Age-dependent anticonvulsant action of clonazepam in the N-methyl-D-aspartate model of seizures

Animal Models in Epileptic Spasms and the Development of Novel Treatment Options

SUMMARY

The infantile spasms (IS) syndrome is a catastrophic developmental epileptic encephalopathy syndrome characterized by an age-specific expression of epileptic spasms that are associated with extremely abnormal, oftentimes described as chaotic, interictal EEG pattern known as hypsarrhythmia. Patients with IS generally have poor neurodevelopmental outcomes, in large part because of the frequent epileptic spasms and interictal EEG abnormalities. Current first-line treatments such as adrenocorticotropic hormone or vigabatrin are often ineffective and are associated with major toxic side effects. There is therefore a need for better and safer treatments for patients with IS, especially for the intractable population. Hope is on the horizon as, over the past 10 years, there has been robust progress in the development of etiology-specific animal models of IS. These models have been used to identify potential new treatments for IS and are beginning to provide some important insights into the pathophysiological substrates for this disease. In this review, we will highlight strengths and weaknesses of the currently available animal models of IS in addition to new insights into the pathophysiology and treatment options derived from these models.

Modeling epileptic spasms during infancy: Are we heading for the treatment yet?

Infantile spasms (IS or epileptic spasms during infancy) were first described by Dr. William James West (aka West syndrome) in his own son in 1841. While rare by definition (occurring in 1 per 3200-3400 live births), IS represent a major social and treatment burden. The etiology of IS varies - there are many (>200) different known pathologies resulting in IS and still in about one third of cases there is no obvious reason. With the advancement of genetic analysis, role of certain genes (such as ARX or CDKL5 and others) in IS appears to be important. Current treatment strategies with incomplete efficacy and serious potential adverse effects include adrenocorticotropin (ACTH), corticosteroids (prednisone, prednisolone) and vigabatrin, more recently also a combination of hormones and vigabatrin. Second line treatments include pyridoxine (vitamin B6) and ketogenic diet. Additional treatment approaches use rapamycin, cannabidiol, valproic acid and other anti-seizure medications. Efficacy of these second line medications is variable but usually inferior to hormonal treatments and vigabatrin. Thus, new and effective models of this devastating condition are required for the search of additional treatment options as well as for better understanding the mechanisms of IS. Currently, eight models of IS are reviewed along with the ideas and mechanisms behind these models, drugs tested using the models and their efficacy and usefulness. Etiological variety of IS is somewhat reflected in the variety of the models. However, it seems that for finding precise personalized approaches, this variety is necessary as there is no "one-size-fits-all" approach possible for both IS in particular and epilepsy in general.

Neonatal and Infantile Epilepsy: Acquired and Genetic Models

The incidence of seizures and epilepsies is particularly high during the neonatal and infantile periods. We will review selected animal models of early-life epileptic encephalopathies that have addressed the dyscognitive features of frequent interictal spikes, the pathogenesis and treatments of infantile spasms (IS) or Dravet syndrome, disorders with mammalian target of rapamycin (mTOR) dysregulation, and selected early-life epilepsies with genetic defects. Potentially pathogenic mechanisms in these conditions include interneuronopathies in IS or Dravet syndrome and mTOR dysregulation in brain malformations, tuberous sclerosis, and related genetic disorders, or IS of acquired etiology. These models start to generate the first therapeutic drugs, which have been specifically developed in immature animals. However, there are challenges in translating preclinical discoveries into clinically relevant findings. The advances made so far hold promise that the new insights may potentially have curative or disease-modifying potential for many of these devastating conditions.

Pathogenesis and new candidate treatments for infantile spasms and early life epileptic encephalopathies: A view from preclinical studies

Early onset and infantile epileptic encephalopathies (EIEEs) are usually associated with medically intractable or difficult to treat epileptic seizures and prominent cognitive, neurodevelopmental and behavioral consequences. EIEEs have numerous etiologies that contribute to the inter- and intra-syndromic phenotypic variability. Etiologies include structural and metabolic or genetic etiologies although a significant percentage is of unknown cause. The need to better understand their pathogenic mechanisms and identify better therapies has driven the development of animal models of EIEEs. Several rodent models of infantile spasms have emerged that recapitulate various aspects of the disease. The acute models manifest epileptic spasms after induction and include the NMDA rat model, the NMDA model with prior prenatal betamethasone or perinatal stress exposure, and the γ-butyrolactone induced spasms in a mouse model of Down syndrome. The chronic models include the tetrodotoxin rat model, the aristaless related homeobox X-linked (Arx) mouse models and the multiple-hit rat model of infantile spasms. We will discuss the main features and findings from these models on target mechanisms and emerging therapies. Genetic models have also provided interesting data on the pathogenesis of Dravet syndrome and proposed new therapies for testing. The genetic associations of many of the EIEEs have also been tested in rodent models as to their pathogenicity. Finally, several models have tested the impact of subclinical epileptiform discharges on brain function. The impact of these advances in animal modeling for therapy development will be discussed.

Basic mechanisms of catastrophic epilepsy -- overview from animal models

Infantile spasms are age-specific seizures of infantile epileptic encephalopathies that are usually associated with poor epilepsy and neurodevelopmental outcomes. The current treatments are not always effective and may be associated with significant side effects. Various mechanisms have been proposed as pathogenic for infantile spasms, including cortical or brainstem dysfunction, disruption of normal cortical-subcortical communications, genetic defects, inflammation, stress, developmental abnormalities. Many of these have been recently tested experimentally, resulting into the emergence of several animal models of infantile spasms. The stress theory of spasms yielded the corticotropin releasing hormone (CRH)-induced model, which showed the higher proconvulsant potency of CRH in developing rats, although only limbic seizures were observed. Models of acute induction of infantile spasms in rodents include the N-methyl-d-aspartate (NMDA) model of emprosthotonic seizures, the prenatal betamethasone and prenatal stress variants of the NMDA model, and the γ-butyrolactone induced spasms in a Down's syndrome mouse model. Chronic rodent models of infantile spasms include the tetrodotoxin model and the multiple-hit models in rats, as well as two genetic mouse models of interneuronopathies with infantile spasms due to loss of function of the aristaless X-linked homeobox-related gene (ARX). This review discusses the emerging mechanisms for generation of infantile spasms and their associated chronic epileptic and dyscognitive phenotype as well as the recent progress in identifying pathways to better treat this epileptic encephalopathy.

Animal models

Epilepsy accounts for a significant portion of the dis-ease burden worldwide. Research in this field is fundamental and mandatory. Animal models have played, and still play, a substantial role in understanding the patho-physiology and treatment of human epilepsies. A large number and variety of approaches are available, and they have been applied to many animals. In this chapter the in vitro and in vivo animal models are discussed,with major emphasis on the in vivo studies. Models have used phylogenetically different animals - from worms to monkeys. Our attention has been dedicated mainly to rodents.In clinical practice, developmental aspects of epilepsy often differ from those in adults. Animal models have often helped to clarify these differences. In this chapter, developmental aspects have been emphasized.Electrical stimulation and chemical-induced models of seizures have been described first, as they represent the oldest and most common models. Among these models, kindling raised great interest, especially for the study of the epileptogenesis. Acquired focal models mimic seizures and occasionally epilepsies secondary to abnormal cortical development, hypoxia, trauma, and hemorrhage.Better knowledge of epileptic syndromes will help to create new animal models. To date, absence epilepsy is one of the most common and (often) benign forms of epilepsy. There are several models, including acute pharmacological models (PTZ, penicillin, THIP, GBL) and chronic models (GAERS, WAG/Rij). Although atypical absence seizures are less benign, thus needing more investigation, only two models are so far available (AY-9944,MAM-AY). Infantile spasms are an early childhood encephalopathy that is usually associated with a poor out-come. The investigation of this syndrome in animal models is recent and fascinating. Different approaches have been used including genetic (Down syndrome,ARX mutation) and acquired (multiple hit, TTX, CRH,betamethasone-NMDA) models.An entire section has been dedicated to genetic models, from the older models obtained with spontaneous mutations (GEPRs) to the new engineered knockout, knocking, and transgenic models. Some of these models have been created based on recently recognized patho-genesis such as benign familial neonatal epilepsy, early infantile encephalopathy with suppression bursts, severe myoclonic epilepsy of infancy, the tuberous sclerosis model, and the progressive myoclonic epilepsy. The contribution of animal models to epilepsy re-search is unquestionable. The development of further strategies is necessary to find novel strategies to cure epileptic patients, and optimistically to allow scientists first and clinicians subsequently to prevent epilepsy and its consequences.

Increased seizure susceptibility induced by prenatal methamphetamine exposure in adult female rats is not affected by early postnatal cross-fostering

Our previous studies repeatedly demonstrated that prenatal methamphetamine (MA) exposure alters seizure susceptibility in adult rats. Both the inhibitory GABA system and the excitatory NMDA system play a role in the effect of MA on epileptic seizures. On the basis of our previous behavioral results, the effect of cross-fostering on seizure susceptibility in adult female rats was examined in the present study. Bicuculline (GABA(A) receptor antagonist) and NMDA (NMDA receptor agonist) were used to induce seizures in adult female offspring exposed to MA in the prenatal and/or preweaning periods. Female dams were injected with MA (5mg/kg daily) or physiological saline (S) for approximately 9 weeks [about 3 weeks prior to impregnation, for the entire gestation period (22 days), and in the preweaning period (21 days)]. Absolute controls (C) did not receive any injections. On postnatal day 1, pups were cross-fostered so that each mother received pups from all three treatments. Thus, nine groups (based on the prenatal and postnatal drug exposures) of adult female rats were tested in each seizure test: C/C, C/S, C/MA, S/C, S/S, S/MA, MA/C, MA/S, MA/MA. The present study demonstrated that both the excitatory NMDA system and the inhibitory GABA system are involved in the proconvulsive effect of MA during prenatal and partially also postnatal development in female rats. However, because our results did not show any improvement in seizure susceptibility in prenatally MA-exposed animals that were fostered by control mothers (MA/C) relative to their siblings fostered by MA-treated mothers (MA/MA), our hypothesis of the cross-fostering effect seems to be incorrect in contrast to our behavioral studies.

Effect of cross-fostering on seizures in adult male offspring of methamphetamine-treated rat mothers

Stimulant drugs are often associated with increased seizure susceptibility. Inhibitory gamma-aminobutyric acid (GABA) and excitatory N-methyl-D-aspartate (NMDA) systems play a role in the effect of stimulants in the genesis of epileptic seizures. Our previous studies showed that prenatal methamphetamine (MA) exposure induced long-term changes in seizure susceptibility. The aim of the present study was to investigate the effect of cross-fostering on the prenatal and postnatal MA-exposed rats, respectively, on their seizures in adulthood. Bicuculline (GABA(A) receptor antagonist), NMDA (NMDA receptor agonist) and flurothyl (a convulsant gas) were used to induce seizures in adult male offsprings. Female dams were injected with MA (5 mg/kg daily) or physiological saline (S) for approx. 9 week [about 3 week prior to impregnation, for the entire gestation period (22 days) and in preweaning period (21 days)]. Absolute controls (C) did not receive any injections. On postnatal day 1, pups were cross-fostered so that each mother received pups from all three treatments. Thus, nine groups (based on the prenatal and postnatal drug exposure) of adult male rats were tested in each seizure test: C/C; C/S; C/MA; S/C; S/S; S/MA; MA/C; MA/S; MA/MA. The present study demonstrates that the effect of prenatal and/or postnatal MA exposure is seizure model specific. In addition, our data show that there is an effect of cross-fostering on seizures; particularly, the effect of prenatal MA exposure shown in animals fostered by control mothers is no longer apparent in animals fostered postnatally by MA-treated mothers. Such effect of postnatal treatment is not manifested in prenatal controls. In summary, it seems that: (1) prenatal MA exposure alters seizure susceptibility more than postnatal MA exposure; (2) especially in seizures induced by chemicals that affect GABAergic system (bicuculline, flurothyl) notable effect of adoption (cross-fostering) is apparent; (3) in seizure models that are associated with NMDA system (NMDA, flurothyl), effect of prenatal stress seems to play a role.

Vigabatrin but not valproate prevents development of age-specific flexion seizures induced by N-methyl-D-aspartate (NMDA) in immature rats

In immature rats, N-methyl-D-aspartate (NMDA) induces several seizure types: flexion seizures (FS; in rats younger than 3 weeks), clonic seizures (in animals older than 3 weeks), and clonic-tonic seizures (CTS; in rats of all ages). FS represent a model of human infantile spasms. Effects of vigabatrin and valproate against all types of NMDA-induced seizures were studied in rats at postnatal days 12 (P12) and 25 (P25). NMDA (60 or 300 mg/kg) was injected to animals pretreated with vigabatrin (300-1,200 mg/kg; 24 h before NMDA) or valproate (100-400 mg/kg; 15 min before NMDA). Vigabatrin suppressed FS in P12 rats, but was ineffective against CTS in both age groups. Valproate suppressed CTS in P12, but not in P25 rats. Clonic seizures were rare in NMDA-treated P25 rats, but valproate pretreatment increased their incidence significantly. Neither drug decreased NMDA-induced mortality, which occurred within approximately 15 min after NMDA administration and reached almost 100% in all groups.

Comparative effects of levobupivacaine and racemic bupivacaine on excitotoxic neuronal death in culture and N-methyl-d-aspartate-induced seizures in mice

We compared the neurotoxic profile of racemic bupivacaine and levobupivacaine in: (i) a mouse model of N-methyl-D-aspartate (NMDA)-induced seizures and (ii) in an in vitro model of excitotoxic cell death. When used at high doses (36 mg/kg) both bupivacaine and levobupivacaine reduced the latency to NMDA-induced seizures and increased seizure severity. However, levobupivacaine-treated animals underwent less severe seizures as compared with bupivacaine-treated animals. Lower doses of levobupivacaine and bupivacaine had opposite effects on NMDA-induced seizures. At doses of 5 mg/kg, levobupivacaine increased the latency to partial seizures and prevented the occurrence of generalized seizures, whereas bupivacaine decreased the latency to partial seizures and did not influence the development of generalized seizures. In in vitro experiments, we exposed primary cultures of mouse cortical cells, containing both neurons and astrocytes, to 100 microM NMDA for 10 min for the induction of excitotoxic neuronal death. This treatment killed 70-80% of the neuronal population, as assessed 24 h after the excitotoxic pulse. In this particular model, both levobupivacaine and bupivacaine were neuroprotective against NMDA toxicity. However, neuroprotection by levobupivacaine was seen at lower concentrations (with respect to bupivacaine) and was maintained at concentrations of 3 mM, which are much higher than the plasma security threshold for the drug in vivo. In contrast, no protection against NMDA toxicity was detected when 3 mM concentrations of bupivacaine were applied to the cultures. Our data show a better neurotoxic profile of levobupivacaine as compared to racemic bupivacaine, and are indicative of a safer profile of levobupivacaine in clinical practice.

Quinolinic acid promotes seizures and decreases glutamate uptake in young rats: reversal by orally administered guanosine

Quinolinic acid (QA) has been used as a model for experimental overstimulation of the glutamatergic system. Glutamate uptake is the main mechanism involved in the maintenance of extracellular glutamate below toxic levels. Guanosine systemically administered prevents quinolinic acid-induced seizures in adult mice and increases basal glutamate uptake by cortical astrocyte culture and slices from young rats. The immature brain differs from the adult brain in its susceptibility to seizures, seizure characteristics, and responses to antiepileptic drugs (AED). Here we investigated the effect of guanosine p.o. on QA-induced seizures in young rats (P12-14) and upon ex vivo glutamate uptake by cortical slices from these animals. I.c.v. infusion of 250 nmol QA induced seizures in all animals and decreased glutamate uptake. I.p. injection of MK-801 and phenobarbital 30 min before QA administration prevented seizures in all animals. Guanosine (7.5 mg/kg) 75 min before QA prevented seizures in 50% of animals as well as prevented the decrease of glutamate uptake in the protected animals. To investigate if the anticonvulsive effect of guanosine was specific for QA-induced seizures, the picrotoxin-induced seizures model was also performed. Pretreatment with phenobarbital i.p. (60 mg/kg-30 min) prevented picrotoxin-induced seizures in all animals, whereas guanosine p.o. (7.5 mg/kg-75 min) and MK-801 i.p. (0.5 mg/kg-30 min) had no effect. Thus, guanosine protection on the QA-induced seizures in young rats and on the decrease of glutamate uptake showed some specificity degree towards the QA-induced toxicity. This points that guanosine could be considered for treatments of epilepsy, and possibly other neurological disorders in children.

NMDA-induced seizures in developing rats cause long-term learning impairment and increased seizure susceptibility

N-methyl-D-aspartate (NMDA) receptors play a prominent role in the pathogenesis of epilepsy, yet few studies have used NMDA as a convulsant in whole animals. In developing rats, systemic NMDA induces seizures with a unique seizure phenotype ("emprosthotonic" or hyperflexion seizures) and electrographic pattern (electrodecrement). These features are not seen in kainic acid-induced seizures, suggesting that seizures activated by NMDA might cause different long-term consequences. Therefore, we investigated the effects of NMDA seizures during development on cognitive function and susceptibility to seizures in adulthood. Rat pups (P12-20) were injected with saline (n=36) or NMDA (n=64) at convulsant doses (15-30mg/kg, i.p.). After NMDA injection, a characteristic sequence of seizure activity was seen: initial behavioral arrest, followed by hyperactivity, agitation, and then emprosthotonus and generalized tonic-clonic seizures. Seizures were terminated 30min later by ketamine (50mg/kg, i.p.). On P85, rats underwent behavioral testing in the water maze. Rats that had experienced NMDA seizures as pups took significantly longer to learn the platform location over 5 days of testing, compared to controls. On P90, rats were injected with pentylenetetrazol (PTZ, 50mg/kg, i.p.) to assess their susceptibility to generalized seizures. NMDA-treated rats had decreased latency and increased duration of class V PTZ seizures. Cresyl violet-stained sections of cortex and hippocampus had no obvious cell loss or gliosis. In summary, NMDA causes a unique seizure phenotype in the developing brain, with subsequent deficits in spatial learning and an increased susceptibility to PTZ seizures in adulthood. This study provides additional evidence for long-term alterations of neuronal excitability and cognitive capacity associated with seizures during development.

Toxic cocaine- and convulsant-induced modification of forced swimming behaviors and their interaction with ethanol: comparison with immobilization stress

BACKGROUND

Swimming behaviors in the forced swimming test have been reported to be depressed by stressors. Since toxic convulsion-inducing drugs related to dopamine [cocaine (COC)], benzodiazepine [methyl 6,7-dimethoxy-4-ethyl-beta-carboline-carboxylate (DMCM)], gamma-aminobutyric acid (GABA) [bicuculline (BIC)], and glutamate [N-methyl-D-aspartate (NMDA)] receptors can function as stressors, the present study compared their effects on the forced swimming behaviors with the effects of immobilization stress (IM) in rats. Their interactions with ethanol (EtOH), the most frequently coabused drug with COC which also induces convulsions as withdrawal symptoms but interferes with the convulsions caused by other drugs, were also investigated.

RESULTS

Similar to the IM (10 min) group, depressed swimming behaviors (attenuated time until immobility and activity counts) were observed in the BIC (5 mg/kg IP) and DMCM (10 mg/kg IP) groups at the 5 h time point, after which no toxic behavioral symptoms were observed. However, they were normalized to the control levels at the 12 h point, with or without EtOH (1.5 g/kg IP). In the COC (60 mg/kg IP) and NMDA (200 mg/kg IP) groups, the depression occurred late (12 h point), and was normalized by the EtOH cotreatment. At the 5 h point, the COC treatment enhanced the swimming behaviors above the control level.

CONCLUSIONS

Although the physiological stress (IM), BIC, and DMCM also depressed the swimming behaviors, a delayed occurrence and EtOH-induced recovery of depressed swimming were observed only in the COC and NMDA groups. This might be correlated with the previously-reported delayed responses of DA and NMDA neurons rather than direct effects of the drugs, which could be suppressed by EtOH. Furthermore, the characteristic psychostimulant effects of COC seemed to be correlated with an early enhancement of swimming behaviors.

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 microg/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.

Estrogen differentially alters NMDA- and kainate-induced seizures in prenatally morphine- and saline-exposed adult female rats

The purpose of the present study was to investigate the effects of prenatal exposure to morphine on seizure susceptibility in adult female rats. Adult female rats, exposed to saline or morphine on prenatal days 11-18, were ovariectomized (OVX) and some were injected 48 h prior to seizure testing with estradiol benzoate (EB). To assess the latency to onset of stereotypy and seizures, females received systemic injections of N-methyl-D-aspartate (NMDA; 150, 175, 200 mg/kg) or kainic acid (KA; 10 or 15 mg/kg). Prenatal morphine exposure increased the latency to onset of wet-dog-shakes (WDS) in both OVX and OVX, EB-injected females after the higher dose of KA. However, prenatal morphine exposure increased the latency to onset of stereotypy only in OVX, EB-injected females after the highest dose of NMDA. Prenatal morphine exposure also increased the latency to onset of seizures after the lower dose of KA, but did not change the latency to onset of NMDA-induced seizures. Additionally, an EB injection increased the latency to onset of seizures in both saline- and morphine-exposed females after the lowest dose of NMDA, but decreased the latency to onset of seizures after the lower dose of KA. Thus, the present study demonstrates that prenatal morphine exposure has different effects on the estrogen regulation of the onset of seizures and stereotypy induced by NMDA or KA in adult, OVX female rats.

N-Methyl-D-aspartic acid- and metaphit-induced audiogenic seizures in rat model of seizures

The effects of NMDA (N-methyl-D-aspartic acid) on metaphit (1-[1(3-isothiocyanatophenyl)-cyclohexyl]piperidine)-induced audiogenic seizures in adult male Wistar albino rats were studied with the aim of developing a suitable animal model of seizures. The animals were divided into four experimental groups: 1, saline control; 2, metaphit-injected; 3, metaphit + NMDA administered and 4, NMDA-treated. Upon the treatment, the rats were exposed to sound stimulation (100 +/- 3 dB, for 60 s) at hourly intervals and the incidence and severity (running, clonus and tonus) of seizures were analysed. In group 3, only the animals which did not exhibit any metaphit-induced audiogenic seizures over 8 h were given a subconvulsive NMDA dose after the eighth audiogenic testing. For EEG recordings, three gold-plated screws were implanted into the rat skull. In most animals, metaphit led to EEG abnormalities and elicited epileptiform activity recorded as spikes, polyspikes and spike-wave complexes. Maximum incidence and severity of metaphit-induced convulsions occurred 8 h after injection (incidence 9/12), abating gradually until disappearing 30 h later. NMDA alone provoked no seizure response but the initial signs characterized by isolated spike activity evolving into sporadic slow-wave complexes, thus representing a proconvulsive brain state, were observed. This compound led to stereotyped behaviour seen as asymmetric posture, loss of righting reflex and tonic hind limb extension lasting for 60-90 min. It also potentiated metaphit-induced audiogenic seizures. Potentiation of metaphit-related audiogenic seizures by NMDA was recorded in three out of 17 rats that had never displayed seizures in eight previous testings, with a maximum incidence of eight out of 17 animals, 13-14 h after metaphit administration and seizures lasted for 10 h.

Age-specific N-methyl-D-aspartate-induced seizures: perspectives for the West syndrome model

PURPOSE

With intraperitoneal N-methyl-D-aspartate (NMDA; 15-200 mg/kg) administration, we attempted to develop an animal model of age-specific West syndrome to serve for testing of putative anticonvulsant drugs and to determine the mechanisms of this disorder.

METHODS

Experiments were performed in 12-, 18-, and 60-day-old (adult) rats. The effects of systemic pretreatment with hydrocortisone (5-25 mg/kg), pyridoxine (20-250 mg/kg), and sodium valproate (VPA; 200 and 400 mg/kg) against the NMDA-induced automatisms, emprosthotonic (hyperflexion), and clonic-tonic seizures were determined. NMDA-induced EEG changes and alterations of the performance in horizontal bar, rotorod, open field, and elevated plus-maze tests were recorded.

RESULTS

In young rats, hydrocortisone had proconvulsant effects. High doses of pyridoxine induced epileptiform activity independent of and distinct from that induced by NMDA. Only VPA had moderate effects against the NMDA-induced syndrome. EEG consisted of periods of suppression mixed with ictal activity of serrated waves and high-voltage chaotic EEG activity. In adult rats, EEG alterations involved spike and spike-and-wave activity. NMDA also deteriorated performance of young rats in the open field, rotorod, and elevated plus maze tests.

CONCLUSIONS

NMDA syndrome in rats fulfills some, but not all, criteria of the West syndrome model, such as occurrence of flexion seizures, nonspecific diffuse EEG changes, refractoriness to antiepileptic therapy (but a response to VPA), as well as long-term alteration of behavioral tasks. However, NMDA-induced seizures represent an acute model without the occurrence of spontaneous seizures, whereas in the clinical situation, both the seizures and neurologic deterioration are chronic. Further, in the West syndrome and the NMDA seizure model, there is an incongruent response to therapy with antiepileptic drugs.