Cortico-cerebellar connectivity underlying motor control in chronic post-stroke individuals.

The robust, reciprocal anatomical connections between the cerebellum and contralateral sensorimotor cerebral hemisphere underscores the strong physiological interdependence between these two regions in relation to human behavior. Previous studies have shown that damage to sensorimotor cortex can result in a lasting reduction of cerebellar metabolism, the magnitude of which has been linked to poor rehabilitative outcomes. A better understanding of movement-related cerebellar physiology as well as cortico-cerebellar coherence (CCC) in the chronic, post-stroke state may be key to developing novel neuromodulatory techniques that promote upper limb motor rehabilitation. As a part of the first in-human phase-I trial investigating the effects of deep brain stimulation of the cerebellar dentate nucleus (DN) on chronic, post-stroke motor rehabilitation, we collected invasive recordings from DN and scalp EEG in subjects (both sexes) with middle cerebral artery stroke during a visuo-motor tracking task. We investigated the excitability of ipsilesional cortex, DN and the their interaction as a function of motor impairment and performance. Our results indicate that 1) event-related oscillations in the ipsilesional cortex and DN were significantly correlated at movement onset in the low-ß band, with moderately and severely impaired subjects showing desynchronization and synchronization, respectively. 2) Significant CCC was observed during isometric 'hold' period in the low-ß band, which was critical for maintaining task accuracy. Our findings support a strong coupling between ipsilesional cortex and DN in the low-ß band during motor control across all impairment levels which encourages the exploitation of the cerebello-thalamo-cortical pathway as a neuromodulation target to promote rehabilitation.Significance Statement:Cerebral infarct due to stroke can lead to lasting reduction in cerebellar metabolism resulting in poor rehabilitative outcomes. Thorough investigation of the cerebellar electrophysiology as well as cortico-cerebellar connectivity in humans that could provide key insights to facilitate development of novel neuromodulatory technologies, has been lacking. As a part of the first in-human phase-I trial investigating deep brain stimulation of the cerebellar dentate nucleus (DN) for chronic, post-stroke motor rehabilitation, we collected invasive recordings from DN and scalp EEG while stroke patients performed a motor task. Our data indicate strong coupling between ipsilesional sensorimotor cortex and DN in the low-ß band across all impairment levels encouraging the exploration of electrical stimulation of the DN.

Physiological changes in the pallidum in a progressive model of Parkinson's disease: Are oscillations enough?

Neurophysiological changes in the basal ganglia thalamo-cortical circuit associated with the development of parkinsonian motor signs remain poorly understood. Theoretical models have ranged from those emphasizing changes in mean discharge rate to increased oscillatory activity within the beta range. The present study characterized neuronal activity within and across the internal and external segments of the globus pallidus as a function of motor severity using a staged, progressively severe 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinsonism in three rhesus monkeys. An increase in coherence between neuronal pairs across the external and internal globus pallidus was present in multiple frequency bands in the parkinsonian state; both the peak frequency of oscillatory coherence and the variability were reduced in the parkinsonian state. The incidence of 8-20Hz oscillatory activity in the internal globus pallidus increased with the progression of the disease when pooling the data across the three animals; however it did not correlate with motor severity when assessed individually and increased progressively in only one of three animals. No systematic relationship between mean discharge rates or the incidence or structure of bursting activity and motor severity was observed. These data suggest that exaggerated coupling across pallidal segments contribute to the development of the parkinsonian state by inducing an exaggerated level of synchrony and loss of focusing within the basal ganglia. These data further point to the lack of a defined relationship between rate changes, the mere presence of oscillatory activity in the beta range and bursting activity in the basal ganglia to the motor signs of Parkinson's disease.

Male and female Fmr1 knockout mice on C57 albino background exhibit spatial learning and memory impairments.

Impaired spatial learning is a prominent deficit in fragile X syndrome (FXS). Previous studies using the Fmr1 knockout (KO) mouse model of FXS have not consistently reported a deficit in spatial learning. Fmr1 KO mice bred onto an albino C57BL/6J-Tyr(c-Brd) background showed significant deficits in several primary measures of performance during place navigation and probe trials in the Morris water maze. Fmr1 KO mice were also impaired during a serial reversal version of the water maze task. We examined fear conditioning as an additional cognitive screen. Knockout mice exhibited contextual memory deficits when trained with unsignaled shocks; however, deficits were not found in a separate group of KO mice trained with signaled shocks. No potentially confounding genotypic differences in locomotor activity were observed. A decreased anxiety-like profile was apparent in the open field, as others have noted, and also in the platform test. Also as previously reported, startle reactivity to loud auditory stimuli was decreased, prepulse inhibition and social interaction increased in KO mice. Female Fmr1 KO mice were tested along with male KO mice in all assays, except for social interaction. The female and male KO exhibited very similar impairments indicating that sex does not generally drive the behavioral symptoms of the disorder. Our results suggest that procedural factors, such as the use of albino mice, may help to reliably detect spatial learning and memory impairments in both sexes of Fmr1 KO mice, making it more useful for understanding FXS and a platform for evaluating potential therapeutics.

Deep brain stimulation of the ventral internal capsule/ventral striatum for obsessive-compulsive disorder: worldwide experience.

Psychiatric neurosurgery teams in the United States and Europe have studied deep brain stimulation (DBS) of the ventral anterior limb of the internal capsule and adjacent ventral striatum (VC/VS) for severe and highly treatment-resistant obsessive-compulsive disorder. Four groups have collaborated most closely, in small-scale studies, over the past 8 years. First to begin was Leuven/Antwerp, followed by Butler Hospital/Brown Medical School, the Cleveland Clinic and most recently the University of Florida. These centers used comparable patient selection criteria and surgical targeting. Targeting, but not selection, evolved during this period. Here, we present combined long-term results of those studies, which reveal clinically significant symptom reductions and functional improvement in about two-thirds of patients. DBS was well tolerated overall and adverse effects were overwhelmingly transient. Results generally improved for patients implanted more recently, suggesting a 'learning curve' both within and across centers. This is well known from the development of DBS for movement disorders. The main factor accounting for these gains appears to be the refinement of the implantation site. Initially, an anterior-posterior location based on anterior capsulotomy lesions was used. In an attempt to improve results, more posterior sites were investigated resulting in the current target, at the junction of the anterior capsule, anterior commissure and posterior ventral striatum. Clinical results suggest that neural networks relevant to therapeutic improvement might be modulated more effectively at a more posterior target. Taken together, these data show that the procedure can be successfully implemented by dedicated interdisciplinary teams, and support its therapeutic promise.

Haplotypes and gene expression implicate the MAPT region for Parkinson disease: the GenePD Study.

BACKGROUND: Microtubule-associated protein tau (MAPT) has been associated with several neurodegenerative disorders including forms of parkinsonism and Parkinson disease (PD). We evaluated the association of the MAPT region with PD in a large cohort of familial PD cases recruited by the GenePD Study. In addition, postmortem brain samples from patients with PD and neurologically normal controls were used to evaluate whether the expression of the 3-repeat and 4-repeat isoforms of MAPT, and neighboring genes Saitohin (STH) and KIAA1267, are altered in PD cerebellum. METHODS: Twenty-one single-nucleotide polymorphisms (SNPs) in the region of MAPT on chromosome 17q21 were genotyped in the GenePD Study. Single SNPs and haplotypes, including the H1 haplotype, were evaluated for association to PD. Relative quantification of gene expression was performed using real-time RT-PCR. RESULTS: After adjusting for multiple comparisons, SNP rs1800547 was significantly associated with PD affection. While the H1 haplotype was associated with a significantly increased risk for PD, a novel H1 subhaplotype was identified that predicted a greater increased risk for PD. The expression of 4-repeat MAPT, STH, and KIAA1267 was significantly increased in PD brains relative to controls. No difference in expression was observed for 3-repeat MAPT. CONCLUSIONS: This study supports a role for MAPT in the pathogenesis of familial and idiopathic Parkinson disease (PD). Interestingly, the results of the gene expression studies suggest that other genes in the vicinity of MAPT, specifically STH and KIAA1267, may also have a role in PD and suggest complex effects for the genes in this region on PD risk.

Herbicide exposure modifies GSTP1 haplotype association to Parkinson onset age: the GenePD Study.

BACKGROUND: Polymorphisms in the glutathione S-transferase pi gene (GSTP1), encoding GSTP1-1, a detoxification enzyme, may increase the risk of Parkinson disease (PD) with exposure to pesticides. Using the GenePD Study sample of familial PD cases, we explored whether GSTP1 polymorphisms were associated with the age at onset of PD symptoms and whether that relation was modified by exposure to herbicides. METHODS: Seven single-nucleotide polymorphisms (SNPs) were genotyped and tested for association with PD onset age in men in three strata: no exposure to herbicides, residential exposure to herbicides, and occupational exposure to herbicides. Haplotypes were similarly evaluated in stratified analyses. RESULTS: Three SNPs were associated with PD onset age in the group of men occupationally exposed to herbicides. Three additional SNPs had significant trends for the association of PD onset age across the herbicide exposure groups. Haplotype results also provided evidence that the relation between GSTP1 and onset age is modified by herbicide exposure. One haplotype was associated with an approximately 8-years-earlier onset in the occupationally exposed group and a 2.8-years-later onset in the nonexposed group. CONCLUSIONS: Herbicide exposure may be an effect modifier of the relation between glutathione S-transferase pi gene polymorphisms and onset age in familial PD.

Retention time for corticosteroid-sparing systemic immunosuppressive agents in patients with inflammatory eye disease.

BACKGROUND: Multiple immunosuppressive drugs have been used to manage inflammatory eye disease when control cannot be achieved by corticosteroid alone. However, although clinical studies support the effectiveness of most of these agents, comparative studies have not been undertaken. Retention time, a measure of the duration of treatment with any given drug, is a crude indicator of drug effectiveness and tolerability that facilitates such a comparison. The retention time was compared for corticosteroid-sparing immunosuppressive agents in patients attending our tertiary referral inflammatory eye disease clinic. METHODS: The clinical records of all patients attending an inflammatory eye disease clinic at the Casey Eye Institute over a 1-year period (2003) were reviewed. From these records, we collected the following clinical data: age; sex; ocular diagnosis; and use of steroid-sparing systemic immunosuppression, including drugs, duration of treatment and, if ceased, reasons for cessation. Cox regression analysis, adjusted for clustering, was used to compare other drugs against methotrexate. RESULTS: 107 of 302 (35%) patients seen at the inflammatory eye disease clinic in 2003 had a total of 193 current or past prescriptions for systemic steroid-sparing immunosuppressive agents. The treated group, most of whom had uveitis, included 32 men and 75 women, aged 5-86 years. Most commonly prescribed were methotrexate (66 uses, 34%), ciclosporin (37 uses, 19%), azathioprine (26 uses, 13%), mycophenolate mofetil (22 uses, 11%) and cyclophosphamide (15 uses, 8%). Patients were retained significantly less on ciclosporin (p = 0.004), azathioprine (p = 0.04), mycophenolate mofetil (p = 0.04) and cyclophosphamide (p<0.001) compared with methotrexate. Reasons for cessation included adverse events, lack of effectiveness, success or remission, cost and desire for fertility. CONCLUSIONS: In patients with inflammatory eye disease, methotrexate may offer a superior combination of effectiveness and tolerability over other commonly used corticosteroid-sparing immunosuppressive agents. In this study, there was a twofold risk of not being retained on azathioprine, mycophenolate mofetil and ciclosporin and a fourfold risk of not being retained on cyclophosphamide compared with methotrexate.

BDNF genetic variants are associated with onset age of familial Parkinson disease: GenePD Study.

Brain-derived neurotrophic factor (BDNF) stimulates neuronal growth and protects nigral dopamine neurons in animal models of Parkinson disease (PD). Therefore, BDNF is a candidate gene for PD. The authors investigated five single-nucleotide polymorphisms in 597 cases of familial PD. Homozygosity for the rare allele of the functional BDNF G196A (Val66Met) variant was associated with a 5.3-year older onset age (p = 0.0001). These findings suggest that BDNF may influence PD onset age.

Adenoviral clostridial light chain gene-based synaptic inhibition through neuronal synaptobrevin elimination.

Clostridial neurotoxins have assumed increasing importance in clinical application. The toxin's light chain component (LC) inhibits synaptic transmission by digesting vesicle-docking proteins without directly altering neuronal health. To study the properties of LC gene expression in the nervous system, an adenoviral vector containing the LC of tetanus toxin (AdLC) was constructed. LC expressed in differentiated neuronal PC12 cells was shown to induce time- and concentration-dependent digestion of mouse brain synaptobrevin in vitro as compared to control transgene products. LC gene expression in the rat lumbar spinal cord disrupted hindlimb sensorimotor function in comparison to control vectors as measured by the Basso-Beattie-Bresnahan (BBB) scale (P<0.001) and rotarod assay (P<0.003). Evoked electromyography (EMG) showed increased stimulus threshold and decreased response current amplitude in LC gene-transferred rats. At the peak of functional impairment, neither neuronal TUNEL staining nor reduced motor neuron density could be detected. Spontaneous functional recovery was observed to parallel the cessation of LC gene expression. These results suggest that light chain gene delivery within the nervous system may provide a nondestructive means for focused neural inhibition to treat a variety of disorders related to excessive synaptic activity, and prove useful for the study of neural circuitry.

Performance on the PD test battery by relatives of patients with progressive supranuclear palsy.

OBJECTIVE: To determine whether there is a greater prevalence of asymptomatic first-degree relatives (FDR) of patients with progressive supranuclear palsy (PSP) performing abnormally on the PD test battery (PD Battery) compared to sex- and age-matched normal control (NC) individuals. The PD Battery incorporates tests of motor function, olfaction, and mood. It has high specificity and sensitivity in distinguishing mildly affected PD patients from NC individuals in previous studies. METHODS: This test battery and regression analysis-derived scoring equations were applied to asymptomatic FDR. RESULTS: Twenty-three FDR and 23 NC individuals were tested. Of the FDR, 39% scored in the abnormal range, whereas none of the NC individuals achieved abnormal scores. This difference was significant. Further analysis demonstrated that the two groups differed significantly on a measure of simple reaction time. CONCLUSIONS: The proportion of FDR who demonstrated abnormal performance on the PD Battery was greater than NC individuals. Thus, the PD Battery may detect the asymptomatic carrier state or risk for PSP or a subclinical effect of a shared environmental exposure.

Deep brain stimulation in epilepsy.

Since the pioneering studies of Cooper et al. to influence epilepsy by cerebellar stimulation, numerous attempts have been made to reduce seizure frequency by stimulation of deep brain structures. Evidence from experimental animal studies suggests the existence of a nigral control of the epilepsy system. It is hypothesized that the dorsal midbrain anticonvulsant zone in the superior colliculi is under inhibitory control of efferents from the substantia nigra pars reticulata. Inhibition of the subthalamic nucleus (STN) could release the inhibitory effect of the substantia nigra pars reticulata on the dorsal midbrain anticonvulsant zone and thus activate the latter, raising the seizure threshold. Modulation of the seizure threshold by stimulation of deep brain structures-in particular, of the STN-is a promising future treatment option for patients with pharmacologically intractable epilepsy. Experimental studies supporting the existence of the nigral control of epilepsy system and preliminary results of STN stimulation in animals and humans are reviewed, and alternative mechanisms of seizure suppression by STN stimulation are discussed.

Motor initiation and execution in essential tremor and Parkinson's disease.

Clinical differentiation of essential tremor (ET) from idiopathic Parkinson's disease (iPD) is based on the lack of akinesia and bradykinesia. Nevertheless, early tremor-predominant iPD often is difficult to distinguish from ET. Motor initiation and execution in ET, iPD, and normal control (NC) subjects were investigated. Individuals with iPD, ET and NC performed a reaction-time wrist flexion and extension task. Motor performances were similar between ET and iPD and both were different than normal control subjects. Both the patients with iPD and ET had longer reaction times and slower movement velocities than NC subjects. This may help to explain some of the difficulties in distinguishing patients with these two diseases. The similarities of motor performance suggest that while ET and iPD may be separate disease entities, they may share similar pathogenic motor mechanisms from the perspective of an integrated motor system that drives the motor cortex.

Mechanisms of deep brain stimulation and future technical developments.

Possible mechanisms underlying the therapeutic effect of deep brain stimulation (DBS) are reviewed, particularly the notion that DBS is inhibitory. Computer simulations are described that model the effect of different frequencies and regularity of neuronal activity (target neuron), either spontaneous or stimulated, on information transfer between two other neurons. Most simulations resulted in a loss of information. These were the least with high frequency and regular activity or stimulation of the target neuron with regularity having the least deleterious effect on information transfer. The simulations suggest that irregular activity in neurons converging with other neurons can result in a loss of information transfer. This may explain why increased irregularity in globus pallidus activity associated with Parkinson's disease, dystonia and hemiballismus may result in symptoms. Further, the therapeutic effect of DBS may be due to driving neurons at higher and perhaps more importantly, regular frequencies. There were simulations in which information transfer was augmented suggesting the presence of stochastic resonance. This most often occurred with low frequency activity in the target neuron. It is hypothesized that low frequency activity, either spontaneous or stimulated, could account for involuntary movements, including tremor. Future directions and challenges to DBS are also discussed.