Electroencephalographic Characteristics of Audiogenic Seizures Induced in Metaphit-Treated Small Rodents

Adult male mice, rats, and guinea pigs were subjected to intense sound stimulation of an electric bell (100 dB, 12 kHz for 60 s) after a single intraperitoneal (i.p.) injection of metaphit (1-(1-(3 isothiocyanatophenyl)-cyclohexyl)piperidine) (50 mg/kg). When the animals were tested 24 h after administration of metaphit, audiogenic seizures were observed. None of the control saline-injected animals had convulsions. EEG recordings demonstrated the appearance of paroxysmal activity and spike-wave complexes in the trace from cortical and hippocampal electrodes, with frequency and amplitude increasing with time. Behaviorally, myoclonic jerks of facial muscles, ears, and neck appeared, but no correlation was noted between EEG and the motor phenomena. Auditory stimulation was necessary to elicit the full-blown sequence of seizure responses consisting of wild running followed by clonic and then tonic extension. At the time of seizures, repetitive high-amplitude spikes and waves appeared in the EEG, followed by profound EEG and behavioral depression. None of the animals died during or immediately after seizures. The seizure response to sound stimulation of mice, rats, and guinea pigs was phenomenologically similar, with minor differences in quantitative pattern of convulsive components, which suggests that all three animal species share the common property of extreme susceptibility to audiogenic stimulation caused by metaphit administration.     

Metaphit-Induced Audiogenic Seizures in Mice: I. Pharmacologic Characterization

Summary: Metaphit [an analogue of phencyclidine (PCP) with an acylating isothiocyanate group] induced audiogenie clonic to clonic-tonic seizures in mice exposed to audio stimulation 24 h after metaphit administration. The incidence of seizures was reduced by treatment 30 min before audio stimulation with specific PCP-like compounds [5-methyl-10, ll-dihydro-5H-dibenzo(a, d)cyclohepten-5,10-imine maleate (MK-801), and PCP itself], competitive N-methyl-d -aspartate antagonists 2-amino-5- phosphonopentanoic acid (AP-5 and NPC-12626), antiepileptic drugs [phenobarbital (PB), phenytoin (PHT)], and γ-aminobutyric acid (GABA) agonists (muscimol and diazepam). In contrast, when given in conjunction with metaphit, most of these drugs were ineffective in protecting animals from audiogenic seizures 24 h later. Only compounds with long half-lives (t½) such as MK-801, PB, and PHT had a protective effect. High-performance liquid chromatography (HPLC) determination of [³H]MK-801 showed its long-term presence in the brain after intraperitoneal (i.p.) administration of [³H]MK-801. Audiogenic seizures observed 24 h after metaphit administration were potentiated by administration of the GABA antagonist picrotoxin 15 min before audio stimulation, and picrotoxin-induced spontaneous seizures were enhanced by pretreatment (24 h earlier) with a dose of metaphit that in itself did not produce spontaneous seizures at the time of the picrotoxin test. Similar observations were made with N-methyl d -aspartic acid (NMDA) instead of picrotoxin. Thus, an interplay exists between excitatory glutaminergic and inhibitory GABAergic circuitries in the metaphit seizure model.     

Kindling of audiogenic seizures in the rat

A strain of Wistar rats was inbred in our laboratory for its susceptibility to sound. The seizures are characterized by one or two wild running fits which terminate in a tonic dorsiflexion with open mouth, followed by a catatonic state. During the tonic phase of the seizure, the cortical EEG is flattened for 2 to 3 s. Then, a slow and regular low-voltage (9-12 c/s) activity is observed during 40 to 60 s. When these animals are submitted to daily sound-stimulations, the behavioral as well as the EEG manifestations of the audiogenic seizures change progressively. After 5 to 30 exposures, the wild running becomes disorganized by occurrence of myoclonic jerks of the limbs and the body. In some animals, the tonic extension disappears and a myoclonic seizure develops progressively with facial and forelimb clonus, rearing and falling. In other animals, the tonic phase still occurs and is followed by a generalized clonic phase. During both the myoclonic and the tonicoclonic seizures, rhythmic spikes, polyspikes and spike and waves of high amplitude (1-10 c/s) during 40 to 120 s are observed on EEG recordings. These EEG modifications often outlast the sound stimulation. The pharmacological reactivity in rats exposed to single or repeated audiogenic seizures is similar: phenytoin and carbamazepine suppress both kinds of seizures at low doses whereas ethosuximide is efficacious only at high doses. In order to know whether the repeated exposure to sound or the repetition of seizures are responsible of the observed changes in audiogenic seizures, animals susceptible to sound were exposed daily to the seizure-inducing sound after previous injection of Diazepam, which prevented them from convulsing. On the other hand, sound susceptible animals were injected daily with a dose of PTZ inducing one or several convulsions without exposure to sound. None of these treatments ever facilitated the development of kindled audiogenic seizures. The progressive modification of behavioral and EEG modifications occurring when audiogenic seizures are repeated suggests that kindling has developed, the seizure extending from the brainstem to forebrain structures.     

Antiepileptic activity of delta sleep-inducing peptide and its analogue in metaphit-provoked seizures in rats.

PROBLEM: Previous studies have shown that humoral, endogenous and somnogenic, delta sleep-inducing peptide (DSIP) has influence on insomnia, pain, adaptation to stress, epilepsy, etc. We investigated the potential of DSIP and its analogue DSIP-12 (a nonapeptide with alanine in position 2 of DSIP molecule substituted by beta-alanine) to antagonize metaphit (1-[1(3-isothiocyanatophenyl)-cyclohexyl]piperidine) induced generalized, reflex audiogenic seizures in adult male Wistar albino rats. METHODS: The rats divided in four groups received (i.p.): saline; metaphit; metaphit+DSIP; and metaphit+DSIP-12, respectively. Metaphit-treated animals displaying seizure in eight previous tests received DSIP or DSIP-12 and afterwards audiogenic stimuli were applied at hourly intervals for the next 30 h. The animals were exposed to sound stimulation 60 min after metaphit administration and further on at hourly intervals. Incidence and severity of seizures were behaviorally analyzed. Selected EEGs and power spectra were recorded and analyzed. RESULTS AND CONCLUSIONS: Metaphit led to hypersynchronous epileptiform activity (polyspikes and spike-wave complexes) and increased power spectra 0.5-30 h after the treatment. Severity of metaphit seizures increased with time to reach the peak 7-12 h after injection. DSIP and DSIP-12 significantly (*P<0.05 and **P<0.01) increased in delta and theta frequency bands and decreased the incidence, mean seizure grade and duration of metaphit convulsions. The results suggest that DSIP and DSIP-12 may be considered as potential antiepileptics in the animal model, DSIP-12 being more efficient than DSIP.     

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

Summary 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 lowamplitude discharge, 9 to 12c/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.     

Anticonvulsive and antiepileptogenic effects of levetiracetam in the audiogenic kindling model

Purpose: To study anticonvulsive and antiepileptogenic effects of singe levetiracetam (LEV) administration in the model of audiogenic kindling.
Methods: Rats of Krushinsky-Molodkina (KM) strain genetically susceptible to severe audiogenic seizures received one intraperitoneal injection of saline, low (6 mg/kg) or high (50 mg/kg) dose of LEV before or after audiogenic kindling. One hour postinjection, an audiogenic seizure was induced to assess anticonvulsive effect of LEV in nonkindled and kindled rats. To examine antiepileptogenic activity of LEV, nonkindled rats injected with the drug or saline were kindled with repeated sound stimulations. Audiogenic kindling development manifested in an appearance and progressive prolongation of an additional seizure phase, post-tonic–clonus. The latency and duration of audiogenic seizures and the duration of every seizure phase (running, tonic, post-tonic–clonic) were measured.
Results: One hour posttreatment, LEV dose-dependently lengthened the latency and reduced the duration of audiogenic seizures in both nonkindled and kindled rats. The seizure shortening resulted from selective suppression of tonic and kindled post-tonic–clonic phases. The dose of 50 mg/kg completely blocked tonic and clonic convulsions 1 h postinjection. The anticonvulsive effect of LEV was more pronounced in kindled than in nonkindled rats. Single LEV injection in the dose of 50 mg/kg prior audiogenic kindling significantly suppressed subsequent kindling progression indicating profound antiepileptogenic potency of the drug.
Conclusions: The present study shows that LEV exerts both short-lasting anticonvulsive effect on audiogenic seizures and very long-lasting antiepileptogenic effect on audiogenic kindling. Remarkably, a single injection of LEV is enough to significantly suppress kindling progression in KM rats.     

Combined diazepam and MK-801 therapy provides synergistic protection from tetramethylenedisulfotetramine-induced tonic–clonic seizures and lethality in mice

The synthetic rodenticide, tetramethylenedisulfotetramine (TMDT), is a persistent and highly lethal GABA-gated Cl⁻ channel blocker. TMDT is clandestinely produced, remains popular in mainland China, and causes numerous unintentional and deliberate poisonings worldwide. TMDT is odorless, tasteless, and easy to manufacture, features that make it a potential weapon of terrorism. There is no effective treatment. We previously characterized the effects of TMDT in C57BL/6 mice and surveyed efficacies of GABAergic and glutamatergic anticonvulsant treatments. At 0.4 mg/kg i.p., TMDT produced neurotoxic symptomatology consisting of twitches, clonic and tonic–clonic seizures, often progressing to status epilepticus and death. If administered immediately after the occurrence of the first clonic seizure, the benzodiazepine diazepam (DZP) effectively prevented all subsequent seizure symptoms, whereas the NMDA receptor antagonist dizocilpine (MK-801) primarily prevented tonic–clonic seizures. The latter agent, however, appeared to be more effective at preventing delayed death. The present study further explored these phenomena, and characterized the therapeutic actions of DZP and MK-801 as combinations. Joint treatment with both DZP and MK-801 displayed synergistic protection against tonic–clonic seizures and 24 h lethality as determined by isobolographic analysis. Clonic seizures, however, remained poorly controlled. A modification of the treatment regimen, where DZP was followed 10 min later by MK-801, yielded a reduction in both types of seizures and improved overall outcome. Simultaneous monitoring of subjects via EEG and videography confirmed effectiveness of this sequential regimen. We conclude that TMDT blockage at GABA_A receptors involves early activation of NMDA receptors, which contribute to persistent ictogenic activity. Our data predict that a sequential combination treatment with DZP followed by MK-801 will be superior to either individual therapy with, or simultaneous administration of, these two agents in treating TMDT poisoning.     

Audiogenic kindling in the Wistar rat: a potential model for recruitment of limbic structures

Repetitive high intensity (110 dB) sound stimulation induces a forebrain-kindling phenomenon in animals predisposed to sound induced seizures. Wistar audiogenic rats (WARs) have been reported to develop a mixed brainstem-limbic seizure pattern, after more than five to ten stimuli. Besides the original brainstem wild running and tonic-clonic seizures, new behavioral patterns appear resembling those of electrical amygdala kindling. Although audiogenic kindling is a well-known phenomenon, electrographic limbic recruitment during the kindling has never been reported. Our objective was to use electrophysiology to test the hypothesis of gradual and sequential involvement of the amygdala and then cortex during audiogenic kindling. We used video-EEG recordings with cortical and deep electrode implants (inferior colliculus and basolateral amygdaloid nuclei) during audiogenic kindling on eight WARs, and their respective controls, submitted to a protocol of three acoustic stimuli per day. A new design for 'on site' source follower circuits was used in order to minimize noise during the recording of EEG data from the wild running episode and the subsequent tonic-clonic or motor limbic seizures. The video-EEG equipment assembled allowed synchronous recordings of both behavior and EEG. WARs first recordings showed electrodecremental responses after seizure onset and a probable epileptiform activity, particularly in the inferior colliculus, during the tonic phase of seizure. All animals showed very similar polyspike-wave activity in the amygdala, after behavioral seizure patterns (Racine's scale) occurred. The morphology of such epileptiform EEG activity is very similar to that reported for electrical amygdala kindling. Also, when audiogenic kindling continued, both inferior colliculus and cortical electrodes presented high amplitude and synchronized epileptiform polyspike activity.     

Vigabatrin in low doses selectively suppresses the clonic component of audiogenically kindled seizures in rats

PURPOSE: The effect of systemic administration of the gamma-aminobutyric acid (GABA)-transaminase inhibitor vigabatrin (VGB) on different components of convulsions was tested in the model of audiogenically kindled seizures, which consist of brainstem (running, tonus) and forebrain (clonus) elements. METHODS: Audiogenically susceptible rats of Krushinsky-Molodkina (KM), Wistar, and WAG/Rij strains received repeated sound stimulation (60 dB, 10-80 kHz) until kindled audiogenic seizures were reliably elicited. Kindled audiogenic seizures consisted of running, tonic, and generalized clonic phases in KM rats (severe audiogenic seizures) and of running and Racine stage 5 facial/forelimb clonus in Wistar and WAG/Rij rats (moderate seizures). Vehicle, 100, or 200 mg/kg of VGB was intraperitoneally injected 2, 4 and 24 h before the induction of kindled audiogenic seizures. RESULTS: At both doses, VGB did not change the seizure latency and the duration of running and tonic convulsions, but suppressed clonic ones in all rat strains. In KM rats, the mean duration of posttonic clonus was significantly reduced at 24 h after 100 mg/kg and from 4 h after 200 mg/kg. In Wistar and WAG/Rij rats, the mean duration of facial/forelimb clonus was reduced from 4 and 2 h after 100- and 200-mg/kg administration, respectively; 24 h after the high-dose injection, clonus was completely blocked in all rats of both strains. No difference in efficacy of VGB between Wistar and WAG/Rij rats was observed. CONCLUSIONS: VGB more effectively suppresses clonic convulsions than running and tonic ones in audiogenically kindled rats. It is supposed that this selective anticonvulsive effect of VGB results from different sensitivities of forebrain and brainstem epileptic networks to the presumed GABA enhancement.     

Metaphit-Induced Audiogenic Seizures in Mice: II. Studies on N-Methyl-d-Aspartic Acid,GABA, and Sodium Channel Receptors and on the Disposition of Metaphit in the Brain

Summary: We previously demonstrated that metaphit (a phencyclidine analogue with an acylating isothiocyanate group) induces occurrence of audiogenic seizures in mice exposed to audio stimulation 24 h after metaphit administration. We have studied various receptor systems associated with excitatory and inhibitory networks: sites for competitive and noncompetitive antagonists of the N-methyl d -aspartic acid (NMDA) receptor complex, for [³H]muscimol on the -γ-aminobutyric acid (GABA) receptor complex, and for [³H]batrachotoxinin A20-a-benzoate on the voltage-dependent sodium channel. Mice were examined for neurochemical changes at 24 h after pretreatment with metaphit, when susceptibility to audiogenic seizures is greatest. Ex vivo receptor binding studies detected no changes; in vivo labeling of the phencyclidine site in the NMDA receptor complex was reduced by 20% in cortical and midbrain regions. A separate group of experiments was aimed at measuring brain levels of metaphit. One minute after retroorbital administration of [³H]metaphit at a dose sufficient to produce susceptibility to audiogenic seizures 24 h later, the brain level of [³H]metaphit (determined by high-performance liquid chromatography, HPLC) was 49 pmol/mg tissue; at 1, 4, and 24 h, the level was 12, 6, and 1.4 pmol/mg tissue or μM if metaphit was evenly distributed throughout the brain. Although the observed metaphit concentrations during the first 4 h are high enough to acylate receptors, no firm evidence for acylation was found for most of the examined receptors. Finally, the time course of the brain level of metaphit showing a continuous decrease is entirely different from that of development of the seizure susceptibility, which peaks at 18–24 h.     

A comparison of the anticonvulsant effects of competitive and non-competitive antagonists of the N-methyl-D-aspartate receptor

The anticonvulsant activity of two competitive antagonists of the N-methyl-D-aspartate (NMDA) receptor, 2-amino-7-phosphonoheptanoic acid (APH) and 3-[2-carboxypiperazin-4-yl]-propyl-1-phosphonate (CPP), and two non-competitive NMDA antagonists, phencyclidine (PCP) and (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801), were compared in 4 models of induced seizures in mice. All 4 drugs protected against tonic extensor seizures induced by pentylenetetrazol (PTZ), by submaximal (15 mA) electroconvulsive shock (ECS) and by maximal (50 mA) ECS. Similar orders of potency (i.e., MK-801 greater than PCP greater than or equal to CPP greater than APH) were seen in each of the 3 seizure models. All 4 drugs failed to block clonic seizures induced by picrotoxin in the dose ranges that protected from tonic seizures. These data are consistent with other data demonstrating that competitive and non-competitive NMDA antagonists have similar pharmacologic effects. These results also support the suggestion that the anticonvulsant effects of competitive and non-competitive NMDA antagonists are mediated by the NMDA receptor-ionophore complex.     

Effects of Valproate, Phenytoin, and MK-801 in a Novel Model of Epileptogenesis

Summary: Purpose: We have developed and characterized a novel model of epileptogenesis based on the convulsive actions of flurothyl in mice. The hallmark feature of this model is a reliable change in the type of seizure expressed in response to flurothyl from generalized clonic to generalized tonic seizures. The purpose of our study was to evaluate the effects of chronic administration of valproate (VPA), phenytoin (PHT), and MK-801 on the change in seizure phenotype observed in our model system.
Methods: Male C57BL/6J mice received flurothyl seizures on 8 consecutive days. Two hours after the last generalized seizure, chronic drug or vehicle was administered twice daily at 12-h intervals for 28 days. The drugs evaluated were VPA (250 mg/kg), PHT (30 mg/kg), and MK-801 (0.5 mg/kg). After a 7-day drug washout period, mice were retested with flurothyl.
Results: Among uninjected or vehicle-injected control mice, there was a significant increase in the proportion of animals expressing tonic seizures after the 28-day stimulation-free interval. Chronic administration of VPA or MK-801, but not PHT, blocked the characteristic change in seizure type from clonic to tonic.
Conclusions: The change in seizure phenotype observed after exposure to our paradigm indicates a fundamental reorganization in the propagation of flurothyl-initiated seizures. As in electrical kindling, VPA and MK-801 are effective at blocking or retarding the reorganization, whereas PHT is not. The concordance in pharmacologic profiles between kindling and our model suggests that the processes underlying changes in seizure susceptibility in these two models share mechanisms in common.     

Brainstem seizure severity regulates forebrain seizure expression in the audiogenic kindling model

PURPOSE: Although sound-induced (audiogenic) seizures in the genetically epilepsy-prone rat (GEPR) initially occur independent of the forebrain, repeated audiogenic seizures recruit forebrain seizure circuits in a process referred to as audiogenic kindling. In GEPR-3s, audiogenic kindling results in facial and forelimb (F&F) clonic seizures that are typical of forebrain seizures. However, in GEPR-9s, audiogenic kindling produces posttonic all-limb clonus not usually observed during forebrain seizures. We hypothesized that the more severe brainstem seizures of the GEPR-9 prevent the expression of F&F clonic seizures during audiogenic kindling. Therefore attenuation of audiogenic seizures during audiogenic kindling in GEPR-9s should allow F&F clonic seizures to be expressed. Likewise, intensifying audiogenic seizure severity in GEPR-3s should inhibit audiogenically kindled F&F clonic seizures. We have tested this hypothesis in the present study. METHODS: Lesions of the superior colliculus or treatment with low-dose phenytoin were used to suppress audiogenic seizure severity in GEPR-9s. Depletion of brain serotonin was used to increase the seizure severity in GEPR-3s. All GEPRs were then subjected to audiogenic kindling. Behavioral and electrographic seizures were assessed. RESULTS: Suppression of audiogenic seizure severity during audiogenic kindling in GEPR-9s increased the incidence forebrain seizure behavior. Kindled GEPR-9s that continued to display full tonic seizures did not exhibit forebrain convulsions, but did show posttonic clonus and forebrain seizure activity in the EEG. GEPR-3s chronically depleted of brain serotonin, along with displaying tonic brainstem seizures, tended to display less severe forebrain seizures during audiogenic kindling. CONCLUSIONS: These findings support the concept that severe brainstem seizures prevent the behavioral expression of forebrain seizures in audiogenically kindled GEPR-9s. It appears that the severe brainstem seizure of the GEPR-9 does not allow the forebrain seizure to manifest its typical behavioral concomitants despite electrographic evidence that spike-wave discharge is occurring in the forebrain.     

Sensitization to noise-mediated induction of seizure susceptibility by MK-801 and phencyclidine

The effect of single administrations of MK-801 (5-methyl-10,11-dihydro-5H-dibenzo[a,d]cylohepten-5,10-imine) or PCP (phencyclidine) on the induction of audiogenic seizure susceptibility by noise in immature rats was examined. Treatments with these non-competitiveN-methyl-D-aspartate (NMDA) receptor antogonist resulted in increases in noise exposure-dependent susceptibility. In neonatally drug-treated rats, seizures during adulthood were found to occur with significantly higher incidence and severity. Furthermore, drug treatments were found to lengthen what is normally a restricted developmental period within which susceptibility can be induced by noise exposure. The 801 exhibited predictable anticonvulsant effects. These data suggests acute PCP or MK-801 exposures may transiently exacerbate risks inherent in certain forms of trauma. The mechanism underlying these effects is unknown although certain inferences are possible and may reveal much about epileptogenesis in this model.     

Anticonvulsant action of a non-competitive antagonist of NMDA receptors (MK-801) in the kindling model of epilepsy

Anticonvulsant action of MK-801, a novel non-competitive antagonist of N-methyl-d-aspartate (NMDA) receptors, was investigated in the kindling model of epilepsy in rats. The results obtained were as follows. (1) Both the seizure stage and afterdischarge duration of previously kindled seizures from the amygdala were significantly suppressed following systemic injection of MK-801 (0.25–4 mg/kg) in a dose-dependent manner. The maximum effects were observed between 2 and 4 h after the injection. (2) The MK-801 also showed significant anticonvulsant effedts on kindled seizures from the frontal cortex and the ventral and dorsal hippocampus. The efficacy however, significantly differed between these kindled sites. (3) Daily treatment of MK-801 (0.25 and 1 mg/kg) prior to each electrical stimulation of the amygdala significantly retarded kindling seizure development and increased the total amount of afterdischarge (accumulated AD) required to reach the first stage 5 seizure. During drug sessions of 1 mg/kg MK-801 for 19 days, all rats showed only partial seizures and the growth of afterdischarge was strongly prevented. (4) Pretreatment with reserpine did not antagonize the anticonvulsant effects of MK-801 on previously kindled seizures from the amydala, suggesting that the effects may not be mediated by catecholaminergic systems. These results indicate that MK-801 has potent anticonvulsant actions on kindled seizures from both limbic and cortical foci, the NMDA system may play a critical role in the seizure-triggering mechanism of kindling. The possible application of NMDA antagonists in clinical epilepsy is suggested.     

EEG wavelet analyses of the striatum-substantia nigra pars reticulata-superior colliculus circuitry: audiogenic seizures and anticonvulsant drug administration in Wistar audiogenic rats (War strain)

The importance of the substantia nigra pars reticulata (SNPr), striatum (STR) and superior colicullus (SC) in the blockade of experimental seizures is well known. But, in audiogenic seizures (brainstem tonic-clonic seizures), the anticonvulsant activity of these nuclei is still controversial. In the present study we aimed to analyze the STR-SNPr-CS circuitry in the audiogenic seizures of Wistar audiogenic rat (WAR). Behavioral and electroencephalographic (EEG) data were collected from WARs under no treatment or injection with systemic (phenobarbital) or intracerebral (intranigral) drugs (muscimol and phenobarbital). The main EEG frequency oscillation of STR, SNPr and SC seen before, during and after audiogenic seizures or during seizure protection, was determinated with wavelet spectral analyses. This method allows the association between behavior and EEG (video-EEG). Audiogenic seizures last only for half a minute in average, suggesting that the interruptions of seizures are probably not due to exhaustion. Systemic phenobarbital caused an acute and dose-dependent behavioral and EEGraphic anticonvulsant effect both in WARs. The dose of phenobarbital 15mg/kg protected animals almost completely, without side effects such as ataxia and sedation. In our data, this endogenous "natural" seizure blockade (or termination) seems to be similar to the "forced" seizure abolition, like the one caused by a systemic non-ataxic phenobarbital dose, because in both cases an intense decrease in the EEG main frequency oscillation can be seen in SNPr and SC. Intranigral phenobarbital or muscimol did not protect animals, and actually induced an increase in the main EEG frequency oscillation in SC. The main finding of the present study is that, in contrast to what is well believed about the incapacity to control audiogenic seizures by the striato-nigro-tectal circuitry, we collected here evidences that these nuclei are involved in the ability to block these seizures. However, the striato-nigro-tectal circuitry in WARs, a genetically developed strain, seems to have different functional mechanisms when compared with normal rats.     

Effects of the NMDA receptor antagonist MK-801 against amygdaloid-kindled seizures in the rat

The effects of acute and subchronic administration of the noncompetitive NMDA receptor antagonist MK-801 on the duration and severity of amygdaloid-kindled seizures in rats were determined to evaluate its anticonvulsant activity. Both the highest acute (1000 micrograms/kg) and subchronic regimens (2 x 300 micrograms/kg, 7 days) produced significant reductions in the seizure stage and afterdischarge duration. Although ataxia may have affected the seizure stage, MK-801 attenuated the primary afterdischarge suggesting anticonvulsant effects in the fully amygdaloid-kindled rat. Since tolerance develops to the behavioral effects of MK-801, other noncompetitive NMDA antagonists related to MK-801 seem to warrant evaluation as anticonvulsants.     

Effects of MK-801 and Phenytoin on Flurothyl-Induced Seizures During Development

Summary We determined the effects of the N-methyl-Daspartate (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-, 1 5, 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.     

Effect of precollicular transection on audiogenic seizures in genetically epilepsy-prone rats

Previous studies have demonstrated that generalized tonic-clonic seizures (GTCS) consisting of running/bouncing clonic and tonic extension can still be elicited in rats after brain transections which separate forebrain from brain stem, showing that forebrain circuitry is not required for GTCS. Inasmuch as sound-induced generalized tonic-clonic seizures in rodents are characterized by running-bouncing clonic and tonic convulsions, we have hypothesized that these are brain stem seizures that can occur independently of the forebrain. To test this hypothesis, we examined the response of two strains of genetically epilepsy-prone rats (GEPR-3s and GEPR-9s) to seizure-evoking auditory stimuli 3 h after a precollicular transection or sham surgery performed under ether anesthesia. In addition, the effect of a precollicular transection on audiogenic seizures was evaluated in normal rats made susceptible to such seizures by infusing NMDA into the inferior colliculus. Following the transection 58% of GEPR-9s displayed a sound-induced tonic-clonic convulsion and the remaining 42% exhibited a sound-induced seizure when subjected to stimulation 5 min after a subconvulsant dose of pentylenetetrazol (PTZ). While sham surgery and the precollicular transection both reduced sound-induced seizure severity in GEPR-3s, the full seizure response could be elicited by sound stimulation following a subconvulsant dose of PTZ. Moreover, the audiogenic seizures in normal rats rendered susceptible by NMDA were unaltered by the precollicular transection. These findings show that the anatomical circuitry required for generalized tonic-clonic seizures evoked by sound stimulation in rodents resides within the brain stem.