Spontaneous recurrent seizures in an intra-amygdala kainate microinjection model of temporal lobe epilepsy are differentially sensitive to antiseizure drugs.

The discovery and development of novel antiseizure drugs (ASDs) that are effective in controlling pharmacoresistant spontaneous recurrent seizures (SRSs) continues to represent a significant unmet clinical need. The Epilepsy Therapy Screening Program (ETSP) has undertaken efforts to address this need by adopting animal models that represent the salient features of human pharmacoresistant epilepsy and employing these models for preclinical testing of investigational ASDs. One such model that has garnered increased interest in recent years is the mouse variant of the Intra-Amygdala Kainate (IAK) microinjection model of mesial temporal lobe epilepsy (MTLE). In establishing a version of this model, several methodological variables were evaluated for their effect(s) on pertinent quantitative endpoints. Although administration of a benzodiazepine 40 min after kainate (KA) induced status epilepticus (SE) is commonly used to improve survival, data presented here demonstrates similar outcomes (mortality, hippocampal damage, latency periods, and 90-day SRS natural history) between mice given midazolam and those that were not. Using a version of this model that did not interrupt SE with a benzodiazepine, a 90-day natural history study was performed and survival, latency periods, SRS frequencies and durations, and SRS clustering data were quantified. Finally, an important step towards model adoption is to assess the sensitivities or resistances of SRSs to a panel of approved and clinically used ASDs. Accordingly, the following ASDs were evaluated for their effects on SRSs in these mice: phenytoin (20 mg/kg, b.i.d.), carbamazepine (30 mg/kg, t.i.d.), valproate (240 mg/kg, t.i.d.), diazepam (4 mg/kg, b.i.d.), and phenobarbital (25 and 50 mg/kg, b.i.d.). Valproate, diazepam, and phenobarbital significantly attenuated SRS frequency relative to vehicle controls at doses devoid of observable adverse behavioral effects. Only diazepam significantly increased seizure freedom. Neither phenytoin nor carbamazepine significantly altered SRS frequency or freedom under these experimental conditions. These data demonstrate that SRSs in this IAK model of MTLE are pharmacoresistant to two representative sodium channel-inhibiting ASDs (phenytoin and carbamazepine) and partially sensitive to GABA receptor modulating ASDs (diazepam and phenobarbital) or a mixed-mechanism ASD (valproate). Accordingly, this model is being incorporated into the NINDS-funded ETSP testing platform for treatment resistant epilepsy.

Deep brain stimulation probing performance is enhanced by pairing stimulus with epileptic seizure.

The unpredictability of spontaneous and recurrent seizures significantly impairs the quality of life of patients with epilepsy. Probing neural network excitability with deep brain electrical stimulation (DBS) has shown promising results predicting pathological shifts in brain states. This work presents a proof-of-principal that active electroencephalographic (EEG) probing, as a seizure predictive tool, is enhanced by pairing DBS and the electrographic seizure itself. The ictogenic model used consisted of inducing seizures by continuous intravenous infusion of pentylenetetrazol (PTZ - 2.5 mg/ml/min) while a probing DBS was delivered to the thalamus (TH) or amygdaloid complex to detect changes prior to seizure onset. Cortical electrophysiological recordings were performed before, during, and after PTZ infusion. Thalamic DBS probing, but not amygdaloid, was able to predict seizure onset without any observable proconvulsant effects. However, previously pairing amygdaloid DBS and epileptic polyspike discharges (day-1) elicited distinct preictal cortically recorded evoked response (CRER) (day-2) when compared with control groups that received the same amount of electrical pulses at different moments of the ictogenic progress at day-1. In conclusion, our results have demonstrated that the pairing strategy potentiated the detection of an altered brain state prior to the seizure onset. The EEG probing enhancement method opens many possibilities for both diagnosis and treatment of epilepsy.

A Caenorhabditis elegans assay of seizure-like activity optimised for identifying antiepileptic drugs and their mechanisms of action.

BACKGROUND: Epilepsy affects around 1% of people, but existing antiepileptic drugs (AEDs) only offer symptomatic relief and are ineffective in approximately 30% of patients. Hence, new AEDs are sorely needed. However, a major bottleneck is the low-throughput nature of early-stage AED screens in conventional rodent models. This process could potentially be expedited by using simpler invertebrate systems, such as the nematode Caenorhabditis elegans. NEW METHOD: Head-bobbing convulsions were previously reported to be inducible by pentylenetetrazol (PTZ) in C. elegans with loss-of-function mutations in unc-49, which encodes a GABAA receptor. Given that epilepsy-linked mutations in human GABAA receptors are well documented, this could represent a clinically-relevant system for early-stage AED screens. However, the original agar plate-based assay is unsuited to large-scale screening and has not been validated for identifying AEDs. Therefore, we established an alternative streamlined, higher-throughput approach whereby mutants were treated with PTZ and AEDs via liquid-based incubation. RESULTS: Convulsions induced within minutes of PTZ exposure in unc-49 mutants were strongly inhibited by the established AED ethosuximide. This protective activity was independent of ethosuximide's suggested target, the T-type calcium channel, as a null mutation in the worm cca-1 ortholog did not affect ethosuximide's anticonvulsant action. COMPARISON WITH EXISTING METHOD: Our streamlined assay is AED-validated, feasible for higher throughput compound screens, and can facilitate insights into AED mechanisms of action. CONCLUSIONS: Based on an epilepsy-associated genetic background, this C. elegans unc-49 model of seizure-like activity presents an ethical, higher throughput alternative to conventional rodent seizure models for initial AED screens.

A New Rat Model of Seizures Suitable for Screening Antiepileptic Electrical Stimulation Therapies.

The antiepileptic effects of the electrical stimulation therapies developed for patients with intractable epilepsies depend critically on the stimulation parameters, including the pulse duration, current, and frequency. Consequently, optimization of such therapies requires many animals for testing each of the stimulation parameters alone or in combination, which is costly and time consuming. This drawback could be reduced by testing several stimulation paradigms in each animal, but this requires an animal model of long-lasting seizures allowing such repetitive tests. This study was performed to validate such a model of long-lasting seizures. The present analysis was performed on electrocorticogram and intracortical signals collected from the somatosensory cortex of 11 Sprague Dawley rats. A protocol of controlled intravenous infusion of pentylenetetrazol (PTZ) was developed to induce spike-and-wave (SW) seizures and maintain stable those seizures for the whole experimental time. SW discharges were induced and maintained stable for 2 h in all rats through a two-stage infusion of PTZ. During the first stage, the SW discharges were induced by 2.5 min infusion of 10 mg/kg/min PTZ. During the second stage, the SW discharges were maintained at a stable level of frequency and power for 2 h via a 0.21 mg/kg/min PTZ infusion rate. The proposed animal model of seizures is characterized by SW discharges which remain stable for 2 h. This 2-h long time interval allows repetitive tests with different stimulation parameters in each animal, which may lead to a significant reduction of the number of animals necessary for optimizing electrical stimulation therapies developed to inhibit seizures.

[COMPARISON OF CHRONIC ANTICONVULSANT ACTIVITY AND SAFETY OF IEM-2062, SODIUM VALPROATE AND ME-MANTINE IN THE PENTYLENETETRAZOL KINDLING MODEL IN RATS].

IEM-2062 [1-(6-aminohexylamino)-1-phenylcyclohexyl dihydrochloride], causing a combined block NMDA and AMPA receptors, after chronic oral administration in doses, respectively, 0.3 and 3 mg/kg, induce maximal anticonvulsant effect in the pentylenetetrazol kindling rats because decrease the number of completely kindling rats by 100 %, and also decrease in 2.5-3.3 times the average severity of clonic-tonic kindling seizures. IEM-2062 causes significant anticon- 299 vulsant effects in the widest range of doses, 1-48 mg/kg, which is 24-22 times more than that of memantine (12-20 mg/kg) and sodium valproate (100-200 mg/kg). Sodium valproate and memantine cause significant disturbances of locomotor activity in the «open field¼ test in doses causing maximal anticonvulsant effect in the kindling rats. At the same time IEM-2062 cause disturbance of locomotor activity only in very high dose of 92 mg/kg, which exceeds in 30.7 times the dose causing the maximum anticonvulsive effect in the kindling rats. Thus, IEM-2062 reduces the severity of kindling seizures in 1.7-1.9 times stronger than sodium valproate and memantine and also by 30.7 times is safer than sodium valproate and memantine.

Gastrodin Attenuates Pentylenetetrazole-Induced Seizures by Modulating the Mitogen-Activated Protein Kinase-Associated Inflammatory Responses in Mice.

Gastrodin, the major component isolated from the rhizome of the Chinese traditional medicinal herb Gastrodia elata ("Tianma"), has a long history in the treatment of epilepsy and other neurological disorders. However, the molecular mechanisms are not clear. Here, we found that gastrodin ameliorated pentylenetetrazole (PTZ)-induced epileptic seizures with improvement of the electroencephalographic pattern in mice. Further studies demonstrated that gastrodin decreased the levels of the pro-inflammatory cytokines interleukin-1ß and tumor necrosis factor-α while increasing interleukin-10, an anti-inflammatory cytokine in the brain. Furthermore, gastrodin attenuated the PTZ-induced microglial activation along with inhibition of mitogen-activated protein kinases, cAMP response element binding protein, and NF-κB. Our data suggest that gastrodin attenuates seizures by modulating the mitogen-activated protein kinase-associated inflammatory responses.

Effects of D-penicillamine on pentylenetetrazole-induced seizures in mice: involvement of nitric oxide/NMDA pathways.

Besides the clinical applications of penicillamine, some reports show that use of D-penicillamine (D-pen) has been associated with adverse effects such as seizures. So, the purpose of this study was to evaluate the effects of D-pen on pentylenetetrazole (PTZ)-induced seizures in male NMRI mice. It also examined whether N-methyl-D-aspartate (NMDA) receptor/nitrergic system blockage was able to alter the probable effects of D-pen. Different doses of D-pen (0.1, 0.5, 1, 10, 100, 150, and 250 mg/kg) were administered intraperitoneally (i.p.) 90 min prior to induction of seizures. D-Penicillamine at a low dose (0.5 mg/kg, i.p.) had anticonvulsant effects, whereas at a high dose (250 mg/kg, i.p.), it was proconvulsant. Both anti- and proconvulsant effects of D-pen were blocked by a single dose of a nonspecific inhibitor of nitric oxide synthase (NOS), L-NAME (10 mg/kg, i.p.), and a single dose of a specific inhibitor of neuronal nitric oxide synthase (nNOS), 7-nitroindazole (30 mg/kg, i.p.). A selective inhibitor of iNOS, aminoguanidine (100 mg/kg, i.p.), had no effect on these activities. An NMDA receptor antagonist, MK-801 (0.05 mg/kg, i.p.), alters the anti- and proconvulsant effects of D-pen. The results of the present study showed that the nitric oxide system and NMDA receptors may contribute to the biphasic effects of D-pen, which remain to be clarified further.

Design, synthesis and pharmacological evaluation of N3 aryl/ heteroaryl substituted 2-((benzyloxy and phenylthio) methyl) 6,7- dimethoxyquinazolin-4(3H)-ones as potential anticonvulsant agents.

Novel N3 aryl/heteroaryl substituted 2-((benzyloxy and phenylthio) methyl) 6,7-dimethoxyquinazolin-4(3H)- ones (8a-8l) were synthesized and evaluated for their anticonvulsant activity using various models of epilepsy, such as maximal electroshock (MES), subcutaneous pentylenetetrazole (scPTZ) and intracerebroventricular AMPA (α-amino-3- hydroxy-5-methyl-4-isoxazolepropionic acid)-induced seizures in mice. The rotarod test has been used to determine the acute neurotoxicity. Further, the serum enzymatic activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were assessed along with histopathological examination of liver. Among all the derivatives, compound 8f displayed significant activity profile based on the overall magnitude of activity and minimum neurotoxicity.

Antiepileptic activity of lobeline isolated from the leaf of Lobelia nicotianaefolia and its effect on brain GABA level in mice.

OBJECTIVE: To investigate the anticonvulsant activity of the lobeline isolated from the Lobelia nicotianaefolia in chemoconvulsant-induced seizures and its biochemical mechanism by investigating relationship between seizure activities and altered gamma amino butyric acid (GABA) in brain of mice in Pentylenetetrazol (PTZ) seizure models. METHODS: The anticonvulsant activity of the isolated lobeline (5, 10, 20 and 30 mg/kg, i.p.) was investigated in PTZ and strychnine induced seizures in mice and the effect of isolated lobeline on brain GABA level in seizures induced by PTZ. Diazepam was used as reference anticonvulsant drugs for comparison. RESULTS: Isolated lobeline (10, 20 and 30 mg/kg, i.p.) significantly delayed and antagonized (P < 0.050-0.001) the onset of PTZ-induced seizures. It also antagonized strychnine induced seizures. The mortality was also prevented in the test group of animals. In biochemical evaluation, isolated lobeline (5, 10 and 20 mg/kg, i.p.) significantly increased the brain GABA level. And at dose of 30 mg/kg GABA level showed slight decrease in PTZ model. CONCLUSIONS: In our findings, isolated lobeline (20mg/kg) exhibited potent anticonvulsant activity against PTZ induced seizures. Also a biochemical evaluation suggested significant increase in barain GABA level at 20 mg/kg i.p. of isolated lobeline. Hence, we may propose that lobeline reduces epileptic seizures by enhancing the GABA release supporting the GABAergic mechanism.

Video-electroencephalography in conscious non human primate using radiotelemetry and computerized analysis: refinement of a safety pharmacology model.

INTRODUCTION: Electroencephalography (EEG) investigations are occasionally required as follow-up studies for safety pharmacology core battery (S7A). Video-EEG monitoring is a standard diagnostic tool in humans but limited data is available on its use in telemetered freely moving macaque monkeys for safety pharmacology investigations. While proconvulsant risk evaluations are routinely conducted in rodents, pharmacological or pharmacokinetic considerations lead to the use of non human primates in toxicology and safety pharmacology in some cases. METHODS: Cynomolgus monkeys were instrumented with telemetry implants. Placement of EEG electrode was based on the 10-20 system using three derivations (C3-O1, Cz-Oz and C4-O2). EEG trace analysis was carried out using NeuroScore software. After 24 h of continuous video-EEG monitoring, animals received pentylenetetrazole (PTZ, 10 mg/kg/15 min) until convulsions were noted. Convulsions were immediately treated with diazepam (1.0 mg/kg). A seizure detection protocol with a dynamic spike train threshold was used for the entire EEG monitoring period (total of 44 h) including periods when PTZ was administered. Spectral analysis was done to quantify the absolute and relative amplitude of EEG frequency bands (delta, theta, alpha, sigma and beta waves). Sleep stages were quantified and EEGs during seizures were analyzed using fast Fourier transformation (FFT) to assess dominant frequencies. RESULTS: Spike trains were detected by computerized analysis in all animals presenting PTZ-induced seizures while paroxysmal activities were systematically predictive (at least 4-min prior to generalized seizures). Beta activity increased with visual stimulation using monkey treats. Characteristics of EEG for all sleep stages (I, II, III and IV) were present in all animals. Delta activity was predominant in normal awake EEG as well as in all sleep stages. Seizure peak frequency was 3-6 Hz on FFT, corresponding to the discharge of the underlying generator. DISCUSSION: EEG-video monitoring can be useful when using non human primates to characterize neurological adverse effects with unpredictable onset. Computerized video-EEG analysis was a valuable tool for safety pharmacology investigations including proconvulsant risk assessment, spectral analysis of frequency bands and sleep stage determination.

Dose-dependent anticonvulsant effects of linoleic and alpha-linolenic polyunsaturated fatty acids on pentylenetetrazol induced seizures in rats.

PURPOSE: Linoleic and alpha-linolenic polyunsaturated fatty acids, derived from plant oils, have been reported to reduce neuronal excitability ex vivo and in cell culture. The evidence derived from animal seizure models, however, has been contradictory. The goal of the present study was to assess the dose-dependent anticonvulsant effects of a fatty acid mixture containing linoleic and alpha-linolenic acids in a 4 to 1 ratio (the "SR-3" compound). METHODS: The maximal pentylenetetrazol seizure model and Long-Evans hooded rats were used. RESULTS: Daily intraperitoneal injection of SR-3 for 21 consecutive days raised omega-3 polyunsaturated fatty acid (n-3 PUFA) composition in the unesterified fatty acid fraction of brain lipids (p < 0.05), and increased latency to seizure onset when administered at 200 mg/kg (p < 0.05), but not at 40 mg/kg (p > 0.05). There were no significant effects of SR-3 on seizure occurrence or on seizure severity (p > 0.05). A toxic effect of the SR-3 compound on peristalsis was observed at a dose of 400 mg/kg and above. CONCLUSION: Linoleic and alpha-linolenic polyunsaturated fatty acids in a 4 to 1 ratio raises n-3 PUFA composition of unesterified fatty acids in the brain and increases resistance to pentylenetetrazol-induced seizures.

Anticonvulsant effects of linolenic acid are unrelated to brain phospholipid cell membrane compositions.

PURPOSE: Recent studies have revealed that polyunsaturated fatty acids (PUFAs) have anticonvulsive properties. Clinical trials using PUFAs reported conflicting results. It was suggested that PUFAs have anticonvulsant effects via modifications of brain phospholipids. Moreover, some authors suggested that the effect of the ketogenic diet (KD) leads to a high PUFA content. The aim of the study was to evaluate the anticonvulsant properties of a mixture containing alpha-linolenic acid (ALA) and linolenic acid (LA). METHODS: Four-week-old male Wistar rats were fed one of the following diets for 30 days: KD, standard diet, and standard diet with daily LA/ALA oral supplementation. Pentylenetetrazol (PTZ) threshold was used to assess the anticonvulsive effects of the diets. Nutritional status was monitored by body composition evaluation. Fatty acids composition of both plasma and brain phospholipids were also assessed. RESULTS: Animals fed the KD and those who had the daily LA/ALA supplementation exhibited an increase in PTZ threshold. The animals did not show any modification of body composition or brain phospholipid composition. The plasma fatty acids composition was modified by KD and LA/ALA. A decrease in arachidonic acid (AA) concentrations was observed in both the KD and LA/ALA groups, while an increase in eicosapentanoic acid (EPA) and ALA concentrations was only observed in the LA/ALA group. CONCLUSIONS: Our study shows that LA/ALA supplementation exerts anticonvulsive properties comparable to KD. Nutritional status can not explain the anticonvulsive effects of PUFAs supplementation. Brain phospholipids were not different within groups. The anticonvulsive effects of LA supplementation seem to be unrelated to brain phospholipid composition.

The fruit essential oil of Pimpinella anisum L. (Umblliferae) induces neuronal hyperexcitability in snail partly through attenuation of after-hyperpolarization.

AIM OF THE STUDY: Many biological actions of Pimpinella anisum L. (Ainse), including antiepileptic activity have been demonstrated; however, there is no data concerning its precise cellular mechanisms of action. We determined whether the fruit essential oil of anise affect the bioelectrical activity of snail neurons in control condition or after pentylenetetrazol (PTZ) induced epileptic activity. MATERIALS AND METHODS: Intracellular recordings were made under the current clamp condition and the effects of anise oil (0.01% or 0.05%) alone or in combination with PTZ were assessed on the firing pattern, action potential configuration and postspike potentials. RESULTS: Anise oil changed the firing pattern from regular tonic discharge to irregular and then to bursting in intact cells or resulted in the robustness of the burst firing and the steepness of the paroxysmal shift induced by PTZ treatment. It also significantly increased the firing frequency and decreased both the after-hyperpolarization potential (AHP) following single action potential and the post-pulse AHP. CONCLUSIONS: Likely candidate cellular mechanisms underlying the hyperexcitability produced by anise oil include enhancement of Ca(2+) channels activity or inhibition of voltage and/or Ca(2+) dependent K(+) channels activity underlying AHPs. These finding indicates that a certain caution is needed when Pimpinella anisum is used for treating patients suffering from epilepsy.

The effect of traditional herbal medicines; Uyakujunkisan on trigeminal neuralgia in an elderly patient--a case report and literature review.

This report describes the successful treatment of a 72-year-old female with refractory trigeminal neuralgia using a traditional herbal medicine, Uyakujunkisan (UJS). The case report is of a 65-year-old female who developed right-sided trigeminal neuralgia that was partially responsive to carbamazepine (CZ). The pain gradually increased in intensity and at 72 years of age she presented for herbal medicine therapy. Cranial MRI demonstrated vascular compression of the right trigeminal nerve at the cerebellopontine angle by the anterior inferior cerebellar artery. Although microvascular decompression was considered, UJS was prescribed after informed consent. After 3 weeks of treatment with UJS, dramatic improvement of symptoms permitted a decrease in CZ dose.

Timed pentylenetetrazol infusion test: a comparative analysis with s.c.PTZ and MES models of anticonvulsant screening in mice.

The intravenous pentylenetetrazol (i.v.PTZ) seizure test provides threshold dose for induction of seizures in individual animals. In the present study, the i.v. and s.c.PTZ seizure models in mice were compared for seizure pattern, intra- and interanimal variability. Anticonvulsant activities of several antiepileptic drugs (AEDs) at non-ataxic dose levels were evaluated in the PTZ and maximal electroshock (MES) seizure tests. In the i.v.PTZ test, at 0.5 ml/min rate of administration, the mean threshold PTZ doses for induction of clonus and tonic extensor were 44.17 and 99.59 mg/kg, respectively. The intra- and interanimal variabilities in the seizure response were low in the i.v.PTZ as compared to the s.c.PTZ model. Phenobarbital sodium, ethosuximide, sodium valproate, diazepam, tiagabine, oxcarbazepine and zonisamide enhanced threshold or onset latency for clonus in the i.v. and s.c.PTZ tests, respectively. Levetiracetam and pregabalin were active in the i.v.PTZ test, but had no effect in the s.c.PTZ test. Ability of AEDs to protect from tonic extensor was compared in the MES and i.v.PTZ tests. For this effect, phenobarbital sodium, phenytoin, carbamazepine, sodium valproate, gabapentin, oxcarbazepine, zonisamide and pregabalin were effective in the i.v.PTZ and MES tests. Ethosuximide, diazepam and levetiracetam were effective in the i.v.PTZ test, but not the MES test. On the contrary, lamotrigine and topiramate were active in the MES, but not the i.v.PTZ test. These results indicate that it is advantageous to use i.v.PTZ test as an acute seizure model for screening of antiepileptic drugs. This model can identify molecules with varied mechanism of action and broad clinical utility in the treatment of epilepsy.

The use of the dog electroencephalogram (EEG) in safety pharmacology to evaluate proconvulsant risk.

INTRODUCTION: The dog is frequently used for cardiovascular safety pharmacology and for toxicology studies, but is not often used for central nervous system (CNS) safety pharmacology purposes. We have therefore examined the electroencephalogram (EEG) in conscious dogs by means of radio-telemetry methods using the proconvulsant agent pentylenetetrazole (PTZ) as reference substance. Assessment of proconvulsant risk is an important aspect of CNS safety evaluation and the EEG is a sensitive technique for identifying pathologic brain activity, most importantly paroxysmal activity. METHODS: Dogs were implanted with epidural electrodes wired to subcutaneously placed radiotransmitters. Following baseline recording, the test substance was administered and the EEG and electromyogram (EMG) activities were recorded from dogs placed in slings. The EEG was assessed visually for abnormal activity and dogs were also continuously observed for the appearance of overt convulsive activity. The PTZ infusion was stopped and diazepam was administered as soon as clear and sustained EEG effects and/or behavioural symptoms occurred. RESULTS: Slow i.v. infusion of PTZ (1.5 mg/kg/min) induced clear paroxysmal effects on the EEG trace in the form of spike and wave trains of 4-5 Hz. Paroxysmal activity associated with clonic convulsions occurred between 17 and 36 min after the start of infusion (a mean of 24 min) but in most cases paroxysmal activity was observed approximately 60 s prior to any overt convulsive activity. DISCUSSION: These data show the usefulness of the telemetered dog EEG in safety pharmacology. The dog EEG is appropriate in situations where results from cardiovascular and CNS safety tests in the same species are required, or where the use of other species is contraindicated because of metabolic or pharmacokinetic particularities.

Potentiation of panic-like behaviors of the rat by subconvulsive doses of strychnine.

The present study was carried out to determine possible panicogenic effects of strychnine administered in subconvulsive doses to rats. Two experiments were conducted to assess two major features of panic in animal models: panic-related flight (through the observation of wild running [WR]) and defensive fights. In the first one, 20 adult male Wistar rats were injected with six different doses of strychnine ranging from 0.5 to 4.0 mg/kg. After 15 min of free observation, the animals were submitted to high-intensity acoustic stimulation and the incidence of WR was recorded. Higher doses of strychnine (above 2.5 mg/kg) easily evoked seizures, but lower doses raised the incidence of WR in a dose-dependent manner. The most effective dose for WR (1.5 mg/kg) was used in the second experiment, in which we investigated the effects of strychnine on sleep-deprivation-induced fights (SDIFs) that have defensive characteristics. For this purpose, 40 subjects were submitted to 5 days of REM-sleep deprivation by the single-platform method and were then assigned into two groups, i.e., strychnine vs. control. After the injections, the animals were observed in social groupings for SDIF recordings over a period of 60 min. The strychnine-treated groups had more SDIF than the control groups (P<.05, Mann-Whitney U test). We conclude that the high level of neural excitability promoted by partial blockade of the glycinergic system can contribute to the manifestation of panic reactions.

Effect of some convulsants on the protective activity of loreclezole and its combinations with valproate or clonazepam in amygdala-kindled rats.

Loreclezole (5 mg/kg) exerted a significant protective action in amygdala-kindled rats, reducing both seizure and afterdischarge durations. The combinations of loreclezole (2.5 mg/kg) with valproate, clonazepam, or carbamazepine (applied at their subprotective doses) also exhibited antiseizure effect in this test. However, only two first combinations occurred to be of pharmacodynamic nature. Among several chemoconvulsants, bicuculline, N-methyl-D-aspartic acid and BAY k-8644 (the opener of L-type calcium channels) reversed the protective activity of loreclezole alone and its combination with valproate. On the other hand, bicuculline, aminophylline and BAY k-8644 inhibited the anticonvulsive action of loreclezole combined with clonazepam. The results support the hypothesis that the protective activity of loreclezole and its combinations with other antiepileptics may involve potentiation of GABAergic neurotransmission and blockade of L-type of calcium channels.

Cardiovascular regulation through hypothalamic GABA(A) receptors in a genetic absence epilepsy model in rat.

PURPOSE: Gamma-aminobutyric acid (GABA) plays a vital role in both central cardiovascular homeostasis and pathogenesis of epilepsy. Epilepsy affects autonomic nervous system functions. In this study, we aimed to clarify the role of GABAA receptors in hypothalamic cardiovascular regulation in a genetically determined animal model of absence epilepsy. METHODS: Nonepileptic Wistar rats and genetic absence epilepsy rats from Strasbourg (GAERS) were instrumented with a guide cannula for drug injection and extradural electrodes for EEG recording. After a recovery period, iliac arterial catheters were inserted for direct measurement of mean arterial pressure and heart rate. Bicuculline, a GABA(A)-receptor antagonist, was injected into the dorsomedial (DMH) or posterior (PH) hypothalamic nuclei of nonepileptic control rats or GAERS. Blood pressure, heart rate, and EEG recordings were performed in conscious unrestrained animals. RESULTS: Bicuculline injections into the hypothalamus produced increases in blood pressure and heart rate of both control rats and GAERS. The DMH group of GAERS showed a twofold increase in the blood pressure and the heart rate compared with those of control rats. Pressor responses to bicuculline, when microinjected into the PH, were similar in the nonepileptic animals and GAERS. Conversely, the amplitude of tachycardic responses to the administration of bicuculline into the PH was significantly higher in GAERS compared with those of control rats. CONCLUSIONS: The bicuculline-induced increases in blood pressure and heart rate were more prominent when given in the DMH of GAERS. These results indicate an increased GABA(A) receptor-mediated cardiovascular response through the DMH in conscious rats with absence epilepsy.

[The intracerebral route of kynurenine administration is one of the reasons for the resistance of kynurenine-induced seizures to diazepam]. / Vnutrimozgovoi put' vvedeniia kinurenina--odna iz prichin rezistentnosti kinureninovykh sudorog k diazepamu.

It has been shown many times that in experiments on mice systemic administration of anticonvulsive doses of diazepam caused a 15-20-fold higher effect against the endogenous convulsant kynurenine (injection into the brain ventricles) than against corasol (systemic injection). In the present work diazepam (0.5-2.0 mg/kg, intraperitoneal injection) prevented convulsions induced in nonbred and C57B1/6 mice by equally effective doses of corasol injected subcutaneously (80 mg/kg) better than in injection into the brain ventricles (500 micrograms). In injection of the three drugs into the ventricles diazepam (0.5-10 micrograms) relieved to a similar degree convulsions induced by equally effective doses of corasol (500 micrograms) and kynurenine (50 micrograms). It follows from this that the unique resistance the kynurenine convulsions to diazepam is due to the fact that only kynurenine is injected into the brain ventricles whereas all the other convulsants compared with it are administered systemically. It is suggested that besides the route of administration, the more significant dependence of kynurenine convulsions on GAMA(B) receptors and the activity of the brain dopaminergic system is responsible for the difference in the diazepam sensitivity of kynurenine and corasol convulsions.