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

Network-wide effects of pallidal deep brain stimulation normalised abnormal cerebellar cortical activity in the dystonic animal model

BACKGROUND

Deep brain stimulation (DBS) targeting globus pallidus internus (GPi) is a recognised therapy for drug-refractory dystonia. However, the mechanisms underlying this effect are not fully understood. This study explores how pallidal DBS alters spatiotemporal pattern formation of neuronal dynamics within the cerebellar cortex in a dystonic animal model, the dtsz hamster.

METHODS

We conducted in vitro analysis using a high-density microelectrode array (HD-MEA) in the cerebellar cortex. For investigating the spatiotemporal pattern, mean firing rates (MFR), interspike intervals (ISI), spike amplitudes, and cerebellar connectivity among healthy control hamsters, dystonic dtsz hamsters, DBS- and sham-DBS-treated dtsz hamsters were analysed. A nonlinear data-driven method characterised the low-dimensional representation of the patterns in MEA data.

RESULTS

Our HD-MEA recordings revealed reduced MFR and spike amplitudes in the dtsz hamsters compared to healthy controls. Pallidal DBS induced network-wide effects, normalising MFR, spike amplitudes, and connectivity measures in hamsters, thereby countervailing these electrophysiological abnormalities. Additionally, network analysis showed neural activity patterns organised into communities, with higher connectivity in both healthy and DBS groups compared to dtsz.

CONCLUSIONS

These findings suggest that pallidal DBS exerts some of its therapeutic effects on dystonia by normalising neuronal activity within the cerebellar cortex. Our findings of reduced MFR and spike amplitudes in the dtsz hamsters could be a hint of a decrease in neuronal fibres and synaptic plasticity. Treatment with pallidal DBS led to cerebellar cortical activity similar to healthy controls, displaying the network-wide impact of local stimulation.

Multitarget Multiscale Simulation for Pharmacological Treatment of Dystonia in Motor Cortex

A large number of physiomic pathologies can produce hyperexcitability in cortex. Depending on severity, cortical hyperexcitability may manifest clinically as a hyperkinetic movement disorder or as epilpesy. We focus here on dystonia, a movement disorder that produces involuntary muscle contractions and involves pathology in multiple brain areas including basal ganglia, thalamus, cerebellum, and sensory and motor cortices. Most research in dystonia has focused on basal ganglia, while much pharmacological treatment is provided directly at muscles to prevent contraction. Motor cortex is another potential target for therapy that exhibits pathological dynamics in dystonia, including heightened activity and altered beta oscillations. We developed a multiscale model of primary motor cortex, ranging from molecular, up to cellular, and network levels, containing 1715 compartmental model neurons with multiple ion channels and intracellular molecular dynamics. We wired the model based on electrophysiological data obtained from mouse motor cortex circuit mapping experiments. We used the model to reproduce patterns of heightened activity seen in dystonia by applying independent random variations in parameters to identify pathological parameter sets. These models demonstrated degeneracy, meaning that there were many ways of obtaining the pathological syndrome. There was no single parameter alteration which would consistently distinguish pathological from physiological dynamics. At higher dimensions in parameter space, we were able to use support vector machines to distinguish the two patterns in different regions of space and thereby trace multitarget routes from dystonic to physiological dynamics. These results suggest the use of in silico models for discovery of multitarget drug cocktails.

Changes in GABAergic inputs in the paraventricular nucleus maintain sympathetic vasomotor tone in chronic heart failure

The paraventricular nucleus (PVN) of the hypothalamus is an important region of the brain involved in the regulation of sympathetic vasomotor tone. Accumulating evidence supports the idea that a change in hypothalamic γ-aminobutyric acid (GABA)-ergic inhibitory and glutamatergic excitatory inputs contribute to the exacerbated sympathetic drive in chronic heart failure (HF). The purpose of this study was to determine whether a possible imbalance between glutamatergic and GABAergic inputs to the PVN contributes to increased sympathetic outflow in HF in two different sympathetic territories. Renal (RSNA) and splanchnic sympathetic nerve activity (SSNA), mean arterial blood pressure (MAP) and heart rate were recorded from urethane-anesthetized HF or sham rats. The NMDA-glutamate and GABA-A receptor densities within the PVN were quantified in HF and sham rats by autoradiography. Bilateral microinjection of kynurenic acid (4nmol) into the PVN decreased MAP and RSNA and SSNA in HF but not in sham rats. Furthermore, in response to GABA-A blockade in the PVN by bicuculline (400 pmol), hypertension and SSNA were reduced in HF compared to sham. The quantification of ionotropic NMDA receptors and GABA-A receptors in the PVN showed a significant reduction of GABA-A in HF rats; however, the NMDA density in the PVN did not differ between groups. Thus, this study provides evidence that the sympathoexcitation is maintained by an imbalance between GABAergic and glutamatergic inputs in the PVN in HF. The reduced GABAergic input results in relatively augmented glutamatergic actions in the PVN of HF rats.

The differential modulation of the ventral premotor-motor interaction during movement initiation is deficient in patients with focal hand dystonia

A major feature of focal hand dystonia (FHD) pathophysiology is the loss of inhibition. One inhibitory process, surround inhibition, for which the cortical mechanisms are still unknown, is abnormal in FHD. As the ventral premotor cortex (PMv) plays a key role in the sensorimotor processing involved in shaping finger movements and has many projections onto the primary motor cortex (M1), we hypothesized that the PMv-M1 connections might play a role in surround inhibition. A paired-pulse transcranial magnetic stimulation paradigm was used in order to evaluate and compare the PMv-M1 interactions during different phases (rest, preparation and execution) of an index finger movement in patients with FHD and controls. A sub-threshold conditioning pulse (80% resting motor threshold) was applied to the PMv at 6 ms before M1 stimulation. The right abductor pollicis brevis, a surround muscle, was the target muscle. In healthy controls, the results showed that PMv stimulation induced an ipsilateral ventral premotor-motor inhibition at rest. This cortico-cortical interaction changed into an early facilitation (100 ms before movement onset) and turned back to inhibition 50 ms later. In patients with FHD, this PMv-M1 interaction and its modulation were absent. Our results show that, although the ipsilateral ventral premotor-motor inhibition does not play a key role in the genesis of surround inhibition, PMv has a dynamic influence on M1 excitability during the early steps of motor execution. The impaired cortico-cortical interactions observed in patients with FHD might contribute, at least in part, to the abnormal motor command.

Rats with different thresholds for DMCM-induced clonic convulsions differ in the sleep-time of diazepam and [(3)H]-Ro 15-4513 binding

The current study investigated the possible inherent relationship between convulsions and sleep involving the GABA(A)/benzodiazepine site complex. The aim of this study was to determine if rats with high (HTR) and low (LTR) thresholds for clonic convulsions induced by DMCM, a benzodiazepine inverse agonist, differ in the following aspects: (1) sensitivity to the hypnotic effects of the GABA(A) positive allosteric modulators diazepam, pentobarbital and ethanol and (2) in the binding of [(3)H]-flunitrazepam, a benzodiazepine agonist, measured by autoradiography, and [(3)H]-Ro 15-4513, a benzodiazepine partial inverse agonist, to membranes from discrete brain regions. The LTR subgroup presented a shorter diazepam-induced sleeping time compared to that of the HTR subgroup. Biochemical assays revealed that the LTR subgroup did not differ in [(3)H]-flunitrazepam binding compared to the HTR subgroup. With respect to the binding of [(3)H]-Ro 15-4513, the LTR subgroup had higher binding in the brainstem and lower binding in the striatum compared to the HTR subgroup. These results suggest that differences in the benzodiazepine site on the GABA(A) receptor may underlie the susceptibility to DMCM-induced convulsions and sensitivity to the hypnotic effect of diazepam.

In vivo evidence for GABA(A) receptor changes in the sensorimotor system in primary dystonia

BACKGROUND

Preclinical and clinical evidence suggests that impaired gamma-aminobutyric (GABA) control, leading to disinhibition within the sensorimotor system, might play a role in dystonia. Aim of this study is the in vivo assessment of the GABAergic system in dystonia using positron emission tomography (PET) and (11) C-flumazenil, a selective GABA(A) receptor ligand.

METHODS

Fourteen subjects with primary dystonia (9 carriers of the DYT1 mutation and 5 sporadic cases) were compared to 11 controls, using a simplified reference tissue model to measure binding potential.

RESULTS

Voxel-based analyses showed a reduction in GABA(A) receptor expression/affinity both in DYT1 carriers and sporadic patients in primary motor and premotor cortex, primary and secondary somatosensory cortex, and in the motor component of the cingulate gyrus.

CONCLUSIONS

Dysfunction of GABA(A) receptors in sensorimotor systems in primary (genetic and sporadic) dystonia supports the view that lack of GABAergic control may be associated with the generation of dystonic movements.

Effects of Striatal GABAA-Receptor Blockade on Striatal and Cortical Activity in Monkeys

To elucidate the role of ambient striatal γ-aminobutyric acid (GABA) in the regulation of neuronal activity in the basal ganglia–thalamocortical circuits, we studied the effects of blocking striatal GABAA receptors on the electrical activities of single striatal neurons, on local field potentials (LFPs) in the striatum, and on motor cortical electroencephalograms (EEGs) in two monkeys. Striatal LFPs were recorded with a device that allowed us to simultaneously record field potentials and apply drugs by reverse microdialysis at the same site. Administration of the GABAA-receptor antagonist gabazine (SR95531, 10 and 500 μM) induced large-amplitude LFP fluctuations at the infusion site, occurring every 2–5 s for about 2 h after the start of the 20-min drug administration. These events were prevented by cotreatment with a GABAA-receptor agonist (muscimol, 100 μM) or a combination of ionotropic glutamate receptor antagonists (CNQX and MK-801, each given at 100 μM). Gabazine (10 μM) also increased the firing of single neurons recorded close to the injection site, but in most cases there was no correlation between single-neuron activity and the concomitantly recorded LFP signals from the same striatal region. In contrast, intrastriatal application of gabazine increased the correlation between striatal LFPs and EEG, and resulted in the appearance of recurrent EEG events that were temporally related to the striatal LFP events. These data provide evidence that a GABAergic “tone” in the monkey striatum controls the spontaneous activity of striatal neurons, as well as the level of striatal and cortical synchrony.

Voxel based morphometry reveals specific gray matter changes in primary dystonia

The present study assessed patterns of brain tissue alterations in different types of primary dystonia using voxel-based morphometry (VBM). Nine patients with primary generalized dystonia (GD), 11 patients with primary cervical dystonia (CD), and 11 patients with primary focal hand dystonia (FHD) as well as 31 age and gender-matched controls were included. When compared with healthy controls, patients with primary dystonia (n=31) showed gray matter volume increase bilaterally in the globus pallidus internus, nucleus accumbens, prefrontal cortex, as well as unilaterally in the left inferior parietal lobe. This is the first study using VBM in patients with different types of primary dystonia, showing a common pattern of gray matter changes.

Screening of GABAA-receptor gene mutations in primary dystonia

Several lines of evidence suggest that GABA-ergic neurotransmission plays a role in the pathogenesis of primary dystonia in humans. In this study, we tested the hypothesis that mutations in the GABRA1, GABRB3, and GABRG2 genes encoding the alpha1, beta3, and gamma subunits of the GABA(A) receptor are involved in familial primary dystonia. All exons and exon-intron boundaries of the above genes were amplified by PCR from genomic DNA in 28 patients who had primary dystonia and a positive family history but had no mutation in any other genes known to be involved in primary dystonia. The PCR products were analyzed by single strand conformation polymorphism followed by sequencing of variant conformers compared with normal controls (n = 54). We found no mutations in these genes. We did, however, find a new polymorphism, 559 + 80G>A in intron 5 of GABRA1, and we also confirmed several that were previously reported, including 315C>T in exon 3 and 588C>T in exon 5 of GABRG2, but there were no significant differences between controls and patients in the allele and genotype frequencies of these polymorphisms. In conclusion, mutations of GABRA1, GABRB3, and GABRG2 appear not to play a major role in the development of familial primary dystonia.

GABAergic circuits in the basal ganglia and movement disorders

GABA is the major inhibitory neurotransmitter in the basal ganglia, and GABAergic pathways dominate information processing in most areas of these structures. It is therefore not surprising that abnormalities of GABAergic transmission are key elements in pathophysiologic models of movement disorders involving the basal ganglia. These include hypokinetic diseases such as Parkinson's disease, and hyperkinetic diseases, such as Huntington's disease or hemiballism. In this chapter, we will briefly review the major anatomic features of the GABAergic pathways in the basal ganglia, and then describe in greater detail the changes of GABAergic transmission, which are known to occur in movement disorders.

Prenatal stress and early adoption effects on benzodiazepine receptors and anxiogenic behavior in the adult rat brain

Chronic maternal stress during pregnancy has been associated with behavioral alterations that persist into adulthood. Moreover, adoption procedures performed immediately after birth can reverse these alterations. In this study, we examined the effects of prenatal restraint stress and adoption at birth (cross-fostering) on the behavioral response to an anxiety-provoking situation and on the adult male offspring expression of benzodiazepine (BDZ) receptors in selected brain areas. Adult offspring of rats stressed during the last week of pregnancy exhibited higher levels of anxiety than control rats. The anxiogenic behavior found at the elevated plus maze (EPM) has been related to the reduced levels of BDZ receptor levels in specific brain areas. Adult offspring of rats stressed during pregnancy exhibited a decrease in the number of BDZ receptors binding sites in the central amygdaloid nucleus (Ce), CA1, CA3, and the dentate gyrus regions of the hippocampus when compared to controls. Regarding the adoption procedure, control pups raised by a foster gestationally stressed mother showed similar levels of anxiety as stressed groups. Stressed offspring raised by a foster control mother showed reduced anxiety levels compared to that of the control groups. Adoption per se showed no difference in time spent, neither in the open arms of the plus maze nor in BDZ receptor levels, when compared to the corresponding control and stressed groups. Stressed offspring raised by a foster control mother reverted BDZ receptor levels to control values. However, control pups raised by a gestationally stressed foster mother showed similar values compared to the control offspring in hippocampus, in spite of showing an anxiogenic behavior in the EPM. We found a significant increase of Ce BDZ receptor levels in control offspring raised by a foster stressed mother that could be explained as a compensatory effect to a GABA receptor desensitization. In summary, the behavioral outcome of the adult offspring is vulnerable both to the stress experience during the late prenatal period as well as to possible variations in care during lactation by mothers subjected to chronic stress during gestation. There seems to be a direct correlation between anxiety state and BDZ receptor levels in the adult offspring raised by their biological mothers. However, the mechanism of BDZ regulation leading to an anxious behavior might be different if the insult is received only postnatally as opposed to both pre and postnatally.

Mapping convulsants' binding to the GABA-A receptor chloride ionophore: a proposed model for channel binding sites

Gamma-aminobutyric acid (GABA) type A receptors play a key role in brain inhibitory neurotransmission, and are ligand-activated chloride channels blocked by numerous convulsant ligands. Here we summarize data on binding of picrotoxin, tetrazoles, beta-lactams, bicyclophosphates, butyrolactones and neurotoxic pesticides to GABA-A ionophore, and discuss functional and structural overlapping of their binding sites. The paper reviews data on convulsants' binding sensitivity to different point mutations in ionophore-lining second trans-membrane domains of GABA-A subunits, and maps possible location of convulsants' sites within the chloride ionophore. We also discuss data on inhibition of glycine, glutamate, serotonin (5-HT3) and N-acetylcholine receptors by GABA-A channel blockers, and examine the applicability of this model to other homologous ionotropic receptors. Positioning various convulsant-binding sites within ionophore of GABA-A receptors, this model enables a better understanding of complex architectonics of ionotropic receptors, and may be used for developing new channel-modulating drugs.

Learning deficits induced by sleep deprivation and recovery are not associated with altered [3H]muscimol and [3H]flunitrazepam binding

Several studies have shown that sleep deprivation produces deficits in learning tasks, but mechanisms underlying these effects remain unclear. Other lines of evidence indicate an involvement of brain GABA systems in cognitive processes. Here, we investigated the possibility that alterations in GABA(A) or benzodiazepine (BDZ) receptor binding might underlie avoidance deficits induced by sleep deprivation. Rats were deprived of sleep for 96 h using the platform method and then trained in a step-through inhibitory avoidance task, or allowed to recover sleep for 24 h before training (sleep rebound group). Thirty minutes after training, animals were given a retention test. Both sleep-deprived and sleep-recovered animals showed a significant impairment in avoidance responding compared to cage controls, and the sleep-deprived group performed significant worse than the sleep-recovered group. A separate group of animals was sacrificed either immediately after 96 h of sleep deprivation or after 96 h of sleep deprivation followed by 24 h of sleep recovery. [(3)H]muscimol and [(3)H]flunitrazepam binding were examined by quantitative autoradiography in 42 brain regions, including areas involved in cognitive processes. No significant differences among groups were found in any brain region, except for a reduction in [(3)H]flunitrazepam binding in the frontal cortex of sleep-recovered animals. These results confirm the deleterious effects of sleep loss on inhibitory avoidance learning, but suggest that such deficits cannot be attributed to altered GABA(A) or BDZ binding in brain.

Treatment of inferior lateral pterygoid muscle dystonia with zolpidem tartrate, botulinum toxin injections, and physical self-regulation procedures: a case report

The following case report depicts the management of a patient suffering with a jaw opening oromandibular dystonia using a combination of botulinum toxin injections, zolpidem, and relaxation procedures. Eventually the botulinum toxin injections were eliminated, and the patient was maintained with only zolpidem and relaxation procedures.

GABAergic function in Alzheimer's disease: evidence for dysfunction and potential as a therapeutic target for the treatment of behavioural and psychological symptoms of dementia

Alzheimer's disease (AD) is characterized by disruptions in multiple major neurotransmitters. While many studies have attempted to establish whether GABA is disrupted in AD patients, findings have varied. We review evidence for disruptions in GABA among patients with AD and suggest that the variable findings reflect subtypes of the disease that are possibly manifested clinically by differing behavioural symptoms. GABA, the major inhibitory neurotransmitter, has long been a target for anxiolytics, hypnotic sedatives, and anticonvulsants. We review the clinical use of GABAergic agents in treating persons with AD symptoms. While newer generation GABAergic medications are now available, they have yet to be evaluated among patients with AD.

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

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

Role of GABA A and GABA B receptors in GABA-induced inhibition of rat red nucleus neurons

We investigated GABA receptor subtypes mediating GABA-induced inhibition of red nucleus (RN) neuronal firing recorded extracellularly from anaesthetized rats. GABA response was mimicked by the GABA(A) agonists muscimol and isoguvacine in all cases and was partially blocked by the GABA(A) antagonist bicuculline. The GABA(B) agonist baclofen induced a long-lasting inhibition in 84% of cells. Neurons responding to either GABA(A) or GABA(B) agonists were equally distributed within the RN. The GABA(C) receptor agonist cis-amino-crotonic acid (CACA) did not modify RN neuronal firing; at high doses CACA occasionally induced inhibition abolished by bicuculline and thus mediated by GABA(A) receptors. We conclude that the inhibitory effects of GABA in the RN are mediated by both GABA(A) and GABA(B) receptors, whereas GABA(C) receptors are not involved.

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

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

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

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

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

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

Paradoxical aggravation of paroxysmal dystonia during chronic treatment with phenobarbital in a genetic rodent model

Recent studies in mutant hamsters (dt(sz)), an animal model of primary paroxysmal dystonia, indicated that altered function of the gamma-aminobutyric acid (GABA)ergic system plays a critical role in the pathogenesis of dystonia. In the present study, dt(sz) hamsters were chronically treated with phenobarbital, which has been found to exert antidystonic effects in mutant hamsters after acute administration. In untreated dt(sz) hamsters, the severity of dystonia follows an age-dependent time course with a maximum between the 30th and 40th day of life, followed by a continuous decline of severity until complete remission occurs at the age of about 70 days. In contrast to acute effects, chronic treatment with phenobarbital via drinking water starting at an age of 21 days (i.e., after weaning) worsened dystonia and retarded the spontaneous remission. The unexpected prodystonic effect was more marked after administration of higher doses and when chronic treatment with phenobarbital started at an age of 1 day (neonatal administration via breast milk). After withdrawal of phenobarbital at the age of 70 days, the severity rapidly declined in all treated groups. When phenobarbital was readministered 1 week later, the hamsters again exhibited severe dystonia. The mechanism of these unexpected findings is unknown. Tentatively, activity-dependent GABA-mediated excitation caused by chronic treatment with phenobarbital may be important for the prodystonic effects under pathological conditions in dt(sz) hamsters.

Ictal SPECT in paroxysmal non-kinesigenic dyskinesia. Case report and review of the literature

Purpose: Paroxysmal non-kinesigenic dyskinesia (PNKD) should be included in the list of differential diagnosis in patients with refractory epilepsy. Although the pathophysiological mechanisms that underlie this disorder remain controversial, it is now accepted that the basal ganglia are the anatomical substrate responsible for it.Material and methods: We report a 16-year-old mentally retarded male with PNKD admitted for video-EEG monitoring and ictal SPECT, which showed hyperperfusion on the right caudate and thalamus.Conclusion: This case supports more evidence for the involvement of the caudate nucleus and thalamus in the mechanisms responsible for the production of PNKD.

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.

Immediate increase in benzodiazepine binding in rat brain after a single brief experience in the plus maze: a paradoxical effect

A single drug-free experience in the elevated plus-maze is well documented to reduce the behavioral effects of benzodiazepines (BZs) in subsequent tests. To ascertain the possible role of altered BZ receptor binding to in this phenomenon, rats received a 5-min exposure to the elevated plus maze and were immediately sacrificed. Receptor autoradiography revealed that [3H]flunitrazepam binding was significantly elevated in several amygdaloid and hippocampal nuclei (range: 13-23%); [3H]muscimol binding in adjacent sections was not significantly altered. These results suggest that BZ receptors can change very rapidly in response to anxiogenic conditions. However, the unexpected finding that [3H]flunitrazepam binding is increased by maze exposure suggests that the subsequent loss of BZ anxiolytic effects in the plus-maze is probably unrelated to alterations in BZ binding in brain.

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

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

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

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

Pathology of idiopathic dystonia: findings from genetic animal models

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

Differential expression of glutamate decarboxylase messenger RNA in cerebellar Purkinje cells and deep cerebellar nuclei of the genetically dystonic rat

The genetically dystonic rat exhibits a motor syndrome that closely resembles the human disease, generalized idiopathic dystonia. Although in humans dystonia is often the result of pathology in the basal ganglia, previous studies have revealed electrophysiological abnormalities and alterations in glutamate decarboxylase, the synthetic enzyme for GABA, in the cerebellum of dystonic rats. In this study, we further characterized the alterations in cerebellar GABAergic transmission in these mutants by examining the expression of the messenger RNA encoding glutamate decarboxylase (67000 mol. wt) with in situ hybridization histochemistry at the single cell level in Purkinje cells and neurons of the deep cerebellar nuclei. Glutamate decarboxylase (67000 mol. wt) messenger RNA levels were increased in the Purkinje cells and decreased in the deep cerebellar nuclei of dystonic rats compared to control littermates, suggesting opposite changes in GABAergic transmission in Purkinje cells and in their target neurons in the deep cerebellar nuclei. In contrast, levels of glutamate decarboxylase (67000 mol. wt) messenger RNA in the pallidum, and of enkephalin messenger RNA in the striatum, were unaffected in dystonic rats. The data indicate that both the Purkinje cells and GABAergic neurons of the deep cerebellar nuclei are the site of significant functional abnormality in the dystonic rat.

The early-onset torsion dystonia gene (DYT1) encodes an ATP-binding protein

Early-onset torsion dystonia is a movement disorder, characterized by twisting muscle contractures, that begins in childhood. Symptoms are believed to result from altered neuronal communication in the basal ganglia. This study identifies the DYT1 gene on human chromosome 9q34 as being responsible for this dominant disease. Almost all cases of early-onset dystonia have a unique 3-bp deletion that appears to have arisen idependently in different ethnic populations. This deletion results in loss of one of a pair of glutamic-acid residues in a conserved region of a novel ATP-binding protein, termed torsinA. This protein has homologues in nematode, rat, mouse and humans, with some resemblance to the family of heat-shock proteins and Clp proteases.

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

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

The autoradiographic perspective of central benzodiazepine receptors; a short review

1. We reviewed studies performed to characterize central benzodiazepine binding sites. 2. An overview of the different radioligands used to characterize BZ1 and BZ2 binding sites and a mapping of these central benzodiazepine sites are described. 3. Saturation studies carried out by autoradiogram quantification also are reviewed. 4. The specific use of the autoradiographic technique to carry out studies on ontogeny, development, and phylogeny is discussed, as well as studies performed using this technique on some diseases and experimental conditions, such as drug treatments or chemical and mechanical lesions.

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

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

Quantitative autoradiography reveals regionally selective changes in dopamine D1 and D2 receptor binding in the genetically dystonic hamster

Dystonia has been proposed to be caused by abnormal input from thalamus to premotor cortex due to altered activity of the striatum projecting by way of the globus pallidus and substantia nigra pars reticulata to the thalamus. However, in the case of idiopathic dystonia, i.e. the most common form of dystonia in humans, there is only limited evidence to support such a neuroanatomic concept. In view of the problems of studying the pathophysiology of idiopathic dystonia in patients, genetically determined animal models of idiopathic dystonia may be used as a practical means of studying brain dysfunctions involved in this movement disorder. The genetically dystonic hamster is an animal model of idiopathic dystonia that displays sustained abnormal movements and postures either spontaneously or in response to mild environmental stimuli. Autoradiographic analysis of dopamine D1 receptor density, using the ligand [3H]SCH 23390, revealed significant decreases of D1 binding in several parts of the striatum and substantia nigra pars reticulata of dystonic hamsters. Binding of the D2 ligand [3H]YM-09151-2 was decreased in the dorsomedial caudate-putamen, but increased in nucleus accumbens. In most other sites studied, no significant changes were found in either [3H]SCH 23390 or [3H]YM-09151-2 binding. By studying groups of dystonic hamsters in the absence and presence of dystonic attacks, it was shown that most changes in D1 and D2 binding were not secondary to abnormal movement but rather due to the dystonic condition of the animals. The study provides evidence of altered dopamine receptor binding in dystonia and confirms the concept that basal ganglia dysfunction may be a primary component of dystonia.

Increased levels of kynurenic acid in brains of genetically dystonic hamsters

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

GabaA Receptors: Pharmacology, Behavioral Roles, and Motor Disorders

τ-Aminobutyric acid (GABA), the most prevalent inhibitory neurotransmitter in the mammalian brain, exerts its main action through GABAA receptors. They belong to the superfamily of ligand-gated ion channels and respond to GABA by the opening of an intrinsic anion channel. Multiple GABAA receptor subtypes in the brain show differential regional and developmental expression patterns. The receptors have a pentameric structure and are formed from members of at least three different subunit families (α1–6, β1–3, and τ1–3). The regulation of functional properties by GABA and its analogs and by benzodiazepine (BZ) receptor ligands differs dramatically with the type of α variant in the receptor complex. Additional variations of GABAA receptors result from substitution of γ subunits. The role of the β subunits, which are essential for receptor assembly, is less well defined on a functional basis. Besides their involvement in anxiolysis and sedation, GABAA receptors clearly have an impact on motor coordination. However, with the possible exception of the alcohol-and BZ-sensitive alcohol non-tolerant (ANT) rat line, it is not well documented whether a genetic alteration in this receptor system is directly involved in the impairment of animal or human motor activity.

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

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