Reduced regional cerebral blood flow in Huntington's disease studied by SPECT

Endothelial Dysfunction in Huntington's Disease: Pathophysiology and Therapeutic Implications

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized by motor, cognitive, and psychiatric symptoms. While traditionally viewed through the lens of neuronal dysfunction, emerging evidence highlights the critical role of endothelial dysfunction in HD pathogenesis. This review provides a comprehensive overview of endothelial dysfunction in HD, drawing on findings from both animal models and human studies. Key features of endothelial dysfunction in HD include impaired angiogenesis, altered cerebral blood flow, compromised neurovascular coupling and cerebrovascular reactivity, and increased blood-brain barrier permeability. Genetic factors such as the mutant huntingtin protein, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), Brain-derived neurotrophic factor (BDNF), and the adenosine A2A receptor (ADORA2A) interact to influence endothelial function in complex ways. Various therapeutic approaches targeting endothelial dysfunction, including antioxidants, nitric oxide enhancers, calcium channel blockers, statins, and metformin, have shown promise in preclinical HD models but face translational challenges, particularly regarding optimal timing of intervention and patient stratification. The implications of these findings suggest that reconceptualizing HD as a neurovascular disorder, rather than purely neuronal, could lead to more effective treatment strategies. Future research priorities should include: (1) developing validated vascular biomarkers for disease progression, (2) advancing neuroimaging techniques to monitor endothelial dysfunction in real-time. These directions will be crucial for bridging the current gap between preclinical promise and clinical success in vascular-targeted HD therapeutics.

Resting-state functional abnormalities in ischemic stroke: a meta-analysis of fMRI studies

Ischemic stroke is a leading neurological cause of severe disabilities and death in the world and has a major negative impact on patients' quality of life. However, the neural mechanism of spontaneous fluctuating neuronal activity remains unclear. This meta-analysis explored brain activity during resting state in patients with ischemic stroke including 22 studies of regional homogeneity, amplitude of low-frequency fluctuation, and fractional amplitude of low-frequency fluctuation (692 patients with ischemic stroke, 620 healthy controls, age range 35-80 years, 41% female, 175 foci). Results showed decreased regional activity in the bilateral caudate and thalamus and increased regional activity in the left superior occipital gyrus and left default mode network (precuneus/posterior cingulate cortex). Meta-analysis of the amplitude of low-frequency fluctuation studies showed that increased activity in the left inferior frontal gyrus was reduced across the progression from acute to chronic phases. These findings may indicate that disruption of the subcortical areas and default mode network could be one of the core functional abnormalities in ischemic stroke. Altered brain activity in the inferior frontal gyrus could be the imaging indicator of brain recovery/plasticity after stroke damage, which offers potential insight into developing prediction models and therapeutic strategies for ischemic stroke rehabilitation and recovery.

Investigating the Interplay between Cardiovascular and Neurodegenerative Disease

Neurological diseases, including neurodegenerative diseases (NDDs), are the primary cause of disability worldwide and the second leading cause of death. The chronic nature of these conditions and the lack of disease-modifying therapies highlight the urgent need for developing effective therapies. To accomplish this, effective models of NDDs are required to increase our understanding of underlying pathophysiology and for evaluating treatment efficacy. Traditionally, models of NDDs have focused on the central nervous system (CNS). However, evidence points to a relationship between systemic factors and the development of NDDs. Cardiovascular disease and related risk factors have been shown to modify the cerebral vasculature and the risk of developing Alzheimer's disease. These findings, combined with reports of changes to vascular density and blood-brain barrier integrity in other NDDs, such as Huntington's disease and Parkinson's disease, suggest that cardiovascular health may be predictive of brain function. To evaluate this, we explore evidence for disruptions to the circulatory system in murine models of NDDs, evidence of disruptions to the CNS in cardiovascular disease models and summarize models combining cardiovascular disruption with models of NDDs. In this study, we aim to increase our understanding of cardiovascular disease and neurodegeneration interactions across multiple disease states and evaluate the utility of combining model systems.

Selective vulnerability of layer 5a corticostriatal neurons in Huntington's disease

The properties of the cell types that are selectively vulnerable in Huntington's disease (HD) cortex, the nature of somatic CAG expansions of mHTT in these cells, and their importance in CNS circuitry have not been delineated. Here, we employed serial fluorescence-activated nuclear sorting (sFANS), deep molecular profiling, and single-nucleus RNA sequencing (snRNA-seq) of motor-cortex samples from thirteen predominantly early stage, clinically diagnosed HD donors and selected samples from cingulate, visual, insular, and prefrontal cortices to demonstrate loss of layer 5a pyramidal neurons in HD. Extensive mHTT CAG expansions occur in vulnerable layer 5a pyramidal cells, and in Betz cells, layers 6a and 6b neurons that are resilient in HD. Retrograde tracing experiments in macaque brains identify layer 5a neurons as corticostriatal pyramidal cells. We propose that enhanced somatic mHTT CAG expansion and altered synaptic function act together to cause corticostriatal disconnection and selective neuronal vulnerability in HD cerebral cortex.

Systematic Review and Meta-Analyses of Word Production Abilities in Dysfunction of the Basal Ganglia: Stroke, Small Vessel Disease, Parkinson's Disease, and Huntington's Disease

Clinical populations with basal ganglia pathologies may present with language production impairments, which are often described in combination with comprehension measures or attributed to motor, memory, or processing-speed problems. In this systematic review and meta-analysis, we studied word production in four (vascular and non-vascular) pathologies of the basal ganglia: stroke affecting the basal ganglia, small vessel disease, Parkinson's disease, and Huntington's disease. We compared scores of these clinical populations with those of matched cognitively unimpaired adults on four well-established production tasks, namely picture naming, category fluency, letter fluency, and past-tense verb inflection. We conducted a systematic search in PubMed and PsycINFO with terms for basal ganglia structures, basal ganglia disorders and language production tasks. A total of 114 studies were included, containing results for one or more of the tasks of interest. For each pathology and task combination, effect sizes (Hedges' g) were extracted comparing patient versus control groups. For all four populations, performance was consistently worse than that of cognitively unimpaired adults across the four language production tasks (p-values < 0.010). Given that performance in picture naming and verb inflection across all pathologies was quantified in terms of accuracy, our results suggest that production impairments cannot be fully explained by motor or processing-speed deficits. Our review shows that while language production difficulties in these clinical populations are not negligible, more evidence is necessary to determine the exact mechanism that leads to these deficits and whether this mechanism is the same across different pathologies.

Selective Vulnerability of Layer 5a Corticostriatal Neurons in Huntington's Disease

The properties of the cell types that are selectively vulnerable in Huntington's disease (HD) cortex, the nature of somatic CAG expansions of mHTT in these cells, and their importance in CNS circuitry have not been delineated. Here we employed serial fluorescence activated nuclear sorting (sFANS), deep molecular profiling, and single nucleus RNA sequencing (snRNAseq) to demonstrate that layer 5a pyramidal neurons are vulnerable in primary motor cortex and other cortical areas of HD donors. Extensive mHTT -CAG expansions occur in vulnerable layer 5a pyramidal cells, and in Betz cells, layer 6a, layer 6b neurons that are resilient in HD. Retrograde tracing experiments in macaque brains identify the vulnerable layer 5a neurons as corticostriatal pyramidal cells. We propose that enhanced somatic mHTT -CAG expansion and altered synaptic function act together to cause corticostriatal disconnection and selective neuronal vulnerability in the HD cerebral cortex.

Dual phase 18F-FP CIT PET and 99mTc- ECD SPECT findings of Huntington's disease

Fluorine-18 N-3-fluoropropyl-2-beta-carboxymethoxy-3-beta-(4-iodophenyl) nortropane (18F- FP CIT) has been used for the differential diagnosis of atypical parkinsonian disorders, and Technetium 99m ethyl cysteinate dimer (99mTc- ECD) has been used for evaluation of cerebral blood flow. A 60-year-old female with a history of Huntington's disease (HD) with full mutation of cytosine-adenine-guanine (GAG) 18/43 repeats underwent early and late 18F- FP CIT positron emission tomography/computed tomography (PET/CT) and 99mTc- ECD single-photon emission computed tomography (SPECT). The 18F-FP CIT PET/CT showed decreased uptake in both basal ganglia, both frontal and parietotemporal lobes at early images, and decreased presynaptic dopamine transporter (DAT) binding in both ventral & posterior putamen at late images. 99mTc- ECD SPECT showed decreased perfusion in both basal ganglia, both frontal and temporal lobes. Early 18F- FP CIT PET/CT and 99mTc- ECD SPECT images showed similar findings in Huntington's disease.

From Neurodevelopmental to Neurodegenerative Disorders: The Vascular Continuum

Structural and functional integrity of the cerebral vasculature ensures proper brain development and function, as well as healthy aging. The inability of the brain to store energy makes it exceptionally dependent on an adequate supply of oxygen and nutrients from the blood stream for matching colossal demands of neural and glial cells. Key vascular features including a dense vasculature, a tightly controlled environment, and the regulation of cerebral blood flow (CBF) all take part in brain health throughout life. As such, healthy brain development and aging are both ensured by the anatomical and functional interaction between the vascular and nervous systems that are established during brain development and maintained throughout the lifespan. During critical periods of brain development, vascular networks remodel until they can actively respond to increases in neural activity through neurovascular coupling, which makes the brain particularly vulnerable to neurovascular alterations. The brain vasculature has been strongly associated with the onset and/or progression of conditions associated with aging, and more recently with neurodevelopmental disorders. Our understanding of cerebrovascular contributions to neurological disorders is rapidly evolving, and increasing evidence shows that deficits in angiogenesis, CBF and the blood-brain barrier (BBB) are causally linked to cognitive impairment. Moreover, it is of utmost curiosity that although neurodevelopmental and neurodegenerative disorders express different clinical features at different stages of life, they share similar vascular abnormalities. In this review, we present an overview of vascular dysfunctions associated with neurodevelopmental (autism spectrum disorders, schizophrenia, Down Syndrome) and neurodegenerative (multiple sclerosis, Huntington's, Parkinson's, and Alzheimer's diseases) disorders, with a focus on impairments in angiogenesis, CBF and the BBB. Finally, we discuss the impact of early vascular impairments on the expression of neurodegenerative diseases.

Purine Nucleotides Metabolism and Signaling in Huntington's Disease: Search for a Target for Novel Therapies

Huntington’s disease (HD) is a multi-system disorder that is caused by expanded CAG repeats within the exon-1 of the huntingtin (HTT) gene that translate to the polyglutamine stretch in the HTT protein. HTT interacts with the proteins involved in gene transcription, endocytosis, and metabolism. HTT may also directly or indirectly affect purine metabolism and signaling. We aimed to review existing data and discuss the modulation of the purinergic system as a new therapeutic target in HD. Impaired intracellular nucleotide metabolism in the HD affected system (CNS, skeletal muscle and heart) may lead to extracellular accumulation of purine metabolites, its unusual catabolism, and modulation of purinergic signaling. The mechanisms of observed changes might be different in affected systems. Based on collected findings, compounds leading to purine and ATP pool reconstruction as well as purinergic receptor activity modulators, i.e., P2X7 receptor antagonists, may be applied for HD treatment.

Impaired response of cerebral oxygen metabolism to visual stimulation in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disease caused by a CAG triplet repeat expansion in the Huntingtin gene. Metabolic and microvascular abnormalities in the brain may contribute to early physiological changes that subserve the functional impairments in HD. This study is intended to investigate potential abnormality in dynamic changes in cerebral blood volume (CBV) and cerebral blood flow (CBF), and cerebral metabolic rate of oxygen (CMRO2) in the brain in response to functional stimulation in premanifest and early manifest HD patients. A recently developed 3-D-TRiple-acquisition-after-Inversion-Preparation magnetic resonance imaging (MRI) approach was used to measure dynamic responses in CBV, CBF, and CMRO2 during visual stimulation in one single MRI scan. Experiments were conducted in 23 HD patients and 16 healthy controls. Decreased occipital cortex CMRO2 responses were observed in premanifest and early manifest HD patients compared to controls (P < 0.001), correlating with the CAG-Age Product scores in these patients (R2 = 0.4, P = 0.001). The results suggest the potential value of this reduced CMRO2 response during visual stimulation as a biomarker for HD and may illuminate the role of metabolic alterations in the pathophysiology of HD.

Blood-Brain Barrier Disruption: A Common Driver of Central Nervous System Diseases

The brain is endowed with a unique cellular composition and organization, embedded within a vascular network and isolated from the circulating blood by a specialized frontier, the so-called blood-brain barrier (BBB), which is necessary for its proper function. Recent reports have shown that increments in the permeability of the blood vessels facilitates the entry of toxic components and immune cells to the brain parenchyma and alters the phenotype of the supporting astrocytes. All of these might contribute to the progression of different pathologies such as brain cancers or neurodegenerative diseases. Although it is well known that BBB breakdown occurs due to pericyte malfunctioning or to the lack of stability of the blood vessels, its participation in the diverse neural diseases needs further elucidation. This review summarizes what it is known about BBB structure and function and how its instability might trigger or promote neuronal degeneration and glioma progression, with a special focus on the role of pericytes as key modulators of the vasculature. Moreover, we will discuss some recent reports that highlights the participation of the BBB alterations in glioma growth. This pan-disease analysis might shed some light into these otherwise untreatable diseases and help to design better therapeutic approaches.

Investigation of Axial and Angular Sampling in Multi-Detector Pinhole-SPECT Brain Imaging

We designed a dedicated multi-detector multi-pinhole brain SPECT scanner to generate images of higher quality compared to general-purpose systems. The system, AdaptiSPECT-C, is intended to adapt its sensitivity-resolution trade-off by varying its aperture configurations allowing both high-sensitivity dynamic and high-spatial-resolution static imaging. The current system design consists of 23 detector heads arranged in a truncated spherical geometry. In this work, we investigated the axial and angular sampling capability of the current stationary system design. Two data acquisition schemes using limited rotation of the gantry and two others using axial translation of the imaging bed were also evaluated concerning their impact on image quality through improved sampling. Increasing both angular and axial sampling in the current prototype system resulted in quantitative improvements in image quality metrics and qualitative appearance of the images as determined in studies with specifically selected phantoms. Visual improvements for the brain phantoms with clinical distributions were less pronounced but presented quantitative improvements in the fidelity (normalized root-mean-square error (NRMSE)) and striatal specific binding ratio (SBR) for a dopamine transporter (DAT) distribution, and in NRMSE and activity recovery for a brain perfusion distribution. More pronounced improvements with increased sampling were seen in contrast recovery coefficient, bias, and coefficient of variation for a lesion in the brain perfusion distribution. The negligible impact of the most cranial ring of detectors on axial sampling, but its significant impact on sensitivity and angular sampling in the cranial portion of the imaging volume-of-interest were also determined.

Neurodegenerative Diseases - Is Metabolic Deficiency the Root Cause?

Neurodegenerative diseases, including Alzheimer, Parkinson, Huntington, and amyotrophic lateral sclerosis, are a prominent class of neurological diseases currently without a cure. They are characterized by an inexorable loss of a specific type of neurons. The selective vulnerability of specific neuronal clusters (typically a subcortical cluster) in the early stages, followed by the spread of the disease to higher cortical areas, is a typical pattern of disease progression. Neurodegenerative diseases share a range of molecular and cellular pathologies, including protein aggregation, mitochondrial dysfunction, glutamate toxicity, calcium load, proteolytic stress, oxidative stress, neuroinflammation, and aging, which contribute to neuronal death. Efforts to treat these diseases are often limited by the fact that they tend to address any one of the above pathological changes while ignoring others. Lack of clarity regarding a possible root cause that underlies all the above pathologies poses a significant challenge. In search of an integrative theory for neurodegenerative pathology, we hypothesize that metabolic deficiency in certain vulnerable neuronal clusters is the common underlying thread that links many dimensions of the disease. The current review aims to present an outline of such an integrative theory. We present a new perspective of neurodegenerative diseases as metabolic disorders at molecular, cellular, and systems levels. This helps to understand a common underlying mechanism of the many facets of the disease and may lead to more promising disease-modifying therapeutic interventions. Here, we briefly discuss the selective metabolic vulnerability of specific neuronal clusters and also the involvement of glia and vascular dysfunctions. Any failure in satisfaction of the metabolic demand by the neurons triggers a chain of events that precipitate various manifestations of neurodegenerative pathology.

The visual cortex and visual cognition in Huntington's disease: An overview of current literature

The processing of visual stimuli from retina to higher cortical areas has been extensively studied in the human brain. In Huntington's disease (HD), an inherited neurodegenerative disorder, it is suggested that visual processing deficits are present in addition to more characteristic signs such as motor disturbances, cognitive dysfunction, and behavioral changes. Visual deficits are clinically important because they influence overall cognitive performance and have implications for daily functioning. The aim of this review is to summarize current literature on clinical visual deficits, visual cognitive impairment, and underlying visual cortical changes in HD patients. A literature search was conducted using the electronic database of PubMed/Medline. This review shows that changes of the visual system in patients with HD were not the primary focus of currently published studies. Still, early atrophy and alterations of the posterior cerebral cortex was frequently observed, primarily in the associative visual cortical areas such as the lingual and fusiform gyri, and lateral occipital cortex. Changes were even present in the premanifest phase, before clinical onset of motor symptoms, suggesting a primary region for cortical degeneration in HD. Although impairments in visuospatial processing and visual perception were reported in early disease stages, heterogeneous cognitive batteries were used, making a direct comparison between studies difficult. The use of a standardized battery of visual cognitive tasks might therefore provide more detailed information regarding the extent of impairments in specific visual domains. Further research could provide more insight into clinical, functional, and pathophysiological changes of the visual pathway in HD.

Synaptopathic mechanisms of neurodegeneration and dementia: Insights from Huntington's disease

Dementia encapsulates a set of symptoms that include loss of mental abilities such as memory, problem solving or language, and reduces a person's ability to perform daily activities. Alzheimer's disease is the most common form of dementia, however dementia can also occur in other neurological disorders such as Huntington's disease (HD). Many studies have demonstrated that loss of neuronal cell function manifests pre-symptomatically and thus is a relevant therapeutic target to alleviate symptoms. Synaptopathy, the physiological dysfunction of synapses, is now being approached as the target for many neurological and psychiatric disorders, including HD. HD is an autosomal dominant and progressive degenerative disorder, with clinical manifestations that encompass movement, cognition, mood and behaviour. HD is one of the most common tandem repeat disorders and is caused by a trinucleotide (CAG) repeat expansion, encoding an extended polyglutamine tract in the huntingtin protein. Animal models as well as human studies have provided detailed, although not exhaustive, evidence of synaptic dysfunction in HD. In this review, we discuss the neuropathology of HD and how the changes in synaptic signalling in the diseased brain lead to its symptoms, which include dementia. Here, we review and discuss the mechanisms by which the 'molecular orchestras' and their 'synaptic symphonies' are disrupted in neurodegeneration and dementia, focusing on HD as a model disease. We also explore the therapeutic strategies currently in pre-clinical and clinical testing that are targeted towards improving synaptic function in HD.

Impaired Picture Arrangement subscores (WAIS-III) associated with decreased place orientation and frontal/occipital blood flow in Alzheimer's disease: Implications for social judgment dysfunction. The Osaki-Tajiri Project

Alzheimer's disease (AD) patients manifest not only memory impairment but also deficit of social judgment. However, contrary to frequently recognized deficit, only two neuropsychological tests have been established for assessing "judgment" : the Cognitive Abilities Screening Instrument domain Abstraction & judgment and the Picture Arrangement subscale of WAIS-III. For the former, we previously reported an association with decreased regional cerebral blood flow (rCBF) in the left parietal lobe. Herein, we analyzed the scores of the Picture Arrangement test. Forty-nine AD patients were classified into two groups, i.e., the high and low PA score groups. The ^99mTc-ECD SPECT investigation was performed with the voxel-based analysis using SPM5. The Mini-Mental State Examination subscores of "place orientation" showed a correlation with the PA scores. The low PA score group exhibited significantly decreased rCBFs in the Left Inferior Frontal Gyrus (LIFG), Left Superior Frontal Gyrus (LSFG) and Right Occipital Lobe (ROL), compared with the high PA score group. The ability of PA may be associated with the place orientation, which may be necessary to re-arrange the pictures. The ROL was related to visual recognition. The LSFG may be involved in executive function or "frontal reasoning."

Quantitative Susceptibility Mapping Suggests Altered Brain Iron in Premanifest Huntington Disease

BACKGROUND AND PURPOSE

In patients with premanifest (nonsymptomatic) and advanced Huntington disease, changes in brain iron levels in the basal ganglia have been previously reported, especially in the striatum. Quantitative susceptibility mapping by using MR phase imaging allows in vivo measurements of tissue magnetic susceptibility, which has been shown to correlate well with iron levels in brain gray matter and is believed to be more specific than other imaging-based iron measures. The purpose of this study was to investigate the use of magnetic susceptibility as a biomarker of disease progression.

MATERIALS AND METHODS

Fifteen subjects with premanifest Huntington disease and 16 age-matched healthy controls were scanned at 7T. Magnetic susceptibility, effective relaxation, and tissue volume in deep gray matter structures were quantified and compared with genetic and clinical measures.

RESULTS

Subjects with premanifest Huntington disease showed significantly higher susceptibility values in the caudate nucleus, putamen, and globus pallidus, indicating increased iron levels in these structures. Significant decreases in magnetic susceptibility were found in the substantia nigra and hippocampus. In addition, significant volume loss (atrophy) and an increase effective relaxation were observed in the caudate nucleus and putamen. Susceptibility values in the caudate nucleus and putamen were found to be inversely correlated with structure volumes and directly correlated with the genetic burdens, represented by cytosine-adenine-guanine repeat age-product-scaled scores.

CONCLUSIONS

The significant magnetic susceptibility differences between subjects with premanifest Huntington disease and controls and their correlation with genetic burden scores indicate the potential use of magnetic susceptibility as a biomarker of disease progression in premanifest Huntington disease.

In Vivo NMR Studies of the Brain with Hereditary or Acquired Metabolic Disorders

Metabolic disorders, whether hereditary or acquired, affect the brain, and abnormalities of the brain are related to cellular integrity; particularly in regard to neurons and astrocytes as well as interactions between them. Metabolic disturbances lead to alterations in cellular function as well as microscopic and macroscopic structural changes in the brain with diabetes, the most typical example of metabolic disorders, and a number of hereditary metabolic disorders. Alternatively, cellular dysfunction and degeneration of the brain lead to metabolic disturbances in hereditary neurological disorders with neurodegeneration. Nuclear magnetic resonance (NMR) techniques allow us to assess a range of pathophysiological changes of the brain in vivo. For example, magnetic resonance spectroscopy detects alterations in brain metabolism and energetics. Physiological magnetic resonance imaging (MRI) detects accompanying changes in cerebral blood flow related to neurovascular coupling. Diffusion and T1/T2-weighted MRI detect microscopic and macroscopic changes of the brain structure. This review summarizes current NMR findings of functional, physiological and biochemical alterations within a number of hereditary and acquired metabolic disorders in both animal models and humans. The global view of the impact of these metabolic disorders on the brain may be useful in identifying the unique and/or general patterns of abnormalities in the living brain related to the pathophysiology of the diseases, and identifying future fields of inquiry.

Cerebrovascular and blood-brain barrier impairments in Huntington's disease: Potential implications for its pathophysiology

OBJECTIVE

Although the underlying cause of Huntington's disease (HD) is well established, the actual pathophysiological processes involved remain to be fully elucidated. In other proteinopathies such as Alzheimer's and Parkinson's diseases, there is evidence for impairments of the cerebral vasculature as well as the blood-brain barrier (BBB), which have been suggested to contribute to their pathophysiology. We investigated whether similar changes are also present in HD.

METHODS

We used 3- and 7-Tesla magnetic resonance imaging as well as postmortem tissue analyses to assess blood vessel impairments in HD patients. Our findings were further investigated in the R6/2 mouse model using in situ cerebral perfusion, histological analysis, Western blotting, as well as transmission and scanning electron microscopy.

RESULTS

We found mutant huntingtin protein (mHtt) aggregates to be present in all major components of the neurovascular unit of both R6/2 mice and HD patients. This was accompanied by an increase in blood vessel density, a reduction in blood vessel diameter, as well as BBB leakage in the striatum of R6/2 mice, which correlated with a reduced expression of tight junction-associated proteins and increased numbers of transcytotic vesicles, which occasionally contained mHtt aggregates. We confirmed the existence of similar vascular and BBB changes in HD patients.

INTERPRETATION

Taken together, our results provide evidence for alterations in the cerebral vasculature in HD leading to BBB leakage, both in the R6/2 mouse model and in HD patients, a phenomenon that may, in turn, have important pathophysiological implications.

Plasma inflammatory biomarkers for Huntington's disease patients and mouse model

Huntington's disease (HD), caused by expanded CAG repeats encoding a polyglutamine tract in the huntingtin (HTT) protein, presents with a predominant degeneration of neurons in the striatum and cortex. Lines of evidence have observed neuroinflammation, particularly microglial activation, is involved in the pathogenesis of HD. Given that HTT is also expressed in peripheral inflammatory cells, it is possible that inflammatory changes detected in peripheral plasma may be biologically relevant and parallel the neuroinflammatory process of HD patients. By examining the expression levels of 13 microglia-derived inflammatory markers in the plasma of 5 PreHD carriers, 15 HD patients and 16 healthy controls, we found plasma levels of IL-6, MMP-9, VEGF and TGF-β1 were significantly increased in HD patients when compared with the controls, while plasma level of IL-18 were significantly reduced in HD patients compared with controls. Plasma level of IL-6 was reversely correlated with the UHDRS independence scale and functional capacity. To understand the temporal correlation between these inflammatory markers and HD progression, their levels were further tested in plasma from R6/2 mouse HD model at different ages. In rotarod test, R6/2 HD mice started to manifest HD phenotype at 7.5 weeks of age. Higher plasma VEGF levels of R6/2 mice than those of age-matched wild-type (WT) littermates were noted from 7 (presymptomatic stage) to 13 weeks of age (late symptomatic stage). The plasma IL-6 levels of R6/2 mice were higher than those of the WT littermates from 9 (early symptomatic stage) to 13 weeks of age. R6/2 mice demonstrated higher MMP-9 and TGF-β1 levels than their WT littermates from 11 (middle symptomatic stage) to 13 weeks of age. In contrast, the plasma IL-18 level was lower than those in WT littermates since 11 weeks of age. These altered expressions of inflammatory markers may serve as the potential biomarkers for HD onset and progression. Specific inhibition/activation of these inflammatory markers may be the targets of HD drug development.

Abnormal resting-state connectivity of motor and cognitive networks in early manifest Huntington's disease

BACKGROUND

Functional magnetic resonance imaging (fMRI) of multiple neural networks during the brain's 'resting state' could facilitate biomarker development in patients with Huntington's disease (HD) and may provide new insights into the relationship between neural dysfunction and clinical symptoms. To date, however, very few studies have examined the functional integrity of multiple resting state networks (RSNs) in manifest HD, and even less is known about whether concomitant brain atrophy affects neural activity in patients.

METHOD

Using MRI, we investigated brain structure and RSN function in patients with early HD (n = 20) and healthy controls (n = 20). For resting-state fMRI data a group-independent component analysis identified spatiotemporally distinct patterns of motor and prefrontal RSNs of interest. We used voxel-based morphometry to assess regional brain atrophy, and 'biological parametric mapping' analyses to investigate the impact of atrophy on neural activity.

RESULTS

Compared with controls, patients showed connectivity changes within distinct neural systems including lateral prefrontal, supplementary motor, thalamic, cingulate, temporal and parietal regions. In patients, supplementary motor area and cingulate cortex connectivity indices were associated with measures of motor function, whereas lateral prefrontal connectivity was associated with cognition.

CONCLUSIONS

This study provides evidence for aberrant connectivity of RSNs associated with motor function and cognition in early manifest HD when controlling for brain atrophy. This suggests clinically relevant changes of RSN activity in the presence of HD-associated cortical and subcortical structural abnormalities.

Dysfunction of the CNS-heart axis in mouse models of Huntington's disease

Cardiac remodelling and contractile dysfunction occur during both acute and chronic disease processes including the accumulation of insoluble aggregates of misfolded amyloid proteins that are typical features of Alzheimer's, Parkinson's and Huntington's disease (HD). While HD has been described mainly as a neurological disease, multiple epidemiological studies have shown that HD patients exhibit a high incidence of cardiovascular events leading to heart failure, and that this is the second highest cause of death. Given that huntingtin is ubiquitously expressed, cardiomyocytes may be at risk of an HD-related dysfunction. In mice, the forced expression of an expanded polyQ repeat under the control of a cardiac specific promoter led to severe heart failure followed by reduced lifespan. However the mechanism leading to cardiac dysfunction in the clinical and pre-clinical HD settings remains unknown. To unravel this mechanism, we employed the R6/2 transgenic and HdhQ150 knock-in mouse models of HD. We found that pre-symptomatic animals developed connexin-43 relocation and a significant deregulation of hypertrophic markers and Bdnf transcripts. In the symptomatic animals, pronounced functional changes were visualised by cardiac MRI revealing a contractile dysfunction, which might be a part of dilatated cardiomyopathy (DCM). This was accompanied by the re-expression of foetal genes, apoptotic cardiomyocyte loss and a moderate degree of interstitial fibrosis. To our surprise, we could identify neither mutant HTT aggregates in cardiac tissue nor a HD-specific transcriptional dysregulation, even at the end stage of disease. We postulate that the HD-related cardiomyopathy is caused by altered central autonomic pathways although the pathogenic effects of mutant HTT acting intrinsically in the heart may also be a contributing factor.

Huntington's disease (HD) is a neurodegenerative disorder for which the mutation results in an extra-long tract of glutamines that causes the huntingtin protein to aggregate. It is characterized by neurological symptoms and brain pathology that is associated with nuclear and cytoplasmic aggregates and with transcriptional dysregulation. Despite the fact that HD has been recognized principally as a neurological disease, there are multiple epidemiological studies showing that HD patients exhibit a high rate of cardiovascular events leading to heart failure. To unravel the cause of cardiac dysfunction in HD models, we employed a wide range of molecular and physiological methods using two well established genetic mouse models of this disease. We found that pre-symptomatic animals developed aberrant gap junction channel expression and a significant deregulation of hypertrophic markers that may predispose them to arrhythmia and an overall change in cardiac function. These changes were accompanied by the re-expression of foetal genes, apoptotic cardiomyocyte loss and a moderate degree of interstitial fibrosis in the symptomatic animals. Surprisingly, we could identify neither mutant HTT aggregates in cardiac tissue nor a HD-specific transcriptional dysregulation. Therefore, we conclude that the HD-related cardiomyopathy could be driven by altered central autonomic pathways.

Valence-specific conflict moderation in the dorso-medial PFC and the caudate head in emotional speech

Emotional speech comprises of complex multimodal verbal and non-verbal information that allows deducting others' emotional states or thoughts in social interactions. While the neural correlates of verbal and non-verbal aspects and their interaction in emotional speech have been identified, there is very little evidence on how we perceive and resolve incongruity in emotional speech, and whether such incongruity extends to current concepts of task-specific prediction errors as a consequence of unexpected action outcomes ('negative surprise'). Here, we explored this possibility while participants listened to congruent and incongruent angry, happy or neutral utterances and categorized the expressed emotions by their verbal (semantic) content. Results reveal valence-specific incongruity effects: negative verbal content expressed in a happy tone of voice increased activation in the dorso-medial prefrontal cortex (dmPFC) extending its role from conflict moderation to appraisal of valence-specific conflict in emotional speech. Conversely, the caudate head bilaterally responded selectively to positive verbal content expressed in an angry tone of voice broadening previous accounts of the caudate head in linguistic control to moderating valence-specific control in emotional speech. Together, these results suggest that control structures of the human brain (dmPFC and subcompartments of the basal ganglia) impact emotional speech differentially when conflict arises.

Role of cerebral cortex in the neuropathology of Huntington's disease

An expansion of glutamine repeats in the N-terminal domain of the huntingtin protein leads to Huntington's disease (HD), a neurodegenerative condition characterized by the presence of involuntary movements, dementia, and psychiatric disturbances. Evaluation of postmortem HD tissue indicates that the most prominent cell loss occurs in cerebral cortex and striatum, forebrain regions in which cortical pyramidal neurons (CPNs) and striatal medium spiny neurons (MSNs) are the most affected. Subsequent evidence obtained from HD patients and especially from transgenic mouse models of HD indicates that long before neuronal death, patterns of communication between CPNs and MSNs become dysfunctional. In fact, electrophysiological signaling in transgenic HD mice is altered even before the appearance of the HD behavioral phenotype, suggesting that dysfunctional cortical input to the striatum sets the stage for the emergence of HD neurological signs. Striatal MSNs, moreover, project back to cortex via multi-synaptic connections, allowing for even further disruptions in cortical processing. An effective therapeutic strategy for HD, therefore, may lie in understanding the synaptic mechanisms by which it dysregulates the corticostriatal system. Here, we review literature evaluating the molecular, morphological, and physiological alterations in the cerebral cortex, a key component of brain circuitry controlling motor behavior, as they occur in both patients and transgenic HD models.

Prefrontal activity in Huntington's disease reflects cognitive and neuropsychiatric disturbances: the IMAGE-HD study

Functional integrity of prefrontal cortico-striatal circuits underlying executive functioning may be compromised by basal ganglia degeneration during Huntington's disease (HD). This study investigated challenged inhibitory attentional control with a shifting response-set (SRS) task whilst assessing neural response via functional magnetic resonance imaging (fMRI) in 35 healthy controls, 35 matched pre-symptomatic (pre-HD) and 30 symptomatic (symp-HD) participants. A ≥70% performance accuracy threshold allowed confident identification of neural activity associated with SRS performance in a sub-set of 33 healthy controls, 32 pre-HD and 20 symp-HD participants. SRS activated dorsolateral prefrontal and dorsal anterior cingulate cortices, premotor, parietal, and basal ganglia regions and deactivated subgenual anterior cingulate cortex. Symp-HD participants showed greater prefrontal functional responses relative to controls and pre-HD, including larger activations and larger deactivations in response to cognitive challenge, consistent with compensatory neural recruitment. We then investigated associations between prefrontal BOLD responses, SRS performance accuracy and neuropsychiatric disturbance in all participants, including those below SRS performance accuracy threshold. We observed that reduced prefrontal responsivity in symp-HD was associated with reduced accuracy in SRS performance, and with increased neuropsychiatric disturbance within domains including executive dysfunction, pathological impulses, disinhibition, and depression. These findings demonstrate prefrontal response during inhibitory attentional control usefully characterises cognitive and neuropsychiatric status in symp-HD. The functional integrity of compensatory prefrontal responses may provide a useful marker for treatments which aim to sustain cognitive function and delay executive and neuropsychiatric disturbance.

Cognitive functions and corticostriatal circuits: insights from Huntington's disease

The basic mechanisms of information processing by corticostriatal circuits are currently a matter of intense debate amongst cognitive scientists. Huntington's disease, an autosomal-dominant neurogenetic disorder characterized clinically by a triad of motor, cognitive, and affective disturbance, is associated with neuronal loss within corticostriatal circuits, and as such provides a valuable model for understanding the role of these circuits in normal behaviour, and their disruption in disease. We review findings from our studies of the breakdown of cognition in Huntington's disease, with a particular emphasis on executive functions and visual recognition memory. We show that Huntington's disease patients exhibit a neuropsychological profile that shows a discernible pattern of progression with advancing disease, and appears to result from a breakdown in the mechanisms of response selection. These findings are consistent with recent computational models that suggest that corticostriatal circuits compute the patterns of sensory input and response output which are of behavioural significance within a particular environmental context.

Brain structure in preclinical Huntington's disease: a multi-method approach

BACKGROUND

Structural magnetic resonance imaging (MRI) of the brain could be a powerful tool for discovering early biomarkers in clinically presymptomatic carriers of the Huntington's disease gene mutation (preHD). So far, structural changes have been found mainly in preHD approaching the estimated motor onset of the disease (i.e., less than 15 years from onset), whereas structural findings in preHD far from the estimated motor onset have been inconclusive.

OBJECTIVES

The aims of this study were to investigate the sensitivity of different methodological approaches to structural data in far-from-onset preHD (mean estimated time to motor onset = 21.4 years) and to explore the relationship between brain structure, clinical variables and cognition.

METHODS

High-resolution MRI data at 3 T were obtained from 20 preHD individuals and 20 healthy participants and subsequently analyzed using voxel-based morphometry (VBM), cortical surface modeling and subcortical segmentation analysis techniques.

RESULTS

VBM analyses did not reveal significant between-group differences, whereas cortical surface modeling and subcortical segmentation analyses showed significant regional cortical thinning and striatal changes in preHD compared to controls. Significant correlations were found between striatal structure, estimated time to motor onset and executive performance, whereas cortical changes were not significantly correlated with these parameters.

CONCLUSION

These data suggest that a combined methodological approach to structural MRI data could increase the sensitivity for detecting subtle neurobiological changes in early preHD. As consistently shown across different methods, the association between striatal structure and clinical measures supports the notion that changes in striatal volume could represent a more robust marker of disease progression than cortical changes.

Complex relationships between cerebral blood flow and brain atrophy in early Huntington's disease

Alterations in cerebral blood flow (CBF) may play an important role in the pathophysiology of neurodegenerative disorders such as Huntington's disease (HD). While a few reports have suggested reductions in CBF in HD, little is known about their extent and whether, or how, they might be related to atrophy and to clinical symptoms. We used pulsed arterial-spin labeling MRI in conjunction with high-resolution anatomical MRI to non-invasively measure regional CBF in 17 early stage HD subjects and 41 age- and gender-matched healthy controls. We found profound yet heterogeneous CBF reductions in the cortex, extending to the sensorimotor, paracentral, inferior temporal and lateral occipital regions, with sparing of the neighboring postcentral gyrus, insula and medial occipital areas. As expected, CBF in subcortical regions was also profoundly reduced, and to a similar degree. Unexpectedly, however, the association between CBF reductions and regional atrophy was complex, the two being directly associated in certain areas but not with others. In contrast, CBF was associated with performance on the Stroop, suggesting a potentially important role for alterations in CBF in cognitive deficits in HD. The work described here may have broad-reaching implications for our understanding of HD pathogenesis, progression and emerging therapies.

Hypoperfusion in caudate nuclei in patients with brain-lung-thyroid syndrome

Mutations in NKX2-1 cause neurological, pulmonary, and thyroid hormone impairment. Recently, the disease was named brain-lung-thyroid syndrome. Here, we report three patients with brain-lung-thyroid syndrome. All patients were unable to walk until 24 months of age, and still have a staggering gait, without mental retardation. They have also had choreoathetosis since early infancy. Genetic analysis of NKX2-1 revealed a novel missense mutation (p.Val205Phe) in two patients who were cousins and their maternal families, and a novel 2.6-Mb deletion including NKX2-1 on chromosome 14 in the other patient. Congenital hypothyroidism was not detected on neonatal screening in the patient with the missense mutation, and frequent respiratory infections were observed in the patient with the deletion in NKX2-1. Oral levodopa did not improve the gait disturbance or involuntary movement. The results of (99m)Tc-ECD single-photon emission computed tomography (ECD-SPECT) analyzed using the easy Z-score imaging system showed decreased cerebral blood flow in the bilateral basal ganglia, especially in the caudate nuclei, in all three patients, but no brain magnetic resonance imaging (MRI) abnormalities. These brain nuclear image findings indicate that NKX2-1 haploinsufficiency causes dysfunction of the basal ganglia, especially the caudate nuclei, resulting in choreoathetosis and gait disturbance in this disease.

Magnetic resonance perfusion imaging of resting-state cerebral blood flow in preclinical Huntington's disease

Magnetic resonance imaging (MRI) of the brain could be a powerful tool for discovering early biomarkers in clinically presymptomatic carriers of the Huntington's disease gene mutation (preHD). The aim of this study was to investigate the sensitivity of resting-state perfusion MRI in preHD and to identify neural changes, which could serve as biomarkers for future clinical trials. Differences in regional cerebral blood flow (rCBF) in 18 preHD and 18 controls were assessed with a novel MRI method based on perfusion images obtained with continuous arterial spin labeling. High-resolution structural data were collected to test for changes of brain volume. Compared with controls, preHD individuals showed decreased rCBF in medial and lateral prefrontal regions and increased rCBF in the precuneus. PreHD near to symptom onset additionally showed decreased rCBF in the putamen and increased rCBF in the hippocampus. Network analyses revealed an abnormal lateral prefrontal pattern in preHD far and near to motor onset. These data suggest early changes of frontostriatal baseline perfusion in preHD independent of substantial reductions of gray matter volume. This study also shows the feasibility of detecting neural changes in preHD with a robust MRI technique that would be suitable for longitudinal multisite application.

Perfusion magnetic resonance imaging in psychiatry

INTRODUCTION

Cerebral perfusion imaging using magnetic resonance imaging (MRI) is widely used in the research and clinical fields to assess the profound changes in blood flow related to ischemic events such as acute stroke, chronic steno-occlusive disease, vasospasm, and abnormal vessel formations from congenital conditions or tumoral neovascularity. With continuing improvements in the precision of MRI-based perfusion techniques, it is increasingly feasible to use this tool in the study of the subtle brain perfusion changes occurring in psychiatric illnesses. This article aims to review the existing literature on applications of perfusion MRI in psychiatric disorder and substance abuse research. The article also provides a brief introductory overview of dynamic susceptibility contrast MRI and arterial spin labeling techniques. An outlook of necessary steps to bring perfusion MRI into the realm of clinical psychiatry as a diagnostic tool is brought forth. Opportunities for research in unexplored disorders and with higher field strengths are briefly examined.

METHODS

PubMed, ISI Web of Knowledge & Scopus were used to search the literature and cross reference several neuropsychiatric disorders with a search term construct, including "magnetic resonance imaging," "dynamic susceptibility contrast," "arterial spin labeling," perfusion or "cerebral blood flow" or "cerebral blood volume" or "mean transit time." The list of disorders used in the search included schizophrenia, depression and bipolar disorder, dementia and Alzheimer's disease, Parkinson's disease, posttraumatic stress disorder, autism, Asperger disease, attention deficit, Tourette syndrome, obsessive-compulsive disorder, Huntington's disease, bulimia nervosa, anorexia nervosa, and substance abuse. For each disorder for which perfusion MRI studies were found, a brief overview of the disorder symptoms, treatment, prevalence, and existing models is provided, and previous findings from nuclear medicine-based perfusion imaging are overviewed. Findings of perfusion MRI studies are then summarized, and overlap of findings are discussed. Overarching conclusions are made, or an outlook for future work in the area is offered, where appropriate.

RESULTS

Despite the now fairly broad availability of perfusion MRI, only a limited number of studies were found using this technology. The search produced 13 studies of schizophrenia, 7 studies in major depression, 12 studies in Alzheimer's disease, and 2 studies in Parkinson's disease. Drug abuse and other disorders have mainly been studied with nuclear medicine-based perfusion imaging. The literature concerning the use of perfusion imaging in psychiatry has not been reviewed in the last 5 years or more. The use of MRI for perfusion measurements in psychiatry has not been reviewed in 10 years.

CONCLUSIONS

Although MRI-based perfusion imaging in psychiatry has mainly been used as a research tool, a path is progressively being cleared for its application in clinical diagnostic and treatment monitoring. The precision of perfusion MRI methods now rivals that of nuclear medicine-based perfusion imaging techniques. Because of their noninvasive nature, arterial spin labeling methods have gained popularity in studies of neuropsychiatric disorders such as schizophrenia, depression, Alzheimer's, and Parkinson's diseases. Perfusion imaging measurements have yet to be included within the diagnostic criteria of neuropsychiatric disorders despite having shown to have great discriminant power in specific disorders. As this young methodology continues to improve and research studies demonstrate the correlation of measured perfusion abnormalities to microcirculatory abnormalities and neuropsychiatric symptomatology, the idea of including such a test within diagnostic criteria for certain mental illnesses becomes increasingly plausible.

Cortical dysfunction in patients with Huntington's disease during working memory performance

Previous functional neuroimaging studies on executive function suggested multiple functionally aberrant cortical regions in patients with Huntington's disease (HD). However, little is known about the neural mechanisms of working memory (WM) function in this patient population. The objective of this study was to investigate the functional neuroanatomy of WM in HD patients. We used event-related functional magnetic resonance imaging and a parametric verbal WM task to investigate cerebral function during WM performance in 16 healthy control subjects and 12 mild to moderate stage HD patients. We excluded incorrectly performed trials to control for potential accuracy-related activation confounds. Voxel-based morphometry (VBM) was used to control for confounding cortical and subcortical atrophy. We found that HD patients were slower and less accurate than healthy controls across all WM load levels. In addition, HD patients showed lower activation in the left dorso- and ventrolateral prefrontal cortex, the left inferior parietal cortex, the left putamen, and the right cerebellum at high WM load levels only. VBM revealed gray matter differences in the bilateral caudate nucleus and the thalamus, as well as in inferior parietal and right lateral prefrontal regions. However, volumetric abnormalities in the patient group did not affect the activation differences obtained during WM task performance. These findings demonstrate that WM-related functional abnormalities in HD patients involve distinct WM network nodes associated with cognitive control and subvocal rehearsal. Moreover, aberrant cortical function in HD patients may occur in brain regions, which are relatively well preserved in terms of brain atrophy.

The role of the basal ganglia in learning and memory: neuropsychological studies

In recent years, a common approach to understanding how the basal ganglia contribute to learning and memory in humans has been to study the deficits that occur in patients with basal ganglia pathology, such as Parkinson's disease and Huntington's disease. Pharmacological manipulations in patients and in healthy volunteers have also been conducted to investigate the role of dopamine, a neurotransmitter that is crucial for normal striatal functioning. When combined with powerful functional neuroimaging methods such as positron emission tomography and functional magnetic resonance imaging, such studies can provide important new insights into striatal function and dysfunction in humans. In this review, we consider this broad literature in an attempt to define a specific role for the caudate nucleus in learning and memory, and in particular, how this role may differ from that of the putamen. We conclude that the caudate nucleus contributes to learning and memory through the excitation of correct action schemas and the selection of appropriate sub-goals based on an evaluation of action-outcomes; both processes that are fundamental to all tasks involve goal-directed action.

Differential synaptic changes in the striatum of subjects with undifferentiated versus paranoid schizophrenia

Subjects with schizophrenia (SZ) have an increased density of synapses characteristic of corticostriatal or thalamostriatal glutamatergic inputs in the caudate matrix and putamen patches. SZ is a heterogeneous disease in many aspects including symptoms. The purpose of the present study was to determine if the synaptic organization in two different DSM-i.v. subgroups of SZ was differentially affected. Postmortem striatal tissue was obtained from the Maryland Brain Collection from normal controls (NC), chronic paranoid SZs (SZP), and chronic undifferentiated SZs (SZU). Tissue was prepared for calbindin immunocytochemistry to identify patch matrix compartments, prepared for electron microscopy and analyzed using stereological methods. The synaptic density of asymmetric synapses, characteristic of glutamatergic inputs, was elevated equivalently in striatal patches in the SZP and SZU versus NC. The SZU also had an increased density of asymmetric synapses in the striatal matrix compared to NC. Moreover, symmetric axospinous synapses, characteristic of intrinsic inhibitory inputs and dopaminergic afferents, showed a dichotomy in synaptic density between the SZU and SZP in the striatal and caudate matrix. These data show discreet differences in synaptic organization between SZU and SZP and/or NCs. The results suggest that abnormal corticostriatal and/or corticothalamic inputs to striatal patches may be related to limbic dysfunction, which is perturbed in both subtypes of SZ. The selective increase in axospinous synapses in the matrix of the SZU subgroup compared to the SZP may be related to more severe cognitive problems in that subset of SZ compared to SZP.

Altered frontostriatal coupling in pre-manifest Huntington's disease: effects of increasing cognitive load

BACKGROUND AND PURPOSE

Functional neuroimaging studies have suggested a dysfunction of prefrontal regions in clinically pre-symptomatic individuals with the Huntington's disease (HD) gene mutation (pre-HD) during cognitive processing. The objective of this study was to test the impact of cognitive demand on prefrontal connectivity in pre-HD individuals.

METHODS

Sixteen healthy controls and sixteen pre-HD subjects were studied using functional MRI and a verbal working memory task with increasing cognitive load. Load-dependent functional connectivity of the left dorsolateral prefrontal cortex (DLPFC) was investigated by means of psychophysiological interactions.

RESULTS

In pre-HD subjects, aberrant functional connectivity of the left DLPFC was found at high working memory load levels only. Compared with healthy controls, pre-HD individuals exhibited lower connectivity strength in the left putamen, the right anterior cingulate and the left medial prefrontal cortex. Pre-HD individuals close to the onset of motor symptoms additionally exhibited lower connectivity strength in the right putamen and the left superior frontal cortex. The connectivity strength in the left putamen was associated with several clinical measures including CAG repeat length, Unified Huntington's Disease Rating Scale motor score and predicted years to manifest symptom onset.

CONCLUSION

These findings suggest that early prefrontal connectivity abnormalities in pre-HD individuals are modulated by cognitive demand.

Distinguishing between Vascular Dementia and Alzheimer's Disease by Means of the WAIS: A Meta-analysis

This study was intended to, meta-analytically, review whether the subtests of the Wechsler Adult Intelligence Scale are useful in differentiating between vascular dementia and Alzheimer's disease. We expected the Alzheimer's disease group to outperform the vascular dementia group on those subtests that require executive functions, whereas inferior performance of the Alzheimer's disease patients was expected on memory tests. Two steps in the analysis were undertaken in an attempt to clarify this issue. The first step consisted of including all studies examining Wechsler Adult Intelligence Scale subtest performance in vascular dementia and Alzheimer's disease patients. Secondly, a subcortical vascular dementia subgroup was distinguished and performance of this subgroup was compared to that of the Alzheimer's disease group.Overall, the analyses showed that both the vascular dementia and, more strongly, the subcortical vascular dementia group revealed decreased executive functions on several subtests compared to the Alzheimer's disease group. The Alzheimer's disease group showed inferior performance on a single semantic memory test only compared to both the vascular dementia and the subcortical vascular dementia groups. These results indicate that several subtests of the Wechsler Adult Intelligence Scale can differentiate between these two clinical groups, and that most of these tests reveal more impaired performance in the vascular dementia group.

Wisconsin Card Sorting Test performance after putaminal hemorrhagic stroke

The purpose of this study was to compare the performance differences in the Wisconsin Card Sorting Test (WCST) between 55 patients with putaminal hemorrhage (PH) 3 months after stroke and 69 age-matched normal controls. Impairment on WCST was defined as performance greater than 1.64 standard deviation below the control mean. A multivariate analysis of covariance (MANCOVA) controlling for education yielded a significant main effect for group but not for education and interaction of group x education. Univariate analyses revealed significant between-group differences in five WCST measures, including perseverative errors (PE), perseverative responses (PR), conceptual-level responses (CLR), number of categories completed (NCC), and trials to complete the first category (TCC). For patients with PH, z-scores for two WCST indices were within the impaired range: TCC and PR. A high percentage of patients (40-47%) scored in the designated impaired range on NCC, PR, PE, and TCC. The WCST variables discriminated patients from controls with an overall accurate classification rate of 91.9%. Of these, the variables that contributed most to the differentiation between patients and normal controls were PE, CLR, and total number correct (TNC) (a standardized canonical discriminant function coefficient > 0.40). Finally, no significant hemispheric laterality effects emerged on any of the WCST variables. The results of this study provide further evidence of impaired mental set shifting in stroke patients with PH. The implications for rehabilitation professionals are discussed, and recommendations for further research are made.

Brain imaging and cognitive dysfunctions in Huntington's disease

Recent decades have seen tremendous growth in our understanding of the cognitive dysfunctions observed in Huntington's disease (HD). Advances in neuroimaging have contributed greatly to this growth. We reviewed the role that structural and functional neuroimaging techniques have played in elucidating the cerebral bases of the cognitive deficits associated with HD. We conducted a computer-based search using PubMed and PsycINFO databases to retrieve studies of patients with HD published between 1965 and December 2004 that reported measures on cognitive tasks and used neuroimaging techniques. Structural neuroimaging has provided important evidence of morphological brain changes in HD. Striatal and cortical atrophy are the most common findings, and they correlate with cognitive deficits in attention, working memory and executive functions. Functional studies have also demonstrated correlations between striatal dysfunction and cognitive performance. Striatal hypoperfusion and decreased glucose utilization correlate with executive dysfunction. Hypometabolism also occurs throughout the cerebral cortex and correlates with performance on recognition memory, language and perceptual tests. Measures of presynaptic and postsynaptic dopamine biochemistry have also correlated with measurements of episodic memory, speed of processing and executive functioning. Aided by the results of numerous neuroimaging studies, it is becoming increasingly clear that cognitive deficits in HD involve abnormal connectivity between the basal ganglia and cortical areas. In the future, neuroimaging techniques may shed the most light on the pathophysiology of HD by defining neurodegenerative disease phenotypes as a valuable tool for knowing when patients become "symptomatic," having been in a gene-positive presymptomatic state, and as a biomarker in following the disease, thereby providing a prospect for improved patient care.

Synaptic differences in the postmortem striatum of subjects with schizophrenia: a stereological ultrastructural analysis

The striatum processes motor, cognitive, and limbic function, all of which are perturbed in schizophrenia. The present study examined the synaptic organization of the caudate and putamen in schizophrenia. Postmortem striatum was obtained from 10 normal controls (NC) and 17 subjects with schizophrenia (SZ), prepared for electron microscopy, and analyzed using stereological principles. The densities of total synapses, asymmetric synapses (characteristic of excitatory inputs), and asymmetric axospinous synapses (characteristic of cortical input) were higher in the caudate of the SZs vs. NCs. These changes were most profound in the off-drug SZ cases and were also elevated in subjects on antipsychotic drugs (APDs). In comparison to NCs, there were no significant differences in the putamen of the SZ cohort as a whole group; however, there were more asymmetric axospinous synapses in the off-drug subgroup. The increase in density of synapses in the SZs does not appear to be caused by antipsychotic medication and may represent failure of normal synaptic pruning or abnormal sprouting. Higher density of cortical-type synapses in SZs vs. NCs may reflect adaptation of corticostriatal circuitry or hyperstimulation of striatal projection neurons. The abnormal synaptic organization could have several important and different downstream effects depending on the precise circuitry involved and may be related to limbic or cognitive dysfunction in schizophrenia.

In vivo evidence of cerebellar atrophy and cerebral white matter loss in Huntington disease

OBJECTIVE

To investigate the regional pattern of white matter and cerebellar changes, as well as subcortical and cortical changes, in Huntington disease (HD) using morphometric analyses of structural MRI.

METHODS

Fifteen individuals with HD and 22 controls were studied; groups were similar in age and education. Primary analyses defined six subcortical regions, the gray and white matter of primary cortical lobes and cerebellum, and abnormal signal in the cerebral white matter.

RESULTS

As expected, basal ganglia and cerebral cortical gray matter volumes were significantly smaller in HD. The HD group also demonstrated significant cerebral white matter loss and an increase in the amount of abnormal signal in the white matter; occipital white matter appeared more affected than other cerebral white matter regions. Cortical gray and white matter measures were significantly related to caudate volume. Cerebellar gray and white matter volumes were both smaller in HD.

CONCLUSIONS

The cerebellum and the integrity of cerebral white matter may play a more significant role in the symptomatology of HD than previously thought. Furthermore, changes in cortical gray and cerebral white matter were related to caudate atrophy, supporting a similar mechanism of degeneration.

Normal pressure hydrocephalus and cerebral blood flow: a PET study of baseline values

Regional cerebral blood flow (CBF) was studied with O(15)-water positron emission tomography and anatomic region-of-interest analysis on co-registered magnetic resonance in patients with idiopathic (n = 12) and secondary (n = 5) normal pressure hydrocephalus (NPH). Mean CBF was compared with values obtained from healthy volunteers (n = 12) and with clinical parameters. Mean CBF was significantly decreased in the cerebrum and cerebellum of patients with NPH. The regional analysis demonstrated that CBF was reduced in the basal ganglia and the thalamus but not in white matter regions. The results suggest that the role of the basal ganglia and thalamus in NPH may be more prominent than currently appreciated. The implications for theories regarding the pathogenesis of NPH are discussed.

Altered functional MRI responses in Huntington's disease

This study examined the effects of Huntington's disease (HD) on neural activity during performance of the Porteus maze task. fMRI data were acquired from three HD patients and three controls. Reduced fMRI signal was observed in the patients relative to the controls in occipital, parietal and somato-motor cortex and in the caudate, while increased signal was found in HD in the left postcentral and right middle frontal gyri. The altered fMRI responses in HD patients may result from neural, metabolic, neurovascular coupling and/or hemodynamic differences associated with this disorder.

Single photon emission computerized tomography (SPECT) in detecting neurodegeneration in Huntington's disease

Single photon emission computerized tomography (SPECT) studies were performed on 34 manifest Huntington's disease (HD) patients at various stages of clinical pathology ranging from early chorea to late dystonia with or without signs of dementia and 12 pre-symptomatic patients with abnormal terminal CAG expansions. Thirty HD patients with obvious clinical signs and seven pre-symptomatic patients without signs or symptoms of HD displayed selective caudate hypoperfusion by direct visual inspection. Such qualitative, selective striatal hypoperfusion patterns can be indicative of early and persistent metabolic changes in striatal neuropathology. SPECT studies can be useful in documenting early pre-clinical changes in patients with abnormal terminal CAG expansions and in confirming the presence of caudate pathology in patients with clinical signs of HD.

Benzodiazepine receptor quantification in Huntington's disease with [(123)I]omazenil and SPECT

OBJECTIVES

Increasing evidence suggests that metabolic changes predate neuronal death in Huntington's disease and emission tomography methods (PET and SPECT) have shown changes in glucose consumption and receptor function in early and possibly even presymptomatic disease. Because the GABA(A)-benzodiazepine receptor complex (BZR) is expressed on virtually all cerebral neurons BZR density images may be used to detect neuronal death. In this study the regional cerebral [(123)I]iomazenil binding to BZR was determined in patients with Huntington's disease and normal controls by a steady state method and SPECT.

METHODS

Seven patients mildly to moderately affected by Huntington's disease and seven age matched controls were studied. Brain CT was performed on all subjects. In each subject two [(123)I]iomazenil-SPECT measurements were acquired-one with and one without infusion of flumazenil. The affinity constant of flumazenil (Kd) was calculated from the paired distribution volumes (DV) and the free plasma flumazenil concentration. The distribution volume of [(123)I]iomazenil in the unblocked condition (DV(0)) reflects the ratio between BZR density and Kd.

RESULTS

Flumazenil Kd was similar in the Huntington's disease group and the control group (11.3 v 11.2 mM). For the Huntington's disease group a 31% reduction in striatal DV(0) (p=0.03) was found. In the cortical regions, DV(0) was similar in patients and in controls. In Huntington's disease, DV(0) correlated significantly with functional capacity (p=0.04) and chorea symptoms (p=0.02). The clinically least affected patients displayed DV(0)s within the range of those of the control group (19-35 ml/ml).

CONCLUSIONS

The finding of an unchanged Kd of flumazenil in patients indicates that the BZR is functionally intact in Huntington's disease. That is, the reduction in DV(0) for BZR represents a selective decrease in the number of striatal BZRs. DV(0) significantly correlated with functional loss and [(123)I]iomazenil-SPECT could be an important tool for validation of the effect of future therapeutic strategies aimed at limiting oxidative stress and free radicals in Huntington's disease.

Open interconnected model of basal ganglia-thalamocortical circuitry and its relevance to the clinical syndrome of Huntington's disease

The early stages of Huntington's disease (HD) present with motor, cognitive, and emotional symptoms. Correspondingly, current models implicate dysfunction of the motor, associative, and limbic basal ganglia-thalamocortical circuits. Available data, however, indicate that in the early stages of the disease, striatal damage is mainly restricted to the associative striatum. Based on an open interconnected model of basal ganglia-thalamocortical organization, we provide a detailed account of the mechanisms by which associative striatal pathology may lead to the complex pattern of motor, cognitive, and emotional symptoms of early HD. According to this account, the degeneration of a direct and several indirect pathways arising from the associative striatum leads to impaired functioning of: (1) the motor circuit, resulting in chorea and bradykinesia, (2) the associative circuit, resulting in abnormal eye movements, "frontal-like" cognitive deficits and "cognitive disinhibition," and (3) the limbic circuit, resulting in affective and psychiatric symptoms. When relevant, this analysis is aided by comparing the symptomatology of HD patients to that of patients with mild to moderate Parkinson's disease, since in the latter there is similar dysfunction of direct pathways but opposite dysfunction of indirect pathways. Finally, we suggest a potential novel treatment of HD and provide supportive evidence from a rat model of the disease.