Seizure Latency Research Articles

P.6.024 Quality-of-life assessment in atomoxetine-treatedadult patients with attention-deficit/hyperactivity disorder

The effects of tianeptine and fluoxetine on pentylenetetrazole (PTZ)-induced seizures in rats were investigated. Female Wistar rats (172–278 g) were used in the study. Tianeptine (1.25, 2.5, 5, 10 and 20 mg/kg) and fluoxetine (2.5, 5, 10 and 20 mg/kg) or saline were injected to rats intraperitoneally 30 min before PTZ (50 mg/kg) injections. Immediately after PTZ administrations, latency and intensity of the PTZ-induced seizures was recorded and scored, respectively. Fluoxetine (2.5–20 mg/kg) did not produce any significant difference in latency and intensity of the PTZ-induced seizures. Although tianeptine (1.25–20 mg/kg) also did not affect the latency time, it produced significant attenuations in the intensity of the seizures. Tianeptine did not cause any significant change in the locomotor activity of the rats. The results of this preliminary study suggest that tianeptine but not fluoxetine has some inhibitory effects on PTZ-induced seizures in rats.

Investigation of the effects of tianeptine and fluoxetine on pentylenetetrazole-induced seizures in rats

The effects of tianeptine and fluoxetine on pentylenetetrazole (PTZ)-induced seizures in rats were investigated. Female Wistar rats (172–278 g) were used in the study. Tianeptine (1.25, 2.5, 5, 10 and 20 mg/kg) and fluoxetine (2.5, 5, 10 and 20 mg/kg) or saline were injected to rats intraperitoneally 30 min before PTZ (50 mg/kg) injections. Immediately after PTZ administrations, latency and intensity of the PTZ-induced seizures was recorded and scored, respectively. Fluoxetine (2.5–20 mg/kg) did not produce any significant difference in latency and intensity of the PTZ-induced seizures. Although tianeptine (1.25–20 mg/kg) also did not affect the latency time, it produced significant attenuations in the intensity of the seizures. Tianeptine did not cause any significant change in the locomotor activity of the rats. The results of this preliminary study suggest that tianeptine but not fluoxetine has some inhibitory effects on PTZ-induced seizures in rats.

GABA-B receptor activation in the rat globus pallidus potently suppresses pentylenetetrazol-induced tonic seizures

To determine the involvement of the globus pallidus in mediating epilepsy, the effects of microinjection of a GABA uptake blocker (tiagabine), a benzodiazepine agonist (zolpidem) and a GABA-B receptor agonist (baclofen) on pentylenetetrazol (PTZ)-induced tonic seizure were examined in adult rats. Administration of PTZ induced tonic seizures in all control animals, accompanied with a 100% mortality rate. Pretreatment with bilateral intrapallidal microinjection of tiagabine (1 mM) suppressed the incidence of tonic seizures to 67.7% and reduced the mortality rate to 16.7%. Furthermore, the latency to tonic seizures was 1,275 +/- 277 s, which was significantly longer than that of the corresponding control animals (319 +/- 225 s). On the other hand, administration of zolpidem (1 mM) was without significant effects on the mortality rate, the incidence and latency of the tonic seizure. In sharp contrast, microinjection of baclofen (1 mM) completely suppressed PTZ-induced tonic seizures and reduced the mortality rate to 0%. This effect was largely abolished by co-injection of the GABA-B receptor antagonist CGP55845. To elucidate the direct cellular action of baclofen, the excitability and membrane potential of globus pallidus neurons were studied by cell-attached and whole-cell patch-clamp recordings in the brain slice. Bath application of baclofen (50 microM) significantly reduced the firing of these neurons, and was often accompanied by a clear membrane hyperpolarization, in a CGP55845-sensitive manner. These data suggest that activation of GABA-B receptors in globus pallidus could significantly modulate PTZ-induced tonic seizures.

GABA-B Receptor Activation in the Rat Globus pallidus Potently Suppresses Pentylenetetrazol-Induced Tonic Seizures

To determine the involvement of the globus pallidus in mediating epilepsy, the effects of microinjection of a GABA uptake blocker (tiagabine), a benzodiazepine agonist (zolpidem) and a GABA-B receptor agonist (baclofen) on pentylenetetrazol (PTZ)-induced tonic seizure were examined in adult rats. Administration of PTZ induced tonic seizures in all control animals, accompanied with a 100% mortality rate. Pretreatment with bilateral intrapallidal microinjection of tiagabine (1 mM) suppressed the incidence of tonic seizures to 67.7% and reduced the mortality rate to 16.7%. Furthermore, the latency to tonic seizures was 1,275 ± 277 s, which was significantly longer than that of the corresponding control animals (319 ± 225 s). On the other hand, administration of zolpidem (1 mM) was without significant effects on the mortality rate, the incidence and latency of the tonic seizure. In sharp contrast, microinjection of baclofen (1mM) completely suppressed PTZ-induced tonic seizures and reduced the mortality rate to 0%. This effect was largely abolished by co-injection of the GABA-B receptor antagonist CGP55845. To elucidate the direct cellular action of baclofen, the excitability and membrane potential of globus pallidus neurons were studied by cell-attached and whole-cell patch-clamp recordings in the brain slice. Bath application of baclofen (50 µM) significantly reduced the firing of these neurons, and was often accompanied by a clear membrane hyperpolarization, in a CGP55845-sensitive manner. These data suggest that activation of GABA-B receptors in globus pallidus could significantly modulate PTZ-induced tonic seizures.

Effects of some synthetic kynurenines on brain amino acids and nitric oxide after pentylenetetrazole administration to rats.

We have previously proven that some synthetic kynurenines behave as antagonists of the N-methyl-d-aspartate receptor inhibiting neuronal subtype of nitric oxide synthase activity. We now investigate the anticonvulsant activity of four of these kynurenines in pentylenetetrazole (PTZ)-treated rats. The rats were treated with each kynurenine (10-160 mg/kg, s.c.) 30 min before PTZ administration (100 mg/kg, s.c.). Then, latency, duration and intensity of the first seizure and the percent animal survival were noted. PTZ-induced death was counteracted by high doses of kynurenines. Latency of the first seizure was significantly increased and its intensity reduced at the same doses, whereas the duration of the first seizure significantly decreased with doses of 20 mg/kg in most of the kynurenines tested. Three hours after PTZ administration, the surviving animals were sacrificed and the levels of brain amino acids and nitrite were measured. PTZ administration increased glutamate, glutamine, serine and taurine levels in different brain areas. High doses of kynurenines generally counteracted the effects of PTZ on excitatory amino acids, but they also reduced inhibitory aminoacids. However, the most consistent effect of kynurenines was the dose-dependent reduction of brain nitrite levels induced by PTZ. These results reveal a new family of anticonvulsant drugs that affect mainly to nitric oxide production in the brain.

Cholera toxin B decreases bicuculline seizures in prenatally morphine- and saline-exposed male rats

Prenatal morphine exposure on gestation days 11–18 alters bicuculline-induced seizures in rats during development and in adulthood. Adult, morphine-exposed male progeny exhibit an increased latency to bicuculline seizures, which can be reversed by administration of the opioid receptor antagonist naloxone. In chronically morphine-treated adult mice, cholera toxin B (CTX-B) can reverse the effects of chronic morphine administration. Therefore, the present study investigated whether prenatally morphine-exposed rats show a similar response to CTX-B as chronically morphine-treated adult rodents. Prenatally morphine-, saline- and unexposed male progeny were tested for seizure susceptibility with a 7.5-mg/kg intraperitoneal injection of bicuculline in adulthood. CTX-B or saline was injected subcutaneously at 24, 12, and 0.5 h before bicuculline injection. CTX-B decreased the occurrence of bicuculline-induced seizures in both prenatally saline- and morphine-exposed but not unexposed rats. Furthermore, three, but not one, saline injections administered at 12-h intervals prior to bicuculline administration reversed the increase in seizure latency in prenatally morphine-exposed adult males, suggesting an altered responsiveness of the stress system. The present study demonstrates that CTX-B can decrease the occurrence of bicuculline seizures in prenatally stressed rats and that increased seizure latencies in prenatally morphine-exposed male rats may be related to stress responses.

Epoetin alfa has potential efficacy in central nervous system disorders

Recombinant human erythropoietin (rHuEPO, epoetin alfa) is a 165-amino acid glycoprotein that has been shown to initiate response to hypoxia and is most widely known for its efficacy in the treatment of a variety of anemias. A series of experiments were conducted using rodent models to investigate the ability of systemically administered epoetin alfa to cross the blood-brain barrier (BBB) and affect the outcome of hypoxia and injury in the central nervous system. Results demonstrated that endogenous erythropoietin (EPO) and EPO receptors are expressed around animal brain capillaries and that systemically administered epoetin alfa crossed the BBB. The epoetin alfa group experienced significantly reduced ( P <0.01) tissue damage in an ischemic stroke model when the study drug was administered 24 h before inducing stroke compared with control animals. Significant protective effects of epoetin alfa persisted when epoetin alfa was administered up to 6 h poststroke ( P <0.05). Similarly, epoetin alfa reduced trauma-related brain injury when administered 24 h prior to and up to 6 h after blunt trauma when compared with the control group. The volume of tissue necrosis was significantly greater in control animals compared with those that received epoetin alfa ( P <0.05). In addition, these studies led to the postulate that epoetin alfa may also have an effect on nervous system inflammation. This was confirmed using an experimental auto-immune encephalomyelitis model, where rats were shown to have significantly delayed onset ( P <0.01) and reduced severity ( P <0.05) of symptoms after treatment with epoetin alfa. Other studies demonstrated that epoetin alfa had an effect on the latency and severity of seizures and significantly increased ( P <0.0002) survival versus controls when mice were exposed to the neurotoxin kainate (used to induce seizures). These findings suggest future potential therapeutic uses for epoetin alfa beyond its anemia-related effects.

Anticonvulsant effects of thymoquinone, the major constituent of Nigella sativa seeds, in mice.

The anticonvulsant effects of thymoquinone, the major constituent of Nigella sativa seeds, were investigated using pentylenetetrazole (PTZ)- and maximal electroshock (MES)-induced seizure models. We also studied the effect of thymoquinone on pentobarbital-induced hypnosis, locomotor activity, and motor coordination. In PTZ-induced seizure, the intraperitoneally injection of thymoquinone with doses of 40 and 80 mg/kg, prolonged the onset of seizures and reduced the duration of myoclonic seizures. The protective effect of thymoquinone against mortality was 71.4% and 100% in the mentioned doses, respectively. In MES model, thymoquinone failed to reduce the duration of seizure, whereas exhibited a complete protection against mortality. In PTZ model, flumazenil (10 mg/kg, i.p.), an antagonist of benzodiazepine (BZD) site in the GABAA-BZD receptor complex, inhibited the prolongation of seizure latency, but did not show any effect on the duration of myoclonic seizures. Also, pretreatment with naloxone (0.1 and 03 mg/kg, i.p.) inhibited the prolongation of myoclonic seizure latency and antagonized the reduction of myoclonic seizure duration induced by thymoquinone (40 and 80 mg/kg) in the PTZ model. Moreover, thymoquinone (40 and 80 mg/kg) did not have any hypnosis effect in the pentobarbital-induced hypnosis, but impaired the motor coordination and reduced the locomotor activity. These results indicate that thymoquinone may have anticonvulsant activity in the petit mal epilepsy probably through an opioid receptor-mediated increase in GABAergic tone.

TOLERANCE TO PENTYLENTETRAZOL-INDUCED CONVULSIONS AND PROTECTION OF CEREBROVASCULAR INTEGRITY BY CHRONIC NICOTINE

The authors' previous studies have shown that in nicotine-induced seizures sensitivity was decreased and blood-brain barrier (BBB) disruption was prevented as a consequence of nicotine pretreatment. This study aimed to investigate the possible protective actions of nicotine on cerebrovascular permeability and seizures induced by pentylentetrazol (PTZ) injection. Cerebrovascular effects of nicotine were evaluated by measuring the permeability changes of BBB using Evans-Blue (EB) dye and specific gravity (SG), which indicates brain water and protein content. The experiments were carried out on Wistar rats. Animals were randomly divided into two groups. Convulsions were induced by injection of PTZ (80 mg/kg i.v.) in rats either pretreated with nicotine daily with a low dose of 0.8 mg/kg day for 21 days or injected with a single dose of 6 mg/kg mecamylamine. The same procedures were followed in control rats with the exception that they were injected only with saline. PTZ injection caused tonic-clonic convulsions and increased the EB dye leakage and specific gravity values in saline-injected control rat brains. Daily injection of nicotine lessened the intensity of seizures. These were accompanied by marked decreases in both the leakage of EB and brain water content. Acute administration of a nAChR antagonist mecamylamine significantly increased seizure latency and decreased the duration of seizures. Thereby, mecamylamine reduced the EB leakage and water content in most brain regions. These results indicate that development of tolerance to PTZ convulsions can be produced by chronic nicotine administration in rats. The mechanism for this effect currently needs clarification. Moreover, the data also suggest that cholinergic activity may account for occurrence of PTZ-induced convulsions.

Oxygen seizure latency and peroxynitrite formation in mice lacking neuronal or endothelial nitric oxide synthases

Nitric oxide (NO) from endothelial or neuronal NO synthases (eNOS or nNOS) may contribute both to the cerebrovascular responses to oxygen and potentially to the peroxynitrite-mediated toxic effects of hyperbaric oxygen (HBO 2) on the central nervous system (CNS O 2 toxicity). In mice lacking eNOS or nNOS (−/−), regional cerebral blood flow (rCBF) and 3-nitrotyrosine (3-NT), a biochemical marker for peroxynitrite (ONOO −) formation, were measured in the brain during HBO 2 exposure. These variables were then correlated with EEG spiking activity related to CNS O 2 toxicity. In wild-type (WT) mice, HBO 2 exposure transiently reduced rCBF, but by 60 min rCBF was restored to baseline levels and above, followed by EEG spikes. Mice lacking nNOS also showed initial depression of rCBF followed by hyperemia but the delay in the onset of EEG discharges was greater. In contrast, in eNOS-deficient mice rCBF did not decrease and hyperemia was less pronounced during HBO 2. EEG spike latency was longer in eNOS −/− compared to WT or nNOS −/− mice. 3-NT gradually increased in all strains during HBO 2 but accumulation was slower in nNOS −/− mice, consistent with less ONOO − production. These results indicate that NOS-deficient mice have different cerebrovascular responses and tolerance to HBO 2 depending on which enzyme isoform is affected. The data suggest a key role for eNOS-dependent NO production in cerebral vasoconstriction and in the development of hyperoxic hyperemia preceding O 2 seizures, whereas neuronal NO may mediate toxic effects of HBO 2 mainly by its reaction with superoxide to generate the stronger oxidant, peroxynitrite.

Differential effects of fluoxetine enantiomers in mammalian neural and cardiac tissues

Racemic fluoxetine is a widely used SSRI antidepressant compound having also anticonvulsant effect. In addition, it was shown that it blocked several types of voltage gated ion channels including neural and cardiac calcium channels. In the present study the effects of enantiomers of fluoxetine (R(-)-fluoxetine and S(+)-fluoxetine) were compared on neuronal and cardiac voltage-gated Ca2+ channels using the whole cell configuration of patch clamp techniques, and the anticonvulsant action of these enantiomers was also evaluated in a mouse epilepsy model. In isolated pyramidal neurons of the dorsal cochlear nucleus of the rat the effect of fluoxetine (S(+), R(-) and racemic) was studied on the Ca2+ channels by measuring peak Ba2+ current during ramp depolarizations. All forms of fluoxetine reduced the Ba2+ current of the pyramidal cells in a concentration-dependent manner, with a Kd value of 22.3+/-3.6 microM for racemic fluoxetine. This value of Kd was higher by one order of magnitude than found in cardiac myocytes with fluoxetine enantiomers (2.4+/-0.1 and 2.8+/-0.2 microM). Difference between the effects of the two enantiomers on neuronal Ba2+ current was observed only at 5 microM concentration: R(-)-fluoxetine inhibited 28+/-3% of the peak current, while S(+)-fluoxetine reduced the current by 18+/-2% (n=13, P<0.05). In voltage clamped canine ventricular cardiomyocytes both enantiomers of fluoxetine caused a reversible concentration-dependent block of the peak Ca2+ current measured at 0 mV. Significant differences between the two enantiomers in this blocking effect was observed at low concentrations only: S(+)-fluoxetine caused a higher degree of block than R(-)-fluoxetine (56.3+/-2.2% versus 49.1+/-2.2% and 95.5+/-0.9% versus 84.5+/-3.1% block with 3 and 10 microM S(+) and R(-)-fluoxetine, respectively, P<0.05, n=5). Studied in current clamp mode, micromolar concentrations of fluoxetine shortened action potential duration of isolated ventricular cells, while higher concentrations also suppressed maximum velocity of depolarization and action potential amplitude. This shortening effect was significantly greater in the case of S(+) than R(-)-fluoxetine at 1 and 3 microM concentrations, whereas no differences in their effects on depolarization were observed. In pentylenetetrazole-induced mouse epilepsy model fluoxetine pretreatment significantly increased the 60 min survival rate, survival duration and seizure latency. These effects were more pronounced with the R(-) than the S(+) enantiomer. The results indicate that fluoxetine exerts much stronger suppressive effect on cardiac than neuronal calcium channels. At micromolar concentrations (between 1 and 10 microM) R(-)-fluoxetine is more effective than the S(+) enantiomer on neuronal, while less effective on cardiac calcium channels. The stronger anticonvulsant effect of the R(-) enantiomer may, at least partially, be explained by these differences. Used as an antidepressant or anticonvulsant drug, less severe cardiac side-effects are anticipated with the R(-) enantiomer.

Cessation of repeated administration of MK-801 changes the anticonvulsant effect against flurothyl-induced seizure in mice

The effects of acute and repeated administration of MK-801 on flurothyl (FE)-induced seizure were investigated in mice. In the acute effect of MK-801 (0.01–0.1 mg/kg ip) in naive and FE-kindled mice, there were no changes on the latencies of clonic seizures. However, MK-801 dose-dependently inhibited both latencies and incidence of tonic seizures in mice and suppressed the grade of seizure severity in FE-kindled mice. Repeated administration of MK-801 at doses of 0.01 and 0.1 mg/kg 2 h prior to each exposure to FE for 8 days did not show any effects on the latencies of clonic seizure. However, seizure severity was significantly exacerbated in the 0.1 mg/kg treated group when mice were reexposed to FE without MK-801 1 week after the last administration. A week after the repeated administration of MK-801 at a dose of 0.1 mg/kg for 8 days without exposure to FE, mice were exposed to FE 2 h after readministration of MK-801 until tonic seizure occurred. The latencies of clonic seizures were almost the same in the acute experiment in naive controls. The latency of tonic seizure was significantly delayed compared to the acute experiment with MK-801 at a dose of 0.1 mg/kg. These findings suggested that MK-801 possessed an anticonvulsant action against FE-induced tonic seizure. However, the efficacy of this acute effect of MK-801 was impaired at 1 week of withdrawal after repeated administrations. This may be related in part to the changes in sensitivity to NMDA receptors.

Effects of valproate, phenytoin, and zonisamide on clonic and tonic seizures induced by acute and repeated exposure of mice to flurothyl

The effects of valproate (VPA), zonisamide (ZNS), and phenytoin (PHT) on flurothyl (FE)-induced generalized seizure were investigated in mice. In the FE kindling model, eight daily FE-induced generalized clonic seizures followed by a 28-day stimulation-free interval converted the type of seizure expressed in response to FE from clonic to tonic. In an acute FE trial experiment, the latencies of clonic and tonic seizures were prolonged significantly and dose-dependently by the administration of VPA. ZNS and PHT did not show any effect on the latencies of tonic seizure. When the same three drugs were administered to mice daily for 8 days prior to the FE trial, changes in the seizure phenotypes from clonic to tonic seizure were significantly inhibited by VPA and ZNS, but not by PHT. These results suggest that VPA and ZNS possess significant antiepileptogenic properties. PHT apparently does not share this property to the same degree in the present FE-induced model.

Animal Model of Cortical Dysplasia for Screening Candidate AEDs

Seizure activity associated with cortical dysplasia (CD) is often resistant to standard pharmacologic treatments. Although several animal models exhibit CD, virtually nothing is known about antiepileptic drug (AED) responses in these animals. Here we used rats exposed to methylazoxymethanol acetate (MAM) in utero, an animal model featuring nodular heterotopia, to investigate the effects of AEDs in the dysplastic brain. 4-Aminopyridine (AP; 100 μM), a K+ channel blocker, was used to induce interictal epileptiform bursting in acute hippocampal slices from MAM-exposed and age-matched vehicle-injected control animals. Extracellular field recordings were used to monitor seizure activity in vitro. Five commonly used AEDs were tested: Phenobarbital (PB), 25–400 μM; carbamazepine (CBZ), 25–200 μM; valproate (VPA), 0.19–4 mM; ethosuximide (ESM), 0.5–8 mM; and lamotrigine (LTG), 49–390 μM. 4-AP-induced bursting occurred with shorter latencies in slices from MAM-exposed rats in comparison with slices from controls, confirming the intrinsic hyperexcitability of dysplastic tissue. Each AED tested demonstrated significant burst suppression in control slices, but interictal epileptiform bursting in MAM-exposed slices was resistant to these treatments. Even at the highest concentrations, VPA, ESM, and LTG had no effect on burst amplitude in slices from MAM-exposed rats. Pharmacoresistance was further tested by measuring seizure latencies in awake, freely moving rats after kainate administration (15 mg/kg, i.p.) with and without pretreatment with VPA (400 mg/kg, i.p.). Pretreatment with VPA prolonged seizure latency in control rats, but had no effect in MAM-exposed animals. These results suggest MAM-exposed rats exhibit a dramatically reduced sensitivity to commonly prescribed AEDs.

Animal Model of Cortical Dysplasia for Screening Candidate AEDs.

Effects of Antiepileptic Drugs on Induced Epileptiform Activity in a Rat Model of Dysplasia Smyth MD, Barbaro NM, Baraban SC Epilepsy Res 2002;50:251–264 Seizure activity associated with cortical dysplasia (CD) is often resistant to standard pharmacologic treatments. Although several animal models exhibit CD, virtually nothing is known about antiepileptic drug (AED) responses in these animals. Here we used rats exposed to methylazoxymethanol acetate (MAM) in utero, an animal model featuring nodular heterotopia, to investigate the effects of AEDs in the dysplastic brain. 4-Aminopyridine (AP; 100 μM), a K+ channel blocker, was used to induce interictal epileptiform bursting in acute hippocampal slices from MAM-exposed and age-matched vehicle-injected control animals. Extracellular field recordings were used to monitor seizure activity in vitro. Five commonly used AEDs were tested: Phenobarbital (PB), 25–400 μM; carbamazepine (CBZ), 25–200 μM; valproate (VPA), 0.19–4 mM; ethosuximide (ESM), 0.5–8 mM; and lamotrigine (LTG), 49–390 μM. 4-AP-induced bursting occurred with shorter latencies in slices from MAM-exposed rats in comparison with slices from controls, confirming the intrinsic hyperexcitability of dysplastic tissue. Each AED tested demonstrated significant burst suppression in control slices, but interictal epileptiform bursting in MAM-exposed slices was resistant to these treatments. Even at the highest concentrations, VPA, ESM, and LTG had no effect on burst amplitude in slices from MAM-exposed rats. Pharmacoresistance was further tested by measuring seizure latencies in awake, freely moving rats after kainate administration (15 mg/kg, i.p.) with and without pretreatment with VPA (400 mg/kg, i.p.). Pretreatment with VPA prolonged seizure latency in control rats, but had no effect in MAM-exposed animals. These results suggest MAM-exposed rats exhibit a dramatically reduced sensitivity to commonly prescribed AEDs.

Reduced sodium channel density, altered voltage dependence of inactivation, and increased susceptibility to seizures in mice lacking sodium channel beta 2-subunits.

Sodium channel beta-subunits modulate channel gating, assembly, and cell surface expression in heterologous cell systems. We generated beta2(-/-) mice to investigate the role of beta2 in control of sodium channel density, localization, and function in neurons in vivo. Measurements of [(3)H]saxitoxin (STX) binding showed a significant reduction in the level of plasma membrane sodium channels in beta2(-/-) neurons. The loss of beta2 resulted in negative shifts in the voltage dependence of inactivation as well as significant decreases in sodium current density in acutely dissociated hippocampal neurons. The integral of the compound action potential in optic nerve was significantly reduced, and the threshold for action potential generation was increased, indicating a reduction in the level of functional plasma membrane sodium channels. In contrast, the conduction velocity, the number and size of axons in the optic nerve, and the specific localization of Na(v)1.6 channels in the nodes of Ranvier were unchanged. beta2(-/-) mice displayed increased susceptibility to seizures, as indicated by reduced latency and threshold for pilocarpine-induced seizures, but seemed normal in other neurological tests. Our observations show that beta2-subunits play an important role in the regulation of sodium channel density and function in neurons in vivo and are required for normal action potential generation and control of excitability.

Non-competitive NMDA receptor antagonists moderate seizure-induced c- fos expression in the rat cerebral cortex

We examined the effects of non-competitive NMDA glutamate receptor antagonists on seizures elicited by 4-aminopyridine (4-AP), and in particular, on the expression of the transcription factor c- fos induced by these seizures. Induction of c- fos mRNA due to 4-AP-elicited seizures was ascertained by reverse transcription polymerase chain reaction in samples of the neocortex. Adult rats were pretreated with the NMDA receptor antagonists amantadine (40 mg/kg), ketamine (3 mg/kg), dizocilpine (MK-801; 1 mg/kg) or dextrometorphan (40 mg/kg); 4-AP (5 mg/kg) was then injected i.p. Controls were treated with either antagonist only or with 4-AP only. Pretreatment with the antagonists (with the exception of amantadine) increased the latency of behavioural seizures, but not all of the antagonists caused symptomatic seizure protection. In the brains which were processed for Fos immunohistochemistry, quantitative evaluation of immunostained cells was performed in the neocortex and hippocampus. Treatment with either antagonist did not induce by itself c- fos expression, with the exception of amantadine, which caused slight Fos induction in the neocortex. Pretreatment with all the antagonists resulted in decrease of seizure-induced Fos immunoreactivity with respect to non-pretreated animals. Decrease of immunostained cells was significant in the neocortex, in the granule cell layer and hilus of the dentate gyrus, in hippocampal areas CA1 and CA2. MK-801, ketamine and dextrometorphan decreased significantly Fos immunoreactivity also in area CA3. The decrease of Fos immunostaining was not directly correlated with a suppression of behavioural seizures. The results support an important role of NMDA receptors in c- fos gene induction in acute 4-AP seizures.

Arginine vasopressin in the pathogenesis of febrile convulsion and temporal lobe epilepsy.

We aimed to investigate the possible convulsant action of arginine vasopressin (AVP) in both a febrile convulsion model in rat pups and a temporal lobe epilepsy model in adult rats and to define the receptor type which mediates this effect. In rat pups, 125 ng V2 receptor antagonist significantly prevented hyperthermic seizures, but did not affect seizure latency. In adult rats, the only effective dose and agent was 125 ng V2 receptor antagonist, which prevented pilocarpine-induced status epilepticus, extended the status epilepticus latency and improved the 24 h survival rate. These data suggest that AVP has a convulsant activity in febrile convulsions and also in seizures independent of fever, and this effect is mediated by V2 receptors.

Effects of antiepileptic drugs on induced epileptiform activity in a rat model of dysplasia

Seizure activity associated with cortical dysplasia (CD) is often resistant to standard pharmacologic treatments. Although several animal models exhibit CD, virtually nothing is known about antiepileptic drug (AED) responses in these animals. Here we have used rats exposed to methylazoxymethanol acetate (MAM) in utero, an animal model featuring nodular heterotopia, to investigate the effects of AEDs in the dysplastic brain. 4-aminopyridine (100 μM), a K + channel blocker, was used to induce interictal epileptiform bursting in acute hippocampal slices from MAM-exposed and age-matched vehicle-injected control animals. Extracellular field recordings were used to monitor seizure activity in vitro. Five commonly used AEDs were tested: phenobarbital, 25–400 μM; carbamazepine, 25–200 μM; valproate (VPA), 0.19–4 mM; ethosuximide (ESM), 0.5–8 mM; and lamotrigine (LTG), 49–390 μM. 4-AP-induced bursting occurred with shorter latencies in slices from MAM-exposed rats in comparison with slices from controls, confirming the intrinsic hyperexcitability of dysplastic tissue. Each AED tested demonstrated significant burst suppression in control slices, but interictal epileptiform bursting in MAM-exposed slices was resistant to these treatments. Even at the highest concentrations, VPA, ESM and LTG had no effect on burst amplitude in slices from MAM-exposed rats. Pharmaco-resistance was further tested by measuring seizure latencies in awake, freely-moving rats after kainate administration (15 mg/kg, i.p.) with and without pre-treatment with VPA (400 mg/kg i.p.). Pre-treatment with VPA prolonged seizure latency in control rats, but had no effect in MAM-exposed animals. These results suggest MAM-exposed rats exhibit a dramatically reduced sensitivity to commonly prescribed AEDs.

Anticonvulsant activity of a nonpeptide galanin receptor agonist

Galanin is a neuropeptide with a wide variety of biological functions, including that of a strong endogenous anticonvulsant. No nonpeptide ligands, capable of activating galanin receptors, are available today. Based on known pharmacophores of galanin, a combinatorial library was designed, synthesized, and screened at the rat hippocampal galanin receptor. A low molecular weight galanin receptor agonist, 7-((9-fluorenylmethoxycarbonyl)cyclohexylalanyllysyl)amino-4-methylcoumarin (galnon) was found to displace (125)I-galanin with micromolar affinity at Bowes cellular and rat hippocampal membranes. Autoradiographic binding assay on rat spinal cord sections confirmed the ability of galnon to displace (125)I-galanin from its binding sites. Galnon inhibited adenylate cyclase activity, suggesting an agonist action at galanin receptors. When injected i.p. galnon reduced the severity and increased the latency of pentylenetetrazole-induced seizures in mice and reversed the proconvulsant effects of the galanin receptor antagonist M35, injected into a lateral ventricle. Intrahippocampal injection of galnon also shortened the duration of self-sustaining status epilepticus in rats, confirming its agonist properties in vivo. Pretreatment of rats with antisense peptide nucleic acid targeted to galanin receptor type 1 mRNA abolished the effect of galnon, suggesting mediation of its anticonvulsant properties through this receptor subtype. These findings introduce a systemically active nonpeptide galanin agonist anticonvulsant.