Resting regional cerebral glucose metabolism in advanced Parkinson's disease studied in the off and on conditions with [(18)F]FDG-PET

Nicotinamide Riboside Ameliorates Survival Time and Motor Dysfunction in an MPTP-Induced Parkinson's Disease Zebrafish Model through Effects on Glucose Metabolism and Endoplasmic Reticulum Stress

Nicotinamide riboside (NR) is a precursor and exogenous supplement of nicotinamide adenine dinucleotide (NAD+). NR has been shown to play a beneficial role in a variety of neurodegenerative diseases. A phase 1 clinical trial identified NR as a potential neuroprotective therapy for Parkinson's disease (PD). However, the mechanism of action of NR in PD has not been fully elucidated. Therefore, the present study aimed to investigate the potential effects of NR on a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD model in zebrafish and its underlying mechanisms. The results showed that NR improved motor dysfunction, survival time, dopamine neurons, and peripheral neurons, as well as the NAD+ levels in the MPTP-affected PD zebrafish model. In addition, transcriptome sequencing analysis revealed that, after NR treatment, differentially expressed genes were significantly enriched in the glucose metabolism and protein processing pathways in the endoplasmic reticulum (ER). Quantitative PCR (qPCR) revealed that the mRNA levels of the glycoheterotrophic enzyme (involved in glucose metabolism) were significantly decreased, and the glycolytic enzyme mRNA expression levels were significantly increased. The results of the non-targeted metabolomic analysis showed that NR treatment significantly increased the levels of metabolites such as nicotinic acid and nicotinamide, in addition to α-D-glucose from the gluconeogenesis and glycolysis metabolism pathways and some of the glucogenic amino acids, such as glutamine. Importantly, NR ameliorated MPTP-induced endoplasmic reticulum stress (ERS) in the PD zebrafish model through the Perk-Eif2α-Atf4-Chop pathway. These results highlight the neuroprotective effect of NR in the present PD zebrafish model through modulation of glucose metabolism and ER stress via the Perk-Eif2α-Atf4-Chop pathway and provide valuable mechanistic insights into the treatment of PD.

Midbrain dopaminergic degeneration differentially modulates primary motor cortex activity and motor behavior in hemi-parkinsonian rats

Parkinson's disease (PD) is marked by degeneration in the nigrostriatal dopaminergic pathway, affecting motor control via complex changes in the cortico-basal ganglia-thalamic motor network, including the primary motor cortex (M1). The modulation of M1 neuronal activity by dopaminergic inputs, particularly from the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc), plays a crucial role in PD pathophysiology. This study investigates how nigrostriatal dopaminergic degeneration influences M1 neuronal activity in rats using in vivo calcium imaging. Histological analysis confirmed dopaminergic lesion severity, with high lesion level rats showing significant motor deficits. Levodopa treatment improved fine motor abilities, particularly in high lesion level rats. Analysis of M1 calcium signals based on dopaminergic lesion severity revealed distinct M1 activity patterns. Animals with low dopaminergic lesion showed increased calcium events, while high lesion level rats exhibited decreased activity, partially restored by levodopa. These findings suggest that M1 activity is more sensitive to transient fluctuations in dopaminergic transmission, rather than to chronic high or low dopaminergic signaling. This study underscores the complex interplay between dopaminergic signaling and M1 neuronal activity in PD symptoms development. Further research integrating behavioral and calcium imaging data can elucidate mechanisms underlying motor deficits and therapeutic responses in PD.

Spatiotemporal patterns of brain iron-oxygen metabolism in patients with Parkinson's disease

OBJECTIVES

Iron deposition and mitochondrial dysfunction are closely associated with the genesis and progression of Parkinson's disease (PD). This study aims to extract susceptibility and oxygen extraction fraction (OEF) values of deep grey matter (DGM) to explore spatiotemporal progression patterns of brain iron-oxygen metabolism in PD.

METHODS

Ninety-five PD patients and forty healthy controls (HCs) were included. Quantitative susceptibility mapping (QSM) and OEF maps were computed from MRI multi-echo gradient echo data. Analysis of covariance (ANCOVA) was used to compare mean susceptibility and OEF values in DGM between early-stage PD (ESP), advanced-stage PD (ASP) patients and HCs. Then Granger causality analysis on the pseudo-time-series of MRI data was applied to assess the causal effect of early altered nuclei on iron content and oxygen extraction in other DGM nuclei.

RESULTS

The susceptibility values in substantia nigra (SN), red nucleus, and globus pallidus (GP) significantly increased in PD patients compared with HCs, while the iron content in GP did not elevate obviously until the late stage. The mean OEF values for the caudate nucleus, putamen, and dentate nucleus were higher in ESP patients than in ASP patients or/and HCs. We also found that iron accumulation progressively expands from the midbrain to the striatum. These alterations were correlated with clinical features and improved AUC for early PD diagnosis to 0.824.

CONCLUSIONS

Abnormal cerebral iron deposition and tissue oxygen utilization in PD measured by QSM and OEF maps could reflect pathological alterations in neurodegenerative processes and provide valuable indicators for disease identification and management.

CLINICAL RELEVANCE STATEMENT

Noninvasive assessment of cerebral iron-oxygen metabolism may serve as clinical evidence of pathological changes in PD and improve the validity of diagnosis and disease monitoring.

KEY POINTS

• Quantitative susceptibility mapping and oxygen extraction fraction maps indicated the cerebral pathology of abnormal iron accumulation and oxygen metabolism in Parkinson's disease. • Iron deposition is mainly in the midbrain, while altered oxygen metabolism is concentrated in the striatum and cerebellum. • The susceptibility and oxygen extraction fraction values in subcortical nuclei were associated with clinical severity.

Consistent abnormal activity in the putamen by dopamine modulation in Parkinson's disease: A resting-state neuroimaging meta-analysis

OBJECTIVE

This study aimed to elucidate brain areas mediated by oral anti-parkinsonian medicine that consistently show abnormal resting-state activation in PD and to reveal their functional connectivity profiles using meta-analytic approaches.

METHODS

Searches of the PubMed, Web of Science databases identified 78 neuroimaging studies including PD OFF state (PD-OFF) versus (vs.) PD ON state (PD-ON) or PD-ON versus healthy controls (HCs) or PD-OFF versus HCs data. Coordinate-based meta-analysis and functional meta-analytic connectivity modeling (MACM) were performed using the activation likelihood estimation algorithm.

RESULTS

Brain activation in PD-OFF vs. PD-ON was significantly changed in the right putamen and left inferior parietal lobule (IPL). Contrast analysis indicated that PD-OFF vs. HCs had more consistent activation in the right paracentral lobule, right middle frontal gyrus, right thalamus, left superior parietal lobule and right putamen, whereas PD-ON vs. HCs elicited more consistent activation in the bilateral middle temporal gyrus, left occipital gyrus, right inferior frontal gyrus and right caudate. MACM revealed coactivation of the right putamen in the direct contrast of PD-OFF vs. PD-ON. Subtraction analysis of significant coactivation clusters for PD-OFF vs. PD-ON with the medium of HCs showed effects in the sensorimotor, top-down control, and visual networks. By overlapping the MACM maps of the two analytical strategies, we demonstrated that the coactivated brain region focused on the right putamen.

CONCLUSIONS

The convergence of local brain regions and co-activation neural networks are involved the putamen, suggesting its potential as a specific imaging biomarker to monitor treatment efficacy.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk/PROSPERO/], identifier [CRD CRD42022304150].

The Contribution of Type 2 Diabetes to Parkinson's Disease Aetiology

Type 2 diabetes (T2D) and Parkinson's disease (PD) are chronic disorders that have a significant health impact on a global scale. Epidemiological, preclinical, and clinical research underpins the assumption that insulin resistance and chronic inflammation contribute to the overlapping aetiologies of T2D and PD. This narrative review summarises the recent evidence on the contribution of T2D to the initiation and progression of PD brain pathology. It also briefly discusses the rationale and potential of alternative pharmacological interventions for PD treatment.

Early-phase amyloid PET reproduces metabolic signatures of cognitive decline in Parkinson's disease

INTRODUCTION

Recent work suggests that amyloid beta (Aβ) positron emission tomography (PET) tracer uptake shortly after injection ("early phase") reflects brain metabolism and perfusion. We assessed this modality in a predominantly amyloid-negative neurodegenerative condition, Parkinson's disease (PD), and hypothesized that early-phase 18F-florbetaben (eFBB) uptake would reproduce characteristic hypometabolism and hypoperfusion patterns associated with cognitive decline in PD.

METHODS

One hundred fifteen PD patients across the spectrum of cognitive impairment underwent dual-phase Aβ PET, structural and arterial spin labeling (ASL) magnetic resonance imaging (MRI), and neuropsychological assessments. Multiple linear regression models compared eFBB uptake to cognitive performance and ASL MRI perfusion.

RESULTS

Reduced eFBB uptake was associated with cognitive performance in brain regions previously linked to hypometabolism-associated cognitive decline in PD, independent of amyloid status. Furthermore, eFBB uptake correlated with cerebral perfusion across widespread regions.

DISCUSSION

EFBB uptake is a potential surrogate measure for cerebral perfusion/metabolism. A dual-phase PET imaging approach may serve as a clinical tool for assessing cognitive impairment.

Highlights

Images taken at amyloid beta (Aβ) positron emission tomography tracer injection may reflect brain perfusion and metabolism.Parkinson's disease (PD) is a predominantly amyloid-negative condition.Early-phase florbetaben (eFBB) in PD was associated with cognitive performance.eFBB uptake reflects hypometabolism-related cognitive decline in PD.eFBB correlated with arterial spin labeling magnetic resonance imaging measured cerebral perfusion.eFBB distinguished dementia from normal cognition and mild cognitive impairment.Findings were independent of late-phase Aβ burden.Thus, eFBB may serve as a surrogate measure for brain metabolism/perfusion.

The reconfiguration pattern of individual brain metabolic connectome for Parkinson's disease identification

¹⁸F-Fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) is widely employed to reveal metabolic abnormalities linked to Parkinson's disease (PD) at a systemic level. However, the individual metabolic connectome details with PD based on ¹⁸F-FDG PET remain largely unknown. To alleviate this issue, we derived a novel brain network estimation method for individual metabolic connectome, that is, Jensen-Shannon Divergence Similarity Estimation (JSSE). Further, intergroup difference between the individual's metabolic brain network and its global/local graph metrics was analyzed to investigate the metabolic connectome's alterations. To further improve the PD diagnosis performance, multiple kernel support vector machine (MKSVM) is conducted for identifying PD from normal control (NC), which combines both topological metrics and connection. Resultantly, PD individuals showed higher nodal topological properties (including assortativity, modularity score, and characteristic path length) than NC individuals, whereas global efficiency and synchronization were lower. Moreover, 45 most significant connections were affected. Further, consensus connections in occipital, parietal, and frontal regions were decrease in PD while increase in subcortical, temporal, and prefrontal regions. The abnormal metabolic network measurements depicted an ideal classification in identifying PD of NC with an accuracy up to 91.84%. The JSSE method identified the individual-level metabolic connectome of ¹⁸F-FDG PET, providing more dimensional and systematic mechanism insights for PD.

Glucose Metabolism Impairment in Parkinson's Disease

Impairments in systematic and regional glucose metabolism exist in patients with Parkinson's disease (PD) at every stage of the disease course, and such impairments are associated with the incidence, progression, and special phenotypes of PD, which affect each physiological process of glucose metabolism including glucose uptake, glycolysis, tricarboxylic acid cycle, oxidative phosphorylation, and pentose phosphate shunt pathway. These impairments may be attributed to various mechanisms, such as insulin resistance, oxidative stress, abnormal glycated modification, blood-brain-barrier dysfunction, and hyperglycemia-induced damages. These mechanisms could subsequently cause excessive methylglyoxal and reactive oxygen species production, neuroinflammation, abnormal aggregation of protein, mitochondrial dysfunction, and decreased dopamine, and finally result in energy supply insufficiency, neurotransmitter dysregulation, aggregation and phosphorylation of α-synuclein, and dopaminergic neuron loss. This review discusses the glucose metabolism impairment in PD and its pathophysiological mechanisms, and briefly summarized the currently-available therapies targeting glucose metabolism impairment in PD, including glucagon-likepeptide-1 (GLP-1) receptor agonists and dual GLP-1/gastric inhibitory peptide receptor agonists, metformin, and thiazoledinediones.

Primary motor area-related injury of anterior central gyrus in Parkinson's disease with dyskinesia: a study based on MRS and Q-Space

INTRODUCTION

By using magnetic resonance spectroscopy (MRS) and Q-Space imaging technology, this research analyzes the imaging characteristics of white matter fibers in the primary motor cortex and posterior limbs of the subcortical internal capsule in parkinsonian patients with motor disorders. The correlation among the changes in axonal function and structure in the cerebral cortex and subcortical cortex and motor disorder is further revealed.

METHODS

First, motor function and clinical condition of 20 patients with Parkinson's disease is assessed the third section of the Unified Parkinson's Scale and H&Y Parkinson's Clinical Staging Scale. Magnetic resonance (MR) scanning is performed with 1H-MRS. Secondly, the range maps of N-acetylaspartic acid (NAA), Choline (Cho), and Creatine (Cr) in the region of interest (the primary motor area of anterior central cortex gyrus, i.e. M1 region) are obtained, and the ratios of NAA/Cr and Cho are calculated. Third, Q-Space MR diffusion imaging technique is used to collect Q-Space images, and a Dsi-studio workstation is used to post-process the images. The fraction anisotropic (FA), generalized fraction anisotropic (GFA), and apparent diffusion coefficient (ADC) parameters of Q-Space in the primary motor cortex and the region of interest in the posterior limb of the internal capsule are obtained. Finally, the parameters of MRS and Q-Space in the experimental group and the control group are further analyzed by SPSS statistical software.

RESULTS

After assessing with Parkinson's score scale, there is obvious motor dysfunction in the experimental group. The average clinical stage of H&Y is 3.0±0.31. In the analysis of MRS data, the ratio of NAA/Cr in the primary motor area of the anterior central gyrus in the experimental group is significantly lower than that in the control group (P<0.05). In the ADC map obtained by Q-Space imaging technique, the ADC value in the primary motor area of the anterior central gyrus in the experimental group is higher than that in the control group (P<0.05), and the difference is statistically significant (P<0.05). There is no significant difference between the experimental group and the control group (P>0.05) in FA and GFA values of the posterior limb of capsule to characterize the characteristics of white matter fibers.

CONCLUSIONS

In parkinsonian patients with motor dysfunction, there are apparent functional and structural changes in the primary motor area neurons and peripheral white matter of the anterior central gyrus, and no obvious damage to the axonal structure of the descending fibers in the cortex.

Differences in Striatal Metabolism in [18F]FDG PET in Parkinson's Disease and Atypical Parkinsonism

Neurodegenerative parkinsonisms affect mainly cognitive and motor functions and are syndromes of overlapping symptoms and clinical manifestations such as tremor, rigidness, and bradykinesia. These include idiopathic Parkinson's disease (PD) and the atypical parkinsonisms, namely progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), multiple system atrophy (MSA) and dementia with Lewy body (DLB). Differences in the striatal metabolism among these syndromes are evaluated using [¹⁸F]FDG PET, caused by alterations to the dopaminergic activity and neuronal loss. A study cohort of three patients with PD, 29 with atypical parkinsonism (10 PSP, 6 CBD, 2 MSA, 7 DLB, and 4 non-classifiable), and a control group of 25 patients with normal striatal metabolism is available. Standardized uptake value ratios (SUVR) are extracted from the striatum, and the caudate and the putamen separately. SUVRs are compared among the study groups. In addition, hemispherical and caudate-putamen differences are evaluated in atypical parkinsonisms. Striatal hypermetabolism is detected in patients with PD, while atypical parkinsonisms show hypometabolism, compared to the control group. Hemispherical differences are observed in CBD, MSA and DLB, with the latter also showing statistically significant caudate-putamen asymmetry (p = 0.018). These results indicate disease-specific metabolic uptake patterns in the striatum that can support the differential diagnosis.

Brain Glucose Hypometabolism and Iron Accumulation in Different Brain Regions in Alzheimer's and Parkinson's Diseases

The aim of this study was to examine the relationship between the presence of glucose hypometabolism (GHM) and brain iron accumulation (BIA), two potential pathological mechanisms in neurodegenerative disease, in different regions of the brain in people with late-onset Alzheimer's disease (AD) or Parkinson's disease (PD). Studies that conducted fluorodeoxyglucose positron emission tomography (FDG-PET) to map GHM or quantitative susceptibility mapping-magnetic resonance imaging (QSM-MRI) to map BIA in the brains of patients with AD or PD were reviewed. Regions of the brain where GHM or BIA were reported in each disease were compared. In AD, both GHM and BIA were reported in the hippocampus, temporal, and parietal lobes. GHM alone was reported in the cingulate gyrus, precuneus and occipital lobe. BIA alone was reported in the caudate nucleus, putamen and globus pallidus. In PD, both GHM and BIA were reported in thalamus, globus pallidus, putamen, hippocampus, and temporal and frontal lobes. GHM alone was reported in cingulate gyrus, caudate nucleus, cerebellum, and parietal and occipital lobes. BIA alone was reported in the substantia nigra and red nucleus. GHM and BIA are observed independent of one another in various brain regions in both AD and PD. This suggests that GHM is not always necessary or sufficient to cause BIA and vice versa. Hypothesis-driven FDG-PET and QSM-MRI imaging studies, where both are conducted on individuals with AD or PD, are needed to confirm or disprove the observations presented here about the potential relationship or lack thereof between GHM and BIA in AD and PD.

EANM procedure guidelines for brain PET imaging using [18F]FDG, version 3

The present procedural guidelines summarize the current views of the EANM Neuro-Imaging Committee (NIC). The purpose of these guidelines is to assist nuclear medicine practitioners in making recommendations, performing, interpreting, and reporting results of [¹⁸F]FDG-PET imaging of the brain. The aim is to help achieve a high-quality standard of [¹⁸F]FDG brain imaging and to further increase the diagnostic impact of this technique in neurological, neurosurgical, and psychiatric practice. The present document replaces a former version of the guidelines that have been published in 2009. These new guidelines include an update in the light of advances in PET technology such as the introduction of digital PET and hybrid PET/MR systems, advances in individual PET semiquantitative analysis, and current broadening clinical indications (e.g., for encephalitis and brain lymphoma). Further insight has also become available about hyperglycemia effects in patients who undergo brain [¹⁸F]FDG-PET. Accordingly, the patient preparation procedure has been updated. Finally, most typical brain patterns of metabolic changes are summarized for neurodegenerative diseases. The present guidelines are specifically intended to present information related to the European practice. The information provided should be taken in the context of local conditions and regulations.

Motor Cortex Stimulation Reversed Hypernociception, Increased Serotonin in Raphe Neurons, and Caused Inhibition of Spinal Astrocytes in a Parkinson's Disease Rat Model

Persistent pain is a prevalent symptom of Parkinson’s disease (PD), which is related to the loss of monoamines and neuroinflammation. Motor cortex stimulation (MCS) inhibits persistent pain by activating the descending analgesic pathways; however, its effectiveness in the control of PD-induced pain remains unclear. Here, we evaluated the analgesic efficacy of MCS together with serotonergic and spinal glial modulation in an experimental PD (ePD) rat model. Wistar rats with unilateral striatal 6-OHDA and MCS were assessed for behavioral immobility and nociceptive responses. The immunoreactivity of dopamine in the substantia nigra and serotonin in the nucleus raphe magnus (NRM) and the neuronal, astrocytic, and microglial activation in the dorsal horn of the spinal cord were evaluated. MCS, without interfering with dopamine loss, reversed ePD-induced immobility and hypernociception. This response was accompanied by an exacerbated increase in serotonin in the NRM and a decrease in neuronal and astrocytic hyperactivation in the spinal cord, without inhibiting ePD-induced microglial hypertrophy and hyperplasia. Taken together, MCS induces analgesia in the ePD model, while restores the descending serotonergic pathway with consequent inhibition of spinal neurons and astrocytes, showing the role of MCS in PD-induced pain control.

Advances in multimodal data fusion in neuroimaging: Overview, challenges, and novel orientation

Multimodal fusion in neuroimaging combines data from multiple imaging modalities to overcome the fundamental limitations of individual modalities. Neuroimaging fusion can achieve higher temporal and spatial resolution, enhance contrast, correct imaging distortions, and bridge physiological and cognitive information. In this study, we analyzed over 450 references from PubMed, Google Scholar, IEEE, ScienceDirect, Web of Science, and various sources published from 1978 to 2020. We provide a review that encompasses (1) an overview of current challenges in multimodal fusion (2) the current medical applications of fusion for specific neurological diseases, (3) strengths and limitations of available imaging modalities, (4) fundamental fusion rules, (5) fusion quality assessment methods, and (6) the applications of fusion for atlas-based segmentation and quantification. Overall, multimodal fusion shows significant benefits in clinical diagnosis and neuroscience research. Widespread education and further research amongst engineers, researchers and clinicians will benefit the field of multimodal neuroimaging.

Neural substrates underlying progressive micrographia in Parkinson's disease

INTRODUCTION

The neural substrates associated with the development of micrographia remain unknown. We aimed to elucidate the neural substrates underlying micrographia in Parkinson's disease (PD) patients.

METHODS

Forty PD patients and 20 healthy controls underwent handwriting tests that involved free writing and copying. We measured the size of each letter and the resting cerebral glucose metabolic rate of the PD patients and another group of age- and sex-matched 14 healthy controls (HCs), who had not participated in the writing tests, using resting-state 18F-fluorodeoxyglucose positron emission tomography.

RESULTS

In the PD patients, the prevalence of consistent micrographia (CM) associated with free writing was 2.5% for both tasks. Alternatively, the prevalence of progressive micrographia (PM) was 15% for free writing and 17.5% for copying. In the PD patients, there was no significant difference in the letter sizes between these tasks, whereas the variability of the letter sizes for copying was significantly different from that for free writing. The means and decrements in letter sizes in either task were not significantly correlated with the severity of brady/hypokinesia in the PD patients. For free writing, the PD patients with PM showed glucose hypometabolism in the anterior part of the right middle cingulate cortex, including the rostral cingulate motor area, compared with those without PM. For copying, the PD patients with PM showed glucose hypometabolism in the right superior occipital gyrus, including V3A, compared with those without PM.

CONCLUSIONS

These findings suggest that PM in free writing in PD patients is caused by the difficulty of monitoring whether the actual handwriting movements are desirable for maintaining letter size during self-paced handwriting. By contrast, PM in copying in PD patients is evoked by a lack of visual information about the personal handwriting and hand motions that are used as cues for maintaining letter sizes.

Coordinate based meta-analysis of motor functional imaging in Parkinson's: disease-specific patterns and modulation by dopamine replacement and deep brain stimulation

OBJECTIVE

To investigate factors affecting the pattern of motor brain activation reported in people with Parkinson's (PwP), aiming to differentiate disease-specific features from treatment effects.

METHODS

A co-ordinate-based-meta-analysis (CBMA) of functional motor neuroimaging studies involving patients with Parkinson's (PwP), and healthy controls (HC) identified 126 suitable articles. The experiments were grouped based on subject feature, medication status (onMed/offMed), deep brain stimulation (DBS) status (DBSon/DBSoff) and type of motor initiation.

RESULTS

HC and PwP shared similar neural networks during upper extremity motor tasks but with differences of reported frequency in mainly bilateral putamen, insula and ipsilateral inferior parietal and precentral gyri. The activation height was significantly reduced in the bilateral putamen, left SMA, left subthalamus nucleus, right thalamus and right midial global pallidum in PwPoffMed (vs. HC), and pre-SMA hypoactivation correlated with disease severity. These changes were not found in patients on dopamine replacement therapy (PwPonMed vs. HC) in line with a restorative function. By contrast, left SMA and primary motor cortex showed hyperactivation in the medicated state (vs. HC) suggesting dopaminergic overcompensation. Deep-brain stimulation (PwP during the high frequency subthalamus nucleus (STN) DBS vs. no stimulation) induced a decrease in left SMA activity and the expected increase in the left subthalamic/thalamic region regardless of hand movement. We further demonstrated a disease related effect of motor intention with only PwPoffMed showing increased activation in the medial frontal lobe in self-initiated studies.

CONCLUSION

We describe a consistent disease-specific pattern of putaminal hypoactivation during motor tasks that appears reversed by dopamine replacement. Inconsistent reports of altered SMA/pre-SMA activation can be explained by task- and medication-specific variation in intention. Moreover, SMA activity was reduced during STN-DBS, while dopamine-induced hyperactivation of SMA which might underpin hyperdynamic L-dopa related overcompensation.

Imaging of Motor Cortex Physiology in Parkinson's Disease

There is abundant evidence that the pathophysiology of Parkinson's disease (PD) is not confined to the nigrostriatal dopaminergic pathway but propagates along the cortico‐basal ganglia‐thalamo‐cortical neural network. A critical node in this functional circuit impacted by PD is the primary motor cortex (M1), which plays a key role in generating neural impulses that regulate movements. The past several decades have lay witness to numerous in vivo neuroimaging techniques that provide a window into the function and structure of M1. A consistent observation from numerous studies is that during voluntary movement, but also at rest, the functional activity of M1 is altered in PD relative to healthy individuals, and it relates to many of the motor signs. Although this abnormal functional activity can be partially restored with acute dopaminergic medication, it continues to deteriorate with disease progression and may predate structural degeneration of M1. The current review discusses the evidence that M1 is fundamental to the pathophysiology of PD, as measured by neuroimaging techniques such as positron emission tomography, single‐photon emission computed tomography, electroencephalography, magnetoencephalography, and functional and structural MRI. Although novel treatments that target the cortex will not cure PD, they could significantly slow down and alter the progressive course of the disease and thus improve clinical care for this degenerative disease. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society

FDG PET Parkinson's disease-related pattern as a biomarker for clinical trials in early stage disease

Background

The development of therapeutic interventions for Parkinson disease (PD) is challenged by disease complexity and subjectivity of symptom evaluation. A Parkinson's Disease Related Pattern (PDRP) of glucose metabolism via fluorodeoxyglucose positron emission tomography (FDG-PET) has been reported to correlate with motor symptom scores and may aid the detection of disease-modifying therapeutic effects.

Objectives

We sought to independently evaluate the potential utility of the PDRP as a biomarker for clinical trials of early-stage PD.

Methods

Two machine learning approaches (Scaled Subprofile Model (SSM) and NPAIRS with Canonical Variates Analysis) were performed on FDG-PET scans from 17 healthy controls (HC) and 23 PD patients. The approaches were compared regarding discrimination of HC from PD and relationship to motor symptoms.

Results

Both classifiers discriminated HC from PD (p < 0.01, p < 0.03), and classifier scores for age- and gender- matched HC and PD correlated with Hoehn & Yahr stage (R² = 0.24, p < 0.015) and UPDRS (R² = 0.23, p < 0.018). Metabolic patterns were highly similar, with hypometabolism in parieto-occipital and prefrontal regions and hypermetabolism in cerebellum, pons, thalamus, paracentral gyrus, and lentiform nucleus relative to whole brain, consistent with the PDRP. An additional classifier was developed using only PD subjects, resulting in scores that correlated with UPDRS (R² = 0.25, p < 0.02) and Hoehn & Yahr stage (R² = 0.16, p < 0.06).

Conclusions

Two independent analyses performed in a cohort of mild PD patients replicated key features of the PDRP, confirming that FDG-PET and multivariate classification can provide an objective, sensitive biomarker of disease stage with the potential to detect treatment effects on PD progression.

•

The Parkinson's disease-related pattern (PDRP) of glucose metabolic effects is demonstrated in an independent cohort of early stage PD patients.

•

The PDRP pattern of metabolic changes is robust to variations in image processing and choice of classification model.

•

Age-related metabolic changes show partial overlap with the PDRP, suggesting that age-adjustment is an important consideration.

•

The PDRP correlates with motor function as defined by Hoehn & Yahr stage and UPDRS score.

•

An additional data driven metabolic classifier highlights pattern aspects associated with early stage motor decline.

PET imaging in neurology: Alzheimer's and Parkinson's diseases

PET studies play an important role in the early detection of Alzheimer's and Parkinson's diseases (AD and PD). Fluorine-18 fluorodeoxyglucose (F-FDG) PET imaging of regional cerebral glucose metabolism and PET amyloid imaging are the two major PET studies for AD. F-FDG PET is highly sensitive for the early diagnosis of AD, in predicting conversion from mild cognitive impairment to AD, and in differentiating AD from other dementias. PET amyloid imaging is positive in the majority of patients with AD. Negative amyloid PET reduces the likelihood of AD. The main limitations of PET amyloid imaging is its high positivity in the normal elderly population and in other medical conditions with amyloid pathologies. Various PET tracers are available to assess motor and cognitive dysfunctions in PD. PET tracers targeting presynaptic dopaminergic function (F-DOPA, radiolabeled PET tracers assessing the availability of dopamine transporters and vesicular monoamine transporters) and postsynaptic dopamine receptors are used to assess motor dysfunction in PD. PET tracers, particularly dopamine transporters, are highly sensitive in the early diagnosis of PD. Uptake of PET tracers in the striatum is inversely correlated with disease severity. PET is valuable in differentiating PD from other movement disorders. PET studies, particularly F-FDG PET, help to evaluate cortical metabolism in PD patients with cognitive dysfunction and dementia.

Metabolic Topology of Neurodegenerative Disorders: Influence of Cognitive and Motor Deficits

Parkinson disease with and without dementia (PDD and PD, respectively), dementia with Lewy bodies (DLB), and Alzheimer dementia (AD) traditionally have been viewed as distinct clinical and pathologic entities. However, intriguing overlaps in biochemical, clinical, and imaging findings question the concept of distinct entities and suggest a continuous spectrum in which individual patients express PD-typical patterns and AD-typical patterns to a variable degree.

METHODS

Following this concept, we built a topological map based on regional patterns of the cerebral metabolic rate of glucose as measured with (18)F-FDG PET to rank and localize single subjects' disease status according to PD-typical (PD vs. controls) and AD-typical (AD vs. controls) pattern expression in patients clinically characterized as PD, PDD, DLB, amnestic mild cognitive impairment, and AD.

RESULTS

The topology generally confirmed an indivisible spectrum of disease manifestation according to 2 separable expression patterns. The expression values derived from the first pattern were highly correlated with individual cognitive, but not motor, disability. The opposite was found for the corresponding expression values of the second pattern.

CONCLUSION

The metabolic imaging analysis supports the notion that there is a continuous spectrum of neurodegeneration between AD and PD. Furthermore, PDD and DLB may in fact represent 1 overlapping disease entity, characterized by the presence of mixed neuropathology and only different by the time course.

Changes to Intermediary Metabolites in Sporadic andLRRK2Parkinson’s Disease Demonstrated by Proton Magnetic Resonance Spectroscopy

Background. Parkinson's disease (PD) remains a clinical diagnosis and biomarkers are needed to detect the disease as early as possible. Genetically determined PD provides an opportunity for studying metabolic differences in connection with disease development. Objectives. To study the levels of intermediary metabolites in cerebrospinal fluid (CSF) from patients with PD, either of sporadic type or in carriers of the LRRK2 p.G2019S mutation. Methods. Results from patients with sporadic PD or LRRK2-PD were compared with asymptomatic LRRK2 mutation carriers and healthy control individuals. CSF was analysed by proton MR spectroscopy (¹H-MRS) giving reliable results for 16 intermediary metabolites. Partial least squares discriminant analysis (PLS-DA) was applied to study group differences. Results. PLS-DA distinguished PD patients from healthy individuals based on the metabolites identified in CSF, with 2-hydroxybutyrate, glutamine, and dimethyl sulphone largely contributing to the separations. Conclusion. Speculatively, all three metabolites could alter concentration in response to metabolic changes connected with neurodegeneration; glutamine as a means of removing excess nitrogen from brain, dimethyl sulphone as an anti-inflammatory agent, and 2-hydroxybutyrate in connection with altered glutathione metabolism. Potentially, ¹H-MRS is a promising tool for identifying novel biomarkers for PD.

Deep-brain stimulation associates with improved microvascular integrity in the subthalamic nucleus in Parkinson's disease

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has become an accepted treatment for motor symptoms in a subset of Parkinson's disease (PD) patients. The mechanisms why DBS is effective are incompletely understood, but previous studies show that DBS targeted in brain structures other than the STN may modify the microvasculature. However, this has not been studied in PD subjects who have received STN-DBS. Here we investigated the extent and nature of microvascular changes in post-mortem STN samples from STN-DBS PD patients, compared to aged controls and PD patients who had not been treated with STN-DBS. We used immunohistochemical and immunofluorescent methods to assess serial STN-containing brain sections from PD and STN-DBS PD cases, compared to similar age controls using specific antibodies to detect capillaries, an adherens junction and tight junction-associated proteins as well as activated microglia. Cellular features in stained sections were quantified by confocal fluorescence microscopy and stereological methods in conjunction with in vitro imaging tools. We found significant upregulation of microvessel endothelial cell thickness, length and density but lowered activated microglia density and striking upregulation of all analysed adherens junction and tight junction-associated proteins in STN-DBS PD patients compared to non-DBS PD patients and controls. Moreover, in STN-DBS PD samples, expression of an angiogenic factor, vascular endothelial growth factor (VEGF), was significantly upregulated compared to the other groups. Our findings suggest that overexpressed VEGF and downregulation of inflammatory processes may be critical mechanisms underlying the DBS-induced microvascular changes.

Effects of levodopa on regional cerebral metabolism and blood flow

Levodopa (L-dopa) has been at the forefront of antiparkinsonian therapy for a half century. Recent advances in functional brain imaging have contributed substantially to the understanding of the effects of L-dopa and other dopaminergic treatment on the activity of abnormal motor and cognitive brain circuits in Parkinson's disease patients. Progress has also been made in understanding the functional pathology of dyskinesias, a common side effect of l-dopa treatment, at both regional and network levels. Here, we review these studies, focusing mainly on the new mechanistic insights provided by metabolic brain imaging and network analysis.

Brain 18F-FDG PET imaging in the differential diagnosis of parkinsonism

AIM

The aims in this study were to evaluate the role of brain F-FDG PET imaging in differential diagnosis of parkinsonism and to correlate brain metabolism findings with patients' clinical findings.

METHODS

Brain F-FDG PET images were evaluated both visually and quantitatively using the NeuroQ software in 21 parkinsonism patients in whom final clinical diagnoses were established.

RESULTS

Final clinical diagnoses were idiopathic Parkinson disease in 7, multisystem atrophy (MSA) in 7, progressive supranuclear palsy (PSP) in 4, corticobasal degeneration in 2, and Lewy body disease in 1 patient. Asymmetrical cortical hypometabolism was observed in most of the patients in frontal and parietotemporal regions. Fifteen of 21 patients had basal ganglia involvement, which was bilateral in patients with MSA and more frequently unilateral in patients with idiopathic Parkinson disease and PSP. Four patients with PSP and 1 patient with corticobasal degeneration had thalamic hypometabolism. Cerebellar hypometabolism was observed in 4 patients with MSA. The Unified Parkinson Disease Rating Scale motor and bradykinesia scores were higher in patients with basal ganglia involvement.

CONCLUSIONS

Brain F-FDG PET findings in subcortical nuclei and cerebellum were found to be useful in differential diagnosis of patients with parkinsonism. The extent of cerebral cortical and basal ganglia hypometabolism showed correlation with the presentation and severity of clinical findings.

Inhibition of glycolysis attenuates 4-hydroxynonenal-dependent autophagy and exacerbates apoptosis in differentiated SH-SY5Y neuroblastoma cells

How cellular metabolic activities regulate autophagy and determine the susceptibility to oxidative stress and ultimately cell death in neuronal cells is not well understood. An important example of oxidative stress is 4-hydroxynonenal (HNE), which is a lipid peroxidation product that is formed during oxidative stress, and accumulates in neurodegenerative diseases causing damage. The accumulation of toxic oxidation products such as HNE, is a prevalent feature of neurodegenerative diseases, and can promote organelle and protein damage leading to induction of autophagy. In this study, we used differentiated SH-SY5Y neuroblastoma cells to investigate the mechanisms and regulation of cellular susceptibility to HNE toxicity and the relationship to cellular metabolism. We found that autophagy is immediately stimulated by HNE at a sublethal concentration. Within the same time frame, HNE induces concentration dependent CASP3/caspase 3 activation and cell death. Interestingly, both basal and HNE-activated autophagy, were regulated by glucose metabolism. Inhibition of glucose metabolism by 2-deoxyglucose (2DG), at a concentration that inhibited autophagic flux, further exacerbated CASP3 activation and cell death in response to HNE. Cell death was attenuated by the pan-caspase inhibitor Z-VAD-FMK. Specific inhibition of glycolysis using koningic acid, a GAPDH inhibitor, inhibited autophagic flux and exacerbated HNE-induced cell death similarly to 2DG. The effects of 2DG on autophagy and HNE-induced cell death could not be reversed by addition of mannose, suggesting an ER stress-independent mechanism. 2DG decreased LAMP1 and increased BCL2 levels suggesting that its effects on autophagy may be mediated by more than one mechanism. Furthermore, 2DG decreased cellular ATP, and 2DG and HNE combined treatment decreased mitochondrial membrane potential. We conclude that glucose-dependent autophagy serves as a protective mechanism in response to HNE.

[Functional neuroimaging in the diagnosis of patients with Parkinsonism: Update and recommendations for clinical use]

Functional Neuroimaging has been traditionally used in research for patients with different Parkinsonian syndromes. However, the emergence of commercial radiotracers together with the availability of single photon emission computed tomography (SPECT) and, more recently, positron emission tomography (PET) have made them available for clinical practice. Particularly, the development of clinical evidence achieved by functional neuroimaging techniques over the past two decades have motivated a progressive inclusion of several biomarkers in the clinical diagnostic criteria for neurodegenerative diseases that occur with Parkinsonism. However, the wide range of radiotracers designed to assess the involvement of different pathways in the neurodegenerative process underlying Parkinsonian syndromes (dopaminergic nigrostriatal pathway integrity, basal ganglia and cortical neuronal activity, myocardial sympathetic innervation), and the different neuroimaging techniques currently available (scintigraphy, SPECT and PET), have generated some controversy concerning the best neuroimaging test that should be indicated for the differential diagnosis of Parkinsonism. In this article, a panel of nuclear medicine and neurology experts has evaluated the functional neuroimaging techniques emphazising practical considerations related to the diagnosis of patients with uncertain origin parkinsonism and the assessment Parkinson's disease progression.

Examining the relationship between head trauma and neurodegenerative disease: A review of epidemiology, pathology and neuroimaging techniques

Traumatic brain injuries (TBI) are induced by sudden acceleration-deceleration and/or rotational forces acting on the brain. Diffuse axonal injury (DAI) has been identified as one of the chief underlying causes of morbidity and mortality in head trauma incidents. DAIs refer to microscopic white matter (WM) injuries as a result of shearing forces that induce pathological and anatomical changes within the brain, which potentially contribute to significant impairments later in life. These microscopic injuries are often unidentifiable by the conventional computed tomography (CT) and magnetic resonance (MR) scans employed by emergency departments to initially assess head trauma patients and, as a result, TBIs are incredibly difficult to diagnose. The impairments associated with TBI may be caused by secondary mechanisms that are initiated at the moment of injury, but often have delayed clinical presentations that are difficult to assess due to the initial misdiagnosis. As a result, the true consequences of these head injuries may go unnoticed at the time of injury and for many years thereafter. The purpose of this review is to investigate these consequences of TBI and their potential link to neurodegenerative disease (ND). This review will summarize the current epidemiological findings, the pathological similarities, and new neuroimaging techniques that may help delineate the relationship between TBI and ND. Lastly, this review will discuss future directions and propose new methods to overcome the limitations that are currently impeding research progress. It is imperative that improved techniques are developed to adequately and retrospectively assess TBI history in patients that may have been previously undiagnosed in order to increase the validity and reliability across future epidemiological studies. The authors introduce a new surveillance tool (Retrospective Screening of Traumatic Brain Injury Questionnaire, RESTBI) to address this concern.

Critical involvement of the motor cortex in the pathophysiology and treatment of Parkinson's disease

This review examines the involvement of the motor cortex in Parkinson's disease (PD), a debilitating movement disorder typified by degeneration of dopamine cells of the substantia nigra. While much of PD research has focused on the caudate/putamen, many aspects of motor cortex function are abnormal in PD patients and in animal models of PD, implicating motor cortex involvement in disease symptoms and their treatment. Herein, we discuss several lines of evidence to support this hypothesis. Dopamine depletion alters regional metabolism in the motor cortex and also reduces interneuron activity, causing a breakdown in intracortical inhibition. This leads to functional reorganization of motor maps and excessive corticostriatal synchrony when movement is initiated. Recent work suggests that electrical stimulation of the motor cortex provides a clinical benefit for PD patients. Based on extant research, we identify a number of unanswered questions regarding the motor cortex in PD and argue that a better understanding of the contribution of the motor cortex to PD symptoms will facilitate the development of novel therapeutic approaches.

Multiclass classification of FDG PET scans for the distinction between Parkinson's disease and atypical parkinsonian syndromes

Most available pattern recognition methods in neuroimaging address binary classification problems. Here, we used relevance vector machine (RVM) in combination with booststrap resampling (‘bagging’) for non-hierarchical multiclass classification. The method was tested on 120 cerebral ¹⁸fluorodeoxyglucose (FDG) positron emission tomography (PET) scans performed in patients who exhibited parkinsonian clinical features for 3.5 years on average but that were outside the prevailing perception for Parkinson's disease (PD). A radiological diagnosis of PD was suggested for 30 patients at the time of PET imaging. However, at follow-up several years after PET imaging, 42 of them finally received a clinical diagnosis of PD. The remaining 78 APS patients were diagnosed with multiple system atrophy (MSA, N = 31), progressive supranuclear palsy (PSP, N = 26) and corticobasal syndrome (CBS, N = 21), respectively. With respect to this standard of truth, classification sensitivity, specificity, positive and negative predictive values for PD were 93% 83% 75% and 96%, respectively using binary RVM (PD vs. APS) and 90%, 87%, 79% and 94%, respectively, using multiclass RVM (PD vs. MSA vs. PSP vs. CBS). Multiclass RVM achieved 45%, 55% and 62% classification accuracy for, MSA, PSP and CBS, respectively. Finally, a majority confidence ratio was computed for each scan on the basis of class pairs that were the most frequently assigned by RVM. Altogether, the results suggest that automatic multiclass RVM classification of FDG PET scans achieves adequate performance for the early differentiation between PD and APS on the basis of cerebral FDG uptake patterns when the clinical diagnosis is felt uncertain. This approach cannot be recommended yet as an aid for distinction between the three APS classes under consideration.

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Multiclass classification is one of the challenges of computer-aided diagnosis.

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This was addressed here using relevance vector machine and bootstrap aggregation.

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Performance was tested on FDG-PET scans from 120 parkinsonian patients.

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Four diagnostic classes under consideration as defined on average 3.5 years after PET.

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Confusion matrices, majority confidence ratio and discriminant maps were computed.

Microglia, amyloid, and glucose metabolism in Parkinson's disease with and without dementia

[(11)C](R)PK11195-PET measures upregulation of translocator protein, which is associated with microglial activation, [(11)C]PIB-PET is a marker of amyloid, while [(18)F]FDG-PET measures cerebral glucose metabolism (rCMRGlc). We hypothesize that microglial activation is an early event in the Parkinson's disease (PD) spectrum and is independent of the amyloid pathology. The aim of this study is to evaluate in vivo the relationship between microglial activation, amyloid deposition, and glucose metabolism in Parkinson's disease dementia (PDD) and PD subjects without dementia. Here, we evaluated 11 PDD subjects, 8 PD subjects without dementia, and 24 control subjects. Subjects underwent T1 and T2 MRI, [(11)C](R)PK11195, [(18)F]FDG, and [(11)C]PIB PET scans. Parametric maps of [(11)C](R)PK11195 binding potential, rCMRGlc, and [(11)C]PIB uptake were interrogated using region of interest and SPM (statistical parametric mapping) analysis. The PDD patients showed a significant increase of microglial activation in anterior and posterior cingulate, striatum, frontal, temporal, parietal, and occipital cortical regions compared with the controls. The PD subjects also showed a statistically significant increase in microglial activation in temporal, parietal, and occipital regions. [(11)C]PIB uptake was marginally increased in PDD and PD. There was a significant reduction in glucose metabolism in PDD and PD. We have also demonstrated pixel-by-pixel correlation between mini-mental state examination (MMSE) score and microglial activation, and MMSE score and rCMRGlc. In conclusion, we have demonstrated that cortical microglial activation and reduced glucose metabolism can be detected early on in this disease spectrum. Significant microglial activation may be a factor in driving the disease process in PDD. Given this, agents that affect microglial activation could have an influence on disease progression.

Levodopa effects on hand and speech movements in patients with Parkinson's disease: a FMRI study

Levodopa (L-dopa) effects on the cardinal and axial symptoms of Parkinson’s disease (PD) differ greatly, leading to therapeutic challenges for managing the disabilities in this patient’s population. In this context, we studied the cerebral networks associated with the production of a unilateral hand movement, speech production, and a task combining both tasks in 12 individuals with PD, both off and on levodopa (L-dopa). Unilateral hand movements in the off medication state elicited brain activations in motor regions (primary motor cortex, supplementary motor area, premotor cortex, cerebellum), as well as additional areas (anterior cingulate, putamen, associative parietal areas); following L-dopa administration, the brain activation profile was globally reduced, highlighting activations in the parietal and posterior cingulate cortices. For the speech production task, brain activation patterns were similar with and without medication, including the orofacial primary motor cortex (M1), the primary somatosensory cortex and the cerebellar hemispheres bilaterally, as well as the left- premotor, anterior cingulate and supramarginal cortices. For the combined task off L-dopa, the cerebral activation profile was restricted to the right cerebellum (hand movement), reflecting the difficulty in performing two movements simultaneously in PD. Under L-dopa, the brain activation profile of the combined task involved a larger pattern, including additional fronto-parietal activations, without reaching the sum of the areas activated during the simple hand and speech tasks separately. Our results question both the role of the basal ganglia system in speech production and the modulation of task-dependent cerebral networks by dopaminergic treatment.

Attentional set-shifting deficit in Parkinson's disease is associated with prefrontal dysfunction: an FDG-PET study

The attentional set-shifting deficit that has been observed in Parkinson's disease (PD) has long been considered neuropsychological evidence of the involvement of meso-prefrontal and prefrontal-striatal circuits in cognitive flexibility. However, recent studies have suggested that non-dopaminergic, posterior cortical pathologies may also contribute to this deficit. Although several neuroimaging studies have addressed this issue, the results of these studies were confounded by the use of tasks that required other cognitive processes in addition to set-shifting, such as rule learning and working memory. In this study, we attempted to identify the neural correlates of the attentional set-shifting deficit in PD using a compound letter task and 18F-fluoro-deoxy-glucose (FDG) positron emission tomography during rest. Shift cost, which is a measure of attentional set-shifting ability, was significantly correlated with hypometabolism in the right dorsolateral prefrontal cortex, including the putative human frontal eye field. Our results provide direct evidence that dysfunction in the dorsolateral prefrontal cortex makes a primary contribution to the attentional set-shifting deficit that has been observed in PD patients.

Regional cerebral metabolism in mouse under chronic manganese exposure: implications for manganism

Chronic manganese (Mn) exposure in rodents, non-human primates and humans has been linked to Parkinson's disease like condition known as Manganism. Mn being a cofactor for many enzymes in brain has been known to be accumulated in various regions differentially and thus exert toxic effect upon chronic overexposure. In present study, neuropathology of Manganism was investigated by evaluating regional neuronal and astroglial metabolism in mice under chronic Mn exposure. Male C57BL6 mice were treated with MnCl(2) (25 mg/kg, i.p.) for 21 days. Cerebral metabolism was studied by co-infusing [U-(13)C(6)]glucose and [2-(13)C]acetate, and monitoring (13)C labeling of amino acids in brain tissue extract using (1)H-[(13)C] and (13)C-[(1)H]-NMR spectroscopy. Glutamate, choline, N-acetyl aspartate and myo-inositol were found to be reduced in thalamus and hypothalamus indicating a loss in neuronal and astroglial cells due to Mn neurotoxicity. Reduced labeling of Glu(C4) from [U-(13)C(6)]glucose and [2-(13)C]acetate indicates an impairment of glucose oxidation by glutamatergic neurons and glutamate-glutamine neurotransmitter cycle in cortex, striatum, thalamus-hypothalamus and olfactory bulb with chronic Mn exposure. Additionally, reduced labeling of Gln(C4) from [2-(13)C]acetate indicates a decrease in acetate oxidation by astroglia in the same regions. However, GABAergic function was alleviated only in thalamus-hypothalamus. Our findings indicate that chronic Mn impairs excitatory (glutamatergic) function in the majority of regions of brain while inhibitory (GABAergic) activity is perturbed only in basal ganglia.

Cortical hypoperfusion in Parkinson's disease assessed using arterial spin labeled perfusion MRI

Alterations in cerebral perfusion and metabolism in Parkinson's disease have been assessed in several studies, using nuclear imaging techniques and more recently magnetic resonance imaging. However, to date there is no consensus in the literature regarding the extent and the magnitude of these alterations. In this work, arterial spin labeled perfusion MRI was employed to quantify absolute cerebral blood flow in a group of early-to-moderate Parkinson's disease patients and age-matched healthy controls. Perfusion comparisons between the two groups showed that Parkinson's disease is characterized by wide-spread cortical hypoperfusion. Subcortically, hypoperfusion was also found in the caudate nucleus. This pattern of hypoperfusion could be related to cognitive dysfunctions that have been previously observed even at the disease early stages. The present results were obtained by means of whole brain voxel-wise comparisons of absolute perfusion values, using statistical parametric mapping, thus avoiding the potentially biased global mean normalization procedure. In addition, this work demonstrates that between-group comparison of relative perfusion values after global mean normalization, introduced artifactual relative perfusion increases, where absolute perfusion was in fact preserved. This has implications for perfusion studies of other brain disorders.

Brain energization in response to deep brain stimulation of subthalamic nuclei in Parkinson's disease

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment in a subgroup of medically refractory patients with Parkinson's disease (PD). Here, we compared resting-state (18)F-fluorodeoxyglucose (FDG) positron emission tomography images in the stimulator off (DBS_OFF) and on (DBS_ON) conditions in eight PD patients in an unmedicated state, on average 2 years after bilateral electrode implantation. Global standardized uptake value (SUV) significantly increased by ∼11% in response to STN-DBS. To avoid any bias in the voxel-based analysis comparing DBS_ON and DBS_OFF conditions, individual scan intensity was scaled to a region where FDG-SUV did not differ significantly between conditions. The resulting FDG-SUV ratio (FDG-SUVR) was found to increase in many regions in response to STN-DBS including the target area of surgery, caudate nuclei, primary sensorimotor, and associative cortices. Contrary to previous studies, we could not find any regional decrease in FDG-SUVR. These findings were indirectly supported by comparing the extent of areas with depressed FDG-SUVR in DBS_OFF and DBS_ON relatively to 10 normal controls. Altogether, these novel results support the prediction that the effect of STN-DBS on brain activity in PD is unidirectional and consists in an increase in many subcortical and cortical regions.

EANM procedure guidelines for PET brain imaging using [18F]FDG, version 2

These guidelines summarize the current views of the European Association of Nuclear Medicine Neuroimaging Committee (ENC). The purpose of the guidelines is to assist nuclear medicine practitioners in making recommendations, performing, interpreting, and reporting the results of fluorine-18 fluoro-2-deoxyglucose ([(18)F]FDG) PET imaging of the brain. The aim is to help achieve a high standard of FDG imaging, which will increase the diagnostic impact of this technique in neurological and psychiatric practice. The present document replaces a former version of the guidelines that were published in 2002 [1] and includes an update in the light of advances in PET technology, the introduction of hybrid PET/CT systems and the broadening clinical indications for FDG brain imaging. These guidelines are intended to present information specifically adapted for European practice. The information provided should be taken in the context of local conditions and regulations.

Primary motor cortex of the parkinsonian monkey: differential effects on the spontaneous activity of pyramidal tract-type neurons

Dysfunction of primary motor cortex (M1) is thought to contribute to the pathophysiology of parkinsonism. What specific aspects of M1 function are abnormal remains uncertain, however. Moreover, few models consider the possibility that distinct cortical neuron subtypes may be affected differently. Those questions were addressed by studying the resting activity of intratelencephalic-type corticostriatal neurons (CSNs) and distant-projecting lamina 5b pyramidal-tract type neurons (PTNs) in the macaque M1 before and after the induction of parkinsonism by administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Contrary to previous reports, the general population of M1 neurons (i.e., PTNs, CSNs, and unidentified neurons) showed reduced baseline firing rates following MPTP, attributable largely to a marked decrease in PTN firing rates. CSN firing rates were unmodified. Although burstiness and firing patterns remained constant in M1 neurons as a whole and CSNs in particular, PTNs became more bursty post-MPTP and less likely to fire in a regular-spiking pattern. Rhythmic spiking (found in PTNs predominantly) occurred at beta frequencies (14-32 Hz) more frequently following MPTP. These results indicate that MPTP intoxication induced distinct modifications in the activity of different M1 neuronal subtypes. The particular susceptibility of PTNs suggests that PTN dysfunction may be an important contributor to the pathophysiology of parkinsonian motor signs.

Arterial spin labelling reveals an abnormal cerebral perfusion pattern in Parkinson's disease

There is a need for objective imaging markers of Parkinson's disease status and progression. Positron emission tomography and single photon emission computed tomography studies have suggested patterns of abnormal cerebral perfusion in Parkinson's disease as potential functional biomarkers. This study aimed to identify an arterial spin labelling magnetic resonance-derived perfusion network as an accessible, non-invasive alternative. We used pseudo-continuous arterial spin labelling to measure cerebral grey matter perfusion in 61 subjects with Parkinson's disease with a range of motor and cognitive impairment, including patients with dementia and 29 age- and sex-matched controls. Principal component analysis was used to derive a Parkinson's disease-related perfusion network via logistic regression. Region of interest analysis of absolute perfusion values revealed that the Parkinson's disease pattern was characterized by decreased perfusion in posterior parieto-occipital cortex, precuneus and cuneus, and middle frontal gyri compared with healthy controls. Perfusion was preserved in globus pallidus, putamen, anterior cingulate and post- and pre-central gyri. Both motor and cognitive statuses were significant factors related to network score. A network approach, supported by arterial spin labelling-derived absolute perfusion values may provide a readily accessible neuroimaging method to characterize and track progression of both motor and cognitive status in Parkinson's disease.

Molecular imaging and the neuropathologies of Parkinson's disease

The main motor symptoms of Parkinson's disease (PD) are linked to degeneration of the nigrostriatal dopamine (DA) fibers, especially those innervating the putamen. This degeneration can be assessed in molecular imaging studies with presynaptic tracers such as [(18)F]-fluoro-L-DOPA (FDOPA) and ligands for DA transporter ligands. However, the pathologies of PD are by no means limited to nigrostriatal loss. Results of post mortem and molecular imaging studies reveal parallel degenerations of cortical noradrenaline (NA) and serotonin (5-HT) innervations, which may contribute to affective and cognitive changes of PD. Especially in advanced PD, cognitive impairment can come to resemble that seen in Alzheimer's dementia, as can the degeneration of acetylcholine innervations arising in the basal forebrain. The density of striatal DA D(2) receptors increases in early untreated PD, consistent with denervation upregulation, but there is an accelerated rate of DA receptor loss as the disease advances. Animal studies and post mortem investigations reveal changes in brain opioid peptide systems, but these are poorly documented in imaging studies of PD. Relatively minor changes in the binding sites for GABA are reported in cortex and striatum of PD patients. There remains some controversy about the expression of the 18 kDa translocator protein (TSPO) in activated microglia as an indicator of an active inflammatory component of neurodegeneration in PD. A wide variety of autonomic disturbances contribute to the clinical syndrome of PD; the degeneration of myocardial sympathetic innervation can be revealed in SPECT studies of PD patients with autonomic failure. Considerable emphasis has been placed on investigations of cerebral blood flow and energy metabolism in PD. Due to the high variance of these physiological estimates, researchers have often employed normalization procedures for the sensitive detection of perturbations in relatively small patient groups. However, a widely used normalization to the global mean must be used with caution, as it can result in spurious findings of relative hypermetabolic changes in subcortical structures. A meta-analysis of the quantitative studies to date shows that there is in fact widespread hypometabolism and cerebral blood flow in the cerebral cortex, especially in frontal cortex and parietal association areas. These changes can bias the use of global mean normalization, and probably represent the pathophysiological basis of the cognitive impairment of PD.

PET studies of cerebral metabolism in Parkinson disease

A defect in cerebral energy production due to dysfunction of the mitochondrial electron transport system (ETS) has been postulated to be important in the pathogenesis of Parkinson Disease (PD). However, direct in vivo measurements of cerebral mitochondrial function are scant and inconsistent. We directly investigated cerebral mitochondrial function in vivo with positron emission tomography (PET) in 12 patients with early, never-medicated PD and 12 age-matched normal controls by combined measurements of the cerebral metabolic rate of oxygen (CMRO(2)) and the cerebral metabolic rate of glucose (CMRglc). Instead of the decrease in CMRO(2) and CMRO(2)/CMRglc molar ratio characteristic of defects in mitochondrial oxidative metabolism, there was a statistically significant 24% general increase in CMRO(2) and no change in CMRO(2)/CMRglc. Since PD symptoms were already manifest, reduced oxidative activity of the mitochondrial ETS cannot be a primary mechanism of neuronal death in early PD. This increase in metabolism could reflect the increased energy requirements of an injured brain or an uncoupling of ATP production from oxidation in the terminal stage of oxidative phosphorylation. Which is the case in early PD and whether these metabolic abnormalities are important in the pathogenesis of PD will require further study.

Cortical hypometabolism and hypoperfusion in Parkinson's disease is extensive: probably even at early disease stages

Recent cerebral blood flow (CBF) and glucose consumption (CMRglc) studies of Parkinson's disease (PD) revealed conflicting results. Using simulated data, we previously demonstrated that the often-reported subcortical hypermetabolism in PD could be explained as an artifact of biased global mean (GM) normalization, and that low-magnitude, extensive cortical hypometabolism is best detected by alternative data-driven normalization methods. Thus, we hypothesized that PD is characterized by extensive cortical hypometabolism but no concurrent widespread subcortical hypermetabolism and tested it on three independent samples of PD patients. We compared SPECT CBF images of 32 early-stage and 33 late-stage PD patients with that of 60 matched controls. We also compared PET FDG images from 23 late-stage PD patients with that of 13 controls. Three different normalization methods were compared: (1) GM normalization, (2) cerebellum normalization, (3) reference cluster normalization (Yakushev et al.). We employed standard voxel-based statistics (fMRIstat) and principal component analysis (SSM). Additionally, we performed a meta-analysis of all quantitative CBF and CMRglc studies in the literature to investigate whether the global mean (GM) values in PD are decreased. Voxel-based analysis with GM normalization and the SSM method performed similarly, i.e., both detected decreases in small cortical clusters and concomitant increases in extensive subcortical regions. Cerebellum normalization revealed more widespread cortical decreases but no subcortical increase. In all comparisons, the Yakushev method detected nearly identical patterns of very extensive cortical hypometabolism. Lastly, the meta-analyses demonstrated that global CBF and CMRglc values are decreased in PD. Based on the results, we conclude that PD most likely has widespread cortical hypometabolism, even at early disease stages. In contrast, extensive subcortical hypermetabolism is probably not a feature of PD.

Subthalamic nucleus stimulation affects limbic and associative circuits: a PET study

PURPOSE

Although high-frequency deep brain stimulation of the subthalamic nucleus (STN DBS) improves motor symptoms in advanced Parkinson's disease (PD), clinical studies have reported cognitive, motivational and emotional changes. These results suggest that the STN forms part of a broadly distributed neural network encompassing the associative and limbic circuits. We sought to pinpoint the cortical and subcortical brain areas modulated by STN DBS, in order to assess the STN's functional role and explain neuropsychological modifications following STN DBS in PD.

METHODS

We studied resting state glucose metabolism in 20 PD patients before and after STN DBS and 13 age-matched healthy controls using (18)F-FDG PET. We used statistical analysis (SPM2) first to compare pre-stimulation metabolism in PD patients with metabolism in healthy controls, then to study metabolic modifications in PD patients following STN DBS.

RESULTS

The first analysis revealed no pre-stimulation metabolic abnormalities in associative or limbic circuitry. After STN DBS, metabolic modifications were found in several regions known for their involvement in the limbic and associative circuits.

CONCLUSION

These metabolic results confirm the STN's central role in associative and limbic basal ganglia circuits. They will provide information for working hypotheses for future studies investigating neuropsychological changes and metabolic modifications related to STN DBS, with a view to improving our knowledge of this structure's functional role.

Metabolic networks for assessment of therapy and diagnosis in Parkinson's disease

Neuroimaging and modern computational techniques like spatial covariance analysis have contributed greatly to the understanding of neural system abnormalities in neurodegenerative disorders such as Parkinson's disease (PD). The application of network analysis to metabolic PET data obtained from patients with PD has led to the identification and validation of two distinct spatial covariance patterns associated with the motor and cognitive manifestations of the disease. Quantifying the activity of these patterns in individual subjects has provided an objective tool for the assessment of treatment efficacy and differential diagnosis. We have found that activity of the PD motor-related network is modulated by antiparkinsonian treatments such as dopaminergic therapy, deep brain stimulation (DBS), and subthalamic nucleus (STN) gene therapy. By contrast, the cognitive-related network is not altered by these interventions for PD motor symptoms. This pattern may however change in response to therapies targeting the cognitive symptoms of this disorder. Recent work has focused on the identification of specific network biomarkers for atypical parkinsonian conditions such as multiple system atrophy (MSA) and progressive supranuclear palsy (PSP). These disease-related patterns can potentially be used in an automated imaging-based algorithm to classify patients with these disorders.

Multifunctional roles of enolase in Alzheimer's disease brain: beyond altered glucose metabolism

Enolase enzymes are abundantly expressed, cytosolic carbon-oxygen lyases known for their role in glucose metabolism. Recently, enolase has been shown to possess a variety of different regulatory functions, beyond glycolysis and gluconeogenesis, associated with hypoxia, ischemia, and Alzheimer's disease (AD). AD is an age-associated neurodegenerative disorder characterized pathologically by elevated oxidative stress and subsequent damage to proteins, lipids, and nucleic acids, appearance of neurofibrillary tangles and senile plaques, and loss of synapse and neuronal cells. It is unclear if development of a hypometabolic environment is a consequence of or contributes to AD pathology, as there is not only a significant decline in brain glucose levels in AD, but also there is an increase in proteomics identified oxidatively modified glycolytic enzymes that are rendered inactive, including enolase. Previously, our laboratory identified alpha-enolase as one the most frequently up-regulated and oxidatively modified proteins in amnestic mild cognitive impairment (MCI), early-onset AD, and AD. However, the glycolytic conversion of 2-phosphoglycerate to phosphoenolpyruvate catalyzed by enolase does not directly produce ATP or NADH; therefore it is surprising that, among all glycolytic enzymes, alpha-enolase was one of only two glycolytic enzymes consistently up-regulated from MCI to AD. These findings suggest enolase is involved with more than glucose metabolism in AD brain, but may possess other functions, normally necessary to preserve brain function. This review examines potential altered function(s) of brain enolase in MCI, early-onset AD, and AD, alterations that may contribute to the biochemical, pathological, clinical characteristics, and progression of this dementing disorder.