Excitatory amino acid antagonists and pentylenetetrazol-induced seizures during ontogenesis. I. The effects of 2-amino-7-phosphonoheptanoate

Vortioxetine increases absence-like seizures in WAG/Rij rats but decreases penicillin- and pentylenetetrazole-induced seizures in Wistar rats

AIM

Depression is the major psychiatric disorder in patients with epilepsy. Vortioxetine is a novel antidepressant drug for the treatment of major depressive disorders. In the present study, effects of vortioxetine were evaluated in different experimental epilepsy models of rats.

MATERIALS AND METHODS

Fifty-six adult male Wistar rats and 28 WAG/Rij rats were divided into 12 groups of 7 rats each. Experiments were conducted with penicillin (500 IU, i.c.) and pentylenetetrazole models (50 mg/kg, intraperitoneally (i.p.)) in Wistar rats and genetic absence epileptic WAG/Rij rats. The vortioxetine (1, 5, or 10 mg/kg, i.p.) was evaluated in these three models. All groups were compared with their control groups.

RESULTS

In the penicillin-induced seizure model, 1, 5, or 10 mg/kg vortioxetine administration significantly decreased mean spike frequency. In the pentylenetetrazole-induced seizure model, 1, 5, or 10 mg/kg vortioxetine demonstrated a significant dose-dependent decrease in mean spike frequency, an increase in the latency to minor and major seizures, and a decrease in total duration of major seizure and convulsion stage. In genetic absence epileptic WAG/Rij rats, 1 mg/kg vortioxetine caused no significant alteration in the number and duration of SWDs compared to the controls, while 5 and 10 mg/kg doses of vortioxetine increased the number and duration of SWDs. Amplitude of the epileptiform activity did not change in any of the experimental epilepsy models.

CONCLUSION

The results of this study suggested that vortioxetine has anticonvulsant activity in penicillin- and pentylenetetrazole-induced seizure models. However, it exhibited proconvulsant activity in the absence epileptic WAG/Rij rats.

Effect of Alprazolam and Ketamine on Seizures Induced by Two Different Convulsants

Effect of two anticonvulsants with different mechanism of action, i.e. alprazolam and ketamine, was tested in two types of seizure activity. The first one was induced by N-(3,5-dimethoxy-4-propoxyphenylethyl)-aziridine, the second one by pentylenetetrazol. While alprazolam alleviated both the minimal as well as major paroxysms, ketamine supressed only major seizures. These effects are discussed in terms of the both N-methyl-D-aspartate and GABA receptors involvement.

Gastrodin Attenuates Pentylenetetrazole-Induced Seizures by Modulating the Mitogen-Activated Protein Kinase-Associated Inflammatory Responses in Mice

Gastrodin, the major component isolated from the rhizome of the Chinese traditional medicinal herb Gastrodia elata ("Tianma"), has a long history in the treatment of epilepsy and other neurological disorders. However, the molecular mechanisms are not clear. Here, we found that gastrodin ameliorated pentylenetetrazole (PTZ)-induced epileptic seizures with improvement of the electroencephalographic pattern in mice. Further studies demonstrated that gastrodin decreased the levels of the pro-inflammatory cytokines interleukin-1β and tumor necrosis factor-α while increasing interleukin-10, an anti-inflammatory cytokine in the brain. Furthermore, gastrodin attenuated the PTZ-induced microglial activation along with inhibition of mitogen-activated protein kinases, cAMP response element binding protein, and NF-κB. Our data suggest that gastrodin attenuates seizures by modulating the mitogen-activated protein kinase-associated inflammatory responses.

NMDA and AMPA receptors: development and status epilepticus

Glutamate is the main excitatory neurotransmitter in the brain and ionotropic glutamate receptors mediate the majority of excitatory neurotransmission (Dingeldine et al. 1999). The high level of glutamatergic excitation allows the neonatal brain (the 2(nd) postnatal week in rat) to develop quickly but it also makes it highly prone to age-specific seizures that can cause lifelong neurological and cognitive disability (Haut et al. 2004). There are three types of ionotropic glutamate receptors (ligand-gated ion channels) named according to their prototypic agonists: N-methyl-D-aspartate (NMDA), 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl) propanoic acid (AMPA) and kainate (KA). During early stages of postnatal development glutamate receptors of NMDA and AMPA type undergo intensive functional changes owing to modifications in their subunit composition (Carter et al. 1988, Watanabe et al. 1992, Monyer et al. 1994, Wenzel et al. 1997, Sun et al. 1998, Lilliu et al. 2001, Kumar et al. 2002, Matsuda et al. 2002, Wee et al. 2008, Henson et al. 2010, Pachernegg et al. 2012, Paoletti et al. 2013). Participation and role of these receptors in mechanisms of seizures and epilepsy became one of the main targets of intensive investigation (De Sarro et al. 2005, Di Maio et al. 2012, Rektor 2013). LiCl/Pilocarpine (LiCl/Pilo) induced status epilepticus is a model of severe seizures resulting in development temporal lobe epilepsy (TLE). This review will consider developmental changes and contribution of NMDA and AMPA receptors in LiCl/Pilo model of status epilepticus in immature rats.

Behavioral and anticonvulsant effects of the standardized extract of Ficus platyphylla stem bark

ETHNOPHARMACOLOGICAL RELEVANCE

Decoctions of Ficus platyphylla Del.-Holl (Family: Moraceae) are used in Nigeria׳s folk medicine for the management of epilepsy and their efficacies are widely acclaimed among the rural communities of northern Nigeria. The aim of the study is to examine the behavioral and anticonvulsant properties of the standardized methanol extract of Ficus platyphylla (FP) stem bark, in order to scientifically describe its potential values in the management of convulsive disorders.

MATERIALS AND METHODS

High performance liquid chromatography (HPLC) and preliminary phytochemical analysis of the methanol extract were utilized and the intraperitoneal median lethal dose (LD50) determined in mice. The effects of FP were investigated on some murine models of behavior and its anticonvulsant effects studied on pentylenetetrazole (PTZ)-, strychnine (STN)-, picrotoxin (PCT)-, isoniazid (INH)-, aminophylline (AMI)- and maximal electroshock (MES)-induced seizures in mice.

RESULTS

The intraperitoneal oral LD50 of FP was estimated to be 5000mg/kg. FP significantly reduced the locomotor activities including the total distance covered, speed, active time and rearing counts. It shortened the onset and prolonged the duration of diazepam-induced sleep, but had no effect on motor coordination on the rota-rod treadmill or beam-walking assay in mice at the doses tested. The extract protected the mice against PTZ- and STN-induced seizures and significantly delayed the latencies of myoclonic jerks and tonic seizures induced by all the standard convulsant agents (PTZ, PCT, INH, STN and AMI) used in this study, but failed to protect the mice against MES seizures at the doses tested. The HPLC fingerprint of the extract shows a spectrum profile characteristic of Ficus platyphylla, while the preliminary phytochemical screening revealed the presence of saponins, flavonoids and tannins.

CONCLUSION

Our study provides scientific evidence that FP may contain psychoactive principles with potential anticonvulsant properties, thus supporting further development of the psychoactive components of this plant as anticonvulsant agents.

Gonadal status-dependent effects of in vivo β-estradiol administration to female rats on in vitro epileptiform activity induced by low [Mg2+]₀ in combined hippocampus-entorhinal cortex slices

There are controversial data regarding estrogen effects on neuronal excitability. We investigated whether β-estradiol (EB) administration to ovariectomized (OVX) or gonadally intact female rats alters epileptiform activity within the dentate gyrus network induced in vitro by removing [Mg2+]o in combined hippocampus-entorhinal cortex slices. In vivo EB administration significantly influenced the epileptiform activity in gonadal status-dependent manner. The onset of epileptiform discharges was modestly delayed in slices from OVX rats replaced with physiologically relevant doses of EB but the number of discharges was not affected. In contrast, EB administration to gonadally intact rats had robust effects such that: EB delayed the onset of discharges but significantly increased their number within the dentate gyrus network. Our data suggest that EB in physiologically relevant concentrations does not seem to negatively affect hippocampal neuronal excitability, nevertheless supraphysiological EB levels may enhance seizure severity.

Differential antagonism of tetramethylenedisulfotetramine-induced seizures by agents acting at NMDA and GABA(A) receptors

Tetramethylenedisulfotetramine (TMDT) is a highly lethal neuroactive rodenticide responsible for many accidental and intentional poisonings in mainland China. Ease of synthesis, water solubility, potency, and difficulty to treat make TMDT a potential weapon for terrorist activity. We characterized TMDT-induced convulsions and mortality in male C57BL/6 mice. TMDT (ip) produced a continuum of twitches, clonic, and tonic-clonic seizures decreasing in onset latency and increasing in severity with increasing dose; 0.4mg/kg was 100% lethal. The NMDA antagonist, ketamine (35mg/kg) injected ip immediately after the first TMDT-induced seizure, did not change number of tonic-clonic seizures or lethality, but increased the number of clonic seizures. Doubling the ketamine dose decreased tonic-clonic seizures and eliminated lethality through a 60min observation period. Treating mice with another NMDA antagonist, MK-801, 0.5 or 1mg/kg ip, showed similar effects as low and high doses of ketamine, respectively, and prevented lethality, converting status epilepticus EEG activity to isolated interictal discharges. Treatment with these agents 15min prior to TMDT administration did not increase their effectiveness. Post-treatment with the GABA(A) receptor allosteric enhancer diazepam (5mg/kg) greatly reduced seizure manifestations and prevented lethality 60min post-TMDT, but ictal events were evident in EEG recordings and, hours post-treatment, mice experienced status epilepticus and died. Thus, TMDT is a highly potent and lethal convulsant for which single-dose benzodiazepine treatment is inadequate in managing electrographic seizures or lethality. Repeated benzodiazepine dosing or combined application of benzodiazepines and NMDA receptor antagonists is more likely to be effective in treating TMDT poisoning.

Probing the role of the sodium/calcium exchanger in pentylenetetrazole-induced generalized seizures in rats

The Na⁺/Ca²⁺ exchanger (NCX) is thought to play an important role in the pathogenesis of pentylenetetrazole (PTZ)-induced tonic flexion in mice. Here, I investigated the expression of PTZ-induced generalized clonic and tonic-clonic seizures in rats, using two potent NCX reverse mode inhibitors, KB-R7943 and SN-6 for NCX subtypes 3 (NCX3) and 1 (NCX1), respectively. Pretreatment with KB-R7943 (3, 10, and 30 mg/kg; p.o.) significantly reduced the expression of PTZ-induced generalized seizures with clonic and tonic-clonic components in 12-62% and 25-62% of the treated animals, respectively. In the remaining animals that exhibited seizures, KB-R7943 (3 mg/kg; p.o.) pretreatment significantly delayed the onset of the first seizure episode and reduced the seizure severity. Following pretreatment with SN-6 (0.3, 1, 3, 10, and 30 mg/kg; p.o.), clonic and tonic-clonic PTZ-induced generalized seizures were reduced in 25-50% and 38-63% of treated animals, respectively. SN-6 (0.3, 1, and 3 mg/kg; p.o.) also significantly reduced PTZ-induced seizure severity scores, but did not alter seizure latencies. KB-R7943 (3 and 30 mg/kg; p.o.) or SN-6 (3 and 30 mg/kg; p.o.) administration potentiated the sub-anticonvulsant dose of diazepam (2.5 mg/kg; i.p.) that suppresses clonic and tonic-clonic PTZ-induced seizures. These findings suggested that Ca²⁺ influx via the NCX in reverse mode contributes to a neuronal hyperexcitability that leads to clonic and tonic-clonic generalized seizures and that the NCX1 and NCX3 isoforms may serve as novel molecular targets for seizure suppression.

Suppression of c-Fos protein and mRNA expression in pentylenetetrazole-induced kindled mouse brain by isoxylitones

An early immediate gene c-fos has been proposed as the gene responsible for turning on molecular events that might underlie the long-term neural changes occurring during kindling. We have evaluated the effects of novel anticonvulsant isomeric compounds isoxylitones [(E/Z)-2-propanone-1,3,5,5-trimethyl-2-cyclohexen-1-ylidine] on the c-Fos protein and mRNA expression in the brain samples of kindled mice and compared it with the normal and untreated kindled groups. Kindling was induced in male NMRI mice by repeated administration of sub-convulsive dose (50 mg/kg) of pentylenetetrazole (PTZ) until a seizure score of 4-5 was achieved. The c-Fos expression was quantified by combination of immunohistochemistry and RT-PCR protocols. Both the immunohistochemical and RT-PCR analysis revealed a marked increase in the expression of c-fos mRNA and protein in the brain regions tested in case of PTZ-kindled control group compared to normal control. In contrast, the isoxylitone (30 mg/kg)-treated group demonstrated significant reduction of c-Fos expression compared to PTZ-kindled control animals. However, low expression of c-fos mRNA was only detected in the thalamus of the isoxylitone-treated brain samples. Based on these observations, we suggest that isoxylitones may have the capacity to control the seizure pattern by mechanism such as the suppression of c-Fos protein and mRNA levels in different regions of the brain. Further investigations to explore the mechanism of action of these compounds are under process.

Antiepileptic potential of flavonoids fraction from the leaves of Anisomeles malabarica

ETHNOPHARMACOLOGICAL RELEVANCE

The plant Chodara (Anisomeles malabarica R.Br. Family: Lamiaceae) has numerous therapeutic utilities in folk medicine.

AIM OF THE STUDY

To isolate and evaluate the anti-epileptic potential of fractions from the ethyl acetate extract (EAE) of Anisomeles malabarica leaves.

MATERIALS AND METHODS

The EA extract (2.12% w/w) of the leaves of Anisomeles malabarica was prepared and fractionated into total flavonoids fraction (AMFF) and tannins fraction (AMTF), which subsequently evaluated for the antiepileptic activity against PTZ- and MES model in wistar rats. Diazepam and phenytoin (2mg/kg and 25mg/kg, i.p., respectively), were used as a reference drugs. Further, the presence of flavonoid was confirmed by chemical test, TLC and HPTLC were done for the identification of the number of flavonoids with reference to standard.

RESULTS

Single dose pretreatment with AMFF (25 and 50mg/kg, i.p.) has found to be effective against both MES and PTZ-convulsions, but associated with a marked decrease in locomotor activity and motor activity performance (i.e., neurotoxic effects), similar to that of diazepam treatment. Interestingly, chronic treatment with AMFF at lower doses (6.25 and 12.5mg/kg, i.p., 1 week) has also produced significant antiepileptic activity, but without causing neurotoxic effects.

CONCLUSION

Thus, it may be concluded that the flavonoids fraction of the EA extract of Anisomeles malabarica leaves has antiepileptic potential against both MES and PTZ convulsion models. Acute treatment (25 and 50mg/kg, i.p.) is associated with neurotoxic activity. Whereas, chronic treatment (6.25 and 12.5mg/kg, i.p., 1 week) also shown significant antiepileptic effect without causing neurotoxic side effects. However, further research is in progress to determine the component(s) of the flavonoids fraction of Anisomeles malabarica involved and their mechanism of action in bringing about the desirable anti-epileptic effect.

Spermidine influence on the nitric oxide synthase and arginase activity relationship during experimentally induced seizures

Nitric oxide (NO), a potential candidate for a modulator of convulsive activity, is a mediator in several pathological events in the central nervous system. The polyamines, spermidine (Spd) and spermine, are neuromodulators influencing the metabolism of L-arginine and NO production. Here we examined the effects of Spd on NO production and arginase activity during convulsions induced by pentylenetetrazol (PTZ). Male Wistar rats were allocated into four experimental groups of 8 animals each and received the following treatments: I (control)--saline, intraperitoneally (i.p.); II (PTZ)--seizures induced by pentylenetetrazol (100mg/kg bw i.p); III (Spd)--Spd (1 mg/kg bw i.p.) 50 min before PTZ application; IV (Mid)--antiepileptic Midazolam (100 mg/kg bw) 45 min before PTZ. In brain cortex, striatum, hippocampus, cerebellum, and brainstem homogenates, nitrite + nitrate levels and arginase activity were determined. Spermidine showed proepileptic effects. shortening seizure latency and inducing a more profound increase of NO production than PTZ in all brain structures. PTZ reduced arginase activity, whereas Spd pretreatment increased enzyme activity, with the most profound effects in cerebellum and brainstem. The results point out the importance of polyamine and arginine metabolism in the brain during seizures, suggesting a regulatory role for polyamines and arginase in NO production.

Different effects of two N-methyl-D-aspartate receptor antagonists on seizures, spontaneous behavior, and motor performance in immature rats

Typical N-methyl-D-aspartate (NMDA) receptor antagonists exhibit anticonvulsant action and unwanted effects, even in developing rats. Therefore, we studied the actions of the low-affinity, noncompetitive antagonist memantine and the NR2B-specific antagonist ifenprodil. Seizures (minimal clonic and generalized tonic-clonic) were elicited with pentylenetetrazol (100mg/kg subcutaneously) in rats 7, 12, 18, and 25 days old pretreated with memantine (2.5-40 mg/kg intraperitoneally) or ifenprodil (10-60 mg/kg intraperitoneally). The effects of both drugs were studied in open field and motor performance tests in 12-, 18-, and 25-day-old rats. Memantine suppressed generalized tonic-clonic seizures in all age groups; minimal seizures were potentiated. Ifenprodil abolished the tonic phase of generalized tonic-clonic seizures in 7-, 12-, and 18-day-old rats only; minimal seizures remained untouched. Memantine induced locomotor hyperactivity and compromised motor performance in all age groups. Ifenprodil exerted these effects only in 12-day-old rats; older animals were less active in open field tests. Memantine exhibits both anti- and pro-convulsant and behavioral effects typical of NMDA antagonists. Ifenprodil exerted the same effects in 12-day-old rats, but its anticonvulsant action in 18-day-old rats was accompanied by a decrease in locomotion.

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).

Model of infantile spasms induced by N-methyl-D-aspartic acid in prenatally impaired brain

OBJECTIVE

Infantile spasms (a catastrophic epileptic syndrome of childhood) are insensitive to classic antiepileptic drugs. New therapies are limited by lack of animal models. Here we develop a new model of flexion spasms based on prenatal exposure to betamethasone combined with postnatal administration of N-methyl-D-aspartic acid (NMDA) and determine brain structures involved in the induction of flexion spasms.

METHODS

Pregnant rats received two doses of betamethasone on day 15 of gestation. Offspring was injected with NMDA on postnatal day 15. Effects of adrenocorticotropin therapy on the development of age-specific flexion spasms were determined and electroencephalographic correlates recorded. C-fos immunohistochemistry and [14C]2-deoxyglucose imaging identified brain structures involved in the development of flexion spasms.

RESULTS

Prenatal betamethasone exposure sensitizes rats to development of NMDA-induced spasms and, most importantly, renders the spasms sensitive to adrenocorticotropin therapy. Ictal electroencephalogram results correspond to human infantile spasms: electrodecrement or afterdischarges were observed. Imaging studies defined three principal regions involved in NMDA spasms: limbic areas (except the dorsal hippocampus), hypothalamus, and the brainstem.

INTERPRETATION

Despite certain limitations, our new model correlates well with current infantile spasm hypotheses and opens an opportunity for development and testing of new effective drugs.

Spermine and L-Name Pretreatment Effects on Polyamine and Nitric Oxide Metabolism in Rat Brain During Seizures

In the CNS polyamines can exert opposite effects, depending on the concentration and conditions in the cell. Protective or neurotoxic polyamine effects were documented during seizures and repeated CNS excitation. Intensive research of exogenous polyamines effects during seizures induced by numerous agents did not clear up confusions about the duality of effects and the role of polyamines in seizures. In order to understand polyamine modulatory effects in seizures, the importance of NO and polyamine metabolism interdependence and the possible implication of changes of postulated NO and polyamine equillibrium in seizures, the effects of spermine alone and in combination with L-NAME (NOS inhibitor) on seizures induced by pentazol (PTZ) were investigated. To compare the obtained results, the effects of anticonvulsant midazolam on NO production during seizures were also investigated. Seizures were induced by i.p. application of pentazol (100 mg/kg b.w.). Spermine and L-NAME were administered i.p. before PTZ. In the striatum and hippocampus, spermine induced increased NO production (p<0.001) related to values in the group treated by PTZ. Application of L-NAME before spermine and PTZ caused decrease of NO production in comparison with animals treated only by PTZ or spermine and PTZ. L-NAME given before spermine exerts protective effects related to seizures induced by PTZ and to the group treated by spermine, extending the time of seizure symptoms appearance, thus confirming the NO signaling system involvement in spermine effects during seizures. Highly significant PAO activity increase caused by spermine points out the intensified interconversion of spermine into putrescine, in order to maintain the intracellular putrescine concentration. The obtained results prove a strong relationship between the NO signaling system and polyamine metabolism in the brain during seizures and the importance of their changes in this kind of CNS injury.

Sex-specific control of flurothyl-induced tonic-clonic seizures by the substantia nigra pars reticulata during development

The substantia nigra pars reticulata (SNR) plays an important age- and sex-specific role in control of clonic seizures. Its involvement in control of tonic-clonic seizures is contradictory. We investigated the role of the SNR in the tonic-clonic seizures induced in male, female and neonatally castrated male rats using flurothyl. In adult female rats, vaginal impedance determined the changes in progesterone/estrogen ratio. Rats at various postnatal ages received infusions of muscimol or vehicle in the SNRanterior or SNRposterior. Furthermore, in 15-day-old (P15) and adult male rats, ZAPA (a GABA(A) receptor agonist) or AP7 (an NMDA receptor antagonist) was infused. The developmental profile of tonic-clonic seizure threshold differed between male and female rats possibly due to early postnatal testosterone surge in male rats. On the other hand, changing estrogen/progesterone ratio in cycling adult female rats had no effect on seizure threshold. Intranigral muscimol had proconvulsant effects on tonic-clonic seizures only in immature rats, and this effect was dependent on the perinatal testosterone surge. ZAPA had anticonvulsant effects in P15 rats but was not effective in adult rats. Only AP7 had anticonvulsant effects in both adult and P15 rats. Results indicate that thresholds for flurothyl-induced tonic-clonic seizures develop under the control of postnatal testosterone. Although GABAergic inhibition in the SNR affects tonic-clonic seizures in developing rats, only the NMDA antagonist had consistent anticonvulsant effects throughout development.

Pentylenetetrazole induced changes in zebrafish behavior, neural activity and c-fos expression

Rodent seizure models have significantly contributed to our basic understanding of epilepsy. However, medically intractable forms of epilepsy persist and the fundamental mechanisms underlying this disease remain unclear. Here we show that seizures can be elicited in a simple vertebrate system e.g. zebrafish larvae (Danio rerio). Exposure to a common convulsant agent (pentylenetetrazole, PTZ) induced a stereotyped and concentration-dependent sequence of behavioral changes culminating in clonus-like convulsions. Extracellular recordings from fish optic tectum revealed ictal and interictal-like electrographic discharges after application of PTZ, which could be blocked by tetrodotoxin or glutamate receptor antagonists. Epileptiform discharges were suppressed by commonly used antiepileptic drugs, valproate and diazepam, in a concentration-dependent manner. Up-regulation of c-fos expression was also observed in CNS structures of zebrafish exposed to PTZ. Taken together, these results demonstrate that chemically-induced seizures in zebrafish exhibit behavioral, electrographic, and molecular changes that would be expected from a rodent seizure model. Therefore, zebrafish larvae represent a powerful new system to study the underlying basis of seizure generation, epilepsy and epileptogenesis.

Anticonvulsant activity and chemical composition of Artemisia dracunculus L. essential oil

Artemisia dracunculus L. (Asteraceae) has been used orally as an antiepileptic remedy in Iranian folkloric medicine. The anticonvulsant potential and composition of the essential oil obtained from the aerial parts of the plant were assessed in this study. The essential oil exerted dose- and time-dependent antiseizure activity in both maximal electroshock (MES) and pentylenetetrazole models of experimental seizures with ED50 values of 0.84 and 0.26 ml/kg, respectively. At some anticonvulsant doses, the essential oil produced sedation and motor impairment assessed by rotarod test. Gas chromatography (GC)/mass spectrometry (MS) analysis of the essential oil revealed the presence of trans-anethole (21.1%), alpha-trans-ocimene (20.6%), limonene (12.4%), alpha-pinene (5.1%), allo ocimene (4.8%), methyl eugenol (2.2%), beta-pinene (0.8%), alpha-terpinolene (0.5%), bornyl acetate (0.5%) and bicyclogermacrene (0.5%) as the main components. The observed anticonvulsant and sedative effects could be related to the presence of monoterpenoids in the essential oil.

The effects of pentylenetetrazole-induced status epilepticus on behavior, emotional memory, and learning in rats

Status epilepticus (SE) can cause spatial learning, memory, and behavioral deficits; however, little information is available, especially regarding the effects of such seizures on emotional memory and learning functions. We investigated the effects of SE on emotional memory, learning, and behavior in mature rats over short and long periods. SE was induced in 50- to 60-day-old rats (P50-P60) using intraperitoneal injections of pentylenetetrazole (PTZ, n = 20); control rats received saline (n = 10). All animals were tested with elevated T-maze and open-field tests on the 1st, 7th, 14th, and 180th days after SE to evaluate emotional memory, learning, and behavior. The number of fecal boli increased, and one-way escape latency was long in a short period after SE. PTZ-induced SE causes transient memory deficits, which is related to unconditioned fear, but it did not cause any persistent abnormalities of behavior, emotional memory, and learning in mature rats.

Anticonvulsant activity of the leaf essential oil of Laurus nobilis against pentylenetetrazole- and maximal electroshock-induced seizures

The leaf essential oil of Laurus nobilis Linn., Lauraceae, which has been used as an antiepileptic remedy in Iranian traditional medicine, was evaluated for anticonvulsant activity against experimental seizures. The essential oil protected mice against tonic convulsions induced by maximal electroshock and especially by pentylenetetrazole. Components responsible for this effect may be methyleugenol, eugenol and pinene present in the essential oil. At anticonvulsant doses, the essential oil produced sedation and motor impairment. This effect seems to be related in part to cineol, eugenol and methyleugenol. Although the essential oil had an acceptable acute toxicity, further studies are required before any absolute conclusions can be drawn.

Behavioural effects of tetrachloroethylene exposure in rats: acute and subchronic studies

This study was carried out to compare the neurobehavioural profile of acute and subchronic tetrachloroethylene (perchloroethylene, PCE) exposure in rats. In the acute study, a single bolus of 50 and 500 mg/kg of PCE in corn oil was administered by gavage. In the subchronic experiments, rats were exposed to PCE at a dosage of 5 and 50 mg/kg in corn oil, 5 days per week for 8 weeks. Nociception, locomotion and seizure susceptibility was tested using open-field, tail immersion and hot plate and pentylenetetrazol-induced seizures, respectively. Subchronic PCE exposure exhibited higher antinociceptive effect and lower motor activity in comparison with acute exposure. Pentylenetetrazol-induced convulsion thresholds were elevated following acute PCE exposure. In contrast, subchronic PCE exposure only increased thresholds for myoclonic twitch and face and forelimb clonus without altering the thresholds for running and bouncing clonus and tonic hindlimb extension. These findings suggest that subchronic PCE exposure results in progressively greater toxic effects on nociception and locomotor activity. The differential effects on seizure susceptibility between acute and subchronic exposure may represent different alterations on neural circuits involved in seizure generation.

Convulsant action of systemically administered glutamate and bicuculline methiodide in immature rats

Developmental changes of transport of drugs into the brain play an important role in ontogenetic neuropharmacology. Two convulsant drugs with different mechanisms of action (glutamate and bicuculline methiodide) were chosen to demonstrate these changes in developing rats. High dose of glutamate (4 g/kg i.p.) induced both minimal (predominantly clonic) and generalized tonic-clonic seizures in rat pups 7, 12, and 18 days old. In contrast, seizures were only exceptionally observed in 25 and 90 days old animals. Bicuculline methiodide was administered in a dose of 2 or 20 mg/kg i.p. The first sign of bicuculline methiodide action in all age groups was represented by automatisms, a symptomatology never seen after bicuculline hydrochloride administration. Minimal seizures were induced in 12-day-old and in a few 18-day-old and adult rats. Generalized seizures were common after the higher dose of bicuculline methiodide in 7- and 12-day-old rat pups, seldom in 18-day-old ones and never seen in 25-day-old and adult animals. Both glutamate and bicuculline methiodide enter the brain in immature rats but the mechanisms are probably different - glutamate is transported actively through the blood-brain barrier whereas no similar system is known for bicuculline methiodide.

Special considerations in treating children with epilepsy

The incidence of seizures is high in infants and children. Many epileptic syndromes have their onset early in life. The increase in seizure susceptibility of the immature brain may be due to several factors, including an imbalance between excitatory and inhibitory processes, age-specific differences in ionic transport and clearance systems, high incidence of epileptogenic stimuli early in life, and the age-specific expression of pre- and perinatal brain anomalies. All of these factors must be taken into account when developing safe and effective age-specific antiepileptic drugs (AEDs). The use of developmental epilepsy models, followed by clinical trials in children, may help identify such AEDs.

Anticonvulsant action of a NMDA receptor antagonist CGP 40116 varies only quantitatively during ontogeny in rats

Anticonvulsant action of CGP 40116, a competitive antagonist of N-methyl-D-aspartate type of excitatory amino acid receptors, was studied in rats during development (7, 12, 18, 25 and 90 days old). Two types of motor seizures were elicited by a subcutaneous injection of pentylenetetrazol. Pretreatment with CGP 40116 did not influence minimal, predominantly clonic seizures in any age group. Generalized tonic-clonic seizures were at first modified--their tonic phase was restricted to forelimbs, then selectively suppressed--and with increasing dosage the clonic phase was blocked too. This effect exhibited only minor quantitative changes during development.

Prenatal morphine exposure alters ovarian steroid hormonal regulation of seizure susceptibility

The present study examined the ovarian hormonal regulation of seizure susceptibility in prenatally morphine- and saline-exposed adult female rats in the flurothyl seizure model in vivo, and in low-magnesium-induced epileptiform activity in brain slices, in vitro. All females were ovariohysterectomized (OVX); some received either estrogen (E) or progesterone (P) replacement, while others were injected with E + P sequentially. In prenatally saline-treated control females, there was an increase in the flurothyl-induced clonic seizure threshold (anticonvulsant effect) in the presence of both hormones (E + P) compared to OVX controls. In morphine-exposed females, there was an increase in the flurothyl-induced clonic seizure threshold after an E injection alone while there was a reduced tonic--clonic seizure threshold in the presence of both hormones (E + P) compared to the hormone treatment-matched group of saline-exposed females. In control females, in low magnesium medium in vitro, the development of two types of epileptiform activity (seizure-like events and status of short discharges) was not affected by the different hormonal conditions. However, prenatal morphine exposure suppressed the development of both types of epileptiform activity in the E-injected females compared to the E-injected, control females. The present data demonstrate that the anticonvulsant effects of P on seizure susceptibility requires the presence of E. Furthermore, prenatal morphine exposure alters ovarian steroid hormone-regulated seizure susceptibility.

Qualitative changes of anticonvulsant action of felbamate during development in rats

The anticonvulsant action of felbamate (25, 50, 100 and 150 mg/kg i.p.) was tested against motor seizures induced by pentylenetetrazol in five age-groups of rats (7, 12, 18, 25 and 90 days old). In adult rats, felbamate suppressed generalized tonic-clonic seizures leaving intact minimal clonic seizures. In all groups of rat pups felbamate exhibited a specific action against the tonic phase of generalized tonic-clonic seizures. In addition, the highest dose of felbamate was found to suppress minimal seizures in 18-day-old rats. The changes of felbamate action during ontogeny might be due to multiple mechanisms of anticonvulsant action with an uneven developmental profile.

Age-related decrease in the antiseizure effect of ifenprodil against pentylenetetrazole in mice

The developmental change in the antiseizure effect of ifenprodil against pentylenetetrazole (PTZ) was examined in mice. Ifenprodil (i.p.) significantly increased the latency to seizure induced by PTZ in 7- and 10-day-old mice, but not in 14- or 21-day-old mice. Intracerebroventricular administration of ifenprodil also failed to modify the latency to PTZ-induced seizure in 21-day-old mice. Dizocilpine produced an increase in the latency to PTZ-induced seizure in 7- and 21-day-old mice. In an NMDA receptor binding assay using [3H]dizocilpine, ifenprodil was clearly more potent in inhibiting [3H]dizocilpine binding in a forebrain membrane preparation from 7- rather than 21-day-old mice. These results suggest that the remarkable antiseizure effect of ifenprodil against PTZ in 7-day-old mice may be related to the high proportion of ifenprodil-sensitive NMDA receptors in the brain.

Anticonvulsant and proconvulsant roles of nitric oxide in experimental epilepsy models

The effect of acute (120 mg/kg) and chronic (25 mg/kg, twice a day, for 4 days) intraperitonial injection of the nitric oxide (NO) synthase (NOS) inhibitor NG-nitro-L-arginine (L-NOARG) was evaluated on seizure induction by drugs such as pilocarpine and pentylenetetrazole (PTZ) and by sound stimulation of audiogenic seizure-resistant (R) and audiogenic seizure-susceptible (S) rats. Seizures were elicited by a subconvulsant dose of pilocarpine (100 mg/kg) only after NOS inhibition. NOS inhibition also simultaneously potentiated the severity of PTZ-induced limbic seizures (60 mg/kg) and protected against PTZ-induced tonic seizures (80 mg/kg). The audiogenic seizure susceptibility of S or R rats did not change after similar treatments. In conclusion, proconvulsant effects of NOS inhibition are suggested to occur in the pilocarpine model and in the limbic components of PTZ-induced seizures, while an anticonvulsant role is suggested for the tonic seizures induced by higher doses of PTZ, revealing inhibitor-specific interactions with convulsant dose and also confirming the hypothesis that the effects of NOS inhibitors vary with the model of seizure.

Excitatory amino acid antagonists and pentylenetetrazol-induced seizures during ontogenesis. IV. Effects of CGP 39551

We determined anticonvulsant effects of CGP 39551 [(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid 1-ethylester] against pentylenetetrazol-induced seizures in developing, 7-90 day old, rats. The rats received CGP 39551 in doses of 10, 20 or 40 mg/kg IP 30 min prior to the pentylenetetrazol administration (100 mg/kg s.c.). In addition, the 20 mg/kg dose of CGP 39551 was injected 120 min prior to pentylenetetrazol. In adult rats, all doses of CGP 39551 blocked generalized tonic-clonic pentylenetetrazol-induced seizures. In younger rats, higher doses of CGP 39551 and/or a longer delay between the CGP 39551 pretreatment and pentylenetetrazol administration was necessary for similar anticonvulsant effects against tonic-clonic seizures. In contrast, there was no effect of CGP on pentylenetetrazol-induced clonic seizures. The results indicate that CGP 39551 has anticonvulsant features similar to other competitive NMDA receptor antagonists. High doses of CGP 39551 and long pretreatment latency which are necessary in young rats for anticonvulsant effects may reflect the overexpression of NMDA transmission during the second and third postnatal week of the rat. Alternatively in adult rats, we can speculate an anticonvulsant role of a CGP 39551 metabolite or maturation of brain uptake mechanism for CGP 39551.

Resistance of hippocampal synaptic transmission to hypoxia in carbonic anhydrase II-deficient mice

Mutant Car2n/Car2n mice deficient in carbonic anhydrase II (CA II; a major brain CA isozyme) suffer from systemic acidosis and are more resistant to experimental seizures than their normal littermates (+/+ or +/Car2n). The N-methyl-D-aspartate (NMDA) subtype of glutamate receptor has been shown to contribute to long-term potentiation (LTP) of synaptic transmission, hypoxic/ischemic neuronal injury and to be blocked by extracellular protons (acidosis). We compared the effects of hypoxia on synaptic transmission and LTP in field CA1 of hippocampal slices from CA II-deficient mice to their normal littermates. Slices were subjected to successive 5, 10 and 15 min-periods of hypoxia with 30 min-recovery periods in between. Hippocampal slices from mutant, CA II-deficient mice, were more resistant to all periods of hypoxia tested than slices from normal littermates. In a separate set of mutant and normal slices, there were no differences in LTP of population spike amplitude. The relative resistance of CA II-deficient mice to hypoxia-induced damage may be a consequence of severe interstitial acidosis. The sustained influence of increased extracellular proton concentrations may change the characteristics of NMDA receptors resulting in an increased resistance of synaptic transmission in CA II-deficient mice to hypoxia compared to controls.

Effects of MK-801 and phenytoin on flurothyl-induced seizures during development

We determined the effects of the N-methyl-D-aspartate (NMDA) receptor blocker MK-801 (0.05, 0.1, and 0.5 mg/kg intraperitoneally, i.p.) and phenytoin (PHT, 5, 10, and 20 mg/kg i.p.) on flurothyl-induced clonic and tonic-clonic seizures in 9-, 15-, 30-, and 60-day-old male rats. Both agents had seizure-, age-, and dose-specific effects. The highest dose of MK-801 was anticonvulsant against clonic flurothyl-induced seizures only in 9- and 60-day-old rats, but suppressed tonic-clonic seizures in all ages. The lowest dose of MK-801 (0.05 mg/kg) produced significant anticonvulsant effects only in 15 day old rats. PHT did not have any effect on clonic seizures throughout development. Both doses of PHT (10 and 20 mg/kg) were anticonvulsant against tonic-clonic seizures in adult rats but not in any other age group. The results indicate that NMDA receptors play an important role in tonic-clonic flurothyl-induced seizures throughout development (especially in 15-day-old rats) and that the anticonvulsant effects of PHT may vary at different stages of brain development.

Excitatory amino acid antagonists and pentylenetetrazol-induced seizures during ontogenesis: III. The action of kynurenic acid and glutamic acid diethylester

N-methyl-D-aspartate (NMDA) receptor antagonists are anticonvulsant drugs with specific activity against tonic-clonic pentylenetetrazol-induced seizures. However, they do not affect clonic seizures with preserved righting reflexes. In these experiments, we tested the anticonvulsant activity of strychnine-insensitive glycine receptor (at the NMDA site) antagonist kynurenic acid and nonspecific excitatory amino acid receptor antagonist glutamic acid diethylester (GDEE) in the pentylenetetrazol-induced seizure model in developing rats 7, 12, 18, 25, and 90 days old. Control rats were injected with pentylenetetrazol (100 mg/kg subcutaneously). Other rats were pretreated either with kynurenic acid (40, 80, or 240 mg/kg IP) or with GDEE (0.48-480 mg/kg IP), followed by pentylenetetrazol (100 mg/kg). In very young rats (7 and 12 days), both kynurenic acid and GDEE increased the incidence of clonic seizures, whereas the occurrence of tonic-clonic seizures was suppressed or delayed compared to controls. This effect is very similar to the anticonvulsant action of the competitive and noncompetitive NMDA receptor antagonists. In adult rats, the pretreatment with rather higher doses of kynurenic acid or GDEE suppressed or delayed clonic seizures as well as tonic-clonic seizures. Both drugs also induced behavioral side effects: repetitive orientation, wet dog shakes, and frequent jumping. Our data show that there are only weak and nonconsistent age-specific anticonvulsant effects resulting from the blockade of strychnine-insensitive glycine receptor often associated with serious side effects, thus decreasing chances to develop effective antiepileptic treatment in this drug class.

Antiepileptic effects of inhibitors of nitric oxide synthase examined in pentylenetetrazol-induced seizures in rats

The effects of intraperitoneal NG-methyl-L-arginine and N omega-nitro-L-arginine methyl ester, specific inhibitors of nitric oxide (NO) synthase, were examined on the pentylenetetrazol (PTZ)-induced seizures in rats. The incidence and latency for the onset of myoclonic jerks, clonic seizures, and tonic generalized extension were observed as specific parameters among PTZ-induced seizures. Both drugs preferentially suppressed the tonic generalized extension and prolonged the latency for the onset of each parameter, suggesting NO has a significant effect on the PTZ-induced seizure.

Polyamine-enhanced NMDA receptor activity: effect of ethanol

The effect of ethanol on spermidine-enhanced, N-methyl-D-aspartate (NMDA)-induced seizures and c-fos expression was investigated in the rat brain. The latency of tonic-clonic convulsions induced by i.p. administration of NMDA (50 mg/kg) was decreased by prior i.c.v. injection of spermidine (0.1-2.5 mumol) in a dose-dependent manner. Neither NMDA (50 mg/kg) nor spermidine (up to 2.5 mumol) alone induced c-fos mRNA expression in the brain. When both agents were administered, significant induction of c-fos expression occurred 30 min after the convulsion. Prior treatment with ethanol did not alter the curve of spermidine dose-dependency over most of the range. The c-fos expression induced by a combination of NMDA (50 mg/kg) and spermidine (1.0 mumol) was unaffected by ethanol. Only at a high dose of ethanol (2.0 g/kg) and at minimal spermidine enhancement was NMDA-induced seizure and c-fos expression inhibited. These results suggest that polyamines may have an important role in modulating NMDA receptor function in vivo and that polyamine enhancement of NMDA receptor function is relatively insensitive to the inhibitory effects of ethanol.

Developmental changes in seizure susceptibility in carbonic anhydrase II-deficient mice and normal littermates

Mice deficient in carbonic anhydrase II (CA II) were tested along with their normal littermates for susceptibility to seizures induced by flurothyl and loud sound at ages 10-180 days. In the flurothyl seizure model, CA II-deficient mice displayed increased resistance to clonic seizures from 32 to 90 days of age, whereas tonic-clonic seizures were suppressed at all ages. The mortality of CA II-deficient mice was significantly decreased at ages 19-40 days. The incidence of sound-induced seizures was very low and no difference between CA II-deficient and normal mice was found. The anticonvulsant effect of CA II deficiency appears to be dependent on seizure model and seizure type and to have age-specific characteristics.

Ketamine blocks cortical epileptic afterdischarges but not paired-pulse and frequency potentiation

Cortical epileptiform afterdischarges (spike-and-wave rhythm) induced by low-frequency stimulation of the sensorimotor cortex were dose-dependently shortened by ketamine (10, 20 and 40 mg/kg, i.p.). Myoclonic jerking during stimulation was unaffected by ketamine whereas the same motor pattern accompanying afterdischarges was markedly suppressed by this drug. Paired-pulse as well as frequency potentiation of the cortical interhemispheric (transcallosal) responses were not significantly altered by the 40 mg/kg dose of ketamine. The two simple potentiation phenomena studied probably did not play a role in initiation of cortical epileptic afterdischarges.

Picrotoxin-induced tonic-clonic seizures and lethality are decreased by MK-801 in developing rats

The action of MK-801 (NMDA antagonist; 0.1 and 0.5 mg/kg, IP) was tested against picrotoxin-induced seizures (3-6 mg/kg, IP) in rats aged 7, 12, 18, 25, and 90 days. We found MK-801 only inconsistently affected clonic seizures in 12- and 25-day-old rats, whereas tonic-clonic seizures were suppressed or delayed in almost all age groups. In addition, the lethality of picrotoxin was diminished by the higher dose of MK-801 in all age groups. The results suggest: a) different generators for both seizure patterns (clonic and tonic-clonic), b) an involvement of NMDA receptors in the genesis of tonic-clonic seizure pattern, and c) an interaction of MK-801 with GABAergic transmission throughout the entire development studied.

N-methyl-D-aspartate (NMDA)-induced seizures in developing rats

Intraperitoneal administration of N-methyl-D-aspartate (NMDA) elicited epileptic motor seizures in developing rats aged from 7 to 25 days as well as in young adults. The very first sign of NMDA action is locomotor hyperactivity which is followed by clonic and tonic seizures. In rat pups during the first 3 postnatal weeks flexion seizures (emprosthotonus) appeared as the first pattern of motor seizures; later they were replaced by generalized tonic clonic seizures. Only regular tonic-clonic seizures were observed in 25-day-old and adult rats. The youngest animals are the most sensitive to NMDA. CD50 for tonic-colonic seizures is 6.7 mg/kg in 7-day-old rat pups and it increases up to 86.6 mg/kg in 25-day-old animals. Similar changes could also be demonstrated for LD50, a lethal outcome being very frequent. EEG recordings demonstrated mainly suppressed activity, thus exhibiting a lack of correlation with motor phenomena.

Excitatory amino acid antagonists and pentylenetetrazol-induced seizures during ontogenesis. II. The effects of MK-801

MK-801 is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist with anticonvulsant and neuroprotective properties. The action of MK-801 (0.05-10 mg/kg IP) was assessed against pentylenetetrazol-induced seizures (PTZ; 100 mg/kg SC; 30 min after MK-801) in rats aged 7, 12, 18, 25, and 90 days (N = 263). We observed pronounced ataxia and hypermobility after MK-801 pretreatment during the whole ontogenesis, and the animals exhibited head-weaving and body-rolls. After the combination of MK-801 and PTZ "wet dog shakes" were detected in 18-, 25-, and 90-day-old rats (never seen in controls receiving PTZ only). MK-801 only insignificantly modified the latencies of minimal (clonic) seizures in 18-day-old and older rats where this seizure type is regularly elicited. In 12-day-old rats an increased incidence of minimal seizures was detected. MK-801 nearly completely blocked or strongly delayed major (generalized tonic-clonic) seizures and attenuated the seizure severity during ontogenesis in a dose-dependent manner. Present results suggest the important role of NMDA receptors in the genesis of generalized tonic-clonic seizures whilst the role of NMDA receptors in minimal seizures appears to be negligible during the whole ontogenetic development.