Pharmacology of cortical epileptic afterdischarges in rats

An antagonist of calcium permeable AMPA receptors, IEM1460: Anticonvulsant action in immature rats?

AMPA receptors lacking GluA2 subunit are widely distributed in developing brain. IEM1460 as a specific antagonist of these receptors might be a potential age-specific anticonvulsant. Possible anticonvulsant action was assessed in two models of epileptic seizures: pentylenetetrazol (PTZ) - induced convulsions and cortical afterdischarges elicited in 12-, 18- and 25-day-old rats. IEM1460 was administered intraperitoneally in doses of 3, 10 and 20mg/kg. Pretreatment with IEM1460 at the dose of 20mg/kg resulted in delayed onset of PTZ-induced minimal clonic seizures in all age groups. PTZ-induced generalized tonic-clonic seizures were suppressed in 18- and 25-day-old rats by 10 and 20mg/kg doses of IEM1460. Duration of cortical afterdischarges progressively increased with repeated stimulations in control 12-day-old rats. The IEM1460 dose of 10mg/kg fully blocked this prolongation and the 20-mg/kg dose partly suppressed it. Administration of IEM1460 had moderate proconvulsant effect on 18- and 25-day-old animals - afterdischarges were prolonged with repeated stimulations. The duration of cortical epileptic afterdischarges in adult (80-day-old) animals was not affected by IEM1460. Effects of IEM1460 are dependent on the model of seizures used, their ictogenic structures and developmental changes in subunit composition of AMPA receptors.

A1 not A2A adenosine receptors play a role in cortical epileptic afterdischarges in immature rats

Endo- as well as exogenous adenosine exhibits anticonvulsant action. Participation of individual types of adenosine receptors was studied in present experiments in immature rats. Cortical epileptic afterdischarges were used as a model in rat pups 12, 18 and 25 days old. CCPA, an agonist of A1 adenosine receptors, decreased markedly duration of afterdischarges whereas DPCPX, an antagonist of A1 receptors, exhibited strong proconvulsant action. Action of either drug was best expressed in 12-day-old rats and it decreased with age. Drugs influencing A2A adenosine receptors (agonist CGS21680 and antagonist ZM241385) did not exhibit systematic effects in our model. Motor phenomena accompanying cortical stimulation or epileptic afterdischarge were never influenced by any of the four drugs studied. A1 adenosine receptors are important in the model of cortical seizures, especially in the youngest group studied.

Five percent CO₂ is a potent, fast-acting inhalation anticonvulsant

PURPOSE

CO₂ has been long recognized for its anticonvulsant properties. We aimed to determine whether inhaling 5% CO₂ can be used to suppress seizures in epilepsy patients. The effect of CO₂ on cortical epileptic activity accompanying behavioral seizures was studied in rats and nonhuman primates, and based on these data, preliminary tests were carried out in humans.

METHODS

  In freely moving rats, cortical afterdischarges paralleled by myoclonic convulsions were evoked by sensorimotor cortex stimulation. Five percent CO₂ was applied for 5 min, 3 min before stimulation. In macaque monkeys, hypercarbia was induced by hypoventilation while seizure activity was electrically or chemically evoked in the sensorimotor cortex. Seven patients with drug-resistant partial epilepsy were examined with video-EEG (electroencephalography) and received 5% CO₂ in medical carbogen shortly after electrographic seizure onset.

RESULTS

In rats, 5% CO₂ strongly suppressed cortical afterdischarges, by approximately 75%, whereas responses to single-pulse stimulation were reduced by about 15% only. In macaques, increasing pCO₂) from 37 to 44-45 mm Hg (corresponding to inhalation of 5% CO₂ or less) suppressed stimulation-induced cortical afterdischarges by about 70% and single, bicuculline-induced epileptiform spikes by approximately 25%. In a pilot trial carried out in seven patients, a rapid termination of electrographic seizures was seen despite the fact that the application of 5% CO₂ was started after seizure generalization.

CONCLUSIONS

Five percent CO₂ has a fast and potent anticonvulsant action. The present data suggest that medical carbogen with 5% CO₂ can be used for acute treatment to suppress seizures in epilepsy patients.

Seizure severity and duration in the cortical stimulation model of experimental epilepsy in rats: a longitudinal study

The aim of this study was to determine the current intensities necessary to elicit three levels of varying EEG and behavioural phenomena with electrical stimulation, and also to determine the consistency of the EEG and behavioural components of the triggered seizures over time. Electrical stimulation of the primary motor/somatosensory cortex was performed in 16 adult rats with multichannel microwire electrode arrays. Stimulation was delivered at a frequency of 60 Hz (1 ms pulse width), for 2 s duration, as biphasic rectangular pulses over four of the eight available electrode pairs. Current intensity thresholds for interruption of normal behaviour, epileptiform afterdischarge (EAD) longer than 5 s and motor seizures with Racine severity greater than 3 were not correlated to time post-surgery. The Racine threshold was shown to be negatively correlated to the EAD duration and Racine severity of seizures elicited in the following sessions. Seizures were reliably generated in rats through cortical stimulation with microwire electrode arrays and these seizures were not shown to be subject to any kindling type effects up to 53 days post-implantation. Both the electrographic duration and behavioural severity of stimulated seizures remained, on average, constant during this experimental period. Approximately one-third of stimulations did not cause observable motor seizures and of those that did result in seizures, forelimb clonus was the most common manifestation and the mean EAD duration was 18.5 s. No damage beyond that caused by surgical implantation of electrodes was observed in the histological analyses of stimulated and non-stimulated tissue. The consistency, duration and severity of seizures within this timeframe make this cortical stimulation model suitable for investigations into novel therapeutic interventions for epilepsy that require a known seizure focus.

Postictal behavior after two types of cortical epileptic afterdischarges in rats

OBJECTIVE

The aim of this study was to determine if behavioral patterns during the postictal state depend on the type of seizure.

METHODS

Rhythmic electrical stimulation of sensorimotor cortex can elicit two types of epileptic afterdischarges (ADs) in adult rats: the spike-and-wave type accompanied by clonic convulsions, and a transition to a nonconvulsive type characterized by behavioral automatisms (mixed type). Rats in which stimulation did not induce ADs constituted the control group. The behavior of the animals was recorded for 20 minutes after the end of ADs or stimulation.

RESULTS

Stimulation elicited only shortlasting minimal changes in control rats. Spike-and-wave ADs led to alternation of normal and unsteady walking, a decrease in normal sitting and lying (rigid lying appeared instead), and wet dog shakes (WDS). Mixed-type ADs abolished normal walking and sitting and induced unsteady walking, rigid lying, and a substantial number of WDS.

CONCLUSIONS

Abnormal phenomena induced by the two types of ADs differ mostly quantitatively, but also qualitatively.

Biphasic effect of chronic postnatal caffeine treatment on cortical epileptic afterdischarges during ontogeny in rats

EEG and motor phenomena elicited by stimulation of sensorimotor cortex were used to study the effects of chronic postnatal administration of caffeine (10 and 20 mg/kg, s.c. from P7 to P11) in rats. Rhythmic electrical stimulation was applied to 12-, 18-, 25- and 67-day-old rats with implanted electrodes. Animals with the higher dose of caffeine exhibited increased thresholds for elicitation of stimulation-bound movements, spike-and-wave afterdischarges (ADs) and clonic seizures accompanying these ADs at the age of 12 days and decreased duration of spike-and-wave ADs at postnatal days (P) 18 and 25. In contrast, chronic administration of the lower dose of caffeine resulted in a proconvulsant effect expressed as a significant prolongation of spike-and-wave ADs in P12, P18 and P25 groups as well as of the second "limbic" type of ADs (significant only in P12 and P25). The biphasic action of chronic postnatal caffeine treatment was transient and was no longer present in 67-day-old rats. Our results demonstrate that early postnatal caffeine exposure results in either pro- or anticonvulsant effect during brain maturation in relation to the dose used. Caffeine is a mixed adenosine receptor antagonist, therefore its effects could be due to a different action on adenosine receptor subtypes; an additional mechanism of action cannot be excluded.

Anticonvulsant action of an antagonist of metabotropic glutamate receptors mGluR5 MPEP in immature rats

Antagonists of type I of metabotropic glutamate receptors exhibit anticonvulsant action in adult as well as immature rodents. To know the anticonvulsant profile of a specific mGluR5 antagonist MPEP in developing rats, two models of epileptic seizures were used. MPEP (10, 20 or 40 mg/kg i.p.) suppressed in a dose-dependent manner epileptic afterdischarges induced by electrical stimulation of sensorimotor cortical area in three age groups (12, 18 and 25 days old). The anticonvulsant action was more expressed in the youngest group than in older animals so that in 25-day-old rats an additional dose of 80 mg/kg was used. In contrast to this marked anticonvulsant action, MPEP at a dose of 40 mg/kg i.p. in 18-day-old rat pups and at doses of 40 and 80 mg/kg in 25-day-old rat pups did not affect episodes of spike-and-wave rhythm elicited by low doses of pentetrazol. Our results delineate the profile of the anticonvulsant action of MPEP and confirm the higher efficacy of this antagonist at early developmental stages in comparison with prepubertal animals.

Cortical and limbic excitability in rats with absence epilepsy

The classical cortico-reticular theory on absence epilepsy suggests that a hyperexcitable cortex is a precondition for the occurrence of absence seizures. In the present experiment seizure thresholds and characteristics of cortical and limbic epileptic afterdischarges (AD) were determined in a comparative cortical stimulation study in young and old adult genetically epileptic WAG/Rij, congenic ACI and Wistar rats. Fifteen-second series of 8Hz stimulation of the sensory-motor cortex were applied in 80- and 180-day-old rats with implanted electrodes. Strain differences were found for the threshold for movements directly induced by stimulation, low frequency spike-and-wave AD, maximal clonic intensity of seizures accompanying direct stimulation, and frequency characteristics of low frequency AD. None of these results agreed with a higher cortical excitability exclusively in WAG/Rij rats. However, WAG/Rij rats had the longest duration of the low frequency AD, and the lowest threshold for the transition to the limbic type of AD. The decrease of this threshold correlated with the increase of the incidence and total duration of spontaneous SWDs in WAG/Rij rats. It is concluded that the elevated excitability of the limbic system or pathways mediating the spread of the epileptic activity into this system can be attributed to the development of genetic epileptic phenotype in WAG/Rij rats.

Biphasic action of vigabatrin on cortical epileptic after-discharges in rats

The time course of the anticonvulsant effect of vigabatrin against cortically induced epileptic after-discharges (ADs) was studied in freely moving rats with implanted electrodes. Adult rats (n=30) were exposed to five stimulation sessions each consisting of six stimulation series at 20-min intervals. The first session was a control one, then two groups of animals (n=10 each) were given vigabatrin (600 or 1,200 mg/kg i.p.), the control animals received physiological saline. Stimulation sessions were repeated 1, 24, 48, and 96 hours after the injection. Control animals exhibited an increased transition from the spike-and-wave type of AD to the second, "limbic" type and an increased intensity of movements accompanying stimulation. ADs in the second and subsequent sessions were, however, shorter than in the first session. Vigabatrin facilitated the transition to the second type of AD 1 h after administration but suppressed this transition as well as decreased the number of stimulations eliciting ADs 48 h later. AD duration and the severity of clonic seizures accompanying spike-and-wave ADs were influenced similarly. The effects of the lower dose of vigabatrin were more marked than those of the higher dose. The biphasic action of vigabatrin in our model might be due either to uneven changes of GABA concentration in different brain structures or to an additional mechanism of action. Our results in a cortical model of seizure demonstrate that the sequence of pro- and anticonvulsant actions of vigabatrin is not restricted to seizures of limbic origin and might represent a general phenomenon.

Interaction of excitatory amino acid agonists with cortical afterdischarges in developing rats

PURPOSE

To determine the role of excitatory amino acids (EAAs) in genesis of two types of epileptic afterdischarges.

METHODS

Cortical stimulation and recording electrodes were implanted in 12-, 18-, and 25-day-old rats. Epileptic afterdischarges were induced by rhythmic stimulation of sensorimotor cortex. The stimulation was repeated 6 times with 20-min intervals. Ten minutes after the first afterdischarge, N-methyl-d-aspartate, homocysteine, or kainic acid was injected. The doses were chosen individually for different age groups to be subconvulsive. Type and duration of afterdischarges as well as type and severity of motor correlates were evaluated.

RESULTS

N-methyl-d-aspartate prolonged afterdischarges only in 12-day-old rats, whereas two other drugs did it in all age groups. Motor correlates of afterdischarges were changed to flexion seizures in 12-day-old rats after N-methyl-d-aspartate and homocysteine; in 25-day-old rats homocysteine led to generalized tonic-clonic seizures (i.e., both patterns seen after substantially higher doses of these drugs in nonstimulated rats). Seizures lasted tens of minutes. Kainic acid did not change the motor pattern in any age group, but nonconvulsive EEG seizures were recorded in the interstimulation periods mainly in 18- and 25-day-old rats. Increased transition into the limbic type of afterdischarges appeared only after homocysteine in 18- and 25-day-old rats.

CONCLUSIONS

A mutual potentiation of epileptic phenomena was induced by two agents. The actions of N-methyl-d-aspartate and kainic acid differ in all age groups; the effects of homocysteine were identical with those of N-methyl-d-aspartate in 12-day-old rats but not later. Only homocysteine augmented transition into the limbic type of afterdischarges.

Effects of classical antiepileptics on thresholds for phenomena induced by cortical stimulation in rats

Our aim was to study the effects of phenobarbital, phenytoin and ethosuximide on epileptic afterdischarges induced by cortical stimulation in rats. Fifteen-second series of low-frequency (8 Hz) rhythmic stimulation of the sensorimotor cortex were applied in rats with chronically implanted electrodes. Intervals between the stimulation series were at least 10 min and intensity was increased in a step-wise manner. Threshold current intensities were estimated for movements directly induced by stimulation, epileptic afterdischarges of the spike-and-wave type, clonic seizures accompanying this type of afterdischarge and transition into the limbic type of afterdischarge. Phenobarbital, phenytoin and ethosuximide were administered intraperitoneally before the first stimulation series. Phenobarbital (20, 40 and 80 mg kg(-1)) significantly increased the thresholds for the first three phenomena in a dose-dependent manner. Transition into the limbic afterdischarge was influenced only by the highest dose. Phenytoin (60 mg kg(-1)) only increased the thresholds insignificantly and ethosuximide (125 mg kg(-1)) was ineffective. We concluded that our model is useful for testing anticonvulsant effects. Results with three antiepileptic drugs correspond with their efficacy against myoclonic seizures in man.

Changes of cortical epileptic afterdischarges under the influence of convulsant drugs

Convulsant drugs picrotoxin (0.5 and/or 1 mg/kg, intraperitoneal (i.p.)) and pentylenetetrazol (10 and/or 20 mg/kg, i.p.) were used to compromise GABAergic inhibition, caffeine (75 and/or 150 mg/kg, i.p.) to antagonize adenosinergic system to study the role of inhibition in cortical epileptic afterdischarges. Rats with implanted cortical stimulation and registration electrodes were stimulated four times at 10-min intervals, drugs were injected between the first and second stimulation. Four different phenomena were evaluated: movements directly bound to stimulation were intensified by all three drugs, i.e., excitability of the cerebral cortex was increased. Incidence of two types of afterdischarges (spike-and-wave rhythm and "limbic" type) was not changed by any drug, i.e., the transition of epileptic activity into limbic structures was not increased. Afterdischarges were most efficiently prolonged by caffeine, i.e., caffeine probably interferes with mechanism(s) arresting cortical afterdischarges. The intensity of clonic seizures accompanying spike-and-wave afterdischarges, i.e., spread of epileptic activity into the motor system was only transiently increased by picrotoxin, the effects of caffeine did not reach the level of statistical significance. Our results indicate various mechanisms and diverse role of the two inhibitory systems in generation of evaluated phenomena.

Unequal development of thresholds for various phenomena induced by cortical stimulation in rats

Electrical stimulation of sensorimotor cortical area was performed in 9-, 12-, 18-, 25-, 35- and 90-day-old rats with implanted electrodes to establish threshold intensities of currents necessary to elicit four different motor or EEG phenomena. Two different stimulation frequencies (8 and 50 Hz) were used. Development of thresholds for stimulation-bound movements, spike-and-wave afterdischarges and clonic seizures accompanying these afterdischarges was similar: the lowest threshold was found in 18-, respectively, in 18- and 25-day-old rats with the 8 and 50 Hz frequencies. Younger as well as older animals exhibited higher threshold intensities. The fourth phenomenon, transition into another, 'limbic' type of afterdischarges appeared only exceptionally in the youngest rats and its incidence increased whereas the threshold decreased with age. Higher frequency was more efficient in elicitation of limbic afterdischarges than the 8 Hz stimulation in rats aged 18 and more days. Our data represent a background for pharmacological studies and indicate the development of cortical excitability and of connections between the thalamocortical system and limbic structures.

Single systemic dose of vigabatrin induces early proconvulsant and later anticonvulsant effect in rats

Vigabatrin (VGB), an inhibitor of gamma-aminobutyric acid-aminotransferase, exhibits an antiepileptic effect but several studies indicate that its effect may be biphasic. A time course of an effect of a single injection of VGB on hippocampal epileptic afterdischarges (AD) elicited by an electric stimulation of the angular bundle was examined in adult rats with chronically implanted electrodes. VGB (600 or 1200 mg/kg intraperitoneally) proved to be an efficient anticonvulsant in the intervals of 24 and 48 h--duration of ADs was shortened and behavioral phenomena were less intense. In contrast, ADs were lengthened 4 h after administration. The biphasic effect of VGB was demonstrated, the initial proconvulsant effect might be due to a different onset of VGB action in individual brain structures, but an additional mechanism of action cannot be excluded.

Proconvulsant effect of aminophylline on cortical epileptic afterdischarges varies during ontogeny

Effect of aminophylline on epileptic afterdischarges (ADs) induced repeatedly by rhythmic electrical stimulation of sensorimotor cortical area was studied in rat pups 12, 18 and 25 days old. The proconvulsant effect of aminophylline (50 and/or 100 mg/kg i.p.) was more expressed in 12- and 18-day-old rats than in the oldest group. In 12-day-old rat pups there was an enormous increase of transition of the spike-and-wave type of ADs into the second, limbic type, a situation observed only exceptionally under control conditions. A prolongation of ADs was related to this transition (limbic ADs are always longer than spike-and-wave ones). Eighteen-day-old rats exhibit this transition less frequently but a marked prolongation of spike-and-wave ADs was recorded in a part of these animals forming a pattern of status lasting some tens of minutes. Aminophylline led only to a transient prolongation of spike-and-wave ADs in the oldest group. The transition into the limbic type of ADs was seen in this age group only exceptionally what is in contrast to age-matched controls in which this transition is common. The effect of aminophylline on cortical ADs which is most marked in the youngest group changes qualitatively during postnatal development.

GABA uptake blocker NNC-711 exhibits marked anticonvulsant action in two cortical epileptic models in immature rats

PURPOSE

To study the anticonvulsant action of a gamma-aminobutyric acid (GABA) uptake inhibitor NNC-711 in two models of cortical epileptogenesis in immature rats.

METHODS

Twelve-, 18-, and 25-day-old rat pups with implanted electrodes were used in this study. Epileptogenic foci were elicited by a local application of bicuculline methiodide (BMI) on the sensorimotor cortical region by means of an implanted cannula, and cortical epileptic afterdischarges (ADs) were induced by low-frequency stimulation (8 Hz) of the same cortical area. Epileptogenic foci were formed after pretreatment with NNC-711 (1 or 10 mg/kg, i.p.), and epileptic ADs were elicited in the second experimental series. Then NNC-711 was administered in the same doses, and stimulation was repeated.

RESULTS

NNC-711 did not block the formation of epileptogenic foci, but it significantly suppressed the spontaneous transition of interictal focal into ictal activity in all age groups. The intensity of movements accompanying stimulation of the sensorimotor cortex was less under the influence of NNC-711 in the 18- and 25-day-old rats. The duration of cortical ADs was shortened in all age groups, but transient abolition of ADs was observed only after the higher dose in the 25-day-old rats. In addition, the intensity of clonic seizures appearing during ADs decreased, and the transition of ADs into another type due to an involvement of limbic structures failed to appear in the 18- and 25-day-old rats.

CONCLUSIONS

Primary epileptogenesis in the cerebral cortex was hardly influenced by NNC-711, but the spread of epileptic activity was markedly suppressed. This effect was better expressed in the 18- and 25-day-old animals than in the youngest group.

Effect of a subconvulsant dose of kainic acid on thresholds for phenomena elicited by electrical stimulation of sensorimotor cortex in rats

Electrical stimulation of sensorimotor cortex was used to study early and late effects of administration of kainic acid in a dose (6 mg/kg i.p.) eliciting only nonconvulsive seizures in rats. Thresholds for elicitation of four phenomena--movements directly related to stimulation; epileptic afterdischarges (ADs) of the spike-and-wave type; clonic seizures accompanying these ADs; and mixed type of ADs where spike-and-wave activity transgresses into limbic type of epileptic phenomena--were measured. Acute administration of kainic acid resulted in a decrease of the threshold for elicitation of mixed type of ADs. In contrast, 1 week after kainic acid administration, the thresholds for stimulation-bound movements, spike-and-wave ADs and concomitant clonic seizures were increased, but the threshold for mixed type of ADs remained unchanged. The changes in thresholds tended to decrease 2 weeks after kainic acid but statistical significance was reached only for stimulus-bound movements. In addition, repetition of stimulation series after 1 as well as 2 weeks markedly influenced the thresholds.

Effects of a subconvulsant dose of kainic acid on afterdischarges elicited by cortical stimulation in rats

The aim of this study was to test the hypothesis that nonconvulsive seizures elicited by a low dose of kainic acid may induce acute as well as chronic changes in brain function. Cortical epileptic afterdischarges (ADs) characterized by spike-and-wave rhythm and clonic seizures of facial and forelimb muscles were elicited in adult male rats with chronically implanted electrodes. Four stimulations were given in each of four weekly sessions. In the second session, 26 animals were injected with kainic acid (6 mg/kg i.p.) and 19 rats received no injection. The acute effects of kainic acid were to increase the intensity of movements accompanying stimulation and abruptly prolong ADs. Epileptic ADs were followed by a depression of electrocorticographic activity in both noninjected and kainic acid groups. In addition, when kainate was administered, interictal spike activity was registered mostly in the occipital region. One and two weeks after kainate administration, i.e. in the third and fourth stimulation sessions, there was an increased incidence of transitions from spike-and-wave ADs to another, limbic type of afterdischarge. This functional change persisted although no obvious neuronal death was found in the hippocampi of 12 other rats that received the same dose of kainic acid.

Non-NMDA receptor antagonist GYKI 52466 suppresses cortical afterdischarges in immature rats

GYKI 52466 (1-(4-aminophenyl)-4-methyl-7,8-methylendioxy-5H-2,3-benzo-diaz epi ne), a non-competitive non-NMDA receptor antagonist, was tested against epileptic afterdischarges elicited by cortical stimulation in 12-, 18- and 25-day-old rats with implanted electrodes. Shortening of afterdischarges and a decrease in intensity of clonic movements accompanying both stimulation and afterdischarges were induced by the 20 mg/kg dose of GYKI 52466 in 18- and 25-day-old animals, whereas 12-day-old rat pups exhibited only shortening of electroencephalographic afterdischarges. The 10 mg/kg dose of GYKI 52466 did not significantly change afterdischarges in any age group. Motor skills were compromised after the 20 mg/kg dose of GYKI 52466. This effect was again more marked in 18- and 25-day-old animals than in the youngest group. In addition, anxiolytic-like action was observed in the jumping down test in 25-day-old rats. This effect was not influenced by a benzodiazepine antagonist flumazenil. On the contrary, the anticonvulsant action of GYKI 52466 was partly blocked by flumazenil, indicating thus multiple mechanisms of action of GYKI 52466.

Suppression of cortical epileptic afterdischarges in developing rats by anticonvulsants increasing GABAergic inhibition

The anticonvulsant action of three drugs facilitating GABAergic inhibition by different mechanisms (valproate, phenobarbital and progabide) was studied in 229 young rats (12, 18 and 25 days old) with implanted electrodes. Epileptic afterdischarges (ADs) elicited by electrical stimulation of the sensorimotor cortex were used as a model. All three drugs were able to suppress ADs, even the lowest doses used blocked the prolongation seen with repeated stimulations under control conditions. In addition to these general effects, some differences among the three drugs were observed: phenobarbital (10, 20, and 40 mg/kg i.p.) exhibited marked anticonvulsant action in all three age groups whereas valproate (200 and 400 mg/kg i.p.) was somewhat less effective in the youngest rats studied than in the two older groups. Progabide exhibited an effect similar to valproate when a higher dose (150 mg/kg i.p.) was taken into account, but the lower dose (75 mg/kg i.p.) was most efficient in 12 day old rat pups. Our data support the possibility that cortical ADs represent a model of human myoclonic seizures. In addition, they suggest an uneven development of individual components of the GABAergic inhibitory system.