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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 dt sz 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 dt sz 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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

Deep brain stimulation (DBS), a treatment for modulating the abnormal central neuronal circuitry, has become the standard of care nowadays and is sometimes the only option to reduce symptoms of movement disorders such as dystonia. However, on the one hand, there are still open questions regarding the pathomechanisms of dystonia and, on the other hand, the mechanisms of DBS on neuronal circuitry. That lack of knowledge limits the therapeutic effect and makes it hard to predict the outcome of DBS for individual dystonia patients. Finding electrophysiological biomarkers seems to be a promising option to enable adapted individualised DBS treatment. However, biomarker search studies cannot be conducted on patients on a large scale and experimental approaches with animal models of dystonia are needed. In this review, physiological findings of deep brain stimulation studies in humans and animal models of dystonia are summarised and the current pathophysiological concepts of dystonia are discussed., (© 2023. The Author(s).)

The pathophysiology of early-onset torsion dystonia (TOR1A/DYT1) remains unclear. Like 70% of human mutation carriers, rodent models with ΔGAG mutation such as DYT1 knock-in (KI) mice do not show overt dystonia but have subtle sensorimotor deficits and pattern of abnormal synaptic plasticity within the striatal microcircuits. There is evidence that dysfunction of striatal parvalbumin-reactive (Parv+) fast-spiking interneurons (FSIs) can be involved in dystonic signs. To elucidate the relevance of these GABAergic interneurons in the pathophysiology of DYT1 dystonia, we used in vivo optogenetics to specifically inhibit Parv+ and to detect changes in motor behavior and neuronal activity. Optogenetic fibers were bilaterally implanted into the dorsal striatum of male DYT1 KI mice and wild-type (WT) littermates expressing halorhodopsin (eNpHR3.0) in Parv+ interneurons. While stimulations with yellow light pulses for up to 60 min at different pulse durations and interval lengths did not induce abnormal movements, such as dystonic signs, immunohistochemical examinations revealed genotype-dependent differences. In contrast to WT mice, stimulated DYT1 KI showed decreased striatal neuronal activity, that is, less c-Fos reactive neurons, and increased activation of cholinergic interneurons after optogenetic inhibition of Parv+ interneurons. These findings suggest an involvement of Parv+ interneurons in an impaired striatal network in DYT1 KI mice, but at least short-term inhibition of these GABAergic interneurons is not sufficient to trigger a dystonic phenotype, similar to previously shown optogenetic activation of cholinergic interneurons., (© 2022 The Authors. Journal of Neuroscience Research published by Wiley Periodicals LLC.)

During the last decades deep brain stimulation (DBS) has become an important treatment option for a variety of neurological disorders such as drug-intractable dystonia. Yet, the mechanisms of action of DBS are still largely unknown. Dystonia is a heterogenous movement disorder characterized by involuntary muscle contractions causing abnormal movements, postures, or both. The underlying pathophysiological processes remain unclear, but a dysfunction of the basal ganglia circuit is critically involved as supported by the effectiveness of DBS of the globus pallidus internus (GPi) in various types of dystonia. However, the degree of clinical improvement differs among the types of dystonia, as well as from patient to patient, and the delayed response to GPi-DBS in dystonia patients hampers the adjustment and optimization of stimulation parameters. Preclinical studies in suitable animal models can contribute decisively to detect the underlying mechanisms of DBS and biomarkers, to identify new possible stimulation targets and to optimize stimulation patterns. In this review, we give an overview of previous research on DBS in animal models of dystonia. With regard to the aims of research we discuss the opportunities and limitations concerning different available animal models of dystonia and technical challenges., Competing Interests: Declaration of Competing Interest None., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Pallidal deep brain stimulation (DBS) is an important option for patients with severe dystonias, which are thought to arise from a disturbance in striatal control of the globus pallidus internus (GPi). The mechanisms of GPi-DBS are far from understood. Although a disturbance of striatal function is thought to play a key role in dystonia, the effects of DBS on cortico-striatal function are unknown. We hypothesised that DBS, via axonal backfiring, or indirectly via thalamic and cortical coupling, alters striatal function. We tested this hypothesis in the dt sz hamster, an animal model of inherited generalised, paroxysmal dystonia. Hamsters (dystonic and non-dystonic controls) were bilaterally implanted with stimulation electrodes in the GPi. DBS (130 Hz), and sham DBS, were performed in unanaesthetised animals for 3 h. Synaptic cortico-striatal field potentials, as well as miniature excitatory postsynaptic currents (mEPSC) and firing properties of medium spiny striatal neurones were recorded in brain slice preparations obtained immediately after EPN-DBS. The main findings were as follows: a. DBS increased cortico-striatal evoked responses in healthy, but not in dystonic tissue. b. Commensurate with this, DBS increased inhibitory control of these evoked responses in dystonic, and decreased inhibitory control in healthy tissue. c. Further, DBS reduced mEPSC frequency strongly in dystonic, and less prominently in healthy tissue, showing that also a modulation of presynaptic mechanisms is likely involved. d. Cellular properties of medium-spiny neurones remained unchanged. We conclude that DBS leads to dampening of cortico-striatal communication, and restores intrastriatal inhibitory tone., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Deep brain stimulation (DBS) of the globus pallidus internus (GPi, entopeduncular nucleus, EPN, in rodents) has become important for the treatment of generalized dystonia, a severe and often intractable movement disorder. It is unclear if lower frequencies of GPi-DBS or stimulations of the subthalamic nucleus (STN) are of advantage. In the present study, the main objective was to examined the effects of bilateral EPN-DBS at different frequencies (130 Hz, 40 Hz, 15 Hz) on the severity of dystonia in the dt sz mutant hamster. In addition, STN stimulations were done at a frequency, proven to be effective by the present EPN-DBS in dystonic hamsters. In order to obtain precise bilateral electrical stimuli with magnitude of 50 μA, a pulse width of 60 μs and defined frequencies, it was necessary to develop a new optimized stimulator prior to the experiments. Since the individual highest severity of dystonic episodes is known to be reached within three hours after induction in dt sz hamsters, the duration of DBS was 180 min. During DBS with 130 Hz the severity of dystonia was significantly lower within the third hour than without DBS in the same animals (p < 0.05). DBS with 40 Hz tended to exert antidystonic effects after three hours, while 15 Hz stimulations of the EPN and 130 Hz stimulations of the STN failed to show any effects on the severity. DBS of the EPN at 130 Hz was most effective against generalized dystonia in the dt sz mutant. The response to EPN-DBS confirms that the dt sz mutant is suitable to further investigate the effects of long-term DBS on severity of dystonia and neuronal network activities, important to give insights into the mechanisms of DBS., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

In early-onset generalized torsion dystonia, caused by a GAG deletion in TOR1A (DYT1), enhanced striatal cholinergic activity has been suggested to be critically involved. Previous studies have shown increased acetylcholine levels in the striatum of DYT1 knock-in (KI) mice. Ex vivo data indicated that muscarinic receptor antagonists normalize the activity of striatal cholinergic interneurons. Currently receptor subtype specific antagonists are developed for therapy, however, it is yet unknown whether the levels of targeted receptors are unaltered. In the present study, we firstly examined the expression of M1 and M4 receptors in DYT1 KI mice in comparison to wildtype mice. While no changes in mRNA were found in the motor cortex, the expression of M1 was higher in the striatum of DYT1 KI. However, M1 protein did not differ in striatum and cortex between the animal groups as shown by immunohistochemistry and western blot. M4 receptor protein, unaltered in the cortex, was slightly lower in lateral subparts of the striatum, but unchanged in somata of cholinergic interneurons and substance P immunoreactive projection neurons. Functional alterations of the cholinergic system and of aberrant striatal plasticity, demonstrated by previous studies, seem not to be related to overt changes in M1 and M4 expression. This critically informs the ongoing development of respective antagonists for therapy of dystonia., Competing Interests: The authors have declared that no competing interests exist.

The metabotropic glutamate 5 (mGlu 5 ) receptor has been suggested as therapeutic target for L-Dopa-induced dyskinesia which is often associated with dystonic symptoms. Therefore, we investigated the acute effects of the non-competitive mGlu 5 receptor antagonist fenobam as well as the positive modulator 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB) on the severity of inherited dystonia in the mutant dt sz hamster, a phenotypic model with age-dependent episodes of dystonia. Fenobam did not exert significant antidystonic effects (20-50 mg/kg intraperinoneal, i.p.). CDPPB (10, 20 mg/kg i.p.) which was expected to worsen dystonia also failed to show any effects on the severity of dystonia. Interestingly, CDPPB caused axial dyskinesia in addition to the dystonic symptoms in mutant hamsters. This adverse effect could not be observed in non-dystonic control hamsters, indicating possible changes in the expression of mGlu 5 receptors in dystonic hamsters. The mGlu 5 receptor mRNA did not differ between the dt sz mutant and control hamsters, while immunohistochemical studies indicated that the mGlu 5 receptor expression was about 35% higher in striatum and cortex of mutant hamsters at the age of high dystonia severity scores, notably not after spontaneous remission of dystonia, compared to age-matched controls. This difference in mGlu 5 receptor protein may be due to altered protein conformation instead of protein level, as western blots revealed similar amounts of monomeric and dimeric protein in mutant hamsters versus control. Thus, the present data do not provide clear evidence for an important role of the mGlu5 receptor in the pathophysiology and as a therapeutic target for types of inherited dystonia., (Copyright © 2019 Elsevier B.V. All rights reserved.)

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., (Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.)

Hereditary generalized dystonia is often caused by a GAG deletion in TOR1A (DYT1) that encodes for the protein torsinA. Although mutation carriers show alterations in neuronal connectivity and sensorimotor deficits, only 30% develop dystonia. Uncovering the factors triggering the dystonic symptoms and underlying pathophysiology would greatly benefit the development of more effective therapies. In DYT1 knock-in (KI) mice, the expression of torsinA mutant alters the connectivity of neurons and the function of striatal cholinergic interneurons. We aimed to determine if heterozygous DYT1 KI mice exhibit deficits in behavioural tests that explore the connectivity of the sensory and motor system. DYT1 KI mice were tested in cognitive tests and challenging motor paradigms, followed by the adhesive removal test and the adaptive rotating beam test which both require sensorimotor integration. DYT1 KI mice did not exhibit cognitive deficits and were able to perform similarly to wild type mice even in challenging motor tests with relatively stable sensory input. Conversely, DYT1 KI mice spent more time on sensing and removing an adhesive sticker from the back of the nose; they exhibited difficulty to traverse rotating rods, especially if the surface was smooth and the diameter small. Our observations further support a role of sensorimotor integration in manifestation of this movement disorder. Future studies in DYT1 KI mice will explore the involved neurocircuitry and underlying molecular mechanisms., (Copyright © 2016 Elsevier B.V. All rights reserved.)

GABAergic disinhibition has been suggested to play a critical role in the pathophysiology of several basal ganglia disorders, including dystonia, a common movement disorder. Previous studies have shown a deficit of striatal GABAergic interneurons (IN) in the dt sz mutant hamster, one of the few phenotypic animal models of dystonia. However, mechanisms underlying this deficit are largely unknown. In the present study, we investigated the migration and maturation of striatal IN during postnatal development (18days of age) and at age of highest severity of dystonia (33days of age) in this hamster model. In line with previous findings, the density of GAD67-positive IN and the level of parvalbumin mRNA, a marker for fast spiking GABAergic IN, were lower in the dt sz mutant than in control hamsters. However, an unaltered density of Nkx2.1 labeled cells and Nkx2.1 mRNA level suggested that the migration of GABAergic IN into the striatum was not retarded. Therefore, different factors that indicate maturation of GABAergic IN were determined. While mRNA of the KCC2 cation/chloride transporters and the cytosolic carboanhydrase VII, used as markers for the so called GABA switch, as well as BDNF were unaltered, we found a reduced number of IN expressing the alpha1 subunit of the GABA A -receptor (37.5%) in dt sz hamsters at an age of 33days, but not after spontaneous remission of dystonia at an age of 90days. Since IN shift expression from alpha2 to alpha1 subunits during postnatal maturation, this result together with a decreased parvalbumin mRNA expression suggest a delayed maturation of striatal GABAergic IN in this animal model, which might underlie abnormal neuronal activity and striatal plasticity., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Dystonia is a movement disorder, characterized by involuntary muscle contractions resulting in abnormal movements and/or postures. Antidystonic effects of benzodiazepines in patients with different types of dystonia could be replicated in the dt sz mutant hamster, a phenotypic model of paroxysmal dystonia. Compounds with preferred binding at specific subunits of the gamma aminobutyric acid type A (GABA A ) receptor may provide a more beneficial spectrum of effects in comparison with benzodiazepines. We therefore examined the effects of the α1β3γ2 GABA A receptor preferring compound zolpidem (2.0-10.0mg/kg i.p.) and of the α2β3γ2 GABA A receptor preferring compound NS11394 (3.0-30mg/kg i.p.) on the severity of dystonia in the dt sz mutant in comparison with the benzodiazepine clonazepam (0.5-1.0mg/kg i.p.). As expected, clonazepam exerted pronounced antidystonic effects. While zolpidem showed moderate beneficial effects, NS11394 significantly increased the severity of dystonia. The present results indicate for the first time that positive GABA A receptor modulators show contrary effects on dystonia dependent on their preference for alpha-subunits. The potential link between alterations in GABA A receptor subunits and GABAergic disinhibition in dystonia deserves further attention in research on the pathophysiology and therapeutic targets., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Dystonia is a hyperkinetic disabling movement disorder. In the dt(sz) hamster, a model of paroxysmal dystonia, pronounced antidystonic effects of the KV7.2-5 potassium channel opener retigabine and aggravation of dystonia by a selective KV7.2-5 blocker indicated a pathophysiological role of an abnormal expression of KV7 channels. We therefore investigated the expression of KV7 subunits in brains of dystonic hamsters. While KV7.2 and KV7.3 subunits were unaltered, lower KV7.5 mRNA levels became evident in motor areas and in limbic structures of dystonic hamsters. The KV7.2/3 subunit-preferring channel opener N-(6-chloropyridin-3-yl)-3,4- difluorobenzamide (ICA 27243; 10-30 mg/kg i.p.) failed to reduce the severity of dystonia in mutant hamsters, suggesting that the previously observed antidystonic action of retigabine is mediated by the activation of KV7.5 channels. The experiments indicate a functional relevance for KV7.5 channels in paroxysmal dystonia. We suggest that compounds highly selective for subtypes of KV7 channels, i.e. for KV7.5, may provide new therapeutic approaches.

Dystonia is a movement disorder in which abnormal plasticity in the basal ganglia has been hypothesized to play a critical role. In a model of paroxysmal dystonia, the dt(sz) mutant hamster, previous studies indicated striatal dysfunctions, including an increased long-term potentiation (LTP). Beneficial effects were exerted by subunit-unspecific antagonists at NMDA receptors, which blocked LTP. NR2B subtype selective antagonists aggravated dystonia after systemic treatment in dt(sz) hamsters, suggesting that beneficial effects involved the NR2A receptor subtype. In the present study, NVP-AAM077, an antagonist with preferential activity on NR2A-containing NMDA receptors, exerted significant antidystonic effects in mutant hamsters after systemic administration (20 and 30mg/kg i.p.) and delayed the onset of a dystonic episode after intrastriatal injections (0.12 and 0.24μg). As shown by present electrophysiological examinations in corticostriatal slices of dt(sz) hamsters and non-dystonic control hamsters, NVP-AAM077 (50nM) completely blocked LTP in dt(sz) slices, but did not exert significant effects on LTP in non-dystonic controls. In contrast, the NR2B antagonist Ro 25-6981 (1-10μmol) reduced LTP to a lower extent in dt(sz) mutant hamsters than in control animals. By using quantitative RT-PCR, the NR2A/NR2B ratio was found to be increased in the striatum, but not in the cortex of mutant hamsters in comparison to non-dystonic controls. These data indicate that NR2A-mediated activation may be involved in the pathophysiology of paroxysmal dystonia. Since significant antidystonic effects were observed after systemic administration of NVP-AAM077 already at well tolerated doses, antagonists with preferential activity on NR2A-containing NMDA receptors could be interesting candidates for the treatment of dystonia., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Animal models are pivotal for studies of pathogenesis and treatment of disorders of the central nervous system which in its complexity cannot yet be modeled in vitro or using computer simulations. The choice of a specific model to test novel therapeutic strategies for a human disease should be based on validity of the model for the approach: does the model reflect symptoms, pathogenesis and treatment response present in human patients? In the movement disorder dystonia, prior to the availability of genetically engineered mice, spontaneous mutants were chosen based on expression of dystonic features, including abnormal muscle contraction, movements and postures. Recent discovery of a number of genes and gene products involved in dystonia initiated research on pathogenesis of the disorder, and the creation of novel models based on gene mutations. Here we present a review of current models of dystonia, with a focus on genetic rodent models, which will likely be first choice in the future either for pathophysiological or for preclinical drug testing or both. In order to help selection of a model depending on expression of a specific feature of dystonia, this review is organized by symptoms and current knowledge of pathogenesis of dystonia. We conclude that albeit there is increasing need for research on pathogenesis of the disease and development of improved models, current models do replicate features of dystonia and are useful tools to develop urgently demanded treatment for this debilitating disorder., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Dystonia is regarded as a basal ganglia disorder. In the dt(sz) hamster, a genetic animal model of paroxysmal dystonia, previous studies demonstrated a reduced density of striatal GABAergic interneurons which inhibit striatal GABAergic projection neurons. Although the disinhibition of striatal GABAergic projection neurons was evidenced in the dt(sz) hamster, alterations in their density have not been elucidated so far. Therefore, in the present study, the density of striatal methionin-(met-) enkephalin (ENK) immunoreactive GABAergic neurons, which project to the globus pallidus (indirect pathway), was determined in dt(sz) and control hamsters to clarify a possible role of an altered ratio between striatal interneurons and projection neurons. Furthermore, the immunoreactivity of dynorphin A (DYN), which is expressed in entopeduncular fibers of striatal neurons of the direct pathway, was verified by gray level measurements to illuminate the functional relevance of an enhanced striato-entopeduncular neuronal activity previously found in dt(sz) hamsters. While the density of striatal ENK immunoreactive (ENK(+) ) neurons did not significantly differ between mutant and control hamsters, there was a significantly enhanced ratio between the DYN immunoreactive area and the whole area of the EPN in dt(sz) hamsters compared to controls. These results support the hypothesis that a disbalance between a reduced density of striatal interneurons and an unchanged density of striatal projection neurons causes imbalances in the basal ganglia network. The consequentially enhanced striato-entopeduncular inhibition leads to an already evidenced reduced activity and an altered firing pattern of entopeduncular neurons in the dt(sz) hamster., (Copyright © 2011 Wiley-Liss, Inc.)

Early-onset torsion dystonia is an autosomal dominant movement disorder associated with the DYT1 gene (TOR1A) defect which results in a deletion of a glutamic acid residue in the protein torsinA. The pathophysiology of dystonia is poorly understood. Well characterized animal models can help to give insights into the underlying mechanisms and thereby to develop new therapeutics. In the present study, we further characterized transgenic DYT1 mice, which were initially described to exhibit "dystonia-like" postures. In the present study, several behavioural tests in untreated animals did not show strong differences between transgenic and control mice, but nearly all transgenic mice showed "dystonia-like" postures. However, these movements, also observed in control mice, have to be regarded as a clasping reflex. Since dystonia is thought to be related to dopaminergic dysfunctions, pharmacological investigations have been performed to clarify if dopaminergic substances alter motor behaviour in transgenic mice. Chronic treatment with L-DOPA (combined with carbidopa) enhanced the hindlimb claspings only in transgenic mice, while acute applications of drugs, which exert more selective effects on the dopaminergic system, caused similar reactions in transgenic mice and control mice. Therefore, these data do not provide clear evidence for dysfunctions of the dopaminergic system in this mouse model., (© 2010 Elsevier Inc. All rights reserved.)

Previous examinations demonstrated periodic increases in striatal extracellular dopamine levels during dystonic attacks and changes in dopamine D1 and D2 receptor binding in the dt(sz) mutant hamster, an animal model of paroxysmal non-kinesiogenic dyskinesia in which dystonic episodes can be induced by stress. Since dopamine D3 receptors are involved in the regulation of striatal dopamine release, D3 receptor function was investigated by autoradiographic and pharmacological examinations in mutant hamsters in the present study. [(125)I]7-[[(E)-3-iodoprop-2-enyl]-propylamino]-5,6,7,8-tetrahydronaphthalen-2-ol ([(125)I]7-OH-PIPAT) binding was not significantly altered in the striatum, n. accumbens, ventral pallidum or cerebellum in dt(sz) hamsters in comparison to non-dystonic control hamsters. In line with the unaltered D3 receptor binding, the preferential dopamine D3 versus D2 receptor antagonist U-99194 (5,6-dimethoxy-N,N-dipropyl-2,3-dihydro-1H-inden-2-amine hydrochloride) did not exert significant effects on the severity of dystonia in dt(sz) hamsters at doses of 10 to 40mg/kg which induced hyperlocomotion. These results suggest that periodic elevations of dopamine levels in these animals are not related to D3 receptor dysfunctions., (Copyright 2010 Elsevier Inc. All rights reserved.)

The pathophysiology of idiopathic dystonias is still unknown, but it is regarded as a basal ganglia disorder. Previous experiments in the dt(sz) hamster, a model of primary paroxysmal dystonia, demonstrated reduced discharge rates and an abnormal pattern within the entopeduncular nucleus (EPN), a basal ganglia output structure. To clarify if this is based on abnormal gamma-aminobutyric acid(GABA)ergic or glutamatergic input, microinjections into the EPN were done in mutant hamsters in the present study. The GABA(A) receptor antagonists pentylenetetrazole and bicuculline exerted moderate antidystonic effects, while previous systemic administrations worsened dystonia in the dt(sz) mutant. GABA-potentiating drugs, i.e., the GABA(A) receptor agonist muscimol and the GABA transporter inhibitor 1,2,5,6-tetrahydro-1-[2-[[(diphenylmethylene)amino]oxy]ethyl]-3-pyridinecarboxy-lic acid (NNC-711), which are known to improve dystonia after systemic treatment in mutant hamsters, did not exert significant effects after EPN injections, but NNC-711 tended to increase the severity at the highest dose (2.5 ng bilateral). The NMDA receptor antagonist D(-)-2-amino-5-phosphopentanoic acid (AP-5) retarded the onset of a dystonic attack. However, this effect was not dose dependent and the AMPA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzol(f)quinoxaline (NBQX) alone or in combination with AP-5 and NNC-711, also failed to show any effects on dystonia. The present data do not provide clear evidence for an enhanced striatal GABAergic input or a reduced glutamatergic activation of the EPN via the subthalamic nucleus, i.e., more pronounced antidystonic effects of GABA(A) receptor antagonists and stronger prodystonic effects of GABAmimetics and glutamate receptor antagonists were expected. Nevertheless, previously found changes in entopeduncular activity probably play a critical pathophysiological role in dystonic hamsters.

Dystonia is a heterogeneous syndrome of movement disorders characterized by involuntary muscle contractions leading to abnormal movements and postures. While medical treatment is often ineffective, deep brain stimulation (DBS) of the internal pallidum improves dystonia. Here, we studied the impact of DBS in the entopeduncular nucleus (EP), the rodent equivalent of the human globus pallidus internus, on basal ganglia output in the dt(sz)-hamster, a well-characterized model of dystonia by extracellular recordings. Previous work has shown that EP-DBS improves dystonic symptoms in dt(sz)-hamsters. We report that EP-DBS changes firing pattern in the EP, most neurons switching to a less regular firing pattern during DBS. In contrast, EP-DBS did not change the average firing rate of EP neurons. EP neurons display multiphasic responses to each stimulation impulse, likely underlying the disruption of their firing rhythm. Finally, neurons in the substantia nigra pars reticulata display similar responses to EP-DBS, supporting the idea that EP-DBS affects basal ganglia output activity through the activation of common afferent fibers., (Copyright 2010 Elsevier Inc. All rights reserved.)

High frequency stimulation (HFS) of the internal pallidum is effective for the treatment of dystonia. Only few studies have investigated the effects of stimulation on the activity of the cortex-basal ganglia network. We here assess within this network the effect of entopeduncular nucleus (EP) HFS on the expression of c-Fos and cytochrome oxidase subunit I (COI) in the dt(sz)-hamster, a well-characterized model of paroxysmal dystonia. In dt(sz)-hamsters, we identified abnormal activity in motor cortex, basal ganglia and thalamus. These structures have already been linked to the pathophysiology of human dystonia. EP-HFS (i) increased striatal c-Fos expression in controls and dystonic hamsters and (ii) reduced thalamic c-Fos expression in dt(sz)-hamsters. EP-HFS had no effect on COI expression. The present results suggest that EP-HFS induces a new network activity state which may improve information processing and finally reduces the severity of dystonic attacks in dt(sz)-hamsters.

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., ((c) 2008 Wiley-Liss, Inc.)

Previous examinations demonstrated antidystonic effects of the synaptic vesicle protein 2A (SV2A) ligand levetiracetam in the dt(sz) mutant hamster, an animal model of paroxysmal non-kinesiogenic dyskinesia in which dystonic episodes can be induced by stress. In the present study, we examined the effects of the two new, high affinity SV2A ligands, brivaracetam and seletracetam, in comparison to levetiracetam on the severity of dystonia in mutant hamsters. Seletracetam (50 and 75 mg/kg i.p.) and brivaracetam (75 mg/kg i.p.) reduced the severity of dystonia to a comparable extent as levetiracetam (50 and 75 mg/kg i.p.). These data confirm the therapeutic potential of these pyrrolidone derivatives for the treatment of paroxysmal dystonia.

Striatal dysfunctions seem to play a key role in the pathophysiology of dystonia in the dt(sz) mutant hamster, a model of paroxysmal non-kinesigenic dyskinesia, in which stress precipitates dystonic episodes. Previous examinations have shown changes in kynurenic acid levels and antidystonic effects of the kynurenine 3-hydroxylase inhibitor 3,4-dimethoxy-N-[4-(3-nitrophenyl)thiazol-2-yl]benzenesulfon-amide (Ro 61-8048) after systemic treatment in dt(sz) hamsters. In the present study, intrastriatal injections of Ro 61-8048 (60-80 microg/hemisphere) significantly reduced the severity of dystonia in dt(sz) hamsters, suggesting that kynurenine 3-hydroxylase inhibitors may be interesting candidates for managing dyskinesias which are related to striatal dysfunction.

The dtsz hamster represents a model of primary paroxysmal nonkinesiogenic dyskinesia in which dystonic episodes can be induced by stress and anxious stimuli. This disease is regarded as a basal ganglia disorder. In fact, a deficit of striatal interneurons could play a key role in the pathophysiology in dystonic hamsters. Because the involvement of limbic structures cannot be excluded so far, the density of parvalbumin-immunoreactive (PV+) interneurons was determined in the basolateral amygdala in the present study. Compared with nondystonic hamsters, the density of PV+ interneurons was moderately decreased in the dtsz mutant. The functional consequence of this finding was examined by behavioral analyses. Examinations in the elevated plus maze and in a modified open field failed to disclose an enhanced anxiety-related behavior in dtsz hamsters (Mesocricetus auratus). A lower acoustic startle response and a stronger habituation in mutant hamsters than in controls correlated with a decreased body weight. Interestingly, prepulse inhibition was absent in mutant hamsters. The latter finding suggests a disturbed sensorimotor gating that can be related to alterations in both the basal ganglia nuclei and in limbic structures., (Copyright (c) 2008 APA, all rights reserved.)

The pathophysiology of various types of dyskinesias, including dystonias, is poorly understood. Clinical and epidemiological studies in humans revealed that the severity of dyskinesias and the frequency of paroxysmal forms of the disease are altered by factors such as the onset of puberty, pregnancy, cyclical changes and stress, indicating an underlying hormonal component. The dystonic phenotype in the dt(sz) hamster, a genetic animal model of paroxysmal dystonia, has been suggested to be based on a deficit of striatal gamma-aminobutyric acid (GABA)ergic interneurons and changes in the GABA(A) receptor complex. In this animal model, hormonal influences seem to be also involved in the pathophysiology, but an influence of peripheral sex hormones has already been excluded. Possibly, neurosteroids as endogenous regulators of the GABA(A) receptor may be critically involved in the pathophysiology of dystonia in this animal model. Therefore, in the present study, the effects of the neurosteroids allopregnanolone acetate and allotetrahydrodeoxycorticosterone (THDOC), representing positive modulators of the GABA(A) receptor, as well as of the negative GABA(A) receptor modulators pregnenolone sulfate and dehydroepiandrosterone (DHEA), on severity of dystonia were examined in dt(sz) hamsters after acute intraperitoneal injections. Allopregnanolone acetate and THDOC exerted a moderate reduction of dystonia, whereas pregnenolone sulfate and DHEA had no significant effects. Although the effects of allopregnanolone acetate and THDOC were moderate and short-lasting, the present results suggest that changes in neurosteroid levels might be involved in the initiation of dystonic episodes. Future studies have to include measurements of brain neurosteroid levels as well as of chronic neurosteroid administrations to clarify the pathophysiological role and therapeutic potential of neurosteroids in dystonia.

Imbalances of the glutamatergic system are implicated in the pathophysiology of various basal ganglia disorders, but few is known about their role in dystonia, a common neurological syndrome in which involuntary muscle co-contractions lead to twisting movements and abnormal postures. Previous systemic administrations of glutamate receptor antagonists in dtsz hamsters, an animal model of primary paroxysmal dystonia, exerted antidystonic effects and electrophysiological experiments pointed to an enhanced corticostriatal glutamatergic activity. In order to examine the pathophysiological relevance of these findings, we performed striatal microinjections of the alpha-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid (AMPA) receptor antagonist 2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline (NBQX) and the N-methyl-D-aspartate (NMDA) receptor antagonists D(-)-2-amino-5-phosphopentanoic acid (AP-5), (R)-(+)-3-amino-1-hydroxypyrrolidin-2-one (HA-966) and dizocilpine (MK-801). The striatal application of NBQX reduced the severity and increased the latency to onset of dystonia significantly only at a dosage of 0.08 microg per hemisphere, lower (0.03 microg) and higher dosages (0.16 microg and 0.32 microg) failed to exert comparable effects on the severity. None of the striatal injected NMDA receptor antagonists influenced the severity of the dystonic attacks in the mutant hamster. The combined application of NBQX (0.08 microg) with AP-5 (1.0 microg) failed to exert synergistic antidystonic effects, but the beneficial effect on the severity of dystonia of the single application of NBQX was reproduced. Therefore, corticostriatal glutamatergic overactivity mediated by AMPA receptors, but not by NMDA receptors, is possibly important for the manifestation of dystonic attacks in the dtsz hamster mutant.

In the dt(sz) hamster, a model of paroxysmal dystonia, an age-dependent increase in the activity of striatal projection neurons has been hypothesized to be based on a deficit of striatal parvalbumin-immunoreactive (PV(+)) interneurons at an age of most marked expression of dystonia (30-40 days of life). In the present study, the spontaneous age-dependent remission of paroxysmal dystonia in older dt(sz) hamsters (age>90 days) was found to coincide with a normalization of the density of striatal PV(+) interneurons. Furthermore, the arborization of these interneurons was lower in 31 day old dt(sz) hamsters, but was even higher in dt(sz) mutant at an age of >90 days than in control animals. Double-labeling with bromodeoxyuridine failed to show a retarded proliferation, while the number of interneurons with strong expression of PV mRNA was lower in young mutant hamsters. As shown by unaltered density of PV(+) interneurons in sensorimotor cortex of 31 day old dt(sz) hamsters, PV containing interneurons are not reduced throughout the whole brain at the sensitive age. The present data suggest that a retarded postnatal maturation of striatal PV(+) interneurons plays a critical role in paroxysmal dystonia.

The underlying pathophysiological mechanisms of hereditary types of paroxysmal dyskinesias are still unknown, but basal ganglia dysfunctions seem to play a critical role. In fact, numerous pharmacological, neurochemical, immunohistochemical and electrophysiological investigations in the dt(sz) hamsters, a unique rodent model of age-dependent primary paroxysmal dystonia, revealed alterations within the basal ganglia, particularly of the GABAergic and dopaminergic neurotransmitter systems. A deficit in several types of striatal GABAergic interneurons in dt(sz) mutant hamsters seems to play a crucial pathophysiological role, but deficits in other types of striatal interneurons cannot be excluded by previous studies. In view of ameliorating effects of anti-cholinergic drugs in dystonic patients, we therefore investigated the density of striatal cholinergic interneurons in the present study. These interneurons were marked specifically by the enzyme choline acetyltransferase and counted by using a stereological counting method in a blinded fashion. Additionally, acetylcholine receptor binding was determined in mutant and nondystonic control hamsters by autoradiographic analyses with the nonselective muscarinic ligand [(3)H]-quinuclidinyl benzilate (QNB) in 11 brain (sub)regions. There were no significant differences in the density of striatal cholinergic interneurons between dt(sz) mutant hamsters (789 +/- 39 interneurons/mm(3)) and nondystonic controls (807 +/- 36 interneurons/mm(3)). [(3)H]QNB binding was also comparable between mutant and control hamsters. These results point to an unaltered striatal cholinergic neurotransmitter system in dt(sz) hamsters under basal conditions.

Primary dystonia is a common movement disorder with an unknown pathophysiology, but basal ganglia dysfunctions seem to play a critical role. Previous studies in the dtsz mutant hamster, an animal model of primary paroxysmal dystonia, demonstrated a deficit of striatal gamma-amino-butyric acid (GABA) containing interneurons, which normalized at the age of the spontaneous remission of the symptoms. Whereas the reduction of striatal parvalbumin-reactive interneurons is thought to be critically involved in the pathogenesis of dystonia in the hamster mutant, the impact of a reduced density of nitric oxide synthase (NOS) reactive interneurons within the striatum is still unclear. Beside GABA, these interneurons contain somatostatin, neuropeptide Y, nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) and neuronal NOS, an enzyme which produces NO after the activation of the interneurons. In order to clarify if the reduced density of NOS-reactive interneurons contributes by an altered striatal production of nitric oxide (NO) to the occurrence of dystonic attacks in the hamster mutant, we performed microinjections of the NOS inhibitors 7-nitroindazole (7-NI) and Nomega-propyl-L-arginine (NPLA) and of the precursor of NO, L-arginine, into the striata of dtsz hamsters. Neither 7-NI (0.1 and 0.4 microg per hemisphere) and NPLA (2.5, 5 and 7.5 microg per hemisphere) nor L-arginine (9 and 18 microg per hemisphere) exerted any effects on the severity of dystonic movements in the dtsz mutant. Therefore, a critical involvement of striatal changes of NO in the pathophysiology of dystonic attacks in the dtsz hamster cannot be confirmed by the results of these pharmacological examinations. In view of the ontogenetic reduction of the other types of GABAergic interneurons, the deficit of NOS-reactive interneurons is possibly due to the same underlying unknown mechanism, but is less important for the pathophysiology of primary paroxysmal dystonia in the dtsz hamster mutant.

In the dtsz mutant hamster, a model of paroxysmal dyskinesia in which dystonic episodes occur in response to stress, previous studies suggested that retarded development of gamma-aminobutyric acid (GABA)ergic inhibition plays a critical role in the pathogenesis. In the present study, we therefore examined the effects of selective GABA uptake inhibitors on severity of dystonia in dtsz hamsters. R(-)N-(4,4-di(3-methylthien-2-yl)-but-3-enyl) nipecotic acid hydrochloride (tiagabine, 5-20 mg/kg i.p.) and 1-[2-[[(diphenylmethylene) imino]oxy]ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride (NNC-711, 1-10 mg/kg i.p.) significantly reduced the severity of dystonia. These data suggest that GABA uptake inhibitors may provide novel therapeutic approaches for paroxysmal dyskinesias.

Various types of hereditary dystonia are regarded as a basal ganglia disorder, but the underlying mechanisms are still unknown. In the dt hamster, a genetic animal model of age-dependent paroxysmal dystonia, recent studies demonstrated a reduced density of striatal parvalbumin-immunoreactive (PV) GABAergic interneurons at an age of maximum severity of dystonia in comparison with age-matched nondystonic controls. So far, alterations of other types of striatal interneurons in dt hamsters cannot be excluded. Therefore, we determined the density of calretinin-immunoreactive (CR) interneurons in the dt mutant at an age of maximum severity and after spontaneous remission of dystonia in comparison with age-matched nondystonic controls using an image analysis system and a stereologic counting method in a blinded fashion. At an age of maximum severity of dystonia, CR interneuron density was significantly lower in dt hamsters in comparison with controls (-20%), whereas no significant differences between the animal groups could be detected after spontaneous remission of dystonia. The comparison of CR interneuron density between young hamsters with those at an age of > 90 days revealed a significant ontogenetic decrease of CR interneurons in both animal groups (dt hamsters: -38%, controls: -54%). These results demonstrate that alterations of striatal interneuron density in dt mutants are not restricted to PV ones. A deficit of CR interneurons that coexpress GABA may contribute to previous findings of disinhibition of striatal projection neurons in the dt mutant at an age of maximum expression of dystonia.

Previous studies suggested an involvement of gamma-aminobutyric acid (GABA)-mediated excitation by an enhanced efflux of bicarbonate ions in addition to retarded development of GABAergic inhibition in the syndrome of dt(sz) mutant hamsters, a model of paroxysmal dyskinesia in which dystonic episodes occur in response to stress. Acetazolamide blocks bicarbonate regeneration in neurons and can thereby reduce GABA-mediating excitation without affecting GABA-mediated inhibition. In the present study, the effects of acetazolamide (15-60 mg/kg, i.p.) on severity of dystonia were therefore examined in dt(sz) hamsters. Acetazolamide significantly reduced the severity of dystonia at a dose of 60 mg/kg. These data are in line with several case reports from patients with paroxysmal dystonia, suggesting that acetazolamide can be useful in the treatment of this movement disorder. The mechanism of the antidystonic efficacy of acetazolamide has to be examined by further studies.

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.

Dystonias are movement disorders whose pathomechanism is largely unknown. Dystonic dt(sz) hamsters represent a model of primary dystonias, where alterations of striatal interneuron density and sodium channel function in projection neurones were described. Here, using cortico-striatal slices, we explore whether also the communication between neocortex and striatum is altered in dt(sz) hamsters. Field and intracellular recordings were done in dorsomedial striatum. Electrical stimulation was used to mimic neocortical afferents. Neuronal characteristics, synaptic connections, input-output relations and short- and long-term plasticity were analysed. Regarding cellular properties, striatal neurons of affected animals showed no alterations. Concerning network properties, evoked responses at threshold stimulation were mediated by (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptors. In dt(sz) slices, field responses, paired-pulse accentuation and LTP were larger than in control, possibly by an increase in presynaptic release probability at glutamatergic synapses. In summary, the study indicates that a change of cortico-striatal communication is involved in the manifestation of paroxysmal dystonia in the dt(sz) mutant.

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.

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.

Dystonia is a highly frequent movement disorder, the pathogenesis of which remains unclear. The cloning of TorsinA, the gene responsible for early-onset dystonia, was a major breakthrough. However, the function of this protein remains unclear. By sequence homology, TorsinA belongs to the ATPases associated with diverse cellular activities-family, many of whose members are chaperones and/or proteases. We report here that in an in vitro model for oxidative stress, H2O2 treatment, overexpression of TorsinA was protective against cell death. COS-1 cells overexpressing TorsinA demonstrated drastically reduced terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling-staining following exposure to H2O2. Furthermore, transfection with TorsinA significantly increased survival of PC12 after H2O2 treatment. To our knowledge, this is the first demonstration that TorsinA protects against oxidative stress. We speculate that a loss of this cellular function in mutant TorsinA may be linked to the pathogenesis of early-onset dystonia.

The effects of the novel kynurenine 3-hydroxylase inhibitor 3,4-dimethoxy-N-[4-(3-nitrophenyl)thiazol-2-yl]benzenesulfonamide (Ro 61-8048) on severity of dystonia were examined in dt(sz) mutant hamsters, an animal model of paroxysmal dystonia, in which stress precipitates dystonic episodes. Ro 61-8048 (50, 100 and 150 mg/kg i.p.) significantly reduced the severity of dystonia in dt(sz) hamsters without leading to marked central side effects. Determinations of kynurenic acid concentrations in brain homogenates demonstrated that Ro 61-8048 (100 mg/kg i.p.) provoked a two- to threefold increase of the endogeneous broad spectrum glutamate receptor antagonist kynurenic acid in the striatum, cerebellum and brainstem of mutant hamsters. The antidystonic efficacy of Ro 61-8048 at well-tolerated doses suggests that kynurenine 3-hydroxylase inhibitors should be considered as new therapeutic candidates for the treatment of dyskinesias.

Previous studies have shown beneficial effects of the cannabinoid CB(1)/CB(2) receptor agonist (R)-4,5-dihydro-2-methyl-4-(4-morpholinylmethyl)-1-(1-naphthalenylcarbonyl)-6H-pyrrolo [3,2,1-ij]quinolin-6-one mesylate (WIN 55,212-2) in dt(sz) mutant hamsters, a model of idiopathic paroxysmal dystonia (dyskinesia). To examine the pathophysiological significance of the cannabinergic system in the dystonic syndrome, the effect of the cannabinoid CB(1) receptor antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide (SR 141716A) on severity of dystonia was investigated in dt(sz) mutants which exhibit episodes of dystonic and choreoathetotic disturbances in response to mild stress. SR 141716A (5 and 10 mg/kg i.p.) failed to exert any effects on the severity of dystonia. While the antidystonic efficacy of WIN 55,212-2 (5 mg/kg i.p.) was confirmed, cannabidiol (which has low affinity to cannabinoid receptors) tended to delay the progression of dystonia only at a high dose (150 mg/kg i.p.). The antidystonic and cataleptic effects of WIN 55,212-2 (5 mg/kg i.p.) were completely antagonized by pretreatment with SR 141716A at doses of 2.5 mg/kg (catalepsy) and 10 mg/kg (antidystonic efficacy). These data indicate that the antidystonic efficacy of WIN 55,212-2 is selectively mediated via CB(1) receptors. The lack of prodystonic effects of SR 141716A together with only moderate antidystonic effects of WIN 55,212-2 suggests that reduced activation of cannabinoid CB(1) receptors by endocannabinoids is not critically involved in the dystonic syndrome. In view of previous pathophysiological findings in mutant hamsters, the antidystonic efficacy of WIN 55,212-2 can be explained by modulation of different neurotransmitter systems within the basal ganglia.

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., (Copyright 2002 Wiley-Liss, Inc.)

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.

Deep brain stimulation (DBS), a treatment for modulating the abnormal central neuronal circuitry, has become the standard of care nowadays and is sometimes the only option to reduce symptoms of movement disorders such as dystonia. However, on the one hand, there are still open questions regarding the pathomechanisms of dystonia and, on the other hand, the mechanisms of DBS on neuronal circuitry. That lack of knowledge limits the therapeutic effect and makes it hard to predict the outcome of DBS for individual dystonia patients. Finding electrophysiological biomarkers seems to be a promising option to enable adapted individualised DBS treatment. However, biomarker search studies cannot be conducted on patients on a large scale and experimental approaches with animal models of dystonia are needed. In this review, physiological findings of deep brain stimulation studies in humans and animal models of dystonia are summarised and the current pathophysiological concepts of dystonia are discussed. [ABSTRACT FROM AUTHOR]

The pathophysiology of idiopathic dystonias is still unknown, but it is regarded as a basal ganglia disorder. Previous experiments in the dt sz hamster, a model of primary paroxysmal dystonia, demonstrated reduced discharge rates and an abnormal pattern within the entopeduncular nucleus (EPN), a basal ganglia output structure. To clarify if this is based on abnormal γ-aminobutyric acid(GABA)ergic or glutamatergic input, microinjections into the EPN were done in mutant hamsters in the present study. The GABAA receptor antagonists pentylenetetrazole and bicuculline exerted moderate antidystonic effects, while previous systemic administrations worsened dystonia in the dt sz mutant. GABA-potentiating drugs, i.e., the GABAA receptor agonist muscimol and the GABA transporter inhibitor 1,2,5,6-tetrahydro-1-[2-[[(diphenylmethylene)amino]oxy]ethyl]-3-pyridinecarboxy-lic acid (NNC-711), which are known to improve dystonia after systemic treatment in mutant hamsters, did not exert significant effects after EPN injections, but NNC-711 tended to increase the severity at the highest dose (2.5 ng bilateral). The NMDA receptor antagonist d(−)-2-amino-5-phosphopentanoic acid (AP-5) retarded the onset of a dystonic attack. However, this effect was not dose dependent and the AMPA receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzol(f)quinoxaline (NBQX) alone or in combination with AP-5 and NNC-711, also failed to show any effects on dystonia. The present data do not provide clear evidence for an enhanced striatal GABAergic input or a reduced glutamatergic activation of the EPN via the subthalamic nucleus, i.e., more pronounced antidystonic effects of GABAA receptor antagonists and stronger prodystonic effects of GABAmimetics and glutamate receptor antagonists were expected. Nevertheless, previously found changes in entopeduncular activity probably play a critical pathophysiological role in dystonic hamsters. [ABSTRACT FROM AUTHOR]

Previous studies suggested that glutamatergic overactivity contributes to the manifestation of dystonia in the dtsz mutant hamster, a model of idiopathic paroxysmal dyskinesia in which dystonic episodes occur in response to mild stress. Therefore, the role of polyamines, known as positive modulators of NMDA receptors, was examined in the present study. The levels of polyamines (putrescine, spermidine, spermine) were determined in forebrain, cerebellum and brainstem in dtsz hamsters at an age of most marked expression of dystonia (32 days) and in age-matched non-dystonic control hamsters. Spermine was found to be significantly increased in the forebrain (35%) of dystonic animals, while spermidine was unaltered in dystonic brains and only a moderate increase in putrescine (12%) was detected in the cerebellum of dtsz mutants. In view of enhanced spermine levels, the effect of the putative polyamine receptor antagonist ifenprodil on the severity of dystonia was examined in dystonic hamsters. Ifenprodil (5–40 mg/kg i.p.) failed to exert a beneficial effect, but even aggravated dystonia in the dtsz mutant at higher doses. These data together with previous pharmacological findings in mutant hamsters do not completely exclude a pathophysiological role of enhanced polyamine levels but suggest that overstimulation of NMDA receptors which contain NR2B subunits by enhanced spermine levels is not involved in the dystonic syndrome. [Copyright &y& Elsevier]

The metabotropic glutamate 5 (mGlu 5) receptor is critically involved in corticostriatal plasticity which is disturbed in various animal models of dystonia. Recently, the positive allosteric modulator 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB) exerted prodyskinetic effects in a phenotypic model of episodic dystonia. In the DYT1 knock-in (KI) mouse, a model for a persistent type of dystonia, previous ex vivo electrophysiological experiments indicated that mGlu 5 receptors are involved in abnormal striatal plasticity. Therefore, in the present study we examined the mGlu 5 receptor expression in the striatum and cortex of DYT1 KI mice in comparison with wildtype littermates. By immunohistochemistry (IHC) we found a lower expression of mGlu 5 receptors in the cortex (16%) and ventral striatum (10%) but not in the whole striatum of DYT1 KI mice, while mRNA levels were merely lower in the striatum of DYT1 KI mice (43%). However, mGlu 5 receptor protein levels measured by western blotting showed no significant differences in tissue of the whole striatum and in the cortex between both genotypes. Since DYT1 KI mice do not exhibit dystonic symptoms, we investigated if CDPPB provokes dystonia or dyskinesia. CDPPB (10, 20 and 30 mg/kg intraperitoneal, i.p.) did not induce abnormal movements and the locomotor activity did not differ between DYT1 KI and wildtype mice. The present data do not provide evidence for a crucial role of the mGlu 5 receptor in the pathophysiology of DYT1 dystonia, but corticostriatal changes are in line with the hypothesis of maladaptive plasticity in dystonia. • mGlu 5 receptor density is not higher in striatum and cortex of DYT1 mice. • mGlu 5 receptor expression data support maladaptive plasticity hypothesis in dystonia. • No abnormal movements occurred in DYT1 KI mice after application of CDPPB. • mGlu 5 receptors seem not to play a major role in the pathophysiology of dystonia. [ABSTRACT FROM AUTHOR]