Nigrostriatal Dopamine Loss Research Articles

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 4weeks 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.

Nasal application of kisspeptin-54 mitigates motor deficits by reducing nigrostriatal dopamine loss in hemiparkinsonian rats

Parkinson’s Disease is a progressive neurodegenerative disorder characterized by motor symptoms resulting from the loss of nigrostriatal dopaminergic neurons. Kisspeptins (KPs) are a family of neuropeptides that are encoded by the Kiss-1 gene, which exert their physiological effects through interaction with the GPR54 receptor. In the current investigation, we investigated the prospective protective effects of central KP-54 treatments on nigrostriatal dopaminergic neurons and consequent motor performance correlates in 6-hydroxydopamine (6-OHDA)-lesioned rats. Male adult Sprague Dawley rats underwent stereotaxic injection of 6-OHDA into the right medial forebrain bundle to induce hemiparkinsonism. Following surgery, rats received chronic central treatments of nasal or intracerebroventricular KP-54 (logarithmically increasing doses) for seven consecutive days. Motor performance was evaluated seven days post-surgery utilizing the open field test and catalepsy test. The levels of dopamine in the striatum were determined with mass spectrometry. Immunohistochemical analysis was conducted to assess the immunoreactivities of tyrosine hydroxylase (TH) and the GPR54 in the substantia nigra. The dose-response curve revealed a median effective dose value of ≈3 nmol/kg for both central injections. Due to its non-invasive and effective nature, nasal administration was utilized in the second phase of our study. Chronic administration of KP-54 (3nmol/kg, nasally) significantly protected 6-OHDA-induced motor deficits. Nasal KP-54 attenuated the loss of nigrostriatal dopaminergic neurons induced by 6-OHDA. Additionally, significant correlations were observed between motor performance and nigrostriatal dopamine levels. Immunohistochemical analysis demonstrated the localization of the GPR54 within TH-positive nigral cells. These findings suggest the potential efficacy of central KP-54 on motor impairments in hemiparkinsonism.

Alpha-synuclein inclusion responsive microglia are resistant to CSF1R inhibition

BackgroundParkinson’s disease (PD) is a neurodegenerative disorder that is characterized by the presence of proteinaceous alpha-synuclein (α-syn) inclusions (Lewy bodies), markers of neuroinflammation and the progressive loss of nigrostriatal dopamine (DA) neurons. These pathological features can be recapitulated in vivo using the α-syn preformed fibril (PFF) model of synucleinopathy. We have previously determined that microglia proximal to PFF-induced nigral α-syn inclusions increase in soma size, upregulate major-histocompatibility complex-II (MHC-II) expression, and increase expression of a suite of inflammation-associated transcripts. This microglial response is observed months prior to degeneration, suggesting that microglia reacting to α-syn inclusion may contribute to neurodegeneration and could represent a potential target for novel therapeutics. The goal of this study was to determine whether colony stimulating factor-1 receptor (CSF1R)-mediated microglial depletion impacts the magnitude of α-syn aggregation, nigrostriatal degeneration, or the response of microglial in the context of the α-syn PFF model.MethodsMale Fischer 344 rats were injected intrastriatally with either α-syn PFFs or saline. Rats were continuously administered Pexidartinib (PLX3397B, 600 mg/kg), a CSF1R inhibitor, to deplete microglia for a period of either 2 or 6 months.ResultsCSF1R inhibition resulted in significant depletion (~ 43%) of ionized calcium-binding adapter molecule 1 immunoreactive (Iba-1ir) microglia within the SNpc. However, CSF1R inhibition did not impact the increase in microglial number, soma size, number of MHC-II immunoreactive microglia or microglial expression of Cd74, Cxcl10, Rt-1a2, Grn, Csf1r, Tyrobp, and Fcer1g associated with phosphorylated α-syn (pSyn) nigral inclusions. Further, accumulation of pSyn and degeneration of nigral neurons was not impacted by CSF1R inhibition. Paradoxically, long term CSF1R inhibition resulted in increased soma size of remaining Iba-1ir microglia in both control and PFF rats, as well as expression of MHC-II in extranigral regions.ConclusionsCollectively, our results suggest that CSF1R inhibition does not impact the microglial response to nigral pSyn inclusions and that CSF1R inhibition is not a viable disease-modifying strategy for PD.

Feasibility of combining alpha-synuclein aggregation and 6-OHDA in embryonic midbrain culture for modeling dopamine neuron degeneration

Parkinson’s disease (PD) is characterized by the loss of nigrostriatal dopamine (DA) neurons and the presence of alpha-synuclein (αSyn)-positive Lewy body (LB) pathology. In this study, we attempted to recapitulate both these features in a novel in vitro model for PD. To achieve this, we combined the αSyn pre-formed fibril (PFF)-seeded LB-like pathology with 6-hydroxydopamine (6-OHDA)-induced mitochondrial toxicity in mouse embryonic midbrain cultures. To pilot the model for therapeutics testing, we assessed the effects of cerebral dopamine neurotrophic factor (CDNF) on αSyn aggregation and neuron survival. PFF-seeded pathology did not lead to DA neuron loss even with the highest dose of PFFs. The combination of PFFs and 6-OHDA did not trigger additional neurodegeneration or LB–like pathology and instead presented DA neuron loss to a similar extent as with 6-OHDA only. CDNF did not affect the PFF-seeded αSyn pathology or the DA neuron survival in the combination model but showed a trend toward neuroprotection in the 6-OHDA-only cultures.

Recovery of motor function is associated with rescue of glutamate biomarkers in the striatum and motor cortex following treatment with Mucuna pruriens in a murine model of Parkinsons disease

There is growing interest in the use of natural products for the treatment of Parkinson's disease (PD). Mucuna pruriens has been used in the treatment of humans with PD. The goal of this study was to determine if daily oral treatment with an extract of Mucuna pruriens, starting after the MPTP-induced loss of nigrostriatal dopamine in male mice, would result in recovery/restoration of motor function, tyrosine hydroxylase (TH) protein expression in the nigrostriatal pathway, or glutamate biomarkers in both the striatum and motor cortex. Following MPTP administration, resulting in an 80 % loss of striatal TH, treatment with Mucuna pruriens failed to rescue either striatal TH or the dopamine transporter back to the control levels, but there was restoration of gait/motor function. There was an MPTP-induced loss of TH-labeled neurons in the substantia nigra pars compacta and in the number of striatal dendritic spines, both of which failed to be recovered following treatment with Mucuna pruriens. This Mucuna pruriens-induced locomotor recovery following MPTP was associated with restoration of two striatal glutamate transporter proteins, GLAST (EAAT1) and EAAC1 (EAAT3), and the vesicular glutamate transporter 2 (Vglut2) within the motor cortex. Post-MPTP treatment with Mucuna pruriens, results in locomotor improvement that is associated with recovery of striatal and motor cortex glutamate transporters but is independent of nigrostriatal TH restoration.

Striatal serotonin transporter gain-of-function in L-DOPA-treated, hemi-parkinsonian rats

L-DOPA is the standard treatment for Parkinson’s disease (PD), but chronic treatment typically leads to L-DOPA-induced dyskinesia (LID). LID involves a complex interaction between the remaining dopamine (DA) system and the semi-homologous serotonin (5-HT) system. Since serotonin transporters (SERT) have some affinity for DA uptake, they may serve as a functional compensatory mechanism when DA transporters (DAT) are scant. DAT and SERT’s functional contributions in the dyskinetic brain have not been well delineated. The current investigation sought to determine how DA depletion and L-DOPA treatment affect DAT and SERT transcriptional processes, translational processes, and functional DA uptake in the 6-hydroxydopamine-lesioned hemi-parkinsonian rat. Rats were counterbalanced for motor impairment into equally lesioned treatment groups then given daily L-DOPA (0 or 6 mg/kg) for 2 weeks. At the end of treatment, the substantia nigra was processed for tyrosine hydroxylase (TH) and DAT gene expression and dorsal raphe was processed for SERT gene expression. The striatum was processed for synaptosomal DAT and SERT protein expression and ex vivo DA uptake. Nigrostriatal DA loss severely reduced DAT mRNA and protein expression in the striatum with minimal changes in SERT. L-DOPA treatment, while not significantly affecting DAT or SERT alone, did increase striatal SERT:DAT protein ratios. Using ex vivo microdialysis, L-DOPA treatment increased DA uptake via SERT when DAT was depleted. Overall, these results suggest that DA loss and L-DOPA treatment uniquely alter DAT and SERT, revealing implications for monoamine transporters as potential biomarkers and therapeutic targets in the hemi-parkinsonian model and dyskinetic PD patients.

Broad Serotonergic Actions of Vortioxetine as a Promising Avenue for the Treatment of L-DOPA-Induced Dyskinesia.

Parkinson's Disease (PD) is a neurodegenerative disorder characterized by motor symptoms that result from loss of nigrostriatal dopamine (DA) cells. While L-DOPA provides symptom alleviation, its chronic use often results in the development of L-DOPA-induced dyskinesia (LID). Evidence suggests that neuroplasticity within the serotonin (5-HT) system contributes to LID onset, persistence, and severity. This has been supported by research showing 5-HT compounds targeting 5-HT1A/1B receptors and/or the 5-HT transporter (SERT) can reduce LID. Recently, vortioxetine, a multimodal 5-HT compound developed for depression, demonstrated acute anti-dyskinetic effects. However, the durability and underlying pharmacology of vortioxetine's anti-dyskinetic actions have yet to be delineated. To address these gaps, we used hemiparkinsonian rats in Experiment 1, examining the effects of sub-chronic vortioxetine on established LID and motor performance. In Experiment 2, we applied the 5-HT1A antagonist WAY-100635 or 5-HT1B antagonist SB-224289 in conjunction with L-DOPA and vortioxetine to determine the contributions of each receptor to vortioxetine's effects. The results revealed that vortioxetine consistently and dose-dependently attenuated LID while independently, 5-HT1A and 5-HT1B receptors each partially reversed vortioxetine's effects. Such findings further support the promise of pharmacological strategies, such as vortioxetine, and indicate that broad 5-HT actions may provide durable responses without significant side effects.

Adaptive structural changes in the motor cortex and white matter in Parkinson’s disease

Parkinson’s disease (PD) is a movement disorder characterized by the early loss of nigrostriatal dopaminergic pathways producing significant network changes impacting motor coordination. Recently three motor stages of PD have been proposed (a silent period when nigrostriatal loss begins, a prodromal motor period with subtle focal manifestations, and clinical PD) with evidence that motor cortex abnormalities occur to produce clinical PD[8]. We directly assess structural changes in the primary motor cortex and corticospinal tract using parallel analyses of longitudinal clinical and cross-sectional pathological cohorts thought to represent different stages of PD. 18F-FP-CIT positron emission tomography and subtle motor features identified patients with idiopathic rapid-eye-movement sleep behaviour disorder (n = 8) that developed prodromal motor signs of PD. Longitudinal diffusion tensor imaging before and after the development of prodromal motor PD showed higher fractional anisotropy in motor cortex and corticospinal tract compared to controls, indicating adaptive structural changes in motor networks in concert with nigrostriatal dopamine loss. Histological analyses of the white matter underlying the motor cortex showed progressive disorientation of axons with segmental replacement of neurofilaments with α-synuclein, enlargement of myelinating oligodendrocytes and increased density of their precursors. There was no loss of neurons in the motor cortex in early or late pathologically confirmed motor PD compared to controls, although there were early cortical increases in neuronal neurofilament light chain and myelin proteins in association with α-synuclein accumulation. Our results collectively provide evidence of a direct impact of PD on primary motor cortex and its output pathways that begins in the prodromal motor stage of PD with structural changes confirmed in early PD. These adaptive structural changes become considerable as the disease advances potentially contributing to motor PD.

The multimodal serotonin compound Vilazodone alone, but not combined with the glutamate antagonist Amantadine, reduces l-DOPA-induced dyskinesia in hemiparkinsonian rats

Parkinson's disease (PD) is a progressive, neurodegenerative movement disorder caused by loss of nigrostriatal dopamine (DA) neurons. DA replacement therapy using L-3,4-dihydroxyphenylalanine (l-DOPA) improves motor function but often results in l-DOPA-induced dyskinesia (LID) typified by abnormal involuntary movements (AIMs). In states of DA depletion, striatal serotonin (5-HT) hyperinnervation and glutamate overactivity are implicated in LID. To target these co-mechanisms, this study investigated the potential anti-dyskinetic effects of FDA-approved Vilazodone (VZD), a 5-HT transport blocker and partial 5-HT1A agonist, and Amantadine (AMAT), a purported NMDA glutamate antagonist, in 6-hydroxydopamine-lesioned hemiparkinsonian Sprague-Dawley rats. Dose-response curves for each drug against l-DOPA-induced AIMs were determined to identify effective threshold doses. A second cohort of rats was tested using the threshold doses of VZD (1, 2.5 mg/kg, s.c.) and/or AMAT (40 mg/kg, s.c.) to examine their combined, acute effects on LID. In a third cohort, VZD and/or AMAT were administered daily with l-DOPA for 14 days to determine prophylactic effects on LID development. In a final cohort, rats with established LID received VZD and/or AMAT injections for 2 weeks to examine their interventional properties. Throughout experiments, AIMs were rated for dyskinesia severity and forepaw adjusting steps (FAS) were monitored l-DOPA motor efficacy. Results revealed that acute and chronic VZD + l-DOPA treatment significantly decreased AIMs and maintained FAS compared to l-DOPA alone. AMAT + l-DOPA co-administration did not exert any significant effects on AIMs or FAS, while the co-administration of VZD and AMAT with l-DOPA demonstrated intermediate effects. These results suggest that co-administration of low-dose VZD and AMAT with l-DOPA does not synergistically reduce LID in hemiparkinsonian rats. Importantly, low doses of VZD (2.5, 5 mg/kg) did reduce the development and expression of LID while maintaining l-DOPA efficacy, supporting its potential therapeutic utility for PD patients.

Low-dose oral pyrethroid exposure induces gastrointestinal dysfunction and alters nigrostriatal dopamine signaling pathways in mice

BACKGROUND AND AIM: Insecticide exposure is associated with greater risk for developing Parkinson’s disease (PD). PD is characterized by motor impairments due to loss of nigrostriatal dopamine (DA) neurons in the midbrain, and patients commonly experience gastrointestinal (GI) dysfunction long before the onset of motor symptoms. Pyrethroids, synthetic insecticides commonly used around the world, disrupt DA signaling pathways. One of the most common routes of pyrethroid exposure is ingestion, so it is plausible that oral exposure acts locally within the GI tract and facilitates PD pathogenesis via the gut-brain axis. Here, we sought to determine the functional and molecular consequences of oral pyrethroid exposure in the adult mouse gut and brain in the context of idiopathic PD. METHODS: Adult mice were orally gavaged with 3 mg/kg deltamethrin weekly for 3 weeks. Intestinal behaviors were assessed to determine constipation phenotypes. Gut microbiome composition was determined by 16S rRNA sequencing. Intestinal and brain tissues were collected following the final dose to assess changes in gene expression and protein production pathways related to DA and other monoamine signaling, as determined by qPCR and western blot. RESULTS:Oral deltamethrin exposure significantly impaired GI function compared to vehicle controls. We observed reduced fecal output, changed gene and protein levels important for normal gut function, and altered gut microbial composition in deltamethrin-exposed mice, all of which are reflective of changes observed in PD patients. In the brain, oral deltamethrin exposure significantly altered production of proteins important for DA synthesis and reuptake compared to controls. CONCLUSIONS:Low-dose oral pyrethroid exposure induces GI dysfunction and alters DA pathways in the brain. These findings support the idea that pyrethroids induce functional and molecular changes relevant to PD pathology from within the gut, and further investigation is warranted to fully understand this phenomenon as a potential trigger in the etiology of PD. KEYWORDS: Pesticides, Chemical exposures, Neurodegenerative outcomes, Microbes/Microbiome

Effects of statins on dopamine loss and prognosis in Parkinson's disease.

Statins are more widely used not only for the primary and secondary prevention of cardiovascular disease by blocking cholesterol biosynthesis but also for the potential neuroprotective agents during neurological disorders due to their pleiotropic effects. In this study, we investigate whether the previous use of statins affect baseline nigrostriatal dopamine loss at the time of diagnosis and longitudinal motor and cognitive outcomes in patients with Parkinson's disease. Five hundred drug-naïve patients with Parkinson's disease who underwent dopamine transporter imaging were classified into two groups according to the prior use of statins: patients with and without statin use. Multivariate linear regression was used to determine intergroup differences in dopamine transporter availability. We evaluated the longitudinal changes in levodopa-equivalent dose and dementia conversion between the groups using a linear mixed model and survival analysis, respectively. In addition, mediation analysis was applied to examine the effect of total cholesterol. Patients with Parkinson's disease treated with statins had a lower baseline dopamine transporter availability in the anterior (2.13 ± 0.55 versus 2.37 ± 0.67; P = 0.002), posterior (1.31 ± 0.43 versus 1.49 ± 0.54; P = 0.003) and ventral putamina (1.40 ± 0.39 versus 1.56 ± 0.47; P = 0.002) than that in matched patients with Parkinson's disease without statins. After adjusting for age at symptom onset, sex, disease duration and vascular risk factors, linear regression models showed that a previous treatment with statins remained significantly and independently associated with more severely decreased dopamine transporter availability in the anterior putamen (Beta = -0.140, P = 0.004), posterior putamen (Beta = -0.162, P = 0.001) and ventral putamen (Beta = -0.140, P = 0.004). A linear mixed model revealed that patients with Parkinson's disease being treated with statins had a faster longitudinal increase in levodopa-equivalent dose than those without. A survival analysis showed that the rate of dementia conversion was significantly higher in patients with Parkinson's disease with statins (hazard ratio, 2.019; 95% confidence interval, 1.108-3.678; P = 0.022) than those without. Mediation analyses revealed that the effect of statin treatment on baseline dopamine transporter availability and longitudinal outcome was not mediated by total cholesterol levels. This study suggests that statin use may have a detrimental effect on baseline nigrostriatal dopamine degeneration and long-term outcomes in patients with Parkinson's disease.

Differential ultrastructural alterations in the Vglut2 glutamatergic input to the substantia nigra pars compacta/pars reticulata following nigrostriatal dopamine loss in a progressive mouse model of Parkinson's disease.

Loss of nigrostriatal dopamine (DA) in Parkinson's disease results in over-activation/bursting of the subthalamic nucleus (STN). The STN projects to the substantia nigra (SN) pars compacta (SNpc) and pars reticulata (SNpr). The vesicular glutamate transporter 2 (Vglut2) is localized within at least STN terminals synapsing within the SN, but it is not known if there are differential changes in the Vglut2+ input to the SNpc versus SNpr following DA loss. The goal/rationale of this current study was to determine whether there were differential changes in the density/levels of glutamate immuno-gold labeling within Vglut2+ nerve terminals synapsing in the SNpc/SNpr and in the proportion of Vglut2+ terminals contacting tyrosine hydroxylase (TH) positively(+) or negatively(-) labeled dendrites following DA loss. Within the SNpc, there was a significant increase (51.3%) in the density of nerve terminal glutamate immuno-gold labeling within Vglut2+ terminals synapsing on TH(-) dendrites following MPTP versus the vehicle (VEH) group. There was a significant decrease (16%) in the percentage of Vglut2+ terminals contacting TH(+) labeled dendrites in the MPTP- versus VEH-treated group within the SNpc. Within the SNpr, there was a significant decrease in the density of glutamate immuno-gold labeling in Vglut2+ terminals contacting TH(+) (71.5%) and TH(-) (55.5%) labeled dendrites, suggesting an increase in glutamate release. There was no change in the percentage of Vglut2+ terminals contacting TH(+) or TH(-) dendrites in the SNpr. We conclude that there is a differential effect following DA loss on the glutamate input from Vglut2+ terminals synapsing within the SNpr versus SNpc.

Pharmacological targeting of β2 -adrenoceptors is neuroprotective in the LPS inflammatory rat model of Parkinson's disease.

Chronic inflammation may play a role in the pathogenesis of Parkinson's disease (PD). Noradrenaline is an endogenous neurotransmitter with anti-inflammatory properties. In the present investigation, we assessed the immunomodulatory and neuroprotective efficacy of pharmacologically targeting the CNS noradrenergic system in a rat model of PD. The impact of treatment with the β2 -adrenoceptor agonists clenbuterol and formoterol was assessed in the intranigral LPS rat model of PD. The immunomodulatory potential of formoterol to influence the CNS response to systemic inflammation was also assessed. LPS-induced deficits in motor function (akinesia and forelimb-use asymmetry) and nigrostriatal dopamine loss were rescued by both agents. Treatment with the noradrenaline reuptake inhibitor atomoxetine reduced striatal dopamine loss and motor deficits following intranigral LPS injection. Co-treatment with the β2 -adrenoceptor antagonist ICI 118,551 attenuated the protective effects of atomoxetine. Systemic LPS challenge exacerbated reactive microgliosis, IL-1β production, dopamine cell loss in the substantia nigra, nerve terminal degeneration in the striatum, and associated motor impairments in animals that previously received intranigral LPS. This exacerbation was attenuated by formoterol treatment. The results indicate that pharmacologically targeting β2 -adrenoceptors has the propensity to regulate the neuroinflammatory phenotype in vivo and may be a potential neuroprotective strategy where inflammation contributes to the progression of dopaminergic neurodegeneration. In accordance with this, clinical agents such as β2 -adrenoceptor agonists may prove useful as immunomodulatory agents in the treatment of neurodegenerative conditions associated with brain inflammation.

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.

Clinical, Dopaminergic, and Metabolic Correlations in Parkinson Disease: A Dual-Tracer PET Study.

Neuroimaging indicators of Parkinson disease have been developed and applied in clinical practices. Dopaminergic imaging reflects nigrostriatal dopaminergic dysfunction, and metabolic network imaging offers disease-related metabolic changes at a system level. We aimed to elucidate the association between Parkinsonian symptoms and neuroimaging, and interactions between different imaging techniques. We conducted a dual-tracer PET study for the combined assessments of dopaminergic binding (C-CFT) and glucose metabolism (F-FDG) in 103 participants with Parkinson disease (65 male and 38 female subjects). The detailed clinical rating scores were systematically collected in all members. The interactions among dopaminergic bindings, metabolic changes, and clinical manifestations were evaluated at voxel, regional, and network levels. Striatal DAT binding correlated with akinesia-rigidity (P < 0.001) but not with tremor; the metabolic PET imaging, nonspecific to the dopaminergic dysfunction, disclosed a set of brain regions correlating with the cardinal symptoms, including tremor. In addition, the unilateral symptom correlated with the contralateral nigrostriatal dopamine loss, but with bilateral metabolic changes, suggesting their differences in the application of disease-related mechanistic studies. Further imaging-imaging correlation study revealed that dopaminergic dysfunction correlated with widely distributed metabolic changes in Parkinson disease, and the modest correlations supported the findings on the clinical-imaging correlation. In this dual-tracer PET study, we demonstrated the robust interactions among dopaminergic dysfunction, metabolic brain changes and clinical manifestations at voxel, regional, and network levels. Our findings might promote the understanding in the proper application of dopaminergic and metabolic PET imaging in Parkinson disease and offer more evidence in support of Parkinsonian pathophysiological mechanisms.

Impaired finger dexterity and nigrostriatal dopamine loss in Parkinson's disease.

Impaired finger dexterity occurs in Parkinson's disease (PD) and has been considered a limb-kinetic apraxia associated with primary sensory cortical dysfunction. To study the role of nigrostriatal dopamine loss and elementary parkinsonian motor deficits in impaired finger dexterity of PD. Thirty-two right-handed untreated PD patients and 30 right-handed healthy controls were included. All patients underwent [18F] FP-CIT positron emission tomography studies. We examined the associations among unilateral coin rotation (CR) score, Unified Parkinson's Disease Rating Scale (UPDRS) subscores for bradykinesia and rigidity of the corresponding arm, and contralateral regional striatal dopamine transporter (DAT) uptake. We also measured the effect of oral levodopa dose on CR scores and UPDRS subscores. PD patients performed worse than controls on the CR task. Unilateral arm UPDRS bradykinesia scores were associated with DAT uptake in the contralateral putamen. The left CR score was associated with left arm bradykinesia and rigidity scores and DAT uptake in the right posterior putamen, whereas no such associations were found for the right CR score. There was a significant effect of handedness on the association of putamen DAT uptake with CR scores, but not with UPDRS subscores. An oral levodopa challenge improved CR scores and UPDRS subscores on both sides. Impaired finger dexterity in PD is related to elementary parkinsonian motor deficits and nigrostriatal dopamine loss. Impaired dominant hand dexterity associated with nigrostriatal dopamine loss seems to be compensated to some extent by the dominant cerebral cortex specialized for controlling precise finger movements.

Silencing Alpha Synuclein in Mature Nigral Neurons Results in Rapid Neuroinflammation and Subsequent Toxicity.

Human studies and preclinical models of Parkinson’s disease implicate the involvement of both the innate and adaptive immune systems in disease progression. Further, pro-inflammatory markers are highly enriched near neurons containing pathological forms of alpha synuclein (α-syn), and α-syn overexpression recapitulates neuroinflammatory changes in models of Parkinson’s disease. These data suggest that α-syn may initiate a pathological inflammatory response, however the mechanism by which α-syn initiates neuroinflammation is poorly understood. Silencing endogenous α-syn results in a similar pattern of nigral degeneration observed following α-syn overexpression. Here we aimed to test the hypothesis that loss of α-syn function within nigrostriatal neurons results in neuronal dysfunction, which subsequently stimulates neuroinflammation. Adeno-associated virus (AAV) expressing an short hairpin RNA (shRNA) targeting endogenous α-syn was unilaterally injected into the substantia nigra pars compacta (SNc) of adult rats, after which nigrostriatal pathology and indices of neuroinflammation were examined at 7, 10, 14 and 21 days post-surgery. Removing endogenous α-syn from nigrostriatal neurons resulted in a rapid up-regulation of the major histocompatibility complex class 1 (MHC-1) within transduced nigral neurons. Nigral MHC-1 expression occurred prior to any overt cell death and coincided with the recruitment of reactive microglia and T-cells to affected neurons. Following the induction of neuroinflammation, α-syn knockdown resulted in a 50% loss of nigrostriatal neurons in the SNc and a corresponding loss of nigrostriatal terminals and dopamine (DA) concentrations within the striatum. Expression of a control shRNA did not elicit any pathological changes. Silencing α-syn within glutamatergic neurons of the cerebellum did not elicit inflammation or cell death, suggesting that toxicity initiated by α-syn silencing is specific to DA neurons. These data provide evidence that loss of α-syn function within nigrostriatal neurons initiates a neuronal-mediated neuroinflammatory cascade, involving both the innate and adaptive immune systems, which ultimately results in the death of affected neurons.

Impaired finger dexterity and nigrostriatal dopamine loss in Parkinson’s disease

Objective: To study the role of nigrostriatal dopamine loss and elementary parkinsonian motor deficits in impaired finger dexterity of Parkinson’s disease (PD).

Abnormal somatosensory temporal discrimination in Parkinson’s disease: Pathophysiological correlates and role in motor control deficits

ObjectiveThe somatosensory temporal discrimination threshold (STDT), defined as the shortest time interval required for two tactile stimuli to be perceived as separate, is longer in patients with Parkinson’s disease (PD). In this review, we discuss STDT findings in healthy subjects and in PD patients and the relationship between altered STDT and motor disturbances. MethodsA search was conducted on PubMed for papers dealing with PD and temporal discrimination published from January 1990 to July 2017. ResultsAbnormal STDT in PD correlates with disease duration, disease severity and degree of nigrostriatal dopamine loss, and responds to dopaminergic medication. In PD, a prolonged STDT does not correlate, or only marginally correlates, with clinically assessed bradykinesia of finger tapping. By contrast, a prolonged STDT correlates with the variability in amplitude and speed of finger tapping as assessed by means of neurophysiological techniques and may contribute to impaired finger dexterity in PD. ConclusionsWe suggest that abnormal temporal processing of sensory information in PD generates incorrect signals for the execution and control of voluntary movements. SignificanceThis review sheds light on unsolved questions regarding the relationship between STDT alterations and motor disturbances in PD and proposes directions for future research on this topic.

Characterization of early-onset motor deficits in the Pink1−/− mouse model of Parkinson disease

In Parkinson disease (PD), a complex neurodegenerative disorder that affects nearly 10 million people worldwide, motor skills are significantly impaired. However, onset and progression of motor deficits and the neural correlates of these deficits are poorly understood. We used a genetic mouse model of PD (Pink1−/−), with phenotypic similarities to human PD, to investigate the manifestation of early-onset sensorimotor deficits. We hypothesized this mouse model would show early vocalization and gross motor dysfunction that would be progressive in nature. Pink1−/− mice, compared to wild type (WT) controls, were evaluated at 2, 3, 4, 5, and 6 months of age. To quantify deficit progression, ultrasonic vocalizations and spontaneous locomotor activity (cylinder test and pole test) were analyzed. Although somewhat variable, in general, Pink1−/− mice produced significantly more simple calls with reduced intensity as well as a larger percentage of cycle calls compared to WT counterparts. However, there were no significant differences in duration, bandwidth, or peak frequency for any of the ultrasonic call types between genotypes. Pink1−/− mice showed a significant impairment in limb motor skills with fewer hindlimb steps, forelimb steps, and rears and lands in the cylinder test compared to WT. Additionally, Pink1−/− mice took significantly longer to turn and traverse during the pole test. Immunohistochemical staining showed no significant difference in the number of tyrosine hydroxylase (TH) positive cells in the substantia nigra or density of TH staining in the striatum between genotypes. These data suggest the Pink1−/− mouse model may be instrumental in defining early motor biomarkers of PD in the absence of nigrostriatal dopamine loss.