Sex and estrus cycle differences in the modulatory effects of morphine on seizure susceptibility in mice

PURPOSE: To evaluate the effects of sex and estrus cycle on biphasic anticonvulsant and proconvulsant modulation of seizure threshold by morphine. METHODS: The threshold for the clonic seizures (CST) induced by acute intravenous administration of gamma-aminobutyric acid (GABA)-antagonist pentylenetetrazole (PTZ) was assessed in male and female mice. Estrus cycle was assessed by vaginal smears. The effect of removing circulating sex hormones was assessed by gonadectomy. RESULTS: At baseline, diestrus females had a higher CST compared with males and estrus females. Morphine at lower doses (0.5-3 mg/kg) had a significant anticonvulsant effect in males and estrus females compared with that in vehicle-treated controls, whereas female mice in diestrus phase showed a relative subsensitivity to this effect. Morphine at higher doses (30 and 60 mg/kg) significantly decreased CST in males and diestrus females, with less relative effect in estrus mice. In both phases, morphine exerted stronger effects in males compared with females. Ovariectomy brought the baseline CST to the male level and resulted in significant expression of both phases of morphine effect but did not abolish the sex difference in responsiveness to morphine. CONCLUSIONS: The biphasic modulation of seizure threshold is subject to both constitutive sex differences in sensitivity to morphine and hormonal fluctuations during the estrus cycle.     

Administration of lithium and magnesium chloride inhibited tolerance to the anticonvulsant effect of morphine on pentylenetetrazole-induced seizures in mice

Although morphine has an anticonvulsant effect in several animal models of seizures, its potential clinical application in epilepsy may be hindered by its adverse effects like opioid tolerance. The present study evaluated the development of tolerance to the anticonvulsant effect of morphine in a model of clonic seizures induced with pentylenetetrazole (PTZ) in male Swiss mice. We also examined whether administration of either lithium chloride (LiCl) or magnesium chloride (MgCl(2)) was able to prevent the probable tolerance. Our data demonstrated that the anticonvulsant effect of a potent dose of morphine (1mg/kg) was abolished in chronic morphine-treated mice (mice administered the same dose of morphine intraperitoneally twice daily for 4 days). Four days of pretreatment with low and noneffective doses of MgCl(2) (2 and 5mg/kg) and LiCl (5mg/kg) inhibited the development of tolerance to the anticonvulsant effect of morphine (1mg/kg, ip). Moreover, a single acute injection of the aforementioned agents at the same doses reversed the expression of tolerance to the anticonvulsant effects of morphine (1mg/kg, ip). Chronic 17-day treatment with LiCl (600 mg/L in drinking water) also inhibited the development of tolerance to the anticonvulsant effects of 1mg/kg morphine. These results demonstrate that the anticonvulsant effect of morphine is subject to tolerance after repeated administration. Both development and expression of tolerance are inhibited by either LiCl or MgCl(2). As both LiCl and MgCl(2) can modulate the function of N-methyl-d-aspartate (NMDA) receptors, we discuss how NMDA receptor functioning might be involved in the effects of LiCl and MgCl(2) on the development of tolerance to the anticonvulsant effect of morphine.     

The role of alpha2-adrenoceptors in the modulatory effects of morphine on seizure susceptibility in mice

PURPOSE: To evaluate the effect of the alpha2-adrenoceptor agonist clonidine and the antagonist yohimbine on the dual modulation of seizure susceptibility induced by morphine and the anticonvulsant effect of acute stress in mice. METHODS: The thresholds for the clonic seizures induced after intravenous administration of pentylenetetrazole (PTZ) or bicuculline were assessed in mice weighing 23-30 g. Acute stress was induced by restraining mice for 2 h in a restrainer. RESULTS: Morphine at lower doses (0.5, 1, and 3 mg/kg) increased and, at higher doses (15, 30, and 75 mg/kg), decreased the seizure threshold. Pretreatment with clonidine (0.001-0.1 mg/kg) inhibited the anticonvulsant effect of morphine, while potentiating its proconvulsant effect. Conversely, yohimbine (0.5-2 mg/kg) potentiated the anticonvulsant effect of morphine but inhibited its proconvulsant effects. Acute stress induced an anticonvulsant effect that was reversible by naloxone (1 mg/kg) or clonidine (0.05-0.1 mg/kg) or a combination of their lower doses (0.3 and 0.01 mg/kg, respectively), while being potentiated by yohimbine (1 mg/kg). CONCLUSIONS: alpha2-Adrenoceptors play a dual role in the anticonvulsant effects of morphine. The activation of these receptors also can decrease the anticonvulsant effect of acute restraint stress in mice.     

Effect of sildenafil on the anticonvulsant action of classical and second‐generation antiepileptic drugs in maximal electroshock‐induced seizures in mice

Purpose: The goal of the present study was to evaluate the effects of sildenafil on the threshold for electrically induced seizures in mice. In addition, interactions between sildenafil and classical and second‐generation antiepileptic drugs (AEDs), that is, carbamazepine (CBZ), phenobarbital (PB), phenytoin (PHT), valproate (VPA), lamotrigine (LTG), topiramate (TPM), and oxcarbazepine (OXC) were evaluated. Methods: Two electroconvulsive tests were used: maximal electroshock seizure threshold (MEST) and maximal electroshock seizure (MES) tests in mice. Acute adverse effects of the studied combinations were investigated in the chimney test, step‐through passive avoidance task, and grip‐strength test. Total brain and free plasma concentrations of AEDs were also determined. Results: Sildenafil raised the threshold for electroconvulsions in a dose‐dependent manner. It also increased the anticonvulsant activity of CBZ, VPA, and TPM in the MES test, whereas the activity of the remaining AEDs was not significantly changed. Sildenafil increased total brain and free (protein unbound) plasma CBZ concentrations and total brain VPA concentration. Neither sildenafil nor its coadministration with the studied AEDs affected motor coordination and long‐term memory in mice. Interestingly, sildenafil dose‐dependently enhanced the skeletal muscle strength in mice, although combinations of sildenafil with AEDs were ineffective in this respect. Conclusions: Sildenafil significantly raised the threshold for electroconvulsions in mice without any impairment of motor performance and long‐term memory, but it enhanced muscle strength. Treatment of patients on CBZ or VPA with sildenafil may not be recommended due to pharmacokinetic interactions. Coadministration of sildenafil with other AEDs, especially with TPM, seems to be a reasonable choice.     

The anticonvulsant profile of rufinamide (CGP 33101) in rodent seizure models

Purpose: To evaluate the anticonvulsant profile and behavioral toxicity of rufinamide in animal seizure models compared to the established antiepileptic drugs (AEDs): phenytoin, phenobarbital, valproate, and ethosuximide, or vehicle.
Methods: In acute studies of anticonvulsant efficacy, the AEDs were administered via oral (CF1 mice and Sprague–Dawley rats) and intraperitoneal (CF1 mice) routes. The AEDs were assessed for their ability to inhibit seizures induced by maximal electroshock (MES) or subcutaneous pentylenetetrazol, and ability to block seizures induced by subcutaneous strychnine, bicuculline, or picrotoxin. Tolerance of oral rufinamide was assessed in rats following 5-day (versus single-dose) treatment with oral rufinamide using the dose equivalent necessary to achieve a 50% decrease in seizure frequency (ED₅₀). Metabolic tolerance was also evaluated using an in vitro liver microsomal assay.
Results: Oral rufinamide suppressed pentylenetetrazol-induced seizures in mice (ED₅₀ 45.8 mg/kg) but not rats, and was active against MES-induced tonic seizures in mice (ED₅₀ 23.9 mg/kg) and rats (ED₅₀ 6.1 mg/kg). Intraperitoneal rufinamide suppressed pentylenetetrazol-, bicuculline-, and picrotoxin-induced clonus in mice (ED₅₀ 54.0, 50.5, and 76.3 mg/kg, respectively). Rufinamide was partially effective in the mouse strychnine test. The behavioral toxicity of rufinamide was similar to or better than established AEDs tested in this study. In general, the protective index of rufinamide was greater than that of the other AEDs.
Conclusions: The efficacy and behavioral toxicity profiles in these animal models suggest that rufinamide may be effective in the treatment of generalized and partial seizures.     

Mouth breathing increases the pentylenetetrazole-induced seizure threshold in mice: a role for ATP-sensitive potassium channels

Nasal obstruction and consequent mouth breathing have been shown to change the acid–base balance, producing respiratory acidosis. Additionally, there exists a large body of evidence maintaining that acidosis affects the activity of ATP-sensitive potassium (K_ATP) channels, which play a crucial role in the function of the central nervous system (CNS), for example, in modulating seizure threshold. Thus, in the study described here, we examined whether mouth breathing, induced by surgical ligation of nostrils, could affect the seizure threshold induced by pentylenetetrazole in male NMRI mice. Using the selective K_ATP channel opener (diazoxide) and blocker (glibenclamide), we also evaluated the possible role of K_ATP channels in this process. Our data revealed that seizure threshold was increased 6 to 72 hours after nasal obstruction, reaching a peak 48 hours afterward, compared with either control or sham-operated mice (P < 0.01). There was a significant decrease in pH of arterial blood samples and increase in CO₂ partial pressure (PCO₂) during this time. Systemic injection of glibenclamide (1 and 2 mg/kg, ip, daily) significantly prevented the increase in seizure threshold in 48-hour bilaterally nasally obstructed mice, whereas it had no effect on seizure threshold in sham-operated mice. Systemic injection of diazoxide (25 mg/kg, ip, daily) had no effect on seizure threshold in all groups, whereas higher doses (50 and 100 mg/kg, ip, daily) significantly increased seizure threshold in both 48-hour-obstructed and sham-operated mice. The decrease in seizure threshold induced by glibenclamide (2 mg/kg, ip, daily) was prevented by diazoxide (25 mg/kg, ip, daily). These results demonstrate for the first time that mouth breathing, which could result in respiratory acidosis, increases seizure threshold in mice and K_ATP channels may play a role in this effect.     

Evaluation of interactions between cannabinoid compounds and diazepam in electroshock-induced seizure model in mice

Several studies have shown that cannabinoids have anticonvulsant properties that are mediated through activation of the cannabinoid CB1 receptors. In addition, endogenous cannabinoid compounds (endocannabinoids) regulate synaptic transmission and dampen seizure activity via activation of the same receptors. The aim of this study was to evaluate the possible interactions between antiepileptic effects of cannabinoid compounds and diazepam using electroshock-induced model of seizure in mice. Electroconvulsions were produced by means of an alternating current (ear-clip electrodes, fixed current intensity 35 mA, stimulus duration 0.2 s) and tonic hindlimb extension was taken as the endpoint. All experiments were performed on groups of ten mice and the number of animals who did not display seizure reported as percent protection. Intraperitoneal (i.p.) administration of diazepam (0.25-2 mg/kg) and CB1 receptor agonist WIN55212-2 (0.5-4 mg/kg) dose dependently produced an antiepileptic effect evaluated in terms of increased percentage of protection against electroshock-induced seizure. Logistic regression analysis indicated synergistic interactions in anticonvulsant action after co-administration of diazepam and WIN55212-2 in fixed-ratio combination of 3:1 (diazepam:WIN55212-2), while an additive effect was resulted after co-administration of 1:1 and 1:3 fixed-ratio combinations. Administration of various doses of the endocannabinoid reuptake inhibitor, AM404, did not produce any effect on electroshock-induced seizure. Moreover, co-administration of AM404 and diazepam did not produce significant interaction in antiepileptic properties of these compounds. Administration of the fatty acid amide hydrolase inhibitor, URB597, produced significant antiepileptic effect. Co-administration of URB597 and diazepam led to an antagonistic interaction in protection against shock-induced seizure. Co-administration of different doses of the cannabinoid CB1 receptor antagonist, AM251 did not alter the antiepileptic effect of diazepam in the electroshock-induced seizure test. These results demonstrate that endocannabinoid system participates in the modulation of seizure and combination of small doses of exogenous CB1 receptor agonists with diazepam may have effective consequences in seizure control. Furthermore, inhibiting the endocannabinoid degradation could be more efficacious in modulating seizure than preventing their uptake. This study also suggests that the effects of cannabinoids on epilepsy depend on the relative cannabinoid responsiveness of GABAergic and glutamatergic neurotransmission. While, the antiepileptic effects of cannabinoid compounds are likely by affecting excitatory glutamate neurotransmission, the antagonistic interaction between cannabinoid compounds and diazepam to protect seizure is due to the cannabinoid action on inhibitory GABAergic system.     

Electromagnetic waves of 900 MHz in acute pentylenetetrazole model in ontogenesis in mice

Abstract. The purpose of this study was to measure the effects of electromagnetic waves (EMW) at 900 MHz. EMW were produced by a signal generator and were administered to mice via an antenna. The frequency of the waves was tested by a spectrum analyser and a frequency-meter. The emitted power was 0.25 mW. A total of 117 mice (59 prepubertal and 58 adult) was used. Mice were exposed to EMW or sham radiation for 2 h and 20 h before an injection of pentylenetetrazole (PTZ). A statistically significant difference was found between the latency measurements within 20 h for prepubertal mice in stages 1 and 2 (p<0.05). The effects on prepubertal mice of long-term 900 MHz EMW in a PTZ model may be an indication of possible problems in developing brains.     

The effect of the 'classic' ketogenic diet on animal seizure models

Bough et al. have recently demonstrated anticonvulsant effects of the 'classic' ketogenic diet (KD) in the pentylenetetrazol infusion model in rats. Proconvulsant effects were seen, however, when the 'classic' diet was tested against maximal electroshock (MES) seizures. These differing results may reflect the fact that the two models involve different kinds of epileptogenic stimulus, or, as Bough et al. note that the two tests involve different stimulation paradigms. The pentylenetetrazol infusion paradigm is a threshold test, whereas the MES test employs a stimulus which is well above threshold. The present experiments were designed to test the effects of the 'classic' KD against seizures triggered in rats by both threshold and suprathreshold levels of electricity and pentylenetetrazol. The threshold tests employed were the pentylenetetrazol infusion test, and the threshold electroconvulsive shock (ECS) test. The subcutaneous pentylenetetrazol (scMET) test was also included, since it is sometimes considered to be a 'threshold' test. The suprathreshold tests employed were the maximal pentylenetetrazol test (MMT) and the maximal electroshock test (MES). The KD failed to suppress seizures in either of the tests involving suprathreshold stimulation (MMT and MES), although there was a significant increase in latency in the MMT test. Small but significant threshold elevations (15-20%) were seen, however, in both the pentylenetetrazol infusion test and the ECS threshold test. No seizure suppression was seen in the scMET test, which actually employs a suprasthreshold stimulus. These data indicate that the KD has significant anticonvulsant effects against both chemically and electrically triggered seizures, but that they consist of small elevations in threshold which will be seen only when threshold measures are used.     

舒必利消除小鼠对吗啡的条件性位置偏爱

目的对阿片类成瘾觅药行为的药物干预的可能性进行探索。方法将４０只雄性昆明种小鼠随机分为盐水组、吗啡组（９ｍｇ／ｋｇ，皮下注射）、舒必利（２０ｍｇ／ｋｇ，皮下注射）＋吗啡组、舒必利（３０ｍｇ／ｋｇ，皮下注射）＋吗啡组，每组１０只，观察多巴胺Ｄ２受体拮抗剂舒必利对吗啡所致小鼠条件性位置偏爱的效应。结果吗啡组在相应的箱体中停留的时间较对侧显著延长（Ｐ＜０．０１）。盐水组、舒必利２０ｍｇ／ｋｇ＋吗啡组、舒必利３０ｍｇ／ｋｇ＋吗啡组与吗啡组之间比较，显示吗啡组在其相应的箱体中停留的时间显著增加（Ｐ＜０．０５），而其它组无显著增加。结论提示预先给予舒必利能消除吗啡产生的条件性位置偏爱。     

Assessment of the convulsant liability of antidepressants using zebrafish and mouse seizure models

In the past, antidepressants have been thought to possess proconvulsant properties. This assumption remains controversial, however, because anticonvulsant effects have been attributed to certain antidepressants. To date, it remains unclear which antidepressants can be used for the treatment of patients with epilepsy with depression. The present study was designed to determine the anticonvulsant and/or proconvulsant effects of three antidepressants (citalopram, reboxetine, bupropion) against pilocarpine- and pentylenetetrazole-induced acute seizures in larval zebrafish and mice. In zebrafish, all antidepressants were anticonvulsant in the pentylenetetrazole model. In addition, citalopram was anticonvulsant in the zebrafish pilocarpine model, whereas reboxetine and bupropion were without significant effect. In mice all three antidepressants increased some thresholds for pentylenetetrazole-induced convulsive-like behaviors at varying doses, whereas thresholds for pilocarpine-induced convulsive-like behaviors were generally lowered, particularly at the highest doses tested. In general we conclude that the convulsant liability of antidepressants is model and concentration dependent.     

NG-nitro-L-arginine,a nitric oxide synthase inhibitor,and seizure susceptibility in four seizure models in mice

Summary Nitric oxide may be involved in seizure phenomena even though data often seem to be contradictory. This prompted us to study the influence of nitric oxide upon electrically and chemically induced seizures. The effects of nitric oxide synthase inhibitor, N^G-nitro-L-arginine (NNA), on pentylenetetrazol-, aminooxyacetic acid-, aminophylline-induced seizures or electroconvulsive shock were evaluated. NNA was applied at 1, 10 and 40 mg/kg 0.5 and 2.0 h before chemical seizures and at 1 and 40 mg/kg 0.5 and 2.0 h prior to electroconvulsions. The nitric oxide synthase inhibitor (up to 40 mg/kg) did not affect the susceptibility of mice to pentylenetetrazol, aminooxyacetic acid or electroconvulsions. However, NNA significantly enhanced the convulsive properties of aminophylline when applied at 40 mg/kg, 0.5 h before the test. The CD₅₀ value for aminophylline-induced clonus and tonus/mortality was decreased from 233 to 191 and from 242 to 212 mg/kg, respectively. However, this pretreatment also led to a significant increase in the plasma levels of theophylline. Our results suggest that differential effects of NNA on chemically-induced convulsions might in some cases be associated with a pharmacokinetic interaction.     

Profile of Anticonvulsant Activity and Minimal Toxicity of Methyl 4-[(p-Chlorophenyl)amino]-6-Methyl-2-Oxo-Cyclohex-3-En-l-Oate and Some Prototype Antiepileptic Drugs in Mice and Rats

The anticonvulsant and toxic properties of methyl 4-[(p-chlorophenyl)amino]-6-methyl-2-oxo-cyclohex-3-en-l-oate (ADD 196022), were compared with those of phenytoin (PHT), carbamazepine (CBZ), and valproate (VPA). These compounds were evaluated in mice and rats using well-standardized anticonvulsant testing procedures. Results indicate that ADD 196022 is a very potent anticonvulsant in the maximal electroshock seizure (MES) model. The compound was effective in nontoxic doses after intraperitoneal (i.p.) administration in mice and oral administration in rats. In mice, i.p. administration of ADD 196022 resulted in an ED₅₀ value of 26.2 mg/kg as compared with a value of 6.48 mg/kg for PHT in the same assay. ADD 196022 was more potent that PHT in the oral rat model, having an ED₅₀ value of 5.79 mg/kg as compared to 23.2 mg/kg for PHT. ADD 196022 was ineffective in nontoxic doses against all other seizure models evaluated and thus has a pharmacologic profile similar to that of PHT.     

Anticonvulsant properties of the novel nootropic agent nefiracetam in seizure models of mice and rats

PURPOSE: Nefiracetam (NEF) is a novel pyrrolidone-type nootropic agent, and it has been reported to possess various pharmacologic effects as well as cognition-enhancing effects. The present study focused on the anticonvulsant effect of NEF and its potential for antiepileptic therapy. METHODS: The anticonvulsant properties of NEF were investigated in experimental seizure models of mice and rats, compared with levetiracetam (LEV) and other standard antiepileptic drugs [AEDs; zonisamide (ZNS), phenytoin (PHT), carbamazepine (CBZ), valproic acid (VPA), diazepam (DZP), and ethosuximide (ESM)]. With reference to standard programs for evaluating potential AEDs, the study included the traditional maximal electroshock seizure and subcutaneous chemoconvulsant (pentylenetetrazole, bicuculline, picrotoxin, strychnine, or N-methyl-D-aspartate) seizure tests and two threshold models (the increasing-current electroshock seizure test and intravenous pentylenetetrazole seizure threshold test). Neurotoxic activities were examined with the rotarod test and traction test. RESULTS: NEF inhibited electroshock-induced seizures at nontoxic doses, whereas it had no effect on seizures chemically induced by pentylenetetrazole, bicuculline, picrotoxin, strychnine, or N-methyl-D-aspartate. The anticonvulsant spectrum of NEF paralleled that of ZNS, PHT, and CBZ. The anticonvulsant efficacy of NEF was comparable with that of ZNS and less potent than that of PHT, CBZ, and DZP. However, the safety margin of NEF was superior to that of ZNS, CBZ, VPA, and DZP. LEV showed only slight anticonvulsant effects in threshold models, and it was not effective in conventional screening models. CONCLUSIONS: These results suggest that NEF has distinct anticonvulsant spectrum and mechanisms from those of LEV. NEF is an orally active and safe AED, and it possesses a potential for antiepileptic therapy.     

Acetylcholinesterase changes in the central nervous system of mice during the development of morphine tolerance addiction and withdrawal

The distribution of acetylcholinesterase in the brain is studied during the development of morphine tolerance and through a period of withdrawal to elucidate the possible role of this enzyme in producing physical dependence in mice. Tolerance and physical dependence are produced in male albino mice by giving morphine sulphate subcutaneously at eight hourly intervals, in an increasing dose of 10 mg/kg body weight every 24 hours, for 15 days. The animals are considered addicted, when they received an otherwise lethal dose, 150 mg/kg three times a day. The enzyme shows a marked elevation in the overall distribution during the development of physical dependence. The habenular complex, nuclei anterioventralis and medialis thalami, nucleus caudatus putamen, amygdaloideus lateralis, septal nuclei, nucleus nervi hypoglossi, nucleus reticularis lateralis, tuberculum olfactorium, nucleus tractus diagonalis brocae, stratum pyramidale hippocampi, nucleus paraventricularis thalami, nucleus dorsalis nervi vagi, nucleus tractus spinalis nervi trigemini and nucleus reticularis thalami show an increase in the enzyme activity. This enhancement is not linear with the increase in dosage. Withdrawal is characterised by a sudden fall in the activity of acetylcholinesterase in the above mentioned areas of brain.     

Assessment of seizure susceptibility in pilocarpine epileptic and nonepileptic Wistar rats and of seizure reinduction with pentylenetetrazole and electroshock models

Purpose:   Pentylenetetrazole (PTZ) and maximal electroshock (MES) models are often used to induce seizures in nonepileptic control animals or naive animals. Despite being widely used to screen antiepileptic drugs (AEDs), both models have so far failed to detect potentially useful AEDs for treating drug-resistant epilepsies. Here we investigated whether the acute induction of MES and PTZ seizures in epileptic rats might yield a distinct screening profile for AEDs.
Methods:   Status epilepticus (SE) was induced in adult male Wistar rats by intraperitoneal pilocarpine injection (Pilo, 320 mg/kg, i.p.). One month later, controls or naive animals (Cont) that did not develop SE postpilocarpine (N-Epi) and pilocarpine-epileptic rats (Epi) received one of the following: phenobarbital (PB, 40 mg/kg), phenytoin (PHT, 50 mg/kg), or valproic acid (VPA, 400 mg/kg). Thirty min later the animals were challenged with either subcutaneous MES or PTZ (50 mg/kg, s.c.).
Results:   VPA, PB, and PHT were able to prevent MES in all groups tested (Cont, N-Epi, and Epi groups), whereas for the PTZ model, only the Cont group (naive animals) had seizure control with the same AEDs. In addition, Epi and N-Epi groups when challenged with PTZ exhibited a higher incidence of severe seizures (scores IV-IX) and SE (p   <   0.05, Fisher's exact test).
Conclusions:   Our findings suggest that the induction of acute seizures with PTZ, but not with MES, in animals pretreated with pilocarpine (regardless of SE induction) might constitute an effective and valuable method to screen AEDs and to study mechanisms involved in pharmacoresistant temporal lobe epilepsy (TLE).     

Effects of seizure severity and seizure repetition on postictal cardiac arrhythmia following maximal electroshock

Convulsive seizures triggered by maximal electroshock (MES) induce profound abnormalities in neural regulation of cardiac rhythm that are manifested by a period of marked cardiac arrhythmia in the immediate postictal state. It is not known whether seizure severity or seizure experience may influence the duration of cardiac arrhythmia in the postictal state. We varied the duration of MES administered to rats to vary seizure severity, as measured by the extensor to flexion (E/F) ratio. In separate experiments, rats were subjected to daily MES. Finally, we pretreated rats with ketamine prior to MES to block seizures hindlimb extension. In all animals, the R-R interval was plotted on the tachogram, and the duration of the arrhythmia was measured. Increases in MES duration increased significantly the E/F ratio and prolonged significantly the postictal cardiac arrhythmia. Repetition of MES caused a kindling effect with respect to seizure severity resulting in a significant increase of the E/F ratio and significant increases in the duration of postictal arrhythmia. Blocking of the hindlimb extension by ketamine abolished arrhythmia suggesting that the arrhythmia is not caused directly by MES. Severity of tonic convulsive seizures is a determinant of disordered cardiac autonomic regulation and directly influences the duration of cardiac arrhythmia during the immediate postictal state following MES. Seizure repetition also increases abnormalities of postictal neural regulation of the heart, but further studies are needed to determine whether this effect is independent of seizure severity increases.     

Influence of D-Cycloserine on the Anticonvulsant Activity of Phenytoin and Carbamazepine Against Electroconvulsions in Mice

Summary: Purpose: D-Cycloserine (DCS) is a high-efficacy partial agonist at the strychnine-insensitive glycine modulatory site within the N-methyl+-aspartate (NMDA)-receptor/ionophore complex. Previous studies demonstrated that DCS exhibits anticonvulsant activity in a variety of experimental epilepsy models. In this study, we determined the influence of DCS in subprotective doses on the anticonvulsant action of phenytoin (PHT) and carbamazepine (CBZ) in mice. Methods: Two electroconvulsive tests were used, i.e., determination of seizure threshold and maximal electro-shock seizures. Antiepileptic drug-induced motor and long-term memory deficits were quantified by using the chimney test and the passive-avoidance test, respectively. In addition, plasma levels of PHT and CBZ were measured by fluorescence polarization immunoassay to exclude any pharmacokinetic interactions. Results: DCS, when used alone in doses of 80 and 160 mg/kg, significantly increased the threshold for electro-convulsive seizures. DCS in a wide range of doses (1.25–40 mg/kg) was combined with either PHT or CBZ and tested in electroconvulsive tests. DCS, at doses of 2.5 and 10 mg/kg, was the most effective in potentiating the threshold-increasing action of PHT; higher doses of DCS (20 and 40 mg/kg) were required to achieve a similar effect of CBZ. In maximal electroshock-induced seizures, DCS (10 mg/kg) augmented the protective action of PHT, but was ineffective at a dose of 40 mg/kg with CBZ. DCS did not potentiate the neurotoxicity produced by PHT and CBZ in the chimney test. Both PHT and CBZ induced impairments of long-term memory; PHT-induced memory adverse effects were counteracted by DCS (10 mg/kg). There was no such effect on CBZ-induced memory impairment, and a worsening influence was observed. Any pharmacokinetic interactions were excluded by measuring total and free plasma levels of both antiepileptic drugs. Conclusion: Our results suggest that combining DCS with PHT and CBZ may be beneficial in treating epileptic seizures.