Dystonic Hamsters Research Articles

Deep brain stimulation by optimized stimulators in a phenotypic model of dystonia: Effects of different frequencies

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 dtsz 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 dtsz 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 dtsz mutant. The response to EPN-DBS confirms that the dtsz 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.

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.

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

Striatal cholinergic dysfunction has been suggested to play a critical role in the pathophysiology of dystonia. In the dtsz 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 dtsz 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.

Lower KV7.5 Potassium Channel Subunit Expression in an Animal Model of Paroxysmal Dystonia.

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.

Changes in dynorphin immunoreactivity but unaltered density of enkephalin immunoreactive neurons in basal ganglia nuclei of genetically dystonic hamsters

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.

Effects of pharmacological entopeduncular manipulations on idiopathic dystonia in the dt sz mutant hamster

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.

High frequency stimulation of the entopeduncular nucleus sets the cortico-basal ganglia network to a new functional state in the dystonic hamster

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.

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.

Decreased density of amygdaloid parvalbumin-positive interneurons and behavioral changes in dystonic hamsters (Mesocricetus auratus).

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.

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.

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.

Striatal dopamine transporter density in first episode schizophrenia assessed with IPT-SPECT

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

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

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

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

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

CGS 21680 exerts marked antidystonic effects in a genetic model of paroxysmal dyskinesia

The effect of the adenosine A 2A receptor agonist CGS 21680 (2-carboxyethyl)phenylethylamino]-5′- N-ethylcarbonyamido-adenosine) on severity of dystonia was examined in genetically dystonic hamsters which exhibit attacks of dystonic and choreoathetotic disturbances in response to mild stress. CGS 21680 significantly reduced the severity of dystonia (0.5, 1.0 and 2.0 mg/kg i.p.). The marked antidystonic effects of CGS 21680 in the hamster model suggest that this compound may represent an interesting candidate for the therapy of paroxysmal dystonia. Furthermore, the present data indicate that the precipitating effect of caffeine in patients with paroxysmal dystonia is probably due to its adenosine receptor antagonistic action.

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

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

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.

In vivo extracellular electrophysiology of pallidal neurons in dystonic and nondystonic hamsters

In the dt(sz) hamster, a model of idiopathic paroxysmal dystonia, recent findings indicated a decreased neuronal activity within the globus pallidus (GP) and an impaired gamma aminobutyric acid (GABA)ergic function when compared to nondystonic controls. Therefore, in the present study, extracellular single-unit recordings combined with systemical application of a subconvulsant prodystonic dose of pentylenetetrazole (PTZ) were used to compare the electrophysiological properties of GP neurons in anesthetized dt(sz) hamsters and nondystonic controls. The spontaneous discharge rate of GP neurons was not decreased but a trend towards a wide-ranged distribution was found in mutants compared to controls. Since the single-unit activity of striatal neurons was recently shown to be significantly increased in dt(sz) hamsters, the lack of significant changes in GP discharge rates was unpredicted. We suggest that this is due to antagonistic convergent striatal and subthalamic inputs and to lateral monosynaptic inhibition known for striatum and GP. While no significant changes of the discharge rate of GP neurons could be detected, the spike morphology was significantly altered in dt(sz) hamsters, suggesting subtle impaired information processing in the GP. The lack of marked changes in basal firing pattern may be related to the anesthesia. Administration of PTZ (25 mg/kg i.p.) at a subconvulsant dose, which aggravates dystonia in awake dt(sz) hamsters, seemed to induce more marked changes in spike morphology and firing pattern in mutants than in controls, although the discharge rate did not differ significantly between both animal groups in response to PTZ. In view of recent findings, we assume that GABAergic dysfunctions in dystonic hamsters are of regionally different extent.

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

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

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

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