Glutamate/dopamine D1/D2 balance in the basal ganglia and its relevance to Parkinson's disease

Dopamine loss alters glutamate synapses and transporters in the medial prefrontal cortex and anxiety-related behaviour in a male MPTP rodent model of Parkinson's disease

Anxiety is a prominent non-motor symptom of Parkinson's disease (PD). Changes in the B-spectrum recordings in PD patients of the prefrontal cortex correlate with increased anxiety. Using a rodent model of PD, we reported alterations in glutamate synapses in the striatum and substantia nigra following dopamine (DA) loss. We hypothesize that DA loss will result in increased anxiety-related behaviours and that this will be associated with alterations in glutamate synapses and transporters within the medial prefrontal cortex (mPFC). Following 4 weeks of progressive 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration, there was an increase in anxiety-related behaviours and a 78% decrease in plasma corticosterone levels versus the vehicle (VEH)-treated mice. This was associated with a 30% decrease in the density of dendritic spines in Layers Il/Ill, and a 53% decrease in the density of glutamate immuno-gold labelling within vesicular glutamate transporter 1 (Vglut1)-labelled nerve terminals and spines, with no change within vesicular glutamate transporter 2 (Vglut2) positive terminals/spines in the MPTP versus VEH groups. Our prior work determined that a decrease in striatal glutamate terminal density was associated with an increase in extracellular glutamate levels. There was an increase in protein expression of Vglut1 (40%), Vglut2 (37%) and glutamate aspartate transporter (GLAST) (225%), and a decrease in glutamate transporter 1 (GLT-1) (50%) and excitatory amino acid carrier 1 (EAAC1) (51%), in the MPTP versus VEH groups within the mPFC. These data suggest that the decrease in dendritic spines within the mPFC following nigrostriatal DA loss may be due to increased extracellular glutamate levels (decrease in glutamate transporters), leading to an increase in anxiety-related behaviours.

Memantine for the patients with mild cognitive impairment in Parkinson's disease: a pharmacological fMRI study

BACKGROUND

Mild cognitive impairment in Parkinson's disease (PD-MCI) is associated with an increased risk of cognitive decline. PD-MCI is characterized by impairments in executive function and visuospatial recognition. The visuospatial n-back test is useful for assessing both domains. The 0-back test reflects visuospatial recognition, while the 1-back and 2-back tests reflect working memory. Cholinesterase inhibitors are effective in the treatment of PD-MCI and dementia in PD (PDD). Although some studies have reported the efficacy of memantine for PDD, the therapeutic efficacy of memantine in patients with PD-MCI remains uncertain.

METHODS

This study aimed to investigate the effects of memantine on brain function in patients with PD-MCI, using a randomized double-blinded crossover protocol and functional MRI (fMRI). Ten patients who completed 16 weeks of follow-up were included. They were randomly assigned to either the memantine or placebo. Patients in the memantine group received 5 mg/day of memantine in the first week. The memantine dose was increased by 5 mg/day per week, until a final dose of 20 mg/day. Patients in the placebo group received the placebo following the same regimen as memantine. After the intervention, they underwent a 4 weeks washout period. Following the crossover protocol, a second intervention was conducted after the washout period. In each intervention, fMRI and neuropsychological tests were performed at the maximum dose period. Comparing the memantine and placebo groups, we investigated difference in the brain regions using the visuospatial n-back test.

RESULTS

There were no significant regions enhanced by memantine comparing with placebo at any load of n-back tests. In contrast, exploring regions reduced by memantine, we found significant reduction of activations within right lingual gyrus and left superior frontal gyrus in comparison between 2-back and 0-back test. A number of correct answers of the 2-back test and time to complete Trail Making Test-A were worse during memantine intervention.

CONCLUSIONS

Memantine did not improve visuospatial working memory of the patients with PD-MCI. Treatment for PD should be planned carefully considering the impact on cognitive function. Further study is needed to establish new therapeutic strategy.

TRIAL REGISTRATION

UMIN000046104. Retrospectively registered. First registration date: 28 Sept 2017.

Antipsychotic-like profile of CIQ isomers in animal models of schizophrenia

Earlier, we have shown the efficacy of racemic (±) CIQ, a positive allosteric modulator of GluN2C/2D receptor against MK-801 induced impairment of prepulse inhibition as well as working memory. The present study investigated the antipsychotic-like profile of different CIQ (±, +, -) isomers against schizophrenia-like symptoms in series of behavioural animal models like apomorphine climbing, social isolation behaviour and NMDA receptor antagonist MK-801 induced cognitive deficits. Further, we also tested CIQ (±, +, -) isomers in neurodevelopmental model against MK-801induced deficits using open field test, Y-maze test and novel object recognition test. CIQ (±, +, -) isomers decreased climbing behaviour, increased social interaction and improved the MK-801 induced deficits in working memory in Y-maze. Further, CIQ (±, +) but not CIQ (-) improved the recognition memory in novel object recognition test as well as reduced hyperlocomotion and stereotyped behaviour. We conclude that CIQ (±, +) but not CIQ (-) exhibit the significant antipsychotic-like profile.

A role for α-Synuclein in axon growth and its implications in corticostriatal glutamatergic plasticity in Parkinson's disease

BACKGROUND

α-Synuclein (α-Syn) is a protein implicated in the pathogenesis of Parkinson's disease (PD). α-Syn has been shown to associate with membranes and bind acidic phospholipids. However, the physiological importance of these associations to the integrity of axons is not fully clear.

METHODS

Biochemical, immunohistochemical and ultrastructural analyses in cultured neurons, transgenic mouse brains, PD and control human brains.

RESULTS

We analyzed the ultrastructure of cross-sectioned axons localized to white matter tracts (WMTs), within the dorsal striatum of old and symptomatic α-Syn transgenic mouse brains. The analysis indicated a higher density of axons of thinner diameter. Our findings in cultured cortical neurons indicate a role for α-Syn in elongation of the main axon and its collaterals, resulting in enhanced axonal arborization. We show that α-Syn effect to enhance axonal outgrowth is mediated through its activity to regulate membrane levels of the acidic phosphatidylinositol 4,5-bisphosphate (PI4,5P2). Moreover, our findings link α-Syn- enhanced axonal growth with evidence for axonal injury. In relevance to disease mechanisms, we detect in human brains evidence for a higher degree of corticostriatal glutamatergic plasticity within WMTs at early stages of PD. However, at later PD stages, the respective WMTs in the caudate are degenerated with accumulation of Lewy pathology.

CONCLUSIONS

Our results show that through regulating PI4,5P2 levels, α-Syn acts to elongate the main axon and collaterals, resulting in a higher density of axons in the striatal WMTs. Based on these results we suggest a role for α-Syn in compensating mechanisms, involving corticostriatal glutamatergic plasticity, taking place early in PD.

A novel missense variant in GPT2 causes non-syndromic autosomal recessive intellectual disability in a consanguineous Iranian family

Intellectual disability (ID) affects 1-3% of the general population worldwide. Genetic factors play an undeniable role in the etiology of Non-Syndromic Intellectual disability (NS-ID). Nowadays, whole-exome sequencing (WES) technique is used frequently to identify the causative genes in such heterogeneous diseases. Herein, we subjected four patients with initial diagnostics of NS-ID in a consanguineous Iranian family. To find the possible genetic cause(s), Trio-WES was performed on the proband and his both healthy parents. Sanger sequencing was performed to confirm the identified variant by WES and also investigate whether it co-segregates with the patients' phenotype in the family. Using several online in-silico predictors, the probable impacts of the variant on structure and function of GPT2 protein were predicted. A novel variant, c.266A>G; p.(Glu89Gly), in exon 3 of GPT2 (NM_133443.3) was identified using Trio-WES. The candidate variant was also verified by Sanger sequencing. All affected members showed the common clinical features suffering from a non-progressive mild-to-severe ID. Also, different clinical observations compared to previously reported cases such as no facial features, no obvious structural malformations, ability to speak but with difficulty, and lack of any morphological defects were noted for the first time in this family. The c.266A>G; p.(Glu89Gly) variant reported here is the sixth variant identified up to now in the GPT2 gene, to be associated with NS-ID. Our data support the potential malfunction of the substituted GPT2 protein resulted from the novel variant, however, we strongly suggest confirming this finding more by doing functional analysis.

Glatiramer Acetate Reverses Motor Dysfunction and the Decrease in Tyrosine Hydroxylase Levels in a Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease and there are no effective treatments that either slow or reverse the degeneration of the dopamine (DA) pathway. Using a 4-week progressive MPTP (1-methyl-1,2,3,6-tetrahydropyridine) neurotoxin model of PD, which is characterized by neuroinflammation, loss of nigrostriatal DA, and motor dysfunction, as seen in patients with PD, we tested whether post-MPTP treatment with glatiramer acetate (GA), an immunomodulatory drug, could reverse these changes. GA restored the grip dysfunction and gait abnormalities that were evident in the MPTP treated group. The reversal of the motor dysfunction was attributable to the substantial recovery in tyrosine hydroxylase (TH) protein expression in the striatum. Within the substantia nigra pars compacta, surface cell count analysis showed a slight increase in TH+ cells following GA treatment in the MPTP group, which was not statistically different from the vehicle (VEH) group. This was associated with the recovery of BDNF (brain derived neurotrophic factor) protein levels and a reduction in the microglial marker, IBA1, protein expression within the midbrain. Alpha synuclein (syn-1) levels within the midbrain and striatum were decreased following MPTP, while GA facilitated recovery to VEH levels in the striatum in the MPTP group. Although DA tissue analysis revealed no significant increase in striatal DA or 3,4-Dihydroxyphenylacetic acid levels (DOPAC) in the MPTP group treated with GA, DA turnover (DOPAC/DA) recovered back to VEH levels following GA treatment. GA treatment effectively reversed clinical (motor dysfunction) and pathology (TH, IBA1, BDNF expression) of PD in a murine model.

REM Sleep Behavior Disorder (RBD) in Dementia with Lewy Bodies (DLB)

Rapid eye movement sleep behavior disorder (RBD) is a parasomnia, with abnormal dream-enacting behavior during the rapid eye movement (REM) sleep. RBD is either idiopathic or secondary to other neurologic disorders and medications. Dementia with Lewy bodies (DLB) is the third most common cause of dementia, and the typical clinical presentation is rapidly progressive cognitive impairment. RBD is one of the core features of DLB and may occur either in advance or simultaneously with the onset of DLB. The association between RBD with DLB is widely studied. Evidences suggest that both DLB and RBD are possibly caused by the shared underlying synucleinopathy. This review article discusses history, clinical manifestations, possible pathophysiologies, and treatment of DLB and RBD and provides the latest updates.

[Memantine: from the original brand to generics]

Memantine is the first clinically available glutamate antagonist, with an antagonist action at the N-methyl-D-aspartate receptors in the brain, for correction of cognitive and behavioral functions in neurodegenerative disorders. Glutamate mediated excitotoxic neuronal damage has been implicated in Alzheimer's disease (AD) and other parkinsonism-related dementias and, therefore, memantine represents a novel mode of action to counteract the glutamate-mediated excitotoxicity. In moderate to severe AD, 20 mg of memantine shows a positive effect on cognition, mood, behavior and the ability to perform activities of daily living. Long-term studies show good tolerability of memantine with an acceptable side-effect profile. In recent years, there have been a proliferation of a number of companies producing generic memantine with different trade names. In Russia, the first memantine generic drug noojerone was approved in 2010 and its use has since been supported by a growing evidence base of efficacy in real-life clinical practice. Postmarketing studies show that noojerone provides long-term and effective therapy in patients with moderate and severe Alzheimer's dementia. This observation is supported by the clinically significant therapeutic effect of noojerone on cognitive and daily functioning, behavioral and psychotic symptoms of dementia and a reduction of the burden on caregivers. This generic version of memantine is affordable and, therefore, reduces financial burden on patients and improves compliance with treatment.

Deconstructing behavioral neuropharmacology with cellular specificity

Behavior has molecular, cellular, and circuit determinants. However, because many proteins are broadly expressed, their acute manipulation within defined cells has been difficult. Here, we combined the speed and molecular specificity of pharmacology with the cell type specificity of genetic tools. DART (drugs acutely restricted by tethering) is a technique that rapidly localizes drugs to the surface of defined cells, without prior modification of the native target. We first developed an AMPAR antagonist DART, with validation in cultured neuronal assays, in slices of mouse dorsal striatum, and in behaving mice. In parkinsonian animals, motor deficits were causally attributed to AMPARs in indirect spiny projection neurons (iSPNs) and to excess phasic firing of tonically active interneurons (TANs). Together, iSPNs and TANs (i.e., D2 cells) drove akinesia, whereas movement execution deficits reflected the ratio of AMPARs in D2 versus D1 cells. Finally, we designed a muscarinic antagonist DART in one iteration, demonstrating applicability of the method to diverse targets.

Exercise in an animal model of Parkinson's disease: Motor recovery but not restoration of the nigrostriatal pathway

Many clinical studies have reported on the benefits of exercise therapy in patients with Parkinson's disease (PD). Exercise cannot stop the progression of PD or facilitate the recovery of dopamine (DA) neurons in the substantia nigra pars compacta (SNpc) (Bega et al., 2014). To tease apart this paradox, we utilized a progressive MPTP (1-methyl-4-phenyl-1,2,3,6-tetra-hydropyridine) mouse model in which we initiated 4weeks of treadmill exercise after the completion of toxin administration (i.e., restoration). We found in our MPTP/exercise (MPTP+EX) group several measures of gait function that recovered compared to the MPTP only group. Although there was a small recovery of tyrosine hydroxylase (TH) positive DA neurons in the SNpc and terminals in the striatum, this increase was not statistically significant. These small changes in TH could not explain the improvement of motor function. The MPTP group had a significant 170% increase in the glycosylated/non-glycosylated dopamine transporter (DAT) and a 200% increase in microglial marker, IBA-1, in the striatum. The MPTP+EX group showed a nearly full recovery of these markers back to the vehicle levels. There was an increase in GLT-1 levels in the striatum due to exercise, with no change in striatal BDNF protein expression. Our data suggest that motor recovery was not prompted by any significant restoration of DA neurons or terminals, but rather the recovery of DAT and dampening the inflammatory response. Although exercise does not promote recovery of nigrostriatal DA, it should be used in conjunction with pharmaceutical methods for controlling PD symptoms.

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.

Memantine and Cognition in Parkinson's Disease Dementia/Dementia With Lewy Bodies: A Meta-Analysis

Background

The aim of this work was to utilize meta-analysis in examining the effects of memantine on neuropsychological functioning in patients with Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB).

Methods

Included studies fulfilled these criteria: included objective cognitive measures, a comparison group of participants not taking memantine, and provided sufficient data for calculation of effect size. We examined effect sizes across global cognition and five specific neuropsychological domains. Moderator variables examined included neuropsychological domain, diagnostic cohort (PDD, DLB, or mixed PDD-DLB cohort), study design (open label or placebo-controlled), and trial length.

Results

Six publications met inclusion criteria totaling 57 effects. Homogeneity analysis across cognitive domains revealed a small overall effect size (d = 0.25) that was significantly heterogeneous (P < 0.001). Specific neuropsychological domains did not moderate effect size, though. Moderator analysis studies using a mix of DLB and PDD subjects showed larger effects than those that included DLB or PDD patients only. Additionally, open-label trials had significantly (P < 0.001) larger effect sizes (d = 1.32) than placebo-controlled trials (d = 0.12).

Conclusions

The present study indicates that effect-size heterogeneity across studies of memantine in DLB and PDD patients is moderated by diagnostic makeup of the cohort and study design. The small overall effect size noted in placebo-controlled trials versus open-label trials indicates that memantine has minimal effects on cognition in PDD and DLB and is unlikely to demonstrate clinically significant improvements in cognition.

Memantine for Lewy body disorders: systematic review and meta-analysis

OBJECTIVE

To clarify whether memantine is more efficacious in several outcomes and safer than placebo in patients with Lewy body disorders, we performed a meta-analysis of memantine in patients with Lewy body disorders.

METHODS

The meta-analysis included randomized controlled trials of memantine for Lewy body disorders in all patients with Lewy body disorders. Motor function, activities of daily living, Neuropsychiatric Inventory, Mini-Mental State Exam, discontinuation rate, and individual side effects were evaluated.

RESULTS

No significant effects of memantine on motor function scores, Mini-Mental State Exam scores, Neuropsychiatric Inventory scores, and activity of daily living scores were found. However, memantine was superior to placebo in Alzheimer's Disease Cooperative Study-Clinical Global Impression of Change scores (standardized mean difference: -0.26; 95% confidence interval: -0.51 to -0.02; z = 2.08; p = 0.04; two studies; N = 258). Dropout due to all causes, inefficacy, or adverse events were similar in both groups. Moreover, no significant differences in serious adverse events, somnolence/tiredness, stroke, dizziness/vertigo, and confusion were found between the groups.

CONCLUSION

Our results suggest that memantine did not have a benefit for the treatment of Lewy body disorders in cognition and motor function. However, memantine may be superior to placebo for the overall impression of the disorders. Further, memantine is well tolerated.

Efficacy and safety of cholinesterase inhibitors and memantine in cognitive impairment in Parkinson's disease, Parkinson's disease dementia, and dementia with Lewy bodies: systematic review with meta-analysis and trial sequential analysis

OBJECTIVE

Recently, several large randomised controlled trials about the treatments of cognitive impairment or dementia due to Parkinson's disease (CIND-PD or PDD) and dementia with Lewy bodies (DLB) were completed. Here, we systematically reviewed the studies (including the recent reports) to provide updated evidence for the treatments of CIND-PD, PDD and DLB.

METHODS

We searched Cochrane Dementia and Cognitive Improvement Group Specialised Register, Pubmed, Embase, and other sources for eligible trials. We selected global impression and cognitive function as primary efficacy outcomes, and dropouts and adverse events as safety outcomes. Furthermore, Meta-analysis and trial sequential analysis (TSA) were used here.

RESULTS

Ten trials were included in this study. Cholinesterase inhibitors and memantine produced small global efficacy on clinicians' global impression of change (CGIC), from a weighted mean difference of -0.40 (95% CI -0.77 to -0.03) to -0.65 (95% CI -1.28 to -0.01); however, cholinesterase inhibitors but not memantine significantly improved cognition on Mini-Mental State Examination (MMSE), from 1.04 (95% CI 0.43 to 1.65) to 2.57 (95% CI 0.90 to 4.23). Additionally, both of them had good safety outcomes, although rivastigmine showed an increased risk on adverse events than placebo (risk ratio, RR 1.19, TSA adjusted 95% CI 1.04 to 1.36), these events were usually mild or moderate, and the risk disappeared on serious adverse events.

CONCLUSIONS

Cholinesterase inhibitors and memantine slightly improve global impression; however, only cholinesterase inhibitors enhance cognitive function. Besides, all the drugs have good safety outcomes. But the limited trials precluded the generalisation of these outcomes.

Tea polyphenols alleviate motor impairments, dopaminergic neuronal injury, and cerebral α-synuclein aggregation in MPTP-intoxicated parkinsonian monkeys

Tea polyphenols (TPs) are bioactive flavanol-related catechins that have been shown to protect dopaminergic (DAergic) neurons against neurotoxin-induced injury in mouse Parkinson's disease (PD) models. However, the neuroprotective efficacy of TP has not been investigated in nonhuman PD primates, which can more accurately model the neuropathology and motor impairments of human PD patients. Here, we show that oral administration of TP alleviates motor impairments and DAergic neuronal injury in the substantia nigra in N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated PD monkeys, indicating an association between protection against motor deficits and preservation of DAergic neurons. We also show a significant inhibition of MPTP-induced accumulation of neurotoxic α-synuclein (α-syn) oligomers in the striatum and other brain regions, which may contribute to the neuroprotection and improved motor function conferred by TP. The association between reduced α-syn oligomerization and neuroprotection was confirmed in cultured DAergic cells. The most abundant and bioactive TP in the mixture used in vivo, (-)-epigallocatechin-3-gallate, reduced intracellular levels of α-syn oligomers in neurons treated with α-syn oligomers, 1-methyl-4-phenylpyridiniumion, or both, accompanied by increased cell viability. The present study provides the first evidence that TP can alleviate motor impairments, DAergic neuronal injury, and α-syn aggregation in nonhuman primates.

D-Serine in Neuropsychiatric Disorders: New Advances

D-Serine (DSR) is an endogenous amino acid involved in glia-synapse interactions that has unique neurotransmitter characteristics. DSR acts as obligatory coagonist at the glycine site associated with the N-methyl-D-aspartate subtype of glutamate receptors (NMDAR) and has a cardinal modulatory role in major NMDAR-dependent processes including NMDAR-mediated neurotransmission, neurotoxicity, synaptic plasticity, and cell migration. Since either over- or underfunction of NMDARs may be involved in the pathophysiology of neuropsychiatric disorders; the pharmacological manipulation of DSR signaling represents a major drug development target. A first generation of proof-of-concept animal and clinical studies suggest beneficial DSR effects in treatment-refractory schizophrenia, movement, depression, and anxiety disorders and for the improvement of cognitive performance. A related developing pharmacological strategy is the indirect modification of DSR synaptic levels by use of compounds that alter the function of main enzymes responsible for DSR production and degradation. Accumulating data indicate that, during the next decade, we will witness important advances in the understanding of DSR role that will further contribute to elucidating the causes of neuropsychiatric disorders and will be instrumental in the development of innovative treatments.

Ceftriaxone increases glutamate uptake and reduces striatal tyrosine hydroxylase loss in 6-OHDA Parkinson's model

Excess glutamatergic neurotransmission may contribute to excitotoxic loss of nigrostriatal neurons in Parkinson's disease (PD). Here, we determined if increasing glutamate uptake could reduce the extent of tyrosine hydroxylase (TH) loss in PD progression. The beta-lactam antibiotic, ceftriaxone, increases the expression of glutamate transporter 1 (GLT-1), a glutamate transporter that plays a major role in glutamate clearance in central nervous system and may attenuate adverse behavioral or neurobiological function in other neurodegenerative disease models. In association with >80% TH loss, we observed a significant decrease in glutamate uptake in the established 6-hydroxydopamine (6-OHDA) PD model. Ceftriaxone (200 mg/kg, i.p.) increased striatal glutamate uptake with >5 consecutive days of injection in nonlesioned rats and lasted out to 14 days postinjection, a time beyond that required for 6-OHDA to produce >70% TH loss (∼9 days). When ceftriaxone was given at the time of 6-OHDA, TH loss was ∼57% compared to ∼85% in temporally matched vehicle-injected controls and amphetamine-induced rotation was reduced about 2-fold. This attenuation of TH loss was associated with increased glutamate uptake, increased GLT-1 expression, and reduced Serine 19 TH phosphorylation, a calcium-dependent target specific for nigrostriatal neurons. These results reveal that glutamate uptake can be targeted in a PD model, decrease the rate of TH loss in a calcium-dependent manner, and attenuate locomotor behavior associated with 6-OHDA lesion. Given that detection of reliable PD markers will eventually be employed in susceptible populations, our results give credence to the possibility that increasing glutamate uptake may prolong the time period before locomotor impairment occurs.

Schizophrenia: from dopaminergic to glutamatergic interventions

Schizophrenia might be considered a neurodevelopmental disease. However, the fundamental process(es) associated with this disease remain(s) uncertain. Many lines of evidence suggest that schizophrenia is associated with excessive stimulation of dopamine D2 receptors in the associative striatum, with a lack of stimulation of dopamine D1 receptors in prefrontal cortex, and with modifications in prefrontal neuronal connectivity involving glutamate transmission at N-methyl aspartate (NMDA) receptors. This article, whilst briefly discussing the current knowledge of the disease, mainly concentrates on the NMDA hypofunction hypothesis. However, there are also potential consequences for a Dopamine imbalance on NMDA function. Thus, it is proposed that schizophrenia has a complex aetiology associated with strongly interconnected aberrations of dopamine and glutamate transmission.

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.

D-serine adjuvant treatment alleviates behavioural and motor symptoms in Parkinson's disease

Parkinson's disease (PD) manifestations include motor symptoms and behavioural deficits that resemble schizophrenia negative symptoms. The N-methyl-D-aspartate subtype of glutamate receptor (NMDAR) represents a novel pharmacological target in PD. D-serine (DSR) allosterically modulates in-vivo NMDAR-mediated neurotransmission and has been shown to improve negative and antipsychotic drug-induced parkinsonian symptoms in schizophrenia patients. This pilot study assessed DSR effects in ten PD patients who completed a 6-wk double-blind, placebo-controlled, crossover adjuvant treatment trial with 30 mg/kg.d DSR. Primary outcome analyses consisted of separate repeated-measures multivariate analyses of variance for Unified Parkinson's Disease Rating Scale (UPDRS), Simpson-Angus Scale for Extrapyramidal Symptoms (SAS), Abnormal Involuntary Movement Scale (AIMS), and Positive and Negative Syndrome Scale (PANSS) scores. DSR treatment was well tolerated and resulted in increased DSR serum levels (p=0.001) and significantly reduced UPDRS (p=0.02), SAS (p=0.009) and PANSS (0.05) total scores. These preliminary findings suggest that DSR treatment may be beneficial in PD. Larger-sized studies with optimized DSR dosages are warranted.

Parkinson's disease therapeutics: new developments and challenges since the introduction of levodopa

The demonstration that dopamine loss is the key pathological feature of Parkinson's disease (PD), and the subsequent introduction of levodopa have revolutionalized the field of PD therapeutics. This review will discuss the significant progress that has been made in the development of new pharmacological and surgical tools to treat PD motor symptoms since this major breakthrough in the 1960s. However, we will also highlight some of the challenges the field of PD therapeutics has been struggling with during the past decades. The lack of neuroprotective therapies and the limited treatment strategies for the nonmotor symptoms of the disease (ie, cognitive impairments, autonomic dysfunctions, psychiatric disorders, etc.) are among the most pressing issues to be addressed in the years to come. It appears that the combination of early PD nonmotor symptoms with imaging of the nigrostriatal dopaminergic system offers a promising path toward the identification of PD biomarkers, which, once characterized, will set the stage for efficient use of neuroprotective agents that could slow down and alter the course of the disease.

Antipsychotic Drugs Alter Functional Connectivity between the Medial Frontal Cortex, Hippocampus, and Nucleus Accumbens as Measured by H215O PET

To evaluate changes in functional connectivity as a result of treatment with antipsychotic drugs (APDs) in subjects with schizophrenia (SZ), we identified a limited number of regions that have been implicated in the mechanism of action of APDs and that are part of a neuronal network known to be modulated by dopamine (DA). These regions consisted of the nucleus accumbens (NAcc), the hippocampus (Hip), and the medial frontal cortex (MFC). SZ participants were blindly randomized into a haloperidol treatment group (n = 12) and an olanzapine treatment group (n = 17). Using PET with 15O, we evaluated changes in functional connectivity between these regions during rest and task performance at three treatment time points: (1) at baseline, after withdrawal of all psychotropic medication (2 weeks), (2) after 1 week on medication, and (3) after 6 weeks on medication. Results from the two treatment groups were combined during analysis to investigate the common effects of APDs on functional connectivity. We found that the functional connectivity between MFC and NAcc significantly increased at week one, and then significantly decreased from week one to week 6. The functional connectivity between MFC and Hip significantly decreased at week one and week 6 relative to baseline. Critically, the strength of the functional connectivity between the MFC and Hip after 1 week of treatment was predictive of treatment response. This pattern of changes may represent an important biomarker for indexing treatment response. The regulation by APDs of the balance between prefrontal and limbic inputs to the striatum may be crucial to restoring adaptive behavior.

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.

GluR1 phosphorylation and persistent expression of levodopa-induced motor response alterations in the Hemi-Parkinsonian rat

The phosphorylation of glutamate receptor 1 (GluR1) has been increasingly implicated in the formation and maintenance of plastic responses. To investigate molecular mechanisms that underlie the persisting alterations in motor response occurring with levodopa treatment of parkinsonian patients, we evaluated the time course of these changes in relation to the phosphorylation of GluR1 in 6-hydroxydopamine (6-OHDA) lesioned animals. Three weeks of twice-daily levodopa administration to rats shortened the duration of the rotational responses and increased the peak turning responses, which lasted at least 7 days after withdrawal of chronic levodopa treatment. The shortened response duration and increased peak turning, resembling human wearing-off fluctuations and dyskinesia, were associated with a marked increase in Ser-845 phosphorylated GluR1 (pGluR1S845) immunoreactivity in lesioned striatum in response to levodopa treatment. The time course of changes in GluR1 phosphorylation correlated with the time course of changes in motor behavior after withdrawal of chronic levodopa therapy. Our immunostaining data showed that these changes were confined to parvalbumin-positive neurons where GluR1 are exclusively expressed. Both the altered motor response and the degree of pGluR1S845 were attenuated by the intrastriatal administration of protein kinase A (PKA) inhibitor Rp-cAMPS or GluR1 antisense oligonucleotides. The results suggest that Ser-845 GluR1 phosphorylation within parvalbumin-positive neurons contributes to the persistence of the motor response alterations produced by chronic intermittent dopaminergic stimulation.

Memantine for patients with Parkinson's disease dementia or dementia with Lewy bodies: a randomised, double-blind, placebo-controlled trial

BACKGROUND

Previous studies have suggested that patients with Lewy-body-related dementias might benefit from treatment with the N-methyl D-aspartate receptor antagonist memantine, but further data are needed. Therefore, the efficacy and safety of memantine were investigated in patients with mild to moderate Parkinson's disease dementia (PDD) or dementia with Lewy bodies (DLB).

METHODS

Patients (≥50 years of age) with mild to moderate PDD or DLB were recruited from 30 specialist centres in Austria, France, Germany, the UK, Greece, Italy, Spain, and Turkey. They were randomly assigned to placebo or memantine (20 mg per day) according to a computer-generated list. Patients and all physicians who had contact with them were masked to treatment assignment. No primary endpoint was defined. Safety analyses were done for all patients who took at least one dose of memantine or placebo, and efficacy analyses were done for all patients who had at least one valid postbaseline assessment. This trial is registered with ClinicalTrials.gov, number NCT00855686.

FINDINGS

Of the 199 patients randomly assigned to treatment, 34 with DLB and 62 with PDD were given memantine, and 41 with DLB and 58 with PDD were given placebo. 159 (80%) patients completed the study: 80 in the memantine group and 79 in the placebo group. 93 patients treated with memantine and 97 patients treated with placebo were included in the efficacy analysis. At week 24, patients with DLB who received memantine showed greater improvement according to Alzheimer's disease cooperative study (ADCS)-clinical global impression of change scores than did those who received placebo (mean change from baseline 3·3 vs 3·9, respectively, difference -0·6 [95% CI -1·2 to -0·1]; p=0·023). No significant differences were noted between the two treatments in patients with PDD (3·6 with memantine vs 3·8 with placebo, -0·1 [-0·6 to 0·3]; p=0·576) or in the total population (3·5 with memantine vs 3·8 with placebo, -0·3 [-0·7 to 0·1]; p=0·120). Neuropsychiatric-inventory scores showed significantly greater improvement in the memantine group than in the placebo group (-4·3 vs 1·7, respectively, -5·9 [-11·6 to -0·2]; p=0·041) in patients with DLB, but not in those with PDD (-1·6 vs -0·1, respectively, -1·4 [-5·9 to 3·0]; p=0·522) or in the total patient population (-2·6 vs 0·4, respectively, -2·9 [-6·3 to 0·5]; p=0·092). In most of the cognitive test scores, ADCS-activities of daily living, and Zarit caregiver burden scores, there were no significant differences between the two treatment groups in any of the study populations. The incidence of adverse events and number of discontinuations due to adverse events were similar in the two groups. The most common serious adverse events were stroke (n=3 in memantine group), falls (n=2 in memantine group; n=1 in placebo group), and worsening of dementia (n=2 in memantine group).

INTERPRETATION

Memantine seems to improve global clinical status and behavioural symptoms of patients with mild to moderate DLB, and might be an option for treatment of these patients.

FUNDING

Lundbeck.

Modulation of limbic circuitry predicts treatment response to antipsychotic medication: a functional imaging study in schizophrenia

The regional neuronal changes taking place in the early and late stages of antipsychotic treatment are still not well characterized in humans. In addition, it is not known whether these regional changes are predictive of or are correlated with treatment response. Using PET with 15O, we evaluated the time course of regional cerebral blood flow (rCBF) patterns generated by a first (haloperidol) and a second (olanzapine) generation antipsychotic drug in patients with schizophrenia during a 6-week treatment trial. Patients were initially scanned after withdrawal of all psychotropic medication (2 weeks), and then blindly randomized to treatment with haloperidol (n=12) or olanzapine (n=17) for a period of 6 weeks. Patients were scanned again after 1 and 6 weeks of treatment. All assessments, including scanning sessions, were obtained in a double-blind manner. As hypothesized, we observed rCBF changes that were common to both the drugs, implicating cortico-subcortical and limbic neuronal networks in antipsychotic action. In addition, in these regions, some patterns seen at weeks 1 and 6 were distinctive, indexing neuronal changes related to an early (ventral striatum, hippocampus) and consolidated (anterior cingulate/medial frontal cortex) stage of drug response. Finally, both after 1 and 6 weeks of treatment, we observed differential patterns of rCBF activation between good and poor responders. After 1 week of treatment, greater rCBF increase in the ventral striatum and greater decrease in the hippocampus were associated with good response.

Neurobiology of dopamine in schizophrenia

This chapter is an update on the dopamine (DA) imbalance in schizophrenia, including the evidence for subcortical hyperstimulation of D2 receptors underlying positive symptoms and cortical hypodopaminergia-mediating cognitive disturbances and negative symptoms. After a brief review of the anatomical neurocircuitry of this transmitter system as a background, we summarize the evidence for dopaminergic alterations deriving from pharmacological, postmortem, and imaging studies. This evidence supports a prominent role for D2 antagonism in the treatment of positive symptoms of schizophrenia and strongly suggests the need for alternative approaches to address the more challenging problem of negative symptoms and cognitive disturbances.

Differential synaptic plasticity of the corticostriatal and thalamostriatal systems in an MPTP-treated monkey model of parkinsonism

Two cardinal features of Parkinson's disease (PD) pathophysiology are a loss of glutamatergic synapses paradoxically accompanied by an increased glutamatergic transmission to the striatum. The exact substrate of this increased glutamatergic drive remains unclear. The striatum receives glutamatergic inputs from the thalamus and the cerebral cortex. Using vesicular glutamate transporters (vGluTs) 1 and 2 as markers of the corticostriatal and thalamostriatal afferents, respectively, we examined changes in the synaptology and relative prevalence of striatal glutamatergic inputs in methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys using electron microscopic immunoperoxidase and confocal immunofluorescence methods. Our findings demonstrate that the prevalence of vGluT1-containing terminals is significantly increased in the striatum of MPTP-treated monkeys (51.9 +/- 3.5% to 66.5 +/- 3.4% total glutamatergic boutons), without any significant change in the pattern of synaptic connectivity; more than 95% of vGluT1-immunolabeled terminals formed axo-spinous synapses in both conditions. In contrast, the prevalence of vGluT2-immunoreactive terminals did not change after MPTP treatment (21.7 +/- 1.3% vs. 21.6 +/- 1.2% total glutamatergic boutons). However, a substantial increase in the ratio of axo-spinous to axo-dendritic synapses formed by vGluT2-immunoreactive terminals was found in the pre-caudate and post-putamen striatal regions of MPTP-treated monkeys, suggesting a certain degree of synaptic reorganization of the thalamostriatal system in parkinsonism. About 20% of putative glutamatergic terminals did not show immunoreactivity in striatal tissue immunostained for both vGluT1 and vGluT2, suggesting the expression of another vGluT in these boutons. These findings provide striking evidence that suggests a differential degree of plasticity of the corticostriatal and thalamostriatal system in PD.

Polymorphisms in human dopamine D2 receptor gene affect gene expression, splicing, and neuronal activity during working memory

Subcortical dopamine D2 receptor (DRD2) signaling is implicated in cognitive processes and brain disorders, but the effect of DRD2 variants remains ambiguous. We measured allelic mRNA expression in postmortem human striatum and prefrontal cortex and then performed single nucleotide polymorphism (SNP) scans of the DRD2 locus. A previously uncharacterized promoter SNP (rs12364283) located in a conserved suppressor region was associated with enhanced DRD2 expression, whereas previously studied DRD2 variants failed to affect expression. Moreover, two frequent intronic SNPs (rs2283265 and rs1076560) decreased expression of DRD2 short splice variant (expressed mainly presynaptically) relative to DRD2 long (postsynaptic), a finding reproduced in vitro by using minigene constructs. Being in strong linkage disequilibrium with each other, both intronic SNPs (but not rs12364283) were also associated with greater activity of striatum and prefrontal cortex measured with fMRI during working memory and with reduced performance in working memory and attentional control tasks in healthy humans. Our results identify regulatory DRD2 polymorphisms that modify mRNA expression and splicing and working memory pathways.

Differential desensitization of dopamine D2 receptor isoforms by protein kinase C: The importance of receptor phosphorylation and pseudosubstrate sites

Altered regulation of dopamine D(2) receptors is implicated in addiction, schizophrenia and movement disorders, as well as lactotroph growth and regulation. Dopamine D(2S) and dopamine D(2L) receptors are alternately-spliced variants that differ by 29 amino acids in the third intracellular (i3) domain and display different sensitivity to desensitization by protein kinase C (PKC). In the present studies we determined the specific phosphorylation sites on the dopamine D(2S) receptor that confer PKC-mediated desensitization. In dopamine D(2L) receptors, we identified a PKC pseudosubstrate site responsible for the relative insensitivity of the receptor to PKC-induced uncoupling. In transiently transfected Ltk(-) fibroblast cells, 2-min preactivation of PKC with 12-O-tetradecanoyl 4beta-phorbol 13alpha-acetate (TPA) completely inhibited calcium mobilization induced by the dopamine D(2S) receptor, but not the dopamine D(2L) variant. Point mutation of i3 PKC sites Ser228/229Gly rendered the dopamine D(2S) receptor resistant to PKC action, with lesser effects of other Ser and Thr mutations. Inactivation of the PKC pseudosubstrate motif in the dopamine D(2L) receptor sensitized the receptor to PKC, and this was reversed by mutation of i3 PKC sites Ser228/229. A phospho-specific antibody generated against phospho-Ser228/229 demonstrated PKC-induced phosphorylation at these sites of dopamine D(2S), but not D(2L) receptors, in Ltk(-) cells. Conversely, the pseudosubstrate dopamine D(2L) receptor mutant displayed PKC-induced phosphorylation at Ser228/229, which was abolished when these sites were mutated. Similar phosphorylation results were observed using GH4 cells stably transfected with dopamine D(2) receptors and mutants. Thus the relative location of phosphorylation and pseudosubstrate sites provides an important determinant substrate sensitivity to PKC.

Glutamate and schizophrenia: phencyclidine, N-methyl-D-aspartate receptors, and dopamine-glutamate interactions

Schizophrenia is a serious mental disorder that affects up to 1% of the population worldwide. As of yet, neurochemical mechanisms underlying schizophrenia remain unknown. To date, the most widely considered neurochemical hypothesis of schizophrenia is the dopamine hypothesis, which postulates that symptoms of schizophrenia may result from excess dopaminergic neurotransmission particularly in striatal brain regions, along with dopaminergic deficits in prefrontal brain regions. Alternative neurochemical models of schizophrenia, however, have been proposed involving glutamatergic mechanisms in general and N-methyl-D-aspartate (NMDA) receptors in particular. A potential role for glutamatergic mechanisms in schizophrenia was first proposed approximately 15 years ago based on the observation that the psychotomimetic agents phencyclidine (PCP) and ketamine induce psychotic symptoms and neurocognitive disturbances similar to those of schizophrenia by blocking neurotransmission at NMDA-type glutamate receptors. Since that time, significant additional evidence has accumulated supporting a role for NMDA hypofunction in the pathophysiology of schizophrenia. Clinical challenge studies with PCP and ketamine have confirmed the close resemblance between NMDA antagonist-induced symptoms and neurocognitive deficits and those observed in schizophrenia, and suggest that NMDA dysfunction may lead to secondary dopaminergic dysregulation in striatal and prefrontal brain regions. As compared to dopaminergic agents, NMDA antagonists induce negative and cognitive symptoms of schizophrenia, as well as positive symptoms. Treatment studies with NMDA modulators, such as glycine, d-serine, and glycine transport inhibitors (GTIs), have yielded encouraging findings, although results remain controversial. Finally, genetic linkage and in vivo neurochemical studies in schizophrenia highlight potential etiological mechanisms giving rise to glutamatergic/NMDA dysfunction in schizophrenia.

Changes in subcellular distribution and phosphorylation of GluR1 in lesioned striatum of 6-hydroxydopamine-lesioned and l-dopa-treated rats

Recent evidence has linked striatal amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor function to the adverse effects of long-term dopaminergic treatment in Parkinson's disease. The phosphorylation of AMPA subunit, GluR1, reflects AMPA receptor activity. To determine whether serine phosphorylation of GluR1 subunit by activation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) contributes to the process, we examined the effects of unilateral nigrostriatal depletion with 6-hydroxydopamine and subsequent L: -dopa treatment on motor responses and phosphorylation states. Three weeks of L: -dopa administration to rats shortened the duration of the rotational response. We found a significant reduction in the abundance of both phosphorylated GluR1 at serine-831 site (pGluR1S831) and GluR1 in the cell plasma membrane of lesioned striatum. Chronic treatment of lesioned rats with L: -dopa markedly upregulated the phosphorylation of GluR1 in lesioned striatum with a concomitant normalization of the plasma membrane GluR1 abundance, which lasted at least 1 day after withdrawal of chronic L: -dopa treatment. Our immunostaining data showed that these changes were confined to parvalbumin-positive neurons where GluR1 subunits are exclusively expressed. Both the altered motor response duration and the degree of pGluR1S831 were attenuated by the intrastriatal administration of CaMKII inhibitor KN-93. These findings suggest that activation of CaMKII contributes to both development and maintenance of motor response duration alterations, through a mechanism that involves an increase in pGluR1S831 within parvalbumin-positive neurons.

Tandospirone, a 5-HT1A agonist, ameliorates movement disorder via non-dopaminergic systems in rats with unilateral 6-hydroxydopamine-generated lesions

Serotonin 1A (5-HT1A) receptors are distributed throughout the brain with their highest concentrations in the frontal cortex, subthalamic nucleus and entopeduncular nucleus as well as the dorsal and median raphe nucleus. There is growing evidence that 5-HT1A receptor agonists have an antidepressant effect in individuals with major depressive disorders. Recent clinical studies suggest that tandospirone, a highly potent and selective 5-HT1A receptor agonist used clinically as an antidepressant in Japan and China, may act as an antiparkinsonian drug. In the present study, we investigated the effect of tandospirone on contralateral rotational behavior in a unilateral hemiparkinsonian rat model produced with 6-hydroxydopamine (6-OHDA). Tandospirone, as well as 8-hydroxy-2-(di-n-propylamino) tetralin (8-OHDPAT), significantly increased contralateral turnings in a dose-dependent manner (0.5-10 mg/kg). Tandospirone also remarkably potentiated the contralateral turning induced by 0.025 mg/kg of apomorphine. Pretreatment with WAY-100635, a 5-HT1A receptor antagonist, almost completely blocked the contralateral turning behavior evoked by tandospirone and 8-OHDPAT, but not that by apomorphine. SCH-23390, a selective dopamine D1 receptor antagonist, did not affect on the tandospirone-induced rotational behavior. These results suggested that tandospirone could act on postsynaptic 5-HT1A receptors and modulate excitatory amino acid pathways in the basal ganglia. Thus, tandospirone could have therapeutic potential for the treatment of Parkinson's disease by modulating neuronal activities of non-dopaminergic pathways.

Chronic high-frequency stimulation of the subthalamic nucleus and L-DOPA treatment in experimental parkinsonism: effects on motor behaviour and striatal glutamate transmission

Hyperactivity of striatal glutamatergic synaptic transmission in response to dopamine depletion plays a major role in the pathogenesis of parkinsonian motor symptoms. In the present study we investigated the impact, on this hyperactivity, of chronic dyskinesiogenic L-DOPA treatment, combined or not with high-frequency stimulation (HFS) of the subthalamic nucleus (STN). In vitro patch-clamp recordings were performed from striatal spiny neurons of hemiparkinsonian rats (intranigral 6-OHDA injection). Here we show that dyskinesiogenic L-DOPA treatment exacerbated striatal glutamatergic hyperactivity induced by 6-OHDA lesion. Chronic 5-day STN HFS had the opposite effect, reducing striatal glutamatergic transmission in both parkinsonian and dyskinetic animals. Consistently, chronic HFS stimulation could progressively ameliorate motor parkinsonian signs (akinesia) but, conversely, did not improve L-DOPA-induced dyskinesia (LID). Thus, the effects of L-DOPA and HFS on corticostriatal transmission seem to be dissociated. These data show for the first time that dyskinesiogenic L-DOPA treatment and chronic STN HFS with antiakinetic effects induce opposite plastic rearrangements in the striatum. The interaction between these two treatments provides further evidence that striatal glutamatergic hyperactivity is a pathophysiological correlate of akinesia rather than LID.

Localization and function of pre- and postsynaptic kainate receptors in the rat globus pallidus

Kainate receptors (KARs) are widely expressed the basal ganglia. In this study, we used electron microscopic immunocytochemistry and whole-cell recording techniques to examine the localization and function of KARs in the rat globus pallidus (GP). Dendrites were the most common immunoreactive elements, while terminals forming symmetric or asymmetric synapses and unmyelinated axons comprised most of the presynaptic labeling. To determine whether synaptically released glutamate activates KARs, we recorded excitatory postsynaptic currents (EPSCs) in the GP following single-pulse stimulation of the internal capsule. 4-(8-Methyl-9H-1,3-dioxolo[4,5 h]{2,3}benzodiazepine-5-yl)-benzenamine hydrochloride (GYKI 52466, 100 microm), an alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionic acid (AMPA) receptor antagonist, reduced but did not completely block evoked EPSCs. The remaining EPSC component was mediated through activation of KARs because it was abolished by 6-cyano-7-nitroquinoxaline-2, 3-dione (CNQX), an AMPA/KAR antagonist. The rise time (10-90%) and decay time constant (tau) for those EPSCs were longer than those of AMPA-mediated EPSCs recorded before GYKI 52466 application. KAR activation inhibited EPSCs. This inhibition was associated with a significant increase in paired-pulse facilitation ratio, suggesting a presynaptic action of KAR. KAR inhibition of EPSCs was blocked by the G-protein inhibitor, N-ethylmaleimide (NEM), or the protein kinase C (PKC) inhibitor calphostin C. Our results demonstrate that KAR activation has dual effects on glutamatergic transmission in the rat GP: (1) it mediates small-amplitude EPSCs; and (2) it reduces glutamatergic synaptic transmission through a presynaptic G-protein coupled, PKC-dependent, metabotropic mechanism. These findings provide evidence for the multifarious functions of KARs in regulating synaptic transmission, and open up the possibility for the development of pharmacotherapies to reduce the hyperactive subthalamofugal projection in Parkinson's disease.

Blockade of mGluR glutamate receptors in the subthalamic nucleus ameliorates motor asymmetry in an animal model of Parkinson's disease

It has been suggested that Group I metabotropic glutamate receptor antagonists could have potential therapeutic value in the treatment of Parkinson's disease. There is evidence that when given systemically, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a metabotropic glutamate receptor type 5 (mGluR5) antagonist, produces anti-parkinsonian effects in animal models, but the site of action has not been directly established. In the present study, we examined whether the subthalamic nucleus (STN) and its output structures may mediate such an effect using a unilateral rat model of Parkinson's disease. A battery of simple behavioral tests, reliably sensitive to dopamine depletion, was applied consecutively: (i) prior to surgery; (ii) 3 weeks following a unilateral 6-hydroxydopamine lesion of the substantia nigra pars compacta; (iii) at 1 h, 24 h and 4 days following a microinjection of MPEP, via an indwelling cannula, into the STN, entopeduncular nucleus (EP) or substantia nigra zona reticulata. Unilaterally dopamine-depleted animals typically had severe motor and sensorimotor asymmetries 3 weeks following surgery. Microinjection of 25 nmol MPEP into the STN of these animals significantly attenuated these asymmetries relative to vehicle. Further microinjections of lower doses (5 and 10 nmol) revealed a dose-response effect. Microinjection of MPEP into either the EP or substantia nigra zona reticulata was without effect. These data suggest that MPEP may act at the level of the STN to reduce glutamatergic overactivity and thereby induce anti-parkinsonian effects.

Different effects of 7-nitroindazole in reserpine-induced hypolocomotion in two strains of mice

There are a number of reasons for believing that nitric oxide participates in motor control in the striatum. Therefore, effects of neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI) were studied on the reserpine model of Parkinson's disease in Swiss and C57BL/6 mice using the open-field test. Mice received reserpine (1 mg/kg administered intraperitoneally). A significant hypolocomotion was observed 24 h and 48 h after reserpine injection. The treatment with 7-nitroindazole (25 mg/kg, administered intraperitoneally, 30 min after reserpine) attenuated reserpine-induced hypolocomotion 24 h and 48 h after the treatment in Swiss mice, but not completely in C57BL/6 mice. These results suggest that nitric oxide functions as an intercellular messenger in motor circuits in the brain. Moreover, our data suggests that the comparison of such mouse strains may provide information on genetic basis for strain differences in different sensitivity to these drugs.

Dyskinesias induced by subthalamotomy in Parkinson's disease are unresponsive to amantadine

BACKGROUND

Dyskinesias are a transient but severe complication of subthalamotomy in some patients.

PATIENTS AND METHODS

Three patients with Parkinson's disease undergoing bilateral micro-recording guided surgery of the subthalamic nucleus (STN) are described; deep brain stimulation (DBS) was used in one case, and subthalamotomy in the other two. Prior to surgery, levodopa induced dyskinesia had improved (< or = 50%) under treatment with amantadine (400 mg/day, po) in all three patients. The patient treated with DBS developed severe dyskinesia a few days after discharge and began self medication with amantadine but showed no improvement. This suggested a possible lack of response to amantadine for treatment of dyskinesias induced by surgery of the STN.

RESULTS

Both patients treated with bilateral subthalamotomy developed unilateral choreoballistic movements immediately after surgery, despite not taking levodopa (L-dopa). Patients were scored using the dyskinesia scale and started treatment with 400 mg amantadine (po) for 4 days within the first postoperative week with no effect on dyskinesia score or its phenomenology. Amantadine was therefore discontinued. One month after surgery both patients were free of involuntary movements with an improvement of about 60% in the "off" state UPDRS motor score. Six month follow up showed maintained antiparkinsonian benefit, without need for levodopa treatment and complete absence of dyskinesia.

CONCLUSION

The present findings suggest that: (i) amantadine probably exerts its anti-dyskinetic effect by acting on the "indirect" pathway; (ii) the pathophysiological mechanisms of subthalamotomy induced dyskinesias may differ from those involved in L-dopa induced dyskinesias; (iii) dyskinesias induced by STN surgery resolve spontaneously as compensatory mechanisms develop.

Selective deficits in the expression of striatal-enriched mRNAs in Huntington's disease

We have identified and cataloged 54 genes that exhibit predominant expression in the striatum. Our hypothesis is that such mRNA molecules are likely to encode proteins that are preferentially associated with particular physiological processes intrinsic to striatal neurons, and therefore might contribute to the regional specificity of neurodegeneration observed in striatal disorders such as Huntington's disease (HD). Expression of these genes was measured simultaneously in the striatum of HD R6/1 transgenic mice using Affymetrix oligonucleotide arrays. We found a decrease in expression of 81% of striatum-enriched genes in HD transgenic mice. Changes in expression of genes associated with G-protein signaling and calcium homeostasis were highlighted. The most striking decrement was observed for a newly identified subunit of the sodium channel, beta 4, with dramatic decreases in expression beginning at 8 weeks of age. A subset of striatal genes was tested by real-time PCR in caudate samples from human HD patients. Similar alterations in expression were observed in human HD and the R6/1 model for the striatal genes tested. Expression of 15 of the striatum-enriched genes was measured in 6-hydroxydopamine-lesioned rats to determine their dependence on dopamine innervation. No changes in expression were observed for any of these genes. These findings demonstrate that mutant huntingtin protein causes selective deficits in the expression of mRNAs responsible for striatum-specific physiology and these may contribute to the regional specificity of degeneration observed in HD.

Changes in gait and symptoms after bilateral pallidotomy: a client with Parkinson's disease

A single-subject, time-series design was used to describe a female with young-onset Parkinson's disease who, after a period of 15 years, was demonstrating long term side effects of medication in addition to the progression of Parkinson's disease. She underwent a bilateral pallidotomy to address these problems. Prior to her surgery, her spatiotemporal gait kinematics were measured at intervals before and after medication ingestion. The identical procedures were undertaken one month and at four months post-pallidotomy. In all three sessions, the Webster Scale scored her symptoms while her medication was not working (Off) and again when effective (On). After surgery, she was interviewed to obtain a qualitative impression of the outcome. Before the surgery, the gait parameters demonstrated a fluctuating profile. Forty-five minutes post-medication, her gait parameters approached normal levels but significant dyskinetic movements were evident. Her Webster Scale scores indicated advanced Parkinson's disease particularly when Off One-month post-pallidotomy, her gait parameters were more consistent with dyskinesias mildly present. Her Webster Scale scores were reduced while both Off and On. Four months post-pallidotomy her gait parameters were entirely consistent and within normal limits. Her Webster Scale scores were the same Off and On and no dyskinesias were detectable. The excellent result was probably enhanced by the patient's dedication to regular exercise designed to minimize secondary physical complications.

Effect of kynurenine 3-hydroxylase inhibition on the dyskinetic and antiparkinsonian responses to levodopa in Parkinsonian monkeys

Homeostatic interactions between dopamine and glutamate are central to the normal physiology of the basal ganglia. This relationship is altered in Parkinsonism and in levodopa-induced dyskinesias (LID), resulting in an upregulation of corticostriatal glutamatergic function. Kynurenic acid (KYNA), a tryptophan metabolite with antagonist activity at ionotropic glutamate receptors and the capability to inhibit glutamate release presynaptically, might therefore be of therapeutic value in LID. To evaluate this hypothesis, we used a pharmacological tool, the kynurenine 3-hydroxylase inhibitor Ro 61-8048, which raises KYNA levels acutely. Ro 61-8048 was tested in MPTP cynomolgus monkeys with a stable parkinsonian syndrome and reproducible dyskinesias after each dose of levodopa. Serum and CSF concentrations of KYNA and its precursor kynurenine increased dose-dependently after Ro 61-8048 administration, alone or in combination with levodopa. Coadministration of Ro 61-8048 with levodopa produced a moderate but significant reduction in the severity of dyskinesias while maintaining the motor benefit. These results suggest that elevation of KYNA levels through inhibition of kynurenine 3-hydroxylase constitutes a promising novel approach for managing LID in Parkinson's disease.

Mechanism of action of antipsychotic drugs: from dopamine D(2) receptor antagonism to glutamate NMDA facilitation

BACKGROUND

The fundamental pathologic processes associated with schizophrenia remain uncertain.

OBJECTIVE

The goal of this article was to review imaging evidence suggesting that schizophrenia is associated with excessive stimulation of D(2) receptors, as well as imaging experiments supporting the hypothesis that this dysregulation might be secondary to N- methyl-d-aspartate (NMDA) dysfunction.

CONCLUSIONS

Recent imaging data support the association of schizophrenia with a dopamine endophenotype involving excessive subcortical dopamine function. Animal and imaging data are consistent with the idea that this abnormality might be secondary to a synaptic disconnectivity involving the prefrontal cortex, which is well modeled by NMDA antagonist administration. In turn, this dopamine dysregulation might worsen synaptic connectivity and NMDA function. Thus, both glutamate/dopamine and dopamine/glutamate interactions may be relevant to schizophrenia pathophysiology and treatment. A deficit in glutamate transmission may lead to the dopamine endophenotype associated with this illness, and dopamine alterations in turn might exacerbate glutamate transmission deficits. The view that NMDA alterations are primary and dopamine alterations are secondary is probably oversimplistic, as both sets of abnormalities reinforce each other. A consequence of this general model is that direct intervention to support NMDA function might be beneficial as an augmentation strategy for the treatment of schizophrenia. Thus, it is proposed that schizophrenia is associated with strongly interconnected abnormalities of glutamate and dopamine transmission: NMDA hypofunction in the prefrontal cortex and its connections might generate a pattern of dysregulation of dopamine systems that, in turn, further weakens NMDA-mediated connectivity and plasticity.