The Dystonias

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.

Neuropathology of cervical dystonia

The aim of this study was to search for neuropathological changes in postmortem brain tissue of individuals with cervical dystonia (CD). Multiple regions of formalin-preserved brains were collected from patients with CD and controls and examined with an extensive battery of histopathological stains in a two-stage study design. In stage one, 4 CD brains underwent a broad screening neuropathological examination. In stage two, these 4 CD brains were combined with 2 additional CD brains, and the subjective findings were quantified and compared to 16 age-matched controls. The initial subjective neuropathological assessment revealed only two regions with relatively consistent changes. The substantia nigra had frequent ubiquitin-positive intranuclear inclusions known as Marinesco bodies. Additionally, the cerebellum showed patchy loss of Purkinje cells, areas of focal gliosis and torpedo bodies. Other brain regions showed minor or inconsistent changes. In the second stage of the analysis, quantitative studies failed to reveal significant differences in the numbers of Marinesco bodies in CD versus controls, but confirmed a significantly lower Purkinje cell density in CD. Molecular investigations revealed 4 of the CD cases and 2 controls to harbor sequence variants in non-coding regions of THAP1, and these cases had lower Purkinje cell densities regardless of whether they had CD. The findings suggest that subtle neuropathological changes such as lower Purkinje cell density may be found in primary CD when relevant brain regions are investigated with appropriate methods.

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 effects of reversible inactivation of the subthalamo-pallidal pathway on the behaviour of naive and hemiparkinsonian monkeys

This study was designed to further investigate the role of the subthalamic nucleus (STN) and globus pallidus internus (GPi) in the pathophysiology of Parkinson's disease. The prevailing theory about the pathophysiology of Parkinson's disease (PD) predicts that there is overactivity of the subthalamo-pallidal pathway. In order to inactivate that pathway, naive and hemiparkinsonian monkeys were locally administered either muscimol (to reversibly inactivate the contralateral STN) or kynurenic acid (to reduce glutamatergic activity in the contralateral GPi). Three naive and 2 hemiparkinsonian monkeys were studied. Intra-carotid MPTP was administered to produce 2 hemiparkinsonian monkeys. Injection sites of muscimol and kynurenic acid in the brain were confirmed electrophysiologically and histologically. Injections of muscimol into the STN in naive and hemiparkinsonian monkeys caused reversible contralateral dystonia, but did not alleviate Parkinsonism. Only one kynurenic acid injection into GPi partially alleviated Parkinsonism. On the basis of the results in this study, aspects of the currently accepted hypothesis of the pathophysiology of PD cannot be confirmed. However, this study reports that the STN has an important role in the production of dystonia. This experimental model of dystonia will prove suitable for further study of both the mechanisms causing dystonia as well as for possible therapeutic approaches to its treatment.

Experimental therapeutics for dystonia

Dystonia is a neurological syndrome characterized by excessive involuntary muscle contractions leading to twisting movements and unnatural postures. It has many different clinical manifestations, and many different causes. More than 3 million people worldwide suffer from dystonia, yet there are few broadly effective treatments. In the past decade, progress in research has advanced our understanding of the pathogenesis of dystonia to a point where drug discovery efforts are now feasible. Several strategies can be used to develop novel therapeutics for dystonia. Existing therapies have only modest efficacy, but may be refined and improved to increase benefits while reducing side effects. Identifying rational targets for drug intervention based on the pathogenesis of dystonia is another strategy. The surge in both basic and clinical research discoveries has provided insights at all levels, including etiological, physiological and nosological, to enable such a targeted approach. The empirical approach to drug discovery, whereby compounds are identified using a nonmechanistic strategy, is complementary to the rational approach. With the recent development of multiple animal models of dystonia, it is now possible to develop assays and perform drug screens on vast numbers of compounds. This multifaceted approach to drug discovery in dystonia will likely provide lead compounds that can then be translated for clinical use.

Age-related changes in striatal nitric oxide synthase-immunoreactive interneurones in the dystonic dt sz mutant hamster

The dt(sz) mutant hamster represents a model of paroxysmal dyskinesia in which dystonic episodes can be age-dependently induced by stress. GABAergic interneurones which co-express calcium binding proteins were found to be reduced in the striatum of the dt(sz) mutant. Other types of striatal interneurones have so far not been examined. In the present study, we therefore determined the density of nitric oxide synthase (NOS)-immunoreactive interneurones in the striatum of the dt(sz) mutant in comparison with nondystonic control hamsters. At the age of most marked expression of dystonia (30-40 days of life), the density of NOS-positive interneurones was decreased in the striatum of dt(sz) hamsters (-21%) in comparison with age-matched nondystonic control hamsters. Spontaneous remission of dystonia (age >90 days) coincided with a normalization of the density of NOS-reactive interneurones within the whole striatum of dt(sz) hamsters, but there remained a reduced density in distinct subregions. Together with previous findings the present data indicate that the development of striatal interneurones is retarded in mutant hamsters. The age-related deficit of NOS-reactive interneurones may at least in part contribute to an abnormal activity of striatal GABAergic projection neurones and thereby to the age-dependent dystonic syndrome in the dt(sz) mutant.

Motor disturbances in mice with deficiency of the sodium channel gene Scn8a show features of human dystonia

The med(J) mouse with twisting movements related to deficiency of the sodium channel Scn8a has been proposed as a model of kinesiogenic dystonia. This prompted us to examine the phenotype of these mice in more detail. By cortical electroencephalographic (EEG) recordings, we could not detect any changes, demonstrating that the motor disturbances are not epileptic in nature, an important similarity to human dystonia. The significantly decreased body weight of med(J) mice was related to reduced food intake. Observations in the open field and by video recordings revealed that the mice exhibit sustained abnormal postures and movements of limbs, trunk and tail not only during locomotor activity but also at rest. With the exception of the head tremor, the other motor impairments were persistent rather than paroxysmal. When several neurological reflexes were tested, alterations were restricted to the posture and righting reflexes. Results of the wire hang test confirmed the greatly reduced muscle strength in the med(J) mouse. In agreement with different types of human dystonia, biperiden, haloperidol and diazepam moderately reduced the severity of motor disturbances in med(J) mice. In view of the sodium channel deficiency in med(J) mice, the beneficial effects of the sodium channel blocker phenytoin was an unexpected finding. By immunohistochemical examinations, the density of nigral dopaminergic neurons was found to be unaltered, substantiating the absence of pathomorphological abnormalities within the brain of med(J) mice shown by previous studies. With the exception of muscle weakness, many of the features of the med(J) mouse are similar to human idiopathic dystonia.

Dopamine D(1) and D(2) receptors in the forebrain of dystonia musculorum mutant mice: an autoradiographic survey in relation to dopamine contents

Dystonia musculorum (dt(J)/dt(J)) mutant mice suffer from a degeneration of spinocerebellar tracts as well as a dystrophy of peripheral sensory tracts. This neurological mutant has been proposed as an animal model of human cerebellar ataxia, in particular of the Friedreich's type; thus, it was deemed of interest to examine the endogenous contents of dopamine (DA) and metabolites as well as the distribution of DA receptors of the D(1) and D(2) subtypes, in order to delimit the biochemical characteristics of this pathological disorder, and determine an eventual dopaminergic dysfunction in this mutant. Tissue DA and its major metabolites 3, 4-dihydroxyphenylacetic acid, homovanillic acid and 3-methoxytyramine were measured by HPLC coupled to electrochemical detection in six cortical regions, in four divisions of rostral neostriatum and two halves of caudal neostriatum, as well as in olfactory bulb, nucleus accumbens, septum, amygdala, hippocampus, thalamus, hypothalamus, brainstem, cerebellum, substantia nigra, and ventral tegmental area. The only significant difference between dt(J)/dt(J) mice and wild-type controls was an increase in hypothalamic DA contents (+47%). Quantitative autoradiography with [(3)H]SCH23390 and [(3)H]raclopride, to label D(1) and D(2) receptors, respectively, revealed only moderate changes in receptor densities in a few localized regions. In dt(J)/dt(J) mutants, D(1) receptor numbers were found to be higher in thalamus (+27%) as well as in the medio-dorsal (+16%) and in the latero-dorsal (+16%) quadrants of rostral neostriatum, while D(2) receptor densities were greater in the medio-ventral (+32%) and the latero-dorsal (+17%) quadrants. The present results indicate an overall conservation of dopaminergic functions, albeit the few localized sites of increased D(1) and D(2) receptor densities, and that are seemingly independent of the DA innervation pattern, as revealed by the tissue measurements of DA and metabolites. They also rule out a major pathology linked to deficits in DA neurotransmission, and validate this mutant as an animal model of human cerebellar ataxia, probably of the Friedreich type.

Calcium channel agonists and dystonia in the mouse

Systemic administration of the L-type calcium channel agonists +/-Bay K 8644 or FPL 64176 causes a characteristic pattern of motor dysfunction in normal C57BL/6J mice that resembles generalized dystonia. There is no associated change in the electroencephalogram, confirming that the motor disorder does not reflect epileptic seizures. However, the electromyogram reveals an increase in baseline motor unit activity with prolonged phasic discharges consistent with dystonia. The duration and severity of dystonia is dependent on the dose administered and the age of the animal at testing. The effects are transient, with the return of normal motor behavior 1-4 hours after treatment. Similar effects can be provoked by intracerebral administration of small amounts of the drugs, indicating a centrally mediated response. Dystonia can be attenuated by co-administration of dihydropyridine L-type calcium channel antagonists (nifedipine, nimodipine, and nitrendipine) but not by non-dihydropyridine antagonists (diltiazem, verapamil, and flunarizine). These results implicate abnormal function of L-type calcium channels in the expression of dystonia in this model.

Piracetam and levetiracetam, two pyrrolidone derivatives, exert antidystonic activity in a hamster model of paroxysmal dystonia

The effects of the nootropic drug piracetam and its analogue, the antiepileptic drug levetiracetam (ucb L059) on severity of dystonic attacks were studied in a mutant hamster model of idiopathic generalized dystonia. Both drugs significantly decreased the severity of dystonia. In contrast to seizure models, in which levetiracetam is much more potent as an anticonvulsant than piracetam, the antidystonic potency of levetiracetam was only moderately higher than that of piracetam. The antidystonic activity of piracetam and levetiracetam was not associated with any behavioral side effects. The data indicate that piracetam and levetiracetam are interesting novel treatments for idiopathic dystonia.

Subconvulsive dose of pentylenetetrazole increases the firing rate of substantia nigra pars reticulata neurons in dystonic but not in nondystonic hamsters

Dystonic attacks, including twisting movements, can be initiated by mild stress in mutant (gene symbol dt(sz)) Syrian golden hamsters, an animal model of idiopathic paroxysmal dystonia. Previous studies suggested that dysfunctions in basal ganglia, which are not restricted to periods of attacks, are involved in the dystonic syndrome in mutant hamsters. Therefore, in the present study in anesthetized animals, we examined whether the spontaneous firing rate of extracellularly recorded neurons of the substantia nigra pars reticulata (SNr) differs between dt(sz) and age-matched nondystonic control hamsters. Furthermore, we investigated the responsiveness of these nondopaminergic, presumably GABAergic neurons to a subconvulsive dose (25mg/kg i.p.) of systemically applied pentylenetetrazole (PTZ), which exerts prodystonic effects in mutant hamsters. The mean basal (spontaneous) firing rate of SNr neurons was not altered in mutant hamsters. However, within 5 min after i.p. injection of PTZ, the mean firing rate of SNr neurons significantly increased to about 160% of predrug control values in dt(sz) but not in control hamsters. Although the present study failed to reveal changes in the basal firing rate of SNr neurons in mutant hamsters, the abnormal response to PTZ is in line with previous pharmacological and biochemical data indicating disturbed function of the GABAergic system.

Alterations in spontaneous single unit activity of striatal subdivisions during ontogenesis in mutant dystonic hamsters

The pathophysiology of idiopathic dystonia, characterized by sustained twisting movements and postures, is still unknown. Clinically, however, the basal ganglia are thought to be the main causative origin of idiopathic dystonia. In the dtsz hamster, a genetic animal model for idiopathic paroxysmal dystonia, the attacks occur in response to mild stress and the severity of dystonia is age-dependent. Previous autoradiographic studies in the dtsz hamster revealed a decreased dopamine D1 and D2 receptor binding and an increased [3H]-2-deoxyglucose uptake in the dorsomedial caudate-putamen (CPu), a region supposed to be critically involved in dystonia. Therefore, we were interested whether the spontaneous firing rate of dorsomedial striatal neurons is age-dependently altered in comparison to age-matched non-dystonic control hamsters. Extracellular recordings of spontaneous single unit activity of dorsomedial and ventromedial Type II striatal neurons, i.e., biphasic positive-negative action potentials, from fentanyl anesthetized animals revealed a drastically increased firing rate in the dorsomedial CPu of mutants during age of maximum severity of dystonia. In post-dystonic dtsz hamsters, i.e., after remission of stress-inducible dystonia, no significant differences regarding the dorsomedial CPu could be obtained. We conclude that the dorsomedial subregion of the CPu seems to be critically involved in the dystonic syndrome of dtsz hamsters and that a transiently reduced inhibitory control over excitatory cortico-striatal processes, possibly due to an altered development of GABAergic inhibition, occurs during ontogenesis in dtsz hamsters.

[3H]-2-deoxyglucose uptake study in mutant dystonic hamsters: abnormalities in discrete brain regions of the motor system

The genetically dystonic (dtSZ) hamster, an animal model of idiopathic paroxysmal dystonia, displays attacks of generalized twisting movements and abnormal postures of limbs and trunk either spontaneously or in response to mild stress. This experimental model may be helpful to give insights into the pathophysiology of idiopathic dystonia in man. In the present study, the regional uptake of [3H]-2-deoxyglucose (2-DG) was examined in brains (75 brain regions) of dtSZ hamsters during the expression of severe dystonia. 2-DG autoradiography revealed significant changes of 2-DG uptake in discrete brain regions of dtSZ hamsters compared with age-matched, nondystonic control hamsters. In dystonic hamsters, a dramatic increase of 2-DG uptake was observed in the red nucleus (159% over control). Furthermore, enhanced 2-DG uptake was found in the ventromedial, ventrolateral, and anteroventral nuclei of the thalamus (19-42%) and in the medial vestibular nucleus (23%). A significant decrease in 2-DG uptake in deep cerebellar nuclei (-30%) may be the result of decreased synaptic activity of GABAergic neurons within these structures resulting in enhanced excitatory output to red nucleus, thalamic, and vestibular nuclei. In dtSZ hamsters, the 2-DG uptake was not significantly altered overall within the basal ganglia. Significant increases of 14% were, however, found in discrete parts of the caudate putamen in which recent studies revealed changes of dopamine receptors. Altered neural activity within the basal ganglia may therefore contribute to increased 2-DG uptake in the ventral thalamic nuclei as well as to decreased 2-DG uptake (-13%) found in the reticular thalamic nucleus. Although the present data are in line with the concept that abnormal thalamocortical activity seems to be critically involved in the dystonic syndrome, altered activities in other motor areas than output structures of the basal ganglia, such as in the red nucleus, may contribute to clinical manifestation of dystonia in mutant hamsters.

Quantitative EEG analysis of depth electrode recordings from several brain regions of mutant hamsters with paroxysmal dystonia discloses frequency changes in the basal ganglia

Computerized EEG spectral analyses of depth electrode recordings from striatum (caudate/putamen; CPu), globus pallidus (GP), and parietal cortex (pCtx) were performed before and after dystonic attacks in freely moving mutant dt(sz) hamsters with paroxysmal dystonia. In these hamsters, sustained attacks of abnormal movements and postures can be reproducibly induced by stress, such as placing the animals in a new environment. Data recorded from mutant hamsters were compared with recordings from age-matched nondystonic control hamsters. The predominant EEG changes in CPu and GP of dystonic hamsters were significant decreases in the high-frequency beta2 range and there was a tendency to increase in delta and theta activities. These changes were seen both before and after onset of dystonic attacks, indicating a permanent disturbance of neural activities in the basal ganglia of dystonic animals. No such changes were seen in the pCtx. Furthermore, no epileptic or epileptiform activity was seen in any of the recordings, substantiating a previous notion from cortical and hippocampal recordings that paroxysmal dystonia in these mutant hamsters has no epileptogenic basis. The present finding of abnormal synchronization of neural activity in the CPu and GP of dystonic hamsters adds to the belief that the striatopallidal-thalamocortical circuit is the most likely site in which to search for the unknown defect in primary (idiopathic) dystonia. As suggested by this study, quantitative EEG analysis can increase the likelihood of detecting subtle EEG abnormalities in different types of idiopathic dystonia and thereby improves our understanding of the pathogenetic mechanisms of this movement disorder.

Pathology of idiopathic dystonia: findings from genetic animal models

Dystonia is a common movement disorder which is thought to represent a disease of the basal ganglia. However, the pathogenesis of the idiopathic dystonias, i.e. the neuroanatomic and neurochemical basis, is still a mystery. Research in dystonia is complicated by the existence of various phenotypic and genotypic subtypes of idiopathic dystonia, probably related to heterogeneous dysfunctions. In neurological diseases in which no obvious neuronal degeneration can be found, such as in idiopathic dystonia, the identification of a primary defect is difficult, because of the large number of chemically distinct, but functionally interrelated, neurotransmitter systems in the brain. The variable response to pharmacological agents in patients with idiopathic dystonia supports the notion that the underlying biochemical dysfunctions vary in the subtypes of idiopathic dystonia. Hence, in basic research it is important to clearly define the involved type of dystonia. Animal models of dystonias were described as limited. However, over the last years, there has been considerable progress in the evaluation of animal models for different types of dystonia. Apart from animal models of symptomatic dystonia, genetic animal models with inherited dystonia which occurs in the absence of pathomorphological alterations in brain and spinal cord are describe. This review will focus mainly on genetic animal models of different idiopathic dystonias and pathophysiological findings. In particular, in the case of the mutant dystonic (dt) rat, a model of generalized dystonia, and in the case of the genetically dystonic hamster (dt(sz)), a model of paroxysmal dystonic choreoathetosis has been used, as these show great promise in contributing to the identification of underlying mechanisms in idiopathic dystonias, although even a proper animal model will probably never be equivalent to a human disease. Several pathophysiological findings from animal models are in line with clinical observations in dystonic patients, indicating abnormalities not only in the basal ganglia and thalamic nuclei, but also in the cerebellum and brainstem. Through clinical studies and neurochemical data several similarities were found in the genetic animal models, although the current data indicates different defects in dystonic animals which is consistent with the notion that dystonia is a heterogenous disorder. Different supraspinal dysfunctions appear to lead to manifestation of dystonic movements and postures. In addition to increasing our understanding of the pathophysiology of idiopathic dystonia, animal models may help to improve therapeutic strategies for this movement disorder.

Prodystonic effects of riluzole in an animal model of idiopathic dystonia related to decreased total power in the red nucleus?

The effects of riluzole (2-amino-6-trifluoromethoxy benzothiazole) on the severity of dystonia were examined in mutant hamsters (dtsz), an animal model of idiopathic dystonia in which dystonic attacks can be age dependently induced by mild stress. Previous studies in hamsters have shown antidystonic activity of various glutamate receptor antagonists whereas lamotrigine, considered as an inhibitor of glutamate release, exerted prodystonic effects. The latter, unexpected, finding prompted us to investigate riluzole which is thought to possess antiglutamatergic properties with mechanisms similar to those of lamotrigine. Riluzole (2, 5, 10 or 20 mg/kg i.p.) dose dependently decreased the latency to onset of dystonic attacks. A dose of 10 or 20 mg/kg significantly increased the severity of dystonia. Even in dtsz hamsters older than 70 days, i.e., after spontaneous remission of age-dependent dystonia, riluzole (10 or 20 mg/kg) provoked severe long-lasting (> 4 h) dystonic attacks. At a dose of 20 mg/kg, riluzole provoked short-lasting (< 1 h) dystonic disturbances also in non-dystonic control hamsters. Electroencephalographic recordings from depth electrodes in the red nucleus, where recent studies have shown abnormal neural activity before and during dystonic attacks in dtsz hamsters, revealed that riluzole (10 mg/kg) tended to cause a further decrease of the total power in dtsz hamsters and significantly reduced the total power in control animals. This finding may indicate that the prodystonic effects of riluzole are related to alterations of rubrospinal activity. With regard to antidystonic effects of glutamate receptor antagonists demonstrated in previous studies, the prodystonic effects of riluzole and, as shown by recent experiments, of lamotrigine also, may be due to the lack of selectivity of these drugs to inhibit glutamate release.

The electrical activity is impaired in the red nucleus of dt(sz) mutant hamsters with paroxysmal dystonia: an EEG power spectrum analysis of depth electrode recordings

The genetically dystonic (dt(sz)) hamster is an animal model of paroxysmal dystonia that displays attacks of sustained abnormal movements and postures in response to mild stress. Dysfunctions within the basal ganglia may be critically involved in the pathophysiology of dystonia in mutant hamsters. Furthermore, previous observations from autoradiographic studies pointed to an altered neural activity in the red nucleus (RN). In the present study, computerized EEG spectral analysis of depth electrode recordings from the RN was performed before and after dystonic attacks in freely moving dt(sz) hamsters and compared to age-matched non-dystonic controls. No epileptic activity was seen in any of the recordings, substantiating previous notions that paroxysmal dystonia in these mutants has no epileptogenic basis. The predominant EEG changes in RN of dystonic hamsters were a decrease in total power over the range of 1.25-42.00 Hz, a decrease in maximum power and a shift of frequency at maximum power to lower frequencies. With regard to selected frequency bands, there was a decrease in the alpha, beta and gamma band. Although the observed changes of neural activity in the RN are probably based on a primary dysfunction in related structures, the present data demonstrate its importance in the expression of dystonic movements.

Stuttering may be a type of action dystonia

We observed abnormal involuntary movements, involving principally the facial and neck muscles, in 23 patients with stuttering. These movements were similar to involuntary movements seen in distinct dystonic syndromes. There was a history of stuttering in the first degree relatives of six patients. The association of stuttering with degenerative neurologic disorders and focal brain lesions, cerebral blood flow changes in patients with developmental stuttering, its occurrence as a side effect of centrally acting drugs, induction and alleviation of stuttering by mechanical perturbation, or by electrical stimulation of the thalamus, a strong genetic predisposition with male preponderance, and the statistically significant occurrence of stuttering in the family history of patients with idiopathic torsion dystonia suggest an organic basis for developmental stuttering. These findings and the reported similarities between the involuntary movements associated with stuttering and dystonic involuntary movements support the hypothesis that stuttering is a form of segmental or focal action dystonia.

Antidystonic effects of L-type Ca2+ channel antagonists in a hamster model of idiopathic dystonia

The effects of selective L-type Ca2+ channel antagonists on severity of dystonia were investigated in a mutant hamster model of idiopathic generalized dystonia. Nimodipine and diltiazem significantly decreased the severity of dystonia. Nimodipine was more potent in this respect and did not cause any behavioral side effects. The present data therefore suggest that Ca2+ channel antagonists could be useful in the treatment of idiopathic dystonia. The antidystonic effect of diltiazem and nimodipine may be based on their antidopaminergic action. However, the lack of significant effects of the L-type channel agonist (+/-)-BAY k-8644 (1-5 mg/kg; methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoro-methylphenyl) -pyridine-5-carboxylate)) on severity of dystonia may indicate that voltage-gated Ca2+ channels are not critically involved in the pathophysiology of dystonia in mutant hamsters.

Increased levels of kynurenic acid in brains of genetically dystonic hamsters

Recent pharmacological studies have shown antidystonic effects of NMDA and non-NMDA receptor antagonists in an inbred line of Syrian hamsters (dt(sz)) with primary generalized dystonia, i.e. a neurological syndrome of sustained muscle contractions which occurs in the absence of any pathomorphological alterations. This prompted us to examine the levels of kynurenic acid (KYNA), the endogenous broad spectrum antagonist of the excitatory amino acid receptors. The concentrations of KYNA were determined by HPLC in forebrain, cerebellum, brainstem and plasma in dystonic hamsters and age-matched non-dystonic controls. Dystonia in mutant hamsters is transient and disappears completely at the age of 70 days. In order to examine if neurochemical changes are associated with dystonia, KYNA was determined at the age of maximum severity (30 days) and after remission (70 days). The levels of KYNA were significantly increased in forebrain, cerebellum and brainstem (37-130 percent) in dystonic hamsters at the age of maximum severity of dystonia (30 days of life) compared to both a genetically related non-dystonic inbred line and a non-related outbred line of hamsters. The increase of KYNA in brain regions was accompanied by enhanced plasma levels. However, there was no correlation between brain and plasma levels. Since the changes in KYNA levels disappeared in parallel with dystonia (70 days), the present data provide further evidence that abnormal activity of excitatory amino acids may be pathogenetically involved in dystonia in mutant hamsters. With regard to the recent finding of antidystonic effects of glutamate receptor antagonists the increased levels of kynurenic acid may be interpreted as a counteracting process to an overactivity of the glutamatergic system.

Alterations in the brain GABAA/benzodiazepine receptor-chloride ionophore complex in a genetic model of paroxysmal dystonia: a quantitative autoradiographic analysis

Dystonia is a relatively common syndrome of sustained muscle contractions, frequently causing twisting and repetitive movements or abnormal postures. The most frequent type of dystonia is idiopathic generalized dystonia, whose pathophysiology is largely unknown. In this respect, mutant animal strains with inborn dystonia may be helpful to elucidate the pathophysiological defects involved in idiopathic dystonia. The genetically dystonic (dtsz) hamster is an animal model of paroxysmal dystonia that displays attacks of generalized dystonia either spontaneously or in response to mild environmental stimuli. In the present study, a quantitative autoradiographic analysis of ligand binding to different sites of the GABAA/benzodiazepine receptor-chloride ionophore complex was carried out in 123 brain areas from genetically dystonic mutant hamsters and age-matched control hamsters. Animals were killed 2 weeks after their last dystonic attack. Analysis of the GABA-binding site of the receptor complex, using the ligand [3H]muscimol, and the benzodiazepine site labelled with [3H]flunitrazepam revealed no significant alterations in the binding of either ligand in any of the brain regions examined. In contrast, widespread changes were observed in binding densities of [35S]t-butylbicyclophosphorothionate ([35S]t-butylbicyclophosphorothionate), which labels the picrotoxinin site of the GABAA receptor-chloride ionophore complex. Significantly increased [35S]t-butylbicyclophosphorothionate binding was found in several parts of the thalamus, cortex, and hippocampus as well as in the red nucleus, the subthalamic nucleus, and the granular layer of the cerebellum. Since high-affinity [35S]TBPS binding is thought to represent the closed conformation of the GABA-gated chloride ionophore, increased TBPS binding would indicate an impaired GABAergic function. The study is consistent with the concept that dystonia is caused by impaired connections between the basal ganglia, the thalamus, and frontal association areas. The data on increased [35S]TBPS binding are the first evidence implicating alterations in the GABA-gated chloride ion channel function in a movement disorder, i.e. idiopathic generalized dystonia.

The novel antiepileptic drug, lamotrigine, exerts prodystonic effects in a mutant hamster model of generalized dystonia

Recent findings of antidystonic effects of NMDA and non-NMDA receptor antagonists in an inbred line of Syrian hamsters with primary generalized dystonia prompted us to investigate the effects of lamotrigine, an inhibitor of veratrine-induced glutamate release, on the severity of dystonia in mutant hamsters. In mutant dystonic hamsters the dystonic attacks which can be induced by mild environmental stimuli or handling are age-dependent with maximum severity between days 30 and 40 of life (maximum period). Thereafter the severity of dystonia slowly declines (post-maximum period) until the susceptibility to induction of dystonia disappears completely at an age of about 70 days. Lamotrigine (5.0, 10.0 or 30.0 mg/kg i.p.) dose dependently decreased the latency to onset of dystonic attacks. Furthermore, at a dose of 30 mg/kg the dystonic attacks were aggravated when lamotrigine was administered during the max and post-max period. Even in mutant hamsters older than 70 days, i.e. after spontaneous remission of dystonia, and in an inbred line of non-dystonic Syrian hamsters with genetic origin similar to the mutant hamsters, lamotrigine (10.0 or 30.0 mg/kg i.p. and 30.0 mg/kg p.o.) provoked dystonic disturbances. In a genetically different outbred line of Syrian hamsters, lamotrigine did not cause dystonic movements. The unexpected finding that lamotrigine exerts prodystonic effects in genetically susceptible hamsters may be due to the lack of selectivity of lamotrigine to block glutamate release. Tentatively, simultaneous inhibition of GABA (gamma-aminobutyric acid) release might be critically involved in the prodystonic activity of lamotrigine.

(+)-WIN 55,212-2, a novel cannabinoid receptor agonist, exerts antidystonic effects in mutant dystonic hamsters

The effects of the novel high affinity cannabinoid receptor agonist (+)-WIN 55,212-2 ((R)-4,5-dihydro-2-methyl-4(4-morphoinylmethyl)-1-(1-naphthalen ylcarbonyl)-6H-pyrrolo[3,2,1-ij]quinolin-6-one) on severity of dystonia were investigated in mutant Syrian hamsters with primary generalized dystonia. Following injections of (+)-WIN 55,212-2 (1.0-5.0 mg/kg i.p.) a dose-dependent reduction of the severity of dystonia was observed. At antidystonic doses (2.5 and 5.0 mg/kg i.p.) (+)-WIN 55,212-2 caused a reduction of spontaneous motor activity and catalepsy. 1 mg/kg of (+)-WIN 55,212-2 exhibited neither antidystonic effects nor any side effects. However, the coadministration of 1.0 mg/kg (+)-WIN 55,212-2 with an ineffective dose of diazepam (0.1 mg/kg i.p.) exerted antidystonic effects in the absence of severe side effects. Although psychotropic effects of cannabinoids, such as (+)-WIN 55,212-2, limit the therapeutical utility of cannabinoids, the present data indicate that cannabinoids exert antidystonic effects and that low doses of cannabinoids may increase antidystonic efficacy of benzodiazepines.

Marked regional disturbances in brain metabolism of monoaminergic neurotransmitters in the genetically dystonic hamster

The genetically dystonic hamster is an animal model of idiopathic (torsion) dystonia that displays sustained abnormal movements and postures either spontaneously or in response to mild environmental stimuli. Since dystonic attacks occur in the absence of any lesion which can be defined by standard histopathological techniques in the central nervous system, the presumption is that dystonia in mutant hamsters is due to some biochemical disturbance activity in brain regions involved in motor functions. In the present study we determined the monoamine neurotransmitters dopamine, noradrenaline, adrenaline and serotonin (5-HT) as well as the dopamine metabolites homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC) and the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) in 14 brain regions of male and female dystonic hamsters and age-matched non-dystonic controls. All determinations were done at age of maximum susceptibility for induction of dystonic attacks. Since both genders of dystonic hamsters exhibit the same characteristic age-dependent time-course of dystonia, it was assumed that only those biochemical alterations are critically involved in dystonia that occur in both female and male animals. The neurochemical data show that except for a significant decrease of dopamine and HVA in the olfactory bulb, no consistent changes in dopamine metabolism are present across brain regions, including the basal ganglia, of dystonic hamsters. In contrast, marked increases in noradrenaline and 5-HT or 5-HIAA were found in several brain areas of both genders, indicating an enhanced activity of central noradrenergic and serotonergic nuclei in the brainstem. The present results suggest the involvement of noradrenergic and serotonergic neural systems in the pathophysiology of dystonia. Based on these data and recent theoretical suggestions from clinical findings, drugs which reduce noradrenergic and serotonergic neurotransmission may be a useful therapeutic approach to dystonia.

The atypical neuroleptic, clozapine, exerts antidystonic activity in a mutant hamster model. Comparison with haloperidol

The effects of the atypical neuroleptic clozapine were studied in an inbred line of Syrian golden hamsters with generalized dystonia, i.e. a frequent movement disorder in humans. The effects of clozapine were compared with those of the classical neuroleptic, haloperidol. Clozapine, 7.5-20 mg/kg i.p., potently reduced the severity of dystonic attacks in the mutant hamster model, but induced marked sedation at these doses. Lower doses were ineffective. Haloperidol, 0.5 mg/kg i.p., significantly reduced the severity of dystonia without marked sedation. The finding that clozapine possesses antidystonic potency similar to that of haloperidol in a genetic model of dystonia might suggest that this atypical neuroleptic is an effective alternative in the treatment of dystonic patients who respond to neuroleptics, particularly because of the clinical evidence that clozapine is almost devoid of extrapyramidal adverse effects.

The glycine/NMDA receptor ligand (+)-HA-966 but not D-cycloserine has potent antidystonic efficacy in a genetic animal model of dystonia

The effects of R-(+)-HA-966 ((+)-3-amino-1-hydroxypyrrolid-2-one), a low-efficacy partial agonist of the glycine modulatory site of the NMDA receptor complex, were studied in an inbred line of Syrian golden hamsters with generalized dystonia, a frequent movement disorder in humans. The effects of R-(+)-HA-966 were compared with those of D-cycloserine, a glycine/NMDA receptor ligand with higher intrinsic activity. R-(+)-HA-966, 30-60 mg/kg i.p., potently reduced the severity of dystonic attacks in the mutant hamster model of dystonia without inducing any behavioural adverse effects. D-Cycloserine did not exert antidystonic activity at i.p. doses of 10-40 mg/kg, which might be due to its much higher intrinsic activity at the glycine site. The data indicate that the antidystonic effect of (+)-HA-966 is related to antagonism of NMDA receptor-mediated excitatory neurotransmission.

The AMPA receptor antagonist NBQX exerts antidystonic effects in an animal model of idiopathic dystonia

The effects of the AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate) antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline) were studied in an inbred line of Syrian golden hamsters with paroxysmal dystonia. The severity of dystonia in these mutant hamsters was significantly reduced by NBQX at doses of 10-20 mg/kg i.p. Coadministration of the transport inhibitor probenecid prolonged the antidystonic action of NBQX, indicating that NBQX may be rapidly eliminated by a process sensitive to probenecid. A similar potent and long-lasting antidystonic effect was obtained when NBQX was administered as an aqueous suspension rather than an aqueous solution, which may be explained by retarded absorption of NBQX after its injection as a suspension. The antidystonic activity of the AMPA antagonist NBQX may indicate that an overactivity of excitatory acidergic neurotransmission is involved in the pathophysiology of dystonia in genetically dystonic hamsters.

Abnormal cerebellar output in rats with an inherited movement disorder

Biochemical and metabolic mapping techniques have consistently identified the deep cerebellar nuclei (DCN) of the genetically dystonic rat as a site of abnormality. Extracellular single-unit recording techniques were used to assess the functional significance of these findings in affected rats and normal littermates between 16 and 25 days of age. Cells in the medial nucleus of the mutant rats had significantly increased spontaneous firing rates in comparison with cells from normal rats. In both the medial and the interpositus nuclei, cells from the mutants fired more rhythmically than those from the normal rats. When harmaline was administered systemically to activate the olivo-cerebellar system, in normal rats, increased firing rate and bursting patterns of activity were seen. There was no reliable change in the average firing rate or rhythmicity of cells in the medial nucleus of the dystonic rats, although previous studies have shown that harmaline activates neurons in the inferior olive in the mutants. It is likely that naturally stimulated olivary activity also fails to modulate cerebellar output in this model of inherited movement disorder. Anatomical studies did not reveal any consistent changes in the number of Purkinje cells, the volume of the DCN, or the soma size of DCN neurons. Since the electrophysiological findings cannot be ascribed to a loss of the Purkinje cells that normally provide an inhibitory input to the cerebellar nuclei, the results of this study indicate the presence of a functional defect in the control of cerebellar output in the dystonic rat that accounts for the failure of these animals to display harmaline tremor and which may be critical to the motor syndrome.

Abnormalities in Amino Acid Neurotransmitters in Discrete Brain Regions of Genetically Dystonic Hamsters

The concentrations of 11 amino acids, including the neurotransmitters gamma-aminobutyric acid, glutamate, aspartate, glycine, and taurine, were determined by HPLC in 12 brain regions of genetically dystonic (dtSZ) hamsters and age-matched nondystonic controls. Since dystonia in mutant dtSZ hamsters is transient and disappears after about 70 days of age, amino acids were determined at the age of maximum severity of dystonia (30-40 days) and after disappearance of the disease, to examine which neurochemical changes were related to dystonia. In dtSZ hamsters with the maximum severity of dystonia, significant changes in concentrations of the neurotransmitters gamma-aminobutyric acid, glutamate, aspartate, and taurine were found in several regions involved in motor functions, e.g., cerebellum, thalamus, and corpus striatum. Most of these changes were not permanent but disappeared in parallel with dystonia, implicating a causal relationship between altered aminoacidergic neurotransmission and dystonia in mutant dtSZ hamsters.

Effects of pharmacological manipulation of dopaminergic and cholinergic neurotransmission in genetically dystonic hamsters

In an inbred line of Syrian hamsters, attacks of sustained dystonic postures of the limbs and trunk can be initiated by handling or mild environmental stimuli (e.g. new cage). The severity of the dystonic syndrome in these mutant hamsters (gene symbol dtSZ) is age-dependent, with a peak at about 30-40 days of age. A scoring system for grading the type and severity of the dystonic attacks can be used to study the activity of drugs against dystonic movements with individual pre- and post-drug vehicle trials as control. The effects of drugs which alter dopaminergic or cholinergic functions in the brain were studied in selectively bred dystonic hamsters and age-matched non-dystonic controls. The dopamine precursor levodopa (injected together with carbidopa) and the dopamine receptor agonist apomorphine increased the severity of dystonia in hamsters when administered prior to the age of maximum severity of dystonia. A very similar effect was observed with the cholinomimetic pilocarpine. In contrast, the dopamine receptor antagonist haloperidol caused a marked overall reduction in dystonic movements. Anticholinergic drugs, i.e. trihexyphenidyl and biperiden, increased the latency to onset of the dystonic attack, but did not reduce its severity. No differences were observed between dystonic and non-dystonic hamsters with respect to extent and duration of stereotypies induced by dopaminergic and cholinergic drugs or hypolocomotion and catalepsy produced by haloperidol. The data suggest that dopaminergic hyperactivity might be involved in the pathophysiology of dystonia in dtSZ mutant hamsters.

[Spasmodic torticollis and frontal meningioma]

A 57 year-old man developed a spasmodic torticollis with involuntary deviation of the head to the right-side. He had a left paramedian frontal meningioma. The association of spasmodic torticollis and other movement disorders has been reported with contralateral lesions in the basal ganglia. Its occurrence in association to a frontal lesion appears to be much less frequent suggesting a possible disorder of frontostriatal connections.

Enhanced sensitivity to quipazine in the genetically dystonic rat (dt)

Both normal and genetically dystonic (dt) rats show a high-frequency forepaw tremor in response to systemic administration of the serotonin (5-HT) agonist quipazine at 8 days of age. The response declines with age in normal, but not dystonic, rats. By 16 days of age and after the development of a generalized movement disorder, the dystonic rat exhibits enhanced sensitivity to the tremorogenic effects of the drug in comparison with normal rats. Tremor was blocked by pretreatment with ketanserin, suggesting that it is mediated by 5-HT2 receptors. The dystonic rat has previously been shown to be insensitive to the tremorogenic effects of harmaline, a drug presumed to act indirectly through serotonergic neurons. This finding, coupled with the increased sensitivity to quipazine, suggests the presence of an abnormality in serotonergic systems in the mutants. Since there is evidence of abnormality in the olivo-cerebellar system in the dystonic rat, the alternative hypothesis that a nonserotonergic defect in the olivo-cerebellar system accounts for both the failure of behavioral response to harmaline and the persistent expression of a response to quipazine is also discussed.

Tremor of tongue and dysarthria as the sole manifestation of Wilson's disease

Neurological form of Wilson's disease in children usually manifests with dystonia as the initial sign. Tremor of extremities, dysarthria and ataxia may follow. Copper deposits in gray and white matter along with the basal ganglia. A pediatric case presenting with tremor of the tongue and dysarthria as the only findings of Wilson's disease is reported. Tongue tremor should also be taken into notice within the basal ganglia symptomatology.