Volumetric analysis of age- and sex-related changes in the corpus striatum and thalamus in the 1-18 age group: a retrospective magnetic resonance imaging study.

Studies of the development and asymmetry of the corpus striatum and thalamus in early childhood are rare. Studies investigating these structures across the lifespan have not presented their changes during childhood and adolescence in detail. For these reasons, this study investigated the effect of age and sex factors on the development and asymmetry of the corpus striatum and thalamus in the 1-18 age group. In this retrospective study, we included 652 individuals [362 (56%) males] aged 1-18 years with normal brain MRI between 2012 and 2021. Absolute and relative volumes of the corpus striatum and thalamus were obtained by segmentation of three-dimensional T1-weighted MRIs with volBrain1.0. We created age-specific volume data and month-based development models with the help of SPSS (ver.28). The corpus striatum and thalamus had cubic absolute volumetric developmental models. The relative volume of the caudate and thalamus (only males) is consistent with the decreasing "growth" model, the others with the decreasing cubic model. The absolute volumes of the males' bilateral corpus striatum and thalamus and the relative volumes of the caudate and thalamus of the females were significantly larger (P < 0.05). The caudate showed right > left lateralization; putamen, globus pallidus, and thalamus showed left > right lateralization.

[Bacosides: a study of neurobiological activity, prospects for application]. / Bakozidy: izuchenie neirobiologicheskoi aktivnosti i perspektivy primeneniya.

Bacosides are the main biologically active components derived from the plant bacopa monnieri (Bacopa monnieri (L.) Wettst.), which has been used as a nootropic in Indian medicine for many centuries. In recent years, these compounds have attracted attention because of their wide range of neurobiological effects. The neuroprotective effects of bacosides on brain neurons under the influence of various damaging factors (neurotoxins, oxidative stress, beta-amyloid deposition, cigarette smoke, etc.) have been established. It was shown that these substances reduce the levels of inflammatory cytokines and inhibit the processes of demyelination of neurons. The anticonvulsant effect of bacosides has been established. These compounds also improve cognitive functions, including memory and learning abilities. The effects associated with the influence on the dopaminergic and serotonergic systems of the striatum are of interest for the therapy of morphine addiction. The theoretical justifications for the future use of bacosides as a multipurpose means of complex therapy of individual diseases in neurological and psychiatric practice are presented.

Thalamic Foxp2 regulates output connectivity and sensory-motor impairments in a model of Huntington's Disease.

BACKGROUND: Huntington's Disease (HD) is a disorder that affects body movements. Altered glutamatergic innervation of the striatum is a major hallmark of the disease. Approximately 30% of those glutamatergic inputs come from thalamic nuclei. Foxp2 is a transcription factor involved in cell differentiation and reported low in patients with HD. However, the role of the Foxp2 in the thalamus in HD remains unexplored. METHODS: We used two different mouse models of HD, the R6/1 and the HdhQ111 mice, to demonstrate a consistent thalamic Foxp2 reduction in the context of HD. We used in vivo electrophysiological recordings, microdialysis in behaving mice and rabies virus-based monosynaptic tracing to study thalamo-striatal and thalamo-cortical synaptic connectivity in R6/1 mice. Micro-structural synaptic plasticity was also evaluated in the striatum and cortex of R6/1 mice. We over-expressed Foxp2 in the thalamus of R6/1 mice or reduced Foxp2 in the thalamus of wild type mice to evaluate its role in sensory and motor skills deficiencies, as well as thalamo-striatal and thalamo-cortical connectivity in such mouse models. RESULTS: Here, we demonstrate in a HD mouse model a clear and early thalamo-striatal aberrant connectivity associated with a reduction of thalamic Foxp2 levels. Recovering thalamic Foxp2 levels in the mouse rescued motor coordination and sensory skills concomitant with an amelioration of neuropathological features and with a repair of the structural and functional connectivity through a restoration of neurotransmitter release. In addition, reduction of thalamic Foxp2 levels in wild type mice induced HD-like phenotypes. CONCLUSIONS: In conclusion, we show that a novel identified thalamic Foxp2 dysregulation alters basal ganglia circuits implicated in the pathophysiology of HD.

Ten-m3 plays a role in the formation of thalamostriatal projections.

The importance of the thalamostriatal pathway for a myriad of brain functions is becoming increasingly apparent. Little is known about the formation of this pathway in mice. Further, while Ten-m3, a member of the Ten-m/teneurin/Odz family, is implicated in the proper wiring of mature thalamostriatal projections, its developmental time course is unknown. Here, we describe the normal development of thalamostriatal projections arising from the parafascicular nucleus (PFN) and show a role for Ten-m3 in its formation. Ten-m3 is expressed in both the PFN and the striatum by embryonic day 17 (E17). By postnatal day 3 (P3), it had a patchy appearance in the striatum, overlaid on a high dorsal-low ventral expression gradient in both structures. In wild-type mice, axons from the PFN begin to innervate the striatum by E17. By P3, terminals had ramified but were not confined to any striatal subregion. By P7, the axons had begun to avoid striosomes. The first indication of clustering of thalamic terminals within the striatal matrix was also seen at this time point. The compartmental targeting and clustering of PFN projections became more apparent by P10. Analysis of Ten-m3 knockout mice showed that while the early developmental progression of the thalamostriatal pathway is conserved, by P10 differences emerged, with a loss of topographic precision and the absence of terminal clustering. No evidence of the involvement of EphA7 downstream of Ten-m3 was found. Overall, our results suggest that Ten-m3 plays a role in the consolidation and refinement of thalamic axons to a specific subregion of the striatal matrix.

The respective activation and silencing of striatal direct and indirect pathway neurons support behavior encoding.

The basal ganglia are known to control actions and modulate movements. Neuronal activity in the two efferent pathways of the dorsal striatum is critical for appropriate behavioral control. Previous evidence has led to divergent conclusions on the respective engagement of both pathways during actions. Using calcium imaging to evaluate how neurons in the direct and indirect pathways encode behaviors during self-paced spontaneous explorations in an open field, we observed that the two striatal pathways exhibit distinct tuning properties. Supervised learning algorithms revealed that direct pathway neurons encode behaviors through their activation, whereas indirect pathway neurons exhibit behavior-specific silencing. These properties remain stable for weeks. Our findings highlight a complementary encoding of behaviors with congruent activations in the direct pathway encoding multiple accessible behaviors in a given context, and in the indirect pathway encoding the suppression of competing behaviors. This model reconciles previous conflicting conclusions on motor encoding in the striatum.

Robust hierarchically organized whole-brain patterns of dysconnectivity in schizophrenia spectrum disorders observed after personalized intrinsic network topography.

BACKGROUND: Spatial patterns of brain functional connectivity can vary substantially at the individual level. Applying cortical surface-based approaches with individualized rather than group templates may accelerate the discovery of biological markers related to psychiatric disorders. We investigated cortico-subcortical networks from multi-cohort data in people with schizophrenia spectrum disorders (SSDs) and healthy controls (HC) using individualized connectivity profiles. METHODS: We utilized resting-state and anatomical MRI data from n = 406 participants (n = 203 SSD, n = 203 HC) from four cohorts. Functional timeseries were extracted from previously defined intrinsic network subregions of the striatum, thalamus, and cerebellum as well as 80 cortical regions of interest, representing six intrinsic networks using (1) volume-based approaches, (2) a surface-based group atlas approaches, and (3) Personalized Intrinsic Network Topography (PINT). RESULTS: The correlations between all cortical networks and the expected subregions of the striatum, cerebellum, and thalamus were increased using a surface-based approach (Cohen's D volume vs. surface 0.27-1.00, all p < 10-6 ) and further increased after PINT (Cohen's D surface vs. PINT 0.18-0.96, all p < 10-4 ). In SSD versus HC comparisons, we observed robust patterns of dysconnectivity that were strengthened using a surface-based approach and PINT (Number of differing pairwise-correlations: volume: 404, surface: 570, PINT: 628, FDR corrected). CONCLUSION: Surface-based and individualized approaches can more sensitively delineate cortical network dysconnectivity differences in people with SSDs. These robust patterns of dysconnectivity were visibly organized in accordance with the cortical hierarchy, as predicted by computational models.

Current coffee consumption is associated with decreased striatal dopamine transporter availability in Parkinson's disease patients and healthy controls.

BACKGROUND: Coffee is the most widely consumed psychostimulant worldwide. Emerging evidence indicates that coffee consumption habit significantly reduces the risk of developing Parkinson's disease (PD). However, the effect of coffee consumption on nigrostriatal dopaminergic neurodegeneration is still largely unknown. We therefore aim to investigate the role of coffee consumption in nigrostriatal dopaminergic neurodegeneration using dopamine transporter (DAT) imaging in PD and healthy controls (HC). METHODS: A total of 138 PD patients and 75 HC with questionnaires about coffee consumption, and DAT scans were recruited from the Parkinson's Progression Markers Initiative cohort. Demographic, clinical, and striatal DAT characteristics were compared across subgroups of current, former, and never coffee consumers in PD and HC, respectively. Furthermore, partial correlation analyses were performed to determine whether there was a relationship between coffee cups consumed per day and striatal DAT characteristics in each striatal region. In addition, the factors that may have influenced the loss of nigrostriatal dopaminergic neurons were included in multiple linear regression analyses to identify significant contributing factors to DAT availability in each striatal region. RESULTS: PD patients had lower DAT availability in each striatal region than HC (p < 0.001). In PD patients, there were significant differences in DAT availability in the caudate (p = 0.008, Bonferroni corrected) across three PD subgroups. Specifically, post hoc tests showed that current coffee consumers had significantly lower DAT availability in the caudate than former coffee consumers (p = 0.01) and never coffee consumers (p = 0.022). In HC, there were significant differences in DAT availability in the caudate (p = 0.031, Bonferroni uncorrected) across three HC subgroups. Specifically, post hoc tests showed that current coffee consumers had significantly lower DAT availability in the caudate than former coffee consumers (p = 0.022). Moreover, correlation analysis revealed that cups per day were negatively correlated with DAT availability in the caudate in current consumers of PD patients (r = - 0.219, p = 0.047). In addition, multiple linear regression analyses showed that current coffee consumption remained an independent predictor of decreased DAT availability in the caudate in PD patients and HC. CONCLUSIONS: This study demonstrates that current coffee consumption is associated with decreased striatal DAT availability in the caudate. However, the effects of caffeine on striatal DAT may fade and disappear after quitting coffee consumption. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01141023.

Thalamo-cortical and cerebello-cortical functional connectivity in development.

The thalamus is a critical relay center for neural pathways involving sensory, motor, and cognitive functions, including cortico-striato-thalamo-cortical and cortico-ponto-cerebello-thalamo-cortical loops. Despite the importance of these circuits, their development has been understudied. One way to investigate these pathways in human development in vivo is with functional connectivity MRI, yet few studies have examined thalamo-cortical and cerebello-cortical functional connectivity in development. Here, we used resting-state functional connectivity to measure functional connectivity in the thalamus and cerebellum with previously defined cortical functional networks in 2 separate data sets of children (7-12 years old) and adults (19-40 years old). In both data sets, we found stronger functional connectivity between the ventral thalamus and the somatomotor face cortical functional network in children compared with adults, extending previous cortico-striatal functional connectivity findings. In addition, there was more cortical network integration (i.e. strongest functional connectivity with multiple networks) in the thalamus in children than in adults. We found no developmental differences in cerebello-cortical functional connectivity. Together, these results suggest different maturation patterns in cortico-striato-thalamo-cortical and cortico-ponto-cerebellar-thalamo-cortical pathways.

Bacillus calmette gaurine vaccine ameliorates the neurotoxicity of quinolinic acid in rats via the modulation of antioxidant, inflammatory and apoptotic markers.

A mutation in the Huntingtin gene causes 'Huntington's disease, which presents as a motor and behavioral impairment. Due to the limited drug therapy for this disease, scientists are constantly searching for newer and alternative drugs that may either retard or prevent the progress of the disease. This study aims to explore the neuroprotective potential of Bacillus Calmette Gaurine (BCG) vaccine against quinolinic acid-induced (QA) neurotoxicity in rats. QA (200 nmol/2 µl, i.s) was injected bilaterally into the rat striatum, after which a single dose of BCG (2 × 10^7, cfu) was given to the rats. Animals were assessed for behavioral parameters on the 14th and 21st days. On the 22nd day, animals were sacrificed, brains were harvested, and striatum was separated to evaluate biochemical, inflammatory, and apoptotic mediators. Histopathological studies were performed using Hematoxyline and Eosin staining to assess neuronal morphology. BCG treatment reversed motor abnormalities, reduced oxidative stress and neuroinflammatory markers, apoptotic mediators and striatal lesions induced by QA treatment. In conclusion, treat' 'ing rats with BCG vaccine (2 × 10^7, cfu) mitigated the quinolinic acid-induced Huntington's disease-like symptoms. Hence, BCG vaccine (2 ×10^7, cfu) could be used as an adjuvant in managing HD.

Association of coffee consumption and striatal volume in patients with Parkinson's disease and healthy controls.

BACKGROUND: Mounting studies have demonstrated that coffee consumption significantly reduces the risk of developing Parkinson's disease (PD). However, there have been few investigations about the role of chronic coffee consumption in nigrostriatal structural neurodegeneration in PD. We aimed to investigate whether chronic coffee consumption is associated with the change in striatal volume in PD. METHODS: In this study, 130 de novo patients with PD and 69 healthy controls were enrolled from the Parkinson's Progression Markers Initiative cohort. Patients with PD and healthy controls were, respectively, divided into three subgroups, including current, ever, and never coffee consumers. Then, striatal volume was compared across the three subgroups. Correlation analyses were performed to assess the relationship between cups consumed per day and striatal volume. Furthermore, we included the factors that may have influenced nigrostriatal dopaminergic neurons in multiple linear regression analyses to identify significant contributing factors to striatal volume in each investigated striatal region. RESULTS: Current coffee consumers had decreased striatal volume compared with ever consumers in controls but not patients with PD. Furthermore, the correlation analyses revealed that cups per day were negatively correlated with striatal volume in current consumers of patients with PD and controls. In addition, multiple linear regression analyses showed that current coffee consumption remained as an independent predictor of a decrease in striatal volume in controls. CONCLUSIONS: Our study showed that chronic coffee consumption was negatively correlated with striatal volume. In addition, our study showed that chronic coffee consumption was associated with the change in striatal volume in current-rather than ever coffee consumers, which suggests that the chronic effects of caffeine on striatal morphology may fade and even compensate after quitting coffee. Our study provides evidence for the effect of chronic coffee consumption on striatal volume in human brain in vivo.

The rostral intralaminar nuclear complex of the thalamus supports striatally mediated action reinforcement.

The dorsal striatum (DS) mediates the selection of actions for reward acquisition necessary for survival. Striatal pathology contributes to several neuropsychiatric conditions, including aberrant selection of actions for specific rewards in addiction. A major source of glutamate driving striatal activity is the rostral intralaminar nuclei (rILN) of the thalamus. Yet, the information that is relayed to the striatum to support action selection is unknown. Here, we discovered that rILN neurons projecting to the DS are innervated by a range of cortical and subcortical afferents and that rILN→DS neurons stably signaled at two time points in mice performing an action sequence task reinforced by sucrose reward: action initiation and reward acquisition. In vivo activation of this pathway increased the number of successful trials, whereas inhibition decreased the number of successful trials. These findings illuminate a role for the rostral intralaminar nuclear complex in reinforcing actions.

Dopaminergic connectivity reconfiguration in the dementia with Lewy bodies continuum.

INTRODUCTION: The impairment of nigrostriatal dopaminergic network is a core feature of dementia with Lewy bodies (DLB). The involvement and reconfiguration of extranigrostriatal dopaminergic circuitries in the DLB continuum is still theme of debate. We aim to investigate in vivo the dynamic changes of local and long-distance dopaminergic networks across DLB continuum. METHODS: Forty-nine patients (including 29 with dementia and 20 prodromal cases) and fifty-two controls entered the study. Each subject underwent a standardized clinical and neurological examination and performed Brain SPECT to measuring brain dopamine transporter (DAT) density. Spatially normalized images underwent the occipital-adjusted specific binding to obtain parametric data. The ANCOVA was applied to assess 123I-FP-CIT differences between pDLB, overt-DLB and CG, considering age, gender, and motor impairment as variables of no interest. Between-nodes correlation analysis measured molecular connectivity within the ventral and dorsal dopaminergic networks. RESULTS: Prodromal DLB and DLB patients showed comparable nigrostriatal deficits in basal ganglia regions compared with CG. Molecular connectivity analyses revealed extensive connectivity losses, more in ventral than in dorsal dopaminergic network in DLB dementia. Conversely, the prodromal group showed increased connectivity compared to CG, mostly putamen-thalamus-cortical and striatal-cortical connectivity. CONCLUSIONS: This study indicates a comparable basal ganglia deficit in nigrostriatal projections in DLB continuum and supports a different reorganization of extra-striatal dopaminergic connectivity in the prodromal phases of DLB. The shift from an increased to a decreased bilateral putamen-thalamus-cortex connectivity might be a hallmark of transition from prodromal to dementia DLB stages.

The deep cerebellar nuclei to striatum disynaptic connection contributes to skilled forelimb movement.

Cerebellar-thalamo-striatal synaptic communication has been implicated in a wide range of behaviors, including goal-directed actions, and is altered in cerebellar dystonia. However, its detailed connectivity through the thalamus and its contribution to the execution of forelimb movements is unclear. Here, we use trans-synaptic and retrograde tracing, ex vivo slice recordings, and optogenetic inhibitions during the execution of unidirectional or sequential joystick displacements to demonstrate that the deep cerebellar nuclei (DCN) influence the dorsal striatum with a very high probability. We show that this mainly occurs through the centrolateral (CL), parafascicular (PF), and ventrolateral (VL) nuclei of the thalamus, observing that the DCN→VL and DCN→CL pathways contribute to the execution of unidirectional forelimb displacements while the DCN→PF and DCN→thalamo→striatal pathways contribute to the appropriate execution of forelimb reaching and sequential displacements. These findings highlight specific contributions of the different cerebellar-thalamo-striatal paths to the control of skilled forelimb movement.

Vitamin D (VD3) Intensifies the Effects of Exercise and Prevents Alterations of Behavior, Brain Oxidative Stress, and Neuroinflammation, in Hemiparkinsonian Rats.

In the present study, we investigated the effects of physical exercise in the presence of Vitamin D3 (VD3), on 6-hydroxydopamine (6-OHDA)-lesioned hemiparkinsonian rats. The animals were divided into sham-operated (SO), 6-OHDA-lesioned, and 6-OHDA-lesioned plus VD3 (1 µg/kg, 21 days), in the absence (no exercise, NE) and presence (with exercise, WE) of physical exercise on a treadmill (30 min, speed of 20 cm/s, once a day/21 days). This procedure started, 24 h after the stereotaxic surgery (injections of 6-OHDA into the right striatum). The animals were then subjected to behavioral (rotarod, open field, and apomorphine tests) and their brain areas were dissected for neurochemical, dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) determinations, and immunohistochemical studies for tyrosine hydroxylase (TH), dopamine transporter (DAT), and vitamin D receptor (VD3R). The effects on the brain oxidative stress: nitrite/nitrate, glutathione (GSH), and malondialdehyde (MDA) measurements were also evaluated. Behavioral changes of the 6-OHDA lesioned group were improved by exercise plus VD3. Similar results were observed in dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations increased by exercise and VD3, compared with SO groups. Additionally, tyrosine hydroxylase (TH) and dopamine transporter (DAT) immunoexpressions were decreased in the 6-OHDA-lesioned groups, with values normalized after exercise and VD3. The VD3 receptor immunoexpression decreased in the 6-OHDA (NE) group, and this was attenuated by exercise, especially after VD3. While 6-OHDA lesions increased, VD3 supplementation decreased the oxidative stress, which was intensified by exercise. VD3 showed neuroprotective properties that were intensified by physical exercise. These VD3 actions on hemiparkinsonian rats are possibly related to its antioxidant and anti-inflammatory effects.

AAV5-miHTT-mediated huntingtin lowering improves brain health in a Huntington's disease mouse model.

Huntingtin (HTT)-lowering therapies show great promise in treating Huntington's disease. We have developed a microRNA targeting human HTT that is delivered in an adeno-associated serotype 5 viral vector (AAV5-miHTT), and here use animal behaviour, MRI, non-invasive proton magnetic resonance spectroscopy and striatal RNA sequencing as outcome measures in preclinical mouse studies of AAV5-miHTT. The effects of AAV5-miHTT treatment were evaluated in homozygous Q175FDN mice, a mouse model of Huntington's disease with severe neuropathological and behavioural phenotypes. Homozygous mice were used instead of the more commonly used heterozygous strain, which exhibit milder phenotypes. Three-month-old homozygous Q175FDN mice, which had developed acute phenotypes by the time of treatment, were injected bilaterally into the striatum with either formulation buffer (phosphate-buffered saline + 5% sucrose), low dose (5.2 × 109 genome copies/mouse) or high dose (1.3 × 1011 genome copies/mouse) AAV5-miHTT. Wild-type mice injected with formulation buffer served as controls. Behavioural assessments of cognition, T1-weighted structural MRI and striatal proton magnetic resonance spectroscopy were performed 3 months after injection, and shortly afterwards the animals were sacrificed to collect brain tissue for protein and RNA analysis. Motor coordination was assessed at 1-month intervals beginning at 2 months of age until sacrifice. Dose-dependent changes in AAV5 vector DNA level, miHTT expression and mutant HTT were observed in striatum and cortex of AAV5-miHTT-treated Huntington's disease model mice. This pattern of microRNA expression and mutant HTT lowering rescued weight loss in homozygous Q175FDN mice but did not affect motor or cognitive phenotypes. MRI volumetric analysis detected atrophy in four brain regions in homozygous Q175FDN mice, and treatment with high dose AAV5-miHTT rescued this effect in the hippocampus. Like previous magnetic resonance spectroscopy studies in Huntington's disease patients, decreased total N-acetyl aspartate and increased myo-inositol levels were found in the striatum of homozygous Q175FDN mice. These neurochemical findings were partially reversed with AAV5-miHTT treatment. Striatal transcriptional analysis using RNA sequencing revealed mutant HTT-induced changes that were partially reversed by HTT lowering with AAV5-miHTT. Striatal proton magnetic resonance spectroscopy analysis suggests a restoration of neuronal function, and striatal RNA sequencing analysis shows a reversal of transcriptional dysregulation following AAV5-miHTT in a homozygous Huntington's disease mouse model with severe pathology. The results of this study support the use of magnetic resonance spectroscopy in HTT-lowering clinical trials and strengthen the therapeutic potential of AAV5-miHTT in reversing severe striatal dysfunction in Huntington's disease.

Connectivity of the corticostriatal and thalamostriatal systems in normal and parkinsonian states: An update.

The striatum receives abundant glutamatergic afferents from the cortex and thalamus. These inputs play a major role in the functions of the striatal neurons in normal conditions, and are significantly altered in pathological states, such as Parkinson's disease. This review summarizes the current knowledge of the connectivity of the corticostriatal and thalamostriatal pathways, with emphasis on the most recent advances in the field. We also discuss novel findings regarding structural changes in cortico- and thalamostriatal connections that occur in these connections as a consequence of striatal loss of dopamine in parkinsonism.

The Protein-Rich Fraction from Spirulina platensis Exerts Neuroprotection in Hemiparkinsonian Rats by Decreasing Brain Inflammatory-Related Enzymes and Glial Fibrillary Acidic Protein Expressions.

Spirulina platensis is a cyanobacterium with high protein content and presenting neuroprotective effects. Now, we studied a protein-enriched fraction (SPF), on behavior, neurochemical and immunohistochemical (IHC) assays in hemiparkinsonian rats, distributed into the groups: SO (sham-operated), 6-hydroxydopamine (6-OHDA), and 6-OHDA (treated with SPF, 5 and 10 mg/kg, p.o., 15 days). Afterward, animals were subjected to behavioral tests and euthanized, and brain areas used for neurochemical and IHC assays. SPF partly reversed the changes in the apomorphine-induced rotations, open field and forced swim tests, and also the decrease in striatal dopamine and 3,4-dihydroxyphenylacetic acid contents seen in hemiparkinsonian rats. Furthermore, SPF reduced brain oxidative stress and increased striatal expressions of tyrosine hydroxylase and dopamine transporter and significantly reduced hippocampal inducible nitric oxide synthase, cyclooxygenase-2 and glial fibrillary acidic protein expressions. The data suggest that the protein fraction from S. platensis, through its brain anti-inflammatory and antioxidative actions, exerts neuroprotective effects that could benefit patients affected by neurodegenerative diseases, like Parkinson's disease.