Clinical efficacy and safety of imepitoin in comparison with phenobarbital for the control of idiopathic epilepsy in dogs.

The anticonvulsant activity and safety of imepitoin, a novel antiepileptic drug licensed in the European Union, were evaluated in a multicentre field efficacy study as well as in a safety study under laboratory conditions. Efficacy of imepitoin was compared with phenobarbital in 226 client-owned dogs in a blinded parallel group design. The administration of imepitoin twice daily in incremental doses of 10, 20 or 30 mg/kg demonstrated comparable efficacy to phenobarbital in controlling seizures in dogs. The frequency of adverse events including somnolence/sedation, polydipsia and increased appetite was significantly higher in the phenobarbital group. In phenobarbital-treated dogs, significantly increased levels of alkaline phosphatase, gamma-glutamyl-transferase and other liver enzymes occurred, while no such effect was observed in the imepitoin group. In a safety study under laboratory conditions, healthy beagle dogs were administered 0, 30, 90 or 150 mg/kg imepitoin twice daily for 26 weeks. A complete safety evaluation including histopathology was included in the study. A no-observed-adverse-event level of 90 mg/kg twice daily was determined. These results indicate that imepitoin is a potent and safe antiepileptic drug for dogs.

Imepitoin as novel treatment option for canine idiopathic epilepsy: pharmacokinetics, distribution, and metabolism in dogs.

Imepitoin is a novel anti-epileptic licensed in the European Union for the treatment of canine idiopathic epilepsy. The aim of this study was to characterize the pharmacokinetics of imepitoin in dogs and to evaluate the interaction with drug metabolizing enzymes. Upon administration of imepitoin tablets at a dose of 30 mg/kg to beagle dogs, high plasma levels were observed within 30 min following oral dosing, with maximal plasma concentrations of 14.9-17.2 µg/mL reached after 2-3 h. In a crossover study, co-administration of imepitoin tablets with food reduced the total AUC by 30%, but it did not result in significant changes in Tmax and Cmax , indicating lack of clinical relevance. No clinically relevant effects of sex and no accumulation or metabolic tolerance were observed upon twice daily dosing. Following single dose administration of 10-100 mg/kg, dose linearity was found. Administering [(14) C] imepitoin, high enteral absorption of 92% and primary fecal excretion were identified. Plasma protein binding was only 55%. At therapeutic plasma concentrations, imepitoin did not inhibit microsomal cytochrome P450 family liver enzymes in vitro. In rats, no relevant induction of liver enzymes was found. Therefore, protein binding or metabolism-derived drug-drug interactions are unlikely. Based on these data, imepitoin can be dosed twice daily, but the timing of tablet administration in relation to feeding should be kept consistent.

Antidystonic effects of Kv7 (KCNQ) channel openers in the dt sz mutant, an animal model of primary paroxysmal dystonia.

BACKGROUND AND PURPOSE: Mutations in neuronal Kv7 (KCNQ) potassium channels can cause episodic neurological disorders. Paroxysmal dyskinesias with dystonia are a group of movement disorders which are regarded as ion channelopathies, but the role of Kv7 channels in the pathogenesis and as targets for the treatment have so far not been examined. EXPERIMENTAL APPROACH: In the present study, we therefore examined the effects of the activators of neuronal Kv7.2/7.3 channels retigabine (5, 7.5, 10 mg kg(-1) i.p. and 10, 20 mg kg(-1) p.o.) and flupirtine (10, 20 mg kg(-1) i.p.) and of the channel blocker 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone (XE-991, 3 and 6 mg kg(-1) i.p.) in the dt sz mutant hamster, a model of paroxysmal dyskinesia in which dystonic episodes occur in response to stress. KEY RESULTS: Retigabine (10 mg kg(-1) i.p., 20 mg kg(-1) p.o.) and flupirtine (20 mg kg(-1) i.p.) significantly improved dystonia, while XE-991 caused a significant aggravation in the dt sz mutant. The antidystonic effect of retigabine (10 mg kg(-1) i.p.) was counteracted by XE-991 (3 mg kg(-1) i.p.). CONCLUSIONS AND IMPLICATIONS: These data indicate that dysfunctions of neuronal Kv7 channels deserve attention in dyskinesias. Since retigabine and flupirtine are well tolerated in humans, the present finding of pronounced antidystonic efficacy in the dt sz mutant suggests that neuronal Kv7 channel activators are interesting candidates for the treatment of dystonia-associated dyskinesias and probably of other types of dystonias. The established analgesic effects of Kv7 channel openers might contribute to improvement of these disorders which are often accompanied by painful muscle spasms.

The anti-hyperalgesic activity of retigabine is mediated by KCNQ potassium channel activation.

Retigabine (N-(2-amino-4-(4-fluorobenzylamino)-phenyl) carbamic acid ethyl ester) has a broad anticonvulsant spectrum and is currently in clinical development for epilepsy. The compound has an opening effect on neuronal KCNQ channels. At higher concentrations an augmentation of gamma-aminobutyric acid (GABA) induced currents as well as a weak blocking effect on sodium and calcium currents were observed. The goal of this study was to characterise the activity of retigabine in models of acute and neuropathic pain and to investigate if the potassium channel opening effect of retigabine contributes to its activity. Retigabine was tested in mice and rats in the tail flick model of acute pain and in the nerve ligation model with tight ligation of the 5th spinal nerve (L5) using both thermal and tactile stimulation. While retigabine like gabapentin had almost no analgesic effect in mice it showed some analgesic effects in rats in the tail flick model. These effects could not be antagonised with linopirdine, a selective KCNQ potassium channel blocker, indicating a different mode of action for this activity. In L5-ligated rats retigabine significantly and dose-dependently elevated the pain threshold and prolonged the withdrawal latency after tactile and thermal stimulation, respectively. In the L5 ligation model with thermal stimulation retigabine 10 mg/kg p.o. was as effective as 100 mg/kg gabapentin or 10 mg/kg tramadol. The L5 model with tactile stimulation was used to test the role of the KCNQ potassium channel opening effect of retigabine. If retigabine 10 mg/kg p.o. was administered alone it was as effective as tramadol 10 mg/kg p.o. in elevating the pain threshold. Linopirdine (1 and 3 mg/kg i.p.) had nearly no influence on neuropathic pain response. If we administered both retigabine and linopirdine the effect of retigabine was abolished or diminished depending on the dose of linopirdine used.In summary, retigabine is effective in predictive models for neuropathic pain. The activity is comparable to tramadol and is present at lower doses compared with gabapentin. Since the anti-allodynic effect can be inhibited by linopirdine we can conclude that the potassium channel opening properties of retigabine are critically involved in its ability to reduce neuropathic pain response.

In vivo efficacy in airway disease models of N-(3,5-dichloropyrid-4-yl)-[1-(4-fluorobenzyl)-5-hydroxy-indole-3-yl]-glyoxylic acid amide (AWD 12-281), a selective phosphodiesterase 4 inhibitor for inhaled administration.

N-(3,5-Dichloro-pyrid-4-yl)-[1-(4-fluorobenzyl)-5-hydroxy-indole-3-yl]-glyoxylic acid amide (AWD 12-281) is a highly potent and selective phosphodiesterase 4 (PDE4) inhibitor that was designed to have a metabolic profile that was optimized for topical administration. The aim of the current study was to explore the pharmacological profile of intratracheally administered AWD 12-281 in different models of asthma and chronic obstructive pulmonary disease (COPD) in comparison with steroids. To assess the anti-inflammatory potential of AWD 12-281, the antigen-induced cell infiltration in bronchoalveolar lavage fluid (BALF) of Brown Norway rats was determined. AWD 12-281 (ID50 of 7 microg/kg i.t.) as well as beclomethasone (0.1microg/kg i.t.) suppresses late-phase eosinophilia when administered intrapulmonary. Furthermore, AWD 12-281 has also strong anti-inflammatory properties when tested in lipopolysaccharide-induced acute lung neutrophilia in Lewis rats (ID50 of 0.02 microg/kg i.t.), ferrets (ID50 of 10 microg/kg i.t.), and domestic pigs (2-4 mg/pig i.t. or 1 mg/kg i.v.). In pigs, AWD 12-281 was as effective as beclomethasone (0.4 mg/pig i.t.) and dexamethasone (0.28 mg/kg i.v.), although at 3 to 10 times the dosage. The bronchodilatory activity of AWD 12-281 was assessed in sensitized guinea pigs. AWD 12-281 (1.5 mg/kg i.t., 1-h pretreatment) inhibited allergen-induced bronchoconstriction by 68% (parameter airway resistance). In sensitized BP-2 mice AWD 12-281 abolished the allergen-induced bronchial hyperresponsiveness and eosinophilia in BALF, showing dose dependence. When given orally, i.v. or i.t., AWD 12-281 has a considerably lower emetic potential than cilomilast in ferrets and roflumilast in pigs. When given topically by inhalation, no emesis could be induced in dogs up to the highest feasible dose (15 mg/kg in 50% lactose blend). These results indicate that AWD 12-281 is a unique potential new drug for the topical treatment of asthma and COPD.

Effects of retigabine on rhythmic synchronous activity of human neocortical slices.

The antiepileptic effects of the novel antiepileptic drug retigabine (D-23129) [N-(2-amino-4-(4-flurobenzylamino)phenyl) carbamid acid ethyl ester] were tested in neocortical slice preparations (n=23) from 17 patients (age, 3-42 years) who underwent surgery for the treatment of intractable epilepsy. Epileptiform events consisted of spontaneously occurring rhythmic sharp waves, as well as of epileptiform field potentials (EFP) elicited by superfusion with Mg(2+)-free solution without or with addition of 10 micromol/l bicuculline. (1) Spontaneous rhythmic sharp waves (n=6), with retigabine application, the repetition rate was decreased down to 12-47% of initial value (10 micromol/l, n=3) after 180 min or suppressed completely within 12 min (50 micromol/l, n=3). (2) Low Mg(2+) EFP (n=9), with retigabine application, the repetition rate was decreased down to 50 and 65% of initial value (10 micromol/l; n=2) after 180 min or suppressed completely after 9-55 min (10, 50 and 100 micromol/l; n=2 in each case). In one slice only a transient reduction of the repetition rate was seen with 10 micromol/l retigabine. (3) Low Mg(2+) EFP with addition of bicuculline (n=8), with retigabine application, the repetition rate was decreased down to 12-55% of initial value (10 micromol/l; n=4) after 180 min or suppressed completely after 6-30 min (50 and 100 micromol/l; n=2 in each case). The depressive effect of retigabine was reversible in all but one slice. The results show a clear antiepileptic effect of retigabine in human neocortical slices on spontaneously occurring rhythmic sharp waves and different types of induced seizure activity.

A neurochemical study of the novel antiepileptic drug retigabine in mouse brain.

The novel antiepileptic drug, retigabine, has been reported to have multiple mechanisms of action, including potentiation of gamma -aminobutyric acid (GABA) and glutamate synthesis. We have investigated its effects on several GABA- and glutamate-related neurochemical parameters in mouse brain. Mice were administered retigabine either as a single dose or daily for 5 days. At 4 h after dosing, brains were removed and analysed for GABA, glutamate, and glutamine concentrations and for the activities of GABA-transaminase and glutamic acid decarboxylase. Single doses of retigabine significantly lowered brain concentrations of glutamate and glutamine. Repeated treatment significantly reduced the activity of GABA-transaminase. The drug was essentially without effect on all other parameters investigated. These results suggest that retigabine blocks GABA metabolism rather than enhancing GABA synthesis. In addition, the drug may also lower brain concentrations of the excitatory neurotransmitter glutamate and its precursor, glutamine. These effects may contribute to the antiepileptic action of retigabine.

Flupirtine and retigabine prevent L-glutamate toxicity in rat pheochromocytoma PC 12 cells.

Flupirtine is an analgesic drug thought to have NMDA receptor antagonistic and antiapoptotic effects. We investigated the effects of Ethyl-2-amino-6-(4-(4-fluorbenzyl)amino)-pyridine-3-carbamamic+ ++ acid, maleate (flupirtine) and the related compound N-(2-amino-4-(4-fluorobenzylamino)-phenyl)-carbamic acid, ethyl ester) (retigabine) (Desaza-flupirtine) on the toxicity of L-glutamate and L-3,4-dihydroxyphenylalanine (L-DOPA) in rat pheochromocytoma PC 12 cells in vitro. Both drugs (10 microM) markedly decreased nonreceptor-mediated necrotic cell death in PC 12 cultures treated with L-glutamate (10 mM) for 72 h. In contrast, apoptosis induced by L-DOPA (250 microM) after 48 h was not affected by either substance. While L-DOPA elicited massive generation of reactive oxygen intermediates, L-glutamate-induced cell death was accompanied by only slightly increased levels of reactive oxygen intermediates. Flupirtine and retigabine exerted anti-oxidative effects in PC 12 cultures independent of their ability to prevent cell death. Further examination of the protective action of flupirtine and retigabine against L-glutamate toxicity showed that it had no influence on monoamine oxidase (monoamine: oxygen oxidoreductase (deaminating), EC 1.4.3.4., MAO) activity. Thus, flupirtine and retigabine provided protection against cystine deprivation and L-glutamate toxicity but did not protect against L-glutamate under cystine-free conditions indicating that both compounds are sufficiently effective to compensate the oxidative stress elicited by cystine deprivation but not excessive activity of monoamine oxidase after L-glutamate treatment.

The novel anticonvulsant retigabine activates M-currents in Chinese hamster ovary-cells tranfected with human KCNQ2/3 subunits.

Retigabine (D-23129) is a novel antiepileptic compound with broad spectrum and potent anticonvulsant properties, both in vitro and in vivo. The compound was shown to activate a K(+) current in neuronal cells. The pharmacology of the induced current displays concordance with the published pharmacology of the M-channel, which recently was correlated to the KCNQ2/3 K(+) channel heteromultimere. We examined the effect of retigabine on KCNQ2/3 expressed in Chinese hamster ovary cells. The compound concentration-dependently activated a K(+) current in transfected cells clamped at -50 mV. The activation was induced by a shift of the opening threshold to more negative potentials. The effect was not mediated by an interaction with the cAMP modulatory site and could be partially blocked by the M-channel antagonist linopirdine. The data display that retigabine is the first described M-channel agonist and support the hypothesis that M-channel agonism is a new mode of action for anticonvulsant drugs. Since the function of this channel is reduced in a hereditary epilepsy syndrome, retigabine may be the first anticonvulsant to directly target the deficit observed in a channelopathy.

Effects of retigabine (D-23129) on different patterns of epileptiform activity induced by low magnesium in rat entorhinal cortex hippocampal slices.

PURPOSE: The objective of this study was to evaluate the effect of a new antiseizure drug, retigabine (D-23129; N-(2-amino-4-[fluorobenzylamino]-phenyl) carbamic acid ethyl ester) on low-Mg2+-induced epileptiform discharges in rat in vitro. METHODS: Three types of epileptiform discharges (recurrent short discharges in the hippocampus, seizure-like events, and late recurrent discharges in the entorhinal cortex) were elicited in rat combined entorhinal cortex-hippocampal slices by perfusion with low-Mg2+-artificial cerebrospinal fluid (ACSF). The antiepileptic properties of retigabine were evaluated as effect on the frequency and amplitude of the epileptiform activities as well as time of onset of the effect in the entorhinal cortex (EC) and in hippocampal area CA1 (CA1) by using extracellular recording techniques. RESULTS: Retigabine (20 microM) reversibly suppressed the recurrent short discharges otherwise sensitive only to high doses of valproate (VPA) but insensitive to standard antiepileptic drugs (AEDs) in CA1, whereas 10 microM reduced the frequency of discharges by 34+/-18.8%, with no significant effect on the amplitude. In EC, retigabine (50 microM) reversibly suppressed the seizure-like events, whereas 20 microM blocked seizure-like events in 71.5% of the slices. The seizure-like events were also sensitive to standard AEDs. Late recurrent discharges in EC that are not blocked by standard AEDs were reversibly suppressed by retigabine (100 microM), whereas 50 microM reduced the frequency of the discharges by 94.4+/-7.7%, and 20 microM, by 74.2+/-18.0%, with no significant effect on the amplitude. CONCLUSIONS: Retigabine is an effective AED with suppressive effects on recurrent short discharges and on late recurrent discharges normally insensitive to standard AEDs.

Investigations into the mechanism of action of the new anticonvulsant retigabine. Interaction with GABAergic and glutamatergic neurotransmission and with voltage gated ion channels.

Retigabine (N-(2-amino-4-(4-fluorobenzylamino)phenyl) carbamic acid ethyl ester, CAS 150812-12-7, D-23129) is a novel anticonvulsant currently undergoing phase II clinical trials. The compound was shown to possess broad spectrum and potent anticonvulsant properties both in vitro and in vivo. The mechanism of action of this drug is currently not fully understood. In previous studies a potent opening effect on K+ channels and an increased release of newly synthesized gamma-aminobutyric acid (GABA) were reported. The aim of this study was to investigate the interaction of retigabine with GABA, kainate and N-methyl-D-aspartate (NMDA) induced currents as well as with voltage gated Na+ and Ca++ channels. Retigabine concentration dependently potentiated GABA induced currents in rat cortical neurones. Significant effects were only seen with concentrations of 10 mumol/l and above. The action of retigabine was not antagonised by flumazenil indicating interaction with other than benzodiazepine binding sites. In comparison with the K+ channel opening effect which can be seen at concentrations as low as 0.1 mumol/l the contribution of this mechanism to the anticonvulsant activity of retigabine may be minor. Inhibitory effects observed on voltage activated Na+ and Ca++ channels as well as on kainate induced currents were only observed at the highest concentration tested (100 mumol/l) and can be considered non specific. No significant interaction with NMDA induced currents was observed.

The anticonvulsant retigabine potently suppresses epileptiform discharges in the low Ca ++ and low Mg++ model in the hippocampal slice preparation.

Retigabine (N-(2-amino-4-(4-fluorobenzylamino)-phenyl) carbamic acid ethyl ester, D-23129) is a broad acting anticonvulsant currently undergoing phase II clinical trials. An opening effect on leakage conductance K+ channels, potentiation of GABA induced currents and a weak blocking effect on Na+ and Ca++ channels were previously reported. The goal of this study was to investigate whether retigabine is capable of blocking epileptiform discharges in the low Ca++ and low Mg++ model in the hippocampal slice preparations and whether the anti-burst activity can be related to the K+ channel opening effect. In the low Ca++ model, synaptic transmission is blocked and discharges evolve from ephaptically-coupled neurons. Compounds which directly interfere with the threshold for action potential induction via alteration of ion channel function (i.e. Na+ channel blocker) may alter the discharges, while compounds interfering with synaptic transmission are not active. Retigabine suppressed the discharges in a concentration-dependent manner. A significant reduction in frequency without effect on amplitude was observed after application of 1 microM, and a full block of all discharges after application of 25 microM. The opener of the ATP sensitive K+ channels cromakalim was also active. Application of 300 microM cromakalim yielded to a lower frequency with no effects on the amplitude of discharges. Treatment with phenytoin and carbamazepine resulted in a marked reduction in amplitude accompanied by a rise in frequency; only at higher concentrations was a full block observed. The effect of retigabine therefore differs from sodium channel blockers and can be related to the K+ channel opening effect. In the low Mg++ model, excitatory neurotransmission is augmented by reducing the Mg++ block of NMDA channels. This results in development of interictal-like epileptiform activity in area CA1 in isolated hippocampal slices. Treatment with retigabine 10 microM resulted in a significant reduction of the discharges, and discharges were fully blocked after application of 25 microM. Qualitatively similar effects were observed with cromakalim and valproate, albeit at higher concentrations. The data indicate that retigabine exerts potent broad spectrum activity making it an interesting candidate for treatment of drug resistant patients.

3-Amino- and 5-aminopyrazoles with anticonvulsant activity.

New 3-amino- and 5-aminopyrazoles were synthesised. 3-Aminopyrazoles exert a strong anticonvulsant effect, 4-Chlorophenyl-3-(morpholin-4-yl)-1 H-pyrazole 2 distinctively blocks sodium channels and is strongly effective in the Maximal Electroshock Seizure (MES) test.

Characterization of the K+ channel opening effect of the anticonvulsant retigabine in PC12 cells.

Retigabine (D-23129) is a new anticonvulsant compound which acts as a K+ channel opener in neuronal cells. The aim of the present study was to further characterize the retigabine induced K+ current. In nerve growth factor treated PC12 cells and in rat cortical neurones the application of retigabine activated a K+ current. In contrast, however, no K+ current activation was observed in untreated PC12 and in glial cells which were cultivated together with the neuronal cells. To characterise the retigabine activated K+ current, K+ channel blockers were used. The retigabine induced current was not affected by 1 and 10 mM 4-aminopyridine (4AP). Ba2+ 1 mM resulted in a reduction of 88.6+/-3.0% (n = 5); 10 mM abolished the current. Tetraetylamonium (TEA), 1 and 10 mM, reduced the current by 23.6+/-3.1 and 61.6+/-3.7%, respectively. To investigate the current/voltage (I/V) relation of the current initiated by retigabine (10 microM), cells were clamped to a holding potential of -80 mV and a ramp stimulation protocol (-120 to +60 mV in 5 s) was applied prior to and during application of retigabine. Subtraction of the two traces yielded the current induced by retigabine. A nearly linear relationship was determined between - 120 and -40 mV. At potentials positive to - 40 mV, the response was variable. This was due to the additionally observed weak blocking effect of retigabine on delayed rectifier (Kdr) currents. If the ramp was applied in the presence of 10 mM 4AP to block Kdr, a nearly linear I/V-relationship was present from -120 to +60 mV. The comparison of the I/V relation and pharmacology with published K+ channel subtypes gives evidence that an unknown neuronal K+ channel subtype may be involved.

The novel anticonvulsant AWD 140-190 acts as a highly use-dependent sodium channel blocker in neuronal cell preparations.

The effect of the new anticonvulsant drug AWD 140-190 (4-(p-bromophenyl)-3-morpholino-1H-pyrrole-2-carboxylic acid methyl ester) on neuronal sodium channels was evaluated in differentiated NG 108-15 cells using the patch clamp technique. AWD 140-190 blocked neuronal sodium channels more potently than phenytoin in a dose-dependent manner (1-30 microM). As with phenytoin, the blocking effect was voltage and frequency dependent. However, comparing equi-effective doses of AWD 140-190 and phenytoin, the frequency dependence was two to three times stronger. This pronounced use dependent effect of AWD 140-190 may be the reason for the superior tolerability and anticonvulsant activity in experimental models of epilepsy.

Characterization of phenytoin-resistant kindled rats, a new model of drug-resistant partial epilepsy: influence of experimental and environmental factors.

It has been recently shown that the variable anticonvulsant effect of phenytoin in the kindling model is not a characteristic of all kindled rats. In a population of amygdala-kindled Wistar rats, subgroups can be selected which consistently respond to phenytoin with an increase in afterdischarge threshold (responders) or which never show such an increase (non-responders). This study examined retrospectively the influence of technical and environmental factors on the results of several prospectively performed phenytoin selections during the last few years. Male and female Wistar rats were implanted with bipolar electrodes aimed at the basolateral amygdala and subsequently kindled. The fully kindled rats were tested for their ability to consistently respond to phenytoin (75 mg/kg i.p.) with an increase of afterdischarge threshold in three consecutive trials. Analysis of 158 Wistar rats of both genders revealed no significant influence of either plasma concentration of phenytoin, kindling parameters, precise electrode location, or differences in focal histology on the result of phenytoin selection. Furthermore, the ability to respond to phenytoin was not associated with the season or the ambient atmospheric pressure during the selection procedure. The data suggest that the difference between phenytoin responders and non-responders is not due to experimental factors, but may rather be genetically determined.

Effects of retigabine (D-23129) on different patterns of epileptiform activity induced by 4-aminopyridine in rat entorhinal cortex hippocampal slices.

The purpose of this study was to evaluate the effects of the new anticonvulsant drug N-(2-amino-4-[fluorobenzylaminol-phenyl) carbamic acid ethyl ester (retigabine, D-23129, ASTA Medica, Dresden, Germany) on different patterns of epileptiform activity induced by 4-aminopyridine (4AP) in rat entorhinal cortex hippocampal slices. Application of 4AP (100 microM) induced in entorhinal cortex two different types of epileptiform activities; seizure-like events (SLE) and interictal epileptiform discharges (IED). Bicuculline (10 microM) changed 4AP-induced SLE and IED to recurrent epileptiform discharges (RED). IED were isolated after blockade of the SLE by glutamate receptor antagonists for alpha-amino-3-hydroxy-5-methylisoxazole4-proprionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors, i.e. 1,2,3,4 tetrahydro-6-nitro-2,3-dioxo-benzolflquinoxaline-7-sulfonamide (NBQX, 10 microM) and 2-amino-5-phosphonovaleric acid (APV, 30 microM). Anticonvulsant properties of retigabine were evaluated as effect on the frequency and amplitude of SLE, IED and RED. Retigabine suppressed all types of epileptiform events in a dose dependent and reversible manner. SLE were suppressed in 71.4 and 100% of slices by 5 and 10 microM, respectively. The frequency of IED was significantly reduced by 20 microM retigabine (40.9+/-24.5%) and IED were blocked completely by 50 microM retigabine. When IED were isolated by application of glutamate antagonists 20 microM retigabine was sufficient to block this activity completely. RED induced by combined application of bicuculline and 4AP were blocked in 71.4% of the tested slices with 100 microM retigabine. The frequency of the RED in the remaining slices was reduced by 96.1+/-6.1%. We conclude that retigabine acts on a large variety of different epileptiform activities in temporal lobe structures that are known to develop readily pharmacoresistant seizures.

Retigabine strongly reduces repetitive firing in rat entorhinal cortex.

Retigabine (D-23129) [N-(2-amino-4-(4-fluorobenzylamino)phenyl) carbamic acid ethyl ester] is a novel antiepileptic drug. The compound was shown to possess anticonvulsant properties both in vivo and in vitro. We investigated the effects of retigabine on neurones in the rat medial entorhinal cortex using conventional intracellular recordings in combined hippocampal-entorhinal cortex slices. Retigabine strongly reduced the number of action potentials elicited by 1 s long depolarising current injections. Both the amplitudes of monosynaptic inhibitory postsynaptic potentials/currents (IPSP/Cs) and the amplitudes of excitatory postsynaptic potentials (EPSPs) remained unaffected. The drug increased outward rectification and induced a membrane-potential hyperpolarisation in most of the tested neurones. The findings suggest that retigabine exerts its anticonvulsant effects by activation of a K(+)conductance, however it cannot be excluded from our experiments that other mechanisms may be involved in the effect of retigabine on membrane properties.

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.