Cerebellar circuitry is activated during convulsive episodes in the tottering (tg/tg) mutant mouse

Striatal parvalbumin interneurons are activated in a mouse model of cerebellar dystonia

Dystonia is thought to arise from abnormalities in the motor loop of the basal ganglia; however, there is an ongoing debate regarding cerebellar involvement. We adopted an established cerebellar dystonia mouse model by injecting ouabain to examine the contribution of the cerebellum. Initially, we examined whether the entopeduncular nucleus (EPN), substantia nigra pars reticulata (SNr), globus pallidus externus (GPe) and striatal neurons were activated in the model. Next, we examined whether administration of a dopamine D1 receptor agonist and dopamine D2 receptor antagonist or selective ablation of striatal parvalbumin (PV, encoded by Pvalb)-expressing interneurons could modulate the involuntary movements of the mice. The cerebellar dystonia mice had a higher number of cells positive for c-fos (encoded by Fos) in the EPN, SNr and GPe, as well as a higher positive ratio of c-fos in striatal PV interneurons, than those in control mice. Furthermore, systemic administration of combined D1 receptor agonist and D2 receptor antagonist and selective ablation of striatal PV interneurons relieved the involuntary movements of the mice. Abnormalities in the motor loop of the basal ganglia could be crucially involved in cerebellar dystonia, and modulating PV interneurons might provide a novel treatment strategy.

The cerebellum contributes to generalized seizures by altering activity in the ventral posteromedial nucleus

Thalamo-cortical networks are central to seizures, yet it is unclear how these circuits initiate seizures. We test whether a facial region of the thalamus, the ventral posteromedial nucleus (VPM), is a source of generalized, convulsive motor seizures and if convergent VPM input drives the behavior. To address this question, we devise an in vivo optogenetic mouse model to elicit convulsive motor seizures by driving these inputs and perform single-unit recordings during awake, convulsive seizures to define the local activity of thalamic neurons before, during, and after seizure onset. We find dynamic activity with biphasic properties, raising the possibility that heterogenous activity promotes seizures. Virus tracing identifies cerebellar and cerebral cortical afferents as robust contributors to the seizures. Of these inputs, only microinfusion of lidocaine into the cerebellar nuclei blocks seizure initiation. Our data reveal the VPM as a source of generalized convulsive seizures, with cerebellar input providing critical signals.

Physiology of Dystonia: Animal Studies

Dystonia is currently ranked as the third most prevalent motor disorder. It is typically characterized by involuntary muscle over- or co-contractions that can cause painful abnormal postures and jerky movements. Dystonia is a heterogenous disorder-across patients, dystonic symptoms vary in their severity, body distribution, temporal pattern, onset, and progression. There are also a growing number of genes that are associated with hereditary dystonia. In addition, multiple brain regions are associated with dystonic symptoms in both genetic and sporadic forms of the disease. The heterogeneity of dystonia has made it difficult to fully understand its underlying pathophysiology. However, the use of animal models has been used to uncover the complex circuit mechanisms that lead to dystonic behaviors. Here, we summarize findings from animal models harboring mutations in dystonia-associated genes and phenotypic animal models with overt dystonic motor signs resulting from spontaneous mutations, neural circuit perturbations, or pharmacological manipulations. Taken together, an emerging picture depicts dystonia as a result of brain-wide network dysfunction driven by basal ganglia and cerebellar dysfunction. In the basal ganglia, changes in dopaminergic, serotonergic, noradrenergic, and cholinergic signaling are found across different animal models. In the cerebellum, abnormal burst firing activity is observed in multiple dystonia models. We are now beginning to unveil the extent to which these structures mechanistically interact with each other. Such mechanisms inspire the use of pre-clinical animal models that will be used to design new therapies including drug treatments and brain stimulation.

The functional anatomy of dystonia: Recent developments

While dystonia has traditionally been viewed as a disorder of the basal ganglia, the involvement of other key brain structures is now accepted. However, just what these structures are remains to be defined. Neuroimaging has been an especially valuable tool in dystonia, yet traditional cross-sectional designs have not been able to separate causal from compensatory brain activity. Therefore, this chapter discusses recent studies using causal brain lesions, and animal models, to converge upon the brain regions responsible for dystonia with increasing precision. This evidence strongly implicates the basal ganglia, thalamus, brainstem, cerebellum, and somatosensory cortex, yet shows that different types of dystonia involve different nodes of this brain network. Nearly all of these nodes fall within the recently identified two-way networks connecting the basal ganglia and cerebellum, suggesting dysfunction of these specific pathways. Localisation of the functional anatomy of dystonia has strong implications for targeted treatment options, such as deep brain stimulation, and non-invasive brain stimulation.

Altered brain state during episodic dystonia in tottering mice decouples primary motor cortex from limb kinematics

Episodic Ataxia Type 2 (EA2) is a rare neurological disorder caused by a mutation in the CACNA1A gene, encoding the P/Q-type voltage-gated Ca2+ channel important for neurotransmitter release. Patients with this channelopathy exhibit both cerebellar and cerebral pathologies, suggesting the condition affects both regions. The tottering (tg/tg) mouse is the most commonly used EA2 model due to an orthologous mutation in the cacna1a gene. The tg/tg mouse has three prominent behavioral phenotypes: a dramatic episodic dystonia; absence seizures with generalized spike and wave discharges (GSWDs); and mild ataxia. We previously observed a novel brain state, transient low-frequency oscillations (LFOs) in the cerebellum and cerebral cortex under anesthesia. In this study, we examine the relationships among the dystonic attack, GSWDs, and LFOs in the cerebral cortex. Previous studies characterized LFOs in the motor cortex of anesthetized tg/tg mice using flavoprotein autofluorescence imaging testing the hypothesis that LFOs provide a mechanism for the paroxysmal dystonia. We sought to obtain a more direct understanding of motor cortex (M1) activity during the dystonic episodes. Using two-photon Ca2+ imaging to investigate neuronal activity in M1 before, during, and after the dystonic attack, we show that there is not a significant change in the activity of M1 neurons from baseline through the attack. We also conducted simultaneous, multi-electrode recordings to further understand how M1 cellular activity and local field potentials change throughout the progression of the dystonic attack. Neither putative pyramidal nor inhibitory interneuron firing rate changed during the dystonic attack. However, we did observe a near complete loss of GSWDs during the dystonic attack in M1. Finally, using spike triggered averaging to align simultaneously recorded limb kinematics to the peak Ca2+ response, and vice versa, revealed a reduction in the spike triggered average during the dystonic episodes. Both the loss of GSWDs and the reduction in the coupling suggest that, during the dystonic attack, M1 is effectively decoupled from other structures. Overall, these results indicate that the attack is not initiated or controlled in M1, but elsewhere in the motor circuitry. The findings also highlight that LFOs, GSWDs, and dystonic attacks represent three brain states in tg/tg mice.

Dystonia and Cerebellum: From Bench to Bedside

Dystonia pathogenesis remains unclear; however, findings from basic and clinical research suggest the importance of the interaction between the basal ganglia and cerebellum. After the discovery of disynaptic pathways between the two, much attention has been paid to the cerebellum. Basic research using various dystonia rodent models and clinical studies in dystonia patients continues to provide new pieces of knowledge regarding the role of the cerebellum in dystonia genesis. Herein, we review basic and clinical articles related to dystonia focusing on the cerebellum, and clarify the current understanding of the role of the cerebellum in dystonia pathogenesis. Given the recent evidence providing new hypotheses regarding dystonia pathogenesis, we discuss how the current evidence answers the unsolved clinical questions.

Dentate nucleus as target for deep brain stimulation in dystono-dyskinetic syndromes

PURPOSE

To discuss the potential of deep brain stimulation (DBS) of the dentate nucleus as a treatment for dystono-dyskinetic syndromes.

METHODS

An extensive literature review covered the anatomy and physiology of the dentate nucleus and the experimental evidence for its involvement in the pathophysiology of dystonia and dyskinesia.

RESULTS

Evidence from animal models and from functional imaging in humans is strongly in favor of involvement of the dentate nucleus in dystono-dyskinetic syndromes. Results from previous surgical series of dentate nucleus stimulation were promising but precise description of movement disorders being treated were lacking and outcome measures were generally not well defined.

CONCLUSIONS

In the light of new evidence regarding the involvement of the dentate nucleus in dystono-dyskinetic syndromes, we present a review of the current literature and discuss why the question of dentate nucleus stimulation deserves to be revisited.

Acute cerebellar knockdown of Sgce reproduces salient features of myoclonus-dystonia (DYT11) in mice

Myoclonus dystonia (DYT11) is a movement disorder caused by loss-of-function mutations in SGCE and characterized by involuntary jerking and dystonia that frequently improve after drinking alcohol. Existing transgenic mouse models of DYT11 exhibit only mild motor symptoms, possibly due to rodent-specific developmental compensation mechanisms, which have limited the study of neural mechanisms underlying DYT11. To circumvent potential compensation, we used short hairpin RNA (shRNA) to acutely knock down Sgce in the adult mouse and found that this approach produced dystonia and repetitive, myoclonic-like, jerking movements in mice that improved after administration of ethanol. Acute knockdown of Sgce in the cerebellum, but not the basal ganglia, produced motor symptoms, likely due to aberrant cerebellar activity. The acute knockdown model described here reproduces the salient features of DYT11 and provides a platform to study the mechanisms underlying symptoms of the disorder, and to explore potential therapeutic options.

Current Opinions and Areas of Consensus on the Role of the Cerebellum in Dystonia

A role for the cerebellum in causing ataxia, a disorder characterized by uncoordinated movement, is widely accepted. Recent work has suggested that alterations in activity, connectivity, and structure of the cerebellum are also associated with dystonia, a neurological disorder characterized by abnormal and sustained muscle contractions often leading to abnormal maintained postures. In this manuscript, the authors discuss their views on how the cerebellum may play a role in dystonia. The following topics are discussed: The relationships between neuronal/network dysfunctions and motor abnormalities in rodent models of dystonia. Data about brain structure, cerebellar metabolism, cerebellar connections, and noninvasive cerebellar stimulation that support (or not) a role for the cerebellum in human dystonia. Connections between the cerebellum and motor cortical and sub-cortical structures that could support a role for the cerebellum in dystonia. Overall points of consensus include: Neuronal dysfunction originating in the cerebellum can drive dystonic movements in rodent model systems. Imaging and neurophysiological studies in humans suggest that the cerebellum plays a role in the pathophysiology of dystonia, but do not provide conclusive evidence that the cerebellum is the primary or sole neuroanatomical site of origin.

Heterozygous Gnal Mice Are a Novel Animal Model with Which to Study Dystonia Pathophysiology

Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions and its pathophysiological mechanisms are still poorly understood. Dominant mutations of the GNAL gene are a cause of isolated dystonia (DYT25) in patients. Some mutations result in a complete loss of function of the encoded protein, Gα_olf, an adenylyl-cyclase-stimulatory G-protein highly enriched in striatal projection neurons, where it mediates the actions of dopamine and adenosine. We used male and female heterozygous Gnal knock-out mice (Gnal^+/-) to study how GNAL haplodeficiency is implicated in dystonia. In basal conditions, no overt dystonic movements or postures or change in locomotor activity were observed. However, Gnal haploinsufficiency altered self-grooming, motor coordination, and apparent motivation in operant conditioning, as well as spine morphology and phospho-CaMKIIβ in the striatum. After systemic administration of oxotremorine, an unselective cholinergic agonist, Gnal^+/- mice developed more abnormal postures and movements than WT mice. These effects were not caused by seizures as indicated by EEG recordings. They were prevented by the M1-preferring muscarinic antagonists, telenzepine, pirenzepine, and trihexyphenidyl, which alleviate dystonic symptoms in patients. The motor defects were worsened by mecamylamine, a selective nicotinic antagonist. These oxotremorine-induced abnormalities in Gnal^+/- mice were replicated by oxotremorine infusion into the striatum, but not into the cerebellum, indicating that defects in striatal neurons favor the appearance of dystonia-like movement alterations after oxotremorine. Untreated and oxotremorine-treated Gnal^+/- mice provide a model of presymptomic and symptomatic stages of DYT25-associated dystonia, respectively, and clues about the mechanisms underlying dystonia pathogenesis.SIGNIFICANCE STATEMENT Adult-onset dystonia DYT25 is caused by dominant loss-of-function mutations of GNAL, a gene encoding the stimulatory G-protein Gαolf, which is critical for activation of the cAMP pathway in the striatal projection neurons. Here, we demonstrate that Gnal-haplodeficient mice have a mild neurological phenotype and display vulnerability to developing dystonic movements after systemic or intrastriatal injection of the cholinergic agonist oxotremorine. Therefore, impairment of the cAMP pathway in association with an increased cholinergic tone creates alterations in striatal neuron functions that can promote the onset of dystonia. Our results also provide evidence that untreated and oxotremorine-treated Gnal-haplodeficient mice are powerful models with which to study presymptomic and symptomatic stages of DYT25-associated dystonia, respectively.

Extensive Direct Subcortical Cerebellum-Basal Ganglia Connections in Human Brain as Revealed by Constrained Spherical Deconvolution Tractography

The connections between the cerebellum and basal ganglia were assumed to occur at the level of neocortex. However evidences from animal data have challenged this old perspective showing extensive subcortical pathways linking the cerebellum with the basal ganglia. Here we tested the hypothesis if these connections also exist between the cerebellum and basal ganglia in the human brain by using diffusion magnetic resonance imaging and tractography. Fifteen healthy subjects were analyzed by using constrained spherical deconvolution technique obtained with a 3T magnetic resonance imaging scanner. We found extensive connections running between the subthalamic nucleus and cerebellar cortex and, as novel result, we demonstrated a direct route linking the dentate nucleus to the internal globus pallidus as well as to the substantia nigra. These findings may open a new scenario on the interpretation of basal ganglia disorders.

Are the neuromotor disabilities of bilirubin-induced neurologic dysfunction disorders related to the cerebellum and its connections?

Investigators have hypothesized a range of subcortical neuropathology in the genesis of bilirubin-induced neurologic dysfunction (BIND). The current review builds on this speculation with a specific focus on the cerebellum and its connections in the development of the subtle neuromotor disabilities of BIND. The focus on the cerebellum derives from the following observations: (i) the cerebellum is vulnerable to bilirubin-induced injury; perhaps the most vulnerable region within the central nervous system; (ii) infants with cerebellar injury exhibit a neuromotor phenotype similar to BIND; and (iii) the cerebellum has extensive bidirectional circuitry projections to motor and non-motor regions of the brainstem and cerebral cortex that impact a variety of neurobehaviors. Future study using advanced magnetic resonance neuroimaging techniques have the potential to shed new insights into bilirubin's effect on neural network topology via both structural and functional brain connectivity measurements.

Animal models for dystonia

Symptomatic animal models have clinical features consistent with human disorders and are often used to identify the anatomical and physiological processes involved in the expression of symptoms and to experimentally demonstrate causality where it would be infeasible in the patient population. Rodent and primate models of dystonia have identified basal ganglia abnormalities, including alterations in striatal GABAergic (ie, transmitting or secreting γ-aminobutyric acid) and dopaminergic transmission. Symptomatic animal models have also established the critical role of the cerebellum in dystonia, particularly abnormal glutamate signaling and aberrant Purkinje cell activity. Further, experiments suggest that the basal ganglia and cerebellum are nodes in an integrated network that is dysfunctional in dystonia. The knowledge gained from experiments in symptomatic animal models may serve as the foundation for the development of novel therapeutic interventions to treat dystonia. © 2013 Movement Disorder Society.

Dystonia as a network disorder: what is the role of the cerebellum?

The dystonias are a group of disorders defined by sustained or intermittent muscle contractions that result in involuntary posturing or repetitive movements. There are many different clinical manifestations and causes. Although they traditionally have been ascribed to dysfunction of the basal ganglia, recent evidence has suggested dysfunction may originate from other regions, particularly the cerebellum. This recent evidence has led to an emerging view that dystonia is a network disorder that involves multiple brain regions. The new network model for the pathogenesis of dystonia has raised many questions, particularly regarding the role of the cerebellum. For example, if dystonia may arise from cerebellar dysfunction, then why are there no cerebellar signs in dystonia? Why are focal cerebellar lesions or degenerative cerebellar disorders more commonly associated with ataxia rather than dystonia? Why is dystonia more commonly associated with basal ganglia lesions rather than cerebellar lesions? Can answers obtained from animals be extrapolated to humans? Is there any evidence that the cerebellum is not involved? Finally, what is the practical value of this new model of pathogenesis for the neuroscientist and clinician? This article explores potential answers to these questions.

New roles for the cerebellum in health and disease

The cerebellum has a well-established role in maintaining motor coordination and studies of cerebellar learning suggest that it does this by recognizing neural patterns, which it uses to predict optimal movements. Serious damage to the cerebellum impairs this learning and results in a set of motor disturbances called ataxia. However, recent work implicates the cerebellum in cognition and emotion, and it has been argued that cerebellar dysfunction contributes to non-motor conditions such as autism spectrum disorders (ASD). Based on human and animal model studies, two major questions arise. Does the cerebellum contribute to non-motor as well as motor diseases, and if so, how does altering its function contribute to such diverse symptoms? The architecture and connectivity of cerebellar circuits may hold the answers to these questions. An emerging view is that cerebellar defects can trigger motor and non-motor neurological conditions by globally influencing brain function. Furthermore, during development cerebellar circuits may play a role in wiring events necessary for higher cognitive functions such as social behavior and language. We discuss genetic, electrophysiological, and behavioral evidence that implicates Purkinje cell dysfunction as a major culprit in several diseases and offer a hypothesis as to how canonical cerebellar functions might be at fault in non-motor as well as motor diseases.

Enhanced inhibitory neurotransmission in the cerebellar cortex of Atp1a3-deficient heterozygous mice

Dystonia is characterized by excessive involuntary and prolonged simultaneous contractions of both agonist and antagonist muscles. Although the basal ganglia have long been proposed as the primary region, recent studies indicated that the cerebellum also plays a key role in the expression of dystonia. One hereditary form of dystonia, rapid-onset dystonia with parkinsonism (RDP), is caused by loss of function mutations of the gene for the Na pump α3 subunit (ATP1A3). Little information is available on the affected brain regions and mechanism for dystonia by the mutations in RDP. The Na pump is composed of α and β subunits and maintains ionic gradients of Na(+) and K(+) across the cell membrane. The gradients are utilized for neurotransmitter reuptake and their alteration modulates neural excitability. To provide insight into the molecular aetiology of RDP, we generated and analysed knockout heterozygous mice (Atp1a3(+/-)). Atp1a3(+/-) showed increased symptoms of dystonia that is induced by kainate injection into the cerebellar vermis. Atp1a3 mRNA was highly expressed in Purkinje cells and molecular-layer interneurons, and its product was concentrated at Purkinje cell soma, the site of abundant vesicular γ-aminobutyric acid transporter (VGAT) signal, suggesting the presynaptic localization of the α3 subunit in the inhibitory synapse. Electrophysiological studies showed that the inhibitory neurotransmission at molecular-layer interneuron-Purkinje cell synapses was enhanced in Atp1a3(+/-) cerebellar cortex, and that the enhancement originated via a presynaptic mechanism. Our results shed light on the role of Atp1a3 in the inhibitory synapse, and potential involvement of inhibitory synaptic dysfunction for the pathophysiology of dystonia.

Cerebellar networks with the cerebral cortex and basal ganglia

The dominant view of cerebellar function has been that it is exclusively concerned with motor control and coordination. Recent findings from neuroanatomical, behavioral, and imaging studies have profoundly changed this view. Neuroanatomical studies using virus transneuronal tracers have demonstrated that cerebellar output reaches vast areas of the neocortex, including regions of prefrontal and posterior parietal cortex. Furthermore, it has recently become clear that the cerebellum is reciprocally connected with the basal ganglia, which suggests that the two subcortical structures are part of a densely interconnected network. Taken together, these findings elucidate the neuroanatomical substrate for cerebellar involvement in non-motor functions mediated by the prefrontal and posterior parietal cortex, as well as in processes traditionally associated with the basal ganglia.

Animal models for drug discovery in dystonia

Dystonia is a neurological disorder characterized by involuntary twisting movements and unnatural postures. There are many different forms of dystonia, which affect over three million people worldwide. Effective treatments are available only for a minority of patients, so new treatments are sorely needed. Several animal species have been used to develop models for different forms of dystonia, each with differing strengths and weaknesses. This review outlines the strategies that have been used to exploit these models for drug discovery. Some have been used to dissect the pathogenesis of dystonia for the identification of molecular targets for intervention. Others have been used for the empirical identification of candidate drugs. Therefore, the animal models provide promising new tools for developing better treatments for dystonia.

Dystonia and the cerebellum: a new field of interest in movement disorders?

Although dystonia has traditionally been regarded as a basal ganglia dysfunction, recent provocative evidence has emerged of cerebellar involvement in the pathophysiology of this enigmatic disease. This review synthesizes the data suggesting that the cerebellum plays an important role in dystonia etiology, from neuroanatomical research of complex networks showing that the cerebellum is connected to a wide range of other central nervous system structures involved in movement control to animal models indicating that signs of dystonia are due to cerebellum dysfunction and completely disappear after cerebellectomy, and finally to clinical observations in secondary dystonia patients with various types of cerebellar lesions. We propose that dystonia is a large-scale dysfunction, involving not only cortico-basal ganglia-thalamo-cortical pathways, but the cortico-ponto-cerebello-thalamo-cortical loop as well. Even in the absence of traditional "cerebellar signs" in most dystonia patients, there are more subtle indications of cerebellar dysfunction. It is clear that as long as the cerebellum's role in dystonia genesis remains unexamined, it will be difficult to significantly improve the current standards of dystonia treatment or to provide curative treatment.

Stress, caffeine and ethanol trigger transient neurological dysfunction through shared mechanisms in a mouse calcium channelopathy

Several episodic neurological disorders are caused by ion channel gene mutations. In patients, transient neurological dysfunction is often evoked by stress, caffeine and ethanol, but the mechanisms underlying these triggers are unclear because each has diverse and diffuse effects on the CNS. Attacks of motor dysfunction in the Ca(V)2.1 calcium channel mouse mutant tottering are also triggered by stress, caffeine and ethanol. Therefore, we used the tottering mouse attacks to explore the pathomechanisms of the triggers. Despite the diffuse physiological effects of these triggers, ryanodine receptor blockers prevented attacks induced by all of them. In contrast, compounds that potentiate ryanodine receptors triggered attacks suggesting a convergent biochemical pathway. Tottering mouse attacks were both induced and blocked within the cerebellum suggesting that the triggers act locally to instigate attacks. In fact, stress, caffeine and alcohol precipitated attacks in Ca(V)2.1 mutant mice in which genetic pathology was limited to cerebellar Purkinje cells, suggesting that the triggers initiate dysfunction within a specific brain region. The surprising biochemical and anatomical specificity of the triggers and the discovery that the triggers operate through shared mechanisms suggest that it is possible to develop targeted therapies aimed at blocking the induction of episodic neurological dysfunction, rather than treating the symptoms once provoked.

Limited regional cerebellar dysfunction induces focal dystonia in mice

Dystonia is a complex neurological syndrome broadly characterized by involuntary twisting movements and abnormal postures. The anatomical distribution of the motor symptoms varies among dystonic patients and can range from focal, involving an isolated part of the body, to generalized, involving many body parts. Functional imaging studies of both focal and generalized dystonias in humans often implicate the cerebellum suggesting that similar pathological processes may underlie both. To test this, we exploited tools developed in mice to generate animals with gradients of cerebellar dysfunction. By using conditional genetics to regionally limit cerebellar dysfunction, we found that abnormalities restricted to Purkinje cells were sufficient to cause dystonia. In fact, the extent of cerebellar dysfunction determined the extent of abnormal movements. Dysfunction of the entire cerebellum caused abnormal postures of many body parts, resembling generalized dystonia. More limited regions of dysfunction that were created by electrical stimulation or conditional genetic manipulations produced abnormal movements in an isolated body part, resembling focal dystonia. Overall, these results suggest that focal and generalized dystonias may arise through similar mechanisms and therefore may be approached with similar therapeutic strategies.

Convergent mechanisms in etiologically-diverse dystonias

INTRODUCTION

Dystonia is a neurological disorder associated with twisting motions and abnormal postures, which compromise normal movements and can be both painful and debilitating. It can affect a single body part (focal), several contiguous regions (segmental), or the entire body (generalized), and can arise as a result of numerous causes, both genetic and acquired. Despite the diversity of causes and manifestations, shared clinical features suggest that common mechanisms of pathogenesis may underlie many dystonias.

AREAS COVERED

Shared themes in etiologically-diverse dystonias exist at several biological levels. At the cellular level, abnormalities in the dopaminergic system, mitochondrial function and calcium regulation are often present. At the anatomical level, the basal ganglia and the cerebellum are frequently implicated. Global CNS dysfunction, specifically aberrant neuronal plasticity, inhibition and sensorimotor integration, are also observed in a number of dystonias. Using clinical data and data from animal models, this article seeks to highlight shared pathways that may be critical in understanding mechanisms and identifying novel therapeutic strategies in dystonia.

EXPERT OPINION

Identifying shared features of pathogenesis can provide insight into the biological processes that underlie etiologically diverse dystonias, and can suggest novel targets for therapeutic intervention that may be effective in a broad group of affected individuals.

The functional neuroanatomy of dystonia

Dystonia is a neurological disorder characterized by involuntary twisting movements and postures. There are many different clinical manifestations, and many different causes. The neuroanatomical substrates for dystonia are only partly understood. Although the traditional view localizes dystonia to basal ganglia circuits, there is increasing recognition that this view is inadequate for accommodating a substantial portion of available clinical and experimental evidence. A model in which several brain regions play a role in a network better accommodates the evidence. This network model accommodates neuropathological and neuroimaging evidence that dystonia may be associated with abnormalities in multiple different brain regions. It also accommodates animal studies showing that dystonic movements arise with manipulations of different brain regions. It is consistent with neurophysiological evidence suggesting defects in neural inhibitory processes, sensorimotor integration, and maladaptive plasticity. Finally, it may explain neurosurgical experience showing that targeting the basal ganglia is effective only for certain subpopulations of dystonia. Most importantly, the network model provides many new and testable hypotheses with direct relevance for new treatment strategies that go beyond the basal ganglia. This article is part of a Special Issue entitled "Advances in dystonia".

The cerebellum and basal ganglia are interconnected

The cerebellum and the basal ganglia are major subcortical nuclei that control multiple aspects of behavior largely through their interactions with the cerebral cortex. Discrete multisynaptic loops connect both the cerebellum and the basal ganglia with multiple areas of the cerebral cortex. Interactions between these loops have traditionally been thought to occur mainly at the level of the cerebral cortex. Here, we review a series of recent anatomical studies in nonhuman primates that challenge this perspective. We show that the anatomical substrate exists for substantial interactions between the cerebellum and the basal ganglia. Furthermore, we discuss how these pathways may provide a useful framework for understanding cerebellar contributions to the manifestation of two prototypical basal ganglia disorders, Parkinson's disease and dystonia.

Channelopathies in Cav1.1, Cav1.3, and Cav1.4 voltage-gated L-type Ca2+ channels

Voltage-gated Ca2+ channels couple membrane depolarization to Ca2+-dependent intracellular signaling events. This is achieved by mediating Ca2+ ion influx or by direct conformational coupling to intracellular Ca2+ release channels. The family of Cav1 channels, also termed L-type Ca2+ channels (LTCCs), is uniquely sensitive to organic Ca2+ channel blockers and expressed in many electrically excitable tissues. In this review, we summarize the role of LTCCs for human diseases caused by genetic Ca2+ channel defects (channelopathies). LTCC dysfunction can result from structural aberrations within their pore-forming alpha1 subunits causing hypokalemic periodic paralysis and malignant hyperthermia sensitivity (Cav1.1 alpha1), incomplete congenital stationary night blindness (CSNB2; Cav1.4 alpha1), and Timothy syndrome (Cav1.2 alpha1; reviewed separately in this issue). Cav1.3 alpha1 mutations have not been reported yet in humans, but channel loss of function would likely affect sinoatrial node function and hearing. Studies in mice revealed that LTCCs indirectly also contribute to neurological symptoms in Ca2+ channelopathies affecting non-LTCCs, such as Cav2.1 alpha1 in tottering mice. Ca2+ channelopathies provide exciting disease-related molecular detail that led to important novel insight not only into disease pathophysiology but also to mechanisms of channel function.

Abnormal activation of the primary somatosensory cortex in spasmodic dysphonia: an fMRI study

Spasmodic dysphonia (SD) is a task-specific focal dystonia of unknown pathophysiology, characterized by involuntary spasms in the laryngeal muscles during speaking. Our aim was to identify symptom-specific functional brain activation abnormalities in adductor spasmodic dysphonia (ADSD) and abductor spasmodic dysphonia (ABSD). Both SD groups showed increased activation extent in the primary sensorimotor cortex, insula, and superior temporal gyrus during symptomatic and asymptomatic tasks and decreased activation extent in the basal ganglia, thalamus, and cerebellum during asymptomatic tasks. Increased activation intensity in SD patients was found only in the primary somatosensory cortex during symptomatic voice production, which showed a tendency for correlation with ADSD symptoms. Both SD groups had lower correlation of activation intensities between the primary motor and sensory cortices and additional correlations between the basal ganglia, thalamus, and cerebellum during symptomatic and asymptomatic tasks. Compared with ADSD patients, ABSD patients had larger activation extent in the primary sensorimotor cortex and ventral thalamus during symptomatic task and in the inferior temporal cortex and cerebellum during symptomatic and asymptomatic voice production. The primary somatosensory cortex shows consistent abnormalities in activation extent, intensity, correlation with other brain regions, and symptom severity in SD patients and, therefore, may be involved in the pathophysiology of SD.

Genetic enhancement of thalamocortical network activity by elevating alpha 1g-mediated low-voltage-activated calcium current induces pure absence epilepsy

Absence seizures are a leading form of childhood epilepsy. Human and mouse P/Q-type calcium channel gene mutations initiate a complex absence epilepsy and ataxia phenotype, and in mice, secondarily elevate neuronal low-voltage-activated T-type calcium currents. These currents influence thalamocortical network activity and contribute to the generation of cortical spike-wave discharges (SWDs) associated with absence seizures. To address whether enhanced thalamocortical T-type currents suffice to induce an epileptic phenotype, two BAC transgenic mouse lines overexpressing the Cacna1g gene for alpha1G T-type calcium channels were generated with low and high transgene copy numbers that exhibit elevated alpha1G expression and showed increased functional T-type currents measured in thalamic neurons. Both lines exhibit frequent bilateral cortical SWDs associated with behavioral arrest but lack other overt neurological abnormalities. These models provide the first evidence that primary elevation of brain T-type currents are causally related to pure absence epilepsy, and selectively identify Cacna1g, one of the three T-type calcium channel genes, as a key component of a genetically complex epileptogenic pathway.

Purkinje cell input to cerebellar nuclei in tottering: ultrastructure and physiology

Homozygous tottering mice are spontaneous ataxic mutants, which carry a mutation in the gene encoding the ion pore of the P/Q-type voltage-gated calcium channels. P/Q-type calcium channels are prominently expressed in Purkinje cell terminals, but it is unknown to what extent these inhibitory terminals in tottering mice are affected at the morphological and electrophysiological level. Here, we investigated the distribution and ultrastructure of their Purkinje cell terminals in the cerebellar nuclei as well as the activities of their target neurons. The densities of Purkinje cell terminals and their synapses were not significantly affected in the mutants. However, the Purkinje cell terminals were enlarged and had an increased number of vacuoles, whorled bodies, and mitochondria. These differences started to occur between 3 and 5 weeks of age and persisted throughout adulthood. Stimulation of Purkinje cells in adult tottering mice resulted in inhibition at normal latencies, but the activities of their postsynaptic neurons in the cerebellar nuclei were abnormal in that the frequency and irregularity of their spiking patterns were enhanced. Thus, although the number of their terminals and their synaptic contacts appear quantitatively intact, Purkinje cells in tottering mice show several signs of axonal damage that may contribute to altered postsynaptic activities in the cerebellar nuclei.

Low-frequency oscillations in the cerebellar cortex of the tottering mouse

The tottering mouse is an autosomal recessive disorder involving a missense mutation in the gene encoding P/Q-type voltage-gated Ca2+ channels. The tottering mouse has a characteristic phenotype consisting of transient attacks of dystonia triggered by stress, caffeine, or ethanol. The neural events underlying these episodes of dystonia are unknown. Flavoprotein autofluorescence optical imaging revealed transient, low-frequency oscillations in the cerebellar cortex of anesthetized and awake tottering mice but not in wild-type mice. Analysis of the frequencies, spatial extent, and power were used to characterize the oscillations. In anesthetized mice, the dominant frequencies of the oscillations are between 0.039 and 0.078 Hz. The spontaneous oscillations in the tottering mouse organize into high power domains that propagate to neighboring cerebellar cortical regions. In the tottering mouse, the spontaneous firing of 83% (73/88) of cerebellar cortical neurons exhibit oscillations at the same low frequencies. The oscillations are reduced by removing extracellular Ca2+ and blocking L-type Ca2+ channels. The oscillations are likely generated intrinsically in the cerebellar cortex because they are not affected by blocking AMPA receptors or by electrical stimulation of the parallel fiber-Purkinje cell circuit. Furthermore, local application of an L-type Ca2+ agonist in the tottering mouse generates oscillations with similar properties. The beam-like response evoked by parallel fiber stimulation is reduced in the tottering mouse. In the awake tottering mouse, transcranial flavoprotein imaging revealed low-frequency oscillations that are accentuated during caffeine-induced attacks of dystonia. During dystonia, oscillations are also present in the face and hindlimb electromyographic (EMG) activity that become significantly coherent with the oscillations in the cerebellar cortex. These low-frequency oscillations and associated cerebellar cortical dysfunction demonstrate a novel abnormality in the tottering mouse. These oscillations are hypothesized to be involved in the episodic movement disorder in this mouse model of episodic ataxia type 2.

The basal ganglia and cerebellum interact in the expression of dystonic movement

Dystonia is a neurological disorder characterized by excessive involuntary muscle contractions that lead to twisting movements or abnormal posturing. Traditional views place responsibility for dystonia with dysfunction of basal ganglia circuits, yet recent evidence has pointed towards cerebellar circuits as well. In the current studies we used two strategies to explore the hypothesis that the expression of dystonic movements depends on influences from a motor network that includes both the basal ganglia and cerebellum. The first strategy was to evaluate the consequences of subthreshold lesions of the striatum in two different animal models where dystonic movements are thought to originate from abnormal cerebellar function. The second strategy employed microdialysis to search for changes in striatal dopamine release in these two animal models where the cerebellum has been already implicated. One of the animal models involved tottering mice, which exhibit paroxysmal dystonia due to an inherited defect affecting calcium channels. In keeping with prior results implicating the cerebellum in this model, surgical removal of the cerebellum eliminated their dystonic attacks. In contrast, subclinical lesions of the striatum with either 6-hydroxydopamine (6OHDA) or quinolinic acid (QA) exaggerated their dystonic attacks. Microdialysis of the striatum revealed dystonic attacks in tottering mice to be associated with a significant reduction in extracellular striatal dopamine. The other animal model involved the induction of dystonia via pharmacological excitation of the cerebellar cortex by local application of kainic acid in normal mice. In this model the site of stimulation determines the origin of dystonia in the cerebellum. However, subclinical striatal lesions with either 6OHDA or QA again exaggerated their generalized dystonia. When dystonic movements were triggered by pharmacological stimulation of the cerebellum, microdialysis revealed significant reductions in striatal dopamine release. These results demonstrate important functional relationships between cerebellar and basal ganglia circuits in two different animal models of dystonia. They suggest that expression of dystonic movements depends on influences from both basal ganglia and cerebellum in both models. These results support the hypothesis that dystonia may result from disruption of a motor network involving both the basal ganglia and cerebellum, rather than isolated dysfunction of only one motor system.

Focal white matter changes in spasmodic dysphonia: a combined diffusion tensor imaging and neuropathological study

Spasmodic dysphonia is a neurological disorder characterized by involuntary spasms in the laryngeal muscles during speech production. Although the clinical symptoms are well characterized, the pathophysiology of this voice disorder is unknown. We describe here, for the first time to our knowledge, disorder-specific brain abnormalities in these patients as determined by a combined approach of diffusion tensor imaging (DTI) and postmortem histopathology. We used DTI to identify brain changes and to target those brain regions for neuropathological examination. DTI showed right-sided decrease of fractional anisotropy in the genu of the internal capsule and bilateral increase of overall water diffusivity in the white matter along the corticobulbar/corticospinal tract in 20 spasmodic dysphonia patients compared to 20 healthy subjects. In addition, water diffusivity was bilaterally increased in the lentiform nucleus, ventral thalamus and cerebellar white and grey matter in the patients. These brain changes were substantiated with focal histopathological abnormalities presented as a loss of axonal density and myelin content in the right genu of the internal capsule and clusters of mineral depositions, containing calcium, phosphorus and iron, in the parenchyma and vessel walls of the posterior limb of the internal capsule, putamen, globus pallidus and cerebellum in the postmortem brain tissue from one patient compared to three controls. The specificity of these brain abnormalities is confirmed by their localization, limited only to the corticobulbar/corticospinal tract and its main input/output structures. We also found positive correlation between the diffusivity changes and clinical symptoms of spasmodic dysphonia (r = 0.509, P = 0.037). These brain abnormalities may alter the central control of voluntary voice production and, therefore, may underlie the pathophysiology of this disorder.

Altered functional expression of Purkinje cell calcium channels precedes motor dysfunction in tottering mice

In tottering mice, a point mutation in the gene encoding P-type (Ca(v)2.1) voltage-gated calcium channels results in ataxia, absence epilepsy, and motor dystonia that appear 3-4 weeks postnatally. The aberrant motor behaviors have been linked to cerebellar dysfunction, and adult Purkinje cells (PCs) of tottering mice exhibit calcium-dependent changes in gene transcription suggestive of altered calcium homeostasis. In an attempt to identify early postnatal events important for the development of the behavioral phenotype, we examined calcium channel expression in cerebellar PCs from postnatal days 6-15 (P6-15). Whole cell recording was combined with selective calcium channel antagonists to allow discrimination of the various voltage-activated calcium channels types; early age-dependent differences between tottering and wild-type PCs were found. Wild-type PCs experienced a steady increase in P current density over this period, resulting in a twofold change by P15. In tottering, by contrast, P current density remained unchanged from P6-8 and was only 25% of the wild-type level by P8. A developmental delay in functional expression was implicated in this early deficit, since ensuing gains over the subsequent week brought tottering P current density close to the wild-type level by P15. At this age, tottering PCs also exhibited a 2.2-fold higher L-type calcium current density than that expressed by wild-type PCs. Increases in N current were apparent at some ages, most strikingly within a subset of tottering PCs at P15. Functional R- and T-type calcium current densities were equivalent to wild-type levels at all ages. We conclude that the tottering mutation brings about selective changes in functional calcium channel expression 1 to 2 weeks prior to the appearance of the behavioral deficits, raising the possibility that they represent an early, primary event along the path to motor dysfunction in tottering.

Neuroanatomical substrates for paroxysmal dyskinesia in lethargic mice

The paroxysmal dyskinesias are a group of neurological disorders described by intermittent attacks of involuntary abnormal movements superimposed on a relatively normal baseline. The neuroanatomical substrates for these attacks are not fully understood, though available evidence from studies of affected people and animal models points to dysfunction in the basal ganglia or cerebellum. In the current studies, the anatomical basis for paroxysmal dyskinesias in lethargic mice was determined via histochemical methods sensitive to changes in regional brain activity followed by surgical elimination of the suspected source. Cytochrome oxidase histochemistry revealed increased activity in the red nucleus. Surgical removal of the cerebellum worsened ataxia but eliminated paroxysmal dyskinesias. These studies support the hypothesis that abnormal cerebellar output contributes to paroxysmal dyskinesias.

Aberrant cerebellar granule cell-specific GABAA receptor expression in the epileptic and ataxic mouse mutant, Tottering

The Tottering (cacna1a(tg)) mouse arose as a consequence of a spontaneous mutation in cacna1a, the gene encoding the pore-forming subunit of the pre-synaptic P/Q-type voltage-gated calcium channel (VGCC, Ca(V)2.1). The mouse phenotype includes ataxia and intermittent myoclonic seizures which have been attributed to impaired excitatory neurotransmission at cerebellar granule cell (CGC) parallel fiber-Purkinje cell (PF-PC) synapses [Zhou YD, Turner TJ, Dunlap K (2003) Enhanced G-protein-dependent modulation of excitatory synaptic transmission in the cerebellum of the Ca(2+)-channel mutant mouse, tottering. J Physiol 547:497-507]. We hypothesized that the expression of cerebellar GABA(A) receptors may be affected by the mutation. Indeed, abnormal GABA(A) receptor function and expression in the cacna1a(tg) forebrain has been reported previously [Tehrani MH, Barnes EM Jr (1995) Reduced function of gamma-aminobutyric acid A receptors in tottering mouse brain: role of cAMP-dependent protein kinase. Epilepsy Res 22:13-21; Tehrani MH, Baumgartner BJ, Liu SC, Barnes EM Jr (1997) Aberrant expression of GABA(A) receptor subunits in the tottering mouse: an animal model for absence seizures. Epilepsy Res 28:213-223]. Here we show a deficit of 40.2+/-3.6% in the total number of cerebellar GABA(A) receptors expressed (gamma2+delta subtypes) in adult cacna1a(tg) relative to controls. [(3)H]Muscimol autoradiography identified that this was partly due to a significant loss of CGC-specific alpha6 subunit-containing GABA(A) receptor subtypes. A large proportion of this loss of alpha6 receptors was attributable to a significantly reduced expression of the CGC-specific benzodiazepine-insensitive Ro15-4513 (BZ-IS) binding subtype, alpha6betagamma2 subunit-containing receptors. BZ-IS binding was reduced by 36.6+/-2.6% relative to controls in cerebellar membrane homogenates and by 37.2+/-3.7% in cerebellar sections. Quantitative immunoblotting revealed that the steady-state expression level of alpha6 and gamma2 subunits was selectively reduced relative to controls by 30.2+/-8.2% and 38.8+/-13.1%, respectively, alpha1, beta3 and delta were unaffected. Immunohistochemically probed control and cacna1a(tg) cerebellar sections verified that alpha6 and gamma2 subunit expression was reduced and that this deficit was restricted to the CGC layer. Thus, we have shown that abnormal cerebellar P/Q-type VGCC activity results in a deficit of CGC-specific subtype(s) of GABA(A) receptors which may contribute to, or may be a consequence of the impaired cerebellar network signaling that occurs in cacna1a(tg) mice.

Expression of Adhesion Factors Induced by Epileptiform Activity in the Endothelium of the Isolated Guinea Pig Brain In Vitro

PURPOSE

Brain inflammation has been recently considered in the pathogenesis of focal epilepsies. Synthesis of pro-inflammatory mediators in the brain was described both in experimental models of seizures and in human postsurgical tissue. Inflammatory mediators may up-regulate endothelial adhesion molecules, therefore promoting adhesion and homing of leucocytes into the brain. In the present study, expression of inducible adhesion factors in brain endothelium was verified after pharmacological induction of seizure-like activity in specific brain areas of the in vitro isolated guinea pig brain.

METHODS

Experiments were performed in isolated guinea-pig brains maintained in vitro by arterial perfusion. In this preparation, brief application of the GABAa receptor-antagonist, bicuculline, consistently induced focal ictal discharges in the limbic region that secondarily diffuse to the neocortex, as verified by simultaneous electrophysiological recording of extracellular activity. At the end of the electrophysiological experiment (after 5 h in vitro), brains were fixed and immunostaining for adhesion molecules P-selectin and ICAM-1 and for Fos protein was evaluated.

RESULTS

Immunohistochemical analysis of isolated brains in which seizure-like activity was induced revealed expression of inducible adhesion factors P-selectin and ICAM-1 in the endothelium of small-medium size brain vessels. In particular, the expression of these molecules was consistently observed in all areas involved in epileptic seizure-like ictal activity (limbic cortices and neocortex), and was infrequently found in regions that generated interictal spiking (piriform cortex), suggesting a trigger role played by seizures for endothelial activation. An increase in Fos protein expression was evident in all analyzed limbic areas and in the neocortex, indicating a correlation between the areas of neuronal and endothelial activation. In control brains maintained in vitro for comparable times without induction of epileptiform activity, no immunoreactivity for Fos and adhesion molecules was observed.

CONCLUSIONS

Seizure-like activity in an in vitro isolated brain preparation induces the expression of adhesion molecules in the cerebral endothelium. These observations indicate that local endothelial activation may represent a crucial step for the development of an inflammatory response induced by seizures, and suggest a possible novel pathogenic mechanism during the process of epileptogenesis.

Ca2+ influx through both L- and N-type Ca2+ channels increases c-fos expression by electrical stimulation of sympathetic neurons

During direct membrane depolarization, Ca2+ influx primarily through L-type Ca2+ (L-) channels initiates activity-dependent gene transcription. This is surprising given that in most neurons a minority of the total Ca2+ current arises from L-channel activity. However, many studies have stimulated Ca2+ influx with unphysiological stimuli such as chronic membrane depolarization using high K+ medium. Few studies have tested whether other Ca2+ channels stimulate gene transcription in adult neurons as a consequence of direct electrical stimulation. Therefore, we evaluated the role of L- and N-type Ca2+ (N-) channel activity in regulating mRNA levels of c-fos, an activity-dependent transcription factor, in adult rat superior cervical ganglion (SCG) neurons as the majority of Ca2+ channels are N-type, while only a minority are L-type. Changes in c-fos mRNA levels were measured using semi-quantitative and single-cell RT-PCR. Phosphorylation of CREB (pCREB) and changes in c-Fos levels were visualized in dissociated cells by immunocytochemistry. Increases in pCREB, c-fos mRNA and c-Fos protein with either K+ or electrical depolarization required Ca2+ influx. These results support previous findings that elevated c-fos levels result from pCREB stimulating c-fos transcription. Elevation of pCREB, c-fos and c-Fos with K+ depolarization depended on L-channel activity. By contrast, antagonizing either channel at 10-Hz stimulation minimized these increases despite unequal numbers of the two channel types. Transition to exclusive L-channel involvement occurred with increasing frequency of stimulation (from 10 to 20 to 50 Hz). Our results demonstrate that N- and L-channel participation in regulating c-fos expression is encoded in the pattern of electrical stimulation.

Potassium channel blockers inhibit the triggers of attacks in the calcium channel mouse mutant tottering

Humans with the disorder episodic ataxia type 2 (EA2) and the tottering mouse mutant exhibit episodic attacks induced by emotional and chemical stress. Both the human and mouse disorders result from mutations in CACNA1A, the gene encoding the alpha(1)2.1 subunit of Ca(v)2.1 voltage-gated calcium channels. These mutations predict reduced calcium currents, particularly in cerebellar Purkinje cells, where these channels are most abundant. 4-Aminopyridine (4-AP), a nonselective blocker of K(v) voltage-gated potassium channels, alleviates attacks of ataxia in EA2 patients. To test the specificity of the effect for K(v) channels, aminopyridine analogs were assessed for their ability to ameliorate attacks of dyskinesia in tottering mice. 4-AP and 3,4-diaminopyridine (3,4-DiAP), which have relatively high affinities for K(v) channels, reduced the frequency of restraint- and caffeine-induced attacks. Furthermore, microinjection of 3,4-DiAP into the cerebellum completely blocked attacks in tottering mice. Other aminopyridine analogs reduced attack frequency but, consistent with their lower affinities for K(v) channels, required comparatively higher doses. These results suggest that aminopyridines block tottering mouse attacks via cerebellar K(v) channels. That both stress- and caffeine-induced attacks were blocked by aminopyridines suggests that these triggers act via similar mechanisms. Although 4-AP and 3,4-DiAP were effective in preventing attacks in tottering mice, these compounds did not affect the severity of "breakthrough" attacks that occurred in the presence of a drug. These results suggest that the aminopyridines increase the threshold for attack initiation without mitigating the character of the attack, indicating that attack initiation is mediated by mechanisms that are independent of the neurological phenotype.

Noradrenergic blockade prevents attacks in a model of episodic dysfunction caused by a channelopathy

Episodic neurological dysfunction often results from ion channel gene mutations. Despite knowledge of the mutations, the factors that precipitate attacks in channelopathies are not clear. In humans, mutations of the calcium channel gene CACNA1A are associated with attacks of neurological dysfunction in familial hemiplegic migraine and episodic ataxia type-2. In tottering mice, a mutation in the same gene causes attacks resembling paroxysmal dyskinesia. Stress, a trigger associated with human episodic disorders, reliably elicits attacks in tottering mice. Because noradrenergic neurotransmission is critical to the stress response and because noradrenergic hyperinnervation is observed in tottering mice, the role of norepinephrine in stress-induced attacks was investigated. Drugs that act at alpha-adrenergic receptors to block noradrenergic transmission prevented attacks. However, agents that facilitate noradrenergic neurotransmission failed to induce attacks. These results suggest that, while noradrenergic neurotransmission may be necessary for attacks, an increase in norepinephrine is not sufficient to induce attacks.

Animal models of focal dystonia

Animal models indicate that the abnormal movements of focal dystonia result from disordered sensorimotor integration. Sensorimotor integration involves a comparison of sensory information resulting from a movement with the sensory information expected from the movement. Unanticipated sensory signals identified by sensorimotor processing serve as signals to modify the ongoing movement or the planning for subsequent movements. Normally, this process is an effective mechanism to modify neural commands for ongoing movement or for movement planning. Animal models of the focal dystonias spasmodic torticollis, writer's cramp, and benign essential blepharospasm reveal different dysfunctions of sensorimotor integration through which dystonia can arise. Animal models of spasmodic torticollis demonstrate that modifications in a variety of regions are capable of creating abnormal head postures. These data indicate that disruption of neural signals in one structure may mutate the activity pattern of other elements of the neural circuits for movement. The animal model of writer's cramp demonstrates the importance of abnormal sensory processing in generating dystonic movements. Animal models of blepharospasm illustrate how disrupting motor adaptation can produce dystonia. Together, these models show mechanisms by which disruptions in sensorimotor integration can create dystonic movements.

Animal models of generalized dystonia

Dystonia is a prevalent neurological disorder characterized by abnormal co-contractions of antagonistic muscle groups that produce twisting movements and abnormal postures. The disorder may be inherited, arise sporadically, or result from brain insult. Dystonia is a heterogeneous disorder because patients may exhibit focal or generalized symptoms associated with abnormalities in many brain regions including basal ganglia and cerebellum. Elucidating the pathogenic mechanisms underlying dystonia has therefore been challenging. Animal models of dystonia exhibit similar heterogeneity and are useful for understanding pathogenesis. The neurochemical and neurophysiological abnormalities in rodents with idiopathic generalized dystonia suggest that dysfunctional output from basal ganglia, cerebellum, or from multiple systems is the cause of motor dysfunction. Findings from drug- or toxin-induced dystonia in rodents and nonhuman primates mirror the genetic models. The parallels between dystonia in humans and animals suggest that the models will continue to prove useful in determining pathogenesis. Furthermore, detailed characterization of the existing models of dystonia and the development of new models hold promise for the identification of novel therapeutics.

Rodent models for dystonia research: Characteristics, evaluation, and utility

A large number of different genetic and acquired disorders of the nervous system may be associated with dystonia. To elucidate its pathogenesis and to facilitate the discovery of potential novel treatments, there has been a growing interest in the development of animal models and particularly rodent models. Multiple animal models for dystonia have now been developed and partially characterized. The results obtained from studies of these models often lead in very different directions, in part because the different models target different aspects of a very heterogeneous disorder. A recent workshop addressed four main issues affecting those who conduct dystonia research with animal models, including the different ways in which dystonic disorders can be modeled in rodents, key features that constitute a useful model, methods used in the evaluation of these models, and recommendations for future research. This review summarizes the main outcomes of this conference. 2005 Movement Disorder Society.

L-type Ca2+ channels in Ca2+ channelopathies

Voltage-gated L-type Ca2+ channels (LTCCs) mediate depolarization-induced Ca2+ entry in electrically excitable cells, including muscle cells, neurons, and endocrine and sensory cells. In this review we summarize the role of LTCCs for human diseases caused by genetic Ca2+ channel defects (channelopathies). LTCC dysfunction can result from structural aberrations within pore-forming alpha1 subunits causing incomplete congenital stationary night blindness, malignant hyperthermia sensitivity or hypokalemic periodic paralysis. However, studies in mice revealed that LTCC dysfunction also contributes to neurological symptoms in Ca2+ channelopathies affecting non-LTCCs, such as Ca(v)2.1 alpha1 in tottering mice. Ca2+ channelopathies provide exciting molecular tools to elucidate the contribution of different LTCC isoforms to human diseases.

Expression of c-fos in the Brain after Activation of L-Type Calcium Channels

In rodents, administration of the L-type calcium channel activators, +/-Bay K 8644 and FPL 64176, causes an unusual neurobehavioral syndrome that includes dystonia and self-injurious biting. To determine the regional influence of these drugs in the brain, the induction of c-FOS was mapped after administration of these drugs to mice. In situ hybridization with an antisense riboprobe directed to c-FOS mRNA revealed widespread induction, with the highest levels in the striatum, cortex, hippocampus, locus coeruleus, and cerebellum. The induction of c-FOS mRNA was dose dependent, reached maximal expression approximately 60 min after drug treatment, and could be blocked by pretreatment with the L-type calcium channel antagonist, nifedipine. Immunohistochemical stains with an antibody directed to c-FOS protein revealed a pattern of induction similar to that obtained with in situ hybridization in most brain regions. These results demonstrate a very heterogeneous influence of L-type calcium channel activation in different brain regions, despite the nearly universal expression of these channels implied by more classical anatomical methods.

Regulation of tyrosine hydroxylase expression in tottering mouse Purkinje cells

Tottering (tg) mice inherit a missense mutation in the Alpha1A subunit of P/Q-type calcium channels. This mutation results in an increased density of L-type calcium channels in the cerebellum and abnormal regulation of tyrosine hydroxylase (TH) gene expression in a subset of cerebellar Purkinje cells, a cell type that does not normally express TH. The behavioral phenotype includes attacks of dyskinesia, which can be blocked by L-type calcium channel antagonists. To test the hypothesis that cerebellar TH mRNA expression can be manipulated in vivo by L-type calcium channel blockade, control and tottering mice were chronically treated with the L-type calcium channel antagonist nimodipine. Chronic nimodipine treatment significantly reduced the expression of TH mRNA in tottering mouse Purkinje cells. This effect was observed without altering the increased density of L-type calcium channels in tottering mouse cerebella. Chronic nimodipine treatment had no effect on TH mRNA expression in tottering mouse catecholaminergic neurons, including those of the locus coeruleus and substantia nigra. However, a small reduction in TH mRNA expression in the substantia nigra of control mice was observed after drug treatment. These data suggest that the abnormal expression of TH in tottering mouse Purkinje cells is regulated by Purkinje cell excitability.

Regulation of expression of the SN1 transporter during renal adaptation to chronic metabolic acidosis in rats

During chronic metabolic acidosis, renal glutamine utilization increases markedly. We studied the expression of the system N1 (SN1) amino acid transporter in the kidney during chronic ammonium chloride acidosis in rats. Acidosis caused a 10-fold increase in whole kidney SN1 mRNA level and a 100-fold increase in the cortex. Acidosis increased Na(+)-dependent glutamine uptake into basolateral and brush-border membrane vesicles (BLMV and BBMV, respectively) isolated from rat cortex (BLMV, 219 +/- 66 control vs. 651 +/- 180 pmol. mg(-1). min(-1) acidosis; BBMV, 1,112 +/- 189 control vs. 1,652 +/- 148 pmol. mg(-1). min(-1) acidosis, both P < 0.05). Na(+)-independent uptake was unchanged by acidosis in BLMV and BBMV. The acidosis-induced increase in Na(+)-dependent glutamine uptake was eliminated by histidine, confirming transport by system N. SN1 protein was detected only in BLMV and BBMV from acidotic rats. After recovery from acidosis, SN1 mRNA and protein and Na(+)-dependent glutamine uptake activity rapidly returned to control levels. These data provide evidence that regulation of expression of the SN1 amino acid transporter is part of the renal homeostatic response to acid-base imbalance.

Abnormal cerebellar signaling induces dystonia in mice

Dystonia is a relatively common neurological syndrome characterized by twisting movements or sustained abnormal postures. Although the basal ganglia have been implicated in the expression of dystonia, recent evidence suggests that abnormal cerebellar function is also involved. In these studies, a novel mouse model was developed to study the role of the cerebellum in dystonia. Microinjection of low doses of kainic acid into the cerebellar vermis of mice elicited reliable and reproducible dystonic postures of the trunk and limbs. The severity of the dystonia increased linearly with kainate dose. Kainate-induced dystonia was blocked by the glutamatergic antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide and reproduced by domoic acid microinjection, suggesting that the induction of dystonia is dependent on glutamatergic activation in this model. The abnormal movements were not associated with kainate-induced seizures, because EEG recordings showed no epileptiform activity during the dystonic events. Neuronal activation, as assessed by in situ hybridization for c-fos, revealed c-fos mRNA expression in the cerebellum, locus ceruleus, and red nucleus. In contrast, regions associated with epileptic seizures, such as the hippocampus, did not exhibit increased c-fos expression after cerebellar kainate injection. Furthermore, in transgenic mice lacking Purkinje cells, significantly less dystonia was induced after kainic acid injection, implicating Purkinje cells and the cerebellar cortex in this model of dystonia. Together, these data suggest that abnormal cerebellar signaling produces dystonia and that the cerebellum should be considered along with the basal ganglia in the pathophysiology of this movement disorder.