Equivalent-time-active-cavitation-imaging enables vascular-resolution blood-brain-barrier-opening-therapy planning

Objective. Linking cavitation and anatomy was found to be important for predictable outcomes in focused-ultrasound blood-brain-barrier-opening and requires high resolution cavitation mapping. However, cavitation mapping techniques for planning and monitoring of therapeutic procedures either (1) do not leverage the full resolution capabilities of ultrasound imaging or (2) place constraints on the length of the therapeutic pulse. This study aimed to develop a high-resolution technique that could resolve vascular anatomy in the cavitation map.Approach. Herein, we develop BandPass-sampled-equivalent-time-active-cavitation-imaging (BP-ETACI), derived from bandpass sampling and dual-frequency contrast imaging at 12.5 MHz to produce cavitation maps prior and during blood-brain barrier opening with long therapeutic bursts using a 1.5 MHz focused transducer in the brain of C57BL/6 mice.Main results. The BP-ETACI cavitation maps were found to correlate with the vascular anatomy in ultrasound localization microscopy vascular maps and in histological sections. Cavitation maps produced from non-blood-brain-barrier disrupting doses showed the same cavitation-bearing vasculature as maps produced over entire blood-brain-barrier opening procedures, allowing use for (1) monitoring focused-ultrasound blood-brain-barrier-opening (FUS-BBBO), but also for (2) therapy planning and target verification.Significance. BP-ETACI is versatile, created high resolution cavitation maps in the mouse brain and is easily translatable to existing FUS-BBBO experiments. As such, it provides a means to further study cavitation phenomena in FUS-BBBO.

Gel nail polish as an alternative to traditional coverslip sealants: A quick solution to a sticky situation

A widespread protocol to seal coverslips on a microscope slide for histological analysis utilizes air-drying nail polish. Nail polish is applied to glue the coverslip in place and prevent the leakage of mounting media. Air drying takes time, typically overnight, and generates an unpleasant smell. Equally familiar is the waiting game, lightly touching the polish to check its dryness, while being careful not to disrupt the coverslip, often leaving sticky spots on one's fingertips. An advantageous solution to these drawbacks is to use gel nail polish, which rapidly hardens and dries by being cured under a LED/UV lamp. We show that UV-cured gel nail polish provides a rapid, stable, scentless, nontoxic, and cost-effective solution for coverslip sealing. Cured in 10 s, with no impact on fluorescent labels, gel polish hardens completely and the slide is ready to be imaged. Furthermore, we show that gel nail polish can be used to generate 3D ridges and structures to support coverslipping thicker samples. Gel nail polish is purposefully unscented, and the brands used in our study employ environmentally conscious, vegan, and cruelty-free ingredients. UV-cured gel nail polish is a cost-effective alternative that presents an easy, accessible, and inexpensive solution to traditional coverslip sealing methods.•Inexpensive method to rapidly seal coverslips onto a microscope slide to immediately image samples for Histological analyses.•Utilizes LED/UV light to cure gel nail polish in 10 s without bleaching fluorophores.•Can be used to generate 3D ridges and structures to support coverslipping thicker samples.

Reproducibility of cerebellar involvement as quantified by consensus structural MRI biomarkers in advanced essential tremor

Essential tremor (ET) is the most prevalent movement disorder with poorly understood etiology. Some neuroimaging studies report cerebellar involvement whereas others do not. This discrepancy may stem from underpowered studies, differences in statistical modeling or variation in magnetic resonance imaging (MRI) acquisition and processing. To resolve this, we investigated the cerebellar structural differences using a local advanced ET dataset augmented by matched controls from PPMI and ADNI. We tested the hypothesis of cerebellar involvement using three neuroimaging biomarkers: VBM, gray/white matter volumetry and lobular volumetry. Furthermore, we assessed the impacts of statistical models and segmentation pipelines on results. Results indicate that the detected cerebellar structural changes vary with methodology. Significant reduction of right cerebellar gray matter and increase of the left cerebellar white matter were the only two biomarkers consistently identified by multiple methods. Results also show substantial volumetric overestimation from SUIT-based segmentation-partially explaining previous literature discrepancies. This study suggests that current estimation of cerebellar involvement in ET may be overemphasized in MRI studies and highlights the importance of methods sensitivity analysis on results interpretation. ET datasets with large sample size and replication studies are required to improve our understanding of regional specificity of cerebellum involvement in ET. PROTOCOL REGISTRATION: The stage 1 protocol for this Registered Report was accepted in principle on 21 March 2022. The protocol, as accepted by the journal, can be found at: https://doi.org/10.6084/m9.figshare.19697776 .

A standardized accelerometry method for characterizing tremor: Application and validation in an ageing population with postural and action tremor

Background

Ordinal scales based on qualitative observation are the mainstay in the clinical assessment of tremor, but are limited by inter-rater reliability, measurement precision, range, and ceiling effects. Quantitative tremor evaluation is well-developed in research, but clinical application has lagged, in part due to cumbersome mathematical application and lack of established standards.

Objectives

To develop a novel method for evaluating tremor that integrates a standardized clinical exam, wrist-watch accelerometers, and a software framework for data analysis that does not require advanced mathematical or computing skills. The utility of the method was tested in a sequential cohort of patients with predominant postural and action tremor presenting to a specialized surgical clinic with the presumptive diagnosis of Essential Tremor (ET).

Methods

Wristwatch accelerometry was integrated with a standardized clinical exam. A MATLAB application was developed for automated data analysis and graphical representation of tremor. Measures from the power spectrum of acceleration of tremor in different upper limb postures were derived in 25 consecutive patients. The linear results from accelerometry were correlated with the commonly used non-linear Clinical Rating Scale for Tremor (CRST).

Results

The acceleration power spectrum was reliably produced in all consecutive patients. Tremor frequency was stable in different postures and across patients. Both total and peak power of acceleration during postural conditions correlated well with the CRST. The standardized clinical examination with integrated accelerometry measures was therefore effective at characterizing tremor in a population with predominant postural and action tremor. The protocol is also illustrated on repeated measures in an ET patient who underwent Magnetic Resonance-Guided Focused Ultrasound thalamotomy.

Conclusion

Quantitative assessment of tremor as a continuous variable using wristwatch accelerometry is readily applicable as a clinical tool when integrated with a standardized clinical exam and a user-friendly software framework for analysis. The method is validated for patients with predominant postural and action tremor, and can be adopted for characterizing tremor of different etiologies with dissemination in a wide variety of clinical and research contexts in ageing populations.

The Netrin-1 Receptor DCC Promotes the Survival of a Subpopulation of Midbrain Dopaminergic Neurons: Relevance for Ageing and Parkinson's Disease

Mechanisms that determine the survival of midbrain dopaminergic (mDA) neurons in the adult central nervous system (CNS) are not fully understood. Netrins are a family of secreted proteins that are essential for normal neural development. In the mature CNS, mDA neurons express particularly high levels of netrin‐1 and its receptor Deleted in Colorectal Cancer (DCC). Recent findings indicate that overexpressing netrin‐1 protects mDA neurons in animal models of Parkinson’s disease (PD), with a proposed pro‐apoptotic dependence function for DCC that triggers cell death in the absence of a ligand. Here, we sought to determine if DCC expression influences mDA neuron survival in young adult and ageing mice. To circumvent the perinatal lethality of DCC null mice, we selectively deleted DCC from mDA neurons utilizing DAT^cre/loxP gene‐targeting and examined neuronal survival in adult and aged animals. Reduced numbers of mDA neurons were detected in the substantia nigra pars compacta (SNc) of young adult DAT^cre/DCC^fl/fl mice, with further reduction in aged DAT^cre/DCC^fl/fl animals. In contrast to young adults, aged mice also exhibited a gene dosage effect, with fewer SNc mDA neurons in DCC heterozygotes (DAT^cre/DCC^fl/wt). Notably, loss of mDA neurons in the SN was not uniform. Neuronal loss in the SN was limited to ventral tier mDA neurons, while mDA neurons in the dorsal tier of the SN, which resist degeneration in PD, were spared from the effect of DCC deletion in both young and aged mice. In the ventral tegmental area (VTA), young adult mice with conditional deletion of DCC had normal mDA neuronal numbers, while significant loss occurred in aged DAT^cre/DCC^fl/fl and DAT^cre/DCC^fl/wt mice compared to age‐matched wild‐type mice. Our results indicate that expression of DCC is required for the survival of subpopulations of mDA neurons and may be relevant to the degenerative processes in PD.

Pitch and Rhythm Perception and Verbal Short-Term Memory in Acute Traumatic Brain Injury

Music perception deficits are common following acquired brain injury due to stroke, epilepsy surgeries, and aneurysmal clipping. Few studies have examined these deficits following traumatic brain injury (TBI), resulting in an under-diagnosis in this population. We aimed to (1) compare TBI patients to controls on pitch and rhythm perception during the acute phase; (2) determine whether pitch and rhythm perception disorders co-occur; (3) examine lateralization of injury in the context of pitch and rhythm perception; and (4) determine the relationship between verbal short-term memory (STM) and pitch and rhythm perception. Music perception was examined using the Scale and Rhythm tests of the Montreal Battery of Evaluation of Amusia, in association with CT scans to identify lesion laterality. Verbal short-term memory was examined using Digit Span Forward. TBI patients had greater impairment than controls, with 43% demonstrating deficits in pitch perception, and 40% in rhythm perception. Deficits were greater with right hemisphere damage than left. Pitch and rhythm deficits co-occurred 31% of the time, suggesting partly dissociable networks. There was a dissociation between performance on verbal STM and pitch and rhythm perception 39 to 42% of the time (respectively), with most individuals (92%) demonstrating intact verbal STM, with impaired pitch or rhythm perception. The clinical implications of music perception deficits following TBI are discussed.

Microstructural Abnormalities of the Dentatorubrothalamic Tract in Cervical Dystonia

BACKGROUND

The dentatorubrothalamic tract (DRTT) remains understudied in idiopathic cervical dystonia (CD), despite evidence that the pathway is relevant in the pathophysiology of the disorder.

OBJECTIVE

The aim of this study was to examine the DRTT in patients with CD using diffusion tensor imaging (DTI)-based tractography.

METHODS

Magnetic resonance imaging scans from 67 participants were collected to calculate diffusion tractography metrics using a binary tractography-based DRTT template. Fractional anisotropy and diffusivity measures of left and right DRTT were computed and compared between 32 subjects with CD and 35 age-matched healthy volunteers.

RESULTS

Fractional anisotropy of right DRTT and mean and axial diffusivity of left DRTT were significantly reduced in patients with CD. Similar abnormalities were observed in patients with focal CD and patients with CD without tremor. DTI metrics did not correlate with disease duration or severity.

CONCLUSIONS

Significant reductions in DTI measures suggest microstructural abnormalities within the DRTT in CD, characterized by a tractography pattern consistent with decreased axonal integrity. © 2021 International Parkinson and Movement Disorder Society.

The Role of the Subthalamic Nucleus in Inhibitory Control of Oculomotor Behavior in Parkinson's Disease

Inhibiting inappropriate actions in a context is an important part of the human cognitive repertoire, and deficiencies in this ability are common in neurological and psychiatric disorders. An anti-saccade is a simple oculomotor task that tests this ability by requiring inhibition of saccades to peripheral targets (pro-saccade) and producing voluntary eye movements toward the mirror position (anti-saccades). Previous studies provide evidence for a possible contribution from the basal ganglia in anti-saccade behavior, but the precise role of different components is still unclear. Parkinson's disease patients with implanted deep brain stimulators (DBS) in subthalamic nucleus (STN) provide a unique opportunity to investigate the role of the STN in anti-saccade behavior. Previous attempts to show the effect of STN DBS on anti-saccades have produced conflicting observations. For example, the effect of STN DBS on anti-saccade error rate is not yet clear. Part of this inconsistency may be related to differences in dopaminergic states in different studies. Here, we tested Parkinson's disease patients on anti- and pro-saccade tasks ON and OFF STN DBS, in ON and OFF dopaminergic medication states. First, STN DBS increases anti-saccade error rate while patients are OFF dopamine replacement therapy. Second, dopamine replacement therapy and STN DBS interact: L-dopa reduces the effect of STN DBS on anti-saccade error rate. Third, STN DBS induces different effects on pro- and anti-saccades in different patients. These observations provide evidence for an important role for the STN in the circuitry underlying context-dependent modulation of visuomotor action selection.

Thalamostriatal degeneration contributes to dystonia and cholinergic interneuron dysfunction in a mouse model of Huntington's disease

Huntington’s disease (HD) is an autosomal dominant trinucleotide repeat disorder characterized by choreiform movements, dystonia and striatal neuronal loss. Amongst multiple cellular processes, abnormal neurotransmitter signalling and decreased trophic support from glutamatergic cortical afferents are major mechanisms underlying striatal degeneration. Recent work suggests that the thalamostriatal (TS) system, another major source of glutamatergic input, is abnormal in HD although its phenotypical significance is unknown. We hypothesized that TS dysfunction plays an important role in generating motor symptoms and contributes to degeneration of striatal neuronal subtypes. Our results using the R6/2 mouse model of HD indicate that neurons of the parafascicular nucleus (PF), the main source of TS afferents, degenerate at an early stage. PF lesions performed prior to motor dysfunction or striatal degeneration result in an accelerated dystonic phenotype and are associated with premature loss of cholinergic interneurons. The progressive loss of striatal medium spiny neurons and parvalbumin-positive interneurons observed in R6/2 mice is unaltered by PF lesions. Early striatal cholinergic ablation using a mitochondrial immunotoxin provides evidence for increased cholinergic vulnerability to cellular energy failure in R6/2 mice, and worsens the dystonic phenotype. The TS system therefore contributes to trophic support of striatal interneuron subtypes in the presence of neurodegenerative stress, and TS deafferentation may be a novel cell non-autonomous mechanism contributing to the pathogenesis of HD. Furthermore, behavioural experiments demonstrate that the TS system and striatal cholinergic interneurons are key motor-network structures involved in the pathogenesis of dystonia. This work suggests that treatments aimed at rescuing the TS system may preserve important elements of striatal structure and function and provide symptomatic relief in HD.

BAG3P215L/KO Mice as a Model of BAG3P209L Myofibrillar Myopathy

BCL-2-associated athanogene 3 (BAG3) is a co-chaperone to heat shock proteins important in degrading misfolded proteins through chaperone-assisted selective autophagy. The recurrent dominant BAG3-P209L mutation results in a severe childhood-onset myofibrillar myopathy (MFM) associated with progressive muscle weakness, cardiomyopathy, and respiratory failure. Because a homozygous knock-in (KI) strain for the mP215L mutation homologous to the human P209L mutation did not have a gross phenotype, compound heterozygote knockout (KO) and KI mP215L mice were generated to establish whether further reduction in BAG3 expression would lead to a phenotype. The KI/KO mice have a significant decrease in voluntary movement compared with wild-type and KI/KI mice in the open field starting at 7 months. The KI/KI and KI/KO mice both have significantly smaller muscle fiber cross-sectional area. However, only the KI/KO mice have clear skeletal muscle histologic changes in MFM. As in patient muscle, there are increased levels of BAG3-interacting proteins, such as p62, heat shock protein B8, and αB-crystallin. The KI/KO mP215L strain is the first murine model of BAG3 myopathy that resembles the human skeletal muscle pathologic features. The results support the hypothesis that the pathologic development of MFM requires a significant decrease in BAG3 protein level and not only a gain of function caused by the dominant missense mutation.

The noradrenergic system is necessary for survival of vulnerable midbrain dopaminergic neurons: implications for development and Parkinson's disease

The cause of midbrain dopaminergic (mDA) neuron loss in sporadic Parkinson's disease (PD) is multifactorial, involving cell autonomous factors, cell-cell interactions, and the effects of environmental toxins. Early loss of neurons in the locus coeruleus (LC), the main source of ascending noradrenergic (NA) projections, is an important feature of PD and other neurodegenerative disorders. We hypothesized that NA afferents provide trophic support for vulnerable mDA neurons. We demonstrate that depriving mDA neurons of NA input increases postnatal apoptosis and decreases cell survival in young adult rodents, with relative sparing of calbindin-positive subpopulations known to be resistant to degeneration in PD. As a mechanism, we propose that the neurotrophin brain-derived neurotrophic factor (BDNF) modulates anterograde survival effects of LC inputs to mDA neurons. We demonstrate that the LC is rich in BDNF mRNA in postnatal and young adult brains. Early postnatal NA denervation reduces both BDNF protein and activation of TrkB receptors in the ventral midbrain. Furthermore, overexpression of BDNF in NA afferents in transgenic mice increases mDA neuronal survival. Finally, increasing NA activity in primary cultures of mDA neurons improves survival, an effect that is additive or synergistic in the presence of different concentrations of BDNF. Taken together, our results point to a novel mechanism whereby LC afferents couple BDNF effects and NA activity to provide anterograde trophic support for vulnerable mDA neurons. Early loss of NA activity and anterograde neurotrophin support may contribute to degeneration of vulnerable neurons in PD and other neurodegenerative disorders.

Impaired TrkB Signaling Underlies Reduced BDNF-Mediated Trophic Support of Striatal Neurons in the R6/2 Mouse Model of Huntington's Disease

The principal projection neurons of the striatum are critically dependent on an afferent supply of brain derived neurotrophic factor (BDNF) for neurotrophic support. These neurons express TrkB, the cognate receptor for BDNF, which activates signaling pathways associated with neuronal survival and phenotypic maintenance. Impairment of the BDNF-TrkB pathway is suspected to underlie the early dysfunction and prominent degeneration of striatal neurons in Huntington disease (HD). Some studies in HD models indicate that BDNF supply is reduced, while others suggest that TrkB signaling is impaired earlier in disease progression. It remains important to determine whether a primary defect in TrkB signaling underlies reduced neurotrophic support and the early vulnerability of striatal neurons in HD. Using the transgenic R6/2 mouse model of HD we found that prior to striatal degeneration there are early deficits in striatal protein levels of activated phospho-TrkB and the downstream-regulated protein DARPP-32. In contrast, total-TrkB and BDNF protein levels remained normal. Primary neurons cultured from R6/2 striatum exhibited reduced survival in response to exogenous BDNF applications. Moreover, BDNF activation of phospho-TrkB and downstream signal transduction was attenuated in R6/2 striatal cultures. These results suggest that neurotrophic support of striatal neurons is attenuated early in disease progression due to defects in TrkB signal transduction in the R6/2 model of HD.

Inter-limb coupling during diadochokinesis in Parkinson's and Huntington's disease

Patients with neurodegenerative diseases often exhibit deficits in bimanual coordination. One characteristic of bimanual movements is inter-limb coupling. It is the property of motor performance harmonization between hands during a bimanual task. The objective of this study was to identify whether spatial and temporal inter-limb coupling occurred in Parkinson's disease (PD) and Huntington's disease (HD) patients. Twenty-three PD patients and 15 healthy controls were tested. Data from 12 choreic HD patients were also taken from a databank. Participants were asked to perform a unimanual and bimanual rapid repetitive diadochokinesis task. The difference between hands in mean amplitude and mean duration of cycles was computed in the unimanual and bimanual tasks for each group. Results show that healthy controls exhibited temporal and spatial inter-limb coupling during the bimanual diadochokinesis task. Conversely, PD and HD patients exhibited temporal inter-limb coupling; but failed to exhibit spatial inter-limb coupling during the bimanual diadochokinesis task. Furthermore, HD patients exhibited reduced levels of structural coupling compared to controls and PD patients. These results suggest that alterations in basal ganglia-thalamo-cortical networks due to PD and HD do not affect temporal inter-limb coupling. However, common pathophysiological changes related to PD and HD may cause altered spatial inter-limb coupling during a rapid repetitive bimanual diadochokinesis task.

Neuronavigation using susceptibility-weighted venography: application to deep brain stimulation and comparison with gadolinium contrast

Careful trajectory planning on preoperative vascular imaging is an essential step in deep brain stimulation (DBS) to minimize risks of hemorrhagic complications and postoperative neurological deficits. This paper compares 2 MRI methods for visualizing cerebral vasculature and planning DBS probe trajectories: a single data set T1-weighted scan with double-dose gadolinium contrast (T1w-Gd) and a multi–data set protocol consisting of a T1-weighted structural, susceptibility-weighted venography, and time-of-flight angiography (T1w-SWI-TOF). Two neurosurgeons who specialize in neuromodulation surgery planned bilateral STN DBS in 18 patients with Parkinson's disease (36 hemispheres) using each protocol separately. Planned trajectories were then evaluated across all vascular data sets (T1w-Gd, SWI, and TOF) to detect possible intersection with blood vessels along the entire path via an objective vesselness measure. The authors' results show that trajectories planned on T1w-SWI-TOF successfully avoided the cerebral vasculature imaged by conventional T1w-Gd and did not suffer from missing vascular information or imprecise data set registration. Furthermore, with appropriate planning and visualization software, trajectory corridors planned on T1w-SWI-TOF intersected significantly less fine vasculature that was not detected on the T1w-Gd (p < 0.01 within 2 mm and p < 0.001 within 4 mm of the track centerline). The proposed T1w-SWI-TOF protocol comes with minimal effects on the imaging and surgical workflow, improves vessel avoidance, and provides a safe cost-effective alternative to injection of gadolinium contrast.

Subthalamic stimulation improves motor function but not home and neighborhood mobility

OBJECTIVE

Subthalamic (STN) deep brain stimulation (DBS) is a recognized therapy for alleviating motor symptoms of Parkinson's disease (PD). However, little is known about its impact on mobility, an important component of quality of life (QoL). To address this issue, we assessed the impact of STN DBS on life-space mobility and QoL.

METHODS

Twenty surgical patients with PD were assessed using mobility and QoL scales and the United Parkinson's disease rating scale, and results were compared before surgery and 6 to 9 months postoperatively.

RESULTS

STN DBS significantly improved motor dysfunction but had a limited impact on measures of life-space mobility and QoL.

INTERPRETATION

STN DBS improves motor function and some components of QoL. However, motor recovery does not translate into improved life-space in the intermediate term. In addition to a focus on motor function, multidisciplinary attention to increasing mobility may further improve QoL in the intermediate and long-term.

Drug-induced dyskinesia in Parkinson's disease. Should success in clinical management be a function of improvement of motor repertoire rather than amplitude of dyskinesia?

BACKGROUND

Dyskinesia, a major complication in the treatment of Parkinson's disease (PD), can require prolonged monitoring and complex medical management.

DISCUSSION

The current paper proposes a new way to view the management of dyskinesia in an integrated fashion. We suggest that dyskinesia be considered as a factor in a signal-to-noise ratio (SNR) equation where the signal is the voluntary movement and the noise is PD symptomatology, including dyskinesia. The goal of clinicians should be to ensure a high SNR in order to maintain or enhance the motor repertoire of patients. To understand why such an approach would be beneficial, we first review mechanisms of dyskinesia, as well as their impact on the quality of life of patients and on the health-care system. Theoretical and practical bases for the SNR approach are then discussed.

SUMMARY

Clinicians should not only consider the level of motor symptomatology when assessing the efficacy of their treatment strategy, but also breadth of the motor repertoire available to patients.

Using a smart phone as a standalone platform for detection and monitoring of pathological tremors

Introduction: Smart phones are becoming ubiquitous and their computing capabilities are ever increasing. Consequently, more attention is geared toward their potential use in research and medical settings. For instance, their built-in hardware can provide quantitative data for different movements. Therefore, the goal of the current study was to evaluate the capabilities of a standalone smart phone platform to characterize tremor. Results: Algorithms for tremor recording and online analysis can be implemented within a smart phone. The smart phone provides reliable time- and frequency-domain tremor characteristics. The smart phone can also provide medically relevant tremor assessments. Discussion: Smart phones have the potential to provide researchers and clinicians with quantitative short- and long-term tremor assessments that are currently not easily available. Methods: A smart phone application for tremor quantification and online analysis was developed. Then, smart phone results were compared to those obtained simultaneously with a laboratory accelerometer. Finally, results from the smart phone were compared to clinical tremor assessments.

Glutamate corelease promotes growth and survival of midbrain dopamine neurons

Recent studies have proposed that glutamate corelease by mesostriatal dopamine (DA) neurons regulates behavioral activation by psychostimulants. How and when glutamate release by DA neurons might play this role remains unclear. Considering evidence for early expression of the type 2 vesicular glutamate transporter in mesencephalic DA neurons, we hypothesized that this cophenotype is particularly important during development. Using a conditional gene knock-out approach to selectively disrupt the Vglut2 gene in mouse DA neurons, we obtained in vitro and in vivo evidence for reduced growth and survival of mesencephalic DA neurons, associated with a decrease in the density of DA innervation in the nucleus accumbens, reduced activity-dependent DA release, and impaired motor behavior. These findings provide strong evidence for a functional role of the glutamatergic cophenotype in the development of mesencephalic DA neurons, opening new perspectives into the pathophysiology of neurodegenerative disorders involving the mesostriatal DA system.

Relationship between BDNF expression in major striatal afferents, striatum morphology and motor behavior in the R6/2 mouse model of Huntington's disease

Patients with Huntington's disease (HD) and transgenic mouse models of HD show neuronal loss in the striatum as a major feature, which contributes to cognitive and motor manifestations. Reduced expression of the neurotrophin brain-derived neurotrophic factor (BDNF) in striatal afferents may play a role in neuronal loss. How progressive loss of BDNF expression in different cortical or subcortical afferents contributes to striatal atrophy and behavioral dysfunction in HD is not known, and may best be determined in animal models. We compared age-dependent alterations of BDNF mRNA expression in major striatal afferents from the cerebral cortex, thalamus and midbrain in the R6/2 transgenic mouse model of HD. Corresponding changes in striatal morphology were quantified using unbiased stereology. Changes in motor behavior were measured using an open field, grip strength monitor, limb clasping and a rotarod apparatus. BDNF expression in cortical limbic and midbrain striatal afferents is reduced by age 4 weeks, prior to onset of motor abnormalities. BDNF expression in motor cortex and thalamic afferents is reduced by 6 weeks, coinciding with early motor dysfunction and reduced striatum volume. BDNF loss in afferents progresses until death at 13-15 weeks, correlating with progressive striatal neuronal loss and motor abnormalities. Mutant huntingtin protein expression in R6/2 mice results in progressive loss of BDNF in both cortical and subcortical striatal afferents. BDNF loss in limbic and dopaminergic striatal inputs may contribute to cognitive/psychiatric dysfunction in HD. Subsequent BDNF loss in cortical motor and thalamic afferents may accelerate striatal degeneration, resulting in progressive involuntary movements.

A multi-modal approach to computer-assisted deep brain stimulation trajectory planning

PURPOSE

Both frame-based and frameless approaches to deep brain stimulation (DBS) require planning of insertion trajectories that mitigate hemorrhagic risk and loss of neurological function. Currently, this is done by manual inspection of multiple potential electrode trajectories on MR-imaging data. We propose and validate a method for computer-assisted DBS trajectory planning.

METHOD

Our framework integrates multi-modal MRI analysis (T1w, SWI, TOF-MRA) to compute suitable DBS trajectories that optimize the avoidance of specific critical brain structures. A cylinder model is used to process each trajectory and to evaluate complex surgical constraints described via a combination of binary and fuzzy segmented datasets. The framework automatically aggregates the multiple constraints into a unique ranking of recommended low-risk trajectories. Candidate trajectories are represented as a few well-defined cortical entry patches of best-ranked trajectories and presented to the neurosurgeon for final trajectory selection.

RESULTS

The proposed algorithm permits a search space containing over 8,000 possible trajectories to be processed in less than 20 s. A retrospective analysis on 14 DBS cases of patients with severe Parkinson's disease reveals that our framework can improve the simultaneous optimization of many pre-formulated surgical constraints. Furthermore, all automatically computed trajectories were evaluated by two neurosurgeons, were judged suitable for surgery and, in many cases, were judged preferable or equivalent to the manually planned trajectories used during the operation.

CONCLUSIONS

This work provides neurosurgeons with an intuitive and flexible decision-support system that allows objective and patient-specific optimization of DBS lead trajectories, which should improve insertion safety and reduce surgical time.

A multicenter pilot study of subcallosal cingulate area deep brain stimulation for treatment-resistant depression

Object

Deep brain stimulation (DBS) has been recently investigated as a treatment for major depression. One of the proposed targets for this application is the subcallosal cingulate gyrus (SCG). To date, promising results after SCG DBS have been reported by a single center. In the present study the authors investigated whether these findings may be replicated at different institutions. They conducted a 3-center prospective open-label trial of SCG DBS for 12 months in patients with treatment-resistant depression.

Methods

Twenty-one patients underwent implantation of bilateral SCG electrodes. The authors examined the reduction in Hamilton Rating Scale for Depression (HRSD-17) score from baseline (RESP50).

Results

Patients treated with SCG DBS had an RESP50 of 57% at 1 month, 48% at 6 months, and 29% at 12 months. The response rate after 12 months of DBS, however, increased to 62% when defined as a reduction in the baseline HRSD-17 of 40% or more. Reductions in depressive symptomatology were associated with amelioration in disease severity in patients who responded to surgery.

Conclusions

Overall, findings from this study corroborate the results of previous reports showing that outcome of SCG DBS may be replicated across centers.

Creation of Computerized 3D MRI-Integrated Atlases of the Human Basal Ganglia and Thalamus

Functional brain imaging and neurosurgery in subcortical areas often requires visualization of brain nuclei beyond the resolution of current magnetic resonance imaging (MRI) methods. We present techniques used to create: (1) a lower resolution 3D atlas, based on the Schaltenbrand and Wahren print atlas, which was integrated into a stereotactic neurosurgery planning and visualization platform (VIPER); and (2) a higher resolution 3D atlas derived from a single set of manually segmented histological slices containing nuclei of the basal ganglia, thalamus, basal forebrain, and medial temporal lobe. Both atlases were integrated to a canonical MRI (Colin27) from a young male participant by manually identifying homologous landmarks. The lower resolution atlas was then warped to fit the MRI based on the identified landmarks. A pseudo-MRI representation of the high-resolution atlas was created, and a non-linear transformation was calculated in order to match the atlas to the template MRI. The atlas can then be warped to match the anatomy of Parkinson's disease surgical candidates by using 3D automated non-linear deformation methods. By way of functional validation of the atlas, the location of the sensory thalamus was correlated with stereotactic intraoperative physiological data. The position of subthalamic electrode positions in patients with Parkinson's disease was also evaluated in the atlas-integrated MRI space. Finally, probabilistic maps of subthalamic stimulation electrodes were developed, in order to allow group analysis of the location of contacts associated with the best motor outcomes. We have therefore developed, and are continuing to validate, a high-resolution computerized MRI-integrated 3D histological atlas, which is useful in functional neurosurgery, and for functional and anatomical studies of the human basal ganglia, thalamus, and basal forebrain.

Three-dimensional somatotopic organization and probabilistic mapping of motor responses from the human internal capsule

Object

The somatotopic organization of the motor fibers within the posterior limb of the internal capsule (IC) in humans remains unclear. Several electrophysiological atlases created from stimulation during stereotactic neurosurgery have suggested that there is considerable overlap between representations of body parts. Overlap reported in these studies may have been due to linear scaling methods applied to the data that were unable to account for individual anatomical variability. In the current work, the authors attempted to overcome these limitations by using a nonlinear registration technique to better understand the spatial location and extent of the body-part representations in the IC.

Methods

Data were acquired during 30 cases of deep brain neurosurgery in which the IC was electrically stimulated to localize the ventrolateral nucleus for a subsequent thalamotomy or implantation of a thalamic deep brain stimulator. Motor responses from the tongue, face, arm, or leg were evoked in the IC and coded in the patient's native MR imaging space. The tagged MR images were then nonlinearly registered to a high-resolution template MR image. This work resulted in a functional electrophysiological atlas demonstrating the locations of body-part representations in the posterior limb of the IC that takes individual anatomical variability into account. To further understand the spatial location and extent of the motor responses, the electrophysiological data points were transformed into 3D probability maps that describe the likelihood of obtaining motor responses in the posterior limb of the IC.

Results

The analyses suggest a reliable face-anterior, arm-intermediate, and leg-posterior somatotopic organization in the posterior limb of the IC with little overlap between the body-part representations.

Conclusions

This probabilistic atlas of functional responses evoked by stimulating the posterior limb of the IC provides better understanding of the anatomical organization of descending motor fibers, can be used for indirect intraoperative confirmation of the location of the ventrolateral thalamus, and is applicable to clinical and research MR imaging studies requiring information on spatial organization of motor fibers at the thalamic level in the human brain.

A review of social and relational aspects of deep brain stimulation in Parkinson's disease informed by healthcare provider experiences

Background. Although the clinical effectiveness of deep brain stimulation (DBS) in Parkinson's disease is established, there has been less examination of its social aspects. Methods and Results. Building on qualitative comments provided by healthcare providers, we present four different social and relational issues (need for social support, changes in relationships (with self and partner) and challenges with regards to occupation and the social system). We review the literature from multiple disciplines on each issue. We comment on their ethical implications and conclude by establishing the future prospects for research with the possible expansion of DBS for psychiatric indications. Conclusions. Our review demonstrates that there are varied social issues involved in DBS. These issues may have significant impacts on the perceived outcome of DBS by patients. Moreover, the fact that the social impact of DBS is still not well understood in emerging psychiatric indications presents an important area for future examination.

Comparison of piece-wise linear, linear, and nonlinear atlas-to-patient warping techniques: analysis of the labeling of subcortical nuclei for functional neurosurgical applications

Digital atlases are commonly used in pre-operative planning in functional neurosurgical procedures performed to minimize the symptoms of Parkinson's disease. These atlases can be customized to fit an individual patient's anatomy through atlas-to-patient warping procedures. Once fitted to pre-operative magnetic resonance imaging (MRI) data, the customized atlas can be used to plan and navigate surgical procedures. Linear, piece-wise linear and nonlinear registration methods have been used to customize different digital atlases with varying accuracies. Our goal was to evaluate eight different registration methods for atlas-to-patient customization of a new digital atlas of the basal ganglia and thalamus to demonstrate the value of nonlinear registration for automated atlas-based subcortical target identification in functional neurosurgery. In this work, we evaluate the accuracy of two automated linear techniques, two piece-wise linear techniques (requiring the identification of manually placed anatomical landmarks), and four different automated nonlinear atlas-to-patient warping techniques (where two of the four nonlinear techniques are variants of the ANIMAL algorithm). Since a gold standard of the subcortical anatomy is not available, manual segmentations of the striatum, globus pallidus, and thalamus are used to derive a silver standard for evaluation. Four different metrics, including the kappa statistic, the mean distance between the surfaces, the maximum distance between surfaces, and the total structure volume are used to compare the warping techniques. The results show that nonlinear techniques perform statistically better than linear and piece-wise linear techniques. In addition, the results demonstrate statistically significant differences between the nonlinear techniques, with the ANIMAL algorithm yielding better results.

The primate centromedian-parafascicular complex: anatomical organization with a note on neuromodulation

In addition to the cerebral cortex, the striatum receives excitatory input from the thalamus. The centromedian (centre median, CM) and parafascicular (Pf) nuclei are an important source of thalamostriatal projections. Anterograde tract-tracing indicates the CM-Pf complex provides dense afferents to the matrix compartment of the striatum. Whereas CM projects to the entire sensorimotor territory of the striatum, the Pf provides complementary input to the entire associative sector. The Pf also provides lighter input to the nucleus accumbens. Both CM and Pf provide light to moderately dense inputs to other components of the basal ganglia in a largely complementary manner, covering motor or associative-limbic territories of the subthalamic nucleus, globus pallidus and ventral midbrain. In turn, the CM and Pf receive mainly segregated input from parallel motor and associative-limbic circuits of the basal ganglia. The CM and Pf may therefore be considered important participants in parallel processing of motor and associative-limbic information in the basal ganglia. Connections of the CM and Pf with other thalamic nuclei suggest they also participate in integrative functions within the thalamus. In addition, inputs from the brainstem reticular core, reciprocal connections with the cerebral cortex and reticular thalamic nucleus suggest a role in state-dependant information processing. Consideration of the differential connections of the CM and Pf, and better understanding of their role in pathophysiology, may eventually lead to development of an important new target for relief of a variety of neurological and psychiatric disorders.

p73 regulates neurodegeneration and phospho-tau accumulation during aging and Alzheimer's disease

The genetic mechanisms that regulate neurodegeneration are only poorly understood. We show that the loss of one allele of the p53 family member, p73, makes mice susceptible to neurodegeneration as a consequence of aging or Alzheimer's disease (AD). Behavioral analyses demonstrated that old, but not young, p73+/- mice displayed reduced motor and cognitive function, CNS atrophy, and neuronal degeneration. Unexpectedly, brains of aged p73+/- mice demonstrated dramatic accumulations of phospho-tau (P-tau)-positive filaments. Moreover, when crossed to a mouse model of AD expressing a mutant amyloid precursor protein, brains of these mice showed neuronal degeneration and early and robust formation of tangle-like structures containing P-tau. The increase in P-tau was likely mediated by JNK; in p73+/- neurons, the activity of the p73 target JNK was enhanced, and JNK regulated P-tau levels. Thus, p73 is essential for preventing neurodegeneration, and haploinsufficiency for p73 may be a susceptibility factor for AD and other neurodegenerative disorders.

Further evidence for an antidepressant potential of the selective sigma1 agonist SA 4503: electrophysiological, morphological and behavioural studies

In this study, we evaluated the ability of the selective sigma1 agonist SA 4503 to produce changes in brain function, similar to those elicited by classical antidepressants. We focused more specifically on the influence of SA 4503 on central serotonergic (5-HT) transmission, and on hippocampal cell proliferation. A 2-d continuous treatment with SA 4503 (1-40 mg/kg.d) increased 5-HT neuron firing rate in a dose-dependent, bell-shaped manner, with a culminating effect of +90% at 10 mg/kg.d. The same dose induced the appearance of a 5-HT1A receptor-mediated inhibitory tonus on hippocampal pyramidal neurons, as revealed by intravenous injections of the selective 5-HT1A antagonist WAY 100635. Moreover, continuous administration of SA 4503 (3 and 10 mg/kg.d, 3 d) dose-dependently enhanced the number of bromodeoxyuridine-positive cells in the subgranular zone of the hippocampus (+48% and +94%, respectively), thus indicating an increased cell proliferation. Finally, a single administration of SA 4503 (3 and 10 mg/kg i.p.) increased the time spent swimming in the forced swimming test. Together, these results provide both functional and behavioural evidence that this compound has an important antidepressant potential. Further, the fact that the functional changes occurred within a short time-frame (2-3 d) suggest that this antidepressant potential might have a rapid onset of action.

Serotonin(4) (5-HT(4)) receptor agonists are putative antidepressants with a rapid onset of action

Current antidepressants are clinically effective only after several weeks of administration. Here, we show that serotonin(4) (5-HT(4)) agonists reduce immobility in the forced swimming test, displaying an antidepressant potential. Moreover, a 3 day regimen with such compounds modifies rat brain parameters considered to be key markers of antidepressant action, but that are observed only after 2-3 week treatments with classical molecules: desensitization of 5-HT(1A) autoreceptors, increased tonus on hippocampal postsynaptic 5-HT(1A) receptors, and enhanced phosphorylation of the CREB protein and neurogenesis in the hippocampus. In contrast, a 3 day treatment with the SSRI citalopram remains devoid of any effect on these parameters. Finally, a 3 day regimen with the 5-HT(4) agonist RS 67333 was sufficient to reduce both the hyperlocomotion induced by olfactory bulbectomy and the diminution of sucrose intake consecutive to a chronic mild stress. These findings point out 5-HT(4) receptor agonists as a putative class of antidepressants with a rapid onset of action.

Group I mGluR5 metabotropic glutamate receptors regulate proliferation of neuronal progenitors in specific forebrain developmental domains

Major classical neurotransmitters including GABA and glutamate play novel morphogenic roles during development of the mammalian CNS. During forebrain neurogenesis, glutamate regulates neuroblast proliferation in different germinal domains using receptor subtype-specific mechanisms. For example, ionotropic N-methyl-D-aspartate (NMDA) or alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) glutamate receptors mediate distinct proliferative effects in ventral or dorsal forebrain germinal domains, and regulate the correct number of neurons that populate the striatum or cerebral cortex. Recent work suggests metabotropic receptors may also mediate glutamate's proliferative effects. Group I mGluR5 receptor subtypes are highly expressed in forebrain germinal zones. Using in vitro and in vivo methods, we demonstrate mGluR5 receptor activation plays an important role in neuroblast proliferation in the ventral telencephalon, and helps determine the complement of striatum projection neurons. mGluR5 receptor-mediated effects on striatal neuronal progenitors are restricted mainly to early cycling populations in the ventricular zone, with little effect on secondary proliferative populations in the subventricular zone. In contrast to proliferative effects in the ventral telencephalon, mGluR5 receptors do not modulate proliferation of dorsal telencephalon-derived cortical neuroblasts. Heterogeneous domain-specific proliferative effects of glutamate-mediated by specific receptor subtypes provide an important developmental mechanism allowing generation of the correct complement of neuronal subtypes that populate the mammalian forebrain.

Mood stability during acute stimulator challenge in Parkinson's disease patients under long-term treatment with subthalamic deep brain stimulation

Acute and chronic behavioral effects of subthalamic stimulation (STN-DBS) for Parkinson's disease (PD) are reported in the literature. As the technique is relatively new, few systematic studies on the behavioral effects in long-term treated patients are available. To further study the putative effects of STN-DBS on mood and emotional processing, 15 consecutive PD patients under STN-DBS for at least 1 year, were tested ON and OFF stimulation while on or off medication, with instruments sensitive to short-term changes in mood and in emotional discrimination. After acute changes in experimental conditions, mood core dimensions (depression, elation, anxiety) and emotion discrimination processing remained remarkably stable, in the face of significant motor changes. Acute stimulator challenge in long-term STN-DBS-treated PD patients does not appear to provoke clinically relevant mood effects.

Towards a multi-modal atlas for neurosurgical planning

Digital brain atlases can be used in conjuction with magnetic resonance imaging (MRI) and computed tomography (CT) for planning and guidance during neurosurgery. Digital atlases are advantageous since they can be warped nonlinearly to fit each patient's unique anatomy. Functional neurosurgery with implantation of deep brain stimulating (DBS) electrodes requires accurate targeting, and has become a popular surgical technique in Parkinsonian patients. In this paper, we present a method for integrating postoperative data from subthalamic (STN) DBS implantation into an antomical atlas of the basal ganglia and thalamus. The method estimates electrode position from post-operative magnetic resonance imaging (MRI) data. These electrodes are then warped back into the atlas space and are modelled in three dimensions. The average of these models is then taken to show the region where the majority of STN DBS electrodes were implanted. The group with more favorable post-operative results was separated from the group which responded to the STN DBS implantation procedure less favourably to create a probablisitic distribution of DBS in the STN electrodes.

Laminar fate of cortical GABAergic interneurons is dependent on both birthdate and phenotype

Pioneering work indicates that the final position of neurons in specific layers of the mammalian cerebral cortex is determined primarily by birthdate. Glutamatergic projection neurons are born in the cortical proliferative zones of the dorsal telencephalon, and follow an "inside-out" neurogenesis gradient: later-born cohorts migrate radially past earlier-born neurons to populate more superficial layers. GABAergic interneurons, the major source of cortical inhibition, comprise a heterogeneous population and are produced in proliferative zones of the ventral telencephalon. Mechanisms by which interneuron subclasses find appropriate layer-specific cortical addresses remain largely unexplored. Major cortical interneuron subclasses can be identified based on expression of distinct calcium-binding proteins including parvalbumin, calretinin, or calbindin. We determined whether cortical layer-patterning of interneurons is dependent on phenotype. Parvalbumin-positive interneurons populate cortical layers with an inside-out gradient, and birthdate is isochronous to projection neurons in the same layers. In contrast, another major GABAergic subtype, labeled using calretinin, populates the cerebral cortex using an opposite "outside-in" gradient, heterochronous to neighboring neurons. In addition to birthdate, phenotype is also a determinant of cortical patterning. Discovery of a cortical subpopulation that does not follow the well-established inside-out gradient has important implications for mechanisms of layer formation in the cerebral cortex.

The neural response to transcranial magnetic stimulation of the human motor cortex. II. Thalamocortical contributions

Beta oscillations (15-30 Hz) constitute an important electrophysiological signal recorded in the resting state over the human precentral gyrus. The brain circuitry involved in generating the beta oscillations is not well understood but appears to involve both cortical and subcortical structures. We have shown that single pulses of transcranial magnetic stimulation (TMS) applied over the primary motor cortex consistently elicit a brief beta oscillation. Reducing the local cortical excitability using low-frequency repetitive TMS does not change the amplitude of the induced beta oscillation (Van Der Werf and Paus in Exp Brain Res DOI 10.1007/s00221-006-0551-2). Here, we investigated the possible involvement of the thalamus in the cortically expressed beta response to single-pulse TMS. We included eight patients with Parkinson's disease who had undergone unilateral surgical lesioning of the ventrolateral nucleus of the thalamus. We administered 50 single pulses of TMS, at an intensity of 120% of resting motor threshold, over the left and right primary motor cortex and, at the same time, recorded the electroencephalogram (EEG) using a 60-electrode cap. We were able to perform analyses on seven EEG data sets and found that stimulation of the unoperated hemisphere (with thalamus) resulted in higher amplitudes of the single-trial induced beta oscillations than in the operated hemisphere (with thalamotomy). The beta oscillation obtained in response to pulses applied over the unoperated hemisphere was also higher than that obtained in healthy controls. We suggest that (1) the beta oscillatory response to pulses of TMS applied over the primary motor cortex is higher in Parkinson's disease patients, (2) thalamotomy serves to reduce the abnormally high TMS-induced beta oscillations, and (3) the motor thalamus facilitates the cortically generated oscillation, through cortico-subcortico-cortical feedback loops.

Anatomical and electrophysiological validation of an atlas for neurosurgical planning

Digital brain atlases can be used in conjunction with magnetic resonance imaging (MRI) and computed tomography (CT) for planning and guidance during neurosurgery. Digital atlases are advantageous, since they can be warped nonlinearly to fit each patient's unique anatomy. Two atlas-to-patient warping techniques are compared in this paper. The first technique uses an MRI template as an intermediary to estimate a nonlinear atlas-to-patient transformation. The second, is novel, and uses a pseudo-MRI volume, derived from the voxel-label-atlas, to estimate the atlas-to-patient transformation directly. Manual segmentations and functional data are used to validate the two methods.

The creation of a brain atlas for image guided neurosurgery using serial histological data

Digital and print brain atlases have been used with success to help in the planning of neurosurgical interventions. In this paper, a technique presented for the creation of a brain atlas of the basal ganglia and the thalamus derived from serial histological data. Photographs of coronal histological sections were digitized and anatomical structures were manually segmented. A slice-to-slice nonlinear registration technique was used to correct for spatial distortions introduced into the histological data set at the time of acquisition. Since the histological data were acquired without any anatomical reference (e.g., block-face imaging, post-mortem MRI), this registration technique was optimized to use an error metric which calculates a nonlinear transformation minimizing the mean distance between the segmented contours between adjacent pairs of slices in the data set. A voxel-by-voxel intensity correction field was also estimated for each slice to correct for lighting and staining inhomogeneity. The reconstructed three-dimensional (3D) histological volume can be viewed in transverse and sagittal directions in addition to the original coronal. Nonlinear transformations used to correct for spatial distortions of the histological data were applied to the segmented structure contours. These contours were then tessellated to create three-dimensional geometric objects representing the different anatomic regions in register with the histological volumes. This yields two alternate representations (one histological and one geometric) of the atlas. To register the atlas to a standard reference MR volume created from the average of 27 T1-weighted MR volumes, a pseudo-MRI was created by setting the intensity of each anatomical region defined in the geometric atlas to match the intensity of the corresponding region of the reference MR volume. This allowed the estimation of a 3D nonlinear transformation using a correlation based registration scheme to fit the atlas to the reference MRI. The result of this procedure is a contiguous 3D histological volume, a set of 3D objects defining the basal ganglia and thalamus, both of which are registered to a standard MRI data set, for use for neurosurgical planning.

The impact of ventrolateral thalamotomy on tremor and voluntary motor behavior in patients with Parkinson’s disease

A preferred target for parkinsonian tremor alleviation is the ventrolateral (VL) thalamus. The goal of the present study is to determine how lesions involving the presumed cerebellar and pallidal recipient areas of the "motor" thalamus would alter the tremor and motor behavior of ten patients with Parkinson's disease (PD). Tremor amplitude, power dispersion (a measure of sharpness of the power spectrum of tremor), and power distribution were quantified using a laser displacement sensor prior to, and a week after, VL thalamotomy. As well, the impact of surgery on tremor seen during movement was quantified in a manual-tracking (MT) task. Tremor-induced noise (a measure of the amount of tremor present during movement) and ERROR (difference between subject's performance and target) were quantified. Finally, bradykinesia was assessed with a rapid alternating movement (RAM) task. Duration, range, and amplitude irregularity of wrist pronation-supination cycles were computed. Both motor tasks were quantified using a highly sensitive forearm rotational sensor. Healthy age-matched control subjects were also tested. Magnetic resonance images with an integrated atlas of thalamic nuclei were used to confirm lesion location. Results show that the lesions were centered upon the posterior portion of the ventral lateral (VLp) nucleus of the thalamus, included the posterior part of the ventral lateral anterior nucleus (VLa), and extended posteriorly to encroach upon the most rostral sector of the sensory ventral posterior nucleus (VPLa). VL thalamotomy significantly decreased tremor amplitude in all cases. Power dispersion was increased significantly so that it became similar to that of control subjects. Changes in power distribution indicate that thalamotomy selectively targeted PD tremor oscillations. Tremor detected during the MT task was also markedly decreased, becoming similar to that of controls. Patients also showed significant decrease in ERROR during MT. RAM duration and range were not significantly modified by the surgery, and patients' performance remained impaired compared to healthy control subjects. Collectively, these results suggest that lesions involving the presumed "cerebellar" and "pallidal" recipient sectors of the motor thalamus do not worsen bradykinesia, suggesting that neural circuits other than the pallido-thalamo-cortical loop may be involved in slowness of movement in PD. A review of alternate pathways is presented.

Flow-based fiber tracking with diffusion tensor and q-ball data: Validation and comparison to principal diffusion direction techniques

In this study, we evaluate the performance of a flow-based surface evolution fiber tracking algorithm by means of a physical anisotropic diffusion phantom with known connectivity. We introduce a novel speed function for surface evolution that is derived from either diffusion tensor (DT) data, high angular resolution diffusion (HARD) data, or a combined DT-HARD hybrid approach. We use the model-free q-ball imaging (QBI) approach for HARD reconstruction. The anisotropic diffusion phantom allows us to compare and evaluate the performance of different fiber tracking approaches in the presence of real imaging artifacts, noise, and subvoxel partial volume averaging of fiber directions. The surface evolution approach, using the full diffusion tensor as opposed to the principal diffusion direction (PDD) only, is compared to PDD-based line propagation fiber tracking. Additionally, DT reconstruction is compared to HARD reconstruction for fiber tracking, both using surface evolution. We show the potential for surface evolution using the full diffusion tensor to map connections in regions of subvoxel partial volume averaging of fiber directions, which can be difficult to map with PDD-based methods. We then show that the fiber tracking results can be improved by using high angular resolution reconstruction of the diffusion orientation distribution function in cases where the diffusion tensor model fits the data poorly.

Defective Fas expression exacerbates neurotoxicity in a model of Parkinson's disease

Fas (CD95), a member of the tumor necrosis factor-receptor superfamily, has been studied extensively as a death-inducing receptor in the immune system. However, Fas is also widely expressed in a number of other tissues, including in neurons. Here, we report that defects in the Fas/Fas ligand system unexpectedly render mice highly susceptible to neural degeneration in a model of Parkinson's disease. We found that Fas-deficient lymphoproliferative mice develop a dramatic phenotype resembling clinical Parkinson's disease, characterized by extensive nigrostriatal degeneration accompanied by tremor, hypokinesia, and loss of motor coordination, when treated with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at a dose that causes no neural degeneration or behavioral impairment in WT mice. Mice with generalized lymphoproliferative disease, which express a mutated Fas ligand, display an intermediate phenotype between that of lymphoproliferative and WT mice. Moreover, Fas engagement directly protects neuronal cells from MPTP/1-methyl-4-phenylpyridinium ion toxicity in vitro. Our data show that decreased Fas expression renders dopaminergic neurons highly susceptible to degeneration in response to a Parkinson-causing neurotoxin. These findings constitute the first evidence for a neuroprotective role for Fas in vivo.

Netrin receptor deficient mice exhibit functional reorganization of dopaminergic systems and do not sensitize to amphetamine

Netrins are guidance cues that play a fundamental role in organizing the developing brain. The netrin receptor, DCC (deleted in colorectal cancer), is highly expressed by dopaminergic (DA) neurons. DCC may therefore participate in the organization of DA circuitry during development and also influence DA function in the adult. Here we show that adult dcc heterozygous mice exhibit a blunted behavioral response to the indirect DA agonist amphetamine and do not develop sensitization to its effects when treated repeatedly. These behavioral alterations are associated with profound changes in DA function. In the medial prefrontal cortex, dcc heterozygotes exhibit increased tyrosine hydroxylase (TH) protein levels and dramatic increases in basal concentrations of DA and DA metabolites. In contrast, in the nucleus accumbens, dcc heterozygotes show no changes in either TH or DA levels, but exhibit decreased concentrations of DA metabolites, suggesting reduced DA activity. In addition, dcc heterozygous mice exhibit a small, but significant reduction in total number of TH-positive neurons in midbrain DA cell body regions. These results demonstrate for the first time that alterations in dcc expression lead to selective changes in DA function and, in turn, to differences in DA-related behaviors in adulthood. These findings raise the possibility that changes in dcc function early in life are implicated in the development of DA dysregulation observed in certain psychiatric disorders, such as schizophrenia, or following chronic use of drugs of abuse.

The impact of ventrolateral thalamotomy on high-frequency components of tremor

OBJECTIVE

The present study assessed the impact of ventrolateral (VL) thalamotomy on the high-frequency components of tremor in patients with Parkinson's disease (PD).

METHODS

Tremor was recorded prior to, and 7 days post-surgery using a laser displacement sensor. In addition, tremor was recorded in 10 age-matched patients with PD showing low amplitude tremor (named PD controls) and in 10 age-matched control subjects. Tremor recordings in patients were performed after a 12h withdrawal from anti-Parkinsonian drugs. Tremor characteristics such as amplitude, median power frequency (MPF) and power dispersion (a measure of concentration of power in the frequency domain) were assessed for all groups (i.e. controls, PD controls, pre-surgery and post-surgery).

RESULTS

All tremor characteristics were similar between controls and PD controls. Tremor amplitude was significantly reduced post-surgery, to become statistically similar to that of controls and PD controls. However, MPF and power dispersion remained lower post-surgery, indicating that although there was normalization of tremor amplitude, tremor showed systematically slower oscillations after the surgical procedure. In order to eliminate amplitude as a possible confounding factor, epochs of post-surgical tremor (5s in duration) were paired for equal amplitude with 5s tremor epochs from matched controls. Results show once again that MPF and power dispersion were lower post-surgery compared to controls. In addition, when amplitude of power was compared within specific frequency bands (0-3.5, 3.5-7.5, 7.5-12.5, 12.5-16.5, 16.5-30 and 30-45), power regained normal values at frequencies below 7.5 Hz. Power within higher frequency bands was systematically lower, indicating that the surgical procedure had an impact on high-frequency components of tremor.

CONCLUSIONS

Results from the present study showed that VL thalamotomy reduced tremor amplitude by selectively targeting centrally driven components of PD tremor. The high-frequency component of physiological tremor failed to emerge after amplitude normalization.

SIGNIFICANCE

The thalamus should then be considered as an important component of the generation and/or propagation of high-frequency components of physiological tremor.

Glutamate and Regulation of Proliferation in the Developing Mammalian Telencephalon

Increasing evidence suggests that classical neurotransmitters play an important morphogenetic role during development of the mammalian central nervous system. Using in vitro and in vivo models, we have previously identified a role for the N-methyl-D-aspartate (NMDA) subclass of glutamate receptors in the proliferation of striatal progenitors. Here, we compare the roles of ionotropic glutamate receptors in the proliferation of either striatal or cortical progenitors. In culture, glutamate receptor activation promoted proliferation of both striatal and cortical neuroblasts. However, cortical and striatal neuroblasts responded to distinct ionotropic receptors. Cortical cultures were sensitive to AMPA/KA receptor blockade, whereas striatal neuroblast proliferation was altered by NMDA antagonists. In vivo, BrdU uptake in the proliferative ventricular zone was reduced in embryos following acute administration of ionotropic glutamate receptor antagonists. In keeping with in vitro observations, proliferation in cortical and striatal ventricular regions was reduced, respectively, by either AMPA/KA or NMDA receptor blockade. We also determined whether forebrain-derived progenitors expanded as neurospheres in the presence of growth factors show similar ionotropic glutamatergic responses. Cells in neither dorsal nor ventral telencephalon-derived neurospheres showed altered proliferation following exposure to either class of ionotropic glutamate receptor antagonist. Together, these findings suggest that glutamate influences the proliferation of forebrain neuronal progenitors, but not more primitive populations represented in multipotential progenitors expanded in vitro. The effects on neuroblast proliferation in different forebrain domains are heterogeneous and are mediated by distinct subclasses of ionotropic glutamate receptors.