Ketamine suppresses both bicuculline- and picrotoxin-induced generalized tonic-clonic seizures during ontogenesis

Respiratory activity during seizures induced by pentylenetetrazole

This study investigated the respiratory activity in adult Wistar rats across different behavioral seizure severity induced by pentylenetetrazole (PTZ). Animals underwent surgery for electrodes implantation, allowing simultaneous EEG and diaphragm EMG (DIAEMG) recordings and the respiratory frequency and DIAEMG amplitude were measured. Seizures were acutely induced through PTZ injection and classified based on a pre-established score, with absence-like seizures (spike wave discharge (SWD) events on EEG) representing the lowest score. The respiratory activity was grouped into the different seizure severities. During absence-like and myoclonic jerk seizures, the breathing frequency decreased significantly (∼50% decrease) compared to pre- and post-ictal periods. Pronounced changes occurred with more severe seizures (clonic and tonic) with periods of apnea, especially during tonic seizures. Apnea duration was significantly higher in tonic compared to clonic seizures. Notably, during PTZ-induced tonic seizures the apnea events were marked by tonic DIAEMG contraction (tonic-phase apnea). In the majority of animals (5 out of 7) this was a fatal event in which the seizure-induced respiratory arrest preceded the asystole. In conclusion, we provide an assessment of the respiratory activity in the PTZ-induced acute seizures and showed that breathing dysfunction is more pronounced in seizures with higher severity.

Hidden behavioral fingerprints in epilepsy

Epilepsy is a major disorder affecting millions of people. Although modern electrophysiological and imaging approaches provide high-resolution access to the multi-scale brain circuit malfunctions in epilepsy, our understanding of how behavior changes with epilepsy has remained rudimentary. As a result, screening for new therapies for children and adults with devastating epilepsies still relies on the inherently subjective, semi-quantitative assessment of a handful of pre-selected behavioral signs of epilepsy in animal models. Here, we use machine learning-assisted 3D video analysis to reveal hidden behavioral phenotypes in mice with acquired and genetic epilepsies and track their alterations during post-insult epileptogenesis and in response to anti-epileptic drugs. These results show the persistent reconfiguration of behavioral fingerprints in epilepsy and indicate that they can be employed for rapid, automated anti-epileptic drug testing at scale.

S-ketamine alleviates carbon tetrachloride-induced hepatic injury and oxidative stress by targeting the Nrf2/HO-1 signaling pathway

The aim of the present study was to investigate the protective effect of S-ketamine (S-KET) against carbon tetrachloride (CCl4) - induced liver damage and oxidative stress, as well as to elucidate the related underlying mechanisms. Blood was collected to measure biochemical parameters (alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), total bilirubin (TB) and γ-glutamyltransferase (γ-GT)) and the liver was harvested for histopathological analysis of enzymes related to the antioxidant response (malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), and glutathione peroxidase (GSH-PX)). Liver cell apoptosis was evaluated using the TUNEL assay. In addition, the expression levels of apoptosis-related proteins and the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathway were detected by Western blot analysis to explore potential mechanisms. S-KET protected the liver from CCl4-induced damage. The changes to the liver biochemical parameters (increased ALT, AST, ALP, TB, and γ-GT) and oxidative stress-related indicators (increased MDA; depleted SOD, GSH, and GSH-PX) induced by CCl4 were inhibited by S-KET. S-Ket also inhibited CCl4-induced cell apoptosis, the changes in expression of related proteins, and blocked CCl4-induced liver injury and oxidative stress via activation of the Nrf2/HO-1 signaling pathway. S-KET effectively protected the liver by inhibition of CCl4-induced damage via upregulation the Nrf2/HO-1 signaling pathway.

Noninvasive transcranial focal stimulation affects the convulsive seizure-induced P-glycoprotein expression and function in rats

Transcranial focal stimulation (TFS) is a noninvasive neuromodulation strategy that reduces seizure activity in different experimental models. Nevertheless, there is no information about the effects of TFS in the drug-resistant phenotype associated with P-glycoprotein (Pgp) overexpression. The present study focused on determining the effects of TFS on Pgp expression after an acute seizure induced by 3-mercaptopropionic acid (MPA). P-glycoprotein expression was analyzed by western blot in the cerebral cortex and hippocampus of rats receiving 5 min of TFS (300 Hz, 50 mA, 200 μs, biphasic charge-balanced squared pulses) using a tripolar concentric ring electrode (TCRE) prior to administration of a single dose of MPA. An acute administration of MPA induced Pgp overexpression in cortex (68 ± 13.4%, p < 0.05 vs the control group) and hippocampus (48.5 ± 14%, p < 0.05, vs the control group). This effect was avoided when TFS was applied prior to MPA. We also investigated if TFS augments the effects of phenytoin in an experimental model of drug-resistant seizures induced by repetitive MPA administration. Animals with MPA-induced drug-resistant seizures received TFS alone or associated with phenytoin (75 mg/kg, i.p.). TFS alone did not modify the expression of the drug-resistant seizures. However, TFS combined with phenytoin reduced seizure intensity, an effect associated with a lower prevalence of major seizures (50%, p = 0.03 vs phenytoin alone). Our experiments demonstrated that TFS avoids the Pgp overexpression induced after an acute convulsive seizure. In addition, TFS augments the phenytoin effects in an experimental model of drug-resistant seizures. According with these results, it is indicated that TFS may represent a new neuromodulatory strategy to revert the drug-resistant phenotype.

X-linked cellular mosaicism underlies age-dependent occurrence of seizure-like events in mouse models of CDKL5 deficiency disorder

CDKL5 deficiency disorder (CDD) is an infantile, epileptic encephalopathy presenting with early-onset seizures, intellectual disability, motor impairment, and autistic features. The disorder has been linked to mutations in the X-linked CDKL5, and mouse models of the disease recapitulate several aspects of CDD symptomology, including learning and memory impairments, motor deficits, and autistic-like features. Although early-onset epilepsy is one of the hallmark features of CDD, evidence of spontaneous seizure activity has only recently been described in Cdkl5-deficient heterozygous female mice, but the etiology, prevalence, and sex-specificity of this phenotype remain unknown. Here, we report the first observation of disturbance-associated seizure-like events in heterozygous female mice across two independent mouse models of CDD: Cdkl5 knockout mice and CDKL5 R59X knock-in mice. We find that both the prevalence and severity of this phenotype increase with aging, with a median onset around 28 weeks of age. Similar seizure-like events are not observed in hemizygous knockout male or homozygous knockout female littermates, suggesting that X-linked cellular mosaicism is a driving factor underlying these seizure-like events. Together, these findings not only contribute to our understanding of the effects of CDKL5 loss on seizure susceptibility, but also document a novel, pre-clinical phenotype for future therapeutic investigation.

Tetramethylenedisulfotetramine neurotoxicity: What have we learned in the past 70 years?

Tetramethylenedisulfotetramine (tetramine, TETS, TMDT) is a seizure-producing neurotoxic chemical formed by the condensation of sulfamide and formaldehyde. Serendipitously discovered through an occupational exposure in 1949, it was promoted as a rodenticide but later banned worldwide due to its danger to human health. However, exceptional activity of the agent against rodent pests resulted in its clandestine manufacture with large numbers of inadvertent, intentional, and mass poisonings, which continue to this day. Facile synthesis, extreme potency, persistence, lack of odor, color, and taste identify it as an effective food adulterant and potential chemical agent of terror. No known antidote or targeted treatment is currently available. In this review we examine the origins of tetramethylenedisulfotetramine, from its identification as a neurotoxicant 70 years ago, through early research, to the most recent findings including the risk it poses in the post-911 world. Included is the information known regarding its in vitro pharmacology as a GABA_A receptor channel antagonist, the toxic syndrome it produces in vivo, and its effect upon vulnerable populations. We also summarize the available information about potential therapeutic countermeasures and treatment strategies as well as the contribution of clinical development of TMDT poisoning to our understanding of epileptogenesis. Finally we identify gaps in our knowledge and suggest potentially fruitful directions for continued research on this dangerous, yet intriguing compound.

Blockade of GluN2B-containing NMDA receptors reduces short-term brain damage induced by early-life status epilepticus

Status epilepticus (SE) during developmental periods can cause short- and long-term consequences to the brain. Brain damage induced by SE is associated to NMDA receptors (NMDAR)-mediated excitotoxicity. This study aimed to investigate whether blockade of GluN2B-containing NMDAR is neuroprotective against SE-induced neurodegeneration and neuroinflammation in young rats. Forty-eight Wistar rats (16 days of life) were injected with pilocarpine (60 mg/kg; i.p.) 12-18 h after LiCl (3 mEq/kg; i.p.). Fifteen minutes after pilocarpine administration, animals received i.p. injections of saline solution (0.9% NaCl; SE + SAL group), ketamine (a non-selective and noncompetitive NMDAR antagonist; 25 mg/kg; SE + KET), CI-1041 (a GluN2B-containing NMDAR antagonist; 10 mg/kg; SE + CI group) or CP-101,606 (a NMDAR antagonist with great selectivity for NMDAR composed by GluN1/GluN2B diheteromers; 10 mg/kg; SE + CP group). Seven days after SE, brains were removed for Fluoro-Jade C staining and Iba1/ED1 immunolabeling. GluN2B-containing NMDAR blockade by CI-1041 or CP-101,606 did not terminate LiCl-pilocarpine-induced seizures. SE + SAL group presented intense neurodegeneration and Iba1⁺/ED1⁺ double-labeling in hippocampus (CA1 and dentate gyrus; DG) and amygdala (MePV nucleus). Administration of CP-101,606 did not alter this pattern. However, GluN2B-containing NMDAR blockade by CI-1041 reduced neurodegeneration and Iba1⁺/ED1⁺ double-labeling in hippocampus and amygdala similar to the reduction observed for SE + KET group. Our results indicate that GluN2B-containing NMDAR are involved in SE-induced neurodegeneration and microglial recruitment and activation, and suggest that stopping epileptic activity is not a condition required to prevent short-term brain damage in young animals.

Treatment with lacosamide impedes generalized seizures in a rodent model of cortical dysplasia

OBJECTIVE

Epilepsy is a common neurologic disorder resulting in spontaneous, recurrent seizures. About 30-40% of patients are not responsive to pharmacologic therapies. This may be due to the differences between individual patients such as etiology, underlying pathophysiology, and seizure focus, and it highlights the importance of new drug discovery and testing in this field. Our goal was to determine the efficacy of lacosamide (LCM), a drug approved for the treatment of focal seizures, in a model of generalized epilepsy with cortical dysplasia (CD). We sought to compare LCM to levetiracetam (LEV), a drug that is currently used for the treatment of both partial and generalized epilepsy and to test its proficiency.

METHODS

Pregnant rats were irradiated to produce pups with malformed cortices in a model of CD, which will be referred to as the "first hit." Adult animals, developed normally (NL) and irradiated (XRT), were surgically implanted with electroencephalography (EEG) electrodes. Baseline EEG was recorded on all rats prior to pretreatments with either LCM, LEV, or placebo (PBO). After 30 min, all rats were injected with a subconvulsive dose of pentylenetetrazole (PTZ), a γ-aminobutyric acid receptor A (GABA_A ) antagonist used to provoke generalized seizures as a "second hit."

RESULTS

LCM and LEV were both effective against seizures induced by PTZ. XRT rats had a higher seizure incidence with longer and more severe seizures than NL rats. Seizure duration was decreased with both LCM and LEV in all animals. In XRT rats, there was a significant reduction in acute seizure incidence and severity with both LCM and LEV after PTZ injection.

SIGNIFICANCE

Our results suggest that LCM could be used as a potential treatment option for generalized epilepsy with CD as the underlying pathology.

Tetramethylenedisulfotetramine: pest control gone awry

Incidences of pesticide poisonings are a significant cause of morbidity and mortality worldwide. The seizure-inducing rodenticide tetramethylenedisulfotetramine is one of the most toxic of these agents. Although banned, it has been responsible for thousands of accidental, intentional, and mass poisonings in mainland China and elsewhere. An optimal regimen for treatment of poisoning has not been established. Its facile synthesis from easily obtained starting materials, extreme potency, and lack of odor, color, or taste make it a potential chemical threat agent. This review describes the toxicologic properties of this agent, more recent advances in our understanding of its properties, and recommendations for future research.

Anesthetic and pathological changes following high doses of ketamine and xylazine in Sprague Dawley rats

The main objective of this study was to compare the effects of ketamine and xylazine in aging rats when coadministered intraperitoneally at high anesthetic doses. Three groups (n=6 rats/group) consisting of rats at 3, 6 and 12 months of age were used. During anesthesia, animals were monitored for heart rate, respiratory frequency, blood oxygen saturation, and rectal temperature. The corneal and paw withdrawal reflex were also examined during anesthesia. During anesthesia, withdrawal and corneal reflexes were absent for progressively longer durations with increasing age. Significant decreases in cardiac and respiratory frequency and, blood oxygen saturation occurred for the 6- and 12-month-old animals. Respiratory frequency and blood oxygen saturation returned to normal at the end of the anesthesia; however, the significant decrease in cardiac frequency persisted in the 6- and 12-month-old animals. Rectal temperature was decreased significantly only in the 3-month-old animals. Pulmonary edema and effusion occurred in 50% of the 12-month-old animals. In conclusion, if ketamine-xylazine are used for anesthesia, the doses should be optimized for the age of the subjects prior to initiation of the research project.

Optogenetic inhibition of chemically induced hypersynchronized bursting in mice

Synchronized activity is common during various physiological operations but can culminate in seizures and consequently in epilepsy in pathological hyperexcitable conditions in the brain. Many types of seizures are not possible to control and impose significant disability for patients with epilepsy. Such intractable epilepsy cases are often associated with degeneration of inhibitory interneurons in the cortical areas resulting in impaired inhibitory drive onto the principal neurons. Recently emerging optogenetic technique has been proposed as an alternative approach to control such seizures but whether it may be effective in situations where inhibitory processes in the brain are compromised has not been addressed. Here we used pharmacological and optogenetic techniques to block inhibitory neurotransmission and induce epileptiform activity in vitro and in vivo. We demonstrate that NpHR-based optogenetic hyperpolarization and thereby inactivation of a principal neuronal population in the hippocampus is effectively attenuating seizure activity caused by disconnected network inhibition both in vitro and in vivo. Our data suggest that epileptiform activity in the hippocampus caused by impaired inhibition may be controlled by optogenetic silencing of principal neurons and potentially can be developed as an alternative treatment for epilepsy.

Treatment of status epilepticus with ketamine, are we there yet?

Status epilepticus (SE), a neurological emergency both in adults and in children, could lead to brain damage and even death if untreated. Generalized convulsive SE (GCSE) is the most common and severe form, an example of which is that induced by organophosphorus nerve agents. First- and second-line pharmacotherapies are relatively consensual, but if seizures are still not controlled, there is currently no definitive data to guide the optimal choice of therapy. The medical community seems largely reluctant to use ketamine, a noncompetitive antagonist of the N-methyl-d-aspartate glutamate receptor. However, a review of the literature clearly shows that ketamine possesses, in preclinical studies, antiepileptic properties and provides neuroprotection. Clinical evidences are scarcer and more difficult to analyze, owing to a use in situations of polytherapy. In absence of existing or planned randomized clinical trials, the medical community should make up its mind from well-conducted preclinical studies performed on appropriate models. Although potentially active, ketamine has no real place for the treatment of isolated seizures, better accepted drugs being used. Its best usage should be during GCSE, but not waiting for SE to become totally refractory. Concerns about possible developmental neurotoxicity might limit its pediatric use for refractory SE.

Sensitive and critical periods in the development of handling induced seizures in mice lacking synapsins: differences between synapsin I and synapsin II knockouts

Mice lacking either synapsin I or synapsin II develop handling induced seizures from around two months of age. In mice lacking synapsin I (synapsin 1 knock-out mice, Syn1KO mice) such seizures can either consist of mild myoclonic jerks or of fully developed generalized tonic-clonic seizures, and the two seizure types are quite evenly distributed. In mice lacking synapsin II (synapsin 2 knock-out mice, Syn2KO mice) all seizures are in the form of generalized tonic-clonic seizures. Through the use of specialized animal rearing procedures whereby human-animal interaction was minimized (minimal handling procedures), this study investigated effects of handling also prior to the emergence of actual seizures. The effect of minimal handling procedures was significant in both genotypes, but most pronounced in Syn1KO mice. In this genotype, minimal handling reduced the frequency of mild seizures, and completely eliminated generalized tonic-clonic seizures when the animals were tested with regular handling at 4 1/2 months of age. Neither seizure frequency nor generalized tonic-clonic seizures could be re-established through regular handling from 4 1/2 to 8 months. This suggests that the period up to 4 1/2 months constitute a sensitive period for seizures in general, and a critical period for generalized tonic-clonic seizures in this genotype. In Syn2KO mice minimal handling did not remove generalized tonic-clonic seizures, as such seizures were present when handling was introduced at 4 1/2 months. We found an initial reduction of seizure frequency, but the seizure frequency eventually reached levels seen in mice kept under regular handling regimes. Thus, it is unlikely that the period up to 4 1/2 months is a sensitive period in the Syn2KO genotype.

Ketamine prevents seizures and reverses changes in muscarinic receptor induced by bicuculline in rats

The cholinergic system has been implicated in several experimental epilepsy models. In a previous study bicuculline (BIC), known to antagonize GABA-A postsynaptic receptor subtype, was administered to rats at subconvulsant (1mg/kg) and convulsant (7.5mg/kg) doses and quinuclidinyl benzilate ([(3)H]-QNB) binding to CNS membranes was determined. It was observed that ligand binding to cerebellum increases while it decreases in the case of hippocampus. Saturation binding curves showed that changes were due to the modification of receptor affinity for the ligand without alteration of binding site number. The purpose of this study was to assay muscarinic receptors employing other BIC dose (5mg/kg), which induces seizures and allows the analysis of a postseizure stage as well. To study further muscarinic receptor involvement in BIC induced seizures, KET was also employed since it is a well known anticonvulsant in some experimental models. The administration of BIC at 5mg/kg to rats produced a similar pattern of changes in [(3)H]-QNB binding to those recorded with 1.0 and 7.5mg/kg doses. Here again, changes were observed in receptor binding affinity without alteration in binding site number for cerebellum or hippocampus membranes. Pretreatment with KET (40 mg/kg) prevented BIC seizures and reverted [(3)H]-QNB binding changes induced by BIC administration. The single administration of KET invariably resulted in [(3)H]-QNB binding decrease to either cerebellar or hippocampal membranes. KET added in vitro decreased ligand binding likewise. Results of combined treatment with KET plus BIC are hardly attributable to the single reversion of BIC effect since KET alone invariably decreased ligand binding. It is suggested that besides alteration of cholinergic muscarinic receptor other(s) neurotransmitter system(s) may well also be involved.

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.

Ketamine reduces neuronal degeneration and anxiety levels when administered during early life-induced status epilepticus in rats

Status epilepticus (SE) when occurred during brain development can cause short- and long-term consequences, which are frequently associated with NMDA-mediated glutamatergic excitotoxicity. In the present work, we investigated the putative neuroprotective role of ketamine, an NMDA receptor antagonist, on early life SE-induced acute neuronal death and long-term behavioral abnormalities. Male Wistar rats (16 postnatal days) were induced to SE by LiCl-pilocarpine i.p. administration (3 mEq/kg; 60 mg/kg, respectively). Fifteen or 60min after pilocarpine injection, animals received a ketamine administration (22.5mg/kg i.p.). Neuronal degeneration was assessed 24h after SE induction. Another subset of animals was destined to behavioral tasks in adulthood (75-80 postnatal days). Fluoro-Jade C labeling revealed a marked neuronal death on CA1 hippocampal subfield, habenula, thalamus and amygdala in SE animals. Ketamine post-SE onset treatment prevented neuronal death in all regions assessed. In the elevated plus maze, SE induced an increase in anxiety-like behaviors whereas ketamine administration during seizures was able to prevent this alteration. Ketamine administration in non-SE animals resulted in high anxiety levels. There were no observed differences among groups in the open field task in all parameters analyzed. Our results suggest that ketamine post-SE onset treatment was effective in preventing acute and long-standing alterations caused by SE early in life, which indicates a putative role of glutamatergic system on SE-induced brain damage as well as long-lasting behavioral consequences.

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.

The NMDA receptor complex as a therapeutic target in epilepsy: a review

A substantial amount of research has shown that N-methyl-D-aspartate receptors (NMDARs) may play a key role in the pathophysiology of several neurological diseases, including epilepsy. Animal models of epilepsy and clinical studies demonstrate that NMDAR activity and expression can be altered in association with epilepsy and particularly in some specific seizure types. NMDAR antagonists have been shown to have antiepileptic effects in both clinical and preclinical studies. There is some evidence that conventional antiepileptic drugs may also affect NMDAR function. In this review, we describe the evidence for the involvement of NMDARs in the pathophysiology of epilepsy and provide an overview of NMDAR antagonists that have been investigated in clinical trials and animal models of epilepsy.

Chronobiological Study of the Pharmacological Response of Rats to Combination Ketamine–Midazolam

Ketamine is commonly administered in combination with benzodiazepines to achieve surgical anaesthesia in rats. The aim of the present study was to analyze the pharmacological response of the combination ketamine-midazolam injected intraperitoneally at different times of day to rats. The study was conducted in July 2003, during the winter in the Southern hemisphere. Female prepuberal Sprague-Dawley rats synchronized to a 12h light:12h dark cycle (light, 07:00-19:00h) were used as experimental animals. A combination treatment of ketamine (40 mg/kg) and midazolam (2 mg/kg) was administered to five different clock-time groups of rats (n=7/group). Duration of the latency period, ataxia, loss-of-righting reflex (LRR), post-LRR ataxia, and total pharmacological response were assessed by visual assessment. Significant treatment-time differences were detected in the duration of LRR, post-LRR ataxia, and total pharmacological response duration. The longest pharmacological response occurred in rats injected during the light (rest) phase, and the shortest pharmacological response occurred in rats injected during the dark (activity) phase. Cosinor analysis documented circadian rhythmicity in the duration of post-LRR ataxia. The findings of the study indicate the duration of CNS-depression of the ketamine-midazolam combination exhibits treatment-time-dependent variation in the rat.

KETAMINE REDUCES LIDOCAINE-INDUCED SEIZURES IN MICE

Systemic toxic reactions to local anesthetics are brought about by absolute overdosage, and, most commonly, inadvertent intravascular injections. The anti-convulsant action of ketamine has been studied. However, the effect of ketamine on lidocaine-induced convulsions has not been reported. This study investigated the effect of ketamine on lidocaine-induced seizures in mice. Mice (32-41 g) were divided into 2 groups, 15 in each group, and were pretreated with intraperitoneal normal saline solution or intraperitenoeal (ip) ketamine before lidocaine. Group 1 (N = 15) received 75 mg kg ip lidocaine; Group 2 (N = 15) received 20 mg kg ketamin ip; 5 min later 75 mg kg lidokaine ip were applied. Clinical features, incidences, latencies, durations, and mortality rate of convulsions were recorded. After 75 mg kg lidocaine injection, ataxia, loss of righting reflex, and generalized tonic-clonic convulsions were seen within 2-5 min in Group 1. Generalized tonic-clonic convulsions were seen in 8 mice and deep sedation was seen in 7 mice in Group 2 (p < .05). Generalized status epilepticus occurred in one mouse in both groups. Three mice from Group l and one mouse from Group 2 died during convulsions. There were no differences between the two groups with regard to the onset and duration of seizures (p > .05). It was concluded that ketamine significantly prevented lidocaine-induced generalized tonic-clonic seizures; on the other hand, the lethality of lidocaine was least reduced by ketamine.

Effects of postnatal caffeine exposure on seizure susceptibility in developing rats

Postnatal caffeine treatment of rats can influence brain excitability during development. To study the mechanism involved in the alterations of seizure susceptibility, we used an animal model that corresponds to the infants treated with caffeine for apnea of prematurity. Seizure susceptibility to four convulsant drugs (pentetrazol, picrotoxin, bicuculline and aminophylline) was assessed in 12- and 25-day-old rats exposed to caffeine at a daily dose of 10 and/or 20 mg/kg s.c. at postnatal days 7-11. Our results demonstrated that the changes in generalized tonic-clonic seizures (GTCS) are more expressed than changes in minimal clonic seizures. There are marked differences among individual convulsants with the highest sensitivity of aminophylline-induced seizures and nearly complete resistance of bicuculline-induced seizures. The changes in individual models are age specific: aminophylline- and picrotoxin-induced seizures are more affected in 12- than in 25-day-old rats whereas PTZ-induced seizures are more changed by early postnatal caffeine exposure in 25- than in 12-day-old animal. Taken together, repeated caffeine treatment from postnatal day 7 to 11 reduces the seizure susceptibility during development and this reduction is also model specific.

Behavioral effects of ketamine and toxic interactions with psychostimulants

Background

The anesthetic drug ketamine (KT) has been reported to be an abused drug and fatal cases have been observed in polydrug users. In the present study, considering the possibility of KT-enhanced toxic effects of other drugs, and KT-induced promotion of an overdose without making the subject aware of the danger due to the attenuation of several painful subjective symptoms, the intraperitoneal (i.p.) KT-induced alterations in behaviors and toxic interactions with popular co-abused drugs, the psychostimulants cocaine (COC) and methamphetamine (MA), were examined in ICR mice.

Results

A single dose of KT caused hyperlocomotion in a low (30 mg/kg, i.p.) dose group, and hypolocomotion followed by hyperlocomotion in a high (100 mg/kg, i.p.) dose group. However, no behavioral alterations derived from enhanced stress-related depression or anxiety were observed in the forced swimming or the elevated plus-maze test. A single non-fatal dose of COC (30 mg/kg, i.p.) or MA (4 mg/kg, i.p.) caused hyperlocomotion, stress-related depression in swimming behaviors in the forced swimming test, and anxiety-related behavioral changes (preference for closed arms) in the elevated plus-maze test. For the COC (30 mg/kg) or MA (4 mg/kg) groups of mice simultaneously co-treated with KT, the psychostimulant-induced hyperlocomotion was suppressed by the high dose KT, and the psychostimulant-induced behavioral alterations in the above tests were reversed by both low and high doses of KT. For the toxic dose COC (70 mg/kg, i.p.)- or MA (15 mg/kg, i.p.)-only group, mortality and severe seizures were observed in some animals. In the toxic dose psychostimulant-KT groups, KT attenuated the severity of seizures dose-dependently. Nevertheless, the mortality rate was significantly increased by co-treatment with the high dose KT.

Conclusion

Our results demonstrated that, in spite of the absence of stress-related depressive and anxiety-related behavioral alterations following a single dose of KT treatment, and in spite of the KT-induced anticonvulsant effects and attenuation of stress- and anxiety-related behaviors caused by COC or MA, the lethal effects of these psychostimulants were increased by KT.

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

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

Bicuculline seizure susceptibility and nigral GABAA alpha1 receptor mRNA is altered in adult prenatally morphine-exposed females

Prenatal morphine exposure (5-10 mg/kg twice daily on gestation days 11-18) can adversely affect neurological development, including seizure susceptibility. The present study examines the effects of prenatal morphine exposure on seizure susceptibility to the GABA antagonist and convulsant bicuculline and GABA(A) alpha(1) receptor mRNA in the substantia nigra (SN) of female rats. The results demonstrate that prenatally morphine-exposed ovariectomized (OVX) females and OVX females with estradiol benzoate (EB) replacement have an increased latency to seizure onset compared to controls. In addition, prenatal morphine exposure decreases the area covered by grains of GABA(A) alpha(1) receptor mRNA in the anterior SN in both OVX and EB+progesterone (P)-treated groups, and decreases the number of GABA(A) alpha(1) receptor mRNA-labeled cells/field in EB females. Furthermore, prenatally morphine- and saline-exposed EB and EB+P females had decreased GABA(A) alpha(1) receptor mRNA-labeled cells/field in the anterior SN compared to OVX animals of the same prenatal exposure. These results demonstrate that the long term effects of prenatal morphine exposure in female rats is dependent on their hormonal status, and suggest that seizure susceptibility may be altered via neuropharmacological changes in the GABA system in the SN.

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

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

Treatment-time-dependent difference of ketamine pharmacological response and toxicity in rats

Circadian rhythms impact many physiological functions that may affect drug pharmacological response. Ketamine is a dissociative agent commonly used for surgical anesthesia in rats. The aim of the present study was to analyze the central nervous system (CNS) depression and lethality of ketamine injected intraperitoneally at different times during the 24 h. The study was conducted in October 2001, spring in the Southern hemisphere. Female prepuberal Sprague-Dawley rats synchronized to a 12h light: 12h dark cycle (light, 07:00h-19:00h) were studied. Ketamine (40 mg/kg) was administered to one of six different clock-time treatment groups (n = 6-7 rats each). Duration of latency period, ataxia, loss of righting reflex (LRR), post-LRR ataxia, and total pharmacological response were determined by visual assessment. To investigate acute toxicity, ketamine lethal dose 50 (148.0 mg/kg) was also administered as a single injection to six different treatment-time groups of rats. Significant temporal differences and circadian rhythms were detected in drug-induced post-LRR ataxia and total pharmacological response duration. The longest pharmacological response occurred in rats injected during the light (rest) phase and the shortest response in the dark (activity) phase. No circadian rhythm was detected in acute toxicity. The study findings indicate that the duration of CNS depression of ketamine in rats exhibits circadian rhythmic variation.

Prenatal morphine exposure decreases susceptibility of adult male rat offspring to bicuculline seizures

The purpose of this study was to investigate the effect of prenatal exposure to morphine (5-10 mg/kg twice daily on days 11-18 of gestation) on bicuculline seizure susceptibility and to examine the interaction of prenatal morphine exposure and hormonal background in adult male rats. The data demonstrate that prenatal morphine exposure does not affect clonic but decreases susceptibility to tonic-clonic bicuculline seizures in intact male rats. Thus, the present data support our previous work demonstrating alterations in seizure susceptibility of adult morphine-exposed animals.

Prenatal morphine exposure induces age- and sex-dependent changes in seizure susceptibility

1. Prenatal exposure to morphine induces long-term alterations in seizure susceptibility, which are age-, sex-, and seizure model-specific. 2. Adult male and female rats exposed prenatally to morphine show decreased susceptibility to GABA-regulated seizures. 3. Prenatally morphine-exposed, adult male rats are more sensitive to excitatory amino acid receptor-mediated seizures than control males, control females, or morphine-exposed females.

Evidence for GABA(A) receptor agonistic properties of ketamine: convulsive and anesthetic behavioral models in mice

We examined the potentiation by ketamine of the gamma-aminobutyric acid(A) (GABA(A)) receptor function using convulsive and anesthetic behavioral models in adult male ddY mice. General anesthetic potencies were evaluated by a rating scale, which provided the data for anesthetic scores, loss of righting reflex, duration, and recovery time. All drugs were administered intraperitoneally. Small subanesthetic doses of ketamine did inhibit tonic seizures induced by a large dose of the GABA(A) receptor antagonist bicuculline (8 mg/kg). The 50% effective dose value was 15 (95% confidence limits 10-22) mg/kg. Even large anesthetic doses (100-150 mg/kg) did not suppress clonic seizures in 50% of the animals. The GABA(A) receptor agonist, muscimol (0.32-1.12 mg/kg), potentiated ketamine-induced anesthesia in a dose-dependent fashion (P < 0.05). Similarly, the benzodiazepine receptor agonist, diazepam (1-3 mg/kg), augmented ketamine anesthesia in a dose-dependent manner (P < 0.05). Bicuculline (2-5 mg/kg) dose-dependently antagonized ketamine-induced anesthesia (P < 0.05). Neither the benzodiazepine receptor antagonist, flumazenil (2-20 mg/kg), nor the GABA synthesis inhibitor, L-allylglycine (200 mg/kg), affected the anesthetic action of ketamine. These results suggest that ketamine has GABA(A) receptor agonistic properties and that ketamine-induced anesthesia is mediated, at least in part, by GABA(A) receptors.

IMPLICATIONS

We examined the potentiation by ketamine of the gamma-aminobutyric acid(A) receptor function using convulsive and anesthetic behavioral models in mice. Subanesthetic doses of ketamine-inhibited tonic convulsions induced by the gamma-aminobutyric acid(A) receptor antagonist bicuculline. The gamma-aminobutyric acid(A) receptor agonist, muscimol, potentiated ketamine-induced anesthesia. Bicuculline antagonized ketamine anesthesia, but the benzodiazepine receptor antagonist, flumazenil, and the gamma-aminobutyric acid synthesis inhibitor, L-allyglycine, did not. The effects of ketamine on the gamma-aminobutyric acid(A) receptors appear to correlate with its anesthetic actions.

Prenatal morphine exposure alters susceptibility to bicuculline seizures in a sex- and age-specific manner

Bicuculline was used to investigate seizure susceptibility in pre- and peripubertal male and female rats exposed prenatally to morphine. Morphine-exposed males showed increased seizure susceptibility at prepubertal and decreased susceptibility at peripubertal ages. There was no difference in seizure susceptibility in morphine-exposed females at either age. Therefore, the present data suggest that males are more vulnerable than females to morphine-induced insults during prenatal brain development.

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.

Acute effects of MK801 on kainic acid-induced seizures in neonatal rats

Kainic acid (KA) causes behavioral and electrographic status epilepticus (SE) in rats of all ages. In adult rats, the noncompetitive N-methyl-D-aspartate (NMDA) channel blocker MK801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine ) is anticonvulsant against KA-induced seizures: it reduces their severity and protects against neuronal damage, although it may worsen electrographic seizures. Here we examined the effects of MK801 on KA seizures in the immature brain. Neonatal rats (P11-P12) were pretreated with MK801 (0.01, 0.1, 0.5 or 1.0 mg/kg, i.p.) or saline twenty minutes prior to KA (2 mg/kg, i.p.). Clinical seizure behavior was monitored for > 6 hrs, and in some rats the EEG was monitored with an intrahippocampal or intracortical electrode. MK801 caused immobility alternating with hyperactivity, ataxia, scratching and sometimes alternate limb cycling, which correlated with the appearance of spikes on the EEG. Compared to KA alone or KA preceded by 0.01 mg/kg MK801, the higher doses of MK801 (0.1, 0.5 and 1.0 mg/kg) significantly lowered the latency to electrographic seizures (P < 0.001), ictal scratching (P < 0.0001), and status epilepticus (P < 0.0001). MK801 pretreatment did not lower significantly the death rate due to KA seizures. No histologic damage was seen after MK801, KA or both agents together. These results suggest that MK801 exacerbates KA-induced seizures in the neonatal brain, and may even cause ictal behavioral and electrographic manifestations by itself. The findings point to an age-dependency of NMDA antagonist action, and suggest caution in considering the use of NMDA antagonists in neonates.

A combined cobalt and C-14 2-deoxyglucose approach to antiepileptic drug assessment

The cobalt model of epilepsy, in combination with the C-14 2-deoxyglucose (2-DG) autoradiographic technique, was used to assess the effects of phenytoin (PHT) and ethosuximide (ESM), two antiepileptic drugs, and ketamine (KET), a drug with anticonvulsant properties, on brain activity. Nine days after the unilateral insertion of a cobalt rod into visual cortex, the nondrugged control rats showed the usual hypermetabolic regions of putative epileptogenic tissue both adjacent to the necrotic cortical cobalt rod implant zone and more distally in the connecting thalamus. PHT and ESM, given a single injections immediately before the 2-DG uptake and clearing period, diminished glucose uptake in the cobalt-induced hypermetabolic "patches" as well as in normal tissue. However, both drugs decreased 2-DG uptake more in the thalamic patches, than in the less hypermetabolic cortical patches, where the drug-induced depression in glucose metabolism was the same as for normal tissue. These findings suggest that PHT and ESM, regardless of their actions on cell receptors and membrane conductances, are ultimately of therapeutic value because more active nervous tissue (such as epileptic tissue) is more vulnerable to the depressing effects of these drugs than is less active tissue. KET, in contrast to PHT and ESM, did not depress metabolic activity throughout the brain generally and even clearly increased it in limbic system structures. Also in contrast to PHT and SEM, KET diminished activity in the cobalt-induced patches without reducing it in the normal tissue of the homotopic control regions. The more selective depressing action of KET, an N-methyl-D-aspartate (NMDA) antagonist, may be related to the role NMDA receptors play in supporting strong nervous activity. The discussion emphasizes the usefulness of a combined cobalt/2-DG approach to antiepileptic drug assessment.

Suppression of cortical epileptic afterdischarges by ketamine is not stable during ontogenesis in rats

Anticonvulsant action of ketamine, a noncompetitive NMDA antagonist, was studied in three groups of immature rats (12-, 18-, and 25-day-old) using cortically elicited epileptic afterdischarges (ADs) as a model. Rats with implanted electrodes were used, so that EEG and motor phenomena could be recorded. Stimulation (bipolar pulses of 1-ms duration and 8-Hz frequency) lasting 15 s was repeated four times with intervals of 10 min. Ketamine was administered IP 5 min after the first AD in doses of 5, 10, 20, or 40 mg/kg. Control groups did not receive any drug. Ketamine shortened ADs and suppressed motor correlates of stimulation as well as of ADs in a dose-dependent manner in 12- and 25-day-old rats. No significant changes were observed in 18-day-old animals, demonstrating thus a rather complicated development of anticonvulsant action of ketamine. Not only NMDA antagonism, but also other possible effects of ketamine must be taken into account.

Developmental seizure models

Seizures frequently occur in children. There are significant differences in the generation, expression and modification of seizures as a function of age. Animal models of epilepsy should depict these age-related differences. In this paper, we summarize the main features of generalized flurothyl, pentylenetetrazol, bicuculline and picrotoxin-induced seizures in adult and immature rats as well as the characteristics of focal seizures induced by amygdala kindling, systemic NMDA and kainic acid. Some of the models may be more advantageous for screening antiepileptic drug effects whereas other models may be more helpful in studying the basic mechanisms of epilepsy.

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.

The disruptive effects of ketamine on passive avoidance learning in mice: involvement of dopaminergic mechanism

The involvement of dopaminergic mechanisms in ketamine-induced disruption of one trial step-through passive avoidance performance was assessed through the coadministration with the dopamine D1 antagonist SCH 23390, the dopamine D2 antagonist YM-091512 and the dopamine autoreceptor agonist at low doses, apomorphine, in mice. Pretraining (10 min before) administration of ketamine (0; saline, 2.5, 5 and 10 mg/kg SC) dose-dependently reduced the latency in the retention trial conducted 24 h after the training. However, ketamine did not affect the retention latency when administered immediately after the training or prior to retention. YM-09151-2 (0.01 and 0.03 mg/kg SC) and apomorphine (0.01 and 0.03 mg/kg SC), but not SCH 23390 (0.01 and 0.03 mg/kg SC), ameliorated the impaired reduction by ketamine (10 mg/kg) in a dose-dependent manner. These results suggest that ketamine obstructs the acquisition of the passive avoidance task, and that this effect is induced by stimulation of dopamine D2 receptors through dopamine release from the presynaptic terminals.

Developmental changes of ketamine action against epileptic afterdischarges induced by hippocampal stimulation in rats

Action of ketamine (5-40 mg/kg) was tested against electrically induced hippocampal afterdischarges (four stimulations in one session; 8 Hz, 15 s) in rats 7, 12, 18, 25 and 90 days old. In control sessions, there was either stable afterdischarge (AD) duration and wet dog shakes (WDS) number or there was an increase in ADs' duration with repeated stimulations. Ketamine had dose-dependent and age-dependent effects. In 7-18-day-old rats, ketamine suppressed better WDS number than AD duration, with nearly absent action on AD duration in 18-day-old animals. Ketamine was equipotent for both phenomena in 25-day-old rats and, in contrast, it decreased more AD duration than WDS number in 90-day-old rats. The data suggest a differentiation induced by ketamine in the expression of motor and electrographic phenomena of the experimental seizures.

Involvement of inhibitory and excitatory neurotransmitters in levofloxacin- and ciprofloxacin-induced convulsions in mice

We studied the effects of gamma-aminobutyric acid (GABA)-benzodiazepine receptor agonists and glutamate receptor antagonists on levofloxacin (LVFX)- and ciprofloxacin (CPFX)-induced convulsions using intrathecal (i.t.) injections in mice. We also studied the effects of these agonists and antagonists on exacerbated convulsions induced by coadministration of the quinolone with 4-biphenylacetic acid (BPAA). The agonists or antagonists were injected i.t. 5 min and BPAA was administered orally 30 min before a single i.t. injection of the quinolone (10 microliters per animal). The animals were observed for clonic convulsion and death, and latency times to the appearance of convulsion were determined. Among the agonists, baclofen showed marked inhibition of both LVFX- and CPFX-induced convulsions, while other compounds such as GABA, muscimol, diazepam, and 3-aminopropylphosphonic acid had slight effects. Among the antagonists, kynurenic acid showed the strongest inhibition of convulsions caused by all doses of LVFX and CPFX and prolonged latency times; gamma-glutamyl-aminomethylsulfonic acid (GAMS) also markedly inhibited convulsions. The antagonists D-AP-5, AP-7, and 6,7-dinitroquinoxaline-2,3-dione (DNQX) had slight effects. Additionally, GAMS, DNQX, and MK-801 significantly lowered the incidence of death in the groups treated with CPFX. The enhanced convulsive activities of LVFX or CPFX by pretreatment with BPAA were clearly blocked by baclofen, kynurenic acid, GAMS, and DNQX. D-AP-5 and AP-7 also showed clear effects on the activity of LVFX. These results suggest that LVFX has fewer effects on the brains than CPFX and that convulsions induced by these quinolones alone and by these quinolones administered with BPAA may be mediated largely through glutamate and GABA(B) rather than GABA(A) receptors in mice.

Models of simple partial and absence seizures in freely moving rats: action of ketamine

The action of ketamine was studied in two models of seizures: a) bilateral neocortical discharges produced by topical application of pentylenetetrazol (model of simple partial seizures); and b) rhythmic spike-and-wave activity induced by systemic administration of pentylenetetrazol (model of absence seizures). Ketamine exerted biphasic effects. In the first model, the dose of 20 mg/kg ketamine significantly suppressed the ictal neocortical discharges (i.e., continuous spiking or ictal activity) accompanied by clonic motor seizures. However, at the dose of 40 mg/kg ketamine significantly accentuated the onset and increased the number of individual discharges (interictal spikes) in bilateral neocortical foci. In the model of rhythmic spike-and-wave activity, the lower dose of ketamine (20 mg/kg) decreased the number of rhythmic spike-and-wave episodes when compared to the higher dose (40 mg/kg) of ketamine, which increased the number of episodes. However, neither result differed significantly from control values. The present results suggest a dose-dependent action of ketamine: Lower doses (10 and 20 mg/kg in the rat) are able to suppress seizure activity, whereas a higher dose (40 mg/kg) potentiates the seizures. Moreover, the action of ketamine may be dependent upon the seizure model used. The study presents a new model of acute epileptic focus in freely moving rats.

Ethosuximide suppresses seizures and lethality induced by picrotoxin in developing rats

The action of ethosuximide (125 or 250 mg/kg, IP) against picrotoxin-induced seizures (3-6 mg/kg, IP) was assessed in rats 12, 18, 25, and 90 days old. In 18-day-old and older controls, picrotoxin regularly elicited clonic seizures; tonic-clonic seizures were induced in all age categories with high consequent mortality. Only the higher dose of ethosuximide (250 mg/kg) increased the latency of clonic seizures in 18- and 25-day-old pups. Tonic-clonic seizures were delayed by ethosuximide in 12-, 18-, and 90-day-old rats. Picrotoxin-induced lethality was suppressed only in 18- and 90-day-old rats by the 250-mg/kg dose of ethosuximide. In contrast, ethosuximide pretreatment increased the incidence of clonic seizures in 12-day-old rats. The results suggest that only high doses of ethosuximide can suppress clonic seizures, and this action is not consistent. Tonic-clonic seizures probably have model-specific sensitivity to ethosuximide because in previous studies ethosuximide completely suppressed pentylenetetrazol-induced tonic-clonic seizures but had no effect on kainic acid-induced tonic-clonic seizures. The suppression of mortality rates is probably due to nonspecific effects of high doses of ethosuximide.

Action of antiepileptic drugs against kainic acid-induced seizures and automatisms during ontogenesis in rats

Kainic acid (KA 4-14 mg/kg) administered intraperitoneally (i.p.) produces automatisms (scratching until third postnatal week, "wet dog" shakes thereafter), and clonic and tonic-clonic seizures in rats aged 7, 12, 18, 25, and 90 days. Administration of carbamazepine (CBZ) i.p. (25 or 50 mg/kg), phenobarbital (PB 20-80 mg/kg), clonazepam (CZP 0.2 or 1 mg/kg), or valproate (VPA 200 mg/kg) influenced neither incidence nor latency of automatisms. Clonic seizures that are regularly observed after the third postnatal week in controls were either abolished or substantially suppressed by any of the aforementioned antiepileptic drugs (AEDs). Tonic-clonic seizures observed in the first 3 postnatal weeks were suppressed only by solvent [including propyleneglycol (PEG), ethanol, and water]; the effect of AEDs on tonic-clonic seizures was proconvulsant instead. The automatisms were most resistant to AED therapy. These results induce some doubts about the adequacy of the KA model for identifying AEDs effective against complex partial seizures, but forthcoming AEDs that suppress automatisms in the KA rat model might also be active against human complex partial seizures.

Pentylenetetrazol-induced seizures in rats: an ontogenetic study

A quantitative description of motor seizures induced by pentylenetetrazol (PTZ, metrazol) was performed. Seizures were induced by PTZ in doses from 40 to 120 mg/kg s.c. in 477 male albino rats of the Wistar strain 7 to 90 days old. Two patterns of seizures were elicited: minimal, i.e. predominantly clonic seizures of facial and forelimb muscles with preserved righting ability, and major, i.e. generalized tonic-clonic seizures with a loss of righting reflex. Minimal seizures could be reliably elicited since the age of 18 days; the CD50 for these seizures did not significantly differ with age. Major seizures were elicited regularly at all developmental stages studied. Their CD50 did not significantly differ among 7-, 12- and 25-day-old rat pups but the value for 18-day-old rats was smaller and for adult animals larger than these three age groups.

Convulsive action and toxicity of uremic guanidino compounds: behavioral assessment and relation to brain concentration in adult mice

Four guanidino compounds that are known to accumulate in uremia, namely creatinine, guanidine, guanidinosuccinic acid and methylguanidine, were administered intraperitoneally and intracerebroventricularly to adult albino mice and the compounds epileptogenic and toxic properties were behaviorally assessed. After intraperitoneal injection, brain concentration of the compounds as a function of injected dose was monitored additionally. Guanidino compound brain concentration was determined by cation exchange chromatography with fluorescence ninhydrin detection. After systemic administration, especially guanidinosuccinic acid and methylguanidine induced long-lasting generalized convulsions which gradually increased in severity. Increasing the dose injected intraperitoneally resulted in linear increase in brain concentration of the injected compounds, in parallel with increase in proportion of animals presenting with convulsions and/or severity of convulsions. Guanidinosuccinic acid brain concentration increased more slowly than that of the other 3 compounds and guanidinosuccinic acid also exerted its effect later than the others. Since none of the other metabolically related guanidino compounds determined was significantly increased in the brains of the injected animals, the observed behavior was most certainly induced by the compounds injected and not by some secondary metabolite. Epileptogenic properties of the four compounds were markedly and qualitatively different in systemic administration, but rather similar in intracerebral administration. A tentative epileptogenic potency order was inferred from the combined behavioral and biochemical results. All 4 of the compounds tested displayed the ability to induce full-blown clonic-tonic convulsions and they did so in a dose-related manner. Guanidinosuccinic acid appeared to be slightly more potent than methylguanidine, but both guanidinosuccinic acid and methylguanidine were considerably more potent than guanidine. Creatinine was many times less potent than the other 3 guanidino compounds. Revised epileptogenic potency order on the basis of guanidino compound brain concentration after systemic administration as well as potency order after intracerebral administration paralleled the potency order of these compounds in their GABA antagonism reported earlier. It was therefore postulated that the GABA antagonism of uremic guanidino compounds could underlie their epileptogenic character. Moreover, these compounds could very likely be at the basis of the neurological complications including epilepsy of uremic patients in whom they accumulate in physiological fluids and brain.

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.

Age dependency of the susceptibility of rats to aminooxyacetic acid seizures

Immature rats are more susceptible to clonic seizures induced by aminooxyacetic acid (AOAA) than mature and senile rats. Highest susceptibility to AOAA seizures was observed in 7-14-day-old rat pups. The lowest susceptibility was recorded in 10-20 month-old rats. AOAA seizures in 14-day-old rats were blocked by clonazepam and valproate, but not by phenobarbital, carbamazepine, diphenylhydantoin, trimethadione or ethosuximide. Morphological analysis of brains from 14-day- and 3-month-old rats which experienced AOAA seizures did not reveal epilepsy-related damage. These observations suggest that immature rat brain is highly prone to convulsions induced by AOAA and that such convulsions are difficult to control by available antiepileptic treatment.