Only certain antiepileptic drugs prevent seizures induced by pilocarpine

Combination of antiseizure medications phenobarbital, ketamine, and midazolam reduces soman-induced epileptogenesis and brain pathology in rats

Objective

Cholinergic‐induced status epilepticus (SE) is associated with a loss of synaptic gamma‐aminobutyric acid A receptors (GABA_AR) and an increase in N‐methyl‐D‐aspartate receptors (NMDAR) and amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptors (AMPAR) that may contribute to pharmacoresistance when treatment with benzodiazepine antiseizure medication is delayed. The barbiturate phenobarbital enhances inhibitory neurotransmission by binding to a specific site in the GABA_AR to increase the open state of the channel, decrease neuronal excitability, and reduce glutamate‐induced currents through AMPA/kainate receptors. We hypothesized that phenobarbital as an adjunct to midazolam would augment the amelioration of soman‐induced SE and associated neuropathological changes and that further protection would be provided by the addition of an NMDAR antagonist.

Methods

We investigated the efficacy of combining antiseizure medications to include a benzodiazepine and a barbiturate allosteric GABA_AR modulator (midazolam and phenobarbital, respectively) to correct loss of inhibition, and ketamine to reduce excitation caused by increased synaptic localization of NMDAR and AMPAR, which are NMDA‐dependent. Rats implanted with transmitters to record electroencephalographic (EEG) activity were exposed to soman and treated with atropine sulfate and HI‐6 one min after exposure and with antiseizure medication(s) 40 minutes after seizure onset.

Results

The triple therapy combination of phenobarbital, midazolam, and ketamine administered at 40 minutes after seizure onset effectively prevented soman‐induced epileptogenesis and reduced neurodegeneration. In addition, dual therapy with phenobarbital and midazolam or ketamine was more effective than monotherapy (midazolam or phenobarbital) in reducing cholinergic‐induced toxicity.

Significance

Benzodiazepine efficacy is drastically reduced with time after seizure onset and inversely related to seizure duration. To overcome pharmacoresistance in severe benzodiazepine‐refractory cholinergic‐induced SE, simultaneous drug combination to include drugs that target both the loss of inhibition (eg, midazolam, phenobarbital) and the increased excitatory response (eg, ketamine) is more effective than benzodiazepine or barbiturate monotherapy.

LMR-101, a novel derivative of propofol, exhibits potent anticonvulsant effects and possibly interacts with a novel target on γ-aminobutyric acid type A receptors

OBJECTIVE

LMR-101 is a bisphenol derivative of propofol, a short-acting general anesthetic, which is also used to manage status epilepticus (SE). We evaluated the sedative and anticonvulsant effects of LMR-101 to discover its potential to manage epilepsy and SE in the clinic.

METHODS

Comparative studies between LMR-101 and propofol were performed in mice to elucidate an appropriate dose range for LMR-101 that produced anticonvulsant effects without significant sedation. Then, the anticonvulsive efficacy for LMR-101 was evaluated using seizure models induced by pentylenetetrazol and (+)-bicuculline. The ability of LMR-101 to inhibit SE was assessed using a rat model of SE induced by pilocarpine. Radioligand binding assay profiles for LMR-101 were performed to evaluate the potential mechanisms of action underlying its anticonvulsant properties.

RESULTS

In the mouse study, LMR-101 exhibited greater anticonvulsant and lesser sedative effect compared with propofol. LMR-101 completely inhibited pentylenetetrazol-induced seizures at a dose of 50 mg/kg and exhibited heavy sedation at 300 mg/kg. Propofol anesthetized all mice and only decreased the seizure rate at 25 mg/kg. LMR-101 also suppressed seizure behaviors evoked by (+)-bicuculline in mice in a dose-dependent manner. In the pilocarpine-induced SE model, LMR-101 significantly decreased the maximum seizure score and seizure duration in a dose-dependent manner. The median effective dose for LMR-101 was 14.30 mg/kg and 121.87 mg/kg to prevent and inhibit sustained SE, respectively. In binding assays, LMR-101 primarily inhibited tert-[³⁵ S] butylbicyclophosphorothionate binding to γ-aminobutyric acid type A (GABA_A ) receptors (half-maximal inhibitory concentration = 2.06 μmol·L^-1 ), but it did not affect [³ H] flunitrazepam or [³ H] muscimol binding.

SIGNIFICANCE

It is anticipated that LMR-101 might play an essential role in the clinical management of epilepsy and SE. LMR-101 also might bind to a novel target site on the GABA_A receptor that is different from existing antiepileptic drugs. Further study of the mechanisms of action of LMR-101 would be of considerable value in the search for new active drug sites on GABA_A receptors.

Characterization and treatment of spontaneous recurrent seizures following nerve agent-induced status epilepticus in mice

PURPOSE

To develop and characterize a mouse model of spontaneous recurrent seizures following nerve agent-induced status epilepticus (SE) and test the efficacy of existing antiepileptic drugs.

METHODS

SE was induced in telemeterized male C57Bl6/J mice by soman exposure, and electroencephalographic activity was recorded for 4-6 weeks. Mice were treated with antiepileptic drugs (levetiracetam, valproic acid, phenobarbital) or corresponding vehicles for 14 d after exposure, followed by 14 d of drug washout. Survival, body weight, seizure characteristics, and histopathology were used to characterize the acute and chronic effects of nerve agent exposure and to evaluate the efficacy of treatments in mitigating or preventing neurological effects.

RESULTS

Spontaneous recurrent seizures manifested in all survivors, but the number and frequency of seizures varied considerably among mice. In untreated mice, seizures became longer over time. Moderate to severe histopathology was observed in the amygdala, piriform cortex, and CA1. Levetiracetam provided modest improvements in neurological parameters such as reduced spike rate and improved histopathology scores, whereas valproic acid and phenobarbital were largely ineffective.

CONCLUSIONS

This model of post-SE spontaneous recurrent seizures differs from other experimental models in the brief latency to seizure development, the occurrence of seizures in 100 % of exposed animals, and the lack of damage to CA4/dentate gyrus. It may serve as a useful tool for rapidly and efficiently screening novel therapies that would be effective against severe epilepsy cases.

Validating a model of benzodiazepine refractory nerve agent-induced status epilepticus by evaluating the anticonvulsant and neuroprotective effects of scopolamine, memantine, and phenobarbital

INTRODUCTION

Organophosphorus nerve agents (OPNAs) irreversibly block acetylcholinesterase activity, resulting in accumulation of excess acetylcholine at neural synapses, which can lead to a state of prolonged seizures known as status epilepticus (SE). Benzodiazepines, the current standard of care for SE, become less effective as latency to treatment increases. In a mass civilian OPNA exposure, concurrent trauma and limited resources would likely cause a delay in first response time. To address this issue, we have developed a rat model to test novel anticonvulsant/ neuroprotectant adjuncts at delayed time points.

METHODS

For model development, adult male rats with cortical electroencephalographic (EEG) electrodes were exposed to soman and administered saline along with atropine, 2-PAM, and midazolam 5, 20, or 40 min after SE onset. We validated our model using three drugs: scopolamine, memantine, and phenobarbital. Using the same procedure outlined above, rats were given atropine, 2-PAM, midazolam and test treatment 20 min after SE onset.

RESULTS

Using gamma power, delta power, and spike rate to quantify EEG activity, we found that scopolamine was effective, memantine was minimally effective, and phenobarbital had a delayed effect on terminating SE. Fluoro-Jade B staining was used to assess neuroprotection in five brain regions. Each treatment provided significant protection compared to saline + midazolam in at least two brain regions.

DISCUSSION

Because our data agree with previously published studies on the efficacy of these compounds, we conclude that this model is a valid way to test novel anticonvulsants/ neuroprotectants for controlling benzodiazepine-resistant OPNA-induced SE and subsequent neuropathology.

Experimental models of status epilepticus and neuronal injury for evaluation of therapeutic interventions

This article describes current experimental models of status epilepticus (SE) and neuronal injury for use in the screening of new therapeutic agents. Epilepsy is a common neurological disorder characterized by recurrent unprovoked seizures. SE is an emergency condition associated with continuous seizures lasting more than 30 min. It causes significant mortality and morbidity. SE can cause devastating damage to the brain leading to cognitive impairment and increased risk of epilepsy. Benzodiazepines are the first-line drugs for the treatment of SE, however, many people exhibit partial or complete resistance due to a breakdown of GABA inhibition. Therefore, new drugs with neuroprotective effects against the SE-induced neuronal injury and degeneration are desirable. Animal models are used to study the pathophysiology of SE and for the discovery of newer anticonvulsants. In SE paradigms, seizures are induced in rodents by chemical agents or by electrical stimulation of brain structures. Electrical stimulation includes perforant path and self-sustaining stimulation models. Pharmacological models include kainic acid, pilocarpine, flurothyl, organophosphates and other convulsants that induce SE in rodents. Neuronal injury occurs within the initial SE episode, and animals exhibit cognitive dysfunction and spontaneous seizures several weeks after this precipitating event. Current SE models have potential applications but have some limitations. In general, the experimental SE model should be analogous to the human seizure state and it should share very similar neuropathological mechanisms. The pilocarpine and diisopropylfluorophosphate models are associated with prolonged, diazepam-insensitive seizures and neurodegeneration and therefore represent paradigms of refractory SE. Novel mechanism-based or clinically relevant models are essential to identify new therapies for SE and neuroprotective interventions.

Evaluation of the antiepileptic effect of curcumin and Nigella sativa oil in the pilocarpine model of epilepsy in comparison with valproate

The present study aimed to investigate the effect of curcumin and Nigella sativa oil (NSO) on amino acid neurotransmitter alterations and the histological changes induced by pilocarpine in the hippocampus and cortex of rats. Epilepsy was induced by i.p. injection of pilocarpine, and the animals were left for 22 days to establish spontaneous recurrent seizures. They were then treated with curcumin, NSO or valproate for 21 days. Pilocarpine induced a significant increase in hippocampal aspartate and a significant decrease in glycine and taurine levels. In the cortex, a significant increase in aspartate, glutamate, GABA, glycine, and taurine levels was obtained after pilocarpine injection. Treatment of pilocarpinized rats with curcumin and valproate ameliorated most of the changes in amino acid concentrations and reduced the histopathological abnormalities induced by pilocarpine. N. sativa oil failed to improve the pilocarpine-induced abnormalities. This may explain the antiepileptic effect of curcumin and suggest its use as an anticonvulsant.

β-Hydroxybutyrate increases the pilocarpine-induced seizure threshold in young mice

This study was designed to investigate the effects of β-hydroxybutyrate (BHB) on pilocarpine-induced seizures in young mice. Eighty-five male, postnatal day 21, ICR mice were used. All mice were pretreated with scopolamine methylbromide (1 mg/kg) 30 min prior to pilocarpine administration. Experimental mice (n=46) were injected intraperitoneally with BHB (20 mmol/kg), 15 min prior to pilocarpine administration; control animals (n=39) were administered normal saline. Pilocarpine (300 mg/kg) was then administered intraperitoneally to induce seizures. Mice were monitored for 2 h after pilocarpine injection, and seizure behavior grades were evaluated according to Racine's scale. All mice developed typical seizure behaviors of grade 3 or higher. Although the severity in terms of seizure behavior grade was not significantly different between groups, the mean (±SD) latency to the onset of seizure was significantly prolonged in BHB-treated mice (5.15±2.19 min) compared with controls (2.95±1.06 min; p<0.001). This study demonstrates that treatment with BHB significantly prolongs the latency to the onset of seizures induced by pilocarpine in mice and suggests that BHB, one of the ketone bodies, may be direct anticonvulsant.

Astroglial loss and edema formation in the rat piriform cortex and hippocampus following pilocarpine-induced status epilepticus

In the present study we analyzed aquaporin-4 (AQP4) immunoreactivity in the piriform cortex (PC) and the hippocampus of pilocarpine-induced rat epilepsy model to elucidate the roles of AQP4 in brain edema following status epilepticus (SE). In non-SE-induced animals, AQP4 immunoreactivity was diffusely detected in the PC and the hippocampus. AQP4 immunoreactivity was mainly observed in the endfeet of astrocytes. Following SE the AQP4-deleted area was clearly detected in the PC, not in the hippocampus. Decreases in dystrophin and α-syntrophin immunoreactivities were followed by reduction in AQP4 immunoreactivity. These alterations were accompanied by the development of vasogenic edema and the astroglial loss in the PC. In addition, acetazolamide (an AQP4 inhibitor) treatment exacerbated vasogenic edema and astroglial loss both in the PC and in the hippocampus. These findings suggest that SE may induce impairments of astroglial AQP4 functions via disruption of the dystrophin/α-syntrophin complex that worsen vasogenic edema. Subsequently, vasogenic edema results in extensive astroglial loss that may aggravate vasogenic edema.

Effects of N(2-propylpentanoyl)urea on hippocampal amino acid neurotransmitters in spontaneous recurrent seizure rats

Background: N(2-propylpentanoyl) urea (VPU) is a new valproic acid (VPA) analog with higher anticonvulsant activity than its parent compound in various animal models including seizure acutely induced by pilocarpine. Objective: Investigate its effects on hippocampal amino acid neurotransmitters in spontaneous recurrent seizure (SRS) rats. Methods: Pilocarpine hydrochloride was used to induce status epilepticus (SE). Animals were visually observed for two hours/day for an episode of SRS for six weeks. Microdialysis experiment was performed to detect hippocampal amino acid neurotransmitters on those rats that developed SRS. Results: In comparison to normal rats, hippocampal glutamate, gamma-aminobutyric acid (GABA), and glycine, significantly increased in SRS rats. Occurrence of SRS in the faces of increased level of inhibitory neurotransmitters suggests the key role played by glutamate in the genesis and control of SRS. Based on the observation in pilocarpine-induced SE, the level of glutamate in SRS rats significantly decreased by a clinically effective anticonvulsant, VPA (300 and 600 mg/kg, i.p). Similar profile on hippocampal glutamate was also exhibited by VPU (50 and 100 mg/kg, i.p.). Conclusion: The possible role of VPU in controlling seizure in SRS rats and subsequently human temporal lobe epilepsy as VPA was suggested.

Evidences for pharmacokinetic interaction of riluzole and topiramate with pilocarpine in pilocarpine-induced seizures in rats

In this study we investigated the effectiveness of two antiepileptic drugs: riluzole and topiramate against pilocarpine-induced seizures, which are considered to be a model of intractable epilepsy commonly used to investigate the antiepileptic effect of drugs and mechanisms of epileptogenesis. Seizures and status epilepticus were induced by pilocarpine in adult male Wistar rats. Riluzole (1-4mg/kg) administered intraperitoneally before pilocarpine dose-dependently protected rats against seizures with the anticonvulsant ED(50) value (50% effective anticonvulsant dose) of 1.8 (1.3-2.6)mg/kg. In contrast, riluzole at 8 and 12mg/kg administered after the onset of pilocarpine-induced seizures affected neither status epilepticus nor mortality of rats. Topiramate significantly enhanced convulsive action of pilocarpine, lowering the convulsant CD(50) value (50% effective convulsant dose) of pilocarpine from 350.8 (329.2-373.8) to 246.4 (218.6-278.2)mg/kg. Riluzole (4mg/kg) lowered plasma and brain concentration of pilocarpine administered at a dose of 400mg/kg from 168.0+/-8.6 to 75.3+/-19.9microg/ml and from 193.7+/-6.6 to 97.0+/-26.1microg/g, respectively. Topiramate (200mg/kg) increased plasma and brain concentration of pilocarpine administered at a dose of 300mg/kg from 78.1+/-2.9 to 106.0+/-6.8microg/ml and from 138.4+/-5.0 to 155.2+/-5.1microg/g, respectively. It seems that both anticonvulsant effect exerted by riluzole and proconvulsant effect exerted by topiramate in pilocarpine model of seizures are due to a pharmacokinetic interaction. Therefore, we postulate that the concentration of pilocarpine should be measured routinely whenever the anticonvulsant effect of drugs is determined in the pilocarpine model of seizures.

In vivo imaging of dopamine receptors in a model of temporal lobe epilepsy

PURPOSE

Alterations in dopamine neurotransmission in animal models of epilepsies have been frequently demonstrated using invasive neuroscience or ex vivo techniques. We aimed to test whether corresponding alterations could be detected by noninvasive in vivo brain imaging with positron emission tomography (PET) in the chronic phase of the rat pilocarpine model of temporal lobe epilepsy.

METHODS

Six pilocarpine-treated Wistar rats exhibiting spontaneous recurrent seizures and nine control rats were studied with PET using [(18)F]-fallypride, a high-affinity dopamine D(2/3) receptor ligand. Parametric images of [(18)F]-fallypride specific binding were calculated using a reference tissue method, and the two groups were contrasted by whole-brain voxel-based analysis implemented in statistical parametric mapping (SPM5).

RESULTS

Dopamine D(2/3) receptor availability was 27% lower in the bilateral anterior caudate-putamen of pilocarpine-treated rats as compared to controls (p < 0.05), but binding was unaffected in other striatal or extrastriatal regions.

CONCLUSIONS

The finding of substantially reduced availability of dopamine D(2/3) receptors in the anterior caudate-putamen of rats during the chronic phase of the pilocarpine model is in agreement with results of invasive (microinjection, microdialysis) animal studies that have revealed increased dopamine tonus and a D(2/3) receptor-mediated anticonvulsant action of dopamine in the anterior segment of the rat striatum. The present PET approach could be prospectively applied for monitoring dopamine receptor changes longitudinally, that is, at different phases of the epileptogenic process, and opens perspectives for testing dopaminergic agents as potential antiepileptogenic drugs.

Anticonvulsant and antioxidant effects of 3-alkynyl selenophene in 21-day-old rats on pilocarpine model of seizures

This study investigated the anticonvulsant effect of 3-alkynyl selenophene (3-ASP) on pilocarpine (PC)-, pentylenetetrazole (PTZ)- and kainic acid (KA)-induced seizures and mortality in 21-day-old rats. Rats were pretreated by oral route (p.o.) with 3-ASP (10, 25 and 50mg/kg) before intraperitoneal (i.p.) administration of PC (400mg/kg), PTZ (80 mg/kg) or KA (45 mg/kg). 3-ASP increased the latency to the seizure onset on PTZ and KA models. At the dose of 50mg/kg, 3-ASP avoided the death caused by PTZ and KA. 3-ASP (50mg/kg) abolished seizures and death induced by PC in rats. To investigate the antioxidant effect of 3-ASP on rats exposed to PC, the activity of glutathione peroxidase (GPx), glutathione-S-transferase (GST), acetylcholinesterase (AChE), Na(+)K(+)ATPase, superoxide dismutase (SOD) and catalase (CAT) as well as the levels of reactive species (RS) and ascorbic acid (AA) were determined in brains of rats. 3-ASP protected against the increase in RS levels and CAT activity induced by PC in brains of rats. The decrease in the levels of AA and inhibition of Na(+)K(+)ATPase, SOD and AChE activities caused by PC were protected by 3-ASP. Subeffective doses of 3-ASP plus diazepam, 5S,10R-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) or 6,7-dinitroquinoxaline-2,3-dione (DNQX) increased the latency to the seizure onset induced by PC, suggesting the involvement of ionotropic glutamatergic and GABAergic receptors in anticonvulsant action of 3-ASP. The anticonvulsant and antioxidant effects of 3-ASP in 21-day-old rats on PC model were demonstrated.

Amiloride delays the onset of pilocarpine-induced seizures in rats

Recent evidence suggests that amiloride, a potent and nonselective blocker of acid-sensing ion channels, suppresses generalized seizures induced by maximal electroshock and pentylenetrazole. Here I further determined and quantified the effects of amiloride on the occurrence of limbic seizures and status epilepticus-induced by intraperitoneal administration of pilocarpine, a muscarinic acetylcholine receptor agonist. Pretreatment with various doses (5, 10, 30, 100, and 200 mg/kg) of amiloride significantly delayed the onset of the first episode of limbic seizures and the occurrence of status epilepticus following administration of pilocarpine (380 mg/kg). At the dose of 100 and 200 mg/kg, amiloride suppressed limbic seizures in 33% of pilocarpine-treated animals and significantly reduced the seizure severity score in 67% of the remaining animals. These findings suggest that amiloride may modulate seizure generation and propagation, probably via mechanisms involving acid-sensing ion channels in the pilocarpine model of temporal lobe epilepsy.

Characterization of the anticonvulsant profile of isonicotinic acid benzylamide in various experimental seizure models in mice

This study focused on the evaluation of anticonvulsant properties of isonicotinic acid benzylamide (iso-Nic-BZA) in numerous experimental seizure models (maximal electroshock [MES]-, bicuculline [BIC]-, pentylenetetrazole [PTZ]-, pilocarpine [PILO]-, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid [AMPA]-, kainic acid [KA]- and N-methyl-d-aspartic acid [NMDA]-induced seizures). Moreover, acute adverse-effect profile of the agent with respect to impairment of motor coordination was assessed in animals subjected to the chimney test. The evaluation of time-course and dose-response relationships for iso-Nic-BZA provided evidence that the compound produced the peak to maximum antielectroshock action and acute adverse effects at 5min after its systemic (i.p.) administration. Iso-Nic-BZA exerted a clear-cut anticonvulsant action against maximal electroshock-induced seizures in mice and its ED(50) value was 70.6 (56.4-88.4)mg/kg. The assessment of acute adverse effects in the chimney test revealed that the agent produced acute neurotoxic effects and its TD(50) value was 135.6 (108.8-169.0)mg/kg. Additionally, iso-Nic-BZA showed the anticonvulsant activity in numerous chemically-induced seizures (AMPA-, BIC-, KA-, and PTZ-evoked clonic convulsions), remaining virtually ineffective (at doses up to 200mg/kg) in PILO- and NMDA-induced seizures in mice. Based on this study, one can conclude that iso-Nic-BZA due to the short time to peak of its maximum anticonvulsant effects (5min after its i.p. administration), deserves more attention as a potential antiepileptic drug for patients in status epilepticus.

Antiepileptic drugs prevent changes induced by pilocarpine model of epilepsy in brain ecto-nucleotidases

Ecto-nucleotidases, one of the main mechanisms involved in the control of adenosine levels in the synaptic cleft, have shown increased activities after the pilocarpine model of epilepsy. Here we have investigated the effect of the antiepileptic drugs (AEDs) on ecto-nucleotidase activities from hippocampal and cerebral cortical synaptosomes of rats at seven days after the induction of the pilocarpine model. Expression of these enzymes were investigated as well. Our results have demonstrated that phenytoin (50 mg/kg) and carbamazepine (30 mg/kg) were able to prevent the increase in ecto-nucleotidase activities elicited by pilocarpine in brain synaptosomes. However, sodium valproate (at 100 mg/kg) was only able to avoid the increase on ATP and ADP hydrolysis in hippocampal synaptosomes. Increase on ATP hydrolysis in hippocampal synaptosomes was also prevented by sodium valproate at 286 mg/kg, which corresponds to ED50 for pilocarpine model. NTPDase1, NTPDase2, NTPDase3, and ecto-5'-nucleotidase expressions were not affected by pilocarpine in cerebral cortex. However, expressions of NTPDase2, NTPDase3, and ecto-5'-nucleotidase were increased by pilocarpine in hippocampus. Our results have indicated that previous treatment with AEDs was able to prevent the increase in hippocampal ecto-nucleotidases of pilocarpine-treated rats. These findings have shown that anticonvulsant drugs can modulate plastic events related to the increase of nucleotidase expression and activities in pilocarpine-treated rats.

Expression of muscarinic and dopaminergic receptors and monoamine levels frontal cortex of epileptic rats

Apart from stroke, epilepsy is the most common neurological disorder with 0.5% of prevalence. The present study was performed in order to determine the monoamine levels, (M(1)-like) muscarinic and (D(1)- and D(2)-like) dopaminergic receptor changes in frontal cortex of adult rats after pilocarpine-induced status epilepticus (SE). Male Wistar rats were treated with a single dose of pilocarpine (400 mg/kg, s.c.) and the control group received 0.9% saline (s.c.). Both groups were sacrificed 1 h after treatment. The frontal cortex was dissected for neurochemical assays. The results show a downregulation of 27% in M(1) muscarinic receptor density, but in the dissociation constant (K(d)) value remained unaltered. D(1) and D(2) dopaminergic receptor densities and their K(d) values remained unaltered. Monoamine and metabolites levels presented decreases of 44%, 27%, 30% and 42% in dopamine (DA), homovanilic acid (HVA), norepinephrine (NE) and 5-hydroxyindoleacetic acid (5-HIAA) contents, respectively. Moreover, in serotonin (5-HT) level remained unaltered and the 4-hydroxy-3-methoxy-phenylacetic acid (DOPAC) concentration was augmented by 34%. The results suggest that dopaminergic system in this area studied may not be directly involved in the seizures and status epilepticus, but different monoamines and metabolites can be modified in this cerebral area during seizure process. In conclusion, the neurochemical alterations that occur in frontal cortex of adult rats observed during the establishment of the status epilepticus induced by pilocarpine are decrease in M(1) receptor density concentration and a reduction in DA and NE levels.

Pilocarpine-induced status epilepticus: Monoamine level, muscarinic and dopaminergic receptors alterations in striatum of young rats

Behavioural changes, muscarinic and dopaminergic receptors density and levels of monoamines were measured in striatum of rats after pilocarpine-induced status epilepticus (SE). Wistar rats at the age of 21 days were treated with pilocarpine (400mg/kg; subcutaneously) whilst the control group was treated with 0.9% saline (s.c.). Both groups were sacrificed 1h following the treatment. SE induced a muscarinic receptor downregulation of 64% in pilocarpine group. This effect was also observed to be 57% in D(1) and 32% in D(2). In the dissociation constant (K(d)) values in muscarinic and D(1) receptor no alterations were verified. On the other hand, the K(d) value for D(2) was observed to increase 41%. High performance liquid chromatography determinations showed 63, 35, 77 and 64% decreases in dopamine, 3-methoxy-phenylacetic acid, serotonin and 5-hydroxyindoleacetic acid contents, respectively. The homovanilic acid level was verified to increase 119%. The noradrenaline content was unaltered. A direct evidence of monoamine levels alterations can be verified during seizure activity and receptor density changes appear to occur in an accentuated way in immature brain during the estabilishment of SE induced by pilocarpine.

The impact of genetic background on neurodegeneration and behavior in seizured mice

We used pilocarpine-induced seizures in mice to determine the impact of genetic background on the vulnerability of hippocampal neurons and associated changes of behavioral performance. The susceptibility of hippocampal neurons to seizure-induced cell death paralleled the severity of the seizures and depended on genetic background. Hippocampal neurons in C57BL/6 mice were most resistant to cell death, whereas they were highly vulnerable in FVB/N mice. The degree of neuronal degeneration in F1 hybrid mice obtained by crossing the two strains was at an intermediate level between the parent strains. Two weeks after the severe seizures, performance in a water-maze place navigation task showed a bimodal distribution. Seventeen of 19 (90%) F1 mice were completely unable to learn while the other two learned reasonably well. Of 28 C57BL/6 mice with similarly severe seizures, six were as strongly impaired as their F1 counterparts (22%). The remaining 22 performed normally, indicating a much lower probability of C57BL/6 mice to be affected. Treated mice showed a deficit of open-field exploration which was strongly correlated with the impairment in the place navigation task and was again more severe in F1 mice. Our results show that the vulnerability of hippocampal neurons to pilocarpine-induced seizures, as well as the associated behavioral changes, depended on genetic background. Furthermore, they confirm and extend our earlier finding that a relatively modest reduction of hippocampal cell death can be associated with dramatic changes of behavioral performance and emphasize the importance of tightly-controlled genetic backgrounds in biological studies.

Long-term behavioral and morphological consequences of nonconvulsive status epilepticus in rats

The aims of the present study were to ascertain whether nonconvulsive status epilepticus (NCSE) could give rise to long-term behavioral deficits and permanent brain damage. Two months after NCSE was elicited with pilocarpine (15 mg/kg i.p.) in LiCl-pretreated adult male rats, animals were assigned to either behavioral (spontaneous behavior, social interaction, elevated plus-maze, rotorod, and bar-holding tests) or EEG studies. Another group of animals was sacrificed and their brains were processed for Nissl and Timm staining as well as for parvalbumin and calbindin immunohistochemistry. Behavioral analysis revealed motor deficits (shorter latencies to fall from rotorod as well as from bar) and disturbances in the social behavior of experimental animals (decreased interest in juvenile conspecific). EEGs showed no apparent abnormalities. Quantification of immunohistochemically stained sections revealed decreased amounts of parvalbumin- and calbindin-immunoreactive neurons in the motor cortex and of parvalbumin-positive neurons in the dentate gyrus. Despite relatively inconspicuous manifestations, NCSE may represent a risk for long-term deficits.

Neuroprotection and epilepsy

During the last years it has become obvious that the current way of treating epilepsy with antiepeileptic drugs is insufficient concerning the modification of the underlying disesease and provides merely a symptomatic treatment, without clear influence on the course of the disease. There is a pressing need to find alternative strategies and to find possibilities to intervene either into the basic processes determining the development of epilepsies or to promote compensatory processes in repairing these dysfunctions. The increasing knowledge about the basic neuronal changes underlying epilepsies allows now to analyse the potential role of neuroprotective agents in in epileptogenesis. In epilepsy the most frequent constellation is the presence of damage and overexcitation together. Increase in excitability may develop after a primary damage as in posttraumatic epilepsy, or outburst of epileptic excitability may cause neuronal damage as in cell loss after status epilepticus or in any case of the so called cytotoxic damage from extensive glutamatergic involvement. Epilepsy in certain forms is a progressive disease. The factors determining the progressive course and the possibe prevention of it is obviously an overlaping field with neuroprotection. Therefore although neuroprotection works only against certain aspects of a complex cascade of pathological events, might be a promising option in several stadiums during the development and course of epilepsy. We provide evidences that some of the new antiepileptic drugs have neuroprotective effect on different animal models of chronic partial epilepsies, and how this effect is fitting to the antiepileptogenic, and seizure supressing effect of the same drugs.

Antiepileptic drugs and apoptosis in the developing brain

Epilepsy is the most common neurologic disorder in young humans. Antiepileptic drugs (AEDs), used to treat seizures in children, infants, and pregnant women, cause cognitive impairment, microcephaly, and birth defects by unknown mechanisms. We tested whether common AEDs cause neurodegeneration in the developing rat brain. Rats aged 3-30 days received phenytoin, phenobarbital, diazepam, clonazepam, vigabatrin, or valproic acid. Histologic examination of the brains revealed that these drugs cause widespread and dose-dependent apoptotic neurodegeneration in the developing rat brain during the brain growth spurt period. Apoptotic neurodegeneration was triggered at plasma drug levels relevant for seizure control in humans. Antiepileptic drugs lead to reduced expression of neurotrophins and decreased concentrations of the active forms of ERK1/2, RAF, and AKT. beta-Estradiol, which stimulates pathways that are activated by neurotrophins, ameliorated AEDs-induced apoptotic neurodegeneration. Our findings present one possible mechanism to explain cognitive impairment and reduced brain mass associated with pre- or postnatal exposure of humans to antiepileptic therapy.

Intact spatial memory in mice with seizure-induced partial loss of hippocampal pyramidal neurons

We generated defined neuronal loss in hippocampus of genetically identical mice by pilocarpine injections and studied the impact of these seizures on the performance of mice in spatial learning and memory. The numbers of TUNEL-positive degenerating cells paralleled the severity of the seizures. When compared to the numbers found for not-seizured control mice, mild, moderate, and severe seizures produced significant increases in TUNEL-positive neurons in CA1 and CA3 regions by 19, 25, and 63%, respectively. Water maze learning was abolished after the severe seizures. However, spatial learning was normal after mild or moderate seizures. Therefore, there was no linear correlation between the impairment of learning and memory performance with the number of degenerating neurons in hippocampus. Our data suggest that normal spatial learning and memory can be achieved without the full number of hippocampal pyramidal neurons in partially lesioned hippocampus.

Electrophysiological, neurochemical and regional effects of levetiracetam in the rat pilocarpine model of temporal lobe epilepsy

This study compared levetiracetam (Keppra) with reference antiepileptic drugs (AEDs) in the rat pilocarpine model of temporal lobe epilepsy. Electroencephalogram (EEG) recordings showed that i.p. administration of valproate (300 mg/kg), phenobarbital (5 mg/kg) and clonazepam (0.5 mg/kg) all significantly delayed the appearance of the first epileptic spike discharge in hippocampus as well as synchronous epileptiform activity in hippocampus and cortex. In contrast, i.p. administration of levetiracetam (17 mg/kg) only significantly delayed the appearance of the latter. This was corroborated by findings showing that i.p. administration of levetiracetam (17 mg/kg) significantly opposed pilocarpine-induced increases in the amplitude of the orthodromic population spike in the hippocampal CA3 area of urethane-anaesthetised rats, while valproate (200 mg/kg), phenobarbital (10 mg/kg) and clonazepam (1 mg/kg) had no effect. Pre-treatment i.p. with phenobarbital (10 mg/kg) and clonazepam (0.5 mg/kg) significantly reversed seizure-induced changes in aspartate and GABA concentrations while valproate (300 mg/kg) significantly reduced aspartate concentrations further. In contrast, levetiracetam (34 mg/kg) significantly counteracted all seizure-induced alterations in amino acid concentrations. Midazolam induced significant seizure protection after microinjection into substantia nigra pars reticulata (SNR, 50 nmol), nucleus accumbens (NA, 25 nmol) and caudate putamen (CP, 25 nmol), whereas phenytoin (50 nmol) only showed significant seizure protection after injection into the latter area. Levetiracetam differed by significant seizure protection after injection into SNR (1,000 nmol) and NA (3,000 nmol). These results suggest that levetiracetam is distinct from other AEDs by its ability to selectively suppress synchronisation of neuronal spike and burst firing in hippocampus.

Safety and tolerance of rapidly infused Depacon. A randomized trial in subjects with epilepsy

BACKGROUND

Valproate sodium injection (Depacon(R)) is an intravenous form of valproate for use in absence and complex partial seizures when circumstances preclude oral administration. Certain situations may warrant larger and more rapid infusions than permitted by the original labeling. This study evaluated the safety of more rapid infusions.

METHODS

Subjects with epilepsy were randomized in a 2:1 ratio to receive up to 15 mg/kg of valproate sodium infused at 3.0 or 1.5 mg/kg/min. Up to four infusions were allowed within 24 h to achieve target plasma valproate concentrations of 50-100 mcg/ml. Primary safety endpoints were the changes in the 5-min and minimum post-first infusion blood pressures (BPs).

RESULTS

One hundred twelve subjects were treated, (3.0 mg/kg/min group: n=72, 1.5 mg/kg/min group: n=40). No significant treatment differences were detected for changes in the primary BP endpoints. Two subjects in the 3.0 mg/kg/min group had potentially clinically significant low systolic BP values during the study. Similar proportions of subjects in the two groups reported adverse events during or within 6 h following the first infusion.

CONCLUSIONS

Valproate sodium injection dosages up to 15 mg/kg and rates of 1.5 and 3.0 mg/kg/min were well tolerated in this population.

Antiepileptic drugs and apoptotic neurodegeneration in the developing brain

Epilepsy is the most common neurological disorder of young humans. Each year 150,000 children in the United States experience their first seizure. Antiepileptic drugs (AEDs), used to treat seizures in children, infants, and pregnant women, cause cognitive impairment, microcephaly, and birth defects. The cause of unwanted effects of therapy with AEDs is unknown. Here we reveal that phenytoin, phenobarbital, diazepam, clonazepam, vigabatrin, and valproate cause apoptotic neurodegeneration in the developing rat brain at plasma concentrations relevant for seizure control in humans. Neuronal death is associated with reduced expression of neurotrophins and decreased concentrations of survival-promoting proteins in the brain. beta-Estradiol, which stimulates pathways that are activated by neurotrophins, ameliorates AED-induced apoptotic neurodegeneration. Our findings present one possible mechanism to explain cognitive impairment and reduced brain mass associated with prenatal or postnatal exposure of humans to antiepileptic therapy.

Effect on epileptogenesis of carbamazepine treatment during the silent period of the pilocarpine model of epilepsy

PURPOSE

This study addresses the question of epileptogenesis by investigating the effects of carbamazepine (CBZ) on the silent period of the pilocarpine model of epilepsy.

METHODS

Adult Wistar rats were subjected to status epilepticus (SE) induced by pilocarpine and treated with CBZ or saline, i.p, during 56 days. Latency for the first spontaneous seizure, incidence, frequency, and duration of seizures were monitored for < or =56 days after treatment. Hippocampal histologic analysis was performed.

RESULTS

CBZ reduced the frequency and duration of the seizures and the hippocampal damage.

CONCLUSIONS

CBZ did not abort the epileptogenesis but minimized the expression of seizures and hippocampal damage.

New insights from the use of pilocarpine and kainate models

Local or systemic administration of pilocarpine and kainate in rodents leads to a pattern of repetitive limbic seizures and status epilepticus, which can last for several hours. A latent period follows status epilepticus and precedes a chronic phase, which is characterized by the occurrence of spontaneous limbic seizures. These distinct features, in a single animal preparation, of an acute damage induced by status epilepticus, a silent interval between injury and the onset of spontaneous seizures, and a chronic epileptic state have allowed antiepileptic drug (AED) studies with different purposes, (a) in the acute phase, identification of compounds with efficacy against refractory status epilepticus and/or neuroprotection against damage induced by sustained seizures; (b) in the latent period, identification of agents with a potential for preventing epileptogenesis and/or against seizure-induced long-term behavioral deficits and (c) in the chronic phase, testing drugs effective against partial and secondarily generalized seizures. Studies on pilocarpine and kainate models have pointed out that some AEDs or other compounds exert an antiepileptogenic effect. The analogy of the latent phase of pilocarpine and kainate models with the acquisition of amygdala kindling should encourage testing of drugs that have proved to suppress the evolution of amygdala kindling. Drug testing in the chronic phase should not address only the suppression of secondarily generalized motor seizures. Most of current tools used to quantify spontaneous seizure events need to be coupled to electrophysiology and more sophisticated systems for recording and analyzing behavior.

Attenuating effects of melatonin on pilocarpine-induced seizures in rats

Daily melatonin (10-50 mg/kg, i.p.) treatment at 08.30 h or 17.00 h for 1 week of female rats (2-months-old) increased the latency to the appearance of the first convulsion in the pilocarpine-induced seizure model. Other behavior parameters remained unaltered. The anticonvulsant effect of melatonin seemed to be more intense at the light-dark transition. Moreover, the effect of repeated melatonin treatment was also age-related, since it showed a lower threshold in 2-month-old than in 21-day-old rats, and the acute treatment was not efficient. [3H]N-methylscopolamine binding was unaltered in the hippocampus and striatum of adult rats after the association of melatonin and pilocarpine. While muscarinic binding was unaltered in adult rats, it increased in the hippocampus of young rats in the presence of melatonin (50 mg/kg) and pilocarpine, and did not change in the striatum. Melatonin partially recovered [3H]GABA binding in the hippocampus in the presence of pilocarpine-induced seizures, and intensified pilocarpine effects in the striatum of adult rats.

Levetiracetam does not modulate neuronal voltage-gated Na+ and T-type Ca2+ currents

This study investigated whether the mechanism of action of levetiracetam (LEV) is related to effects on neuronal voltage-gated Na+ or T-type Ca2+currents. Rat neocortical neurones in culture were subjected to the whole-cell mode of voltage clamping under experimental conditions designed to study voltage-gated Na+ current. Additionally, visually identified pyramidal neurones in the CA1 area of rat hippocampal slices were subjected to the whole-cell mode of voltage clamping under experimental conditions designed to study low-voltage-gated (T-type) Ca2+ current. LEV (10 microM-1 mM) did not modify the Na+ current amplitude and did not change (200 microM) the steady-state activation and inactivation, the time to peak, the fast kinetics of the inactivation and the recovery from the steady-state inactivation of the Na+ current. Likewise, LEV (32-100 microM) did not modify the amplitude and did not change the steady-state activation and inactivation, the time to peak, the fast kinetics of the inactivation and the recovery from the steady-state inactivation of the T-type Ca2+current. In conclusion, neuronal voltage-gated Na+ channels do not appear directly involved in the antiepileptic mechanism of action of LEV, and LEV was devoid of effect on the low-voltage-gated (T-type) Ca2+ current in hippocampal neurones.

Brain-derived neurotrophic factor superinduction parallels anti-epileptic--neuroprotective treatment in the pilocarpine epilepsy model

Antiepileptic drugs provide neuroprotection in several animal models of brain damage, including those induced by status epilepticus (SE). The mechanisms involved in this action are unknown, but neurotrophic factors such as brain-derived neurotrophic factor (BDNF) may play a role. In this study we investigated the changes in BDNF levels in rats in which SE had been induced by pilocarpine injection (400 mg/kg i.p.) and continued for several hours (unprotected group). In other animals (protected groups), SE was suppressed after 30 min by intraperitoneal injection of either diazepam (10 mg/kg) + pentobarbital (30 mg/kg) or paraldehyde (0.3 mg/kg). In diazepam + pentobarbital-treated rats the hippocampal damage caused by SE was significantly lower (p < 0.05) than in unprotected animals. In addition, 2 and 24 h after pilocarpine injection, the levels of BDNF mRNA were moderately increased in the unprotected group, but 'superinduced' in protected animals, especially in the neocortex and hippocampus. A time-dependent increase in BDNF immunoreactivity was also found by western blot analysis in rats treated with diazepam + pentobarbital. In contrast, a decrease of BDNF immunoreactivity occurred in the unprotected group. In conclusion, these results show that neuroprotection induced by anti-epileptic drugs in pilocarpine-treated rats is accompanied by strong potentiation of BDNF synthesis in brain regions involved in SE.

In vivo study of the effect of valpromide and valnoctamide in the pilocarpine rat model of focal epilepsy

PURPOSE

We evaluated the effectiveness of the commonly used antiepileptic drug sodium valproate (400 mg/kg) and two of its amide derivatives, valpromide and valnoctamide (both 100 mg/kg), in an in vivo rat model of focal epilepsy. Our main interest was to get insight into possible changes in extracellular amino acid neurotransmitter levels following administration of the drugs, both in control and in epileptic conditions.

METHODS

Seizures were evoked in freely moving rats by intrahippocampal administration of pilocarpine via a microdialysis probe (10 mM for 40 min at 2 microl/min). Microdialysis was also used as in vivo sampling technique and alterations in extracellular hippocampal glutamate and GABA levels were monitored. Electrophysiological evidence for the presence or absence of seizures was simultaneously recorded with electrocorticography.

RESULTS

The focally evoked pilocarpine-induced seizures were completely prevented by acute intraperitoneal pretreatment with each of the three drugs in the respective doses. Effective protection was reflected in the electrocorticographic recordings and in the lack of sustained elevations of the extracellular glutamate levels after pilocarpine perfusion. Little effects were seen on the basal extracellular amino acid levels after systemic administration of each of the compounds, nor after the intrahippocampal administration of sodium valproate.

CONCLUSIONS

Valnoctamide and valpromide (100 mg/kg) proved to be at least as effective as their parent compound sodium valproate (400 mg/kg) against pilocarpine-induced seizures. All three compounds however failed to induce significant initial alterations in extracellular hippocampal GABA release. This questions the enhancement of GABA-mediated inhibition as being one of their mechanisms of action.

Neurons in layer III of the entorhinal cortex. A role in epileptogenesis and epilepsy?

A preferential lesion of neurons in layer III of the entorhinal cortex (EC) is often observed in patients suffering from temporal lobe epilepsy and in several animal models of the disease. This lesion is duplicated in rats by a focal, intra-entorhinal injection of the "indirect" excitotoxin aminooxyacetic acid (AOAA), providing a model that can be used to study the mechanisms underlying seizure-induced cell death and epilepsy. Doomed neurons in the EC and in several associated limbic structures show pathological changes within hours after the AOAA injection, but GABAergic neurons in layer III of the EC are quite resistant. This pattern of neuron loss eventually results in hippocampal and entorhinal hyperexcitability. Notably, the seizure-induced death of layer III neurons in the EC can be attenuated by eliminating the prominent excitatory input from the presubiculum. Taken together, these results suggest opportunities to target parahippocampal structures for the treatment of temporal lobe epilepsy.

Ricinine-elicited seizures. A novel chemical model of convulsive seizures

The present investigation introduces ricinine-elicited seizures as a novel chemical model of convulsive seizure. Ricinine, a neutral alkaloid obtained from the plant Ricinus communis, induces seizures when administered to mice at doses higher than 20 mg/kg. Animals presenting seizures showed a marked preconvulsive phase followed by short duration hind limb myoclonus, respiratory spasms, and death. The lethal nature of ricinine seizures is also pointed out as a good model to study the events causing death in clonic seizures, particularly those related to respiratory spasms, which are also observed in some types of human epilepsy. The behavioral signs of ricinine-elicited seizures are accompanied by electrographic alterations more evident during the preconvulsive phase in the cerebral cortex and more intense during the ictal phase both in the cortex and in the hippocampus. The ricinine-elicited seizures may be inhibited by diazepam but not by phenobarbital, phenytoin, or ethosuximide. Micromolar concentrations of ricinine cause a small decrease in the binding of [3H]-flunitrazepam to cerebral cortex membranes, but do not alter the binding of other radioligands to AMPA, 5-HT(1A), muscarinic, and alpha(1)-adrenergic receptors. Although ricinine presents a cyanide radical, only higher doses of ricinine (4 mM) caused a small impairment of mitochondrial respiration. These results suggest that the mechanism of action of ricinine probably involves the benzodiazepine site in the GABA(A) receptor. This may represent a new mechanism of drug-elicited seizures that may contribute to a better understanding of epilepsy and to new therapeutic approaches to this disease.