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

Short-term stimulations of the entopeduncular nucleus induce cerebellar changes of c-Fos expression in an animal model of paroxysmal dystonia

Deep brain stimulation (DBS) of the globus pallidus internus (entopeduncular nucleus, EPN, in rodents) is important for the treatment of drug-refractory dystonia. The pathophysiology of this movement disorder and the mechanisms of DBS are largely unknown. Insights into the mechanisms of DBS in animal models of dystonia can be helpful for optimization of DBS and add-on therapeutics. We recently found that short-term EPN-DBS with 130 Hz (50 µA, 60 µs) for 3 h improved dystonia in dtsz hamsters and reduced spontaneous excitatory cortico-striatal activity in brain slices of this model, indicating fast effects on synaptic plasticity. Therefore, in the present study, we examined if these effects are related to changes of c-Fos, a marker of neuronal activity, in brains derived from dtsz hamsters after these short-term DBS or sham stimulations. After DBS vs. sham, c-Fos intensity was increased around the electrode, but the number of c-Fos+ cells was not altered within the whole EPN and projection areas (habenula, thalamus). DBS did not induce changes in striatal and cortical c-Fos+ cells as GABAergic (GAD67+ and parvalbumin-reactive) neurons in motor cortex and striatum. Unexpectedly, c-Fos+ cells were decreased in deep cerebellar nuclei (DCN) after DBS, suggesting that cerebellar changes may be involved in antidystonic effects already during short-term DBS. However, the present results do not exclude functional changes within the basal ganglia-thalamo-cortical network, which will be further investigated by long-term EPN stimulations. The present study indicates that the cerebellum deserves attention in ongoing examinations on the mechanisms of DBS in dystonia.

Alterations of M1 and M4 acetylcholine receptors in the genetically dystonic (dtsz) hamster and moderate antidystonic efficacy of M1 and M4 anticholinergics

Striatal cholinergic dysfunction has been suggested to play a critical role in the pathophysiology of dystonia. In the dt^sz hamster, a phenotypic model of paroxysmal dystonia, M1 antagonists exerted moderate antidystonic efficacy after acute systemic administration. In the present study, we examined the effects of the M4 preferring antagonist tropicamid and whether long-term systemic or acute intrastriatal injections of the M1 preferring antagonist trihexyphenidyl are more effective in mutant hamsters. Furthermore, M1 and M4 receptors were analyzed by autoradiography and immunohistochemistry. Tropicamide retarded the onset of dystonic attacks, as previously observed after acute systemic administration of trihexyphenidyl. Combined systemic administration of trihexyphenidyl (30mg/kg) and tropicamide (15mg/kg) reduced the severity in acute trials and delayed the onset of dystonia during long-term treatment. In contrast, acute striatal microinjections of trihexyphenidyl, tropicamid or the positive allosteric M4 receptor modulator VU0152100 did not exert significant effects. Receptor analyses revealed changes of M1 receptors in the dorsomedial striatum, suggesting that the cholinergic system is involved in abnormal striatal plasticity in dt^sz hamsters, but the pharmacological data argue against a crucial role on the phenotype in this animal model. However, antidystonic effects of tropicamide after systemic administration point to a novel therapeutic potential of M4 preferring anticholinergics for the treatment of dystonia.

Insights into the Pathology of the α3 Na(+)/K(+)-ATPase Ion Pump in Neurological Disorders; Lessons from Animal Models

The transmembrane Na(+)-/K(+) ATPase is located at the plasma membrane of all mammalian cells. The Na(+)-/K(+) ATPase utilizes energy from ATP hydrolysis to extrude three Na(+) cations and import two K(+) cations into the cell. The minimum constellation for an active Na(+)-/K(+) ATPase is one alpha (α) and one beta (β) subunit. Mammals express four α isoforms (α1-4), encoded by the ATP1A1-4 genes, respectively. The α1 isoform is ubiquitously expressed in the adult central nervous system (CNS) whereas α2 primarily is expressed in astrocytes and α3 in neurons. Na(+) and K(+) are the principal ions involved in action potential propagation during neuronal depolarization. The α1 and α3 Na(+)-/K(+) ATPases are therefore prime candidates for restoring neuronal membrane potential after depolarization and for maintaining neuronal excitability. The α3 isoform has approximately four-fold lower Na(+) affinity compared to α1 and is specifically required for rapid restoration of large transient increases in [Na(+)]i. Conditions associated with α3 deficiency are therefore likely aggravated by suprathreshold neuronal activity. The α3 isoform been suggested to support re-uptake of neurotransmitters. These processes are required for normal brain activity, and in fact autosomal dominant de novo mutations in ATP1A3 encoding the α3 isoform has been found to cause the three neurological diseases Rapid Onset Dystonia Parkinsonism (RDP), Alternating Hemiplegia of Childhood (AHC), and Cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS). All three diseases cause acute onset of neurological symptoms, but the predominant neurological manifestations differ with particularly early onset of hemiplegic/dystonic episodes and mental decline in AHC, ataxic encephalopathy and impairment of vision and hearing in CAPOS syndrome and late onset of dystonia/parkinsonism in RDP. Several mouse models have been generated to study the in vivo consequences of Atp1a3 modulation. The different mice show varying degrees of hyperactivity, gait problems, and learning disability as well as stress-induced seizures. With the advent of several Atp1a3-gene or chemically modified animal models that closely phenocopy many aspects of the human disorders, we will be able to reach a much better understanding of the etiology of RDP, AHC, and CAPOS syndrome.

Alternating hemiplegia of childhood-related neural and behavioural phenotypes in Na+,K+-ATPase α3 missense mutant mice

Missense mutations in ATP1A3 encoding Na⁺,K⁺-ATPase α3 have been identified as the primary cause of alternating hemiplegia of childhood (AHC), a motor disorder with onset typically before the age of 6 months. Affected children tend to be of short stature and can also have epilepsy, ataxia and learning disability. The Na⁺,K⁺-ATPase has a well-known role in maintaining electrochemical gradients across cell membranes, but our understanding of how the mutations cause AHC is limited. Myshkin mutant mice carry an amino acid change (I810N) that affects the same position in Na⁺,K⁺-ATPase α3 as I810S found in AHC. Using molecular modelling, we show that the Myshkin and AHC mutations display similarly severe structural impacts on Na⁺,K⁺-ATPase α3, including upon the K⁺ pore and predicted K⁺ binding sites. Behavioural analysis of Myshkin mice revealed phenotypic abnormalities similar to symptoms of AHC, including motor dysfunction and cognitive impairment. 2-DG imaging of Myshkin mice identified compromised thalamocortical functioning that includes a deficit in frontal cortex functioning (hypofrontality), directly mirroring that reported in AHC, along with reduced thalamocortical functional connectivity. Our results thus provide validation for missense mutations in Na⁺,K⁺-ATPase α3 as a cause of AHC, and highlight Myshkin mice as a starting point for the exploration of disease mechanisms and novel treatments in AHC.

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 DYT1 carrier state increases energy demand in the olivocerebellar network

DYT1 dystonia is caused by a GAG deletion in TOR1A, the gene which encodes torsinA. Gene expression studies in rodents and functional imaging studies in humans suggest that DYT1 dystonia may be a network disorder of neurodevelopmental origin. To generate high resolution metabolic maps of DYT1 dystonia and pinpoint dysregulated network elements, we performed 2-deoxyglucose autoradiography and cytochrome oxidase (CO) histochemistry in transgenic mice expressing human mutant (hMT1) torsinA and wild-type littermates. In comparison with controls, hMT1 mice showed increased glucose utilization (GU) in the inferior olive (IO) medial nucleus (IOM), IO dorsal accessory nucleus and substantia nigra compacta, and decreased GU in the medial globus pallidus (MGP) and lateral globus pallidus. The hMT1 mice showed increased CO activity in the IOM and Purkinje cell layer of cerebellar cortex, and decreased CO activity in the caudal caudate-putamen, substantia nigra reticulata and MGP. These findings suggest that (1) the DYT1 carrier state increases energy demand in the olivocerebellar network and (2) the IO may be a pivotal node for abnormal basal ganglia-cerebellar interactions in dystonia.

The neural substrates of rapid-onset Dystonia-Parkinsonism

Although dystonias are a common group of movement disorders the mechanisms by which brain dysfunction results in dystonia are not understood. Rapid-onset Dystonia-Parkinsonism is a hereditary dystonia caused by mutations in the ATP1A3 gene. Affected subjects can be symptom free for years but rapidly develop persistent dystonia and parkinsonism-like symptoms after a stressful experience. Using a mouse model here we show that an adverse interaction between the cerebellum and basal ganglia can account for the symptoms of the patients. The primary instigator of dystonia is the cerebellum whose aberrant activity alters basal ganglia function which in turn causes dystonia. This adverse interaction between the cerebellum and basal ganglia is mediated through a di-synaptic thalamic pathway which when severed is effective in alleviating dystonia. Our results provide a unifying hypothesis for the involvement of cerebellum and basal ganglia in generation of dystonia and suggest therapeutic strategies for the treatment of RDP.

Altered nicotinamide adenine dinucleotide (NADH) fluorescence in dt sz mutant hamsters reflects differences in striatal metabolism between severe and mild dystonia

The dt(sz) mutant hamster represents a unique rodent model of idiopathic paroxysmal dystonia. Previous data, collected post-mortem or in anesthetized hamsters under basal conditions, indicated the critical involvement of enhanced striatal neuronal activity. To assess the importance of an enhanced striatal neuronal activity directly during a dystonic episode, continuous monitoring of changes in brain metabolism and therefore neuronal activity indirectly in awake, freely moving animals is necessary. Determination of CNS metabolism by NADH measurement by laser-induced fluorescence spectroscopy in conscious dt(sz) and nondystonic control hamsters revealed reversible decreased NADH fluorescence during dystonic episodes. The degree of change corresponded to the severity of dystonia. This study represents the first application of this innovative method in freely moving animals exhibiting a movement disorder. Our data clearly confirm that the expression of paroxysmal dystonia in dt(sz) mutant hamsters is associated with enhanced striatal neuronal activity and further underscore the versatile application of NADH fluorescence measurements in neuroscience.

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.

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.

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.

Decreased adenosine receptor binding in dystonic brains of the dtsz mutant

In patients with paroxysmal non-kinesigenic dyskinesias, episodes of dystonia can be provoked by stress and also by methylxanthines (e.g. caffeine), which inhibit adenosine A(1)/A(2A) receptors. In the dt(sz) mutant hamster, a model of this movement disorder, adenosine A(1) receptor antagonists were previously found to worsen dystonia, while adenosine A(1) and A(2A) receptor agonists exerted pronounced beneficial effects. Therefore, in the present study, adenosine receptor A(1) and A(2A) binding was determined by autoradiographic analyses in dt(sz) hamsters under basal conditions, i.e. in the absence of a dystonic attack, and in a group of mutant hamsters which exhibited severe stress-induced dystonic attacks prior to kill. In comparison with non-dystonic control hamsters, [(3)H]DPCPX (8-cyclopentyl-1,3-dipropylxanthine) binding to adenosine A(1) receptors and [(3)H]CGS 21680 (2p-(2carboxyethylphen-ethylamino-5'-N-ethlycarboxamindoadenosine) binding to adenosine A(2A) receptors were significantly lower throughout the brain of dystonic animals. Under normal resting conditions, mutant hamsters showed significant decreases in adenosine A(1) (-12 to-42%) and in A(2A) (-19 to-34%) receptor binding compared with controls. Stressful stimulation increased adenosine A(1) and A(2A) receptor binding in almost all brain regions in both control and dystonic hamsters. The stress-induced increase was more marked in mutant hamsters, leading to a disappearance of differences in most regions compared with stimulated controls, except the striatum. In view of previous findings of striking beneficial effects of adenosine A(1) and A(2A) receptor agonists and of striatal dysfunctions in the dt(sz) mutant, the reduced adenosine receptor binding may be an important factor in the pathogenesis of paroxysmal dystonia.

Striatal increase of extracellular dopamine levels during dystonic episodes in a genetic model of paroxysmal dyskinesia

In vivo microdialysis was used to examine the levels of dopamine, serotonin, and their metabolites dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in the striatum of dt(sz) mutant hamsters, an animal model of paroxysmal dyskinesia, in which stress can precipitate dystonic episodes. Measurements were made under three different conditions in each animal: (1) at baseline in the absence of abnormal involuntary movements, (2) during an episode of paroxysmal dystonia precipitated by handling, and (3) during the recovery (postdystonic) period. In comparison to nondystonic control hamsters, which were treated in the same manner as dystonic animals, no changes could be detected under basal conditions, although the levels of DOPAC and HVA tended to be higher in mutant hamsters. Significantly elevated striatal levels of dopamine and DOPAC became evident during the period of stress-induced dystonic attacks in mutant hamsters. During dystonic episodes, dopamine levels were approximately 6.5-fold higher (followed by a 2.5-fold increase of DOPAC) in dt(sz) hamsters than in normal controls. Before the disappearance of dystonia, the levels of dopamine returned to basal concentrations in mutant hamsters. Consistent with previous pharmacologic findings, paroxysmal dystonia in mutant hamsters is associated with temporary increases of extracellular dopamine levels in the striatum.

Effects of rubral microinjections of muscimol and bicuculline in a genetic animal model of paroxysmal dystonia

Previous studies suggested that GABAergic dysfunctions within the red nucleus are involved in stress-inducible paroxysmal dystonia of the dt(sz) mutant hamster. In the present study, rubral microinjections of the GABAA receptor agonist muscimol exerted only moderate antidystonic effects and the antagonist bicuculline failed to show significant effects on the severity of dystonia. These data indicate that disturbed rubral GABAergic inhibition is not important for the manifestation of dystonia in the dt(sz) mutant.

Tracing the Neuroanatomical Profiles of Reward Pathways with Markers of Neuronal Activation

Functional neuroanatomical tools have played an important role in proposing which structures underlie brain stimulation reward circuitry. This review focuses on studies employing metabolic markers of neuronal and glial activation, including 2-deoxyglucose, cytochrome oxidase, and glycogen phosphorylase, and a marker of cellular activation, the immediate early gene c-fos. The principles underlying each method, their application to the study of brain stimulation reward, and their strengths and limitations are described. The usefulness of this strategy in identifying candidate structures, and the degree of overlap in the patterns of activation arising from different markers is addressed in detail. How these data have contributed to an understanding of the organization of reward circuitry and directed our thinking towards an alternative framework of neuronal arrangement is discussed in the final section.

Comparative analysis of acute and chronic administration of haloperidol and clozapine using [3H] 2-deoxyglucose metabolic mapping

In an effort to compare and contrast the mechanisms of action of typical and atypical antipsychotic drugs, [3H] 2-deoxyglucose metabolic mapping was employed following acute and chronic administration of haloperidol (1 mg/kg i.p. acute and 0.5 mg/kg i.p. chronic) and clozapine (20 mg/kg i.p., both acute and chronic). Optical density ratios (ODR) were measured in 62 brain structures. An overall decrease in ODR was observed in many of the regions analyzed. Acute haloperidol elicited significant decreases, particularly in the thalamus and hippocampus. Acute clozapine decreased glucose uptake in the caudate putamen, hippocampus, central gray, locus coreleus, and the thalamus. In both chronically treated haloperidol and clozapine animals, significant decreases in ODR were seen in the thalamus and hippocampal areas most dramatically, with other changes in the superior colliculus, retrospenial cortex, and the cerebellum. Clozapine caused significant effects in 32 nuclei acutely and only 19 nuclei chronically. Haloperidol caused significant effects in 23 nuclei acutely and 15 nuclei chronically. The pattern of change induced by haloperidol and clozapine were remarkably similar when considering their pharmacology is somewhat different. Both antipsychotics elicited fewer significant changes upon chronic administration.

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.

Regional decreases in NK-3, but not NK-1 tachykinin receptor binding in dystonic hamster (dt(sz)) brains

Although the pathophysiology of primary dystonias is currently unknown, it is thought to involve changes in the basal ganglia-thalamus-cortex circuit, particularly activity imbalances between direct and indirect striatal pathways. Substance P, a member of the tachykinin family of neuropeptides, is a major component in the direct pathway from striatum to basal ganglia output nuclei. In the present study quantitative autoradiography was used to examine changes in neurokinin-1 (NK-1) and neurokinin-3 (NK-3) receptors in mutant dystonic hamsters (dt(sz)), a well characterized model of paroxysmal dystonia. NK-1 receptors were labeled in 10 dystonic brains and 10 age-matched controls with 3 nM [(3)H]-[Sar(9), Met(O(2))(11)]-SP. NK-3 binding sites were labeled in adjacent sections with 2.5 nM [(3)H]senktide. NK-1 binding was found to be unaltered in 27 brain areas examined. In contrast, NK-3 binding was significantly reduced in layers 4 and 5 of the prefrontal (-46%), anterior cingulate (-42%) and parietal (-45%) cortices, ventromedial thalamus (-42%) and substantia nigra pars compacta (-36%) in dystonic brains compared to controls. The latter effects may be particularly relevant in view of evidence that activation of NK-3 receptors on dopaminergic neurons in the substantia nigra pars compacta can increase nigrostriatal dopaminergic activity. Since previous studies indicated that a reduced basal ganglia output in mutant hamsters is based on an overactivity of the direct pathway which also innervates substantia nigra pars compacta neurons, the decreased NK-3 binding could be related to a receptor down-regulation. The present finding of decreased NK-3 receptor density in the substantia nigra pars compacta, thalamic and cortical areas substantiates the hypothesis that disturbances of the basal ganglia-thalamus-cortex circuit play a critical role in the pathogenesis of paroxysmal dystonia.

Changes in AMPA receptor binding in an animal model of inborn paroxysmal dystonia

Previous pharmacological studies suggested that glutamatergic overactivity contributes to manifestation of dystonic attacks in mutant hamsters (dt(sz)), a model of idiopathic paroxysmal dystonia in which episodes of dystonia occur in response to stress. In the present study, [(3)H]AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate) receptor binding was determined by autoradiographic analyses in 41 brain (sub)regions of dt(sz) hamsters under basal conditions, i.e., in the absence of dystonia, and in a group of mutant hamsters that exhibited severe stress-induced dystonic attacks immediately prior to sacrifice. In comparison to nondystonic control hamsters the basal [(3)H]AMPA binding was significantly higher in the ventromedial and ventrolateral caudate putamen, the anterior cingulate cortex, the hippocampus, and the lateral septum of dystonic brains. During dystonic attacks the [(3)H]AMPA binding was significantly lower in the dorsomedial, dorsolateral, and posterior caudate putamen; the ventromedial thalamus; and the frontal cortex of mutant hamsters compared with control animals that were exposed to the same external stimulation. The basal increase in AMPA receptor density within limbic structures may contribute to the susceptibility of stress-inducible dystonic episodes in mutant hamsters. Since AMPA receptor activation is known to cause a fast reduction of the affinity and an internalization of postsynaptic AMPA receptors, the latter finding could reflect a glutamatergic overactivity within the striato-thalamo-cortical circuit during the expression of dystonia, which is in line with previous neurochemical and pharmacological data in dt(sz) hamsters.

Effects of locally administered pentylenetetrazole on nigral single unit activity and severity of dystonia in a genetic model of paroxysmal dystonia

The dt(sz) hamster is a well-established animal model of idiopathic paroxysmal dystonia. Previous investigations of this mutant have indicated dysfunctions of the gamma-aminobutyric acid (GABA)-ergic system within the basal ganglia. Systemic administration of the central stimulant pentylenetetrazole (PTZ) aggravated dystonia at subconvulsant doses, whereas GABA-mimetic drugs have beneficial effects in dt(sz) hamsters. GABA mimetics also provide clinical benefit in humans with idiopathic paroxysmal dystonia. The spontaneous discharge rates of substantia nigra pars reticulata (SNr) neurons was unaltered in anesthetized dt(sz) hamsters, but systemic application of subconvulsant doses of PTZ caused significantly greater increases of discharge rates in dystonic hamsters compared with nondystonic controls. The present study tested the hypothesis that SNr neurons are more sensitive to local application of PTZ in dt(sz) hamsters than in nondystonic hamsters. PTZ applied locally by pressure injection at 2, 3, and 5 mM to the SNr during in vivo single unit recordings revealed a dose-dependent increase of SNr discharge rates in mutants and controls relative to predrug rates, with a significantly greater increase in mutants at 3 mM PTZ. To examine the functional relevance of the increased susceptibility of SNr neurons to PTZ in mutants, the effects of PTZ on severity of dystonia were investigated after microinjections into the SNr of freely moving dt(sz) hamsters. Bilateral nigral microinjection of 40 ng PTZ did not aggravate dystonia but exerted moderate antidystonic effects. Therefore, the previous findings of prodystonic effects of systemic administration of PTZ in dt(sz) hamsters are related to extranigral effects rather than to the elevation of nigral discharge rates in response to systemic, or locally applied, PTZ. The greater susceptibility of neurons within the SNr to PTZ suggests dysfunctions of the GABA(A) receptor in dt(sz) mutants.

Effects of striatal injections of GABA(A) receptor agonists and antagonists in a genetic animal model of paroxysmal dystonia

The underlying mechanisms of idiopathic dystonias are poorly understood. The dystonic phenotype in the dt(sz) mutant hamster, a model of paroxysmal dystonia, has been suggested to be based on a deficit of gamma-aminobutyric acid (GABA)ergic interneurons and changes of the GABA(A)-benzodiazepine receptor complex in the striatum. In order to confirm and extend previous observations, the effects of compounds which bind to different sites of the GABA(A) receptor on the severity of dystonia were determined after striatal microinjections in comparison to systemic treatments in dt(sz) mutants. The GABA(A) receptor agonist (muscimol) and the benzodiazepine (flurazepam) reduced the severity of dystonia after striatal and systemic injections. The antidystonic effects of the barbiturate phenobarbital were less marked both after striatal and intraperitoneal administration of drugs. Intrastriatal injections of GABA delayed the onset of dystonic attacks. Striatal and systemic treatments with the GABA(A) receptor antagonist, bicuculline, and with pentylenetetrazole, which reduces GABAergic function, accelerated the onset of dystonia at subconvulsant doses. The benzodiazepine receptor antagonists flumazenil aggravated dystonia after systemic and intrastriatal injections. In all, the present data substantiate the relevance of striatal GABAergic disinhibition in the pathogenesis of paroxysmal dystonia in dt(sz) mutants.

Sodium currents in striatal neurons from dystonic dt(sz) hamsters: altered response to lamotrigine

Dystonic mutant dt(sz) hamsters are a model for paroxysmal dystonia. Handling/stress provoke the dystonic attacks. This phenomenon subsedes with maturation, but can be reinvoked when these animals receive sodium channel blockers such as lamotrigine, suggesting a dysfunction of striatal sodium channels. Voltage-gated fast sodium currents (I(Na(+))) were studied in acutely isolated striatal neurons from healthy and dt(sz) hamsters in whole-cell voltage clamp recordings. The action of lamotrigine was tested on (a) current/voltage relationship, (b) kinetics, and (c) steady-state inactivation and activation. Under control conditions, properties of I(Na(+)) were not different between healthy and dt(sz) neurons. With lamotrigine, however, (a) peak currents were significantly less depressed by the drug in neurons from dt(sz) hamsters as compared to healthy cells, and (b) the steady-state inactivation curve shift of I(Na(+)) was less pronounced in dt(sz) neurons. The results suggest that in dt(sz) hamsters, fast sodium currents in striatal neurons are more resistant to blockade. This sodium channel alteration might be causal for a functional imbalance between input and output structures of the basal ganglia under conditions of compromised I(+)(Na).

Immunocytochemical characterization of torsin proteins in mouse brain

Early-onset torsion dystonia is a hyperkinetic movement disorder caused by a deletion of one glutamic acid residue in torsinA, a novel member of the AAA-family of ATPases. No mutation has been found so far in the closely related torsinB protein. Little is known about the molecular basis of the disease, and the cellular functions of torsin proteins remain to be investigated. We generated polyclonal anti-peptide antibodies directed against human torsinA and torsinB proteins. In Western blot analysis of mouse brain homogenates, the antibodies specifically recognized 33 kDa endogenous torsinA and 52 kDa endogenous torsinB. Absorption controls showed that labeling was blocked by cognate peptide used for immunization. Immunolocalization studies revealed that torsinA and torsinB were widely expressed throughout the mouse central nervous system. Both proteins were detected in the majority of neurons in nearly all regions. The proteins displayed cytoplasmic distribution, although in some types of neurons localization was perinuclear. Strong labeling of neuronal processes and fibers was detected for both proteins. TorsinA and torsinB have similar CNS distribution, although some differences were observed. Widespread expression suggests that these proteins may play an essential role in normal neuronal functions. The localization of torsinA and torsinB immunoreactivity in neuronal processes points to a potential role for torsin proteins in synaptic functioning.

Deficit of striatal parvalbumin-reactive GABAergic interneurons and decreased basal ganglia output in a genetic rodent model of idiopathic paroxysmal dystonia

The underlying mechanisms of various types of hereditary dystonia, a common movement disorder, are still unknown. Recent findings in a genetic model of a type of paroxysmal dystonia, the dt(sz) mutant hamster, pointed to striatal dysfunctions. In the present study, immunhistochemical experiments demonstrated a marked decrease in the number and density of parvalbumin-immunoreactive GABAergic interneurons in all striatal subregions of mutant hamsters. To examine the functional relevance of the reduction of these inhibitory interneurons, the effects of the GABA(A) receptor agonist muscimol on severity of dystonia were examined after microinjections into the striatum and after systemic administrations. Muscimol improved the dystonic syndrome after striatal injections to a similar extent as after systemic treatment, supporting the importance of the deficiency of striatal GABAergic interneurons for the occurrence of the motor disturbances. The disinhibition of striatal GABAergic projection neurons, as suggested by recent extracellular single-unit recordings in dt(sz) hamsters, should lead to an abnormal neuronal activity in the basal ganglia output nuclei. Indeed, a significantly decreased basal discharge rate of entopeduncular neurons was found in dt(sz) hamsters. We conclude that a deficit of striatal GABAergic interneurons leads by disinhibition of striatal GABAergic projection neurons to a reduced activity in the entopeduncular nucleus, i.e., to a decreased basal ganglia output. This finding is in line with the current hypothesis about the pathophysiology of hyperkinesias. The results indicate that striatal interneurons deserve attention in basic and clinical research of those movement disorders.

Evidence for striatal dopaminergic overactivity in paroxysmal dystonia indicated by microinjections in a genetic rodent model

Mutant dystonic hamsters (dt(sz)), a model of primary paroxysmal dystonia, display attacks of generalized dystonia in response to mild stress in an age-dependent manner. Recent studies in dystonic hamsters have revealed decreased densities of dopamine D(1) and D(2) in the dorsal striatum. This finding has been interpreted as a down-regulation in response to enhanced dopamine release because systemic treatments with neuroleptics reduced the severity of dystonia while levodopa exerted prodystonic effects. Therefore, in the present study we investigated the effects of amphetamine as well as of selective D(1) or D(2) receptor agonists and antagonists on the severity of dystonia after systemic administrations and after microinjections into the dorsal striatum. Amphetamine and the dopamine D(2) agonist quinpirole increased the severity of dystonia after systemic and striatal injections, while the dopamine D(1) agonist SKF 38393 exerted only moderate prodystonic effects after systemic administration of a high dose but not after striatal injections. These results suggest that a predominant overstimulation of D(2) receptors is pathogenetically involved in the dystonic syndrome. Combined systemic or striatal administrations of the D(1) and D(2) receptor agonists did not reveal synergistic prodystonic effects at the examined doses. The selective D(1) antagonist SCH 23390 as well as the D(2) antagonist raclopride tended to decrease the severity of dystonia after systemic administration but failed to exert significant effects after striatal injection. The coadministration of ineffective doses of the antagonists SCH 23390 and raclopride, however, exerted an enormous antidystonic efficacy after both systemic and striatal injections. Since striatal injections of compounds which enhance dopaminergic activity aggravated dystonia, while coinjections of dopamine D1 and D2 receptor antagonists reduced the severity of dystonia, the present findings clearly support the hypothesis that striatal dopaminergic overactivity plays a crucial role for the manifestation of dystonic attacks in the hamster model of paroxysmal dystonia.

Paroxysmal dystonia induced by exercise and acetazolamide

We report a case of a 40-year-old woman with dystonic attacks precipitated by slight exercise. Episodes lasted 2-5 min and were not precipitated by sudden movements or by being startled, drinking alcohol, coffee or tea, or by stress. Secondary dystonia was ruled out and brain magnetic resonance imaging (MRI) was unremarkable. Routine and video electroencephalogram (EEG) during and between attacks were normal. Acetazolamide greatly worsened her condition, whereas gabapentin [1-(aminomethyl) cyclohexaneacetic acid] treatment markedly reduced the frequency and severity of the episodes.

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.

Tyrosine hydroxylase immunoreactivity and [3H]WIN 35,428 binding to the dopamine transporter in a hamster model of idiopathic paroxysmal dystonia

Recent pharmacological studies and receptor analyses have suggested that dopamine neurotransmission is enhanced in mutant dystonic hamsters (dt(sz)), a model of idiopathic paroxysmal dystonia which displays attacks of generalized dystonia in response to mild stress. In order to further characterize the nature of dopamine alterations, the present study investigated possible changes in the number of dopaminergic neurons, as defined by tyrosine hydroxylase immunohistochemistry, as well as binding to the dopamine transporter labelled with [3H]WIN 35,428 in dystonic hamsters. No differences in the number of tyrosine hydroxylase-immunoreactive neurons were found within the substantia nigra and ventral tegmental area of mutant hamsters compared to non-dystonic control hamsters. Similarly, under basal conditions, i.e. in the absence of a dystonic episode, no significant changes in [3H]WIN 35,428 binding were detected in dystonic brains. However, in animals killed during the expression of severe dystonia, significant decreases in dopamine transporter binding became evident in the nucleus accumbens and ventral tegmental area in comparison to controls exposed to the same external stimulation. Since stimulation tended to increase [3H]WIN 35,428 binding in control brains, the observed decrease in the ventral tegmental area appeared to be due primarily to the fact that binding was increased less in dystonic brains than in similarly stimulated control animals. This finding could reflect a diminished ability of the dopamine transporter to undergo adaptive changes in response to external stressful stimulation in mutant hamsters. The selective dopamine uptake inhibitor GBR 12909 (20 mg/kg) aggravated dystonia in mutant hamsters, further suggesting that acute alterations in dopamine transporter function during stimulation may be an important component of dystonia in this model.

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.

Regional alterations in neuronal activity in dystonic hamster brain determined by quantitative cytochrome oxidase histochemistry

The neural mechanisms underlying idiopathic dystonia are currently unknown. Genetic animal models, such as the dt(sz) hamster, a model of idiopathic paroxysmal dystonia, may be helpful to providing insights into the pathophysiology of this common movement disorder. Recent metabolic mapping studies in the hamster model, using 2-deoxyglucose autoradiography, demonstrated altered 2-deoxyglucose uptake in motor areas such as the striatum, ventral thalamic nuclei, red nucleus, and deep cerebellar nuclei, during dystonic attacks. Whereas the 2-deoxyglucose method is thought to reflect mainly acute alterations of synaptic activity, determination of cytochrome oxidase activity has been suggested as a method of choice to examine sustained baseline changes in neuronal activity. Therefore, in the present study quantitative cytochrome oxidase histochemistry was used to identify chronic regional alterations in the absence of dystonic attacks in mutant hamsters. For comparison with recent 2-deoxyglucose studies, cytochrome oxidase activity was also determined during a dystonic attack, which was induced by mild stress. Cytochrome oxidase was determined in 109 brain regions of dystonic hamsters and non-dystonic, age-matched control hamsters. In the absence of a dystonic attack, a tendency to decreased cytochrome oxidase activity was found in most brain regions, possibly due to retarded brain development in mutant hamsters. Significant decreases in cytochrome oxidase activity were found in motor areas and limbic structures, such as hippocampus, piriform cortex, fundus striatum, globus pallidus, substantia nigra pars reticulata, mediodorsal nucleus of the thalamus, ventral pallidum, and interpositus nucleus of the cerebellum. After induction of a dystonic attack, the trend of decreased cytochrome oxidase activity disappeared, except in globus pallidus and interpositus nucleus of the cerebellum. Although the significant alterations in cytochrome oxidase activity in the absence of a dystonic attack were moderate, the data are in line with previous findings in the mutant hamsters, indicating that dysfunctions of the basal ganglia and their output nuclei are involved in the dystonic condition. Altered neural activity in limbic structures, found in the absence of dystonic attacks in mutant hamsters, may contribute to the stress-susceptibility of the animals.