Prefrontal thickening in PD with levodopa-induced dyskinesias: new evidence from cortical thickness measurement

Increased Cortical Thickness in Alzheimer's Disease

OBJECTIVE

Patients with Alzheimer's disease (AD) have diffuse brain atrophy, but some regions, such as the anterior cingulate cortex (ACC), are spared and may even show increase in size compared to controls. The extent, clinical significance, and mechanisms associated with increased cortical thickness in AD remain unknown. Recent work suggested neural facilitation of regions anticorrelated to atrophied regions in frontotemporal dementia. Here, we aim to determine whether increased thickness occurs in sporadic AD, whether it relates to clinical symptoms, and whether it occur in brain regions functionally connected to-but anticorrelated with-locations of atrophy.

METHODS

Cross-sectional clinical, neuropsychological, and neuroimaging data from the Alzheimer's Disease Neuroimaging Initiative were analyzed to investigate cortical thickness in AD subjects versus controls. Atrophy network mapping was used to identify brain regions functionally connected to locations of increased thickness and atrophy.

RESULTS

AD patients showed increased thickness in the ACC in a region-of-interest analysis and the visual cortex in an exploratory analysis. Increased thickness in the left ACC was associated with preserved cognitive function, while increased thickness in the left visual cortex was associated with hallucinations. Finally, we found that locations of increased thickness were functionally connected to, but anticorrelated with, locations of brain atrophy (r = -0.81, p < 0.05).

INTERPRETATION

Our results suggest that increased cortical thickness in Alzheimer's disease is relevant to AD symptoms and preferentially occur in brain regions functionally connected to, but anticorrelated with, areas of brain atrophy. Implications for models of compensatory neuroplasticity in response to neurodegeneration are discussed. ANN NEUROL 2024;95:929-940.

Voxel-based morphometry of grey matter structures in Parkinson's Disease with wearing-off

Our study aimed to investigate the grey matter (GM) changes using voxel-based morphometry (VBM) in Parkinson's disease (PD) patients with wearing-off (WO). 3D-T1-weighted imaging was performed on 48 PD patients without wearing-off (PD-nWO), 39 PD patients with wearing-off (PD-WO) and 47 age and sex-matched healthy controls (HCs). 3D structural images were analyzed by VBM procedure with Statistical Parametric Mapping (SPM12) to detect grey matter volume. Widespread areas of grey matter changes were found in patients among three groups (in bilateral frontal, temporal lobes, lingual gyrus, inferior occipital gyrus, right precuneus, right superior parietal gyrus and right cerebellum). Grey matter reductions were found in frontal lobe (right middle frontal gyrus, superior frontal gyrus and precentral gyrus), right parietal lobe (precuneus, superior parietal gyrus, postcentral gyrus), right temporal lobe (superior temporal gyrus, middle temporal gyrus), bilateral lingual gyrus and inferior occipital gyrus in PD-WO group compared with the PD-nWO group. Our results suggesting that wearing-off may be associated with grey matter atrophy in the cortical areas. These findings may aid in a better understanding of the brain degeneration process in PD with wearing-off.

Multimodal imaging study of the 5-HT1A receptor biased agonist, NLX-112, in a model of L-DOPA-induced dyskinesia

INTRODUCTION

The leading treatment for motor signs of Parkinson's disease is L-DOPA, but, upon extended use, it can lead to levodopa-induced dyskinesia (LID). Serotonergic neurons are involved in LID etiology and previous pre-clinical studies have shown that NLX-112, a 5-HT1A biased agonist, has robust antidyskinetic effects. Here, we investigated its effects in hemiparkinsonian (HPK) rats with a unilateral nigrostriatal 6-OHDA lesion.

METHODS

We compared HPK rats with LID (i.e., sensitized to the dyskinetic effects of chronic L-DOPA) and without LID (HPK-non-LID), using [18F]FDG PET imaging and fMRI functional connectivity following systemic treatment with saline, L-DOPA, NLX-112 or L-DOPA + NLX-112.

RESULTS

In HPK-non-LID rats, [18F]FDG PET experiments showed that L-DOPA led to hypermetabolism in motor areas (cerebellum, brainstem, and mesencephalic locomotor region) and to hypometabolism in cortical regions. L-DOPA effects were also observed in HPK-LID rats, with the additional emergence of hypermetabolism in raphe nuclei and hypometabolism in hippocampus and striatum. NLX-112 attenuated L-DOPA-induced raphe hypermetabolism and cingulate cortex hypometabolism in HPK-LID rats. Moreover, in fMRI experiments NLX-112 partially corrected the altered neural circuit connectivity profile in HPK-LID rats, through activity in regions rich in 5-HT1A receptors.

CONCLUSION

This neuroimaging study sheds light for the first time on the brain activation patterns of HPK-LID rats. The 5-HT1A receptor agonist, NLX-112, prevents occurrence of LID, likely by activating pre-synaptic autoreceptors in the raphe nuclei, resulting in a partial restoration of brain metabolic and connectivity profiles. In addition, NLX-112 also rescues L-DOPA-induced deficits in cortical activation, suggesting potential benefit against non-motor symptoms of Parkinson's disease.

Altered dynamic functional network connectivity in levodopa-induced dyskinesia of Parkinson's disease

AIMS

The aim of this study was to clarify the dynamic neural activity of levodopa-induced dyskinesia (LID) in Parkinson's disease (PD).

METHODS

Using dynamic functional network connectivity (dFNC) analysis, we evaluated 41 PD patients with LID (LID group) and 34 PD patients without LID (No-LID group). Group spatial independent component analysis and sliding-window approach were employed. Moreover, we applied a k-means clustering algorithm on windowed functional connectivity (FC) matrices to identify reoccurring FC patterns (i.e., states).

RESULTS

The optimal number of states was determined to be five, the so-called State 1, 2, 3, 4, and 5. In ON phase, compared with No-LID group, LID group occurred more frequently and dwelled longer in strongly connected State 1, characterized by strong positive connections between visual network (VIS) and sensorimotor network (SMN). When switching from OFF to ON phase, LID group occurred less frequently in State 3 and State 4. Meanwhile, LID group dwelled longer in State 2 and shorter in State 3. No-LID group occurred more frequently in State 5 and less frequently in State 3. Additionally, correlation analysis demonstrated that dyskinesia's severity was associated with frequency of occurrence and dwell time in State 2, dominated by inferior frontal cortex in cognitive executive network (CEN).

CONCLUSION

Using dFNC analysis, we found that dyskinesia may be related to the dysfunctional inhibition of CEN on motor loops and excessive excitation of VIS and SMN, which provided evidence of the changes in brain dynamics associated with the occurrence of dyskinesia.

Altered functional connectivity of cerebellar dentate nucleus in peak-dose dyskinesia in Parkinson’s disease

The cerebellum is associated with the emergence of levodopa-induced dyskinesia (LID) in Parkinson’s disease (PD), yet the neural mechanism remains obscure. Our aim was to ascertain the role of functional connectivity (FC) patterns of the cerebellar dentate nucleus (DN) in the pathogenesis of peak-dose dyskinesia in PD. Twenty-three peak-dose dyskinetic PD patients, 27 non-dyskinetic PD patients, and 36 healthy controls (HCs) were enrolled and underwent T1-weighted and resting-state functional magnetic resonance imaging (rs-fMRI) scans after dopaminergic medication intake. We selected left and right DN as the regions of interest and then employed voxel-wise FC analysis and voxel-based morphometry analysis (VBM). The correlations between the altered FC pattern and clinical scores were also examined. Finally, receiver operating characteristic (ROC) curve analysis was performed to assess the potential of DN FC measures as a feature of peak-dose dyskinesia in PD. Dyskinetic PD patients showed excessively increased FC between the left DN and right putamen compared with the non-dyskinetic. When compared with controls, dyskinetic PD patients mainly exhibited increased FC between left DN and bilateral putamen, left paracentral lobule, right postcentral gyrus, and supplementary motor area. Additionally, non-dyskinetic PD patients displayed increased FC between left DN and left precentral gyrus and right paracentral lobule compared with controls. Meanwhile, increased FC between DN (left/right) and ipsilateral cerebellum lobule VIII was observed in both PD subgroups. However, no corresponding alteration in gray matter volume (GMV) was found. Further, a positive correlation between the z-FC values of left DN-right putamen and the Unified Dyskinesia Rating Scale (UDysRS) was confirmed in dyskinetic PD patients. Notably, ROC curve analyses revealed that the z-FC values of left DN-right putamen could be a potential neuroimaging feature identifying dyskinetic PD patients. Our findings demonstrated that the excessively strengthened connectivity of DN-putamen might contribute to the pathophysiological mechanisms of peak-dose dyskinesia in PD.

White matter connectivity networks predict levodopa-induced dyskinesia in Parkinson's disease

BACKGROUND

Although levodopa-induced dyskinesia-relevant white matter change has been evaluated, it is uncertain whether these changes may reflect the underlying predisposing conditions leading to the development of levodopa-induced dyskinesia.

OBJECTIVE

To elucidate the role of white matter connectivity networks in the development of levodopa-induced dyskinesia in drug-naïve Parkinson's disease.

METHODS

We recruited 30 patients who developed levodopa-induced dyskinesia within 5 years from MRI acquisition (vulnerable-group), 47 patients who had not developed levodopa-induced dyskinesia within 5 years (resistant-group), and 28 controls. We performed comparative analyses of whole-brain white matter integrity and connectivity using tract-based spatial and network- and degree-based statistics. We evaluated the predictability of levodopa-induced dyskinesia development and relationship with its latency, using the average connectivity strength as a predictor in Cox- and linear-regression, respectively.

RESULTS

Mean-diffusivity was lower mainly at the left frontal region in the vulnerable-group compared to the resistant-group. Network-based statistics identified a subnetwork consisting of the bilateral fronto-striato-pallido-thalamic and lateral parietal regions (subnetwork A) and degree-based statistics identified four subnetworks (hub-subnetwork) consisting of edges centered on the left superior frontal gyrus, left putamen, left insular, or left precentral gyrus, where the vulnerable-group had stronger connectivity compared to the resistant-group. Stronger connectivity within the subnetwork A and hub-subnetwork centered on the left superior frontal gyrus was a predictor of levodopa-induced dyskinesia development independent of known risk factors and had an inverse relationship with its latency.

CONCLUSIONS

Our data suggest that white matter connectivity subnetworks within corticostriatal regions play a pivotal role in the development of levodopa-induced dyskinesia.

Effects of Repetitive Transcranial Magnetic Stimulation on Motor Symptoms in Parkinson's Disease: A Meta-Analysis

BACKGROUND

Transcranial magnetic stimulation (TMS) is a non-invasive neuromodulation technique that has been closely examined as a possible treatment for Parkinson's disease (PD). Owing to various rTMS protocols and results, the optimal mode and suitable PD symptoms have yet to be established.

OBJECTIVES

This study intends to systematically evaluate the efficacy of rTMS intervention and identify optimal stimulation protocol of rTMS for specific motor symptoms.

METHODS

PubMed and web of Science databases were searched before January 2022. Eligible studies included sham-controlled and randomized clinical trials of rTMS intervention for motor dysfunction in patients with PD. Standard mean difference (SMD) was calculated with random-effects models. The effects of rTMS on motor symptoms were mainly estimated by the UPDRS-III.

RESULTS

A total of 1172 articles were identified, of which 32 articles met the inclusion criteria for meta-analysis. The pooled evidence suggested that rTMS relieves motor symptoms of patients with PD (SMD 0.64, 95%CI [0.47, 0.80]). High frequency stimulation on M1 is the most effective mode of intervention (SMD 0.79, 95%CI [0.52, 1.07]). HF rTMS has significant therapeutic effects on limbs motor function (SMD 1.93, 95%CI [0.73, 3.12] for upper limb function and SMD 0.88, 95%CI [0.43, 1.33] for lower limb function), akinesia (SMD 1.17, 95%CI [0.43, 1.92), rigidity (SMD 1.02, 95%CI [0.12, 1.92]) and tremor(SMD 0.91, 95%CI [0.15, 1.67]).

CONCLUSION

rTMS therapy is an effective treatment for motor symptoms of PD and the individualized stimulation protocols for different symptoms would further improve its clinical efficacy.

Pallidal Structural Changes Related to Levodopa-induced Dyskinesia in Parkinson's Disease

Background

Despite the clinical impact of levodopa-induced dyskinesia (LID) in Parkinson's disease (PD), the mechanism, especially the role of basal ganglia (BG), is not fully elucidated yet. We investigated the BG structural changes related to LID in PD using a surface-based shape analysis technique.

Methods

We recruited patients with PD who developed LID within 3 years (LID group, 28 patients) and who did not develop it after 7 years (non-LID group, 35 patients) from levodopa treatment for the extreme case-control study. BG structure volumes were measured using volumetry analysis and the surface-based morphometry feature (i.e., Jacobian) from the subcortical surface vertices. We compared the volume and Jacobian of meshes in the regions between the two groups. We also performed a correlation analysis between local atrophy and the severity of LID. Additionally, we evaluated structural connectivity profiles from globus pallidus interna and externa (GPi and GPe) to other brain structures based on the group comparison.

Results

The demographic and clinical data showed no significant difference except for disease duration, treatment duration, parkinsonism severity, and levodopa equivalent dose. The LID group had more local atrophies of vertices in the right GPi than the non-LID group, despite no difference in volumes. Furthermore, the LID group demonstrated significantly reduced structural connectivity between left GPi and thalamus.

Conclusion

This is the first demonstration of distinct shape alterations of basal ganglia structures, especially GPi, related to LID in PD. Considering both direct and indirect BG pathways share the connection between GPi and thalamus, the BG pathway plays a crucial role in the development of LID.

Advantages of Using Both Voxel- and Surface-based Morphometry in Cortical Morphology Analysis: A Review of Various Applications

Surface-based morphometry (SBM) is extremely useful for estimating the indices of cortical morphology, such as volume, thickness, area, and gyrification, whereas voxel-based morphometry (VBM) is a typical method of gray matter (GM) volumetry that includes cortex measurement. In cases where SBM is used to estimate cortical morphology, it remains controversial as to whether VBM should be used in addition to estimate GM volume. Therefore, this review has two main goals. First, we summarize the differences between the two methods regarding preprocessing, statistical analysis, and reliability. Second, we review studies that estimate cortical morphological changes using VBM and/or SBM and discuss whether using VBM in conjunction with SBM produces additional values. We found cases in which detection of morphological change in either VBM or SBM was superior, and others that showed equivalent performance between the two methods. Therefore, we concluded that using VBM and SBM together can help researchers and clinicians obtain a better understanding of normal neurobiological processes of the brain. Moreover, the use of both methods may improve the accuracy of the detection of morphological changes when comparing the data of patients and controls.

In addition, we introduce two other recent methods as future directions for estimating cortical morphological changes: a multi-modal parcellation method using structural and functional images, and a synthetic segmentation method using multi-contrast images (such as T1- and proton density-weighted images).

Histological Correlates of Neuroanatomical Changes in a Rat Model of Levodopa-Induced Dyskinesia Based on Voxel-Based Morphometry

Long-term therapy with levodopa (L-DOPA) in patients with Parkinson’s disease (PD) often triggers motor complications termed as L-DOPA-induced dyskinesia (LID). However, few studies have explored the pathogenesis of LID from the perspective of neuroanatomy. This study aimed to investigate macroscopic structural changes in a rat model of LID and the underlying histological mechanisms. First, we established the hemiparkinsonism rat model through stereotaxic injection of 6-hydroxydopamine (6-OHDA) into the right medial forebrain bundle, followed by administration of saline (PD) or L-DOPA to induce LID. Magnetic resonance imaging (MRI) and behavioral evaluations were performed at different time points. Histological analysis was conducted to assess the correlations between MRI signal changes and cellular contributors. Voxel-based morphometry (VBM) analysis revealed progressive bilateral volume reduction in the cortical and subcortical areas in PD rats compared with the sham rats. These changes were partially reversed by chronic L-DOPA administration; moreover, there was a significant volume increase mainly in the dorsolateral striatum, substantia nigra, and piriform cortex of the lesioned side compared with that of PD rats. At the striatal cellular level, glial fibrillary acidic protein-positive (GFAP+) astrocytes were significantly increased in the lesioned dorsolateral striatum of PD rats compared with the intact side and the sham group. Prolonged L-DOPA treatment further increased GFAP levels. Neither 6-OHDA damage nor L-DOPA treatment influenced the striatal expression of vascular endothelial growth factor (VEGF). Additionally, there was a considerable increase in synapse-associated proteins (SYP, PSD95, and SAP97) in the lesioned striatum of LID rats relative to the PD rats. Golgi-Cox staining analysis of the dendritic spine morphology revealed an increased density of dendritic spines after chronic L-DOPA treatment. Taken together, our findings suggest that striatal volume changes in LID rats involve astrocyte activation, enrichment of synaptic ultrastructure and signaling proteins in the ipsilateral striatum. Meanwhile, the data highlight the enormous potential of structural MRI, especially VBM analysis, in determining the morphological phenotype of rodent models of LID.

Effects of Levodopa Therapy on Cerebral Arteries and Perfusion in Parkinson's Disease Patients

BACKGROUND

Levodopa is the most-commonly used therapy for Parkinson's Disease (PD). Imaging findings show increased cerebral blood flow (CBF) response to levodopa, but the artery morphological change is less studied.

PURPOSE

To investigate the effect of levodopa on cerebral arteries and CBF.

STUDY TYPE

Prospective.

POPULATION

57 PD patients (56 ± 10 years, 26 males) and 17 age-matched healthy controls (AMC, 57 ± 9 years, 9 males) were scanned at baseline (OFF). Patients were rescanned 50 minutes after taking levodopa (ON).

FIELD STRENGTH AND SEQUENCE

3 T; Simultaneous noncontrast angiography intraplaque imaging (SNAP) based on turbo field echo; Pseudo-continuous arterial spin labeling (PCASL) based on echo-planner imaging.

ASSESSMENT

The Unified Parkinson's Disease Rating Scale (UPDRS-III) was used to assess the disease severity. Length and radius of arteries were measured from SNAP images. CBF was calculated from PCASL images globally and regionally.

STATISTICAL TESTS

Mann Whitney U tests were conducted in comparing PD vs. AMC. Wilcoxon matched-pairs signed rank tests were used in comparing OFF vs. ON, and the more-affected vs. the less-affected hemisphere in PD. Linear regressions were performed to test the correlations of neuroimaging findings with behavioral changes. Significance threshold was P < 0.05 with Bonferroni correction.

RESULTS

PD patients were identified with significantly lower CBF (PD OFF Mean = 40.15 ± 5.99, AMC Mean = 43.48 ± 6.21 mL/100 g/min) and shortened total artery length (PD OFF Mean = 5851.07 ± 1393.45, AMC Mean = 7479.16 ± 1335.93 mm). Levodopa elevated CBF of PD brains (PD ON Mean = 41.48 ± 6.32 mL/100 g/min) and expanded radius of proximal arteries. Artery radius change significantly correlated with CBF change in corresponding territories (r = 0.559 for Internal Carotid Arteries, r = 0.448 for Basilar Artery, and r = 0.464 for Middle Cerebral Artery M1). Global CBF significantly related to UPDRS-III (r = -0.391) post-levodopa.

DATA CONCLUSION

Levodopa can increase CBF by dilating proximal arteries.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY STAGE: 4.

Baseline cognitive profile is closely associated with long-term motor prognosis in newly diagnosed Parkinson's disease

OBJECTIVES

To investigate the association between cognitive function at baseline and the progression of motor disability in Parkinson's disease (PD).

METHODS

We consecutively enrolled 257 drug-naïve patients with early-stage PD (follow-up > 2 years) who underwent a detailed neuropsychological test at initial assessment. Factor analysis was conducted to yield four cognitive function factors and composite scores thereof: Factor 1 (visual memory/visuospatial), Factor 2 (verbal memory), Factor 3 (frontal/executive), and Factor 4 (attention/working memory/language). The global cognitive composite score of each patient was calculated based on these factors. Subsequently, we assessed the effect of baseline cognitive function on long-term motor outcomes, namely levodopa-induced dyskinesia (LID), wearing-off, freezing of gait (FOG), and rate of longitudinal increases in levodopa-equivalent dose (LED).

RESULTS

Cox regression analysis demonstrated that higher Factor 3 (frontal/executive) composite scores (i.e., better cognitive performance) were associated with early development of LID [hazard ratio (HR), 1.507; p = 0.003], whereas higher Factor 1 (visual memory/visuospatial) composite scores (i.e., better cognitive performance) were associated with a lower risk for FOG (HR 0.683; p = 0.017). We noted that higher global cognitive composite scores were associated with a lower risk for developing FOG (HR 0.455; p = 0.045). The linear mixed model demonstrated that higher global cognitive composite scores and better cognitive performance in visual memory/visuospatial function were associated with slower longitudinal increases in LED.

CONCLUSIONS

These findings suggest that baseline cognitive profiles have prognostic implications on several motor aspects in patients with PD.

Opposite effects of one session of 1 Hz rTMS on functional connectivity between pre-supplementary motor area and putamen depending on the dyskinesia state in Parkinson's disease

OBJECTIVE

To explore the effects of low-frequency repetitive transcranial magnetic stimulation (LF rTMS) on cortico-striatal-cerebellar resting state functional connectivity in Parkinson's disease (PD), with and without dyskinesias.

METHODS

Because there is increasing evidence of an involvement of the pre-supplementary motor area (pre-SMA) in the pathophysiology of levodopa induced dyskinesias, we targeted the right pre-SMA with LF rTMS in 17 PD patients. We explored the effects of one sham-controlled LF rTMS session on resting state functional connectivity of interconnected brain regions by using functional MRI, and how it is modified by levodopa. The clinical effect on motor function and dyskinesias was documented.

RESULTS

As expected, one LF rTMS session did not alleviate dyskinesias. However, real, and not sham LF rTMS significantly increased the functional connectivity with the right putamen in patients with dyskinesias. In patients without dyskinesias, the real LF rTMS session significantly decreased functional connectivity in the right putamen and the cerebellum. We found no effects on functional connectivity after levodopa ingestion.

CONCLUSION

One session of 1 Hz rTMS has opposing effects on pre-SMA functional connectivity depending on the PD patients' dyskinesia state.

SIGNIFICANCE

Patients dyskinesias state determines the way LF rTMS affects functional connectivity in late stage PD.

Sex effects on brain structure in de novo Parkinson's disease: a multimodal neuroimaging study

Parkinson's disease varies in severity and age of onset. One source of this variability is sex. Males are twice as likely as females to develop Parkinson's disease, and tend to have more severe symptoms and greater speed of progression. However, to date, there is little information in large cohorts on sex differences in the patterns of neurodegeneration. Here we used MRI and clinical information from the Parkinson Progression Markers Initiative to measure structural brain differences between sexes in Parkinson's disease after regressing out the expected effect of age and sex. We derived atrophy maps from deformation-based morphometry of T1-weighted MRI and connectivity from diffusion-weighted MRI in de novo Parkinson's disease patients (149 males: 83 females) with comparable clinical severity, and healthy control participants (78 males: 39 females). Overall, even though the two patient groups were matched for disease duration and severity, males demonstrated generally greater brain atrophy and disrupted connectivity. Males with Parkinson's disease had significantly greater tissue loss than females in 11 cortical regions including bilateral frontal and left insular lobe, right postcentral gyrus, left inferior temporal and cingulate gyrus and left thalamus, while females had greater atrophy in six cortical regions, including regions in the left frontal lobe, right parietal lobe, left insular gyrus and right occipital cortex. Local efficiency of white matter connectivity showed greater disruption in males in multiple regions such as basal ganglia, hippocampus, amygdala and thalamus. These findings support the idea that development of Parkinson's disease may involve different pathological mechanisms and yield distinct prognosis in males and females, which may have implications for research into neuroprotection, and stratification for clinical trials.

Cortical thickness in Parkinson's disease: a coordinate-based meta-analysis

Parkinson's disease (PD) is a common age-related neurodegenerative disease that affects the structural architecture of the cerebral cortex. Cortical thickness (CTh) via surface-based morphometry (SBM) analysis is a popular measure to assess brain structural alterations in the gray matter in PD. However, the results of CTh analysis in PD lack consistency and have not been systematically reviewed. We conducted a comprehensive coordinate-based meta-analysis (CBMA) of 38 CTh studies (57 comparison datasets) in 1,843 patients with PD using the latest seed-based d mapping software. Compared with 1,172 healthy controls, no significantly consistent CTh alterations were found in patients with PD, suggesting CTh as an unreliable neuroimaging marker for PD. The lack of consistent CTh alterations in PD could be ascribed to the heterogeneity in clinical populations, variations in imaging methods, and underpowered small sample sizes. These results highlight the need to control for potential confounding factors to produce robust and reproducible CTh results in PD.

GraphNet-based imaging biomarker model to explain levodopa-induced dyskinesia in Parkinson's disease

BACKGROUND AND OBJECTIVE

Levodopa-induced dyskinesia (LID) is a disabling complication of Parkinson's disease (PD). Imaging-based measurements, especially those related to the surface shape of the basal ganglia, have shown potential for explaining the severity of LID in PD. Here, we aimed to explore a novel application of the methodology to find biomarkers of LID severity in PD using regularization.

METHODS

We proposed an application of graph-constrained elastic net (GraphNet) regularization to detect surface-based shape biomarkers explaining the severity of LID and compared the approach with other conventional regularization methods. To examine the methods, we used two independent datasets, one as a training dataset to build the model, and the other dataset was used to validate the constructed model.

RESULTS

We found that the left striatum (putamen was the greatest and the caudate was second) was the most significant surface-based biomarker related to the severity of LID. Our results improved the interpretability of identified surface-based biomarkers compared to competing methods. We also found that GraphNet regularization improved prediction of the severity of LID better than the conventional regularization methods. Our model performed better in terms of root-mean-squared error and correlation coefficient between predicted and actual clinical scores.

CONCLUSION

The proposed algorithm offers an advantage of interpretable anatomical variations related to the deformation of the cortical surface. The experimental results showed that GraphNet regularization was robust to identify surface-based shape biomarkers related to both hypokinetic and hyperkinetic movement disorders.

Neuroanatomical and Microglial Alterations in the Striatum of Levodopa-Treated, Dyskinetic Hemi-Parkinsonian Rats

Dyskinesia associated with chronic levodopa treatment in Parkinson’s disease is associated with maladaptive striatal plasticity. The objective of this study was to examine whether macroscale structural changes, as captured by magnetic resonance imaging (MRI) accompany this plasticity and to identify plausible cellular contributors in a rodent model of levodopa-induced dyskinesia. Adult male Sprague-Dawley rats were rendered hemi-parkinsonian by stereotaxic injection of 6-hydroxydopamine into the left medial forebrain bundle prior to chronic treatment with saline (control) or levodopa to induce abnormal involuntary movements (AIMs), reflective of dyskinesia. Perfusion-fixed brains underwent ex vivo structural MRI before sectioning and staining for cellular markers. Chronic treatment with levodopa induced significant AIMs (p < 0.0001 versus saline). The absolute volume of the ipsilateral, lesioned striatum was increased in levodopa-treated rats resulting in a significant difference in percentage volume change when compared to saline-treated rats (p < 0.01). Moreover, a significant positive correlation was found between this volume change and AIMs scores for individual levodopa-treated rats (r = 0.96; p < 0.01). The density of Iba1+ cells was increased within the lesioned versus intact striatum (p < 0.01) with no difference between treatment groups. Conversely, Iba1+ microglia soma size was significantly increased (p < 0.01) in the lesioned striatum of levodopa-treated but not saline-treated rats. Soma size was not, however, significantly correlated with either AIMs or MRI volume change. Although GFAP+ astrocytes were elevated in the lesioned versus intact striatum (p < 0.001), there was no difference between treatment groups. No statistically significant effects of either lesion or treatment on RECA1, a marker for blood vessels, were observed. Collectively, these data suggest chronic levodopa treatment in 6-hydroxydopamine lesioned rats is associated with increased striatal volume that correlates with the development of AIMs. The accompanying increase in number and size of microglia, however, cannot alone explain this volume expansion. Further multi-modal studies are warranted to establish the brain-wide effects of chronic levodopa treatment.

Functional Connectivity Signatures of Parkinson's Disease

 Resting-state functional magnetic resonance imaging (RS-fMRI) studies have been extensively applied to analyze the pathophysiology of neurodegenerative disorders such as Parkinson’s disease (PD). In the present narrative review, we attempt to summarize the most recent RS-fMRI findings highlighting the role of brain networks re-organization and adaptation in the course of PD. We also discuss limitations and potential definition of early functional connectivity signatures to track and predict future PD progression. Understanding the neural correlates and potential predisposing factors of clinical progression and complication will be crucial to guide novel clinical trials and to foster preventive strategies.

Altered interhemispheric synchrony in Parkinson's disease patients with levodopa-induced dyskinesias

Levodopa-induced dyskinesias are common motor complication of Parkinson's disease after 4-6 years of treatment. The hallmarks of dyskinesias include unilateral onset and the tendency to appear on the more affected body sides. There is a growing literature documenting the lateralization abnormalities are associated with the emergence of dyskinesias. Our investigation aimed to explore interhemispheric functional and its corresponding morphological asymmetry. A total of 22 dyskinetic patients, 23 nondyskinetic patients, and 26 controls were enrolled. Resting-state functional magnetic resonance imaging scans were performed twice before and after dopaminergic medication. Voxel-mirrored Homotopic Connectivity (VMHC) and Freesurfer were employed to assess the synchronicity of functional connectivity and structural alternations between hemispheres. During OFF state, dyskinetic patients showed desynchronization of inferior frontal cortex (IFC) when compared to nondyskinetic patients. And during ON state, dyskinetic patients showed desynchronization of IFC and pre-supplementary motor area (pre-SMA) when compared to nondyskinetic patients. However, there was no corresponding significant asymmetries in cortical thickness. Moreover, the degree of desynchronization of IFC and pre-SMA in dyskinetic pateients during ON state were negatively correlated with the Abnormal Involuntary Movement Scale (AIMS) scores. Notably, among patients who showed asymmetrical dyskinesias, there was a significant negative correlation between VMHC values of IFC and dyskinesias symptom asymmetry. Our findings suggested that uncoordinated inhibitory control over motor circuits may underlie the neural mechanisms of dyskinesias in Parkinson's disease and be related to its severity and lateralization.

MRI of Motor and Nonmotor Therapy-Induced Complications in Parkinson's Disease

Levodopa therapy remains the most effective drug for the treatment of Parkinson's disease, and it is associated with the greatest improvement in motor function as assessed by the Unified Parkinson's Disease Rating Scale. Dopamine agonists have also proven their efficacy as monotherapy in early Parkinson's disease but also as adjunct therapy. However, the chronic use of dopaminergic therapy is associated with disabling motor and nonmotor side effects and complications, among which levodopa-induced dyskinesias and impulse control behaviors are the most common. The underlying mechanisms of these disorders are not fully understood. In the last decade, classic neuroimaging methods and more sophisticated techniques, such as analysis of gray-matter structural imaging and functional magnetic resonance imaging, have given access to anatomical and functional abnormalities, respectively, in the brain. This review presents an overview of structural and functional brain changes associated with motor and nonmotor therapy-induced complications in Parkinson's disease. Magnetic resonance imaging may offer structural and/or functional neuroimaging biomarkers that could be used as predictive signs of development, maintenance, and progression of these complications. Neurophysiological tools, such as theta burst stimulation and transcranial magnetic stimulation, might help us to integrate neuroimaging findings and clinical features and could be used as therapeutic options, translating neuroimaging data into clinical practice. © 2020 International Parkinson and Movement Disorder Society.

White matter hyperintensities and risk of levodopa-induced dyskinesia in Parkinson's disease

Objective

To investigate whether the burden of white matter hyperintensities (WMHs) is associated with the risk of developing levodopa‐induced dyskinesia (LID) in Parkinson’s disease (PD).

Methods

According to the Clinical Research Center for Dementia of South Korea WMH visual rating scale, 336 patients with drug‐naïve early stage PD (follow‐up >3 years) were divided into two groups of PD with minimal WMHs (PD‐WMH–; n = 227) and moderate‐to‐severe WMHs (PD‐WMH+; n = 109). The Cox regression model was used to estimate the hazard ratio for the development of LID in the PD‐WMH + group compared with the PD‐WMH– group, while adjusting for age at PD onset, sex, striatal dopamine depletion, and PD medication dose. Additionally, we assessed the effects of WMH burden rated by the Scheltens scale and regional WMH distribution on the development of LID.

Results

Patients in the PD‐WMH + group were older and had more severe parkinsonian motor signs despite comparable striatal dopamine transporter availability than those in the PD‐WMH– group. Patients in the PD‐WMH + group had a higher risk of developing LID (hazard ratio, 2.66; P < 0.001) than those in the PD‐WMH– group after adjustment for other confounding factors. A greater WMH burden was associated with earlier occurrence of LID (hazard ratio, 1.04; P = 0.001), although the effects of WMHs on LID development did not exhibit region‐specific patterns.

Interpretation

The present study demonstrates that the burden of WMHs is associated with occurrence of LID in patients with PD, suggesting comorbid WMHs as a risk factor for LID.

Effect of aerobic exercise combined with cognitive remediation on cortical thickness and prediction of social adaptation in patients with schizophrenia

Aerobic exercise is a promising intervention for patients with schizophrenia, but structural neuroplastic effects on brain regions relevant to the pathophysiology of the disease remain unclear. This study aimed to elucidate longitudinal changes in cortical thickness after aerobic exercise intervention in schizophrenia patients and the relationship of these changes to clinical correlates. We investigated 21 schizophrenia patients and 23 healthy controls who performed aerobic exercise and 21 schizophrenia patients who played table soccer. The 12-week exercise intervention was combined with computer-assisted cognitive remediation training from week 6 to week 12. Magnetic resonance imaging (MRI) scans were acquired at baseline and weeks 6, 12, and 24. The thickness of the entorhinal, parahippocampal, and lateral and medial prefrontal cortices was assessed with FreeSurfer 6.0. The schizophrenia aerobic exercise group showed a significant increase of cortical thickness in the right entorhinal cortex at week 6, and we found a significant correlation between the cortical thickness of the right lateral prefrontal cortex at baseline and improvement of social adaptation at week 12. In the schizophrenia table soccer and healthy control groups, we found no significant longitudinal change in cortical thickness through the intervention and follow-up period and no correlation of cortical thickness at baseline with clinical measures. Our results suggest that aerobic exercise in schizophrenia modulates the thickness of the entorhinal cortex, a structure adjacent to the hippocampus. Greater cortical thickness of the right lateral prefrontal cortex appears to predict better clinical response to an aerobic exercise intervention in patients with schizophrenia.

Blood Flow and Glucose Metabolism Dissociation in the Putamen Is Predictive of Levodopa Induced Dyskinesia in Parkinson's Disease Patients

Background: The forefront treatment of Parkinson's disease (PD) is Levodopa. When patients are treated with Levodopa cerebral blood flow is increased while cerebral metabolic rate is decreased in key subcortical regions including the putamen. This phenomenon is especially pronounced in patients with Levodopa-induced dyskinesia (LID). Method: To study the effect of clinically-determined anti-parkinsonian medications, 10 PD patients (5 with LID and 5 without LID) have been scanned with FDG-PET (a probe for glucose metabolism) and perfusion MRI (a probe for cerebral blood flow) both when they are ON and OFF medications. Patients additionally underwent resting state fMRI to detect changes in dopamine-mediated cortico-striatal connectivity. The degree of blood flow-glucose metabolism dissociation was quantified by comparing the FDG-PET and perfusion MRI data. Results: A significant interaction effect (imaging modality × medication; blood flow-glucose metabolism dissociation) has been found in the putamen (p = 0.023). Post-hoc analysis revealed that anti-parkinsonian medication consistently normalized the pathologically hyper-metabolic state of the putamen while mixed effects were observed in cerebral blood flow changes. This dissociation was especially predominant in patients with LID compared to those without. Unlike the prior study, this differentiation was not observed when cortico-striatal functional connectivity was assessed. Conclusion: We confirmed striatal neurovascular dissociation between FDG-PET and perfusion MRI in response to clinically determined anti-parkinsonian medication. We further proposed a novel analytical method to quantify the degree of dissociation in the putamen using only the ON condition scans, Putamen-to-thalamus Hyper-perfusion/hypo-metabolism Index (PHI), which may have the potential to be used as a biomarker for LID (correctly classifying 8 out 10 patients). For wider use of PHI, a larger validation study is warranted.

The increased gray matter volumes of precentral gyri in Parkinson's disease patients with diphasic dyskinesia

Abnormal dopaminergic modulation of the cortico-basal ganglia motor loops results in the emergence of levodopa-induced dyskinesia (LID). We focused on alterations in the gray matter (GM) volume and the cortical thickness of the brain, especially in cortico-basal ganglia motor loops, in Parkinson’s disease (PD) with diphasic dyskinesia. 48 PD patients with diphasic dyskinesia, 60 PD patients without dyskinesia and 48 healthy controls (HC) were included. Voxel-based morphometry (VBM) was applied to get GM images from MRI brain images. FreeSurfer was used to get cortical thickness. Distinct analyses of covariance (ANCOVA) and linear contrasts were performed for early- and late-onset PD groups. The severity of diphasic dyskinesia was evaluated by the Unified Dyskinesia Rating Scale (UDysRS). Finally, the correlations between mean volumes of clusters showing differences and the UDysRS scores were performed by Pearson’s correlation. The GM volumes of precentral gyri were increased in PD patients with diphasic dyskinesia when compared with those without dyskinesia, which were positively correlated with UDysRS scores in PD patients with diphasic dyskinesia. However, there was no significant difference in cortical thickness among groups. The increased precentral gyri GM volumes might be associated with the pathogenesis and the severity of diphasic dyskinesia.

The influence of one session of low frequency rTMS on pre-supplementary motor area metabolites in late stage Parkinson's disease

OBJECTIVE

To study the effect of Low Frequency repetitive Transcranial Magnetic Stimulation (LF rTMS) on brain metabolites in late stage Parkinson's disease (PD) patients (disease duration at least 4 years and Hoehn and Yahr (1969) score at least 2 in OFF). Several neuroimaging data support a role for pre-Supplementary Motor Area (pre-SMA) involvement in the pathogenesis of Parkinson's disease. Proton magnetic resonance spectroscopy (¹H-MRS) measures in vivo metabolites, but results in PD brain remain conflicting and little is known of the effect of LF rTMS thereupon.

METHODS

We investigate the neurochemical profile of the right pre-SMA in 17 late stage PD patients (11 male and 6 female, mean age of 71 years) before and after one session of sham controlled 1 Hz rTMS (1000 pulses, 16 minutes), focusing on the tNAA/tCr and tCho/tCr ratios.

RESULTS

The tNAA/tCr ratio was unaffected by one session of LF rTMS. We did observe a significant effect of real LF rTMS on the tCho/tCr ratio, inversely correlated with disease duration, and not related to the presence of dyskinesias. As expected, one session of LF rTMS did not affect clinical outcome.

CONCLUSIONS

LF rTMS at the right pre-SMA in late stage Parkinson's disease patients does not alter tNAA/tCr, but influences tCho/tCr ratio, in particular in patients with shorter disease duration.

SIGNIFICANCE

Pre-SMA LF rTMS seems to influence membrane turnover, more importantly in patients with shorter disease duration. Larger LF rTMS treatment studies applying multiple sessions are needed.

Impulse control disorders in Parkinson's disease

Impulse control disorders (ICD) are frequent side effects of dopamine replacement therapy (DRT) used in Parkinson's disease (PD) with devastating consequences on the patients and caregivers. ICD are behavioural addictions including compulsive gambling, shopping, sexual behaviour, and binge eating that are mainly associated with dopamine D2/D3 agonists. Their management is a real clinical challenge due to the lack of therapeutic alternative. Clinical studies have identified demographic and clinical risk factors for ICD such as younger age at disease onset, male gender, prior history of depression or substance abuse, REM sleep behaviour disorders and higher rate of dyskinesia. PD patients with ICD may also have a specific pattern of dopaminergic denervation in the ventral striatum. Specific evaluation tools have now been designed to better evaluate the severity and impact of ICD in PD. Patients with ICD display altered processing of reward and loss, and decisional bias associated with altered activity in cortical and subcortical areas such as the orbitofrontal cortex, amygdala, insula, anterior cingular cortex, and ventral striatum. Preclinical studies have demonstrated that D2/D3 agonists induce impairments in behavioural processes likely relevant to ICD such as risk-taking behaviour, preference for uncertainty, perseverative responding and sustained drive to engage in gambling-like behaviour. Whether interactions between dopamine denervation and DRT significantly contribute to the pathogenesis of ICD remains poorly understood so far, although features unique to PD have been identified in patients with ICD. Large-scale longitudinal studies are needed to better identify subjects with increased risk to develop ICD and develop therapeutic options.

Association of grey matter changes with stability and flexibility of prediction in akinetic-rigid Parkinson's disease

Parkinson's disease (PD), which is caused by degeneration of dopaminergic neurons in the midbrain, results in a heterogeneous clinical picture including cognitive decline. Since the phasic signal of dopamine neurons is proposed to guide learning by signifying mismatches between subjects' expectations and external events, we here investigated whether akinetic-rigid PD patients without mild cognitive impairment exhibit difficulties in dealing with either relevant (requiring flexibility) or irrelevant (requiring stability) prediction errors. Following our previous study on flexibility and stability in prediction (Trempler et al. J Cogn Neurosci 29(2):298-309, 2017), we then assessed whether deficits would correspond with specific structural alterations in dopaminergic regions as well as in inferior frontal cortex, medial prefrontal cortex, and the hippocampus. Twenty-one healthy controls and twenty-one akinetic-rigid PD patients on and off medication performed a task which required to serially predict upcoming items. Switches between predictable sequences had to be indicated via button press, whereas sequence omissions had to be ignored. Independent of the disease, midbrain volume was related to a general response bias to unexpected events, whereas right putamen volume correlated with the ability to discriminate between relevant and irrelevant prediction errors. However, patients compared with healthy participants showed deficits in stabilisation against irrelevant prediction errors, associated with thickness of right inferior frontal gyrus and left medial prefrontal cortex. Flexible updating due to relevant prediction errors was also affected in patients compared with controls and associated with right hippocampus volume. Dopaminergic medication influenced behavioural performance across, but not within the patients. Our exploratory study warrants further research on deficient prediction error processing and its structural correlates as a core of cognitive symptoms occurring already in early stages of the disease.

Levodopa treatment and dendritic spine pathology

Parkinson's disease (PD) is a neurodegenerative disorder associated with the progressive loss of nigrostriatal dopaminergic neurons. Levodopa is the most effective treatment for the motor symptoms of PD. However, chronic oral levodopa treatment can lead to various motor and nonmotor complications because of nonphysiological pulsatile dopaminergic stimulation in the brain. Examinations of autopsy cases with PD have revealed a decreased number of dendritic spines of striatal neurons. Animal models of PD have revealed altered density and morphology of dendritic spines of neurons in various brain regions after dopaminergic denervation or dopaminergic denervation plus levodopa treatment, indicating altered synaptic transmission. Recent studies using rodent models have reported dendritic spine head enlargement in the caudate‐putamen, nucleus accumbens, primary motor cortex, and prefrontal cortex in cases where chronic levodopa treatment following dopaminergic denervation induced dyskinesia‐like abnormal involuntary movement. Hypertrophy of spines results from insertion of alpha‐amino‐2,3‐dihydro‐5‐methyl‐3‐oxo‐4‐isoxazolepropanoic acid receptors into the postsynaptic membrane. Such spine enlargement indicates hypersensitivity of the synapse to excitatory inputs and is compatible with a lack of depotentiation, which is an electrophysiological hallmark of levodopa‐induced dyskinesia found in the corticostriatal synapses of dyskinetic animals and the motor cortex of dyskinetic PD patients. This synaptic plasticity may be one of the mechanisms underlying the priming of levodopa‐induced complications such as levodopa‐induced dyskinesia and dopamine dysregulation syndrome. Drugs that could potentially prevent spine enlargement, such as calcium channel blockers, N‐methyl‐D‐aspartate receptor antagonists, alpha‐amino‐2,3‐dihydro‐5‐methyl‐3‐oxo‐4‐isoxazolepropanoic acid receptor antagonists, and metabotropic glutamate receptor antagonists, are candidates for treatment of levodopa‐induced complications in PD. © 2017 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Loss of phosphodiesterase 4 in Parkinson disease

Objective:

To assess in vivo the expression of phosphodiesterase 4 (PDE4) and its relevance to cognitive symptoms in patients with Parkinson disease (PD) using [11C]rolipram PET.

Methods:

We studied 12 levodopa-treated patients with PD with no concurrent diagnosis of mild cognitive impairment or dementia. Their data were compared with those from 12 healthy controls. All participants underwent neuropsychiatric and cognitive assessment using the Cambridge Neuropsychological Test Automated Battery. Parametric images of [11C]rolipram volume of distribution (VT) values were determined with the Logan plot.

Results:

Patients with PD performed worse than healthy controls in cognitive examinations assessing psychomotor speed, episodic memory, and spatial working memory and executive function. Patients with PD showed reductions in [11C]rolipram VT compared to healthy controls, in the caudate (28%), thalamus (23%), hypothalamus (32%), and cortex (16%). Within thalamic subregions, [11C]rolipram VT values in patients with PD were decreased by 12%–32%, with most marked decreases observed in prefrontal and temporal thalamic nuclei, whereas motor nuclei were less affected. Within the cortex, [11C]rolipram VT values in patients with PD were decreased by 11%–20%, with most marked decreases observed in posterior dorsolateral frontal cortex, medial frontal cortex, and supplementary motor area, whereas orbitofrontal cortex was less affected. Worse performance in spatial working memory correlated with lower [11C]rolipram VT values in posterior dorsolateral frontal cortex, medial frontal cortex, supplementary motor area, precentral gyrus, caudate, and prefrontal thalamic nuclei.

Conclusions:

Our findings demonstrate loss of PDE4 expression in the striato-thalamo-cortical circuit, which is associated with deficits of spatial working memory in patients with PD.

Levodopa-induced morphologic changes of prefrontal pyramidal tract-type neurons in a rat model of Parkinson's disease

Long-term administration of levodopa for Parkinson's disease is associated with various motor and non-motor complications. We examined the dendritic spine morphology of pyramidal tract-type neurons in the prefrontal cortex in a rat model of Parkinson's disease chronically treated with levodopa. Dendritic spines showed decreased density and increased average volume after dopamine denervation and levodopa treatment. These morphologic alterations suggest that the prefrontal neurons may maladaptively respond to excitatory input, which might be one of the mechanisms underlying various levodopa-induced complications in patients with Parkinson's disease.

Gender-based analysis of cortical thickness and structural connectivity in Parkinson's disease

Parkinson's disease (PD) is a progressive neurological disorder and appears to have gender-specific symptoms. Studies have observed a higher frequency for development of PD in male than in female. In the current study, we evaluated the gender-based changes in cortical thickness and structural connectivity in PD patients. With informed consent, 64 PD (43 males and 21 females) patients, and 46 (12 males and 34 females) age-matched controls underwent clinical assessment including Mini-Mental State Examination (MMSE) and magnetic resonance imaging on a 1.5 Tesla clinical MR scanner. Whole brain high-resolution T1-weighted images were acquired from all subjects and used to measure cortical thickness and structural network connectivity. No significant difference in MMSE score was observed between male and female both in control and PD subjects. Male PD patients showed significantly reduced cortical thickness in multiple brain regions including frontal, parietal, temporal, and occipital lobes as compared with those in female PD patients. The graph theory-based network analysis depicted lower connection strengths, lower clustering coefficients, and altered network hubs in PD male than in PD female. Male-specific cortical thickness changes and altered connectivity in PD patients may derive from behavioral, physiological, environmental, and genetical differences between male and female, and may have significant implications in diagnosing and treating PD among genders.

Characterization of gray matter atrophy following 6-hydroxydopamine lesion of the nigrostriatal system

BACKGROUND

The unilaterally-lesioned 6-hydroxydopamine (6-OHDA) rat is one of the most commonly used experimental models of Parkinson's disease (PD). Here we investigated whether magnetic resonance imaging (MRI) that is widely used in human PD research, has the potential to non-invasively detect macroscopic structural brain changes in the 6-OHDA rat in ways translatable to humans.

METHODS

We measured the gray matter (GM) composition in the unilateral 6-OHDA rat in comparison to sham animals using whole-brain voxel-based morphometry (VBM) - an unbiased MR image analysis technique. The number of nigral dopamine (DA) neurons and the density of their cortical projections were examined post-mortem using immunohistochemistry.

RESULTS

VBM revealed widespread bilateral changes in gray matter volume (GMV) on a topographic scale in the brains of 6-OHDA rats, compared to sham-operated rats. The greatest changes were in the lesioned hemisphere, which displayed reductions of GMV in motor, cingulate and somatosensory cortex. Histopathological results revealed dopaminergic cell loss in the substantia nigra (SN) and a denervation in the striatum, as well as in the frontal, somatosensory and cingulate cortices.

CONCLUSION

Unilateral nigrostriatal 6-OHDA lesioning leads to widespread GMV changes, which extend beyond the nigrostriatal system and resemble advanced Parkinsonism. This study highlights the potential of structural MRI, and VBM in particular, for the system-level phenotyping of rodent models of Parkinsonism and provides a methodological framework for future studies in novel rodent models as they become available to the research community.

Resting-state connectivity predicts levodopa-induced dyskinesias in Parkinson's disease

Background

Levodopa‐induced dyskinesias are a common side effect of dopaminergic therapy in PD, but their neural correlates remain poorly understood.

Objectives

This study examines whether dyskinesias are associated with abnormal dopaminergic modulation of resting‐state cortico‐striatal connectivity.

Methods

Twelve PD patients with peak‐of‐dose dyskinesias and 12 patients without dyskinesias were withdrawn from dopaminergic medication. All patients received a single dose of fast‐acting soluble levodopa and then underwent resting‐state functional magnetic resonance imaging before any dyskinesias emerged. Levodopa‐induced modulation of cortico‐striatal resting‐state connectivity was assessed between the putamen and the following 3 cortical regions of interest: supplementary motor area, primary sensorimotor cortex, and right inferior frontal gyrus. These functional connectivity measures were entered into a linear support vector classifier to predict whether an individual patient would develop dyskinesias after levodopa intake. Linear regression analysis was applied to test which connectivity measures would predict dyskinesia severity.

Results

Dopaminergic modulation of resting‐state connectivity between the putamen and primary sensorimotor cortex in the most affected hemisphere predicted whether patients would develop dyskinesias with a specificity of 100% and a sensitivity of 91% (P < .0001). Modulation of resting‐state connectivity between the supplementary motor area and putamen predicted interindividual differences in dyskinesia severity (R² = 0.627, P = .004). Resting‐state connectivity between the right inferior frontal gyrus and putamen neither predicted dyskinesia status nor dyskinesia severity.

Conclusions

The results corroborate the notion that altered dopaminergic modulation of cortico‐striatal connectivity plays a key role in the pathophysiology of dyskinesias in PD. © 2016 International Parkinson and Movement Disorder Society

The Effectiveness of Transcranial Brain Stimulation in Improving Clinical Signs of Hyperkinetic Movement Disorders

Repetitive transcranial magnetic stimulation (rTMS) is a safe and painless method for stimulating cortical neurons. In neurological realm, rTMS has prevalently been applied to understand pathophysiological mechanisms underlying movement disorders. However, this tool has also the potential to be translated into a clinically applicable therapeutic use. Several available studies supported this hypothesis, but differences in protocols, clinical enrollment, and variability of rTMS effects across individuals complicate better understanding of efficient clinical protocols. The aim of this present review is to discuss to what extent the evidence provided by the therapeutic use of rTMS may be generalized. In particular, we attempted to define optimal cortical regions and stimulation protocols that have been demonstrated to maximize the effectiveness seen in the actual literature for the three most prevalent hyperkinetic movement disorders: Parkinson's disease (PD) with levodopa-induced dyskinesias (LIDs), essential tremor (ET) and dystonia. A total of 28 rTMS studies met our search criteria. Despite clinical and methodological differences, overall these studies demonstrated that therapeutic applications of rTMS to "normalize" pathologically decreased or increased levels of cortical activity have given moderate progress in patient's quality of life. Moreover, the present literature suggests that altered pathophysiology in hyperkinetic movement disorders establishes motor, premotor or cerebellar structures as candidate regions to reset cortico-subcortical pathways back to normal. Although rTMS has the potential to become a powerful tool for ameliorating the clinical outcome of hyperkinetic neurological patients, until now there is not a clear consensus on optimal protocols for these motor disorders. Well-controlled multicenter randomized clinical trials with high numbers of patients are urgently required.

Morphometric changes in the reward system of Parkinson's disease patients with impulse control disorders

Impulse control disorders (ICDs) occur in a subset of patients with Parkinson's disease (PD) who are receiving dopamine replacement therapy. In this study, we aimed to investigate structural abnormalities within the mesocortical and limbic cortices and subcortical structures in PD patients with ICDs. We studied 18 PD patients with ICDs, 18 PD patients without ICDs and a group of 24 age and sex-matched healthy controls. Cortical thickness (CTh) and subcortical nuclei volume analyses were carried out using the automated surface-based analysis package FreeSurfer (version 5.3.0). We found significant differences in MRI measures between the three groups. There was volume loss in the nucleus accumbens of both PD patients with ICDs and without ICDs compared to the control group. In addition, PD patients with ICDs showed significant atrophy in caudate, hippocampus and amygdala compared to the group of healthy controls. PD patients with ICDs had significant increased cortical thickness in rostral anterior cingulate cortex and frontal pole compared to PD patients without ICDs. Cortical thickness in rostral anterior cingulate and frontal pole was increased in PD patients with ICDs compared to the control group, but the differences failed to reach corrected levels of statistical significance. PD patients with ICDs showed increased cortical thickness in medial prefrontal regions. We speculate that these findings reflect either a pre-existing neural trait vulnerability to impulsivity or the expression of a maladaptive synaptic plasticity under non-physiological dopaminergic stimulation.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

Progression of brain atrophy in the early stages of Parkinson's disease: a longitudinal tensor-based morphometry study in de novo patients without cognitive impairment

The presence of brain atrophy and its progression in early Parkinson's disease (PD) are still a matter of debate, particularly in patients without cognitive impairment. The aim of this longitudinal study was to assess whether PD patients who remain cognitively intact develop progressive atrophic changes in the early stages of the disease. For this purpose, we employed high-resolution T1-weighted MR imaging to compare 22 drug-naïve de novo PD patients without cognitive impairment to 17 age-matched control subjects, both at baseline and at three-year follow-up. We used tensor-based morphometry to explore the presence of atrophic changes at baseline and to compute yearly atrophy rates, after which we performed voxel-wise group comparisons using threshold-free cluster enhancement. At baseline, we did not observe significant differences in regional atrophy in PD patients with respect to control subjects. In contrast, PD patients showed significantly higher yearly atrophy rates in the prefrontal cortex, anterior cingulum, caudate nucleus, and thalamus when compared to control subjects. Our results indicate that even cognitively preserved PD patients show progressive cortical and subcortical atrophic changes in regions related to cognitive functions and that these changes are already detectable in the early stages of the disease.

Brain morphometry and the neurobiology of levodopa-induced dyskinesias: current knowledge and future potential for translational pre-clinical neuroimaging studies

Dopamine replacement therapy in the form of levodopa results in a significant proportion of patients with Parkinson’s disease developing debilitating dyskinesia. This significantly complicates further treatment and negatively impacts patient quality of life. A greater understanding of the neurobiological mechanisms underlying levodopa-induced dyskinesia (LID) is therefore crucial to develop new treatments to prevent or mitigate LID. Such investigations in humans are largely confined to assessment of neurochemical and cerebrovascular blood flow changes using positron emission tomography and functional magnetic resonance imaging. However, recent evidence suggests that LID is associated with specific morphological changes in the frontal cortex and midbrain, detectable by structural MRI and voxel-based morphometry. Current human neuroimaging methods however lack sufficient resolution to reveal the biological mechanism driving these morphological changes at the cellular level. In contrast, there is a wealth of literature from well-established rodent models of LID documenting detailed post-mortem cellular and molecular measurements. The combination therefore of advanced neuroimaging methods and rodent LID models offers an exciting opportunity to bridge these currently disparate areas of research. To highlight this opportunity, in this mini-review, we provide an overview of the current clinical evidence for morphological changes in the brain associated with LID and identify potential cellular mechanisms as suggested from human and animal studies. We then suggest a framework for combining small animal MRI imaging with rodent models of LID, which may provide important mechanistic insights into the neurobiology of LID.

Maladaptive plasticity in levodopa-induced dyskinesias and tardive dyskinesias: old and new insights on the effects of dopamine receptor pharmacology

Maladaptive plasticity can be defined as behavioral loss or even development of disease symptoms resulting from aberrant plasticity changes in the human brain. Hyperkinetic movement disorders, in the neurological or psychiatric realms, have been associated with maladaptive neural plasticity that can be expressed by functional changes such as an increase in transmitter release, receptor regulation, and synaptic plasticity or anatomical modifications such as axonal regeneration, sprouting, synaptogenesis, and neurogenesis. Recent evidence from human and animal models provided support to the hypothesis that these phenomena likely depend on altered dopamine turnover induced by long-term drug treatment. However, it is still unclear how and where these altered mechanisms of cortical plasticity may be localized. This study provides an up-to-date overview of these issues together with some reflections on future studies in the field, particularly focusing on two specific disorders (levodopa-induced dyskinesias in Parkinson’s disease patients and tardive dyskinesias in schizophrenic patients) where the modern neuroimaging approaches have recently provided new fundamental insights.