Convulsant Stimuli Research Articles

Seizure susceptibility to various convulsant stimuli in the BTBR mouse model of autism spectrum disorders.

Background: Autism spectrum disorders (ASDs) are one of the most severe chronic childhood disorders in terms of prevalence, morbidity, and impact on society. Interestingly, several systematic reviews and meta-analyses documented a bidirectional link between epilepsy and ASD, supporting the hypothesis that both disorders may have common neurobiological pathways. According to this hypothesis, an imbalance of the excitatory/inhibitory (E/I) ratio in several brain regions may represent a causal mechanism underpinning the co-occurrence of these neurological diseases. Methods: To investigate this bidirectional link, we first tested the seizure susceptibility to chemoconvulsants acting on GABAergic and glutamatergic systems in the BTBR mice, in which an imbalance between E/I has been previously demonstrated. Subsequently, we performed the PTZ kindling protocol to study the impact of seizures on autistic-like behavior and other neurological deficits in BTBR mice. Results: We found that BTBR mice have an increased susceptibility to seizures induced by chemoconvulsants impairing GABAA neurotransmission in comparison to C57BL/6J control mice, whereas no significant difference in seizure susceptibility was observed after administration of AMPA, NMDA, and Kainate. This data suggests that deficits in GABAergic neurotransmission can increase seizure susceptibility in this strain of mice. Interestingly, BTBR mice showed a longer latency in the development of kindling compared to control mice. Furthermore, PTZ-kindling did not influence autistic-like behavior in BTBR mice, whereas it was able to significantly increase anxiety and worsen cognitive performance in this strain of mice. Interestingly, C57BL/6J displayed reduced sociability after PTZ injections, supporting the hypothesis that a tight connection exists between ASD and epilepsy. Conclusion: BTBR mice can be considered a good model to study epilepsy and ASD contemporarily. However, future studies should shed light on the mechanisms underpinning the co-occurrence of these neurological disorders in the BTBR model.

P2X7-dependent constitutive Interleukin-1β release from pyramidal neurons of the normal mouse hippocampus: Evidence for a role in maintenance of the innate seizure threshold

Disruption of Interleukin-1β (IL-1β) signaling sensitized mice to convulsant stimuli, suggesting that this quintessential cytokine of the innate immune system contributes to maintenance of the innate seizure threshold (ST). However, much remains unknown about where and how IL-1β secretion occurs in the normal brain. This study examined the possibility that neurons of the hippocampus are key sources of constitutive IL-1β secretion and that the release from these cells is dependent on the purinoceptor, P2X7. It was posited that treatment with the P2X7 antagonist, JNJ-47965567 (JNJ), would cause IL-1β to accumulate in cells that produce it, and consequently, lower the ST. No IL-1β immunoreactivity was detected in any region of the hippocampal formation of mice treated with the JNJ vehicle, Sulfobutylether-β-cyclodextrin. In contrast, prominent immunoreactivity was discovered in the pyramidal neurons of the CA3 region 60 min after treatment with the P2X7 antagonist. Lower levels were found in CA1 neurons, and no immunoreactivity was detected in granule cells of the dentate gyrus. JNJ also increased IL-1β immunoreactivity in the cell bodies of hippocampal neurons in culture. Interestingly, JNJ potentiated bicuculline-induced Fos and COX-2 mRNA expression in the cultures and this was blocked by an NMDA receptor antagonist. Moreover, pentylenetetrazole-induced seizure severity and incidence of convulsions were increased in mice treated with JNJ and this resembled that observed with IL-1 signaling-deficient mice. Overall, the results from this study support the notion that constitutive P2X7-dependent IL-1β release from hippocampal pyramidal neurons contributes to maintenance of the ST in the normal brain, perhaps by modulating neuronal excitability. These findings may have implications for epilepsy, a brain disorder in which the ST is compromised.

Anticonvulsant activity of melatonin, but not melatonin receptor agonists Neu-P11 and Neu-P67, in mice

The anticonvulsant activity of melatonin (MLT) have been tested in several in vivo models and against different convulsive stimuli. Although MLT exerts high affinity towards melatonin receptors (MTs), the potential usefulness in the treatment of epilepsy is limited mainly due to its short half-life. Therefore, the purpose of the present study was to compare the anticonvulsant properties of novel MT agonists Neu-P11 and Neu-P67 with MLT in mice. The anticonvulsant activity of tested compounds was evaluated in pentylenetetrazole-(PTZ) and electrically-induced convulsions. The effect of studied compounds on motor coordination and skeletal muscular strength in mice was assessed in the chimney test and grip test, respectively. The locomotor activity after administration of the tested compounds was also evaluated. In the MEST and 6Hz tests, only MLT (50 and 100mg/kg, i.p.) significantly increased the seizure threshold. The i.p. administration of MLT (100mg/kg) and Neu-P67 (200mg/kg) resulted in a significantly elevated PTZ seizure threshold for forelimbs tonus. The compounds did not affect muscle strength. No alterations in motor coordination were noted. However, the locomotor activity was significantly decreased after administration of all tested compounds. Our study confirms the anticonvulsant potency of MLT and shows that novel synthetic MT agonists Neu-P11 and Neu-P67 have no effect on epileptic seizures in mice. Our data suggest that the activation of MT can be used in the treatment of seizures, but further pharmacological characterization is needed to understand the anticonvulsant activity of MLT and to design efficient MT-targeting antiepileptic drugs.

Cortical GABAergic excitation contributes to epileptic activities around human glioma.

Brain gliomas are highly epileptogenic. Excitatory glutamatergic mechanisms are involved in the generation of epileptic activities in the neocortex surrounding gliomas. However, chloride homeostasis is known to be perturbed in glioma cells. Thus, the contribution of γ-aminobutyric acidergic (GABAergic) mechanisms that depend on intracellular chloride merits closer study. We studied the occurrence, networks, cells, and signaling basis of epileptic activities in neocortical slices from the peritumoral surgical margin resected around human brain gliomas. Postoperative glioma tissue from 69% of patients spontaneously generated interictal-like discharges, synchronized, with a high-frequency oscillation signature, in superficial layers of neocortex around areas of glioma infiltration. Interictal-like events depended both on glutamatergic AMPA receptor-mediated transmission and on depolarizing GABAergic signaling. GABA released by interneurons depolarized 65% of pyramidal cells, in which chloride homeostasis was perturbed because of changes in expression of neuronal chloride cotransporters: KCC2 (K-Cl cotransporter 2) was reduced by 42% and expression of NKCC1 (Na-K-2Cl cotransporter 1) increased by 144%. Ictal-like activities were initiated by convulsant stimuli exclusively in these epileptogenic areas. This study shows that epileptic activities are sustained by excitatory effects of GABA in human peritumoral neocortex, as reported in temporal lobe epilepsies, suggesting that both glutamate and GABA signaling and cellular chloride regulation processes, all also involved in oncogenesis as already shown, induce an imbalance between synaptic excitation and inhibition underlying epileptic discharges in glioma patients. Thus, the control of chloride in neurons and glioma cells may provide a therapeutic target for patients with epileptogenic gliomas.

Neurodegenerative Changes in Rat Hippocampal Fields during the Development of Pentylenetetrazole Kindling

Neuron degeneration and death at the focus of hyper-excitation are among the commonest morphological conse-quences of chronic convulsive activity, both clinically andin experimental studies. Chronic convulsive activity is mod-eled using the phenomenon of kindling, whereby an initial-ly normal neural network, influenced by repeated sub-threshold convulsive stimuli, undergoes reorganization suchthat it acquires increased convulsive readiness. One of themost frequently used convulsants in developing kindling isthe GABA

The Auxiliary Subunit KChIP2 Is an Essential Regulator of Homeostatic Excitability

The necessity for, or redundancy of, distinctive KChIP proteins is not known. Deletion of KChIP2 leads to increased susceptibility to epilepsy and to a reduction in IA and increased excitability in pyramidal hippocampal neurons. KChIP2 is essential for homeostasis in hippocampal neurons. Mutations in K(A) channel auxiliary subunits may be loci for epilepsy. The somatodendritic IA (A-type) K(+) current underlies neuronal excitability, and loss of IA has been associated with the development of epilepsy. Whether any one of the four auxiliary potassium channel interacting proteins (KChIPs), KChIP1-KChIP4, in specific neuronal populations is critical for IA is not known. Here we show that KChIP2, which is abundantly expressed in hippocampal pyramidal cells, is essential for IA regulation in hippocampal neurons and that deletion of Kchip2 affects susceptibility to limbic seizures. The specific effects of Kchip2 deletion on IA recorded from isolated hippocampal pyramidal neurons were a reduction in amplitude and shift in the V½ for steady-state inactivation to hyperpolarized potentials when compared with WT neurons. Consistent with the relative loss of IA, hippocampal neurons from Kchip2(-/-) mice showed increased excitability. WT cultured neurons fired only occasional single action potentials, but the average spontaneous firing rate (spikes/s) was almost 10-fold greater in Kchip2(-/-) neurons. In slice preparations, spontaneous firing was detected in CA1 pyramidal neurons from Kchip2(-/-) mice but not from WT. Additionally, when seizures were induced by kindling, the number of stimulations required to evoke an initial class 4 or 5 seizure was decreased, and the average duration of electrographic seizures was longer in Kchip2(-/-) mice compared with WT controls. Together, these data demonstrate that the KChIP2 is essential for physiologic IA modulation and homeostatic stability and that there is a lack of functional redundancy among the different KChIPs in hippocampal neurons.

Molecular mechanisms of drug resistance in status epilepticus

Molecular mechanisms of drug resistance in status epilepticus

Effects of withdrawal from long-term diphenylhydantoin treatment on audiogenic and maximal electroshock-induced seizures in rats.

Rats withdrawal from long-term diphenylhydantoin treatment (DPH) were tested for their sensibility to convulsant stimuli. Animals were more sensitive to convulsions elicited by maximal electroshock and sound, respectively, at 48 and 72 h after drug removal. These results suggest that long-term DPH treatment might develop a central nervous system supersensitivity state.

Cardiovascular protective effect of melatonin in sudden unexpected death in epilepsy: A hypothesis

Epilepsy is the most common neurological disorder, approximately 1% of the population worldwide have epilepsy. Moreover, sudden unexpected death in epilepsy (SUDEP) is the most important direct epilepsy-related cause of death. Information concerning risk factors for SUDEP is conflicting, but potential risk factors include: age, early onset of epilepsy, duration of epilepsy, uncontrolled seizures, seizure frequency, AED number and winter temperatures. Additionally, the cause of SUDEP is still unknown; however, the most commonly suggested mechanisms are cardiac abnormalities during and between seizures. Furthermore, the evidence from the last 10 years suggests that melatonin has an important role in the epileptogenesis process and influences the cardiovascular system as well. The positive effect of melatonin has been demonstrated against different convulsive stimuli in several rodents, including seizures induced by pentylenetetrazole kainate, glutamate, maximal electrical shock and electrically kindled stimulation of amygdala. Clinical studies have also demonstrated a positive role of melatonin on the seizure frequency in children and reduced spiking activity and seizure frequency in patients with intractable epilepsy. In the rat hearts, studies in vivo and in vitro using pharmacological concentrations of melatonin confirmed an anti-arrhythmic effect of this hormone and studies in humans have been shown that chronic heart disease patients have significantly lower melatonin levels in their blood stream than do normal individuals. Thus, caution should be taken in generalization of these findings to epileptic population. Moreover, it is important to note that when dealing with intractable epilepsy that do not respond to any conventional treatment, the additional of melatonin may be evaluated. Taken together, in this paper we suggested a possible relationship between cardiac abnormalities, melatonin and SUDEP.

Central Properties and Chemical Composition of Ocimum basilicum. Essential Oil

Ocimum basilicum. L. (Lamiaceae) is an Egyptian plant used as a folkloric remedy in Egyptian traditional medicine. In the current study, the aerial part of this plant was used, and its essential oil was obtained by hydrodistillation. The essential oil of Ocimum basilicum. (OB) was screened for its composition and some CNS activities (viz., sedative, hypnotic, anticonvulsant, local anesthetic). When tested in mice, OB essential oil had no effect on motor activity up to a dose of 1.2 mL kg−1 at 90 min postadministration. However, higher doses produced motor impairment at all time intervals. Pentobarbitone sleeping time tested in mice was significantly increased by all doses of the essential oil higher than 0.2 mL kg−1. Intraperitoneal administration of OB essential oil significantly increased in a dose-dependent manner the latency of convulsion and percent of animals exhibiting clonic seizures. Likewise, it reduced lethality in response to different convulsive stimulus used in this study. The ED50 values of the essential oil of OB were 0.61 mL kg−1, 0.43 mL kg−1, and 1.27 mL kg−1, against convulsions induced by pentylenetetrazole, picrotoxin, and strychnine, respectively. A study of the local anesthetic activity of the OB essential oil by using a nerve block model employing in frog revealed that it had no local anesthetic effect. The LD50 of the essential oil was 3.64 mL kg−1 [correlation coefficient r = 0.961 and linear regression y. = 147 ln(x.) − 141.7]. Gas chromatography (GC)/mass spectrometry (MS) analysis of the essential oil revealed the presence of linalool (44.18%), 1,8-cineol (13.65%), eugenol (8.59%), methyl cinnamate (4.26%), iso. caryophyllene (3.10%), and α.-cubebene (4.97%) as the main components. The observed anticonvulsant and hypnotic activities in this study could be related to the presence of a variety of terpenes in the essential oil.

Seizure susceptibility to various convulsant stimuli of knockout interleukin-6 mice

In the present study, the susceptibility of knockout interleukin-6 (IL-6 −/−) mice to various convulsant stimuli has been evaluated and compared with other three related mice strains. Animals were treated with chemical convulsants impairing the γ-aminobutyric acid neurotransmission [pentylenetetrazole (PTZ), picrotoxin, bicuculline, methyl-6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM), methyl-β-carboline-3-carboxylate (β-CCM)], enhancing glutamatergic neurotransmission [ N-methyl- d-aspartate (NMDA), α-amino-3hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and kainic acid (KA)] or a K +channel blocker [4-aminopyridine (4-AP)]. The behavioural changes of such convulsant stimuli on IL-6 −/− were observed and compared with those observed in C57, IL-6 +/+ and DBA/2 mice. The occurrence of clonic and/or tonic seizures was scored and statistically analysed to observe possible differences on seizure susceptibility. The IL-6 −/− mice exhibited significantly higher seizure susceptibility to PTZ, β-CCM, DMCM, NMDA, AMPA and KA than did the other mice strains, with the exception of DBA/2 mice. This study demonstrates that IL-6 −/− mice possess an increased susceptibility to some convulsant stimuli. In particular, the major convulsant effects produced by NMDA, AMPA and KA suggest that the excitatory amino acid system is more active in the central nervous system (CNS) of IL-6 −/− mice. The present data suggest that IL-6 −/− mice might be a valid novel epileptic model for the study of pathophysiology and pharmacology of epileptic seizures.

NAALADase (GCP II) inhibition prevents cocaine-kindled seizures

The prediction that inhibition of NAALADase, an enzyme catalyzing the cleavage of glutamate from N-acetyl-aspartyl-glutamate, would produce antiepileptogenic effects against cocaine was tested. Cocaine kindled seizures were developed in male, Swiss–Webster mice by daily administration of 60 mg/kg cocaine for 5 days. The NAALADase inhibitor 2-(phosphonomethyl)pentanedioic acid (2-PMPA) produced dose-dependent protection (10–100 mg/kg) against both the development of seizure kindling and the occurrence of seizures during the kindling process without observable behavioral side-effects. It is not likely that 2-PMPA produced protection against cocaine kindling by altering the potency of the convulsant stimulus as daily administration of 2-PMPA did not alter the convulsant thresholds for cocaine. Lower daily doses of cocaine (40 mg/kg) did not increase the incidence of seizures but produced kindling, as evidenced by the increase in seizure susceptibility when mice were probed with a higher dose of cocaine. 2-PMPA was also effective in preventing the development of sensitization to this covert kindling process. In contrast to its efficacy against cocaine kindled seizures, 2-PMPA failed to attenuate the convulsions engendered by acute challenges with pentylenetetrazole, bicuculline, N-methyl- d-aspartate, maximal electroshock or cocaine. Similarly, acutely-administered 2-PMPA did not block cocaine seizures in fully-kindled mice. NAALADase inhibition thus provides a novel means of attenuating the development of cocaine seizure kindling.

Developmental lead exposure differentially alters the susceptibility to chemoconvulsants in rats

Sprague–Dawley rats were exposed to lead (Pb) acetate (0.2% w/v) in drinking water from postnatal day (PN) 1 through PN 25 followed by discontinuing Pb exposure for 25 days. The convulsion signs produced by the i.v. infusion of convulsants were observed at PN 25 and PN 50. Pb exposure significantly decreased pentylenetetrazol (PTZ)-, picrotoxin (PIC)-, and strychnine (STRY)-induced, but increased N-methyl- d-aspartate (NMDA) and 4-aminopyridine (4-AP)-induced convulsion thresholds at PN 25. After rehabilitation, the Pb-induced changes in PTZ-, NMDA- and 4-AP- induced convulsions persisted till PN 50. In contrast, the thresholds for PIC- and STRY-induced convulsions were reversed to an increase at PN 50. Blood Pb concentrations were 46.9±6.8 and 11.4±1.1 μg/dl at PN 25 and PN 50, respectively. The results demonstrate that developmental Pb exposure does not result in a global and persistent lowering of threshold in response to convulsive stimuli and the Pb-induced changes may be due to a selective modulation of inhibitory and excitatory neurotransmission depending on age and Pb concentration in blood.

TAG-1-Deficient Mice Have Marked Elevation of Adenosine A1 Receptors in the Hippocampus

TAG-1 is a neural recognition molecule in the immunoglobulin superfamily that is predominantly expressed in the developing brain. Several lines of evidence suggest that TAG-1 is involved in the outgrowth, guidance, and fasciculation of neurites. To directly assess the function of TAG-1 in vivo, we have generated mice with a deletion in the gene encoding TAG-1 using homologous recombination in embryonic stem cells. Gross morphological analysis of the cerebellum, the spinal cord, and the hippocampus appeared normal in TAG-1-deficient mice. However, TAG-1 (−/−) mice showed the upregulation of the adenosine A1 receptors determined by [3H]cyclopentyl-1,3-dipropylxanthine in the hippocampus, and their greater sensitivity to convulsant stimuli than that in TAG-1 (+/+) mice. We suspect that the subtle changes in neural plasticity induced by TAG-1 deficiency during development cause the selective vulnerability of specific brain regions and the epileptogenicity in TAG-1 (−/−) mice.

Norepinephrine-Deficient Mice Have Increased Susceptibility to Seizure-Inducing Stimuli

Several lines of evidence suggest that norepinephrine (NE) can modulate seizure activity. However, the experimental methods used in the past cannot exclude the possible role of other neurotransmitters coreleased with NE from noradrenergic terminals. We have assessed the seizure susceptibility of genetically engineered mice that lack NE. Seizure susceptibility was determined in the dopamine beta-hydroxylase null mutant (Dbh -/-) mouse using four different convulsant stimuli: 2,2,2-trifluroethyl ether (flurothyl), pentylenetetrazol (PTZ), kainic acid, and high-decibel sound. Dbh -/- mice demonstrated enhanced susceptibility (i.e., lower threshold) compared with littermate heterozygous (Dbh +/-) controls to flurothyl, PTZ, kainic acid, and audiogenic seizures and enhanced sensitivity (i.e., seizure severity and mortality) to flurothyl, PTZ, and kainic acid. c-Fos mRNA expression in the cortex, hippocampus (CA1 and CA3), and amygdala was increased in Dbh -/- mice in association with flurothyl-induced seizures. Enhanced seizure susceptibility to flurothyl and increased seizure-induced c-fos mRNA expression were reversed by pretreatment with L-threo-3, 4-dihydroxyphenylserine, which partially restores the NE content in Dbh -/- mice. These genetically engineered mice confirm unambiguously the potent effects of the noradrenergic system in modulating epileptogenicity and illustrate the unique opportunity offered by Dbh -/- mice for elucidating the pathways through which NE can regulate seizure activity.

Long-lasting c- fos and NGF mRNA expressions and loss of perikaryal parvalbumin immunoreactivity in the development of epileptogenesis after ethacrynic acid-induced seizure

A single cerebroventricular injection of ethacrynic acid (EA), a Cl −-ATPase inhibitor, induces generalized tonic–clonic convulsions in mice. To clarify whether such convulsive stimulus triggers a long-lasting rearrangement of the neural circuitry culminating in seizure susceptibility, we examined molecular, cellular and behavioral changes following the EA-induced seizure. The expression of immediate early gene c- fos mRNA as an index for cellular activation increased biphasically, with an early transient increase at 60 min and a late prolonged increase on the 10th to 14th day post-EA administration, most remarkably in the hippocampus and pyriform cortex. On the 14th day post-EA seizure, subconvulsive dose of kainic acid (5–17.5 mg/kg) caused severe (stage 5) seizure in 77% of the mice, with 70% mortality. In addition, the expression of nerve growth factor (NGF) also showed biphasic increases with close spatiotemporal correlation with c- fos expression. Moreover, the number of cell somata and the density of axon fibers of parvalbumin (PARV)-positive cells, a subpopulation of GABAergic interneurons, decreased in area dentata, CA1 and CA3 on the 7th and 14th day post-EA seizure. In area dentata and CA1, the density of glutamic acid decarboxylase (GAD)-positive cells also decreased on the 14th day. Thus, the transient EA-induced seizures appear to develop seizure susceptibility by causing damage of a subpopulation of inhibitory interneurons along with increases in the expression of c- fos and NGF in limbic structures.

Neuroactive steroids: potential therapeutic use in neurological and psychiatric disorders.

Neuroactive steroids are a novel class of positive allosteric modulators of the GABAA receptor. Although neuroactive steroids are endogenous neuronal modulators, synthetic entities with improved oral bioavailability have recently been developed. These compounds demonstrate efficacy as anticonvulsants against a range of convulsant stimuli and demonstrate anti-epileptogenic activity in a kindling model of epilepsy. Efficacy has also been reported in preclinical models of anxiety, insomnia, migraine and drug dependence. Clinical evidence to date is generally supportive of these findings and indicates that neuroactive steroids are generally well tolerated. Taken as a whole, current data suggest that neuroactive steroids could have a future role in clinical practice. In this article, Maciej Gasior, Richard Carter and Jeffrey Witkin review preclinical and clinical evidence that forms the basis for predicting the potential therapeutic application of neuroactive steroids.

Nonobligate Role of Early or Sustained Expression of Immediate-Early Gene Proteins c-Fos, c-Jun, and Zif/268 in Hippocampal Mossy Fiber Sprouting

Axon sprouting in dentate granule cells is an important model of structural plasticity in the hippocampus. Although the process can be triggered by deafferentation, intense activation of glutamate receptors, and other convulsant stimuli, the specific molecular steps required to initiate and sustain mossy fiber (MF) reorganization are unknown. The cellular immediate early genes (IEGs) c-fos, c-jun, and zif/268 are major candidates for the initial steps of this plasticity, because they encode transcription factors that may trigger cascades of activity-dependent neuronal gene expression and are strongly induced in all experimental models of MF sprouting. The mutant mouse stargazer offers an important opportunity to test the specific role of IEGs, because it displays generalized nonconvulsive epilepsy and intense MF sprouting in the absence of regional cell injury. Here we report that stargazer mice show no detectable elevations in c-Fos, c-Jun, or Zif/268 immediate early gene proteins (IEGPs) before or during MF growth. Experimental results in stargazer, including (1) a strong IEGP response to kainate-induced convulsive seizures, (2) no IEGP response after prolongation of spike-wave synchronization, (3) no IEGP increase at the developmental onset of seizures or after prolonged seizure suppression, and (4) unaltered levels of the intracellular Ca2+-buffering proteins calbindin-D28k or parvalbumin, exclude the possibility that absence of an IEGP response in stargazer is either gene-linked or suppressed by known refractory mechanisms. These data demonstrate that increased levels of these IEGPs are not an obligatory step in MF-reactive sprouting and differentiate the early downstream molecular cascades of two major seizure types.

Repeated ethanol withdrawal experience selectively alters sensitivity to different chemoconvulsant drugs in mice.

Repeated ethanol withdrawal experience has been shown to result in exacerbated seizures associated with future withdrawal episodes. This sensitization of the withdrawal response has been postulated to represent a "kindling" phenomenon. The present study employed an established model of repeated ethanol withdrawals to examine the potential role of GABA(A), and NMDA and non-NMDA glutamate receptor systems in mediating enhanced seizure activity, as assessed by sensitivity to seizures induced by pentylenetetrazol (PTZ), NMDA, and kainic acid (KA) i.v. infusions, respectively. Adult C3H mice were chronically exposed to ethanol vapor in inhalation chambers. A multiple withdrawal (MW) group received four cycles of 16-h ethanol vapor exposure interrupted by 8-h periods of abstinence; a single withdrawal (SW) group was tested after a single 16-h bout of ethanol intoxication; and the third group was ethanol-naive, serving as controls (C). Results indicated that the MW group evidenced significantly lower PTZ and NMDA seizure thresholds compared to SW and C groups at 8 and 24 h post-withdrawal. In contrast, MW and SW groups exhibited reduced sensitivity (higher seizure threshold) to KA in comparison to controls, and this effect only emerged at 24 h post-withdrawal. Further, MW mice required significantly less additional PTZ or NMDA to induce more severe convulsions once initial signs of seizures were elicited. Conversely, latency and amount of KA required to transition from initial seizure signs to more severe end-stage convulsions was significantly greater for MW and SW groups compared to controls. Taken together, these results suggest that repeated ethanol withdrawal experience does not result in a global non-specific lowering of threshold to convulsive stimuli, but rather, selective changes in CNS mechanisms associated with neural excitability may underlie potentiated withdrawal responses. Thus, reduced GABA(A) receptor function and increased NMDA receptor activity may become exaggerated as a consequence of repeated withdrawal experience, while reduced sensitivity to KA induced seizures may represent a compensatory response to withdrawal-related CNS hyperexcitability.

Felbamate demonstrates low propensity for interaction with methylxanthines and Ca 2+ channel modulators against experimental seizures in mice

The aim of this study was to determine the interaction potential of the new antiepileptic drug felbamate (2-phenyl-1,3-propanediol dicarbamate) with three Ca 2+ channel blockers (nicardipine, nifedipine, and flunarizine), one Ca 2+ channel activator (Bay K 8644; 1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)-phenyl]-3-pyridine carboxylic acid), and two methylxanthines (caffeine and aminophylline (theophylline 2·ethylenediamine)) which are all known to markedly change protective effects of conventional antiepileptic drugs. To do so, the maximal electroshock seizure test in mice (an experimental model predicting drug efficacy in the treatment of human generalized tonic–clonic seizures) was employed to (1) quantify changes in the protective efficacy and potency of felbamate produced by adjunct drugs and (2) assess the ability of aminophylline and caffeine to affect protective efficacy afforded by a submaximal protective dose of felbamate against maximal electroshock-induced seizures. Doses of adjunct drugs were selected based on their effects on the threshold for electroconvulsions and on appropriate literature. Nicardipine (10–30 mg/kg), nifedipine (5–20 mg/kg), flunarizine (2.5–10 mg/kg), Bay K 8644 (2.5–5 mg/kg), and aminophylline (50–75 mg/kg) did not change the protective efficacy and potency of felbamate against maximal electroshock-induced tonic convulsions. Aminophylline in the dose of 100 mg/kg, however, diminished the protective potency of felbamate as evidenced by a statistically significant increase in the protective ED 50 value of felbamate (a dose, in mg/kg, predicted to protect 50% of mice against convulsive stimulus) from 79.6 to 118 mg/kg; P<0.05). Aminophylline and caffeine only at high doses (100 and 161.7 mg/kg, respectively) significantly diminished the protective efficacy of felbamate (110 mg/kg) from 96% to 27% and 40% ( P<0.05), respectively. In conclusion, felbamate shows low interaction potential with Ca 2+ channel modulators and methylxanthines. Such low interaction potential clearly differentiates felbamate from conventional antiepileptic drugs where protective effects are readily altered by the compounds tested in the present study.