Functional Characteristics of the Nav1.1 p.Arg1596Cys Mutation Associated with Varying Severity of Epilepsy Phenotypes.

Mutations of the SCN1A gene, which encodes the voltage-dependent Na+ channel's α subunit, are associated with diverse epileptic syndromes ranging in severity, even intra-family, from febrile seizures to epileptic encephalopathy. The underlying cause of this variability is unknown, suggesting the involvement of additional factors. The aim of our study was to describe the properties of mutated channels and investigate genetic causes for clinical syndromes' variability in the family of five SCN1A gene p.Arg1596Cys mutation carriers. The analysis of additional genetic factors influencing SCN1A-associated phenotypes was conducted through exome sequencing (WES). To assess the impact of mutations, we used patch clamp analysis of mutated channels expressed in HEK cells and in vivo neural excitability studies (NESs). In cells expressing the mutant channel, sodium currents were reduced. NESs indicated increased excitability of peripheral motor neurons in mutation carriers. WES showed the absence of non-SCA1 pathogenic variants that could be causative of disease in the family. Variants of uncertain significance in three genes, as potential modifiers of the most severe phenotype, were identified. The p.Arg1596Cys substitution inhibits channel function, affecting steady-state inactivation kinetics. Its clinical manifestations involve not only epileptic symptoms but also increased excitability of peripheral motor fibers. The role of Nav1.1 in excitatory neurons cannot be ruled out as a significant factor of the clinical phenotype.

Guanfacine inhibits interictal epileptiform events and sodium currents in prefrontal cortex pyramidal neurons.

BACKGROUND: Guanfacine (an alpha-2A receptor agonist) is a commonly used drug with recognized efficacy in the treatment of attention deficit hyperactivity disorder (ADHD). This study aimed to assess the effects of guanfacine on short-lasting (interictal) epileptiform discharges in cortical neurons. Moreover, we assessed the effects of guanfacine on voltage-gated sodium currents. METHODS: We conducted patch-clamp recordings in prefrontal cortex pyramidal neurons obtained from young rats. Interictal epileptiform events were evoked in cortical slices in a zero magnesium proepileptic extracellular solution with an elevated concentration of potassium ions. RESULTS: Interictal epileptiform discharges were spontaneous depolarisations, which triggered action potentials. Guanfacine (10 and 100 µM) inhibited the frequency of epileptiform discharges. The effect of guanfacine on interictal events persisted in the presence of alpha-2 adrenergic receptor antagonist idazoxan. The tested drug inhibited neuronal excitability. Tonic NMDA currents were not influenced by guanfacine. Recordings from dispersed neurons showed that the tested drug (10 and 100 µM) inhibited persistent and fast inactivating voltage-gated sodium currents. CONCLUSIONS: This study shows that guanfacine inhibits interictal discharges in cortical neurons independently of alpha-2A adrenergic receptors. This effect may be mediated by voltage-gated sodium currents. Inhibition of interictal activity by guanfacine may be of clinical importance because interictal events often occur in patients with ADHD and may contribute to symptoms of this disease.

Discovery of (R)-N-Benzyl-2-(2,5-dioxopyrrolidin-1-yl)propanamide [(R)-AS-1], a Novel Orally Bioavailable EAAT2 Modulator with Drug-like Properties and Potent Antiseizure Activity In Vivo.

(R)-7 [(R)-AS-1] showed broad-spectrum antiseizure activity across in vivo mouse seizure models: maximal electroshock (MES), 6 Hz (32/44 mA), acute pentylenetetrazol (PTZ), and PTZ-kindling. A remarkable separation between antiseizure activity and CNS-related adverse effects was also observed. In vitro studies with primary glia cultures and COS-7 cells expressing the glutamate transporter EAAT2 showed enhancement of glutamate uptake, revealing a stereoselective positive allosteric modulator (PAM) effect, further supported by molecular docking simulations. (R)-7 [(R)-AS-1] was not active in EAAT1 and EAAT3 assays and did not show significant off-target activity, including interactions with targets reported for marketed antiseizure drugs, indicative of a novel and unprecedented mechanism of action. Both in vivo pharmacokinetic and in vitro absorption, distribution, metabolism, excretion, toxicity (ADME-Tox) profiles confirmed the favorable drug-like potential of the compound. Thus, (R)-7 [(R)-AS-1] may be considered as the first-in-class small-molecule PAM of EAAT2 with potential for further preclinical and clinical development in epilepsy and possibly other CNS disorders.

New Phenylglycinamide Derivatives with Hybrid Structure as Candidates for New Broad-Spectrum Anticonvulsants.

In the present study, a focused combinatorial chemistry approach was applied to merge structural fragments of well-known TRPV1 antagonists with a potent anticonvulsant lead compound, KA-104, that was previously discovered by our group. Consequently, a series of 22 original compounds has been designed, synthesized, and characterized in the in vivo and in vitro assays. The obtained compounds showed robust in vivo antiseizure activity in the maximal electroshock (MES) test and in the 6 Hz seizure model (using both 32 and 44 mA current intensities). The most potent compounds 53 and 60 displayed the following pharmacological profile: ED50 = 89.7 mg/kg (MES), ED50 = 29.9 mg/kg (6 Hz, 32 mA), ED50 = 68.0 mg/kg (6 Hz, 44 mA), and ED50 = 73.6 mg/kg (MES), ED50 = 24.6 mg/kg (6 Hz, 32 mA), and ED50 = 56.3 mg/kg (6 Hz, 44 mA), respectively. Additionally, 53 and 60 were effective in the ivPTZ seizure threshold and had no influence on the grip strength and body temperature in mice. The in vitro binding and functional assays indicated a multimodal mechanism of action for 53 and 60. These molecules, beyond TRPV1 antagonism, inhibited calcium currents and fast sodium currents in patch-clamp assays. Further studies proved beneficial in vitro ADME-Tox properties for 53 and 60 (i.e., high metabolic stability, weak influence on CYPs, no neurotoxicity, etc.). Overall, 53 and 60 seem to be interesting candidates for future preclinical development in epilepsy and pain indications due to their interaction with the TRPV1 channel.

Beneficial Effects of Capsaicin in Disorders of the Central Nervous System.

Capsaicin is a natural compound found in chili peppers and is used in the diet of many countries. The important mechanism of action of capsaicin is its influence on TRPV1 channels in nociceptive sensory neurons. Furthermore, the beneficial effects of capsaicin in cardiovascular and oncological disorders have been described. Many recent publications show the positive effects of capsaicin in animal models of brain disorders. In Alzheimer's disease, capsaicin reduces neurodegeneration and memory impairment. The beneficial effects of capsaicin in Parkinson's disease and depression have also been described. It has been found that capsaicin reduces the area of infarction and improves neurological outcomes in animal models of stroke. However, both proepileptic and antiepileptic effects of capsaicin in animal models of epilepsy have been proposed. These contradictory results may be caused by the fact that capsaicin influences not only TRPV1 channels but also different molecular targets such as voltage-gated sodium channels. Human studies show that capsaicin may be helpful in treating stroke complications such as dysphagia. Additionally, this compound exerts pain-relieving effects in migraine and cluster headaches. The purpose of this review is to discuss the mechanisms of the beneficial effects of capsaicin in disorders of the central nervous system.

Menthol exerts TRPM8-independent antiepileptic effects in prefrontal cortex pyramidal neurons.

Menthol is a natural compound that evokes cold sensations by activating TRPM8 channels in peripheral sensory receptors. Little is known about the effects of this compound on brain neurons. It has been shown previously that menthol exerts antiepileptic effects in hippocampal neurons by enhancing GABA receptors. The aim of this patch-clamp study was to assess the effects of menthol on sodium currents, action potentials and epileptiform events in cortical neurons. Menthol inhibited fast voltage-gated sodium channels and neuronal excitability defined as the number of action potentials per depolarization step. The influence of menthol on epileptic events was also assessed in this study. Interictal epileptiform events lasting <2 s were recorded in zero magnesium high potassium proepileptic extracellular solution. The frequency of these epileptiform events was inhibited by menthol (200 µM). Ictal epileptic events lasting >100 s were recorded in zero magnesium proepileptic extracellular solution containing 4-AP. The frequency of these ictal events was potently decreased by menthol. TRPM8 channels were not involved in the inhibitory effect of menthol on ictal events because epileptic discharges persisted in the presence of the TRPM8 inhibitor AMTB. Moreover, ictal events were inhibited by therapeutic concentrations of the antiepileptic drug carbamazepine. Menthol and carbamazepine inhibited ictal events to a similar extent. This study showed that menthol exerts antiepileptic effects in cortical neurons.

Prefrontal cortex pyramidal neurons express functional Nav1.8 tetrodotoxin-resistant sodium currents.

It has been repeatedly proved that Nav1.8 tetrodotoxin (TTX)-resistant sodium currents are expressed in peripheral sensory neurons where they play important role in nociception. There are very few publications that show the presence of TTX-resistant sodium currents in central neurons. The aim of this study was to assess if functional Nav1.8 TTX-resistant sodium currents are expressed in prefrontal cortex pyramidal neurons. All recordings were performed in the presence of TTX in the extracellular solution to block TTX-sensitive sodium currents. The TTX-resistant sodium current recorded in this study was mainly carried by the Nav1.8 sodium channel isoform because the Nav1.9 current was inhibited by the -65 mV holding potential that we used throughout the study. Moreover, the sodium current that we recorded was inhibited by treatment with the selective Nav1.8 inhibitor A-803467. Confocal microscopy experiments confirmed the presence of the Nav1.8 α subunit in prefrontal cortex pyramidal neurons. Activation and steady state inactivation properties of TTX-resistant sodium currents were also assessed in this study and they were similar to activation and inactivation properties of TTX-resistant sodium currents expressed in dorsal root ganglia (DRG) neurons. Moreover, this study showed that carbamazepine (60 µM) inhibited the maximal amplitude of the TTX-resistant sodium current. Furthermore, we found that carbamazepine shifts steady state inactivation curve of TTX-resistant sodium currents toward hyperpolarization. This study suggests that the Nav1.8 TTX-resistant sodium channel is expressed not only in DRG neurons, but also in cortical neurons and may be molecular target for antiepileptic drugs such as carbamazepine.

Identification of New Compounds with Anticonvulsant and Antinociceptive Properties in a Group of 3-substituted (2,5-dioxo-pyrrolidin-1-yl)(phenyl)-Acetamides.

We report herein a series of water-soluble analogues of previously described anticonvulsants and their detailed in vivo and in vitro characterization. The majority of these compounds demonstrated broad-spectrum anticonvulsant properties in animal seizure models, including the maximal electroshock (MES) test, the pentylenetetrazole-induced seizure model (scPTZ), and the psychomotor 6 Hz (32 mA) seizure model in mice. Compound 14 showed the most robust anticonvulsant activity (ED50 MES = 49.6 mg/kg, ED50 6 Hz (32 mA) = 31.3 mg/kg, ED50scPTZ = 67.4 mg/kg). Notably, it was also effective in the 6 Hz (44 mA) model of drug-resistant epilepsy (ED50 = 63.2 mg/kg). Apart from favorable anticonvulsant properties, compound 14 revealed a high efficacy against pain responses in the formalin-induced tonic pain, the capsaicin-induced neurogenic pain, as well as in the oxaliplatin-induced neuropathic pain in mice. Moreover, compound 14 showed distinct anti-inflammatory activity in the model of carrageenan-induced aseptic inflammation. The mechanism of action of compound 14 is likely complex and may result from the inhibition of peripheral and central sodium and calcium currents, as well as the TRPV1 receptor antagonism as observed in the in vitro studies. This lead compound also revealed beneficial in vitro ADME-Tox properties and an in vivo pharmacokinetic profile, making it a potential candidate for future preclinical development. Interestingly, the in vitro studies also showed a favorable induction effect of compound 14 on the viability of neuroblastoma SH-SY5Y cells.

Asymmetric synthesis and in vivo/in vitro characterization of new hybrid anticonvulsants derived from (2,5-dioxopyrrolidin-1-yl)phenylacetamides.

In the current studies we carried out an optimized multistep asymmetric synthesis of R-enantiomers (eutomers) for a previously identified series of racemic hybrid anticonvulsants. The spatial structure of selected enantiomers was solved by the use of crystallographic methods. The compound (R)-16 was identified as a lead, which revealed broad-spectrum protective activity in a range of epilepsy models with the following ED50 values: the maximal electroshock (MES) test (36.0 mg/kg), the 6 Hz (32 mA) seizure model (39.2 mg/kg), and the pentylenetetrazole-induced seizure model (scPTZ) (54.8 mg/kg). Furthermore, (R)-16 displayed a low potency for the induction of motor impairment in the rotarod test (TD50 = 468.5 mg/kg), resulting in potentially very beneficial therapeutic window. Finally, (R)-16 showed satisfying ADME-Tox properties in the in vitro assays. Therefore, the data obtained in the current studies justify the further preclinical development of (R)-16 as candidate for potentially broad-spectrum and safe anticonvulsant.

KA-104, a new multitargeted anticonvulsant with potent antinociceptive activity in preclinical models.

OBJECTIVE: The main objective of the present work was to assess the utility of KA-104 as potential therapy for drug-resistant seizures and neuropathic pain, and to characterize its druglike properties in a series of absorption, distribution, metabolism, excretion and toxicity (ADME-Tox) studies. We also aimed to establish its mechanism of action in electrophysiological studies. METHODS: The activity of KA-104 against drug-resistant seizures was tested in the mouse 6-Hz (44-mA) model, whereas the antinociceptive activity was assessed with the capsaicin- and oxaliplatin-induced pain models in mice. The patch-clamp technique was used to study the influence of KA-104 on fast voltage-gated sodium currents in rat prefrontal cortex pyramidal neurons. The pharmacokinetic profile was determined after intraperitoneal (ip) injection in mice. The in vitro ADME-Tox properties were studied by applying routine testing procedures. RESULTS: KA-104 was effective in the 6-Hz (44-mA) model (median effective dose [ED50 ] = 73.2 mg/kg) and revealed high efficacy in capsaicin-induced neurogenic pain as well as in oxaliplatin-induced neuropathic pain in mice. Patch-clamp technique showed that KA-104 reversibly inhibits voltage-gated sodium currents. KA-104 was rapidly absorbed after the ip injection and showed relatively good penetration through the blood-brain barrier. This molecule was also characterized by high passive permeability, moderate influence on CYP2C9, and negligible hepatotoxicity on HepG2 cells. SIGNIFICANCE: The results reported herein indicate that KA-104 is a new wide-spectrum multitargeted anticonvulsant with favorable in vitro ADME-Tox properties. Importantly, this compound may also prove to become an interesting and hopefully more effective therapeutic option for treatment of neuropathic pain.

Structure-activity relationship and cardiac safety of 2-aryl-2-(pyridin-2-yl)acetamides as a new class of broad-spectrum anticonvulsants derived from Disopyramide.

A series of 2-aryl-2-(pyridin-2-yl)acetamides were synthesized and screened for their anticonvulsant activity in animal models of epilepsy. The compounds were broadly active in the 'classical' maximal electroshock seizure (MES) and subcutaneous Metrazol (scMET) tests as well as in the 6 Hz and kindling models of pharmacoresistant seizures. Furthermore, the compounds showed good therapeutic indices between anticonvulsant activity and motor impairment. Structure-activity relationship (SAR) trends clearly showed the highest activity resides in unsubstituted phenyl derivatives or compounds having ortho- and meta- substituents on the phenyl ring. The 2-aryl-2-(pyridin-2-yl)acetamides were derived by redesign of the cardiotoxic sodium channel blocker Disopyramide (DISO). Our results show that the compounds preserve the capability of the parent compound to inhibit voltage gated sodium currents in patch-clamp experiments; however, in contrast to DISO, a representative compound from the series 1 displays high levels of cardiac safety in a panel of in vitro and in vivo experiments.

Capsaicin inhibits sodium currents and epileptiform activity in prefrontal cortex pyramidal neurons.

Capsaicin, a compound found in chili peppers, causes burning sensations by acting on the peripheral sensory system. However, it has also been reported to exert substantial effects on central neurons. The aim of this patch-clamp study was to test the antiepileptic potential of capsaicin in prefrontal cortical pyramidal neurons. Capsaicin at a concentration of 60 µM inhibited neuronal excitability. Moreover, later spikes in response to 50-s-long current steps were much smaller in amplitude in the presence of 60 µM capsaicin than in control solution. The tested compound did not influence the membrane potential. Voltage-clamp recordings showed that capsaicin markedly enhanced the use-dependent block of sodium channels (sodium currents were evoked at frequencies of 0,5 Hz and 10 Hz). The presence of the compound shifted the steady-state inactivation curve of sodium channels towards hyperpolarization, which suggests greater inactivation of sodium channels at rest in the presence of capsaicin. Moreover, capsaicin inhibited epileptiform events evoked in three different proepileptic solutions. Capsaicin abolished interictal-like events lasting less than 1 s recorded in zero magnesium solution with an increased potassium ion concentration. The drug also abolished long ictal events evoked in zero magnesium solution containing 4-AP. Moreover, ictal events recorded in zero magnesium solution containing picrotoxin were substantially shortened in the presence of capsaicin. We suggest that capsaicin exerts an antiepileptic effect. The important mechanism behind this phenomenon seems to be the inhibition of sodium channels, which is an effect of many antiepileptic drugs.

N-Benzyl-(2,5-dioxopyrrolidin-1-yl)propanamide (AS-1) with Hybrid Structure as a Candidate for a Broad-Spectrum Antiepileptic Drug.

In our recent studies, we identified compound N-benzyl-2-(2,5-dioxopyrrolidin-1-yl)propanamide (AS-1) as a broad-spectrum hybrid anticonvulsant which showed potent protection across the most important animal acute seizure models such as the maximal electroshock (MES) test, the subcutaneous pentylenetetrazole (s.c. PTZ) test, and the 6-Hz (32 mA) test in mice. Therefore, AS-1 may be recognized as a candidate for new anticonvulsant effective in different types of human epilepsy with a favorable safety margin profile determined in the rotarod test in mice. In the aim of further pharmacological evaluation of AS-1, in the current study, we examined its activity in the 6-Hz (44 mA) test, which is known as the model of drug-resistant epilepsy. Furthermore, we determined also the antiseizure activity in the kindling model of epilepsy induced by repeated injection of pentylenetetrazole (PTZ) in mice. As a result, AS-1 revealed relatively potent protection in the 6-Hz (44 mA) test, as well as delayed the progression of kindling induced by repeated injection of PTZ in mice at doses of 15 mg/kg, 30 mg/kg, and 60 mg/kg. Importantly, the isobolographic analysis showed that a combination of AS-1 and valproic acid (VPA) at the fixed ratio of 1:1 displayed a supra-additive (synergistic) interaction against PTZ-induced seizures in mice. Thus, AS-1 may be potentially used in an add-on therapy with VPA. Moreover, incubation of zebrafish larvae with AS-1 substantially decreased the number, cumulative but not the mean duration of epileptiform-like events in electroencephalographic assay. Finally, the in vitro ADME-Tox studies revealed that AS-1 is characterized by a very good permeability in the parallel artificial membrane permeability assay test, excellent metabolic stability on human liver microsomes (HLMs), no significant influence on CYP3A4/CYP2D6 activity, and moderate inhibition of CYP2C9 in a concentration of 10 µM, as well as no hepatotoxic properties in HepG2 cells (concentration of 10 µM).

Valproic acid potently inhibits interictal-like epileptiform activity in prefrontal cortex pyramidal neurons.

Valproic acid has a long-standing reputation of effectively treating the symptoms of not only epilepsy but also psychiatric conditions. In the latter, the exact mechanism by which valproate exerts its effect remains unclear. In this study, epileptiform bursts were recorded from pyramidal neurons in the prefrontal cortex (the brain region thought to be involved in psychiatric disorders) using the patch-clamp technique. An extracellular solution with no magnesium ions and elevated potassium levels that is known to induce epileptiform activity in vitro was used. Because of their short durations, the epileptiform bursts were regarded as interictal-like epileptiform activity, which is believed to be involved in cognitive impairment. Interictal discharges occur in many neuropsychiatric disorders as well as in healthy population. Epileptic activity in prefrontal cortex pyramidal neurons was potently inhibited by two therapeutic concentrations of valproic acid (20 µM and 200 µM). Moreover, valproate suppressed spontaneous excitatory postsynaptic potentials. Epileptiform bursts were fully inhibited by NMDA receptor antagonist, which suggests that epileptiform activity is driven by NMDA receptors. The inhibition of excitability in prefrontal cortex pyramidal neurons by valproate was also shown. This study shows that it is possible to evoke NMDA-dependent epileptiform activity in prefrontal cortex pyramidal neurons in vitro. We suggest that the prefrontal cortex is a good region for studying the influence of drugs on interictal epileptiform activity.

KA-11, a Novel Pyrrolidine-2,5-dione Derived Broad-Spectrum Anticonvulsant: Its Antiepileptogenic, Antinociceptive Properties and in Vitro Characterization.

Recently, compound KA-11 was identified as a promising candidate for a new broad-spectrum anticonvulsant. This compound revealed wide protective activity across the most important animal models of seizures such as the maximal electroshock test (MES), the subcutaneous pentylenetetrazole test ( scPTZ), and the six-hertz test (6 Hz, 32 mA). Importantly, KA-11 was devoid of acute neurological activity, which was assessed by applying the chimney test (TD50 value higher than 1500 mg/kg). The preliminary in vivo results confirmed favorable anticonvulsant and safety properties of KA-11. With the aim of further biological characterization of KA-11, in the current studies we evaluated its antiepileptogenic activity in the kindling model of epilepsy induced by repeated injection of PTZ in mice. Furthermore, we assessed the antinociceptive activity of KA-11 in several animal pain models. As a result, KA-11 (at all doses applied: 25, 50, and 100 mg/kg) significantly delayed the progression of kindling induced by repeated injection of PTZ in mice. Additionally, KA-11 revealed potent antinociceptive activity in the formalin-induced tonic pain and, importantly, in the oxaliplatin-induced neuropathic pain model in mice. Moreover, KA-11 did not induce motor deficits in the rotarod test. Patch-clamp experiments revealed that one of the mechanisms of action of KA-11 is inhibition of voltage-gated sodium currents. Compound KA-11 appeared to be safe in relation to hepatotoxic properties as no phospholipidosis induction was determined in HepG2 cells at 50 µM, and a small, statistically significant decrease of cell viability was observed only at the highest used dose of 100 µM. Moreover, KA-11 did not affect the function of CYP2D6. The aforementioned hybrid substance proved to penetrate the biological membranes in the in vitro permeability assays.

Age-dependent expression of Nav1.9 channels in medial prefrontal cortex pyramidal neurons in rats.

Developmental changes that occur in the prefrontal cortex during adolescence alter behavior. These behavioral alterations likely stem from changes in prefrontal cortex neuronal activity, which may depend on the properties and expression of ion channels. Nav1.9 sodium channels conduct a Na+ current that is TTX resistant with a low threshold and noninactivating over time. The purpose of this study was to assess the presence of Nav1.9 channels in medial prefrontal cortex (mPFC) layer II and V pyramidal neurons in young (20-day old), late adolescent (60-day old), and adult (6- to 7-month old) rats. First, we demonstrated that layer II and V mPFC pyramidal neurons in slices obtained from young rats exhibited a TTX-resistant, low-threshold, noninactivating, and voltage-dependent Na+ current. The mRNA expression of the SCN11a gene (which encodes the Nav1.9 channel) in mPFC tissue was significantly higher in young rats than in late adolescent and adult rats. Nav1.9 protein was immunofluorescently labeled in mPFC cells in slices and analyzed via confocal microscopy. Nav1.9 immunolabeling was present in layer II and V mPFC pyramidal neurons and was more prominent in the neurons of young rats than in the neurons of late adolescent and adult rats. We conclude that Nav1.9 channels are expressed in layer II and V mPFC pyramidal neurons and that Nav1.9 protein expression in the mPFC pyramidal neurons of late adolescent and adult rats is lower than that in the neurons of young rats. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1371-1384, 2017.

Valproic acid inhibits TTX-resistant sodium currents in prefrontal cortex pyramidal neurons.

Valproic acid is frequently prescribed and used to treat epilepsy, bipolar disorder and other conditions. However, the mechanism of action of valproic acid has not been fully elucidated. The aim of this study was to assess the influence of valproic acid (200 µM) on TTX-resistant sodium currents in mPFC pyramidal neurons. Valproic acid inhibited the maximal amplitude and did not change the activation parameters of TTX-resistant sodium currents. Moreover, valproic acid (2 µM and 200 µM) shifted the TTX-resistant sodium channel inactivation curve towards hyperpolarisation. In the presence of valproic acid, TTX-resistant sodium currents recovered from inactivation more slowly. Valproic acid did not influence the use-dependent blockade of TTX-resistant sodium currents. This study suggests that a potential new mechanism of the antiepileptic action of valproic acid is, among others, inhibition of TTX-resistant sodium currents.

Somatic and dendritic perforated-patch recordings reveal b-adrenergic receptor-induced depolarization in medial prefrontal cortex pyramidal neurons.

The aim of this perforated-patch study was to test the effect of isoproterenol on the membrane potential in mPFC (medial prefrontal cortex) pyramidal neurons. Isoproterenol depolarized the membrane potential recorded from the soma. This effect was absent in the presence of metoprolol, suggesting the involvement of beta1-adrenergic receptors. The adenylate cyclase activator forskolin also depolarized the membrane potential. Moreover, the effect of isoproterenol was abolished by the adenylate cyclase inhibitor SQ 22536. This suggested that adenylate cyclase was involved in mediating the effect of the beta-adrenergic receptor agonist. The isoproterenol-induced depolarization persisted after inhibition of protein kinase A with H-89. The effect of beta-adrenergic receptor activation on the membrane potential was dependent on Ih channels because it was abolished in the presence of the Ih channel inhibitor ZD 7288. Dendritic recordings were also performed. In the dendritic segments between 100 microm and 150 microm from the soma and between 200 microm and 250 microm from the soma, isoproterenol also depolarized the membrane potential. The magnitude of the beta-adrenergic receptor-stimulated depolarization was the same in the soma and in both dendritic localizations. The depolarization exerted by isoproterenol may influence PFC cognitive functions.

Characterization of Disopyramide derivative ADD424042 as a non-cardiotoxic neuronal sodium channel blocker with broad-spectrum anticonvulsant activity in rodent seizure models.

It was reported that antiarrhythmic drugs (AADs) can be useful in controlling refractory seizures in humans or in enhancing the action of antiepileptic drugs (AEDs) in animal models. Disopyramide phosphate (DISO) is an AAD that blocks sodium channels in cardiac myocytes. We evaluated a DISO derivative, 2-(2-chlorophenyl)-2-(pyridin-2-yl)acetamide (ADD424042) for its anticonvulsant activity in a battery of rodent models of epileptic seizures. The compound displayed a broad spectrum of activity in the 'classical' models as well as in the models of pharmacoresistant seizures. Furthermore, ADD424042 showed good therapeutic indices between the anticonvulsant activity and the motor impairment. On the contrary, no anticonvulsant effects but severe lethality were observed in the primary anticonvulsant testing of the parent DISO. By performing the whole-cell voltage-clamp experiments in dispersed cortical neurons we demonstrated that ADD424042 decreased the maximal amplitude of voltage-gated sodium channels with an IC50 value in nM range. Moreover, the compound enhanced use-dependent block and decreased excitability in pyramidal neurons in the current-clamp experiments in cortical slices. Importantly, we found that ADD424042 possessed either no, or very small cardiotoxic effect. In contrast to DISO, ADD424042 did not produce any apparent changes in electrocardiogram (ECG) and arterial blood pressure recordings. ADD424042 had no effect on QT and corrected QT intervals, at a dose which was 15 times higher than ED50 for the anticonvulsant effect in the MES model. Taken together, these data suggest that ADD424042 has the potential to become a lead structure for novel broadly acting AEDs with wide margin of cardiac safety.

ß-Adrenergic receptor agonist increases voltage-gated Na(+) currents in medial prefrontal cortex pyramidal neurons.

The prefrontal cortex does not function properly in neuropsychiatric diseases and during chronic stress. The aim of this study was to test the effects of isoproterenol, a ß-adrenergic receptor agonist, on the voltage-dependent fast-inactivating Na(+) currents in medial prefrontal cortex (mPFC) pyramidal neurons obtained from young rats. The recordings were performed in the cell-attached configuration. Isoproterenol (2µM) did not change the peak Na(+) current amplitude but shifted the IV curve of the Na(+) currents toward hyperpolarization. Pretreatment of the cells with the ß-adrenergic antagonists propranolol and metoprolol abolished the effect of isoproterenol on the Na(+) currents, suggesting the involvement of ß1-adrenergic receptors. The effect of ß-adrenergic receptor stimulation on the sodium currents was dependent on kinase A and kinase C; the effect was diminished in the presence of the kinase A antagonist H-89 and the kinase C antagonist chelerythrine and abolished when the antagonists were coapplied. Moreover, isoproterenol depolarized the membrane potential recorded using the perforated-patch method, and this depolarization was abolished by cesium ions. Thus, in mPFC pyramidal neurons, stimulation of ß-adrenergic receptors up-regulates the fast-inactivating voltage-gated Na(+) currents evoked by suprathreshold depolarizations.