Non-dystonic Control Hamsters Research Articles

Expression of metabotropic glutamate 5 receptors in the striatum and cortex and effects of modulators on the severity of dystonia in the phenotypic dtsz model

The metabotropic glutamate 5 (mGlu5) 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 mGlu5 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 dtsz 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 mGlu5 receptors in dystonic hamsters. The mGlu5 receptor mRNA did not differ between the dtsz mutant and control hamsters, while immunohistochemical studies indicated that the mGlu5 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 mGlu5 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.

Role of striatal NMDA receptor subunits in a model of paroxysmal dystonia

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 dtsz 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 dtsz 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 dtsz hamsters and non-dystonic control hamsters, NVP-AAM077 (50nM) completely blocked LTP in dtsz 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 dtsz 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.

Persistent changes of corticostriatal plasticity in dtsz mutant hamsters after age-dependent remission of dystonia

Abnormal plasticity in the cortico-basal ganglia–thalamocortical loop has been suggested to represent a key factor in the pathophysiology of dystonia. In a model of primary paroxysmal dystonia, the dtsz mutant hamster, previous experiments have shown a strongly increased long-term potentiation (LTP) in comparison to non-dystonic control hamsters. These basal changes, i.e. in the absence of dystonia, were found in young animals at an age of 5weeks, when the age-dependent dystonia in dtsz mutant reaches highest severity. In the present study we examined in corticostriatal slices (1) whether the increases in synaptic plasticity can be modulated by stressful stimuli which induce dystonic episodes in young mutant hamsters, and (2) whether increases of LTP persist after spontaneous remission of dystonia in animals older than 10weeks. The present data show that in slices of young mutant hamsters the extent of LTP was not influenced by the presence of dystonia: In comparison to age-matched control hamsters, LTP was increased in mutant hamsters independent of preceding stressful stimulation. After remission of dystonia, i.e., in older dtsz mutant hamsters >10weeks, only LTP could be elicited, while in preparations from age-matched control hamsters, either LTP or long-term depression developed, depending on previous behavioral challenge. We conclude that in mature brain, corticostriatal connections have the potential for changes in metaplasticity, while in dtsz mutant hamsters this metaplasticity is persistently infringed even though stress-inducible dystonic symptoms are lost.

P.1.d.008 The involvement of an intact prefrontal cortex–hippocampal circuit in the forced swim test in male and female rats

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 dtsz 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 dtsz 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 30 mg/kg i.p.) and delayed the onset of a dystonic episode after intrastriatal injections (0.12 and 0.24 μg). As shown by present electrophysiological examinations in corticostriatal slices of dtsz hamsters and non-dystonic control hamsters, NVP-AAM077 (50 nM) completely blocked LTP in dtsz slices, but did not exert significant effects on LTP in non-dystonic controls. In contrast, the NR2B antagonist Ro 25-6981 (1–10 μmol) reduced LTP to a lower extent in dtsz 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.

Autoradiographic and pharmacological studies on the role of dopamine D3 receptors in genetically dystonic ( dtsz) hamsters

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. [ 125I]7-[[(E)-3-iodoprop-2-enyl]-propylamino]-5,6,7,8-tetrahydronaphthalen-2-ol ([ 125I]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 40 mg/kg which induced hyperlocomotion. These results suggest that periodic elevations of dopamine levels in these animals are not related to D3 receptor dysfunctions.

Pharmacological and autoradiographic studies on the pathophysiological role of GABA B receptors in the dystonic hamster: pronounced antidystonic effects of baclofen after striatal injections

The GABA B receptor (GABA BR) agonist baclofen is known to have a beneficial potency in patients who suffer from dystonia, a neurological syndrome characterized by involuntary co-contractions of opposing muscles. The underlying mechanisms of this movement disorder are still unclear. Previous studies in the dt sz hamster, an animal model of primary paroxysmal dystonia, revealed alterations of the GABAergic system, including a reduction of striatal GABAergic interneurons and an altered GABA A receptor (GABA AR) binding in several brain regions. In order to clarify the pathophysiological role of central GABA BRs in the hamster mutant, we performed pharmacological and receptor autoradiographic studies. Systemic administration of the GABA BR agonist (R)-baclofen (1.5, 2.5 and 3.5 mg/kg i.p.) produced pronounced antidystonic effects in the dt sz hamster. Striatal microinjections of baclofen (0.125, 0.25 and 0.5 μg/0.5 μl) also strongly reduced the severity of dystonia. Single striatal administration of the selective GABA BR antagonist CGP 35348 [(3-Aminopropyl)(diethoxymethyl)phosphinic acid, 5 and 10 μg/0.5 μl] did not influence the severity of dystonia, but antagonized the antidystonic effect of baclofen. For receptor autoradiographic studies, [H3]-CGP 54626 ([S-(R*,R*)]-[3-[[1-(3,4-Dichlorophenyl)ethyl]amino]-2-hydroxypropyl](cyclohexylmethyl)phosphinic acid) binding was determined in dt sz hamsters in comparison to non-dystonic control hamsters. [H3]-CGP 54626 binding was not altered in motor areas but in some limbic structures of dt sz hamsters. In view of the absence of striatal changes in GABA B binding, the strong antidystonic effect of baclofen after its striatal microinjection is probably related to a suppression of a pathophysiologically increased synaptic activity.

Altered nicotinamide adenine dinucleotide (NADH) fluorescence in dtsz 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.

Extracellular amino acid levels in the striatum of the dtsz mutant, a model of paroxysmal dystonia

The pathophysiology of idiopathic dystonia is still unknown, but it is regarded as a basal ganglia disorder. Previous studies indicated an involvement of a striatal GABAergic disinhibition and a cortico-striatal glutamatergic overactivity in the manifestation of stress-inducible dystonic episodes in the dt sz hamster, a model of idiopathic paroxysmal dystonia. These investigations were carried out postmortem or in anesthetized animals. In the present study, in vivo microdialysis in conscious, freely-moving dt sz and non-dystonic control hamsters was used to examine the levels of GABA, aspartate, glutamate, glutamine, glycine and taurine in each animal during following conditions: (1) at baseline in the absence of dystonia, (2) during an episode of paroxysmal dystonia precipitated by stressful stimuli, (3) during a recovery period and (4) at baseline after complete recovery. In comparison to non-dystonic controls, which were treated in the same manner as the dystonic animals, no differences could be detected under basal conditions. The induction of a dystonic episode in mutant hamsters led to higher contents of glycine in these animals in comparison to stressed but non-dystonic controls. Significant changes of glycine levels within the animal groups were not detected. The levels of the excitatory amino acids glutamate, glutamine and aspartate as well as the levels of the inhibitory amino acids GABA and taurine did not differ between the animal groups or between the periods of measurement. The higher levels of glycine might contribute to the manifestation of paroxysmal dystonia in dt sz hamsters, although unaltered glutamate, glutamine and aspartate levels do not support the hypothesis of a critical involvement of a cortico-striatal overactivity. It seems that a deficiency of GABAergic interneurons, found by previous immunohistochemical examinations, does not lead to reduced extracellular GABA levels in the striatum.

Acetylcholine receptor binding and cholinergic interneuron density are unaltered in a genetic animal model of primary 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 [ 3H]-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). [ 3H]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.

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, [ 3H]DPCPX (8-cyclopentyl-1,3-dipropylxanthine) binding to adenosine A 1 receptors and [ 3H]CGS 21680 (2 p-(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.

Altered expression of preproenkephalin and prodynorphin mRNA in a genetic model of paroxysmal dystonia

The dt sz mutant hamster represents a model of primary paroxysmal dystonia, in which dystonic episodes occur in response to stress. Previous examinations demonstrated striatal dysfunctions in dt sz hamsters. In the present study, in situ hybridization was used to examine preproenkephalin and prodynorphin expression as potential indices of imbalances between the striatopallidal and striatonigral pathways. Brain analyses were performed in dt sz hamsters under basal conditions, i.e., in the absence of dystonia, as well as mutant hamsters that exhibited severe stress-induced dystonic attacks immediately prior to sacrifice. In the striatum the basal expression of prodynorphin tended to be higher, while that of preproenkephalin tended to be lower in mutant hamsters in comparison to non-dystonic control hamsters. Significant basal changes were restricted to higher levels of prodynorphin in the ventrolateral striatum and lower prodynorphin and preproenkephalin mRNA expression in the hippocampus and/or in subregions of the hypothalamus. After stressful stimulation, the neuropeptides increased in several regions in both animals groups. In comparison to stimulated control hamsters, a significantly lower prodynorphin expression was found in several limbic areas of stimulated mutant hamsters during the manifestation of dystonia, while preproenkephalin mRNA was significantly lower in the anterior and dorsal striatal subregions and in nucleus accumbens. Since changes in the expression of these opioid peptides have been suggested to be related to abnormal dopaminergic activity, the present findings may reflect disturbances in striatal dopaminergic systems, and also in limbic structures in the dt sz mutant, particularly during the expression of 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.

Polyamines in a genetic animal model of paroxysmal dyskinesia

Previous studies suggested that glutamatergic overactivity contributes to the manifestation of dystonia in the dt sz 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 dt sz 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 dt sz 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 dt sz 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.

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 (dtsz), a model of idiopathic paroxysmal dystonia in which episodes of dystonia occur in response to stress. In the present study, [3H]AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionate) receptor binding was determined by autoradiographic analyses in 41 brain (sub)regions of dtsz 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 [3H]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 [3H]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 dtsz hamsters.

Spontaneous Remission of Paroxysmal Dystonia Coincides with Normalization of Entopeduncular Activity indtszMutants

Recent studies have shown a dramatically decreased spontaneous discharge rate of entopeduncular neurons in a unique animal model of idiopathic paroxysmal dystonia, the dt(sz) mutant hamster. These changes were found in animals at the age at which the most marked expression of dystonia is usually observed. In this rodent model, the age-dependent disappearance of stress-inducible dystonic attacks at an age of approximately 10 weeks allows investigations of the relevance of pathophysiological changes for the occurrence of dystonia by ontogenetic studies. Therefore, we examined the entopeduncular activity by extracellular single unit recordings in groups of dt(sz) mutants and nondystonic control hamsters at 17-22 weeks of age. In contrast to recent findings, after the complete remission of dystonia, the mean discharge rate of entopeduncular neurons in dt(sz) mutants (28.1 +/- 1.2 spikes/sec) was similar to that of age-matched nondystonic control hamsters (30.8 +/- 0.9 spikes/sec). Thus, the disappearance of paroxysmal dystonia is accompanied by a normalization of the entopeduncular activity in dt(sz) mutants. The present data clearly demonstrate the fundamental importance of a decreased basal ganglia output for the expression of paroxysmal dystonia.

Antidystonic efficacy of nitric oxide synthase inhibitors in a rodent model of primary paroxysmal dystonia.

In a hamster model (genetic symbol dt(sz)) of primary paroxysmal non-kinesiogenic dystonic choreoathetosis, recent studies have shown beneficial effects of glutamate and dopamine receptor antagonists. Nitric oxide (NO), synthesized from L-arginine by NO synthase in response to glutamate receptor activation, elicits cyclic GMP and modulates glutamate-mediated processes and striatal dopamine release. Therefore, the effects of NO synthase inhibitors and of L-arginine on severity of dystonia were investigated in dt(sz) hamsters in which dystonic attacks, characterized by twisting movements and postures, can be induced by stress. The NO synthase inhibitors N(G)-nitro-L-arginine (L-NNA), N(G)-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole significantly reduced the severity of dystonia. At antidystonic effective doses neither L-NNA nor L-NAME caused observable side effects, whereas 7-nitroindazole exerted moderate reduction of locomotor activity. The antidystonic effect of L-NAME was reversed by co-administration of the NO precursor L-arginine. However, L-arginine administered alone did not exert any effect on severity of dystonia. Cerebellar cyclic GMP levels in brains of mutant hamsters in comparison to non-dystonic control hamsters did not significantly differ, but the cerebellar cyclic GMP levels tended to be increased in dt(sz) hamsters during a dystonic attack. L-NAME significantly decreased the cerebellar cyclic GMP levels in both dt(sz) and control hamsters. Although an overproduction of NO is probably not critically involved in the pathogenesis of paroxysmal dystonia, it may contribute to the manifestation of dystonic attacks, as indicated by the antidystonic effects of NO synthase inhibitors. Peripheral side effects may limit the clinical use of NO synthase inhibitors, but more selective inhibitors of the neuronal NO synthase should be considered as interesting candidates for the treatment of paroxysmal dystonia.

Expression of cholecystokinin, somatostatin, thyrotropin-releasing hormone, glutamic acid decarboxylase and tyrosine hydroxylase genes in the central nervous motor systems of the genetically dystonic hamster.

In the dt(sz) mutant hamster with idiopathic generalized dystonia, functional abnormalities of several neurotransmitters have been suggested to play a role in the development of symptoms. In the present study, we have used histochemistry with (35)S-ATP labeled oligonucleotides to determine whether these abnormalities are associated with modulation in the expression of neurotransmitter genes in motor regions. We examined the expression of genes encoding cholecystokinin (CCK), somatostatin (SRIF), thyrotropin-releasing hormone (TRH), glutamic acid decarboxylase (GAD), tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP43) in the cortex and basal ganglia of dystonic hamsters and of non-dystonic control hamsters of a related inbred line and of a non-related outbred line. The distribution of these mRNAs in normal hamster brain was similar to that in normal rat brain. In all cortical regions studied (frontal, parietal and piriformis), the expression of CCK was similar in dystonic and inbred controls but was significantly greater than in outbred controls. In the anterior thalamus, CCK expression was lower in dystonic hamsters than in both control groups. SRIF expression was significantly decreased in the cortex and striatum of dystonic animals than in inbred and outbred control hamsters. GAD expression was lower in the striatum and substantia nigra, pars reticulata of dystonic than in outbred hamsters, but similar values were found in all groups in the other regions studied. TH was lower in the substantia nigra of dystonic than in inbred controls. No changes were found in GAP43 expression. This study demonstrates that changes in modulation of the expression of some peptides and neurotransmitter enzymes can be found in the dystonic hamster, which is in contrast to other animal models such as the dystonic rat, where no such changes have been found. The present data are consistent with previous findings in dt(sz) hamsters that suggest a dysfunction within the basal ganglia-thalamocortical circuits.

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.