Anticonvulsant drugs and their antagonism of kindled amygdaloid seizures in rats

The effects of LY-201116 [4-amino-N-(2,6-dimethylphenyl) benzamide] on the amygdala-kindled rat

The effects of LY-201116, a 4-aminobenzamide, were examined in rats using the amygdala kindling model, both during acquisition of the kindled response and in fully kindled animals. Dose-response and time-response studies for efficacy and rotorod toxicity were completed following intraperitoneal injection of the drug. Afterdischarge duration, behavioral seizure response, kindled seizure threshold and EEG recordings were used to assess efficacy and toxicity of the drug. In the acquisition trial, the drug (7.5 mg/Kg) did not significantly alter the number of stimulations required to produce the first stage 5 kindled response nor did it modify afterdischarge durations. Doses of 11.25 and 15 mg/Kg suppressed afterdischarge and diminished behavioral responses significantly in fully kindled rats, but these doses were also neurotoxic as judged by rotorod performance. The non-selective anticonvulsant effect of 11.25 mg/Kg lasted at least 90 min. A dose of 15 mg/Kg raised kindled seizure threshold and diminished afterdischarge duration. Doses of 20, 30 and 40 mg/Kg produced spontaneous EEG spikes and seizures accompanied by behavioral convulsions. The drug thus exhibited non-selective anticonvulsant effects in fully kindled rats following doses of 11.25 or 15 mg/Kg, but exhibited proconvulsant activity following doses in the range of 20-40 mg/Kg.

Phenytoin potently increases the threshold for focal seizures in amygdala-kindled rats

Previous studies on the effects of phenytoin in the kindling model have yielded equivocal results, in that some groups reported anticonvulsant effects, while others found the drug to be only weakly active, inactive or even proconvulsant. Although part of these discrepancies might relate to factors such as the time of testing, route of administration, doses and administration vehicles, variable results were also obtained by studies in which these factors were comparable. For further investigation of the reasons of the reported discrepancies in the effectiveness of phenytoin in kindled rats, the influence of current intensity on the effects of phenytoin were examined in this model. In fully amygdala-kindled rats, phenytoin was only weakly active against seizures evoked by a fixed suprathreshold current of 500 microA. However, when the current was decreased to 250 microA, phenytoin exerted potent anticonvulsant effects. Determination of the threshold for focal afterdischarges showed that phenytoin, 12.5-75 mg/kg dose-dependently increased the threshold up to about 600% over controls at 75 mg/kg. Average levels in plasma, determined at this dose were about 30 micrograms/ml. In contrast to the potent effect on the seizure threshold, the severity or duration of seizures, evoked in phenytoin-pretreated rats by increasing the current, was not reduced. These data indicate that the primary effect of phenytoin in kindled rats in an increase in focal seizure threshold, while the ability of phenytoin to reduce the spread of seizures appears to be small. The present data might explain the discrepancy in reports on phenytoin in kindled rats, because most studies which found the drug to be ineffective used current intensities far exceeding the seizure threshold.

Quantitative EEG analysis of carbamazepine effects on amygdaloid kindled seizures in cats

We studied the effects of carbamazepine (CBZ) on seizure behaviour and electroencephalographic (EEG) activity in 6 amygdala kindled cats. CBZ reduced the behavioural severity of kindled seizures and prolonged the earlier seizure stages (latency to stage 4). These effects were not always paralleled by a reduction in the duration of seizure activity. EEG activity paradoxically increased in amplitude during early and mid-seizure, then fell in late seizure after CBZ. CBZ also caused an overall decrease in EEG coherence during mid and late seizure. These observations represent a first attempt to use quantitative EEG analysis to investigate the effects of anticonvulsants on electrographic seizure activity. The duration of postictal EEG suppression was reduced after CBZ treatment. The results support the view that CBZ has a major effect on limiting the spread of seizure discharges.

Anticonvulsive properties of F1933 (dulozafone) on kindled seizures in the rat

The anticonvulsive properties of a new compound: F1933 (Dulozafone) were investigated in the amygdala kindling model and compared with those of diazepam. Both drugs protected fully kindled rats against generalized seizures but failed to suppress partial ictal events (amygdala afterdischarges and limbic seizures). The anticonvulsive action of F1933, administered at the ED100, was nearly reversed by the specific antagonist of benzodiazepines receptors; R015-1788 (Flumazenil), suggesting that the effect of F1933 is mediated by this receptor. These results also emphasize the usefulness of kindling to test antiepileptic drugs and to confirm their supposed profile of action.

The effect of the NMDA receptor antagonist, MK-801, on the course and outcome of kindling

A rapid kindling procedure was used to distinguish between the anticonvulsant activity of drugs and their ability to retard the kindling process. MK-801 is a specific ligand at the phencyclidine (PCP) recognition site, and acts as a noncompetitive antagonist of NMDA-type glutamate/aspartate receptors. Intraperitoneal injections of MK-801 (0.5-4.0 mg/kg IP) significantly reduced the cumulated effect of 12 2-hr kindling stimulations, as determined from behavioral measures of seizure activity in immediately ensuing 24-hr drug-free kindling sessions; however, the corresponding electrographic effects did not reach significance. MK-801 also showed significant anticonvulsant activity when injected in fully kindled rats. Higher doses tested were accompanied by locomotor and postural effects. The anticonvulsant benzodiazepine, clonazepam, formulated with a proprietary diluent (as Rivotril, Roche), injected in anticonvulsant doses during the first 12 kindling sessions (0.64 mg/kg IP, repeated after 9 hr) did not significantly affect the course of subsequent sessions of drug-free kindling. Systemic injections of kynurenic acid (300-600 mg/kg IP 4 hours), a nonspecific antagonist of glutamate receptors in vitro, were without significant anticonvulsant or antikindling activity. Activity of NMDA-sensitive glutamate/aspartate receptors associated with the PCP recognition site may induce lasting facilitation of neural transmission; this facilitation may be responsible for the remote propagation and progressive enhancement of seizure activity kindled in the amygdala. The facilitatory process appears to be antagonised by MK-801.

Anticonvulsant modification of cocaine-induced toxicity in the rat

A number of anticonvulsant drugs were studied for their efficacy in preventing seizures and death from intoxication with cocaine. Rats were first pretreated with the test drug then subjected to large doses of intraperitoneally administered cocaine. In this model, control animals developed seizures in approximately 6 min, followed by death in approximately 10 min. Statistically significant protection against seizures and death was afforded by pretreatment with diazepam, phenobarbitol and the blocker of the uptake of gamma-aminobutyric acid (GABA), SKF 100330A. Only partial protection was afforded by the N-methyl-d-aspartate (NMDA) antagonist MK 801, the benzodiazepine antagonist, flumazenil and the novel aminobenzamide, LY 201116. Valproic acid and phenytoin demonstrated limited efficacy against cocaine-induced seizures, without consistently reducing death. Carbamazepine and ethosuximide did not significantly reduce seizures or death. In this model of acute cocaine toxicity, the anticonvulsants diazepam, phenobarbital and the blocker of the uptake of GABA, SKF 100330A were the most effective in protecting rats from cocaine-induced seizures and death. These data offer insight into future approaches for the treatment of patients with the acute toxic effects of cocaine.

Modification of amygdaloid kindling by diazepam in juvenile rats

The amygdaloid kindling phenomenon has been widely used to evaluate and screen potential anticonvulsant compounds in adult rats. In the current study, weanling rats (ages 23-25 days) were implanted chronically with amygdaloid electrodes. They were treated with dimethylsulfoxide (DMSO), 0.5 mg/kg diazepam or 1.0 mg/kg diazepam before twice daily kindling stimulations to determine the effect of diazepam on the acquisition of the kindled seizure. Additional juvenile rats implanted as weanlings and simulated twice daily without drug pretreatment until fully kindled were used to test for the acute anticonvulsant effects of diazepam (0.25-4.0 mg/kg). Diazepam was demonstrated to have anticonvulsant properties in juvenile rats by both prolonging the time to develop the fully kindled response during acquisition and by reducing the elicited seizure severity and the length of the afterdischarge in the fully kindled juvenile rats. Together, these data point to the extension of the anticonvulsant profile of diazepam to now include juvenile amygdaloid kindling in rats. They further point to the potential ability of screening proposed anticonvulsant drugs for their efficacy against amygdaloid kindling in immature rats.

Intravenous phenytoin is an effective anticonvulsant in the kindling model

We reexamined the efficacy of the clinically effective anticonvulsant drug phenytoin in the kindling model. We investigated the effects of varying doses of intravenous phenytoin on serum concentrations and on several indexes of stimulation-evoked kindled seizures. Intravenous phenytoin produced a dose-dependent increase in serum phenytoin concentration and powerfully suppressed both limbic and clonic motor seizures. Although focal afterdischarge threshold was elevated to some extent, the most profound effect of phenytoin was limitation of seizure propagation. Variable and low serum concentrations of intraperitoneal or oral phenytoin may explain previous findings that phenytoin is only partly effective or ineffective against kindled seizures. Together with previous results with other drugs, the excellent correlation among drugs effective against human and kindled seizures strengthens the validity of this model. We suggest that the efficacy of experimental anticonvulsant drugs be established in the kindling model before initiation of clinical trials for partial and secondarily generalized seizures.

The effect of MK-801 on kindled seizures: implications for use and limitations as an antiepileptic drug

MK-801 is a new drug that produces a noncompetitive blockade at the subclass of glutamate receptors activated by N-methyl-D-asparate (NMDA). The antiepileptic properties of MK-801 were studied using kindled seizures as a model of complex partial seizures with secondary generalization. A test protocol was employed that allowed: (1) examination of the efficacy of MK-801 against several parameters that gauge different aspects of epileptogenesis; (2) determination of the time-action profile of these effects; and (3) examination of the toxicity of MK-801 in animals experiencing seizures. The drug was found to be potent against the spread of seizures but less effective against parameters linked to partial seizures. At the higher doses of the drug required to truncate hippocampal afterdischarges, considerable neurotoxicity was encountered. In addition, the antiepileptic effects of MK-801 showed a use dependence so that, at a given time after the drug was administered, a greater suppression of seizures was noted if there had been preceding seizures in the presence of the drug than if there had not been. These findings indicate that there may be limitations to the clinical utility of MK-801 as an antiepileptic agent and that the drug may provide greatest benefit when used for the suppression of seizure generalization and when seizures are closely spaced.

Tolerance to anticonvulsant effects of diazepam, clonazepam, and clobazam in amygdala-kindled rats

Benzodiazepines are effective anticonvulsants, but long-term clinical usefulness is limited by development of tolerance. Tolerance to the actions of three prototype anticonvulsant benzodiazepines (BZDs)--diazepam (DZP), clonazepam (CZP), and clobazam (CLB)--was studied in amygdala-kindled rats. Fully kindled rats were dosed three times daily for 2 or 4 weeks. Amygdala stimulation was given 30 min after drug administration on days 1, 2, 3, 5, and 7 of chronic treatment and then three times weekly. During treatment, tolerance was observed as a loss of drug effect to suppress behavioral and EEG manifestations of seizure activity. Seizure activity remained stable in rats treated with vehicle. Tolerance to the anticonvulsant effects developed most rapidly during CLB treatment and most slowly during CZP treatment. Tolerance to the motor impairment caused by the drugs developed more rapidly. Assay of the amount of drug in brain extracts, using a BZD receptor assay, showed that tolerance was functional, not metabolic. Doubling the dose did not readily restore full anticonvulsant activity. The response to amygdala stimulation 24 h after treatment was stopped showed no residual BZD effect, but there was a rebound in duration of some seizure measures in rats that had been treated with CLB or DZP. Retesting 48 h after treatment was stopped showed that rats were still tolerant. The amygdala-kindled rat is a reliable and sensitive model for studying long-term actions of anticonvulsant BZDs.

Diazepam in the prevention of seizures and death in cocaine-intoxicated rats

Rats were exposed to high-dose intraperitoneal cocaine. Pretreatment with diazepam was found to be highly effective in reducing observed seizures from 90% to 0% and reducing the incidence of death from 85% to 10%. Furthermore, diazepam treatment after cocaine exposure was also effective in decreasing deaths, from 80% to 21%, even when given after the onset of seizures. Although diazepam pretreatment was shown to prevent clinically overt seizures, cortical EEGs in these rats demonstrated a continuum of convulsantlike electrical activity. Our study points to the protective effects of diazepam when given before or after cocaine exposure. Together, these data suggest that diazepam has significant efficacy against cocaine intoxication even though it does not totally suppress cocaine-induced cortical EEG seizure activity.

Development of new pharmacological agents for epilepsy: lessons from the kindling model

The greatest value of the kindling model for new therapy of epilepsy almost certainly lies in elucidating the molecular basis of its development and persistence. Such an understanding may provide a foundation for therapies aimed at prevention or perhaps even cure of some forms of human epilepsy.

A comparison of the anticonvulsant effects of 1,4- and 1,5-benzodiazepines in the amygdala-kindled rat and their effects on motor function

Studies suggest that the 1,5-benzodiazepine clobazam possesses a favorable anticonvulsant profile due to its minimal neurotoxicity. The anticonvulsant and motor impairment effects of clobazam and 2 1,4-benzodiazepine, diazepam and clonazepam, were compared by dose-response analysis in amygdala-kindled rats and on 3 tests of motor function: gross motor impairment, a vertical screen test, and muscle tone. All drugs produced a significant, dose-dependent decrease in the duration of both behavioral and electrographic kindled seizure measures. Forelimb clonus suppression was the most sensitive measure of anticonvulsant drug effect. The order of potency for all effects was clonazepam greater than diazepam greater than clobazam. ED50s for the benzodiazepines' effects on motor impairment were compared to their ability to protect rats from forelimb clonus. Different spectrums of action for the various benzodiazepines were found depending on the comparison measure. Clonazepam had the most favorable ratio of potency for anticonvulsant vs. motor impairment activity when ataxia rating was the comparison measure. Diazepam had the most advantageous profile when the more sensitive screen test was used for comparison. Clobazam was not found to have a superior spectrum of action when compared across these measures. The results emphasize the importance of dose-response analyses and the consideration of behavioral measures used to assess beneficial and adverse effects of anticonvulsants.

Review: cholinergic mechanisms and epileptogenesis. The seizures induced by pilocarpine: a novel experimental model of intractable epilepsy

High-dose treatment with pilocarpine hydrochloride, a cholinergic muscarinic agonist, induces seizures in rodents following systemic or intracerebral administration. Pilocarpine seizures are characterized by a sequential development of behavioral patterns and electrographic activity. Hypoactivity, tremor, scratching, head bobbing, and myoclonic movements of the limbs progress to recurrent myoclonic convulsions with rearing, salivation, and falling, and status epilepticus. The sustained convulsions induced by pilocarpine are followed by widespread damage to the forebrain. The amygdala, thalamus, olfactory cortex, hippocampus, neocortex, and substantia nigra are the most sensitive regions to epilepsy-related damage following convulsions produced by pilocarpine. Spontaneous seizures are observed in the long-term period following the administration of convulsant doses of pilocarpine. Developmental studies show age-dependent differences in the response of rats to pilocarpine. Seizures are first noted in 7-12 day-old rats, and the adult pattern of behavioral and electroencephalographic sequelae of pilocarpine is seen in 15-21-day-old rats. During the third week of life the rats show an increased susceptibility to the convulsant action of pilocarpine relative to older and younger animals. The developmental progress of the convulsive response to pilocarpine does not correlate with evolution of the brain damage. The adult pattern of the damage is seen after a delay of 1-2 weeks in comparison with the evolution of seizures and status epilepticus. The susceptibility to seizures induced by pilocarpine increases in rats aged over 4 months. The basal ganglia curtail the generation and spread of seizures induced by pilocarpine. The caudate putamen, the substantia nigra, and the entopeduncular nucleus govern the propagation of pilocarpine-induced seizures. The antiepileptic drugs diazepam, clonazepam, phenobarbital, valproate, and trimethadione protect against pilocarpine-induced convulsions, while diphenylhydantoin and carbamazepine are ineffective. Ethosuximide and acetazolamide increase the susceptibility to convulsant action of pilocarpine. Lithium, morphine, and aminophylline also increase the susceptibility of rats to pilocarpine seizures. The pilocarpine seizure model may be of value in designing new therapeutic approaches to epilepsy.

Screening and characterization of antiepileptic drugs with rapidly recurring hippocampal seizures in rats

A method to efficiently screen antiepileptic drugs (AED) for their actions against complex partial and secondarily generalized seizures is presented. The procedure relies on rapidly recurring hippocampal seizures (RRHS) in rats which are first used to bring epileptic responses to a stable, fully kindled state and then to test 3 parameters--behavioral seizures, electrographic seizures, and afterdischarge thresholds--before and after drug administration. With the methods described, the effects of a given drug treatment can be thoroughly determined in a single study period. Quantitative determinations of dose-response, time-action and relative potency characteristics are readily ascertained. A battery of known AED, encompassing those in common clinical use, was studied with this system. Kindled motor seizures (classes 4 and 5) were more readily suppressed than limbic behavioral seizures (classes 1-3). Electrographic seizures were usually, but not always, shortened concurrently with suppression of behavioral seizures. Under the conditions of this study, afterdischarge thresholds were not elevated, indicating that a critical role of AED is to counteract seizure spread and prolongation. The overall behavior of the RRHS test system with AED was identical to that with traditional amygdala kindled seizures and results were in good agreement with the clinical responsiveness of the kinds of seizures that these experimental systems model. The features of RRHS make it a useful system for screening new agents for antiepileptic effects, even in circumstances where little or no information about the drug under study is available.

Audiogenic seizures in Wistar rats before and after repeated auditory stimuli: clinical, pharmacological, and electroencephalographic studies

A strain of Wistar rats was inbred for susceptibility to audiogenic seizures characterized by one or two wild running fits followed by tonic dorsiflexion with open mouth and then a catatonic state. During the tonic phase, the cortical EEG was flat for 1 to 2 sec, then changed to a slow, regular low-amplitude discharge, 9 to 12 c/s, for 25 to 60 sec. In these rats exposed to 40 daily 90-sec auditory stimuli, behavior and EEG changed. The wild running became disorganized by myoclonic jerks of the limbs and body. In some animals, the tonic extension disappeared and a myoclonic seizure developed progressively, with facial and forelimb clonus, and rearing and falling. In others, the tonic phase was followed by a generalized clonic phase. The EEG during the myoclonic and tonic-clonic seizures showed high-amplitude rhythmic spikes, polyspikes and spike-waves, 1 to 10 c/s, for 40 to 120 sec, often outlasting the sound stimulus. The effects of ethosuximide, carbamazepine and phenytoin were the same on primary and modified audiogenic seizures. The progressive behavioral and EEG modifications of audiogenic seizures following repeated auditory stimuli suggest that kindling had developed, the seizures being propagated from the brain stem to forebrain structures.

Episodic barrel rotations induced by intrastriatal injection of quinolinic acid in rats. Inhibition by anticonvulsants

Unilateral intrastriatal injection of quinolinic acid (2,3 pyridine dicarboxylate; QUIN) in the rat produces episodic barrel rotations and tonic-clonic forepaw movements, lasting for several hours. We investigated whether intraperitoneal posttreatment with anticonvulsants could abolish this phenomenon when it is already fully developed, and whether their potency ratio was similar in models of epilepsy. All 8 tested antiepileptics, namely carbamazepine, clonazepam, diazepam, diphenylhydantoin, ethosuximide, flunarizine, phenobarbital and sodium valproate decreased this behaviour in a dose-dependent way. Six other drugs with anticonvulsant properties were also effective: DL-2-amino-7-phosphonoheptanoic acid, desipramine, etomidate, ketamine, meprobamate and sabeluzole. The ED50-values for halving the frequency of the episodes of barrel rotation correlated well with published ED50-values for inhibition of tonic hindpaw extension in the maximal metrazol seizure test (rs = .95, p less than 0.001) and with the ED50-values for halving the duration of the forepaw clonus in the rat-kindling model (rs = .93, p less than 0.001). This quinolinic acid test allows visualization of the onset of action of anticonvulsants, with each animal as its own control. In order to assess whether this test is also sensitive to drugs influencing the symptoms of Huntington's disease, the effect of the dopamine antagonists haloperidol and pimozide, the acetylcholinesterase inhibitor physostigmine and the anticholinergics atropine and dexetimide were investigated as well. The experiments suggested that the barrel rotations and clonic forepaw movements, only 3-6 hours after intrastriatal injection of QUIN respond to anticonvulsants, but are not specifically sensitive to drugs used in the symptomatic treatment of Huntington's disease.

Marked increase in anticonvulsant activity but decrease in wet-dog shake behaviour during short-term treatment of amygdala-kindled rats with valproic acid

The anticonvulsant activity of valproic acid (VPA) was determined in amygdala-kindled rats after single and repeated (total of 7 injections given 3 times per day) administration of 200 mg/kg i.p. After a single injection, VPA significantly reduced the severity and duration of the kindled seizures and decreased the duration of after-discharges recorded from the stimulated amygdala, but only 12% of the animals were totally protected from seizures. The percentage of animals totally protected increased to 88% after 7 doses. This pronounced increase in the anticonvulsant activity was not related to alterations in the plasma concentrations of VPA or its major active metabolites. Furthermore, determination of VPA and its metabolites in the substantia nigra after a single and repeated administration yielded the same data, again indicating that the increase in the anticonvulsant activity was not due to drug accumulation. In contrast to the marked increase in the anticonvulsant efficacy of VPA during short-term treatment, wet-dog shake behaviour induced by a single injection of the drug was significantly attenuated after repeated dosing, indicating that the anticonvulsant effect of VPA and the wet-dog shake behaviour induced by the drug were not mediated by the same mechanism. This was substantiated by experiments with one of the major metabolites of VPA in rat plasma, trans-2-en-VPA, which had approximately the same anticonvulsant efficacy as VPA but did not induce wet-dog shakes in rats.

The anticonvulsant action of nafimidone on kindled amygdaloid seizures in rats

The anticonvulsant effectiveness of nafimidone (1-[2-naphthoylmethyl]imidazole hydrochloride) was evaluated in the kindled amygdaloid seizure model in rats. Nafimidone (3.1-120 mg/kg i.p.) was evaluated at 30 min in previously kindled rats using both threshold (20 microA increments) and supranthreshold (400 microA) paradigms. Nafimidone (25-50 mg/kg) significantly reduced supranthreshold elicited afterdischarge length and seizure severity only at doses with some prestimulation toxicity. The maximum anticonvulsant effectiveness for the 25 mg/kg i.p. dose of nafimidone was seen between 15 and 30 min utilizing a suprathreshold kindling paradigm. Nafimidone did not significantly elevate seizure thresholds at the doses tested; however, nafimidone (3.1-50 mg/kg) reduced the severity and afterdischarge duration of threshold elicited seizures in a non-dose response manner. Drug-induced electroencephalographic spikes were seen in both cortex and amygdala in most kindled rats receiving 100-120 mg/kg i.p. within 30 min of dosing before electrical stimulation. The frequency of spike and wave complexes increased in most of these animals leading to drug-induced spontaneous seizures and death in approximately 25% before electrical stimulation. This study has demonstrated that although nafimidone can modify both threshold and suprathreshold elicited kindled amygdaloid seizures, it lacks significant specificity in this model of epilepsy.

An efficient method for time course studies of antiepileptic drugs using the kindled rat seizure model

A new method of testing the time course of anticonvulsant drugs in the kindled rat seizure model was investigated. To determine whether there are inhibitory effects of a kindled seizure on subsequent seizures, groups of 10 rats were made to convulse three times consecutively with interstimulation intervals of 0.5, 1, and 1.5 hr. Only with an interstimulus interval of 0.5 hr was there evidence of potential inhibitory effects lasting long enough to affect subsequent seizures. The time course of the anticonvulsant activity of diazepam was determined using two protocols: one in which groups of kindled rats were stimulated once and a second protocol in which animals were stimulated two times (at least 1.5 hr apart) following diazepam administration. The time courses of diazepam's inhibitory effect on kindled seizures obtained with each protocol were not significantly different. The data indicate that multiple stimulation episodes can be utilized in kindled rats to determine the time course following single administration of antiepileptic drugs.

Effects of drugs on the initiation and maintenance of status epilepticus induced by administration of pilocarpine to lithium-pretreated rats

The ability of various drugs to prevent the onset of status epilepticus induced by administration of the muscarinic agonist, pilocarpine, to lithium-pretreated rats was determined. Motor limbic seizures and status epilepticus occurred in 100% of rats administered pilocarpine (30 mg/kg, s.c.) 20 h after pretreatment with lithium (3 meq/kg, i.p.). The latency to spike activity and to status epilepticus was 20 +/- 1 min and 24 +/- 1 min, respectively. Atropine, diazepam, phenytoin, carbamazepine, phenobarbital, paraldehyde, and L-phenylisopropyladenosine (L-PIA) prevented all phases of seizure activity induced by lithium/pilocarpine treatment. The initiation of status epilepticus was significantly prolonged by pretreatment with sodium valproate. These findings indicate that the seizures induced by administration of lithium and pilocarpine accurately model generalized tonic-clonic epilepsy. The anticonvulsant activity of L-PIA was prevented by prior treatment with the adenosine antagonist, theophylline. The latency to spike and seizure activity was decreased by theophylline, indicating that endogenous adenosine may have a tonic inhibitory influence on cholinergic neurons. Atropine, diazepam, phenobarbital, phenytoin, sodium valproate, L-PIA, and carbamazepine did not interrupt seizure activity when administered 60 min after pilocarpine (approximately 35 min after initiation of status epilepticus). When rats were administered paraldehyde at this time, status epilepticus was rapidly terminated and all rats survived. Thus, status epilepticus induced by lithium and pilocarpine provides a seizure model that is not responsive to conventional anticonvulsants.

Kindling-induced changes in EEG recorded during stimulation from the site of stimulation. III. Direct pharmacological manipulations of the kindled amygdala

In our previous studies, we hypothesized that activation and subsequent collapse of GABA-mediated inhibition during tetanus is an important seizure-triggering mechanism in the kindled epileptogenic focus. To examine this hypothesis, in the present study, we investigated the effects of pharmacological manipulations of the kindled amygdala with several drugs, and measured the kindled seizures as well as the EEG events during tetanus. The results obtained were: (i) The selective GABA-A agonist, muscimol (1 and 5 nM/1 microliter), suppressed kindled seizures in a dose-dependent fashion, and the 5 nM muscimol significantly prolonged EEG suppression and reduced the number of oscillations in the subsequent rhythmic synchronous discharge. Similar effects followed systemic injection of diazepam (2 mg/kg). (ii) The selective GABA-B agonist, baclofen (5 nM), had no effect on kindled seizures nor on the EEG events during tetanus. (iii) The NMDA antagonist, 2-amino-5-phosphonovaleric acid (80 nM), significantly reduced the afterdischarge duration and significantly delayed the appearance of the rhythmic synchronous discharge. However, these effects were not observed immediately, but 24 to 72 h after microinjection. (iv) The muscarinic cholinergic antagonist, atropine (40 and 80 nM), suppressed kindled seizures in a dose-dependent fashion, but the atropine caused marked synchronous discharge both in the awake resting EEG and during tetanic stimulation. We conclude that the GABA-A system, including the benzodiazepine system, is more involved in the seizure-triggering mechanism of amygdala kindling than the GABA-B system, that there is an interaction between the GABA-A and NMDA system, and that the cholinergic participation is independent of the primary seizure-triggering mechanisms.

Only certain antiepileptic drugs prevent seizures induced by pilocarpine

Seizures produced in rats by systemically administered pilocarpine (PILO) provide a model for studying the generation and spread of convulsive activity in the forebrain. PILO, 380 mg/kg, induces a sequence of behavioral and electroencephalographic alterations indicative of motor limbic seizures and status epilepticus which is followed by widespread damage to the limbic forebrain resembling that occurring subsequent to prolonged intractable seizures in humans. The present study was undertaken to determine whether clinically utilized antiepileptic drugs share an ability to suppress seizures and brain damage elicited by PILO in rats. Clonazepam, ED50 0.35 mg/kg (0.25-0.49), phenobarbital, 23.4 mg/kg (18.5-29.6), and valproic acid, 286 mg/kg (202-405), prevented the buildup of limbic seizures and protected against seizure-related brain damage. Pretreatment with trimethadione, 179 mg/kg (116-277), resulted in a moderate protection against PILO-induced seizures, whereas carbamazepine, 10-50 mg/kg, and diphenylhydantoin, 10-200 mg/kg, blocked neither convulsions nor brain damage produced by the drug. Surprisingly, ethosuximide, 196 mg/kg (141-272), and acetazolamide, 505 mg/kg (332-766), both lowered the threshold for seizures induced by PILO and converted a non-convulsant dose of PILO, 200 mg/kg, into a convulsant one. These results indicate that only certain anticonvulsant drugs elevate the threshold for PILO-induced seizures and prevent the occurrence of epilepsy-related brain damage. The resistance of seizures produced by PILO in rats to antiepileptic drugs reaffirms the clinically obvious lack of effective treatments for limbic convulsions.

Glycine potentiates diazepam anticonvulsant activity in electroshock seizures of rats: possible sites of interaction in the brainstem

The effect of orally or intracerebrally injected glycine on the anticonvulsant actions of intraperitoneal diazepam was examined using a tonic-clonic electroshock seizure model in the rat. Orally administered glycine (1.125 g/kg) potentiated the anticonvulsant effect of diazepam (DZP) to convert tonic-clonic electroshock seizures to less severe subthreshold clonic seizures. Oral glycine by itself had no effect on the tonic-clonic seizure response. Bilateral substantia nigra (SN) microinjections of glycine (125 micrograms/site) failed to potentiate intraperitoneal DZP when compared with the most appropriate control, animals treated with DZP and intranigral saline. It was not possible to determine whether bilateral glycine microinjections into the inferior olivary nucleus (IO) potentiated anticonvulsant effects of DZP since glycine alone converted all tonic-clonic seizures to the clonic response. Finally, bilateral glycine microinjection alone into the nucleus reticularis pontis oralis (PNO) produced an anticonvulsant effect when compared to untreated control responses but did not potentiate the anticonvulsant actions of DZP. Although these results may indicate that the glycinergic potentiation of DZP involves a direct pharmacodynamic interaction between these two compounds at specific brain sites, these sites have not yet been demonstrated conclusively.

Acute effect of anticonvulsants on amygdaloid kindled seizures induced with low-frequency stimulations

Acute effects of several antiepileptic drugs on low-frequency amygdaloid-kindled seizures were assessed. The number of stimulating pulses required for the provocation of epileptic afterdischarge (pulse-number threshold, PNT) was used as an indicator for the seizure-generating threshold. The duration of epileptic afterdischarge (AD duration) was used as an indicator for the severity of the induced seizures. Phenytoin (PHT) and carbamazepine (CBZ) reduced AD duration more than did elevating PNT. Conversely, phenobarbital (PB) and diazepam (DZP) elevated PNT more than did reducing AD duration. Weak effects on the two indicators, valproic acid (VPA) and ethosuximide (ESM), were observed. Low-frequency kindling may be a useful experimental model of epilepsy in drug-assessments.

The anticonvulsant action of AHR-11748 on kindled amygdaloid seizures in rats

The anticonvulsant effectiveness of AHR-11748 (3-[3-(trifluoromethyl)phenoxy]-1-azetidinecarboxamide) was evaluated in the kindled amygdaloid seizure model in rats. Doses of AHR-11748 that did not cause prestimulation toxicity significantly attenuated elicited afterdischarge durations and the severity of the accompanying behavioral convulsive response in previously kindled rats. AHR-11748 (25-100 mg/kg i.p.) was evaluated at 30 min in previously kindled rats using both threshold (20 microA increments) and suprathreshold (400 microA) paradigms. AHR-11748 (50-100.mg/kg) reduced suprathreshold elicited after discharges and seizure severity. Utilizing a suprathreshold kindling paradigm, the maximum anticonvulsant effectiveness for the 100 mg/kg i.p. dose of AHR-11748 was seen at 180 min. AHR-11748 significantly elevated seizure thresholds only at the 100 mg/kg dose. AHR-11748 (25-100 mg/kg) significantly reduced the severity of threshold elicited seizures. When AHR-11748 (50 and 100 mg/kg i.p.) was administered daily during kindling acquisition, the number of daily trials necessary to complete kindling significantly increased. A reduction in both the duration and the severity of the responses induced by the daily stimulations during the acquisition period was seen with AHR-11748 treatment. This study has demonstrated that AHR-11748 significantly modifies both the acquisition of kindling and the fully kindled amygdaloid seizures at doses that do not cause behavioral toxicity.

Glycine potentiates the anticonvulsant action of diazepam and phenobarbital in kindled amygdaloid seizures of rats

The effect of glycine on the anticonvulsant activity of diazepam and phenobarbital in fully developed kindled amygdaloid seizures in rats was determined. Glycine alone had no significant effect on the seizure response, either when administered orally 1 hr prior to the seizure test or when given chronically in a 0.5 M solution as the source of water. Administration of glycine (10 mmol/kg, oral) together with diazepam produced a significant reduction in both cortical epileptiform afterdischarge and the severity of seizures at doses of diazepam which had no significant effect on the seizures when administered alone. Glycine potentiated the effects of phenobarbital on the cortical afterdischarge but not the severity of the seizures. The observed potentiation of the effects of diazepam and phenobarbital suggests a glycinergic mechanism in the anticonvulsant action of these drugs which may be mediated in part by the inhibitory gamma-aminobutyric acid (GABA) systems.

Effects of the benzodiazepine antagonists RO 15-1788, CGS-8216 and PK-11195 on amygdaloid kindled seizures and the anticonvulsant efficacy of diazepam

The anticonvulsant effectiveness of the benzodiazepine antagonists RO 15-1788, CGS-8216 and PK-11195 were evaluated against threshold and suprathreshold (400 microA) stimulation in fully amygdaloid-kindled rats. Pretreatment with either RO 15-1788 (3, 10 and 30 mg/kg), CGS-8216 (3, 10 and 30 mg/kg) or PK-11195 (10 and 60 mg/kg) failed in this study to modify consistently either the afterdischarge thresholds or elicited suprathreshold seizures or duration of afterdischarge. Using a double injection paradigm, the effectiveness of these three benzodiazepine antagonists to reverse the anti-convulsant and behavioral effects of diazepam were studied. When diazepam (3 mg/kg) was injected 15 min before or after a second injection of the vehicle control DMSO (0.25 ml/kg), a significant reduction in the duration of afterdischarge and seizure rank, elicited by a suprathreshold stimulation in amygdaloid-kindled rats, occurred. When either CGS 8216 (10 mg/kg) or RO 15-1788 (10 mg/kg) were given 15 min before diazepam (3 mg/kg) prior to stimulation, the anticonvulsant properties of diazepam were blocked. When RO 15-1788 (10 mg/kg) was given 15 min after diazepam, antagonism of the anticonvulsant effects on diazepam was shown. However, when either CGS-8216 (10 mg/kg) or PK-11195 (10 and 60 mg/kg) were given 15 min after diazepam (3 mg/kg), the anticonvulsant properties of diazepam were not blocked. The anticonvulsant effects of diazepam were reversed when CGS-8216 (10 mg/kg) was given 5 min after diazepam (3 mg/kg) or when a larger dose (30 mg/kg) was given at the same 15 min interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Kindling-like phenomenon in the isolated ileum of the guinea-pig

Repeated bursts of low voltage electrical stimulation of the isolated ileum of the guinea-pig gradually leads to the development and progressive intensification of the tissue basal activity, culminating in spontaneous, sudden strong contractions of the preparation, which persist for several hours after the stimulation has been discontinued. The magnitude of these alterations are determined by the parameters of the stimulation, mainly by the number of electrical stimulations, the frequency of stimulation, and the interstimulus interval. Maximal alterations are obtained with periods of stimulation of 20 Hz for 10 sec, pulses of 3.0 msec, repeated every 20 min for 15 times. Phenytoin, flunitrazepam, diazepam, phenobarbital and carbamazepine effectively inhibited the fully developed phenomenon in the tissues. The effect described in this report may be related to kindling in the brain.

The effects of drugs acting at the GABAA-receptor/ionophore after chemical kindling with the benzodiazepine receptor ligand FG 7142

Repeated administration of the beta-carboline benzodiazepine receptor ligand FG 7142 produces sensitization to its effects so that full seizures develop (chemical kindling); initially it is only pro-convulsant. The present study investigated alterations in the function of drugs which act at the different sites at the gamma-aminobutyric acid (GABA) benzodiazepine receptor complex, after repeated administration of FG 7142. In FG 7142 kindled mice decreased anticonvulsant and hypothermic effects of the GABA agonist muscimol were observed. The hypothermic effects of the GABA agonist progabide were reduced. In contrast a small increase in the hypothermic effect of pentobarbitone was seen. The convulsant effects of bicuculline and picrotoxin were unaltered when they were given intravenously but marginally increased when they were given by the intraperitoneal route. No changes were seen in the hypothermic effects of these drugs. No significant changes were seen in the convulsant or hypothermic effects of pentylenetetrazol. These results suggest that kindling with FG 7142 may alter GABA receptor function.

Is amygdala kindling in rats a model for drug-resistant partial epilepsy?

Amygdala-kindled female rats were used to compare the effects of seven antiepileptic drugs that are clinically used for treatment of partial epilepsy with complex symptomatology, on generalized seizures, focal seizures, or electrographic seizure activity at the focus. As a second approach of drug evaluation, drug effects on mean latency, severity, and duration of the seizures were determined. Anticonvulsant potencies obtained were compared with those determined in the maximal electroshock seizure test in female rats. Phenobarbital, phenytoin, carbamazepine, valproic acid, diazepam, clonazepam, but not primidone dose-dependently suppressed generalized motor seizures in kindled rats; however, except for the benzodiazepines, ED50S were substantially higher than those determined in the maximal electroshock seizure test. Compared with their effect on generalized motor seizures, all drugs were much less potent in blocking focal seizures and afterdischarges recorded from the amygdala. The data suggest that with respect to behavioral and pharmacologic characteristics of the amygdala kindling model, fully kindled rats may be a useful model for drug-resistant complex partial seizures with secondary generalization. Results of experiments with novel inhibitors of GABA uptake, which were inactive in the maximal electroshock seizure test but highly potent against kindled seizures, suggest that such drugs might be more effective than current antiepileptic drugs for treatment of partial epilepsy.

Effects of carbamazepine and valproic acid on brain immunoreactive somatostatin and gamma-aminobutyric acid in amygdaloid-kindled rats

Somatostatin and gamma-aminobutyric acid (GABA) concentrations were evaluated in the brain of kindled rats treated chronically with carbamazepine and valproic acid. Kindled seizures were almost completely blocked by treatment with carbamazepine, whereas the effect of valproic acid was partial, suppressing only generalized seizures. The duration of after-discharge in amygdala was suppressed by carbamazepine not by valproic acid. Carbamazepine induced a decrease in immunoreactive somatostatin concentration and an increase in GABA concentration in the temporal cortex of kindled rats. Valproic acid induced only an increase in GABA concentration. The results suggest that somatostatin may be associated with the suppression of focal seizure in amygdala and GABA may have a role in the suppression of generalized seizures.

Acute effects of antidepressants on hippocampal seizures

Electrically kindled hippocampal seizures in rats were used to evaluate the acute effects of the antidepressants amitriptyline, imipramine, desipramine, bupropion, maprotiline, and trazodone on behavioral and electrical convulsions. All of the drugs reduced afterdischarge duration significantly. Behavioral seizures were not significantly reduced by bupropion or trazodone, whereas the other drugs did reduce seizure severity. Afterdischarge threshold was not modified by these drugs. In contrast, phenobarbital significantly elevated threshold and reduced seizure severity and afterdischarge duration. Amitriptyline was the most effective antidepressant, attenuating both seizure severity and afterdischarge duration.

Development of tolerance to the anticonvulsant effect of diazepam in amygdala-kindled rats

The anticonvulsant long-term efficacy of diazepam was studied in amygdala-kindled rats. The drug was administered three times daily at doses of 5 mg/kg i.p. for 2 weeks in fully kindled animals. The severity of the kindled seizures was markedly reduced throughout the period of treatment, while tolerance developed to the effect of diazepam on seizure latency and duration and, less marked, on duration of amygdala afterdischarges. Concomitant determination of plasma concentrations of diazepam and its major metabolite, desmethyldiazepam, showed that diazepam increased during the 2 weeks of treatment, suggesting that the observed tolerance was not metabolic but functional in nature. After cessation of treatment, there was no clear indication for withdrawal symptoms except a significant increase in kindled seizure duration after 2 days. The data demonstrate that amygdala-kindled rats are a useful model to study the long-term efficacy of anticonvulsant drugs.

Acute effects of lithium on hippocampal kindled seizures

The effects of lithium chloride on seizure activity generated by stimulation of hippocampal kindled rats were studied. Acute administration of 0, 0.25, 0.50, 1.5, 3.0, and 5.0 mEq/kg i.p. resulted in serum levels ranging from clinically subtherapeutic to toxic during the subsequent 4 h. Afterdischarge threshold and seizure severity were unchanged by these levels of lithium. Afterdischarge duration was somewhat prolonged, reaching a significant level only for the 3.0-mEq/kg dose. It is concluded that lithium shows a minor proconvulsant effect after acute administration in the kindled hippocampal seizure model.

Comparison of the anticonvulsant effects of two novel GABA uptake inhibitors and diazepam in amygdaloid kindled rats

Two novel, specific inhibitors of GABA uptake, namely SKF 89976-A (N-[4,4-diphenyl-3-butenyl]-nipecotic acid) and SKF 100330-A (N-[4,4-diphenyl-3-butenyl]-guvacine) were tested for anticonvulsant effects in amygdaloid kindled female rats. The anticonvulsant effectiveness of the compounds was compared with that of diazepam. SKF 89976-A and SKF 100330-A produced dose-dependent anticonvulsant effects on all seizure parameters measured in fully kindled rats, i.e. they inhibited seizure severity, increased seizure latency, and decreased the duration of motor seizures and EEG after discharges. ED 50s for inhibition of seizure severity were 4.6 and 15.1 mg/kg (0.014 and 0.045 mmol/kg) i.p. for SKF 100330-A and SKF 89976-A, respectively. For comparison, the ED 50 of diazepam was 1.9 mg/kg (0.0067 mmol/kg) i.p. Observation of behaviour indicated that the novel GABA uptake blockers exerted no side-effects in anticonvulsant doses, whereas diazepam produced sedative effects at all active dosage levels. The data demonstrate that SKF 100330-A and SKF 89976-A are potent, non-sedative anticonvulsant drugs in the kindling model of epilepsy, and these compounds thus may deserve interest as potential antiepileptic drugs with a very selective mechanism of action.

Monoaminergic and local anesthetic components of cocaine's effects on kindled seizure expression

Male Long-Evans rats were kindled via daily electrical stimulation of the left prepyriform cortex. The animals were then used in two experiments which examined the pharmacological basis of cocaine's effects on three mutually exclusive components of the kindled seizure, which were the following: (a) latency to clonus, (b) clonus duration, and (c) duration of AD outlasting clonus. The first experiment compared the effects produced by cocaine HCl (20 mg/kg, IP), lidocaine HCl (20 mg/kg, IP), and amphetamine sulfate (2.5 mg/kg, IP). The results indicated that both cocaine and lidocaine reduced the duration of kindled AD, latency to clonus, and duration of AD persisting beyond clonus, thus suggesting that these cocaine effects are mediated by local anesthetic mechanisms. Only cocaine reduced clonus duration, which suggests that this cocaine effect is not produced by a local anesthetic action. The second experiment examined the effects of cocaine following the administration of three dose levels of the monoamine antagonists haloperidol, prazosin, yohimbine, propranolol, or metergoline (selected for their ability to block dopamine, alpha-1-norepinephrine, alpha-2-norepinephrine, beta-norepinephrine, and serotonin receptors, respectively). The results of this experiment found no support for a monoaminergic contribution to cocaine's effect on clonus latency or AD after clonus. However, results for prazosin, which reduced clonus duration and exhibited an additive effect with cocaine on this variable, suggest that cocaine's norepinephrine action (especially on the alpha-norepinephrine systems) may modulate clonus duration.

Amygdala kindled seizure stage is related to altered benzodiazepine binding site density

Benzodiazepine receptor binding was examined in rats at 3 stages of amygdaloid kindling (i.e., initial afterdischarge, Stage 3 and Stage 5) immediately or 24 hr after seizure. 3H-diazepam binding site density (Bmax) was significantly increased 24 hr after Stage 3 and Stage 5 kindled seizures in the hippocampus but not in the amygdala. There were no significant differences in the dissociation constants (KD) between kindled and control rats at any time point examined for either brain region. These results demonstrate that changes in benzodiazepine binding are observed with partial kindled seizures (i.e., Stage 3), indicating that generalized seizures are not prerequisite to increased benzodiazepine receptor site density.

Hippocampal calcium-binding protein during commissural kindling-induced epileptogenesis: progressive decline and effects of anticonvulsants

Changes in hippocampal calcium-binding protein (CaBP) were examined in rats given kindling stimuli via electrodes chronically implanted in the midline commissural pathway. CaBP levels decreased progressively and were significantly lower (16.6%) than controls after only 10 kindling trials. The maximum fall (33%) was achieved prior to the production of stage 5 motor seizures and additional kindling-induced seizures produced no further decline. Induction of motor seizures with pentylenetetrazol had no effect upon hippocampal CaBP levels. Diazepam treatment during the course of kindling significantly increased the number of stimulation trials required to produce stage 5 motor seizures but did not inhibit the fall in CaBP. Diazepam treatment of fully kindled rats was effective in blocking generalized motor seizures without causing any restoration of the depleted levels of CaBP. Diphenylhydantoin was neither effective during the course of kindling nor in modifying the effect of further stimulations in fully kindled rats. These data indicate that the highly specific decrease in hippocampal CaBP, previously demonstrated to be localized to dentate granule cells and their processes following kindling-induced epilepsy, does not result from the expression of full tonic-clonic (stage 5) motor seizures. The loss of CaBP may be a biochemical factor contributing either to the predisposition of neuronal tissue to seizure activity or to a protective attempt to overcome the deleterious effect of repeated high-frequency stimulation.

Anticonvulsant action of amino acid antagonists against kindled hippocampal seizures

Electrical stimulation of the ventral hippocampus 5 times daily produced significant seizure activity (stage 4), but further stimulations seldom produced full motor seizures (stage 5). Blockade of these seizures with amino acid antagonists, phosphonocarboxylic acids, was achieved but with a reverse order of potency to that seen with the kindled amygdala. Thus APB was the most potent and APH the least potent analog tested. These results indicate that the kindling of different limbic brain areas may involve different neuronal substrates even if the development of the seizure activities are similar.

The effect of a glycine derivative (CP 1552-S) on kindled seizures in rats

The effects of the glycine derivative, CP 1552-S (2-N-pentylaminoacetamide hydrochloride) were evaluated for potential anticonvulsant activity in rats which were cortically- or amygdaloid-kindled. Large doses (300-600 mg/kg, i.p.) of CP 1552 given 30 min before stimulation resulted in significant reductions in duration of afterdischarge after both partially-developed and fully-developed cortically-kindled seizures. The largest dose tested (600 mg/kg, i.p.) markedly reduced the duration of the elicited afterdischarge and the severity of seizure. This dose was associated with prestimulation sedation and a 50% incidence of post-afterdischarge spontaneous, electrical seizure activity. Against kindled amygdaloid seizures, CP 1552-S significantly reduced the duration of afterdischarge at 300 mg/kg (i.p.) without modifying the seizure and without prestimulation behavioral or electrical effects. The largest dose tested (600 mg/kg, i.p.) resulted in a significant reduction of the elicited duration of afterdischarge but was associated with a 25% incidence of prestimulation spontaneous electrical seizure activity and a 45% incidence of post-afterdischarge electrical seizure activity. When CP 1552-S (30-300 mg/kg, i.p.) was administered daily, prior to the amygdaloid kindling stimulus, no difference was noted in the rate of acquisition of the kindled amygdaloid response. It is concluded that the glycine derivative CP 1552-S, has little anticonvulsant activity against the acquisition or development of kindled amygdaloid seizures. It appears to have significant anticonvulsant effects against both cortically- and amygdaloid-kindled afterdischarges with little effect on the behavioral severity of the seizure. Further, large doses of CP 1552-S appeared to result in paradoxical post-afterdischarge and possibly prestimulation electrical seizure activity.

An analysis of the actions of progabide, a specific GABA receptor agonist, on kindling and kindled seizures

The anticonvulsant properties of the specific GABA receptor agonist, progabide, were evaluated in the kindled amygdaloid seizure model in rats. Progabide attenuated afterdischarge durations and the severity of the accompanying convulsive responses in previously kindled rats. This effect occurred only at doses that also produced sedation and ataxia. When administered daily during kindling acquisition, progabide increased the number of trials necessary to complete kindling. The duration and severity of responses induced by stimulations during the acquisition period were reduced in a dose-dependent manner. In spite of these changes during the acquisition period, all subjects exhibited kindled behavior comparable to that of controls when they had accrued the same total afterdischarge experience. In light of these and other data regarding the GABA system and its influences on kindling, we conclude that GABA acts nonspecifically to attenuate various seizure states. It appears that GABA plays no major role in the mechanisms actually responsible for kindling development.

The kindled amygdala model of epilepsy: anticonvulsant action of amino acid antagonists

The amygdalas of rats were stimulated daily to produce kindled epilepsy. Superfusion of the ipsilateral ventricle allowed collection of amino acids before, during and after stimulation. At the stage where stimulation evoked full seizures there was a correlated increase in the extent of glutamate release. Other amino acids, including aspartate, showed no significant changes at this time. Aspartate, threonine and serine showed smaller responses not significantly different from those seen at the pre-kindled stage. Antagonists of excitatory amino acids (omega-phosphono-alpha-amino dicarboxylic acids) effectively antagonized both the behavioral and electrical components of the kindled seizures.