Retigabine Research Articles

Physical dependence liability of retigabine in rats

Aims: Retigabine (RTG) is an antiepileptic drug with a novel mechanism of action acting through the potentiation of KCNQ2/3 potassium channel, which are important in controlling neuronal excitability. In vitro evidence additionally suggests RTG augments GABA-mediated neurotransmission which may contribute a stabilizing effect on neuronal excitability. A key component in non-clinical abuse liability testing is the evaluation of a potential withdrawal syndrome induced by chronic administration, and abrupt cessation, of the test article. The objective of this study was to assess the potential of RTG to induce awithdrawal syndrome following abrupt cessation during chronic administration in Sprague Dawley rats. Methods: Rats were orally treated with 3, 10 and 30mg/kg/day RTG for 28 days and then observed for 14 days following the cessation of RTG treatment. Chlordiazepoxide HCl (CDP) was selected as the positive control. CDP was administered in incremental doses: 20mg/kg on Day 1, 40mg/kg on Day 2 and successive increments of 20mg/kg each day until the dose of 200mg/kgwas reached. This dose was then maintained to Day 28. Results: Following RTG cessation, no changes in body weight, food consumption or body temperature were observed and only some animals showed minor behavioural effects. Discontinuation of RTG after repeated administration induced a behavioural profile distinctly different from that observed following discontinuation of CDP. Conclusions: Whereas robust physiological and behavioural withdrawal symptoms were observed in the CDP-treated animals similar to that documented in the literature for benzodiazepines, the RTG-treated groups showed no withdrawal effects on physiological parameters and only a mild, non dose-dependent increase in behavioural parameters. Based on these findings, chronic administration of RTG in rats did not result in a withdrawal syndrome following abrupt discontinuation. Financial support: Authors did not received any financial support.

Long term retention of retigabine in a cohort of people with drug resistant epilepsy

PurposeTo assess the utility of retigabine (RTG) for epilepsy in clinical practice at a single UK tertiary centre. MethodsWe identified all individuals who were offered RTG from April 2011 to May 2013. We collected demographics, seizure types, previous and current antiepileptic drugs (AEDs), starting and maximum attained daily dose of RTG, clinical benefits, side effects, and reason to discontinue RTG from in- and outpatient encounters until February 28, 2014. Results145 people who had failed a median of 11 AEDs took at least one dose of RTG. One year retention was 32% and decreased following the safety alert by the US Federal Drug Administration (FDA) in April 2013. None became seizure free. 34 people (24%) reported a benefit that was ongoing at last assessment in five (3%). The most relevant benefit was the significant reduction or cessation of drop attacks or seizure-related falls in four women, this persisted at last assessment in two. The presence of simple partial seizures was associated with longer retention, as was a higher attained dose of RTG. Adverse effects were seen in 74% and largely CNS-related or nonspecific and affected the genitourinary system in 13%. ConclusionRetention of RTG was less favourable compared to data from open label extension studies of the regulatory trials. In comparison with historical data on similar retention audits retention of RTG at one year appears to be less than lamotrigine, topiramate, levetiracetam, pregabalin, zonisamide, and lacosamide, and slightly higher than gabapentin.

Retigabine

Retigabine

Identification, characterization, synthesis and HPLC quantification of new process-related impurities and degradation products in retigabine

Two new impurities were described and determined using gradient HPLC method with UV detection in retigabine (RET). Using LC–HRMS, NMR and IR analysis the impurities were identified as RET-dimer I: diethyl {4,4′-diamino-6,6′-bis[(4-fluorobenzyl)amino]biphenyl-3,3′-diyl}biscarbamate and RET-dimer II: ethyl {2-amino-5-[{2-amino-4-[(4-fluorobenzyl) amino] phenyl} (ethoxycarbonyl) amino]-4-[(4-fluorobenzyl)amino] phenyl}carbamate. Reference standards of these impurities were synthesized followed by semipreparative HPLC purification. The mechanism of the formation of these impurities is also discussed. An HPLC method was optimized in order to separate, selectively detect and quantify all process-related impurities and degradation products of RET. The presented method, which was validated in terms of linearity, limit of detection (LOD), limit of quantification (LOQ) and selectivity is very quick (less than 11min including re-equilibration time) and therefore highly suitable for routine analysis of RET related substances as well as stability studies.

Antiseizure drugs differentially modulate theta‐burst induced long‐term potentiation in C57BL/6 mice

Cognitive comorbidities are increasingly recognized as an equal (or even more disabling) aspect of epilepsy. In addition, the actions of some antiseizure drugs (ASDs) can impact learning and memory. Accordingly, the National Institute of Neurological Disorders and Stroke (NINDS) epilepsy research benchmarks call for the implementation of standardized protocols for screening ASDs for their amelioration or exacerbation of cognitive comorbidities. Long-term potentiation (LTP) is a widely used model for investigating synaptic plasticity and its relationship to learning and memory. Although the effects of some ASDs on LTP have been examined, none of these studies employed physiologically relevant induction stimuli such as theta-burst stimulation (TBS). To systematically evaluate the effects of multiple ASDs in the same preparation using physiologically relevant stimulation protocols, we examined the effects of a broad panel of existing ASDs on TBS-induced LTP in area CA1 of in vitro brain slices, prepared in either normal or sucrose-based artificial cerebrospinal fluid (ACSF), from C57BL/6 mice. Coronal brain slices containing the dorsal hippocampus were made using either standard or sucrose-based ACSF. Recordings were obtained from four slices at a time using the Scientifica Slicemaster high throughput recording system. Slices exposed to ASDs were paired with slices from the opposite hemisphere that served as controls. Field excitatory postsynaptic potentials (fEPSPs) were recorded, and all ASDs were applied to slices by bath perfusion for 20min prior to the induction stimulus. LTP was induced by TBS or by high-frequency stimulation (HFS). The following ASDs were examined: 100μM phenobarbital (PB), 80μM phenytoin (PHT), 50μM carbamazepine (CBZ), 600μM valproate (VPA), 60μM topiramate (TPM), 60μM lamotrigine (LTG), 100μM levetiracetam (LEV), 10μM ezogabine (EZG), and 30μM tiagabine (TGB). Among voltage-gated sodium channel inhibitors, CBZ significantly attenuated TBS-induced LTP, PHT attenuated both TBS-induced LTP and post-tetanic potentiation (PTP), and LTG failed to affect LTP but did attenuate PTP. ASDs that modulate γ-aminobutyric acid (GABA)ergic synaptic transmission, such as PB and TGB, significantly attenuated LTP in brain slices prepared in sucrose-based ACSF but not standard ACSF. Third generation ASDs, such as LEV and TPM, did not affect LTP in ACSF- or sucrose-prepared brain slices. Although EZG failed to affect LTP, it did significantly attenuate PTP under both slicing conditions. VPA failed to affect LTP in area CA1, both in C57BL/6 mice and Sprague-Dawley rats, using TBS or HFS. However, VPA did attenuate TBS-induced LTP in the dentate gyrus (DG). The results of experiments describe herein provide a comprehensive summary of the effects of many commonly used ASDs on short- and long-term synaptic plasticity while, for the first time, using physiologically relevant LTP induction protocols and slice preparations from mice. Furthermore, methodologic variables, such as brain slice preparation protocols, were explored. These results provide comparative knowledge of ASD effects on synaptic plasticity in the mouse hippocampus and may ultimately contribute to an understanding of the differences in the cognitive side effect profiles of ASDs and the prediction of cognitive dysfunction associated with novel investigational ASDs.

The effect of ezogabine on the pharmacokinetics of an oral contraceptive agent

Ezogabine (EZG) is a potassium-channel opener that has been approved as adjunctive treatment for partial-onset seizures in adults with epilepsy. This Phase I clinical study evaluated the pharmacokinetics (PK), safety, and tolerability of coadministration of EZG and a combined oral contraceptive (OC). An open-label drug-interaction study was conducted in healthy, female volunteers aged 18 - 55 years with regular menstrual cycles. The effects of steady-state 750 mg EZG on the PK of a combined OC agent containing 1 mg norethindrone and 0.035 mg ethinyl estradiol were evaluated, along with the effect of the contraceptive hormones on EZG PK. Safety was evaluated by clinical laboratory, vital sign, electrocardiogram, physical examination, and adverse event (AE) assessments. Of 30 enrolled volunteers, 25 completed all treatments. OC did not affect the PK of EZG. EZG increased norethindrone area under the concentration-time curve (AUC) by 28%, with no change in the maximum plasma concentration (Cmax). Ethinyl estradiol Cmax was 21% lower with no change in AUC. The majority of AEs were mild in severity, with the most commonly reported being gastrointestinal disorders and nervous system disorders. No deaths or serious AEs were reported in this study. Five volunteers discontinued treatment due to AEs. EZG did not have any clinically relevant impact on exposure of OC hormones in this study, and the OC hormones did not alter EZG PK parameters. This study provides PK evidence that doses of EZG and OCs do not need to be altered when co-administered.

PP201—An Open-Label, Randomized, Single-Centre, Four-Way Crossover Study to Evaluate the Pharmacokinetics of Single, Oral Doses of Retigabine/Ezogabine in Healthy Adult Taiwanese Subjects

Retigabine (RTG)/ezogabine, N-[2-amino-4(4-fluorobenzylamino)-phenyl] carbamic acid ethyl ester, is a novel antiepileptic compound. In 2011, RTG was approved by the FDA and European Commission as adjunctive treatment for partial onset seizures in adults aged ≥18 years. The global pivotal studies did not include Asian countries. The purpose of this study was to characterize the pharmacokinetics (PK) of single 50, 100, 200, and 400-mg doses of RTG and N-acetyl metabolites of RTG (NAMR) in healthy Taiwanese subjects.

Phosphatidylinositol 4,5-bisphosphate alters pharmacological selectivity for epilepsy-causing KCNQ potassium channels

Pharmacological augmentation of neuronal KCNQ muscarinic (M) currents by drugs such as retigabine (RTG) represents a first-in-class therapeutic to treat certain hyperexcitatory diseases by dampening neuronal firing. Whereas all five potassium channel subtypes (KCNQ1-KCNQ5) are found in the nervous system, KCNQ2 and KCNQ3 are the primary players that mediate M currents. We investigated the plasticity of subtype selectivity by two M current effective drugs, retigabine and zinc pyrithione (ZnPy). Retigabine is more effective on KCNQ3 than KCNQ2, whereas ZnPy is more effective on KCNQ2 with no detectable effect on KCNQ3. In neurons, activation of muscarinic receptor signaling desensitizes effects by retigabine but not ZnPy. Importantly, reduction of phosphatidylinositol 4,5-bisphosphate (PIP2) causes KCNQ3 to become sensitive to ZnPy but lose sensitivity to retigabine. The dynamic shift of pharmacological selectivity caused by PIP2 may be induced orthogonally by voltage-sensitive phosphatase, or conversely, abolished by mutating a PIP2 site within the S4-S5 linker of KCNQ3. Therefore, whereas drug-channel binding is a prerequisite, the drug selectivity on M current is dynamic and may be regulated by receptor signaling pathways via PIP2.

M‐type K+ Channel Openers: In vivo Neuroprotective Role during Cerebrovascular Stroke

Stroke is the third leading cause of human death and many models have been used to study the mechanisms of tissue damage and neuronal protection. Investigations of neuroprotection during ischemic stroke through “M‐channels” could underlie potential treatments, since K+ channels stabilize resting potentials by counterbalancing the depolarizing effects of excitatory cation currents. These voltage‐gated channels, with distinct electrophysiological and pharmacological properties, play critical roles in control of neuronal excitability and action potential firing. A known M‐channel activator, retigabine (RTG) and other novel openers, up‐regulate M‐channels by stabilizing their open states through distinct molecular mechanisms. We hypothesize that M current‐mediated neuronal silencing has a neuroprotective role by increasing opening of KCNQ channels, thus decreasing neuronal activity. We used two in vivo mouse models; a cerebral infarct produced by laser‐controlled photothrombosis and the second the middle cerebral artery occlusion (MCAo). M‐current activity was pharmacologically altered in both models and application of M‐channel activators significantly reduced lesion area. Furthermore, retigabine enhanced protection from cerebral inflammatory responses. Thus, this study uses powerful models which may provide novel therapeutics for commonly‐occurring ischemic attacks.

Effect of retigabine on median effective dose of bupivacaine and chloroprocaine for induction of convulsion in mice

Objective To investigate the effect of KCNQ2/3 channel opener retigabine on the median effective dose (ED50) of bupivacaine and chloroprocaine for induction of convulsion in mice and the relationship between KCNQ2/3 channels and the neurotoxicity of local anesthetics.Methods Pathogen-free female Kunming mice,weighing 20-30 g,were used in the study.The experiment was performed in two parts.Part Ⅰ Sixty mice were randomly divided into 2 groups (n =30 each):control group (group C) and retigabine group (group R).The C and R groups were further divided into 3 subgroups with different doses of chlorprocaine (C + L1,C + L2 and C+ L3 groups,and R+ L1,R+ L2 and R+ L3 groups,n =10 each).In groups C and R,0.9％ normal saline 0.005 ml/g and retigabine 20 mg/kg were injected intraperitoneally,respectively,and chlorprocaine was injected intraperitoneally 20 min later.The doses of chlorprocaine were 150.0,172.5 and 198.4 mg/kg in C + L1,C + L2 and C + L3 groups,respectively,and 198.4,228.2 and 262.4 mg/kg in R+ L1,R+ 12 and R+ L3 groups,respectively.Part Ⅱ Eighty mice were randomly divided into 2 groups (n =40 each):control group (group C) and retigabine group (group R).The C and R groups were further divided into 4 subgroups with different doses of bupivacaine (C + B1,C + B2,C + B3 and C + B4 groups,and R + B1,R + B2,R + B3 and R + B4 groups,n =10 each).In groups C and R,0.9％ normal saline 0.005 ml/g and retigabine 20 mg/kg were injected intraperitoneally,respectively,and bupivacaine was injected intraperitoneally 20 min later.The doses of bupivacaine were 37.8,43.5,50.0 and 57.5 mg/kg in C + B1,C + B2,C + B3 and C + B4 groups,respectively,and 50.0,57.5,66.1 and 76.0 mg/kg in R + B1,R + B2,R + B3 and R + B4 groups,respectively.The ED50 and 95％ confidence interval (CI) of bupivacaine and chloroprocaine for induction of convulsion were calculated by Probit analysis.Results The ED50(95％ CI) of chloroprocaine was 165.3 (155.8-175.0) mg/kg,and the ED50(95％CI) of bupivacaine was 41.1 (36.7-44.5) mg/kg in C group.The ED50 (95％ CI) of chloroprocaine was 212.4 (200.2-224.3) mg/kg,and the ED5o (95％ CI)of bupivacaine was 51.5 (945.1-56.0)mg/kg in R group.Compared with group C,the ED50 of bupivacaine and chloroprocaine for induction of convulsion was significantly increased in group R (P ＜ 0.01).Conclusion KCNQ2/3 channel opener retigabine can significantly increase the ED50 of bupivacaine and chloroprocaine for induction of convulsion and reduce convulsion induced by bupivacaine and chloroprocaine in mice,indicating that the neurotoxicity of local anesthetics is related to inhibition of KCNQ2/3 channels. Key words: KCNQ2 potassium channel; KCNQ3 potassium channel; Anesthetics, local; Drug toxicity ; Dose-response relationship, drug

Effects of amino acid substitutions at positions 33 and 37 on UDP-glucuronosyltransferase 1A9 (UGT1A9) activity and substrate selectivity

UGT1A9 contributes to the glucuronidation of numerous drugs and xenobiotics. There is evidence to suggest that the Met33Thr substitution, as occurs in the polymorphic variant UGT1A9*3, variably affects xenobiotic glucuronidation. The equivalent position in UGT1A4 is also known to influence enzyme activity, whilst an N-terminal domain histidine (His37 in UGT1A9) is believed to function as the catalytic base in most UGT enzymes. To elucidate the roles of key amino acids and characterise structure–function relationships, we determined the effects of amino acid substitutions at positions 33 and 37 of UGT1A9 on the kinetics of 4-methylumbelliferone (4-MU), mycophenolic acid (MPA), propofol (PRO), sulfinpyrazone (SFZ), frusemide (FSM), (S)-naproxen (NAP) and retigabine (RTB) glucuronidation, compounds that undergo glucuronidation at either a phenolic (4-MU, MPA, PRO), carboxylate (FSM, NAP), acidic carbon (SFZ) or amine (RTB) function. Substitution of Met33 with Val, Ile, Thr, and Gln, as occur in UGT1A1, UGT1A3, UGT1A4 and UGT1A6 respectively, variably affected kinetics and catalytic efficiency. Whilst Km values were generally higher and Vmax and CLint values were generally lower than for wild-type UGT1A9 with most substrate-mutant pairs, the pattern and the magnitude of the changes in each parameter differed substantially. Moreover, exceptions occurred; CLint values for MPA and FSM glucuronidation by the position-33 mutants were the same as or higher than that of UGT1A9. Mutation of His37 abolished activity towards all substrates, except RTB N-glucuronidation. The data confirm the importance of single amino acids for UGT enzyme activity and substrate selectivity, and support a pivotal role for residue-33 in facilitating substrate binding to UGT1A9.

An Analysis of the Potential for Suicidality with Ezogabine (Retigabine) (P06.109)

An Analysis of the Potential for Suicidality with Ezogabine (Retigabine) (P06.109)

P.2.013 Effects of melatonin on diurnal variations of spontaneous seizures and behavioural changes in kainate model of temporal lobe epilepsy

Hyperexcitability in the medial entorhinal cortex-hippocampal (mEC-HC) circuit in the initial weeks after prolonged seizure activity may contribute to the epileptogenic process in animal models of temporal lobe epilepsy (TLE). The present study examined combined mEC-HC slices (400 μm) using field potential recordings 1–2 weeks following the multiple administration, low-dose kainic acid (KA) model of TLE [Hellier, J.L., Patrylo, P.R., Buckmaster, P.S., Dudek, F.E., 1998. Recurrent spontaneous motor seizures after repeated low-dose systemic treatment with kainate: assessment of a rat model of temporal lobe epilepsy. Epilepsy Res. 31, 73–84]. Field potential recordings in slices from KA-treated rats demonstrated hallmarks of hyperexcitability in the mEC and in the CA1 and CA3 cell body regions of the HC. Spontaneous burst (SB) activity was observed under baseline recording conditions in the mEC of several slices from KA-treated rats, but not in the slices from saline-treated control rats. Elevating ACSF [K+]o (6 mM) in the presence of picrotoxin (50 μM) increased SB rates in all slices tested. However, there was a significantly shorter latency to onset of bursting and prolonged evoked response durations in layer II of the mEC of slices from KA-treated rats versus those from controls. Neither carbamazepine (CBZ) nor phenytoin (PHT) abolished SB activity in slices from KA-treated rats; whereas, SB activity in slices from control rats was dose-dependently reduced at 100 μM CBZ. In contrast, the novel anticonvulsant retigabine (RGB) dramatically reduced SB frequency in both control and KA-treated groups. The hyperexcitability observed in combined mEC-HC brain slices from KA-treated rats suggests that the mEC, as well as the HC, may contribute to the epileptogenic process after KA-induced seizure activity. This model may provide an efficient, flexible in vitro paradigm for differentiating novel AEDs in a model of pharmacoresistant bursting.

M-Type K+ Channel Openers: In Vivo Neuroprotective Role During Cerebrovascular Stroke

Investigations of neuroprotection during ischemic stroke through “M-channels” could underlie potential treatments, since K+ channels stabilize resting potentials by counterbalancing the depolarizing effects of excitatory cation currents. Produced by combinations of KCNQ2-5 subunits, these voltage-gated channels, with distinct electrophysiological and pharmacological properties, play critical roles in control of neuronal excitability and action potential firing. A known M-channel activator, retigabine (RTG) and other novel openers, such as NH29 and QO-58, up-regulate M-channels by stabilizing their open states through distinct molecular mechanisms.

Temperature and pharmacological rescue of a folding-defective, dominantl-negative KV7.2 mutation associated with neonatal seizures

Benign familial neonatal seizures (BFNS) are a dominant epilepsy syndrome caused by mutations in the voltage-gated potassium channels K(V) 7.2 and K(V) 7.3. We examined the molecular pathomechanism of a BFNS-causing mutation (p.N258S) in the extracellular S5-H5 loop of K(V) 7.2. Wild type (WT) and mutant channels, expressed in both Xenopus laevis oocytes and CHO cells, were studied using electrophysiological techniques. The results revealed a pronounced loss-of-function with a dominant-negative effect of the mutant on WT K(V) 7.2 and K(V) 7.3 channels. Since single-channel recordings of K(V) 7.3-K(V) 7.2 and K(V) 7.3-N285S concatemers showed similar properties for both constructs, we hypothesized that the observed reduction in current amplitude was due to a folding and trafficking defect, which was confirmed by biochemical and immunocytochemical experiments revealing a reduced number of mutant channels in the surface membrane. Furthermore, rescuing experiments revealed that upon specific incubation of transfected CHO cells-either at lower temperatures of <30°C or in presence of the agonist retigabine (RTG)-the N258S-derived currents increased fivefold in contrast to the WT. The obtained results represent a first example of temperature and pharmacological rescue of a K(V) 7 mutation and suggest a folding and trafficking deficiency as the cause of reduced current amplitudes with a dominant-negative effect of N258S mutant proteins.

Bladder AEs with retigabine mostly mild and reversible

Bladder AEs with retigabine mostly mild and reversible

Antiepileptogenic and antiictogenic effects of retigabine under conditions of rapid kindling: An ontogenic study

To examine antiepileptogenic and antiictogenic potential of retigabine (RTG) under conditions of rapid kindling epileptogenesis during different stages of development. The experiments were performed in postnatal day 14 (P14), P21, and P35 male Wistar rats. After stereotaxic implantation of hippocampal stimulating and recording electrodes, the effects of RTG on baseline afterdischarge (AD) properties were studied. Next, the animals underwent rapid kindling (sixty 10 s trains, bipolar 20 Hz square wave pulses delivered every 5 min). The progression of seizures (kindling acquisition), and responses to test stimulations after kindling (retention) were compared between RTG and vehicle-treated rats. Additionally, the effects of RTG on the severity of seizures in previously kindled animals were examined. When administered intraperitoneally in doses that induced only mild, or no motor deficits, RTG significantly dampened brain excitability, evident as the increase of AD threshold and shortening of AD duration. During kindling, RTG delayed the development of focal seizures in P14 rats, and prevented the occurrence of full limbic seizures at all three ages. At P14 and P21, but not at P35, pretreatment with RTG prevented the establishment of kindling-induced enhanced seizure susceptibility. Administration of RTG to kindled animals decreased the severity of seizures induced by test stimulation. The effect was most prominent at P14. RTG exerted both antiepileptogenic and antiictogenic effects under conditions of rapid kindling model. These effects were apparent during postneonatal, early childhood, and adolescent stages of development.

Isobolographic characterization of interactions of retigabine with carbamazepine, lamotrigine, and valproate in the mouse maximal electroshock-induced seizure model

The aim of this study was to characterize the pharmacodynamic, pharmacokinetic, and adverse-effect profiles of retigabine (RTG) in combination with carbamazepine (CBZ), lamotrigine (LTG), and valproate (VPA). The isobolographic analysis for parallel and nonparallel dose-response effects was used in the mouse maximal electroshock seizure (MES) model for evaluation of pharmacodynamic interaction. Potential adverse-effect profiles of interactions of RTG with CBZ, LTG, and VPA at the fixed ratio of 1:1 in the MES test were evaluated in the chimney (motor performance), passive avoidance (long-term memory), and grip strength (muscular strength) tests. Free plasma and total brain concentrations of CBZ, LTG, and VPA were determined by immunofluorescence and chromatography to assess pharmacokinetic interaction. In the MES model, RTG administered singly had its dose-response relationship curve (DRRC) parallel to that for VPA and nonparallel to that for CBZ and LTG. With isobolography for parallel DRRCs, the combination of RTG with VPA at fixed ratios of 1:3, 1:1, and 3:1 exerted supraadditive (synergistic) interaction. Isobolography for nonparallel DRRCs revealed that the combinations of RTG with CBZ and LTG at the fixed ratio of 1:1 produced additive interaction. In all combinations, neither motor coordination, long-term memory, nor muscular strength were affected. Only the combination of RTG with VPA at the fixed ratio of 3:1 was complicated by a pharmacokinetic increase in both free plasma and total brain VPA concentrations. All remaining combinations of RTG with VPA, CBZ, and LTG were pharmacodynamic in nature. RTG synergistically interacted with VPA and exerted additive interaction with CBZ and LTG in the mouse MES model.

Retigabine

Retigabine

Phenytoin- and carbamazepine-resistant spontaneous bursting in rat entorhinal cortex is blocked by retigabine in vitro

Hyperexcitability in the medial entorhinal cortex-hippocampal (mEC-HC) circuit in the initial weeks after prolonged seizure activity may contribute to the epileptogenic process in animal models of temporal lobe epilepsy (TLE). The present study examined combined mEC-HC slices (400 microm) using field potential recordings 1-2 weeks following the multiple administration, low-dose kainic acid (KA) model of TLE [Hellier, J.L., Patrylo, P.R., Buckmaster, P.S., Dudek, F.E., 1998. Recurrent spontaneous motor seizures after repeated low-dose systemic treatment with kainate: assessment of a rat model of temporal lobe epilepsy. Epilepsy Res. 31, 73-84]. Field potential recordings in slices from KA-treated rats demonstrated hallmarks of hyperexcitability in the mEC and in the CA1 and CA3 cell body regions of the HC. Spontaneous burst (SB) activity was observed under baseline recording conditions in the mEC of several slices from KA-treated rats, but not in the slices from saline-treated control rats. Elevating ACSF [K(+)](o) (6mM) in the presence of picrotoxin (50 microM) increased SB rates in all slices tested. However, there was a significantly shorter latency to onset of bursting and prolonged evoked response durations in layer II of the mEC of slices from KA-treated rats versus those from controls. Neither carbamazepine (CBZ) nor phenytoin (PHT) abolished SB activity in slices from KA-treated rats; whereas, SB activity in slices from control rats was dose-dependently reduced at 100 microM CBZ. In contrast, the novel anticonvulsant retigabine (RGB) dramatically reduced SB frequency in both control and KA-treated groups. The hyperexcitability observed in combined mEC-HC brain slices from KA-treated rats suggests that the mEC, as well as the HC, may contribute to the epileptogenic process after KA-induced seizure activity. This model may provide an efficient, flexible in vitro paradigm for differentiating novel AEDs in a model of pharmacoresistant bursting.