Chronic intermittent convection-enhanced delivery of vigabatrin to the bilateral subthalamic nucleus in an acute rat seizure model

Targeted intracerebral drug delivery is an attractive experimental approach for the treatment of drug-resistant epilepsies. In this regard, the subthalamic nucleus (STN) represents a focus-independent target involved in the remote modulation and propagation of seizure activity. Indeed, acute and chronic pharmacological inhibition of the STN with vigabatrin (VGB), an irreversible inhibitor of GABA transaminase, has been shown to produce antiseizure effects. This effect, however, is lost over time as tolerance develops with chronic, continuous intracerebral pharmacotherapy. Here we investigated the antiseizure effects of chronic intermittent intra-STN convection-enhanced delivery of VGB in an acute rat seizure model focusing on circumventing tolerance development and preventing adverse effects. Timed intravenous pentylenetetrazol (PTZ) seizure threshold testing was conducted before and after implantation of subcutaneous drug pumps and bilateral intra-STN cannulas. Drug pumps infused vehicle or VGB twice daily (0.4 µg) or once weekly (2.5 µg, 5 µg) over three weeks. Putative adverse effects were evaluated and found to be prevented by intermittent compared to previous continuous VGB delivery. Clonic seizure thresholds were more clearly raised by intra-STN VGB compared to myoclonic twitch. Both twice daily and once weekly intra-STN VGB significantly elevated clonic seizure thresholds depending on dose and time point, with responder rates of up to 100% observed at tolerable doses. However, tolerance could not be completely avoided, as tolerance rates of 40-75% were observed with chronic VGB treatment. Results indicate that the extent of tolerance development after intermittent intra-STN VGB delivery varies depending on infusion dose and regimen.

Long-lasting antiseizure effects of chronic intrasubthalamic convection-enhanced delivery of valproate

Intracerebral drug delivery is an experimental approach for the treatment of drug-resistant epilepsies that allows for pharmacological intervention in targeted brain regions. Previous studies have shown that targeted pharmacological inhibition of the subthalamic nucleus (STN) via modulators of the GABAergic system produces antiseizure effects. However, with chronic treatment, antiseizure effects are lost as tolerance develops. Here, we report that chronic intrasubthalamic microinfusion of valproate (VPA), an antiseizure medication known for its wide range of mechanisms of action, can produce long-lasting antiseizure effects over three weeks in rats. In the intravenous pentylenetetrazole seizure-threshold test, seizure thresholds were determined before and during chronic VPA application (480 μg/d, 720 μg/d, 960 μg/d) to the bilateral STN. Results indicate a dose-dependent variation in VPA-induced antiseizure effects with mean increases in seizure threshold of up to 33%, and individual increases of up to 150%. The lowest VPA dose showed a complete lack of tolerance development with long-lasting antiseizure effects. Behavioral testing with all doses revealed few, acceptable adverse effects. VPA concentrations were high in STN and low in plasma and liver. In vitro electrophysiology with bath applied VPA revealed a reduction in spontaneous firing rate, increased background membrane potential, decreased input resistance and a significant reduction in peak NMDA, but not AMPA, receptor currents in STN neurons. Our results suggest an advantage of VPA over purely GABAergic modulators in preventing tolerance development with chronic intrasubthalamic drug delivery and provide first mechanistic insights in intracerebral pharmacotherapy targeting the STN.

Present in the Aquatic Environment, Unclear Evidence in Top Predators-The Unknown Effects of Anti-Seizure Medication on Eurasian Otters (Lutra lutra) from Northern Germany

Emerging contaminants are produced globally at high rates and often ultimately find their way into the aquatic environment. These include substances contained in anti-seizure medication (ASM), which are currently appearing in surface waters at increasing concentrations in Germany. Unintentional and sublethal, chronic exposure to pharmaceuticals such as ASMs has unknown consequences for aquatic wildlife. Adverse effects of ASMs on the brain development are documented in mammals. Top predators such as Eurasian otters (Lutra lutra) are susceptible to the bioaccumulation of environmental pollutants. Still little is known about the health status of the otter population in Germany, while the detection of various pollutants in otter tissue samples has highlighted their role as an indicator species. To investigate potential contamination with pharmaceuticals, Eurasian otter brain samples were screened for selected ASMs via high-performance liquid chromatography and mass spectrometry. Via histology, brain sections were analyzed for the presence of potential associated neuropathological changes. In addition to 20 wild otters that were found dead, a control group of 5 deceased otters in human care was studied. Even though none of the targeted ASMs were detected in the otters, unidentified substances in many otter brains were measured. No obvious pathology was observed histologically, although the sample quality limited the investigations.

Acute and chronic convection-enhanced muscimol delivery into the rat subthalamic nucleus induces antiseizure effects associated with high responder rates

Intracerebral drug delivery is an emerging treatment strategy aiming to manage seizures in patients with systemic drug-resistant epilepsies. In rat seizure and epilepsy models, the GABA_A receptor agonist muscimol has shown powerful antiseizure potential when injected acutely into the subthalamic nucleus (STN), known for its capacity to provide remote control of different seizure types. However, chronic intrasubthalamic muscimol delivery required for long-term seizure suppression has not yet been investigated. We tested the hypothesis that chronic convection-enhanced delivery (CED) of muscimol into the STN produces long-lasting antiseizure effects in the intravenous pentylenetetrazole seizure threshold test in female rats. Acute microinjection was included to verify efficacy of intrasubthalamic muscimol delivery in this seizure model and caused significant antiseizure effects at 30 and 60 ng per hemisphere with a dose-dependent increase of responders and efficacy and only mild adverse effects compared to controls. For the chronic study, muscimol was bilaterally infused into the STN over three weeks at daily doses of 60, 300, or 600 ng per hemisphere using an implantable pump and cannula system. Chronic intrasubthalamic CED of muscimol caused significant long-lasting antiseizure effects for up to three weeks at 300 and 600 ng daily. Drug responder rate increased dose-dependently, as did drug tolerance rates. Transient ataxia and body weight loss were the main adverse effects. Drug distribution was comparable (about 2-3 mm) between acute and chronic delivery. This is the first study providing proof-of-concept that not only acute, but also chronic, continuous CED of muscimol into the STN raises seizure thresholds.

AB0680 Psychological impact of autologous stem cell transplantation in systemic sclerosis patients and influence of support and coping strategies

Background

In severe cases of systemic sclerosis (SSc), autologous hematopoietic stem cell transplantation (aHSCT) is superior compared to cyclophosphamide with respect to effect on skin and lung manifestations, survival and quality of life. Nevertheless, major physical and psychological impacts have been found in a first qualitative study by Spierings et al. (2020) 1.

Objectives

Assessment of subjectively experienced physical and psychological impacts of aHSCT and exploration of potential interrelations of those impacts.

Methods

A SSc sample was assessed retrospectively after aHSCT in a two-step-approach. In the first step, 6 questionnaires were used: Global physical and mental health (SF-36 and Scleroderma Health Assessment Questionnaire = SHAQ), body image (Adapted Satisfaction with Appearance Scale = ASWAP), coping strategies (Freiburger Fragebogen zur Krankheitsverarbeitung = FKV-15), resilience (Resilienzskala = RS-11), and control beliefs (Fragebogen zur Erfassung von Kontrollüberzeugung zu Krankheit und Gesundheit = KKG). In the second step, semi-structured interviews based on Spierings et al. (2020) 1 were conducted and analysed via mixed methods qualitative content analysis following Mayring (2014).

Results

19 patients (12 female, 7 male, mean age 53.47 years (SD = 9.50)) completed all questionnaires and interviews in a mean time of 6.56 years after aHSCT (SD = 3.90, range 1-12 years). A strong correlation was found between perceived physical impairment (SHAQ) and body image dissatisfaction (ASWAP) (Pearson’s r = .63, p < .001). There was also a strong negative correlation between body image dissatisfaction (ASWAP) and the physical component of SF-36 (pcSF-36; r = -.59, p = .004) and a smaller correlation for the mental component of SF-36 (mcSF-36: r = -.38, p = .054). Depressive coping was negatively associated with SF-36 (pcSF-3: r = -.605, p = .003; mcSF-36: r = -.808, p < .001) (see Figure 1), whereas resilience was associated with a positive impact (pcSF-36: r = .622, p = .002; mcSF-36 r = .595, p = .004). In the qualitative content analysis of the interviews, all patients reported symptom improvements (mainly skin), which were associated with their coping strategies (depressive coping with fewer improvements, active coping with more improvements). Describing their emotional state during aHSCT, 7 patients verbalized “despair”, 6 “loss of control”, 5 “emotional instability”, 4 ”distress due to distance from home”, 4 “loneliness”, 3 “listlessness”, 2 “concern for feelings of relatives”, and 2 “depersonalisation”. As valuable professional emotional support during aHSCT, 6 patients named nurses and 8 named physicians, while the crucial role of daily ward rounds of the specialised transplant team rather than the primary care team was emphasised. The additional support by a psychology team was not deemed necessary by 7 patients, while 4 patients would have wished such a support. 7 patients rated their physical and mental recovery after aHSCT as satisfying, 4 as better than expected, 4 as disappointing, and 3 as causing impatience.

Figure 1.

Correlation of SF-36 (physical and mental component) and FVK-15 (Depressive Coping Score) by Pearson’s Correlation Coefficient

Conclusion

A transient negative impact of aHSCT on mental wellbeing of the majority of SSc patients is evident, but can be relieved by professional teams highly specialised in this particular treatment option.

References

[1]Julia Spierings, et al. From “being at war” to “getting back on your feet”: A qualitative study on experiences of patients with systemic sclerosis treated with hematopoietic stem cell transplantation. Journal of Scleroderma and Related Disorders, vol. 5, 3: pp. 202-209.

Disclosure of Interests

None declared

POS0809 CHARACTERIZATION OF RELAPSES IN PATIENTS WITH GIANT CELL ARTERITIS (GCA) PATIENTS- DATA FROM THE REAL-LIFE TREATMENT AND SAFETY (REATS)-GCA COHORT

Background

Giant cell arteritis (GCA) has the tendency to relapse once treatment is tapered or stopped. Such relapses represent a potential threat to GCA patients as they can lead to severe symptoms and organ damage.

Objectives

To assess the frequency and type of relapses in patients with GCA

Methods

The Real-Life Treatment and Safety (REATS)-GCA cohort has been established by extracting the data on clinical presentation, inflammatory markers, imaging, comorbidities, treatments and serious adverse events of GCA patients from 6 specialized centres in Germany. We undertook descriptive and survival analyses (Kaplan-Meier), and compared baseline characteristics of participants with vs. without relapse. Ethical approval for the cohort was obtained.

Results

We included 395 patients with a mean age of 71 years, including 264 (66.8 %) females and 129 (32.7%) males. Diagnosis of GCA was supported by temporal artery ultrasound in 37%, 18F-FDG-PET/CT in 29%, temporal artery biopsy in 14% of patients and by MRI or clinically in the remaining patients. 31% of patients presented with an isolated cranial manifestation and 18% with isolated extracranial manifestations. Most common presenting symptoms were headache (57%), fatigue (55%), weight loss (42%) and polymyalgia (38%) (Table 1). The most common comorbidities at the time of study inclusion were arterial hypertension (68%), followed by osteoporosis (26%). Within a median total follow-up duration of 22.2 (11.7-40.6) months, 97 of the 395 patients relapsed including 15 patients who relapsed more than once. The median (IQR) time to first relapse was 12.5 (7.1-21.8) months. Median relapse-free survival was 7.8 years with a relapse risk of 12% (CI, 9 to 15%) at 1 year and 38% (CI, 30 to 45%) at 5 years (Figure 1). Most common symptoms at relapse were headache (35%), polymyalgia (23%), fatigue (19%) and night sweats (12%) (Table 1). Three patients relapsed with sudden loss of vision. Among the 114 relapses observed, 94 (83%) occurred under prednisolone treatment with a median dose of 7.0 mg/day (IQR 4.0-12.5). 26 (23%) occurred under methotrexate and 14 (12%) under tocilizumab treatment. Comparing the baseline characteristics that were documented in this study, we did not find a statistically significant difference in relapsing versus non-relapsing GCA patients.

Table 1.Symptom at disease onsetN=395 (%)Symptom at relapseN=97 (%)Headache216 (54.7)Headache35 (30.7)Fatigue208 (52.7)Polymyalgia (PMR)23 (20.2)Weight loss159 (40.3)Fatigue19 (16.7)Polymyalgia (PMR)144 (36.5)Vision impairment13 (11.4)Night sweats140 (35.4)Night sweats12 (10.5)Headache in the temple area125 (31.6)Headache in the temple area12 (10.5)Jaw pain121 (30.6)Jaw pain11 (9.6)Vision impairment118 (29.9)Morning stiffness7 (6.1)Morning stiffness89 (22.5)Weight loss7 (6.1)Fever80 (20.3)Claudication upper limb6 (5.3)Swelling temporal arteries77 (19.5)Arthralgia6 (5.3)Vision loss57 (14.4)Claudication lower limb5 (4.4)Scalp tenderness38 (9.6)Vision loss3 (2.6)Claudication upper limb38 (9.6)Arthritis3 (2.6)Claudication lower limb34 (8.6)Scalp tenderness2 (1.8)Arthralgia28 (7.1)Fever2 (1.8)Arthritis3 (0.8)Swelling temporal arteries2 (1.8)Figure 1.

Conclusion

About one fourth of GCA patients relapsed and the overwhelming majority of relapses occurred before patients were able to stop glucocorticoids. The leading symptoms at relapse are headache and fatigue, while loss of vision is rare (0.76%). Baseline characteristics seem to be poorly informative about the risk of relapse, therefore regular monitoring of GCA patients is necessary.

Acknowledgements

This research was financially supported by Roche Pharma Ag and Chugai Pharma Europe Ltd.

Disclosure of Interests

Verena Schönau Speakers bureau: Novartis, Janssen, Grant/research support from: Roche, Chugai, Giulia Corte: None declared, Sebastian Ott: None declared, Koray Tascilar: None declared, Fabian Hartmann: None declared, Bernhard Manger: None declared, Bernhard Hellmich: None declared, Alexander Pfeil: None declared, Peter Oelzner: None declared, Wolfgang A. Schmidt: None declared, Andreas Krause: None declared, Marc Schmalzing: None declared, Matthias Fröhlich: None declared, Michael Gernert: None declared, Nils Venhoff: None declared, Jörg Henes: None declared, Jürgen Rech Speakers bureau: Abbvie, Biogen, BMS, Chugai, GSK, Lilly, MSD; Novartis, Roche, Sanofi, Sobi, UCB,, Consultant of: Biogen, BMS, Chugai, GSK, Lilly, MSD, Novartis, Roche, Sanofi, Sobi, UCB, Grant/research support from: Sobi, Novartis, Georg Schett: None declared

OV329, a novel highly potent γ-aminobutyric acid aminotransferase inactivator, induces pronounced anticonvulsant effects in the pentylenetetrazole seizure threshold test and in amygdala-kindled rats

OBJECTIVE

An attractive target to interfere with epileptic brain hyperexcitability is the enhancement of γ-aminobutyric acidergic (GABAergic) inhibition by inactivation of the GABA-metabolizing enzyme GABA aminotransferase (GABA-AT). GABA-AT inactivators were designed to control seizures by raising brain GABA levels. OV329, a novel drug candidate for the treatment of epilepsy and addiction, has been shown in vitro to be substantially more potent as a GABA-AT inactivator than vigabatrin, an antiseizure drug approved as an add-on therapy for adult patients with refractory complex partial seizures and monotherapy for pediatric patients with infantile spasms. Thus, we hypothesized that OV329 should produce pronounced anticonvulsant effects in two different rat seizure models.

METHODS

We therefore examined the effects of OV329 (5, 20, and 40 mg/kg ip) on the seizure threshold of female Wistar Unilever rats, using the timed intravenous pentylenetetrazole (ivPTZ) seizure threshold model as a seizure test particularly sensitive to GABA-potentiating manipulations, and amygdala-kindled rats as a model of difficult-to-treat temporal lobe epilepsy.

RESULTS

GABA-AT inactivation by OV329 clearly increased the threshold of both ivPTZ-induced and amygdala-kindled seizures. OV329 further showed a 30-fold greater anticonvulsant potency on ivPTZ-induced myoclonic jerks and clonic seizures compared to vigabatrin investigated previously. Notably, all rats were responsive to OV329 in both seizure models.

SIGNIFICANCE

These results reveal an anticonvulsant profile of OV329 that appears to be superior in both potency and efficacy to vigabatrin and highlight OV329 as a highly promising candidate for the treatment of seizures and pharmacoresistant epilepsies.

Bypassing the Blood-Brain Barrier: Direct Intracranial Drug Delivery in Epilepsies

Epilepsies are common chronic neurological diseases characterized by recurrent unprovoked seizures of central origin. The mainstay of treatment involves symptomatic suppression of seizures with systemically applied antiseizure drugs (ASDs). Systemic pharmacotherapies for epilepsies are facing two main challenges. First, adverse effects from (often life-long) systemic drug treatment are common, and second, about one-third of patients with epilepsy have seizures refractory to systemic pharmacotherapy. Especially the drug resistance in epilepsies remains an unmet clinical need despite the recent introduction of new ASDs. Apart from other hypotheses, epilepsy-induced alterations of the blood-brain barrier (BBB) are thought to prevent ASDs from entering the brain parenchyma in necessary amounts, thereby being involved in causing drug-resistant epilepsy. Although an invasive procedure, bypassing the BBB by targeted intracranial drug delivery is an attractive approach to circumvent BBB-associated drug resistance mechanisms and to lower the risk of systemic and neurologic adverse effects. Additionally, it offers the possibility of reaching higher local drug concentrations in appropriate target regions while minimizing them in other brain or peripheral areas, as well as using otherwise toxic drugs not suitable for systemic administration. In our review, we give an overview of experimental and clinical studies conducted on direct intracranial drug delivery in epilepsies. We also discuss challenges associated with intracranial pharmacotherapy for epilepsies.

T cells, natural killer cells, and γδT cells in a large patient cohort with rheumatoid arthritis: influence of age and anti-rheumatic therapy

Objective: The aim of this cohort study was to evaluate the distribution of natural killer (NK) cells and T-cell subsets, including γδT cells, in the peripheral blood of patients with rheumatoid arthritis (RA) in a large real-life patient cohort, taking into account the patients' demographics, disease characteristics, and anti-rheumatic therapy.Method: The study recruited 508 RA patients between November 2013 and August 2015. Lymphocyte differentiation using eight-colour flow cytometry (fluorescence-activated cell sorting) of the peripheral blood was performed for all patients. Clinical data, including age, gender, disease duration, serostatus, disease activity, antibody status, immunosuppressive therapy including use of different biological disease-modifying anti-rheumatic drugs (bDMARDs) and conventional synthetic DMARDs, were retrospectively assessed using electronic patient files. Multivariate regression analysis was performed to assess the effect of these variables on T-cell, NK-cell, and γδT-cell counts.Results: The median patient age was 61.0 years and 74.1% were female. The median disease duration of RA was 12.0 years. Median Disease Activity Score based on 28-joint count was 2.8 and 56.3% were treated with bDMARDs. There were no differences in immunosuppressive therapy between different age groups. While rituximab, abatacept, and tocilizumab had no influence on lymphocyte subdifferentiation, tumour necrosis factor (TNF) inhibitors and age significantly influenced the numbers of T cells, T-helper cells, T-NK cells, NK cells, and γδT cells.Conclusion: Age and TNF-inhibition therapy influence lymphocyte subdifferentiation in patients with RA. It may be prudent to use age- and therapy-adjusted standard values for lymphocyte subsets during clinical trials and treatment of RA.

Anticonvulsant effects after grafting of rat, porcine, and human mesencephalic neural progenitor cells into the rat subthalamic nucleus

Cell transplantation based therapy is a promising strategy for treating intractable epilepsies. Inhibition of the subthalamic nucleus (STN) or substantia nigra pars reticulata (SNr) is a powerful experimental approach for remote control of different partial seizure types, when targeting the seizure focus is not amenable. Here, we tested the hypothesis that grafting of embryonic/fetal neural precursor cells (NPCs) from various species (rat, human, pig) into STN or SNr of adult rats induces anticonvulsant effects. To rationally refine this approach, we included NPCs derived from the medial ganglionic eminence (MGE) and ventral mesencephalon (VM), both of which are able to develop a GABAergic phenotype. All VM- and MGE-derived cells showed intense migration behavior after grafting into adult rats, developed characteristics of inhibitory interneurons, and survived at least up to 4 months after transplantation. By using the intravenous pentylenetetrazole (PTZ) seizure threshold test in adult rats, transient anticonvulsant effects were observed after bilateral grafting of NPCs derived from human and porcine VM into STN, but not after SNr injection (site-specificity). In contrast, MGE-derived NPCs did not cause anticonvulsant effects after grafting into STN or SNr (cell-specificity). Neither induction of status epilepticus by lithium-pilocarpine to induce neuronal damage prior to the PTZ test nor pretreatment of MGE cells with retinoic acid and potassium chloride to increase differentiation into GABAergic neurons could enhance anticonvulsant effectiveness of MGE cells. This is the first proof-of-principle study showing anticonvulsant effects by bilateral xenotransplantation of NPCs into the STN. Our study highlights the value of VM-derived NPCs for interneuron-based cell grafting targeting the STN.

ERK and ROCK functionally interact in a signaling network that is compensationally upregulated in Spinal Muscular Atrophy

Spinal Muscular Atrophy (SMA) is a motoneuron disease caused by low levels of functional survival of motoneuron protein (SMN). Molecular disease mechanisms downstream of functional SMN loss are still largely unknown. Previous studies suggested an involvement of Rho kinase (ROCK) as well as the extracellular signal-regulated kinases (ERK) pathways in the pathomechanism. Both pathways are bi-directionally linked and inhibit each other. Thus, we hypothesize that both pathways regulate SMA pathophysiology in vivo in a combined manner rather than acting separately. Here, we applied the repurposed drugs, selumetinib, an ERK inhibitor, and the ROCK inhibitor fasudil to severe SMA mice. Thereby, separately applied inhibitors as well as a combination enabled us to explore the impact of the ROCK-ERK signaling network on SMA pathophysiology. ROCK inhibition specifically ameliorated the phenotype of selumetinib-treated SMA mice demonstrating an efficient ROCK to ERK crosstalk relevant for the SMA pathophysiology. However, ERK inhibition alone aggravated the condition of SMA mice and reduced the number of motoneurons indicating a compensatory hyper-activation of ERK in motoneurons. Taken together, we identified a regulatory network acting downstream of SMN depletion and upstream of the SMA pathophysiology thus being a future treatment target in combination with SMN dependent strategies.

Gpm6b deficiency impairs sensorimotor gating and modulates the behavioral response to a 5-HT2A/C receptor agonist

The neuronal tetraspan proteins, M6A (Gpm6a) and M6B (Gpm6b), belong to the family of proteolipids that are widely expressed in the brain. We recently reported Gpm6a deficiency as a monogenetic cause of claustrophobia in mice. Its homolog proteolipid, Gpm6b, is ubiquitously expressed in neurons and oligodendrocytes. Gpm6b is involved in neuronal differentiation and myelination. It interacts with the N-terminal domain of the serotonin transporter (SERT) and decreases cell-surface expression of SERT. In the present study, we employed Gpm6b null mutant mice (Gpm6b(-/-)) to search for behavioral functions of Gpm6b. We studied male and female Gpm6b(-/-) mice and their wild-type (WT, Gpm6b(+/+)) littermates in an extensive behavioral test battery. Additionally, we investigated whether Gpm6b(-/-) mice exhibit changes in the behavioral response to a 5-HT2A/C receptor agonist. We found that Gpm6b(-/-) mice display completely normal sensory and motor functions, cognition, as well as social and emotionality-like (anxiety, depression) behaviors. On top of this inconspicuous behavioral profile, Gpm6b(-/-) mice of both genders exhibit a selective impairment in prepulse inhibition of the acoustic startle response. Furthermore, in contrast to WT mice that show the typical locomotion suppression and increase in grooming activity after intraperitoneal administration of DOI [(±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride], Gpm6b(-/-) mice demonstrate a blunted behavioral response to this 5-HT2A/C receptor agonist. To conclude, Gpm6b deficiency impairs sensorimotor gating and modulates the behavioral response to a serotonergic challenge.

Anticonvulsant Effects by Bilateral and Unilateral Transplantation of GABA-Producing Cells into the Subthalamic Nucleus in an Acute Seizure Model

Neural transplantation of GABA-producing cells into key structures within seizure-suppressing circuits holds promise for medication-resistant epilepsy patients not eligible for resection of the epileptic focus. The substantia nigra pars reticulata (SNr), a basal ganglia output structure, is well known to modulate different seizure types. A recent microinjection study by our group indicated that the subthalamic nucleus (STN), which critically regulates nigral activity, might be a more promising target for focal therapy in epilepsies than the SNr. As a proof of principle, we therefore assessed the anticonvulsant efficacy of bilateral and unilateral allografting of GABA-producing cell lines into the STN using the timed intravenous pentylenetetrazole seizure threshold test, which allows repeated seizure threshold determinations in individual rats. We observed (a) that grafted cells survived up to the end of the experiments, (b) that anticonvulsant effects can be induced by bilateral transplantation into the STN using immortalized GABAergic cells derived from the rat embryonic striatum and cells additionally transfected to obtain higher GABA synthesis than the parent cell line, and (c) that anticonvulsant effects were observed even after unilateral transplantation into the STN. Neither grafting of control cells nor transplantation outside the STN induced anticonvulsant effects, emphasizing the site and cell specificity of the observed anticonvulsant effects. To our knowledge, the present study is the first showing anticonvulsant effects by grafting of GABA-producing cells into the STN. The STN can be considered a highly promising target region for modulation of seizure circuits and, moreover, has the advantage of being clinically established for functional neurosurgery.

Proconvulsant actions of intrahippocampal botulinum neurotoxin B in the rat

Botulinum neurotoxins (BoNTs) may affect the excitability of brain circuits by inhibiting neurotransmitter release at central synapses. There is evidence that local delivery of BoNT serotypes A and E, which target SNAP-25, a component of the release machinery specific to excitatory synapses, can inhibit seizure generation. BoNT serotype B (BoNT/B) targets VAMP2, which is expressed in both excitatory and inhibitory terminals. Here we assessed the effects of unilateral intrahippocampal infusion of BoNT/B in the rat on intravenous pentylenetetrazol (PTZ) seizure thresholds, and on the expression of spontaneous behavioral and electrographic seizures. Infusion of BoNT/B (500 and 1,000 unit) by convection-enhanced delivery caused a reduction in myoclonic twitch and clonic seizure thresholds in response to intravenous PTZ beginning about 6 days after the infusion. Handling-evoked and spontaneous convulsive seizures were observed in many BoNT/B-treated animals but not in vehicle-treated controls. Spontaneous electrographic seizure discharges were recorded in the dentate gyrus of animals that received local BoNT/B infusion. In addition, there was an increased frequency of interictal epileptiform spikes and sharp waves at the same recording site. BoNT/B-treated animals also exhibited tactile hyperresponsivity in comparison with vehicle-treated controls. This is the first demonstration that BoNT/B causes a delayed proconvulsant action when infused into the hippocampus. Local infusion of BoNT/B could be useful as a focal epilepsy model.

Benefits and risks of intranigral transplantation of GABA-producing cells subsequent to the establishment of kindling-induced seizures

Neural transplantation has been investigated experimentally and clinically for the purpose of developing new treatment options for intractable epilepsy. In the present study we assessed the anticonvulsant efficacy and safety of bilateral allotransplantation of genetically engineered striatal GABAergic rat cell lines into the substantia nigra pars reticulata (SNr). Rats with previously-established seizures, induced by amygdala kindling, were used as a model of temporal lobe epilepsy. Three cell lines were transplanted: (1) immortalized GABAergic cells (M213-2O) derived from embryonic rat striatum; (2) M213-2O cells (CL4) transfected with human GAD67 cDNA to obtain higher GABA synthesis than the parent cell line; and (3) control cells (121-1I), also derived from embryonic rat striatum, but which did not show GAD expression. A second control group received injections of medium alone. Transplantation of M213-2O cells into the SNr of kindled rats resulted in significant but transient anticonvulsant effects. Neither control cells nor medium induced anticonvulsant effects. Strong tissue reactions were, however, induced in the host brain of kindled but not of non-kindled rats, and only in animals that received grafts of genetically modified CL4 cells. These tissue reactions included graft rejection, massive infiltration of inflammatory immune cells, and gliosis. The anticonvulsant effect of M213-2O cells emphasizes the feasibility of local manipulations of seizures by intranigral transplantation of GABA-producing cells. On the other hand, the present data suggest that kindling-induced activation of microglia in the SNr can enhance immune reactions to transplanted cells. In this case, under conditions of further immunological stimulation by CL4 cells, transfected with a human cDNA, substantial immune reactions occurred. Thus, it appears that the condition of the host brain and the production of foreign proteins by transplanted cells have to be considered in estimating the risks of rejection of transplants into the brain.

Comparative analysis of anxiety-like behaviors and sensorimotor functions in two rat mutants, ci2 and ci3, with lateralized rotational behavior

There is increasing evidence that developmental anomalies of cerebral asymmetry are involved in the etiology of psychiatric disorders, including schizophrenia, depression and anxiety. Thus, rodents with abnormal cerebral lateralization are interesting tools to study the association between such anomalies and behavioral dysfunction. The most studied indicator of cerebral asymmetry in the rat is that of circling or rotational behavior. We have recently described two rat mutants, ci2 and ci3, in which lateralized rotational behavior occurs either spontaneously or in response to external stimuli, such as new environment or handling. While cochlear and vestibular defects are found in ci2 rats, ci3 rats do not exhibit any inner ear abnormalities. The abnormal motor response to external stimuli raised the possibility that the circling rat mutants may be more likely to express anxiety-related behavior in tests of emotionality. In the present study, we characterized anxiety-related behaviors of ci2 and ci3 rats in the open field, elevated plus-maze and light/dark exploration test. Furthermore, sensorimotor functions of these rats were evaluated by the rotarod, accelerod and wire hang tests. Heterozygous (ci2/+) littermates or rats of the respective background strains (LEW, BH.7A) were used as controls. In contrast to our expectation, both mutants demonstrated less anxiety-related behavior than controls in tests of emotionality. Ci3 rats exhibited normal sensorimotor functions, whereas marked impairment was observed in ci2 rats, which is most likely a consequence of the vestibular dysfunction in these animals. The acoustic startle response (ASR) and prepulse inhibition of ASR did not differ between ci3 rats and controls. The reduced emotionality of the mutant rats indicated by the present experiments may not be specifically linked to anxiety per se, but is maybe more reflective of impulsivity or the inability to normally perceive or process potentially threatening situations. Based on previous findings of dysfunctions of the central dopamine system in ci2 and ci3 mutant rats, we assume that alterations in dopaminergic activity are involved in the maladaptive behavior observed in the present study.

Auditory and vestibular defects and behavioral alterations after neonatal administration of streptomycin to Lewis rats: Similarities and differences to the circling (ci2/ci2) Lewis rat mutant

The clinical usefulness of aminoglycoside antibiotics is limited by their ototoxicity. In rodents, damage to the inner ear is often associated with rotational behavior and locomotor hyperactivity reminiscent of such behaviors resulting from an imbalance of forebrain dopamine systems. Based on previous observations in the circling (ci2/ci2) Lewis (LEW) rat mutant, a spontaneous mutation leading to hair cell loss, deafness, impairment of vestibular functions, lateralized circling, hyperactivity and alterations in the nigrostriatal dopamine system, we have recently hypothesized that vestibular defects during postnatal development, independent of whether induced or inherited, lead to secondary changes in the dopaminergic system within the basal ganglia, which would be a likely explanation for the typical behavioral phenotype seen in such models. In the present study, we directly compared the phenotype induced by streptomycin in LEW rats with that of the ci2 LEW rat mutant. For this purpose, we treated neonatal LEW rats over 3 weeks by streptomycin, which induced bilateral degeneration of cochlear and vestibular hair cells. Following this treatment period, the behavioral syndrome of the streptomycin-treated animals, including the lateralized rotational behavior, was almost indistinguishable from that of ci2 mutant rats. However, in contrast to the ci2 mutant rat, all alterations, except the hearing loss, were only transient, disappearing between 7 and 24 weeks following treatment. In conclusion, in line with our hypothesis, vestibular defects induced in normal LEW rats led to the same phenotypic behavior as the inherited vestibular defect of ci2 mutant rats. However, with increasing time for recovery, adaptation to the vestibular impairment developed in streptomycin-treated rats, while all deficits persisted in the mutant animals. At least in part, the transient nature of the abnormal behaviors resulting from treatment with streptomycin could be explained by adaptation to the vestibular impairment by the use of visual cues, which is not possible in ci2 rats because of progressive retinal degeneration in these mutants. Although further experiments are needed to prove this hypothesis, the present study shows that direct comparisons between these two models serve to understand the mechanisms underlying the complex behavioral phenotype in rodents with vestibular defects and how these defects are compensated.

Pedunculopontine neurons are involved in network changes in the kindling model of temporal lobe epilepsy

It is well known that epileptogenesis is associated with widespread neuronal network changes in brain regions adjacent to the seizure focus but also in remote structures including basal ganglia. Besides the superior colliculus, the pedunculopontine tegmental nucleus (PPN) is one of three main target regions of basal ganglia output activity and is reciprocally connected with the substantia nigra pars reticulata (SNr), which is critically involved in seizure propagation and manipulation. We here tested the hypothesis if, apart from the traditional view that the superior colliculus mediates seizure-gating mechanisms of the SNr, the PPN is involved in kindling-induced network changes. Rats were electrically kindled via the ipsilateral basolateral amygdala. In vivo extracellular single unit recordings of right PPN neurons were performed in kindled rats 1 day after a generalized seizure in order to examine kindling-associated rather than seizure-associated activity changes. The main findings of the study were (1) a seizure-outlasting drastically reduced firing rate of PPN neurons and (2) an increase in burst and irregular firing pattern in kindled rats compared with sham-kindled and naïve controls. These changes are likely to be caused by an altered inhibitory input from the SNr. Furthermore, kindling caused (3) the oscillation frequency of PPN neurons to shift towards lower frequencies. The kindling-induced activity changes were found to be anatomically restricted to the PPN, indicating that network changes follow distinct anatomical routes. We demonstrated that the PPN is strongly affected by the functional reorganization of neurocircuitry associated with kindling. The underlying mechanisms are discussed. The findings are relevant for a better understanding of kindling-associated network changes and might provide new targets for therapeutic manipulations in epilepsies.

Distribution of GABAergic neurons in the striatum of amygdala-kindled rats: An immunohistochemical and in situ hybridization study

A large body of experimental evidence suggests that the basal ganglia circuitry may be part of a remote control system modulating the spread of epileptic seizures. In the kindling model of temporal lobe epilepsy, this endogenous inhibitory control mechanism seems to be impaired. Neurochemical and neurophysiological studies have indicated that the activity of the GABAergic projection from the striatum to the substantia nigra pars reticulata is reduced in kindled rats, but the exact mechanisms involved in this observation are not known. Possible explanations include a kindling-induced loss of striatal GABAergic projection neurons to the substantia nigra or enhanced inhibition of these neurons by GABAergic interneurons. In the present experiments, the GABAergic system of the striatum (caudate-putamen) of amygdala-kindled rats and controls was studied immunohistochemically with a monoclonal antibody to GABA and with nonisotopic in situ hybridization with cRNA probes selective for glutamic acid decarboxylase 65 (GAD65) and GAD67, respectively. Compared to sham controls, an increased density of neurons heavily labeled for GAD67 mRNA was observed in the anterior striatum of kindled rats when cells were counted 6 weeks after the last kindled seizure. This subgroup of striatal GABAergic neurons has been suggested previously to correspond to the medium-sized aspiny interneurons in the striatum, indicating that kindling is associated with an increased activity of these neurons. Our previous finding of reduced GAD and GABA levels in synaptosomes isolated from the substantia nigra of kindled rats together with the present observation of increased density of GABAergic striatal interneurons in such rats suggest that kindling affects the regulation of the GABAergic projections from the striatum to the substantia nigra rather than directly damaging GABAergic neurons in the striatum.

Subregional changes in discharge rate, pattern, and drug sensitivity of putative GABAergic nigral neurons in the kindling model of epilepsy

The substantia nigra pars reticulata (SNr) is thought to act as a seizure-gating mechanism in kindling and other epilepsy models. We investigated whether the kindling process induces site-specific (anterior-posterior) and seizure-outlasting alterations in the activity of putative GABAergic SNr neurons and in their response to pharmacological manipulation. Female Wistar rats were kindled via the basolateral amygdala by daily stimulation. In vivo extracellular single unit recordings of SNr neurons were performed in kindled rats 1 day after a generalized seizure in order to examine activity changes that outlast the kindled seizures. Sham-kindled and naive rats served as controls. We found a significant and seizure-outlasting increase of discharge rates within the posterior but not within the anterior SNr of kindled rats when compared to controls. Furthermore, kindling resulted in seizure-outlasting burst-like firing pattern of SNr neurons. The antiepileptic drug valproic acid (VPA; 100 mg/kg i.v.) significantly reduced SNr discharge rates in all animal groups. Interestingly, neurons located in the anterior SNr of kindled rats were significantly less depressed by VPA compared to the reduction obtained in naive controls. The present data disclose kindling induced functional plasticity within basal ganglia regions. The findings are relevant for a better understanding of the mechanisms underlying the seizure-gating function of the SNr and might provide new targets for rational therapeutic manipulations, which aim to establish a remote control of epileptic seizures.

Neonatal medial prefrontal cortex lesion enhances the sensitivity of the mesoaccumbal dopamine system

Neurodevelopmental models of schizophrenia posit that early brain damage leads to dys- or misconnection effects possibly altering synaptic transmission in brain sites distal of the lesion. We tested the hypothesis that neonatal medial prefrontal cortex (mPFC) lesions affect the sensitivity of the mesoaccumbal dopamine (DA) system. Using extracellular single-unit recordings combined with systemic application of the DA agonist apomorphine, followed by the D2 receptor antagonist haloperidol or the D1 receptor antagonist SCH23390, we compared electrophysiological properties of nucleus accumbens core and shell neurons after bilateral excitotoxic lesions of mPFC induced at postnatal day 7 or in adult rats. Whereas animals with adult mPFC lesions showed an altered discharge pattern within the core region, neonatal mPFC lesions altered the discharge pattern within the shell region. Subcutaneous administration of apomorphine (4 mg/kg) reduced accumbal firing rate in 77% of all neurons. Onset and magnitude of apomorphine-induced inhibition of neuronal activity was faster and stronger in rats with neonatal but not adult mPFC lesions in both core and shell regions. Apomorphine-induced inhibition was partially reversed by 0.1 mg/kg haloperidol only in core region of neonatal lesioned rats. Apomorphine-induced excitation of neuronal activity (in 21% of all neurons) was reversed by the D1 receptor antagonist SCH23390 (0.1 mg/kg) in all excited neurons. These data support the hypothesis that neonatal but not adult lesions of mPFC alter cortico-striatal networks and suggest that disturbance of mPFC development leads to neurodevelopmental changes in mesoaccumbal DA system during adulthood.

Altered spontaneous discharge rate and pattern of basal ganglia output neurons in the circling (ci2) rat mutant

The circling rat is an autosomal recessive mutant (homozygous ci2/ci2) characterized by lateralized rotational behavior, locomotor hyperactivity, ataxia, stereotypic head movements, and deafness. Previous neurochemical investigations showed that ci2 rats of both genders have a lower tissue content of dopamine in the striatum ipsilateral to the preferred direction of circling. For further evaluation as to whether this striatal imbalance has functional consequences within basal ganglia structures, the spontaneous extracellular single unit activity of GABAergic neurons located in the striatum and, downstream to the dopaminergic nigrostriatal system, the substantia nigra pars reticulata (SNr) was recorded bilaterally in anesthetized ci2 rats. Heterozygous (ci2/+) littermates that display normal behavior, and rats from the background strain (LEW/Ztm) served as controls. No significant hemispheric imbalances in striatal discharge rate and firing pattern were evident in ci2 rats. Furthermore, there were no significant intergroup differences in striatal activity. However, the mean spontaneous discharge rate of SNr neurons was significantly increased in both brain sides, and there was a significant shift toward rhythmic burst-like firing in ci2 mutants. Again, no hemispheric differences were detected. The data substantiate previous findings of altered basal ganglia function in ci2 rats. The abnormal basal ganglia output activity, i.e. of the SNr, is likely to contribute to the complex behavioral disturbances seen in ci2 rats.

Genetically engineered GABA-producing cells demonstrate anticonvulsant effects and long-term transgene expression when transplanted into the central piriform cortex of rats

Local application of GABA-potentiating agents can prevent or reduce the development and maintenance of behavioral seizures induced by limbic kindling in rats. Microinjection and lesion studies suggest that the transition zone between anterior and posterior piriform cortex (PC), termed here central PC, is a potential target for transplantation of GABA-producing cells. In the present study, we transplanted conditionally immortalized mouse cortical neurons, engineered with the GABA-synthesizing enzyme GAD(65), to the central PC of rats. Suspensions of 1.5 x 10(5) cells in 1 microl were transplanted bilaterally. Control animals received transplantation of beta-galactosidase (beta-gal)-expressing cells. All rats were subsequently kindled through a chronically implanted electrode placed in the basolateral amygdala. The pre- and postkindling threshold currents for eliciting behavioral seizures were determined before and after kindling. We found the prekindling partial seizure threshold to be significantly increased by about 200% in the rats that received the GABA-producing cells compared to rats receiving beta-gal-producing transplants. After kindling, the seizure threshold tended to be higher by 100% in rats that received GABA-producing cells, although the difference from controls was not statistically significant. GABA-producing transplants had no significant effect on the rate of amygdala kindling, but the latency to the first generalized seizure during kindling was significantly increased in animals receiving GABA-producing cells. The transplanted cells showed long-term GAD(65) expression as verified immunohistologically after termination of the experiments. The findings substantiate and extend previous findings that the central PC is part of the anatomical substrate that facilitates propagation from partial to generalized seizures. The data demonstrate that genetically engineered cells have the potential to raise seizure thresholds when transplanted to the central PC.

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.

Lack of robust anticonvulsant effects of muscimol microinfusions in the anterior substantia nigra of kindled rats

The substantia nigra pars reticulata is thought to control the spread of seizures in various seizure models. Potentiation of gamma-aminobutyrate (GABA)-mediated transmission in this region by intranigral administration of drugs such as muscimol has been shown to inhibit seizure propagation in such models, including the kindling model of epilepsy. More recent studies have shown that the effects on seizures are site-specific within the substantia nigra pars reticulata. Using flurothyl to induce clonic seizures, it was reported that bilateral microinfusions of muscimol into the anterior substantia nigra pars reticulata were anticonvulsant, while similar infusions into the posterior pars reticulata were proconvulsant. This prompted us to reevaluate the effects of intranigral muscimol in the kindling model with particular emphasis on the anterior substantia nigra pars reticulata. In amygdala kindled rats, muscimol was bilaterally infused into the anterior pars reticulata at doses of either 60 or 120 ng. Thirty minutes later, the threshold for induction of afterdischarges in the amygdala and the threshold for generalized seizures were determined in each rat. Furthermore, severity and duration of seizures at threshold currents were recorded. Unexpectedly, muscimol failed to increase seizure thresholds or to significantly reduce seizure severity or duration of motor seizures, although there was a moderate reduction in motor seizure duration in several rats. The data indicate that, in contrast to flurothyl seizures, in kindled rats the anterior pars reticulata of the substantia nigra is not a site at which muscimol causes robust anticonvulsant effects.

Spontaneous remission of paroxysmal dystonia coincides with normalization of entopeduncular activity in dt(SZ) mutants

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.

Kindling causes persistent in vivo changes in firing rates and glutamate sensitivity of central piriform cortex neurons in rats

The present experiments were undertaken to study whether amygdala kindling induces persistent alterations in the functional status of neurons of the central piriform cortex, a subregion of the piriform cortex identified previously as a site involved in the kindling process. Extracellular, single-unit recordings of piriform cortex neurons were made in anesthetized fully kindled rats at an interval of at least five weeks after the last seizure. Electrode implanted but not kindled rats served as sham controls. An additional group of non-implanted rats was used as naive controls. Spontaneously firing piriform cortex neurons were characterized in all groups by smooth, sharp, biphasic (i.e. positive/negative) action potentials with a duration of 0.8-1.8 ms, and were primarily located at the border between piriform cortex layers II and III. In kindled rats, neurons in the central piriform cortex exhibited a significantly higher firing rate compared to controls. Based on median group values, the increase in basal activity in kindled rats averaged about 90%. The responsiveness of piriform cortex neurons to neurotransmitters was tested by microiontophoretic application of glutamate, N-methyl-D-aspartate and GABA. Piriform cortex neurons of kindled rats exhibited a significantly lower responsiveness to the excitatory effect of glutamate than naive controls. A lowered glutamate responsiveness was also seen in sham controls. No significantly altered transmitter sensitivities of piriform cortex neurons from kindled rats were seen with N-methyl-D-aspartate or GABA. The data indicate that amygdala kindling causes persistent interictal changes in both basal activity and glutamate responsiveness of central piriform cortex neurons which could contribute to the abnormal hyperexcitability characteristic of kindling.

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

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

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.

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

Extracellular single-unit recordings of piriform cortex neurons in rats: influence of different types of anesthesia and characterization of neurons by pharmacological manipulation of serotonin receptors

In epilepsy research, there is a growing interest in the role of the piriform cortex (PC) in the development and maintenance of limbic kindling and other types of limbic epileptogenesis leading to complex partial seizures. Neurophysiological studies on PC or amygdala-PC slice preparations from kindled rats showed that kindling of the amygdala induces long-lasting changes in synaptic efficacy in the ipsilateral PC, including spontaneous discharges and enhanced susceptibility of PC neurons to evoked burst responses. These long-lasting electrophysiological changes in the PC during kindling appear to be due, at least in part, to impaired function of gamma-aminobutyric acid (GABA)ergic interneurons. The aim of the present study was to develop an anesthetic protocol allowing electrophysiological single-unit recordings from inhibitory, presumably GABAergic PC interneurons in vivo. In addition to recording of spontaneously active PC neurons, microiontophoretic application of glutamate was used to activate silent neurons. Anesthesia of rats with ketamine/xylazine was not suited for single-unit recordings in the PC because of marked cardiovascular depression. Anesthesia with chloral hydrate allowed recording of spontaneous or glutamate-driven single-unit activity in approximately 40% of all animals. A similar percentage was obtained when recordings were done with the narcotic opioid fentanyl (plus gallamine), after all surgical preparations were performed under anesthesia with repeated administration of the barbiturate methohexital. To avoid brain accumulation of methohexital by repeated applications, we modified the anesthetic protocol in that methohexital was only injected once for initiation of surgical anesthesia, followed by the short-acting anesthetic propofol which does not accumulate upon repeated application. Again, after surgical preparation, electrophysiological recordings were done under fentanyl (plus gallamine). By this procedure, spontaneous or glutamate-driven single-unit activity could be measured in all rats in either layer II or III of the PC. Based on shape and frequency of action potentials, two types of neurons were recorded. The predominant type was similar in its firing characteristics to GABAergic neurons in other brain regions, was mainly located in layer III, and could be suppressed by the serotonin2A receptor antagonist MDL 100,907, suggesting that this type of PC neuron represents inhibitory, putative GABAergic interneurons. This new in vivo preparation may be useful for evaluation of PC neurons in kindled rats.

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.

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 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.

Abnormal c-fos expression in the lateral habenula during dystonic attacks in a hamster model of idiopathic dystonia

The genetically dystonic hamster (dtsz), an animal model of idiopathic dystonia, displays sustained twisting movements and postures either spontaneously or in response to mild stress. In the present study the expression of c-fos immunoreactive neurons (Fos-ir), used as an indicator of neuronal activity, was investigated within various brain regions in dtsz hamsters and non-dystonic control hamsters. Under baseline condition, i.e. in the absence of dystonia, the expression of Fos-ir did not reveal any differences between dtsz hamsters and controls. However, in response to mild stress several brain regions, particularly the lateral habenula (LHb), exhibited differences in c-fos induction in dtsz hamsters and controls. Whereas in the LHb the expression of Fos-ir was markedly enhanced in controls, it showed almost no increase in dystonic hamsters, indicating impaired neuronal activity. Since the lateral habenula receives major input from the basal ganglia via the entopeduncular nucleus, the present data might indicate that basal ganglia are involved in the dystonic syndrome in mutant hamsters.