Hypermetabolism in the cerebellum and brainstem and cortical hypometabolism are independently associated with cognitive impairment in Parkinson’s disease

Cerebellar involvement in Parkinson's disease: Pathophysiology and neuroimaging

ABSTRACT

Parkinson's disease (PD) is a neurodegenerative disease characterized by various motor and non-motor symptoms. The complexity of its symptoms suggests that PD is a heterogeneous neurological disorder. Its pathological changes are not limited to the substantia nigra-striatal system, but gradually extending to other regions including the cerebellum. The cerebellum is connected to a wide range of central nervous system regions that form essential neural circuits affected by PD. In addition, altered dopaminergic activity and α-synuclein pathology are found in the cerebellum, further suggesting its role in the PD progression. Furthermore, an increasing evidence obtained from imaging studies has demonstrated that cerebellar structure, functional connectivity, and neural metabolism are altered in PD when compared to healthy controls, as well as among different PD subtypes. This review provides a comprehensive summary of the cerebellar pathophysiology and results from neuroimaging studies related to both motor and non-motor symptoms of PD, highlighting the potential significance of cerebellar assessment in PD diagnosis, differential diagnosis, and disease monitoring.

Radionuclide Imaging of the Neuroanatomical and Neurochemical Substrate of Cognitive Decline in Parkinson's Disease

Cognitive impairment is a frequent manifestation of Parkinson's disease (PD), resulting in decrease in patients' quality of life and increased societal and economic burden. However, cognitive decline in PD is highly heterogenous and the mechanisms are poorly understood. Radionuclide imaging techniques like positron emission tomography (PET) and single photon emission computed tomography (SPECT) have been used to investigate the neurochemical and neuroanatomical substrate of cognitive decline in PD. These techniques allow the assessment of different neurotransmitter systems, changes in brain glucose metabolism, proteinopathy, and neuroinflammation in vivo in PD patients. Here, we review current radionuclide imaging research on cognitive deficit in PD with a focus on predicting accelerating cognitive decline. This research could assist in the development of prognostic biomarkers for patient stratification and have utility in the development of ameliorative or disease-modifying therapies targeting cognitive deficit in PD.

A review of the neurotransmitter system associated with cognitive function of the cerebellum in Parkinson's disease

The dichotomized brain system is a concept that was generalized from the 'dual syndrome hypothesis' to explain the heterogeneity of cognitive impairment, in which anterior and posterior brain systems are independent but partially overlap. The dopaminergic system acts on the anterior brain and is responsible for executive function, working memory, and planning. In contrast, the cholinergic system acts on the posterior brain and is responsible for semantic fluency and visuospatial function. Evidence from dopaminergic/cholinergic imaging or functional neuroimaging has shed significant insight relating to the involvement of the cerebellum in the cognitive process of patients with Parkinson's disease. Previous research has reported evidence that the cerebellum receives both dopaminergic and cholinergic projections. However, whether these two neurotransmitter systems are associated with cognitive function has yet to be fully elucidated. Furthermore, the precise role of the cerebellum in patients with Parkinson's disease and cognitive impairment remains unclear. Therefore, in this review, we summarize the cerebellar dopaminergic and cholinergic projections and their relationships with cognition, as reported by previous studies, and investigated the role of the cerebellum in patients with Parkinson's disease and cognitive impairment, as determined by functional neuroimaging. Our findings will help us to understand the role of the cerebellum in the mechanisms underlying cognitive impairment in Parkinson's disease.

Hippocampal Perfusion Affects Motor and Cognitive Functions in Parkinson Disease: An Early Phase 18 F-FP-CIT Positron Emission Tomography Study

OBJECTIVE

We investigated whether hippocampal perfusion changes are associated with cognitive decline, motor deficits, and the risk of dementia conversion in patients with Parkinson disease (PD).

METHODS

We recruited patients with newly diagnosed and nonmedicated PD and healthy participants who underwent dual phase 18 F-N-(3-fluoropropyl)-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane positron emission tomography scans. Patients were classified into 3 groups according to hippocampal perfusion measured by standard uptake value ratios (SUVRs): (1) PD hippocampal hypoperfusion group (1 standard deviation [SD] below the mean hippocampal SUVR of healthy controls; PD-hippo-hypo), (2) PD hippocampal hyperperfusion group (1 SD above the mean; PD-hippo-hyper), and (3) the remaining patients (PD-hippo-normal). We compared the baseline cognitive performance, severity of motor deficits, hippocampal volume, striatal dopamine transporter (DAT) availability, and risk of dementia conversion among the groups.

RESULTS

We included 235 patients (PD-hippo-hypo, n = 21; PD-hippo-normal, n = 157; PD-hippo-hyper, n = 57) and 48 healthy participants. Patients in the PD-hippo-hypo group were older and had smaller hippocampal volumes than those in the other PD groups. The PD-hippo-hypo group showed less severely decreased DAT availability in the putamen than the other groups despite similar severities of motor deficit. The PD-hippo-hypo group had a higher risk of dementia conversion compared to the PD-hippo-normal (hazard ratio = 2.59, p = 0.013) and PD-hippo-hyper (hazard ratio = 3.73, p = 0.006) groups, despite similar cognitive performance at initial assessment between groups.

INTERPRETATION

Hippocampal hypoperfusion may indicate a reduced capacity to cope with neurodegenerative processes in terms of the development of motor deficits and cognitive decline in patients with PD. ANN NEUROL 2024;95:388-399.

Aging, Neurodegenerative Disorders, and Cerebellum

An important part of the central nervous system (CNS), the cerebellum is involved in motor control, learning, reflex adaptation, and cognition. Diminished cerebellar function results in the motor and cognitive impairment observed in patients with neurodegenerative disorders such as Alzheimer's disease (AD), vascular dementia (VD), Parkinson's disease (PD), Huntington's disease (HD), spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS), Friedreich's ataxia (FRDA), and multiple sclerosis (MS), and even during the normal aging process. In most neurodegenerative disorders, impairment mainly occurs as a result of morphological changes over time, although during the early stages of some disorders such as AD, the cerebellum also serves a compensatory function. Biological aging is accompanied by changes in cerebellar circuits, which are predominantly involved in motor control. Despite decades of research, the functional contributions of the cerebellum and the underlying molecular mechanisms in aging and neurodegenerative disorders remain largely unknown. Therefore, this review will highlight the molecular and cellular events in the cerebellum that are disrupted during the process of aging and the development of neurodegenerative disorders. We believe that deeper insights into the pathophysiological mechanisms of the cerebellum during aging and the development of neurodegenerative disorders will be essential for the design of new effective strategies for neuroprotection and the alleviation of some neurodegenerative disorders.

Different effect of hypo- and hypermetabolism on cognition in dementia with Lewy bodies: are they coupled or independent?

Patients with dementia with Lewy bodies (DLB) show widespread brain metabolic changes. This study investigated whether brain hypo- and hypermetabolism in DLB have differential effects on cognition. We enrolled 55 patients with DLB (15 prodromal DLB [MCI-LB] and 40 probable DLB) and 13 healthy controls who underwent 18F-fluorodeoxyglucose positron emission tomography and detailed neuropsychological tests. Metabolic indices reflecting associated changes in regional cerebral glucose metabolism were calculated as follows: index(-) for hypometabolism [DLB-hypo] and index(+) for hypermetabolism [DLB-hyper]. The effects of DLB-hypo or DLB-hyper on cognitive function were assessed using a multivariate linear regression model. Additionally, a linear mixed model was used to investigate the association between each index and the longitudinal cognitive decline. There was no correlation between DLB-hypo and DLB-hyper in the disease group. The multivariate linear regression model showed that DLB-hypo was associated with language, visuospatial, visual memory, and frontal/executive functions; whereas DLB-hyper was responsible for attention and verbal memory. There was significant interaction between DLB-hypo and DLB-hyper for verbal and visual memory, which was substantially affected by DLB-hyper in relatively preserved DLB-hypo status. A linear mixed model showed that DLB-hypo was associated with longitudinal cognitive outcomes, regardless of cognitive status, and DLB-hyper contributed to cognitive decline only in the MCI-LB group. The present study suggests that DLB-hypo and DLB-hyper may be independent of each other and differentially affect the baseline and longitudinal cognitive function in patients with DLB.

Cerebello-Parietal Functional Connectivity in Amnestic Mild Cognitive Impairment

The role of the cerebellum in amnestic mild cognitive impairment (aMCI), typically a prodromal stage of Alzheimer's disease, is not fully understood. We studied the lobule-specific cerebello-cerebral connectivity in 15 cognitively normal and 16 aMCI using resting-state functional MRI. Our analysis revealed weaker connectivity between the cognitive cerebellar lobules and parietal lobe in aMCI. However, stronger connectivity was observed in the cognitive cerebellar lobules with certain brain regions, including the precuneus cortex, posterior cingulate gyrus, and caudate nucleus in participants with worse cognition. Leveraging these measurable changes in cerebello-parietal functional networks in aMCI could offer avenues for future therapeutic interventions.

Linking the cerebellum to Parkinson disease: an update

Parkinson disease (PD) is characterized by heterogeneous motor and non-motor symptoms, resulting from neurodegeneration involving various parts of the central nervous system. Although PD pathology predominantly involves the nigral-striatal system, growing evidence suggests that pathological changes extend beyond the basal ganglia into other parts of the brain, including the cerebellum. In addition to a primary involvement in motor control, the cerebellum is now known to also have an important role in cognitive, sleep and affective processes. Over the past decade, an accumulating body of research has provided clinical, pathological, neurophysiological, structural and functional neuroimaging findings that clearly establish a link between the cerebellum and PD. This Review presents an overview and update on the involvement of the cerebellum in the clinical features and pathogenesis of PD, which could provide a novel framework for a better understanding the heterogeneity of the disease.

Atypical brain FDG-PET patterns increase the risk of long-term cognitive and motor progression in Parkinson's disease

INTRODUCTION

Brain hypometabolism patterns have been previously associated with cognitive decline in Parkinson's disease (PD). Our aim is to evaluate the impact of single-subject fluorodeoxyglucose (FDG)-PET brain hypometabolism on long-term cognitive and motor outcomes in PD.

METHODS

Forty-nine non-demented PD patients with baseline brain FDG-PET data underwent an extensive clinical follow-up for 8 years. The ability of FDG-PET to predict long-term cognitive and motor progression was evaluated using Cox regression and mixed ANCOVA models.

RESULTS

Participants were classified according to FDG-PET pattern in PD with typical (n = 26) and atypical cortical metabolism (n = 23). Patients with atypical brain hypometabolic patterns showed higher incidence of dementia (60% vs 3%; HR = 18.3), hallucinations (56% vs 7%, HR = 7.3) and faster motor decline compared to typical pattern group.

CONCLUSION

This study argues for specific patterns of FDG-PET cortical hypometabolism in PD as a prognostic marker for long term cognitive and motor outcomes at single-subject level.

Differential Implications of Cerebral Hypoperfusion and Hyperperfusion in Parkinson's Disease

BACKGROUND

Patients with Parkinson's disease (PD) exhibit widespread brain perfusion changes.

OBJECTIVE

This study investigated whether cerebral regions with hypoperfusion and hyperperfusion have differential effects on motor and cognitive symptoms in PD using early-phase 18 F-N-(3-fluoropropyl)-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane (18 F-FP-CIT) positron emission tomography (PET) scans.

METHODS

We enrolled 394 patients with newly diagnosed PD who underwent dual-phase 18 F-FP-CIT PET scans. Indices reflecting associated changes in regional cerebral hypoperfusion and hyperperfusion on early-phase 18 F-FP-CIT PET scans were calculated as PD[hypo] and PD[hyper] , respectively. The associations of PD[hypo] and PD[hyper] on motor and cognitive symptoms at baseline were assessed using multivariate linear regression. Also, Cox regression and linear mixed models were performed to investigate the effects of baseline PD[hypo] and PD[hyper] on longitudinal outcomes.

RESULTS

There was a weak correlation between PD[hypo] and PD[hyper] (γ = -0.19, P < 0.001). PD[hypo] was associated with baseline Unified Parkinson's Disease Rating Scale Part III scores (β = -1.02, P = 0.045), rapid increases in dopaminergic medications (β = -18.02, P < 0.001), and a higher risk for developing freezing of gait (hazard ratio [HR] = 0.67, P = 0.019), whereas PD[hyper] was not associated. Regarding cognitive function, PD[hypo] was more relevant to the baseline cognitive performance levels of visuospatial, memory, and frontal/executive function than PD[hyper] . However, greater PD[hyper] was associated with future dementia conversion (HR = 1.43, P = 0.004), whereas PD[hypo] was not associated.

CONCLUSIONS

These findings suggest that PD[hypo] and PD[hyper] may differentially affect motor and cognitive functions in patients with PD. © 2023 International Parkinson and Movement Disorder Society.

18F-FDG PET and a classifier algorithm reveal a characteristic glucose metabolic pattern in adult patients with moyamoya disease and vascular cognitive impairment

Vascular cognitive impairment (VCI) is a critical issue in moyamoya disease (MMD). However, the glucose metabolic pattern in these patients is still unknown. This study aimed to identify the metabolic signature of cognitive impairment in patients with MMD using ¹⁸F-2-fluoro-2-deoxy-D-glucose positron emission tomography (¹⁸F-FDG PET) and establish a classifier to identify VCI in patients with MMD. One hundred fifty-two patients with MMD who underwent brain ¹⁸F-FDG PET scans before surgery were enrolled and classified into nonvascular cognitive impairment (non-VCI, n = 52) and vascular cognitive impairment (VCI, n = 100) groups according to neuropsychological test results. Additionally, thirty-three health controls (HCs) were also enrolled. Compared to HCs, patients in the VCI group exhibited extensive hypometabolism in the bilateral frontal and cingulate regions and hypermetabolism in the bilateral cerebellum, while patients in the non-VCI group showed hypermetabolism only in the cerebellum and slight hypometabolism in the frontal and temporal regions. In addition, we found that the patients in the VCI group showed hypometabolism mainly in the left basal ganglia compared to those in the non-VCI group. The sparse representation-based classifier algorithm taking the SUVr of 116 Anatomical Automatic Labeling (AAL) areas as features distinguished patients in the VCI and non-VCI groups with an accuracy of 82.4%. This study demonstrated a characteristic metabolic pattern that can distinguish patients with MMD without VCI from those with VCI, namely, hypometabolic lesions in the left hemisphere played a more important role in cognitive decline in patients with MMD.

Potential mechanisms to modify impaired glucose metabolism in neurodegenerative disorders

Neurodegeneration refers to the selective and progressive loss-of-function and atrophy of neurons, and is present in disorders such as Alzheimer's, Huntington's, and Parkinson's disease. Although each disease presents with a unique pattern of neurodegeneration, and subsequent disease phenotype, increasing evidence implicates alterations in energy usage as a shared and core feature in the onset and progression of these disorders. Indeed, disturbances in energy metabolism may contribute to the vulnerability of neurons to apoptosis. In this review we will outline these disturbances in glucose metabolism, and how fatty acids are able to compensate for this impairment in energy production in neurodegenerative disorders. We will also highlight underlying mechanisms that could contribute to these alterations in energy metabolism. A greater understanding of these metabolism-neurodegeneration processes could lead to improved treatment options for neurodegenerative disease patients.

The Predictive Potential of Altered Voxel-Based Morphometry in Severely Obese Patients With Meibomian Gland Dysfunction

Objective

To investigate voxel-based morphometry (VBM) by using magnetic resonance imaging (MRI) in meibomian gland dysfunction patients with severe obesity (PATs) and to explore the application of VBM in the early diagnosis, prevention of cognitive impairment and targeted treatment of this disease.

Methods

Sixteen PATs and 12 healthy controls (HCs) were enrolled and underwent MRI. Whole-head images were analyzed using VBM and data were compared between groups using an independent samples t-test. Receiver operating characteristic (ROC) curves were utilized to assess the diagnostic value of this approach. Mini-mental state examination (MMSE) scores were used to assess cognitive impairment and were analyzed using an independent samples t-test.

Results

Compared with HCs, the VBM values in PATs were reduced in the left cerebellum and right thalamus but increased in the right brainstem, right precuneus and right paracentral lobule. The results of ROC curve analysis indicated that VBM may be useful in meibomian gland disease diagnosis. Comparison of MMSE scores between groups showed mild cognitive impairment in PATs.

Conclusion

PATs showed altered VBM values in some brain areas. These findings may provide information about the pathophysiology of meibomian gland dysfunction and may help to explain the underlying mechanisms of clinical manifestations in PATs, such as cognitive impairment. Abnormal VBM values in these brain areas may serve as predictive factors for development of meibomian gland disease in severely obese people and as indicators for individualized treatment.

Disruption of cerebellar-cortical functional connectivity predicts balance instability in alcohol use disorder

BACKGROUND

A neural substrate of alcohol-related instability of gait and balance is the cerebellum. Whether disruption of neural communication between cerebellar and cortical brain regions exerts an influence on ataxia in alcohol use disorder (AUD) was the focus of this study.

METHODS

Study groups comprised 32 abstinent AUD participants and 22 age- and sex-matched healthy controls (CTL). All participants underwent clinical screening, motor testing, and resting-state functional MR imaging analyzed for functional connectivity (FC) among 90 regions across the whole cerebrum and cerebellum. Ataxia testing quantified gait and balance with the Fregly-Graybiel Ataxia Battery conducted with and without vision.

RESULTS

The AUD group achieved lower scores than the CTL group on balance performance, which was disproportionately worse for eyes open than eyes closed in the AUD relative to the CTL group. Differences in ataxia were accompanied by differences in FC marked by cerebellar-frontal and cerebellar-parietal hyperconnectivity and cortico-cortical hypoconnectivity in the AUD relative to the control group. Lifetime alcohol consumption correlated significantly with AUD-related FC aberrations, which explained upwards of 69% of the AUD ataxia score variance.

CONCLUSION

Heavy, chronic alcohol consumption is associated with disorganized neural communication among cerebellar-cortical regions and contributes to ataxia in AUD. Ataxia, which is known to accelerate with age and be exacerbated with AUD, can threaten functional independence. Longitudinal studies are warranted to address whether extended sobriety quells ataxia and normalizes aberrant FC contributing to instability.

Spectral guided sparse inverse covariance estimation of metabolic networks in Parkinson's disease

In neurodegenerative disorders, a clearer understanding of the underlying aberrant networks facilitates the search for effective therapeutic targets and potential cures. [¹⁸F]-fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging data of brain metabolism reflects the distribution of glucose consumption known to be directly related to neural activity. In FDG PET resting-state metabolic data, characteristic disease-related patterns have been identified in group analysis of various neurodegenerative conditions using principal component analysis of multivariate spatial covariance. Notably, among several parkinsonian syndromes, the identified Parkinson’s disease-related pattern (PDRP) has been repeatedly validated as an imaging biomarker of PD in independent groups worldwide. Although the primary nodal associations of this network are known, its connectivity is not fully understood. Here, we describe a novel approach to elucidate functional principal component (PC) network connections by performing graph theoretical sparse network derivation directly within the disease relevant PC partition layer of the whole brain data rather than by searching for associations retrospectively in whole brain sparse representations. Using sparse inverse covariance estimation of each overlapping PC partition layer separately, a single coherent network is detected for each layer in contrast to more spatially modular segmentation in whole brain data analysis. Using this approach, the major nodal hubs of the PD disease network are identified and their characteristic functional pathways are clearly distinguished within the basal ganglia, midbrain and parietal areas. Network associations are further clarified using Laplacian spectral analysis of the adjacency matrices. In addition, the innate discriminative capacity of the eigenvector centrality of the graph derived networks in differentiating PD versus healthy external data provides evidence of their validity.

Cognitive impairment in Parkinson's disease: A clinical and pathophysiological overview

Cognitive dysfunction in Parkinson's disease (PD) has received increasing attention, and, together with other non-motor symptoms, exert a significant functional impact in the daily lives of patients. This article aims to compile and briefly summarize selected published data about clinical features, cognitive evaluation, biomarkers, and pathophysiology of PD-related dementia (PDD). The literature search included articles indexed in the MEDLINE/PubMed database, published in English, over the last two decades. Despite significant progress on clinical criteria and cohort studies for PD-mild cognitive impairment (PD-MCI) and PDD, there are still knowledge gaps about its exact molecular and pathological basis. Here we overview the scientific literature on the role of functional circuits, neurotransmitter systems (monoaminergic and cholinergic), basal forebrain, and brainstem nuclei dysfunction in PD-MCI. Correlations between neuroimaging and cerebrospinal fluid (CSF) biomarkers, clinical outcomes, and pathological results are described to aid in uncovering the neurodegeneration pattern in PD-MCI and PDD.

Changes in cortical thickness and volume of cerebellar subregions in patients with bipolar disorders

BACKGROUND

Numerous studies have suggested that structural changes in the cerebellum are implicated in the pathophysiology of bipolar disorder (BD). We aimed to investigate differences in the volume and cortical thickness of the cerebellar subregions between patients with BD and healthy controls (HCs).

METHODS

Ninety patients with BD and one hundred sixty-six HCs participated in this study and underwent T1-weighted structural magnetic resonance imaging. We analyzed the volume and cortical thickness of each cerebellar hemisphere divided into 12 subregions using T1-weighted images of participants. One-way analysis of covariance was used to evaluate differences between the groups, with age, sex, medication, and total intracranial cavity volume used as covariates.

RESULTS

The BD group had significantly increased cortical thickness of the cerebellum in all cerebellar subregions compared to the HC group. The cortical thicknesses of the whole cerebellum and each hemisphere were also significantly thicker in the BD group than in the HC group. The volume of the left lobule IX was significantly lower in patients with BD than in HCs, whereas no significant differences in the volumes were observed in the other subregions.

LIMITATIONS

Our cross-sectional design cannot provide a causal relationship between the increased cortical thickness of the cerebellum and the risk of BD.

CONCLUSIONS

We observed widespread and significant cortical thickening in all the cerebellar subregions. Our results provide evidence for the involvement of the cerebellum in BD. Further studies are required to integrate neurobiological evidence and structural brain imaging to elucidate the pathophysiology of BD.

Correlations of Neuropsychological and Metabolic Brain Changes in Parkinson's Disease and Other α-Synucleinopathies

Cognitive impairment is a common feature in Parkinson's disease (PD) and other α-synucleinopathies as 80% of PD patients develop dementia within 20 years. Early cognitive changes in PD patients present as a dysexecutive syndrome, broadly characterized as a disruption of the fronto-striatal dopamine network. Cognitive deficits in other domains (recognition memory, attention processes and visuospatial abilities) become apparent with the progression of PD and development of dementia. In dementia with Lewy bodies (DLB) the cognitive impairment develops early or even precedes parkinsonism and it is more pronounced in visuospatial skills and memory. Cognitive impairment in the rarer α-synucleinopathies (multiple system atrophy and pure autonomic failure) is less well studied. Metabolic brain imaging with positron emission tomography and [¹⁸F]-fluorodeoxyglucose (FDG-PET) is a well-established diagnostic method in neurodegenerative diseases, including dementias. Changes in glucose metabolism precede those seen on structural magnetic resonance imaging (MRI). Reduction in glucose metabolism and atrophy have been suggested to represent consecutive changes of neurodegeneration and are linked to specific cognitive disorders (e.g., dysexecutive syndrome, memory impairment, visuospatial deficits etc.). Advances in the statistical analysis of FDG-PET images enabling a network analysis broadened our understanding of neurodegenerative brain processes. A specific cognitive pattern related to PD was identified by applying voxel-based network modeling approach. The magnitude of this pattern correlated significantly with patients' cognitive skills. Specific metabolic brain changes were observed also in patients with DLB as well as in a prodromal phase of α-synucleinopathy: REM sleep behavior disorder. Metabolic brain imaging with FDG-PET is a reliable biomarker of neurodegenerative brain diseases throughout their course, precisely reflecting their topographic distribution, stage and functional impact.

Distinguishing between dementia with Lewy bodies and Alzheimer's disease using metabolic patterns

Alzheimer's disease (AD) and dementia with Lewy bodies (DLB) are the 2 most common causes of dementia. We compared the regional metabolism on ¹⁸F-fluorodeoxyglucose positron emission tomography (PET) among 21 control subjects and cognitively impaired patients due to DLB (N = 63) and AD (N = 38). All participants underwent ¹⁸F-Florbetaben (FBB) PET, and all DLB patients had abnormality on dopamine transporter PET. Both the FBB-positive DLB (N = 38) and FBB-negative DLB (N = 25) groups had increased metabolism in the bilateral central cerebellum, posterior putamen, and somatomotor cortices compared with the control and AD groups. Compared with the control group, the DLB and AD groups commonly exhibited hypometabolism in the bilateral lateral temporal, temporo-parietal junction, posterior cingulate, and precuneus cortices. Both DLB groups had additional hypometabolism in the bilateral thalami and dorsolateral prefrontal cortices, whereas the AD group did in the bilateral entorhinal cortices and hippocampi. Our results suggest that hypermetabolism in the somatomotor cortex, posterior putamen, or central cerebellum could be a useful imaging biomarker for detecting DLB patients, while entorhinal/hippocampal hypometabolism could be a specific biomarker for AD.

Temporal changes in neuroinflammation and brain glucose metabolism in a rat model of viral vector-induced α-synucleinopathy

Rat models based on viral vector-mediated overexpression of α-synuclein are regarded as highly valuable models that closely mimic cardinal features of human Parkinson's disease (PD) such as L-DOPA-dependent motor impairment, dopaminergic neurodegeneration and α-synuclein inclusions. To date, the downstream effects of dopaminergic cell loss on brain glucose metabolism, including the neuroinflammation component, have not been phenotyped in detail for this model. Cerebral glucose metabolism was monitored throughout different stages of the disease using in vivo 2-[¹⁸F]-fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) positron emission tomography (PET) and was combined with in vitro [¹⁸F]DPA-714 autoradiography to assess concomitant inflammation. Rats were unilaterally injected with recombinant adeno-associated viral vector serotype 2/7 (rAAV2/7) encoding either A53T α-synuclein or eGFP. Brain [¹⁸F]FDG microPET was performed at baseline, 1, 2, 3, 4, 6, and 9 weeks post-surgery, in combination with behavioral tests. As a second experiment, [¹⁸F]DPA-714 autoradiography was executed across the same timeline. Voxel-based analysis of relative [¹⁸F]FDG uptake showed a dynamic pattern of PD-related metabolic changes throughout the disease progression (weeks 2-9). Glucose hypermetabolism covering a large bilateral area reaching from the insular, motor- and somatosensory cortex to the striatum was observed at week 2. At week 4, hypermetabolism presented in a cluster covering the ipsilateral nigra-thalamic region, whereas hypometabolism was noted in the ipsilateral striatum at week 6. Elevated [¹⁸F]FDG uptake was seen in a cluster extending across the contralateral striatum, motor- and somatosensory cortex at week 9. Increased [¹⁸F]FDG in the region of the substantia nigra was associated with increased [¹⁸F]DPA-714 binding, and correlated significantly with motor symptoms. These findings point to disease-associated metabolic and neuroinflammatory changes taking place in the primary area of dopaminergic neurodegeneration but also closely interconnected motor and somatosensory brain regions.