High γ‐Aminobutyric Acid Content Within the Medial Prefrontal Cortex Is a Functional Signature of Somatic Symptoms Disorder in Patients With Parkinson's Disease

GABAergic imbalance in Parkinson's disease-related depression determined with MEGA-PRESS

OBJECTIVE

The pathogenesis of depression in patients with Parkinson's disease (PD) is poorly understood. Therefore, this study aimed to explore the changes in γ-aminobutyric acid (GABA) and glutamate plus glutamine (Glx) levels in patients with PD with or without depression determined using MEscher-GArwood Point Resolved Spectroscopy (MEGA-PRESS).

MATERIALS AND METHODS

A total of 83 patients with primary PD and 24 healthy controls were included. Patients with PD were categorized into depressed PD (DPD, n = 19) and nondepressed PD (NDPD, n = 64) based on the 17-item Hamilton Depression Rating Scale. All participants underwent T1-weighted imaging and MEGA-PRESS sequence to acquire GABA+ and Glx values. The MEGA-PRESS sequence was conducted using 18.48 mL voxels in the left thalamus and medial frontal cortex. The GABA+, Glx, and creatine values were quantified using Gannet 3.1 software.

RESULTS

The GABA+ and Glx values were not significantly disparate between patients with PD and controls in the thalamus and medial frontal cortex. However, the levels of N-acetyl aspartate/creatine and choline/creatine in the left thalamus were significantly lower in patients with PD than in controls (P = .031, P = .009). The GABA+/Water and GABA+/Creatine in the medial frontal cortex were higher in DPD than in NDPD (P = .001, P = .004). The effects of depression on Glx or other metabolite levels were not evident, and no significant difference in metabolite values was noted in the left thalamus among all groups (P > .05).

CONCLUSIONS

GABA+ levels increased in the medial frontal cortex in DPD, which may be more closely related to depressive pathology. Thus, alterations in GABAergic function in special brain structures may be related to the clinical manifestations of PD symptoms, and hence mediating this function might help in treating depression in PD.

Glutamate Signaling in Patients With Parkinson Disease With REM Sleep Behavior Disorder

BACKGROUND AND OBJECTIVES

Clinical heterogeneity of patients with Parkinson disease (PD) is well recognized. PD with REM sleep behavior disorder (RBD) is a more malignant phenotype with faster motor progression and higher nonmotor symptom burden. However, the neural mechanisms underlying this clinical divergence concerning imbalances in neurotransmitter systems remain elusive.

METHODS

Combining magnetic resonance (MR) spectroscopy and [11C]ABP688 PET on a PET/MR hybrid system, we simultaneously investigated two different mechanisms of glutamate signaling in patients with PD. Patients were grouped according to their RBD status in overnight video-polysomnography and compared with age-matched and sex-matched healthy control (HC) participants. Total volumes of distribution (VT) of [11C]ABP688 were estimated with metabolite-corrected plasma concentrations during steady-state conditions between 45 and 60 minutes of the scan following a bolus-infusion protocol. Glutamate, glutamine, and glutathione levels were investigated with single-voxel stimulated echo acquisition mode MR spectroscopy of the left basal ganglia.

RESULTS

We measured globally elevated VT of [11C]ABP688 in 16 patients with PD and RBD compared with 17 patients without RBD and 15 HC participants (F(2,45) = 5.579, p = 0.007). Conversely, glutamatergic metabolites did not differ between groups and did not correlate with the regional VT of [11C]ABP688. VT of [11C]ABP688 correlated with the amount of REM sleep without atonia (F(1,42) = 5.600, p = 0.023) and with dopaminergic treatment response in patients with PD (F(1,30) = 5.823, p = 0.022).

DISCUSSION

Our results suggest that patients with PD and RBD exhibit altered glutamatergic signaling indicated by higher VT of [11C]ABP688 despite unaffected glutamate levels. The imbalance of glutamate receptors and MR spectroscopy glutamate metabolite levels indicates a novel mechanism contributing to the heterogeneity of PD and warrants further investigation of drugs targeting mGluR5.

Anti-inflammatory effects of myristic acid mediated by the NF-κB pathway in lipopolysaccharide-induced BV-2 microglial cells

Parkinson's disease (PD) is a serious neurodegenerative disorder wherein changes in metabolites related to lipids, glutathione, and energy metabolism occur. Currently, metabolite changes in PD have been reported, yet their role in the prognosis of disease remains poorly understood. Functional metabolites can be used to diagnose diseases, especially PD, and can exert neuroprotective effects. This study used a PD animal model and a lipopolysaccharide (LPS)-mediated inflammatory response model (using the BV-2 mouse microglial cell line) to identify functional metabolites that can identify important metabolic disorders during PD, and comprehensively evaluated their profiles using a metabolomics-based approach. Our results showed that co-treatment with myristic acid and heptadecanoic acid downregulated the expression of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α in BV-2 cells. Additionally, myristic acid and 10 μM heptadecanoic acid significantly inhibited the LPS-induced inflammatory response through the nuclear factor-κB pathway in BV-2 microglial cells, which provides a potential approach for PD treatment. Myristic acid and heptadecanoic acid were the active metabolites found by active metabolomics technology, but at present, there is no research report about their function for PD treatment, and our findings offer a novel research strategy for PD diagnosis and treatment.

Meta-analysis and open-source database for in vivo brain Magnetic Resonance spectroscopy in health and disease

Proton (1H) Magnetic Resonance Spectroscopy (MRS) is a non-invasive tool capable of quantifying brain metabolite concentrations in vivo. Prioritization of standardization and accessibility in the field has led to the development of universal pulse sequences, methodological consensus recommendations, and the development of open-source analysis software packages. One on-going challenge is methodological validation with ground-truth data. As ground-truths are rarely available for in vivo measurements, data simulations have become an important tool. The diverse literature of metabolite measurements has made it challenging to define ranges to be used within simulations. Especially for the development of deep learning and machine learning algorithms, simulations must be able to produce accurate spectra capturing all the nuances of in vivo data. Therefore, we sought to determine the physiological ranges and relaxation rates of brain metabolites which can be used both in data simulations and as reference estimates. Using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, we've identified relevant MRS research articles and created an open-source database containing methods, results, and other article information as a resource. Using this database, expectation values and ranges for metabolite concentrations and T2 relaxation times are established based upon a meta-analyses of healthy and diseased brains.

Meta-analysis and Open-source Database for In Vivo Brain Magnetic Resonance Spectroscopy in Health and Disease

Proton ( 1 H) Magnetic Resonance Spectroscopy (MRS) is a non-invasive tool capable of quantifying brain metabolite concentrations in vivo . Prioritization of standardization and accessibility in the field has led to the development of universal pulse sequences, methodological consensus recommendations, and the development of open-source analysis software packages. One on-going challenge is methodological validation with ground-truth data. As ground-truths are rarely available for in vivo measurements, data simulations have become an important tool. The diverse literature of metabolite measurements has made it challenging to define ranges to be used within simulations. Especially for the development of deep learning and machine learning algorithms, simulations must be able to produce accurate spectra capturing all the nuances of in vivo data. Therefore, we sought to determine the physiological ranges and relaxation rates of brain metabolites which can be used both in data simulations and as reference estimates. Using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, we've identified relevant MRS research articles and created an open-source database containing methods, results, and other article information as a resource. Using this database, expectation values and ranges for metabolite concentrations and T 2 relaxation times are established based upon a meta-analyses of healthy and diseased brains.

Scoping review update on somatic symptom disorder that includes additional Chinese data

Somatic symptom disorder (SSD) is a new diagnosis introduced into the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), which is expected to solve the diagnostic difficulties of patients with medically unexplained symptoms. Based on the previous work, this review aims to comprehensively synthesise updated evidence related to SSD from recent years in English publications and, more extensively, from data published in Chinese language journals. The scoping review update was based on an earlier scoping review and included Chinese language publication data from China National Knowledge Internet (CNKI), WANFANG and WEIPU between January 2013 and May 2022 and data from PubMed, PsycINFO, and Cochrane Library between June 2020 and May 2022. Initially, 2 984 articles were identified, of which 63 full texts were included for analysis. In China, SSD is mainly applied in scientific research, but it also shows good predictive validity and clinical application potential. The mean frequency of SSD was 4.5% in the general population, 25.2% in the primary care population and 33.5% in diverse specialised care settings. Biological factors, such as brain region changes and heart rate variability, are associated with the onset of SSD. Psychological impairment related to somatic symptoms is the best predictor of prognosis. While adolescent SSD was significantly associated with family function, SSD overall is associated with an increased dysfunction of cognition and emotion, decreased quality of life, and high comorbidity with anxiety and depressive disorders. Further research is needed on suicide risk and cultural and gender-related issues. Updating the data of Chinese language studies, our research enriches the evidence-based findings related to the topics addressed in the text sections of the SSD chapter of DSM-5. However, research gaps remain about SSD reliability, population-based prevalence, suicide risk, and cultural and gender-related issues.

Functional Neurologic Disorders, disorders to be managed by neurologists, or are neurologists wandering in a dangerous field with inadequate resources?

In recent years, some neurologists reconsidered their approach to Medically Unexplained Symptoms and proposed Functional Neurologic Disorders (FND) as a new entity, claiming that neurology could offer alternative treatment options to the psychotherapies provided in psychiatry settings. FNDs, for this purpose, should include only the disorders listed as Conversion from the Somatic Symptom and Related Disorders (SSRD) group. The present review analyzes the rationale of this position and challenges the arguments provided for its support. The review also discusses the systematization of these disorders as provided by public health systems. It outlines risks stemming from economic support and public funding uncertainty, given their negligible epidemiological dimensions resulting from the parcellation of SSRD. The review underlines the unresolved issue of Factitious Disorders, which are in the same SSRD category of the international classification but are, nonetheless, overlooked by the theoretical proponents of the FND entity. Comorbidity with other psychiatric disorders is also analyzed. We propose a model that supports the continuum between different SSRD conditions, including Factitious Disorders. The model is based on the emergence of feigned death reflex and deception from frontal lobe dysfunction. Finally, the paper summarizes the wealth of historical psychiatric and psychodynamic approaches and critical reviews. The study also puts in context the categorization and interpretation efforts provided by the most eminent researchers of the past century.

Impact of gradient scheme and non-linear shimming on out-of-voxel echo artifacts in edited MRS

Out-of-voxel (OOV) signals are common spurious echo artifacts in MRS. These signals often manifest in the spectrum as very strong "ripples," which interfere with spectral quantification by overlapping with targeted metabolite resonances. Dephasing optimization through coherence order pathway selection (DOTCOPS) gradient schemes are algorithmically optimized to suppress all potential alternative coherence transfer pathways (CTPs), and should suppress unwanted OOV echoes. In addition, second-order shimming uses non-linear gradient fields to maximize field homogeneity inside the voxel, which unfortunately increases the diversity of local gradient fields outside of the voxel. Given that strong local spatial B0 gradients can refocus unintended CTPs, it is possible that OOVs are less prevalent when only linear first-order shimming is applied. Here we compare the size of unwanted OOV signals in Hadamard-edited (HERMES) data acquired with either a local gradient scheme (which we refer to here as "Shared") or DOTCOPS, and with first- or second-order shimming. We collected data from 15 healthy volunteers in two brain regions (voxel size 30 × 26 × 26 mm3 ) from which it is challenging to acquire MRS data: medial prefrontal cortex and left temporal cortex. Characteristic OOV echoes were seen in both GABA- and GSH-edited spectra for both brain regions, gradient schemes, and shimming approaches. A linear mixed-effect model revealed a statistically significant difference in the average residual based on the gradient scheme in both GABA- (p < 0.001) and GSH-edited (p < 0.001) spectra: that is, the DOTCOPS gradient scheme resulted in smaller OOV artifacts compared with the Shared scheme. There were no significant differences in OOV artifacts associated with shimming method. Thus, these results suggest that the DOTCOPS gradient scheme for J-difference-edited PRESS acquisitions yields spectra with smaller OOV echo artifacts than the Shared gradient scheme implemented in a widely disseminated editing sequence.

Altered Medial Prefrontal Connectivity in Parkinson's Disease Patients with Somatic Symptoms

BACKGROUND

The high co-occurrence of somatic symptom disorder (SSD) in Parkinson's disease (PD) patients suggests overlapping pathophysiology. However, little is known about the neural correlates of SSD and their possible interactions with PD. Existing studies have shown that SSD is associated with reduced task-evoked activity in the medial prefrontal cortex (mPFC), a central node of the default-mode network (DMN). SSD is also associated with abnormal γ-aminobutyric acid (GABA) content, a marker of local inhibitory tone and regional hypoactivity, in the same area when SSD co-occurs with PD.

OBJECTIVES

To disentangle the individual and shared effects of SSD and PD on mPFC neurotransmission and connectivity patterns and help disclose the neural mechanisms of comorbidity in the PD population.

METHODS

The study cohort included 18 PD patients with SSD (PD + SSD), 18 PD patients, 13 SSD patients who did not exhibit neurologic disorders, and 17 healthy subjects (HC). Proton magnetic resonance (MR) spectroscopy evaluated GABA levels within a volume of interest centered on the mPFC. Resting-state functional MR imaging investigated the region's functional connectivity patterns.

RESULTS

Compared to HC or PD groups, the mPFC of SSD subjects exhibited higher GABA levels and connectivity. Higher mPFC connectivity involved DMN regions in SSD patients without PD and regions of the executive and attentional networks (EAN) in patients with PD comorbidity.

CONCLUSIONS

Aberrant reconfigurations of connectivity patterns between the mPFC and the EAN are distinct features of the PD + SSD comorbidity. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Altered Brain Activity in Depression of Parkinson's Disease: A Meta-Analysis and Validation Study

Background

The pathophysiology of depression in Parkinson's disease (PD) is not fully understood. Studies based upon functional MRI (fMRI) showed the alterations in the blood-oxygen-level-dependent (BOLD) fluctuations in multiple brain regions pertaining to depression in PD. However, large variance was observed across previous studies. Therefore, we conducted a meta-analysis to quantitatively evaluate the results in previous publications and completed an independent regions-of-interests (ROIs)-based analysis using our own data to validate the results of the meta-analysis.

Methods

We searched PubMed, Embase, and Web of Science to identify fMRI studies in PD patients with depression. Using signed differential mapping (SDM) method, we performed a voxel-based meta-analysis. Then, a validation study by using multiscale entropy (MSE) in 28 PD patients with depression and 25 PD patients without depression was conducted. The fMRI scan was completed in anti-depression-medication-off state. The ROIs of the MSE analysis were the regions identified by the meta-analysis.

Results

A total of 126 PD patients with depression and 153 PD patients without depression were included in meta-analysis. It was observed that the resting-state activities within the posterior cingulate gyrus, supplementary motor area (SMA), and cerebellum were altered in depressed patients. Then, in the validation study, these regions were used as ROIs. PD patients with depression had significantly lower MSE of the BOLD fluctuations in these regions (posterior cingulate gyrus: F = 0.856, p = 0.049; SMA: F = 0.914, p = 0.039; cerebellum: F = 0.227, p = 0.043).

Conclusion

Our study revealed that the altered BOLD activity in cingulate, SMA, and cerebellum of the brain were pertaining to depression in PD.

Molecular Imaging of the GABAergic System in Parkinson's Disease and Atypical Parkinsonisms

PURPOSE OF REVIEW

During recent years, there has been a growing interest in GABAergic alterations in parkinsonian disorders. This paper aims to review the latest literature published, focusing on in vivo neuroimaging, and to suggest potential future avenues of research in the field.

RECENT FINDINGS

A growing number of neuroimaging studies have focused on the association with different symptoms of Parkinson's disease, thereby suggesting a GABAergic role in motor symptoms, gait disturbances, frontal cognition, somatic symptom disorder, and hallucinations. However, there are a number of conflicting results, and further investigations in larger, clinically well-defined cohorts are needed to elucidate possible correlations. In progressive supranuclear palsy, recent evidence suggests a decrease of GABA in the frontal lobe. In this narrative review, we discuss the possible GABAergic role in the symptoms of PD and atypical parkinsonisms and outline possible research strategies for future neuroimaging of GABAergic changes in parkinsonian disorders.

Functional neurological disorder and somatic symptom disorder in Parkinson's disease

The occurrence of Functional Neurological Disorder (FND) and Somatic Symptom Disorder (SSD) in PD was not commonly accepted until recently, despite some evidence that emerged in the pre and early L-Dopa era. More recently, the recognition of FND and SSD were noted to be relevant for the management of PD. FND and SSD appear early in the course of PD, often preceding motor symptoms, may interfere with treatment outcomes, often acquire psychotic features during progression, and are mixed with and often concealed by the progressive cognitive decline. We review the related features from the range of the available reports and discuss theoretical models conceived to explain the potential pathophysiological background of these disorders. Finally, we suggest that FND and SSD should be included among the non-motor symptoms of PD and be considered a prodromal feature in a subset of patients. This article is part of the Special Issue "Parkinsonism across the spectrum of movement disorders and beyond" edited by Joseph Jankovic, Daniel D. Truong and Matteo Bologna.

Putaminal y-Aminobutyric Acid Modulates Motor Response to Dopaminergic Therapy in Parkinson's Disease

BACKGROUND

Motor response to dopaminergic therapy is a characteristic of patients with Parkinson's disease (PD). Whether nondopaminergic neurotransmitters contribute to treatment response is uncertain.

OBJECTIVES

The aim of this study is to determine whether putaminal y-aminobutyric acid (GABA) levels are associated with dopaminergic motor response.

METHODS

We assessed putaminal GABA levels in 19 PD patients and 13 healthy controls (HCs) utilizing ultra-high field proton magnetic resonance spectroscopy. Motor performance was evaluated using the Movement Disorder Society-Unified Parkinson's Disease Rating Scale, Part III, in the ON and OFF states. Statistical analysis comprised group comparisons, correlation analysis, and multiple linear regression.

RESULTS

In PD, GABA levels were significantly higher compared to HCs (1.50 ± 0.26 mM vs. 1.26 ± 0.31 mM, P = 0.022). Furthermore, GABA levels were independent predictors of absolute and relative dopaminergic treatment response.

CONCLUSIONS

Our findings indicate that elevated putaminal GABA levels are associated with worse dopaminergic response in PD, emphasizing the essential role of nondopaminergic neurotransmitters in motor response. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Upper brainstem GABA levels in Parkinson's disease

OBJECTIVE

The dopaminergic pathology of Parkinson's disease (PD) impacts circuits involving GABAergic neurons, especially in the brainstem, where the disease manifests early. The aim of this study is to test the hypothesis that levels of gamma-aminobutyric acid (GABA) in the upper brainstem are reduced in patients with PD compared to healthy controls, using edited magnetic resonance spectroscopy (MRS of GABA +).

MATERIALS AND METHODS

GABA + levels were examined in 18 PD patients and 18 age- and sex-matched healthy controls (HCs). GABA + -edited MRS was performed in 7.5-ml voxels in the upper brainstem, and the spectra were processed using the Gannet software. Differences in GABA + levels between the two groups were analyzed using independent t test analysis.

RESULTS

GABA + levels were significantly lower (p < 0.05) in the upper brainstem of the patients with PD (4.57 ± 0.94 mM) than the HCs (5.89 ± 1.16 mM).

CONCLUSION

The lower GABA + levels in the upper brainstem of the PD patients suggest that a GABAergic deficit in the brainstem may contribute to the pathology in PD.

Single-dose L-dopa increases upper brainstem GABA in Parkinson's disease: A preliminary study

PURPOSE

Parkinson's disease (PD) is a heterogeneous neurodegenerative disorder, characterized by the dysfunction between dopaminergic and GABAergic neuronal activities. Dopamine (DA) replacement by its precursor L-dopa remains the primary treatment for PD. In this preliminary study, we test the hypotheses that GABA+ levels would be lower in PD patients than controls, and normalized by L-dopa.

METHODS

Eleven PD patients and eleven age-and gender-matched healthy controls underwent a ¹H-MRS scan of the upper brainstem using a J-difference-edited sequence to resolve signals of GABA. PD patients did not take all dopaminergic medicines for at least twelve hours prior to the first scan, and were scanned again after resuming L -dopa (pre- and post-L-dopa). MRS data were processed using the Gannet. Differences of GABA+ (GABA, macromolecules, and homocarnosine) levels within-subject (PD: pre- and post-L-dopa) and between-subjects (HC vs. PD-pre or PD-post) were tested using linear mixed-effects models with Holm-Bonferroni correction applied to pairwise comparisons.

RESULTS

Significant increased GABA+ levels were observed in the upper brainstem of PD patients post-L-dopa compared with pre-L-dopa (p < 0.001). Patients' GABA+ levels before administration of L-dopa were significantly lower than HCs (p = 0.001). Increased GABA+ level by administration of L-dopa in PD patients (post-L-dopa) was lower compared with HCs, but not significantly (p = 0.52).

CONCLUSION

Increased GABA+ levels were present in the upper brainstem with PD patients post-L-dopa, suggesting dopaminergic therapy capable of improving dopamine may improve the GABA+ levels in the upper brainstem, thereby achieving the effect of modulating the GABAergic system in the treatment of PD.