrontal cortex, a subregion of the mPFC, whereas the lesion of the SNc markedly reduced in percentage of PV-positive neurons expressing 5-HT(1A) receptors. Our results indicate that degeneration of the nigrostriatal pathway results in the decreased response of FS interneurons in the mPFC to 5-HT(1A) receptor stimulation, which attributes to down-regulation of 5-HT(1A) receptor expression in these interneurons.

Alterations of emotion, cognition and firing activity of the basolateral nucleus of the amygdala after partial bilateral lesions of the nigrostriatal pathway in rats

Although increasing evidence indicates that psychiatric symptoms are crucial characteristic of the early stage of Parkinson's disease (PD) and precede motor impairments, the neuronal firing activity of the basolateral nucleus of the amygdala (BLA) in the psychiatric symptom of PD and the involved mechanism are still unclear. In the present study, we examined the changes in emotional and cognitive tests not focused on motor fluency and firing activity of projection neurons in the BLA rats with 6-hydroxydopamine (6-OHDA) injected bilaterally into dorsal striatum, and the effects of apomorphine and the medial prefrontal cortex (mPFC) on these changes. Injection of 6-OHDA (10.5 μg) into the dorsal striatum produced 18-22% and 26-30% loss of tyrosine hydroxylase immunoreactive neurons in the ventral tegmental area and substantia nigra pars compacta of rats, respectively. The striatal lesions induced anxiety-like responses in the rats but did not result in depressive-like behavior or cognitive impairments. In the lesioned rats, the firing rate of BLA projection neurons decreased significantly compared with sham-operated rats, and the firing pattern of BLA projection neurons was not changed. No significant differences were observed either in behaviors or firing activity of BLA projection neurons by further ibotenic acid lesions of the mPFC in the lesioned rats. Systemic administration of cumulative apomorphine (10-160 μg/kg) inhibited the firing rate of BLA projection neurons in sham-operated, 6-OHDA-lesioned and combined 6-OHDA- and mPFC-lesioned rats, but the latter needed more apomorphine stimulation. These data suggest that the anxiety in early stage of PD is possibly related to the decrease in firing activity of BLA projection neurons, which may be regulated by the activation of dopamine receptor in the mPFC.

Chronic, systemic treatment with a metabotropic glutamate receptor 5 antagonist produces anxiolytic-like effects and reverses abnormal firing activity of projection neurons in the basolateral nucleus of the amygdala in rats with bilateral 6-OHDA lesions

Although 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a selective metabotropic glutamate receptor 5 antagonist, improves the motor symptoms of Parkinson's disease (PD), the effects of MPEP on the psychiatric symptom of PD and the mechanism involved are still unclear. In the present study, we examined the effects of MPEP in anxiolytic-like behavior and firing activity of projection neurons in the basolateral nucleus of the amygdala (BLA) in rats with 6-hydroxydopamine (6-OHDA) injected bilaterally into dorsal striatum. Rats were divided into three groups, sham-operated group, 6-OHDA lesion with vehicle treatment group and 6-OHDA lesion with MPEP treatment group. Injection of 6-OHDA (10.5 μg) into the dorsal striatum produced 31.5% loss of tyrosine hydroxylase immunoreactive (TH-ir) neurons in the SNpc. The 6-OHDA-lesioned rats showed anxiety behavior and the firing rate of BLA projection neurons decreased significantly compared with sham-operated rats, and no difference was found in the firing pattern of these neurons. Whereas chronic, systemic treatment of MPEP (3 mg/kg/day, i.p.; 14 days) attenuated loss of TH-ir neurons, produced anxiolytic-like effect and normalized the abnormal firing rate of projection neurons of the BLA in rats with the bilateral lesions. Systemic administration of cumulative apomorphine (10-160 μg/kg, i.v.) inhibited the firing rate of BLA projection neurons in sham-operated, 6-OHDA lesion with vehicle-treated and MPEP-treated rats, but the 6-OHDA lesion decreased the response of BLA projection neurons to apomorphine stimulation, while MPEP reversed the reactivity of these neurons. These data demonstrate that the partial lesion of the nigrostriatal pathway causes anxiety symptom and decreases firing rate of BLA projection neurons in the rat. Furthermore, chronic, systemic MPEP treatment has the neuroprotective and anxiolytic-like effects, and reverses the abnormal firing rate of BLA projection neurons, suggesting that MPEP has important implication for the treatment of PD.

Effects of simvastatin and 6-hydroxydopamine on histaminergic H1 receptor binding density in rat brains

Statins have been widely used for the treatment of a variety of medical conditions including psychoneurological disorders beyond their original use in lowering cholesterol. Histamine receptors play an important role in the regulation of neural activity, however, it is unknown whether statins act on histamine receptors, particularly for their neural regulatory effects. This study examined the effects of simvastatin and 6-hydroxydopamine (6-OHDA) lesions on histamine H1 receptors using [(3)H] pyrilamine binding autoradiography. Compared to the saline group, simvastatin (1 mg/kg/day) significantly decreased H1 receptor bindings in the primary motor cortex (M1), ventromedial hypothalamic nucleus (VMH), caudate putamen (CPu), accumbens core (AcbC) and prefrontal cortex (PfC) (all p<0.05); however 10 mg/kg/day simvastatin increased H1 receptor density only in the medial amygdaloid nucleus (Mep) (p<0.05), but had no significant effect in other regions examined. The 6-OHDA lesion did not alter H1 receptor binding density in most brain areas, except a trend decrease in the hippocampus (p=0.07) and a trend increase in the cingulate cortex (p=0.06). These results suggested that simvastatin has different effects on the H1 receptors in different rat brain regions depending on the doses. Therefore, simvastatin can modulate histaminergic neurotransmission in the brain, and support the role of H1 receptors in psychoneurological disorders.

Statins: multiple neuroprotective mechanisms in neurodegenerative diseases

Statins have been widely used for the treatment of a variety of conditions beyond their original role in lowering cholesterol. Since statins have relatively few side effects, they have been recognized as useful medicine to ameliorate neurodegenerative disorders. Current studies on the applications of statins have demonstrated their neuroprotective and clinical significance among neurodegenerative diseases like cerebral ischemic stroke, vascular dementia, Alzheimer's disease, and Parkinson's disease, though the neuroprotective mechanisms are not completely understood. This review will discuss recent development in the use of statins in slowing down the progression of these neurodegenerative diseases. It will summarize the potential mechanisms for statin-mediated neuroprotective effects in neurodegenerative diseases. In detail, this review discuss the roles of statins in lowering cholesterol, reducing reactive oxygen species, impairing β-amyloid production and serum apolipoprotein E levels, enhancing the levels of endothelial nitric oxide synthase and cerebral blood flow, and modulating cognitive related receptors and matrix metalloproteases. Finally, different alterations of various receptors in brain regions following statin treatment and their correlations with cognitive dysfunction in Parkinson's disease will also be reviewed, as well as the potential for therapy in ameliorating the progression of Parkinson's disease. This article is part of a Special Issue entitled "Interaction between repair, disease, & inflammation."

Alterations in 5-HT2A receptor binding in various brain regions among 6-hydroxydopamine-induced Parkinsonian rats

The serotonergic system has close interactions with the dopaminergic system and is strongly implicated in the pathophysiological mechanisms and therapeutic paradigms of Parkinson's disease (PD). This study aims to investigate regional changes in 5-hydroxytryptamine (5-HT) 2A receptors in the rat brain 3 weeks after unilateral medial forebrain bundle lesion by 6-hydroxydopamine (6-OHDA). 5-HT 2A receptor distributions and alterations in the postmortem rat brain were detected by [(3)H]ketanserin-binding autoradiography. In the 6-OHDA-induced Parkinson's rat model, nigrostriatal dopaminergic neuron loss significantly mediated the decreased [(3)H]ketanserin binding, predominantly in the agranular insular cortex (17.3%, P = 0.03), cingulate cortex (18.2%, P < 0.001), prefrontal cortex (8%, P = 0.043), primary somatosensory cortex (17.7%, P = 0.002), and caudate putamen (14.5%, P = 0.02) compared to controls while a profound reduction of tyrosine hydroxylase (TH) immunostaining in the striatum was also observed. Alterations in [(3)H]ketanserin binding in the examined brain areas may represent the specific regions that mediate cognitive dysfunctions via the serotonin system. The downregulation of 5-HT(2A) receptor binding in this study also provides indirect evidence for plasticity in the serotonergic system in the rat brains. This study contributes to a better understanding of the critical roles of 5-HT(2A) receptors in treating neurodegenerative disorders and implicates 5-HT(2A) receptors as a novel therapeutic target in the treatment of PD.

Unilateral lesion of the nigrostriatal pathway decreases the response of interneurons in medial prefrontal cortex to 5-HT 2A/2C receptor stimulation in the rat

The aim of the present study was to investigate changes in the firing rate and pattern of interneurons in the medial prefrontal cortex (mPFC), and effects of 5-HT(2A/2C) receptor agonist DOI and antagonist ritanserin, and the selective 5-HT(2C) receptor antagonist SB 242084 on the neuronal firing in rats with 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta (SNc) by extracellular recording in vivo. The lesion of the SNc decreased the firing rate of the interneurons compared to sham-lesioned rats, and firing pattern of these interneurons changed toward a more burst-firing. Administration of DOI (20-320 microg/kg, i.v.) dose-dependently increased the firing rate of all interneurons examined in sham-lesioned and the 6-OHDA-lesioned rats. The excitation was significant at doses higher than 40 microg/kg and 320 microg/kg in sham-lesioned and the 6-OHDA-lesioned rats, respectively. This dose, which produced marked effect in the 6-OHDA-lesioned rats, was much higher than that of sham-lesioned rats. The local application of DOI (5 microg) in mPFC increased the firing rate of the interneurons in sham-lesioned rats, while having no effect on the firing rate in the 6-OHDA-lesioned rats. The excitatory effect of DOI in sham-lesioned and the 6-OHDA-lesioned rats was completely or partially reversed by ritanserin or SB 242084. The results of our study show that lesion of the SNc leads to a decrease in the firing rate of interneurons in mPFC and fire with a more burst pattern, and decreased response of the interneurons to DOI in rat.

In vivo effects of activation and blockade of 5-HT(2A/2C) receptors in the firing activity of pyramidal neurons of medial prefrontal cortex in a rodent model of Parkinson's disease

In the present study, we examined changes in the firing rate and firing pattern of pyramidal neurons in medial prefrontal cortex (mPFC), and the effects of 5-HT(2A/2C) receptor agonist DOI and antagonist ritanserin on the neuronal firing in rats with 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta by using extracellular recording. The unilateral lesion of the nigrostriatal pathway significantly increased the mean firing rate of pyramidal neurons compared to sham-operated rats, and the firing pattern of these neurons also changed significantly towards a more bursty one. Systemic administration of DOI (20-320 microg/kg, i.v.) increased the mean firing rate of pyramidal neurons in sham-operated and the lesioned rats. The excitation was significant only at doses higher than 160 microg/kg and 320 microg/kg in sham-operated and the lesioned rats, respectively. In addition, the local application of DOI, 5 microg, in mPFC inhibited the firing rate of pyramidal neurons in sham-operated rats, while having no effect on firing rate in the lesioned rats. After treatment with GABAA receptor antagonist picrotoxinin, the local application of DOI, at the same dose, increased the mean firing rate of the neurons in sham-operated rats; however, DOI did not alter the firing activity of the neurons in the lesioned rats. These results indicate that the lesion of the nigrostriatal pathway leads to hyperactivity of pyramidal neurons in mPFC, and the decreased response of pyramidal neurons to DOI, suggesting dysfunction of 5-HT2A and 5-HT2C receptors on pyramidal neurons and GABAergic interneurons in the 6-OHDA-lesioned rats.

The firing activity of pyramidal neurons in medial prefrontal cortex and their response to 5-hydroxytryptamine-1A receptor stimulation in a rat model of Parkinson's disease

The changes in the firing rate and firing pattern of pyramidal neurons in medial prefrontal cortex (mPFC) and the effects of selective 5-hydroxytryptamine-(1A) (5-HT(1A)) receptor agonist (R)-(+)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT) and antagonist N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-2-pyridylcyclohexane carboxamide maleate salt (WAY-100635) on the firing activity of the neurons were studied in sham-lesioned rats and rats with 6-hydroxydopamine lesions of the substantia nigra pars compacta (SNc). The lesion of the SNc increased the firing rate of pyramidal neurons significantly compared to sham-lesioned rats, and the firing pattern of these neurons also changed significantly towards a more burst-firing. The systemic administration of 8-OH-DPAT at doses in the range of 0.5-128 microg/kg showed an excitatory-inhibitory effect on the firing rate of pyramidal neurons in mPFC of sham-lesioned rats. At lower doses, 0.5-32 microg/kg, it evoked excitation of the neurons, and at a high dose, i.e. 128 microg/kg, inhibited the activity of the neurons. In contrast to sham-lesioned rats, 8-OH-DPAT, at the same doses, showed no excitatory effect in the lesioned rats although the inhibitory phase of the effect of 8-OH-DPAT on the firing rate of pyramidal neurons in mPFC was still present. Furthermore, the local application of 8-OH-DPAT, 5 microg, in mPFC inhibited the firing rate of pyramidal neurons in sham-lesioned rats, while having no effect on firing rate in the lesioned rats. The excitatory or inhibitory effects of 8-OH-DPAT were reversed by WAY-100635, indicating that these effects are mediated by 5-HT(1A) receptor. Altogether, these results indicate that the lesion of the SNc leads to hyperactivity of pyramidal neurons in mPFC and the abnormality of response of these neurons to 5-HT(1A) receptor stimulation, suggesting that mPFC may be involved in the pathophysiology of the psychiatric disturbance of Parkinson's disease.

Use of statins and the risk of Parkinson's disease: a retrospective case-control study in the UK

BACKGROUND

Case reports have related the use of HMG-CoA reductase inhibitors ('statins') to Parkinson's disease (PD). Paradoxically, however, statins may have potentially beneficial effects on neurodegenerative diseases due to their anti-inflammatory properties.

OBJECTIVE

To explore the risk of the development of PD in association with untreated hyperlipidaemia and with hyperlipidaemia treated with lipid-lowering drugs in the UK primary care setting.

METHODS

We conducted a case-control analysis using the UK-based General Practice Research Database (GPRD). Cases were incident PD cases > or =40 years of age between 1994 and 2005. One control was matched to each PD case based on age, sex, general practice and index date. Lipid-lowering drug use was assessed by exposure timing (current vs past use) and by exposure duration (1-9, 10-29 or > or =30 prescriptions) prior to the index date for both cases and controls. Odds ratios (OR) were calculated using conditional logistic regression, adjusted for body mass index, smoking and various cardiovascular, metabolic and psychiatric co-morbidities.

RESULTS

We identified 3637 cases with an incident idiopathic PD diagnosis, and the same number of controls. Compared with patients without hyperlipidaemia, those with untreated hyperlipidaemia did not have an altered relative PD risk (adjusted OR 0.98, 95% CI 0.74, 1.30). The adjusted ORs for current use of > or =30 prescriptions for statins or fibrates compared with non-use of statins or fibrates were 1.06 (95% CI 0.75, 1.51) and 1.25 (95% CI 0.51, 3.06), respectively.

CONCLUSIONS

In this observational study, the long-term use of statins or fibrates was not associated with a substantially altered relative risk of developing PD.

Statins in the spectrum of neurologic disease

Overwhelming evidence now shows that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (ie, statins) are safe and effective in primary and secondary prevention of cardiovascular disease. Atherosclerosis, the primary cause of heart disease, is directly and independently related to hypercholesterolemia and inflammation, and statins have multiple and independent effects on these conditions. New evidence for the use of statins in neurologic disease is mounting, and the range of therapeutic applications is formidable. Statins are beginning to show benefits in a wide range of neurologic conditions, from common ischemic stroke to rare congenital neurometabolic storage diseases, from acute brain injury to chronic central nervous system inflammation, and from prevention of neurodegenerative disease to acute neuroprotection. A diverse therapeutic spectrum is explained by shared pathogenetic mechanisms of neurologic disease and the manifold pharmacodynamic effects of statins.

The selective 5-HT1A receptor antagonist WAY-100635 inhibits neuronal activity of the ventromedial prefrontal cortex in a rodent model of Parkinson's disease

OBJECTIVE

The ventral part of the medial prefrontal cortex (mPFC) plays an important role in initiation and control of voluntary movement, mood and cognition. However, after the degeneration of the nigrostriatal pathway, the neuronal activity of the ventral mPFC and the role of serotonin(1A) (5-hydroxytryptamine, 5-HT(1A)) receptors in the firing of the neurons are still unknown. The present study is to investigate the change of neuronal activity in the ventral mPFC and the effect of systemic administration of the selective 5-HT(1A) receptor antagonist WAY-100635 on the activity of the neurons in normal and 6-hydroxydopamine (6-OHDA)-lesioned rats.

METHODS

Single unit responses were recorded extracellularly with glass microelectrodes from ventral mPFC neurons in normal rats and 6-OHDA unilaterally lesioned rats in vivo.

RESULTS

6-OHDA lesion of the substantia nigra pars compacta (SNc) significantly increased the firing rate with no change in the firing pattern of neurons of the ventral mPFC in rats. Systemic administration of WAY-100635 (0.1 mg/kg, i.v.) did not change the mean firing rate and firing pattern of ventral mPFC neurons in normal rats. In contrast, WAY-100635 significantly decreased the mean firing rate of the neurons in rats with 6-OHDA lesion of the SNc.

CONCLUSION

These data suggest that the degeneration of the nigrostriatal pathway results in an increase of neuronal activity of ventral mPFC and dysfunction of 5-HT(1A) receptor.

Role of HMG-CoA reductase inhibitors in neurological disorders : progress to date

Inhibitors of HMG-CoA reductase (statins) are cholesterol-lowering agents that dramatically reduce morbidity and mortality in patients with established cardiovascular disease. In addition, they exhibit pleiotropic effects that operate independently of lipid modification. Statin administration results in greater nitric oxide bioavailability, improved endothelial function, enhanced cerebral blood flow, immune modulation with anti-inflammatory action, decreased platelet aggregation and antioxidant activity. Some or all of these effects may improve outcome or ameliorate symptoms in neurological disorders. This article examines the potential role of statins in treating stroke, Alzheimer's disease, multiple sclerosis and Parkinson's disease. Studies are ongoing in this controversial area, but there are no firm conclusions. The appropriateness of initiating statin therapy for neurological disorders is not established at this time. The exception is stroke, in which recurrence is significantly reduced by statin therapy.

Echinacoside prevents the striatal extracellular levels of monoamine neurotransmitters from diminution in 6-hydroxydopamine lesion rats

We investigated the effects of echinacoside, a phenylethanoid glycoside isolated and purified from the stems of Cistanche salsa, a Chinese herbal medicine, on the striatal extracellular levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in 6-hydroxydopamine (6-OHDA) lesion rats. Seven days after 6-OHDA was injected into the right striatum of rats, the striatal extracellular levels of DA, DOPAC and HVA fell significantly (P<0.01 vs. vehicle), as demonstrated by the method of cerebral microdialysis and high performance liquid chromatography with electrochemical detection. However, simultaneous treatment with echinacoside (7.0, 3.5mg/kg) attenuated the diminution of them (P<0.01 vs. model). The results implied that echinacoside could protect the striatal dopaminergic neurons from injury induced by 6-OHDA and may be useful in the prevention and treatment of Parkinson's disease (PD).

Effects of high dose of simvastatin on levels of dopamine and its reuptake in prefrontal cortex and striatum among SD rats

Statins are increasingly being used for the treatment of a variety of conditions beyond their original indication for cholesterol lowering. We previously reported that simvastatin increased dopamine receptors in the rat prefrontal cortex [Q. Wang, W.L. Ting, H. Yang, P.T. Wong, High doses of simvastatin upregulate dopamine D(1) and D(2) receptor expression in the rat prefrontal cortex: possible involvement of endothelial nitric oxide synthase, Br. J. Pharmacol. 144 (2005) 933-939] and restored its downregulation in a model of Parkinson's disease (PD) [Q. Wang, P.H. Wang, C. McLachlan, P.T. Wong, Simvastatin reverses the downregulation of dopamine D1 and D2 receptor expression in the prefrontal cortex of 6-hydroxydopamine-induced Parkinsonian rats, Brain Res. 1045 (2005) 229-233]. Here we explore the effects of simvastatin treatment on tissue dopamine content and reuptake. Sprague-Dawley rats were given simvastatin (1 and 10 mg kg(-1)day(-1), p.o.) for 4 weeks. Brain tissue from prefrontal cortex and striatum were taken out for dopamine content and its reuptake. Using high-performance liquid chromatographic-mass spectrometer (HPLC-MS), simvastatin (10 mg kg(-1)day(-1)) was found to increase dopamine content by 110% in the striatum but decreased by 76% in the prefrontal cortex compared with the saline treated group. Dopamine (DA) reuptake was unchanged in both brain regions. These results suggest that chronic treatment with high dose of simvastatin may affect DA tissue level in prefrontal cortex and striatum without changing on DA reuptake. This may have important clinical implications in psychiatric and striatal dopaminergic disorders.