Neuropharmacology beyond reductionism - A likely prospect.

Neuropharmacology had several major past successes, but the last few decades did not witness any leap forward in the drug treatment of brain disorders. Moreover, current drugs used in neurology and psychiatry alleviate the symptoms, while hardly curing any cause of disease, basically because the etiology of most neuro-psychic syndromes is but poorly known. This review argues that this largely derives from the unbalanced prevalence in neuroscience of the analytic reductionist approach, focused on the cellular and molecular level, while the understanding of integrated brain activities remains flimsier. The decline of drug discovery output in the last decades, quite obvious in neuropharmacology, coincided with the advent of the single target-focused search of potent ligands selective for a well-defined protein, deemed critical in a given pathology. However, all the widespread neuro-psychic troubles are multi-mechanistic and polygenic, their complex etiology making unsuited the single-target drug discovery. An evolving approach, based on systems biology considers that a disease expresses a disturbance of the network of interactions underlying organismic functions, rather than alteration of single molecular components. Accordingly, systems pharmacology seeks to restore a disturbed network via multi-targeted drugs. This review notices that neuropharmacology in fact relies on drugs which are multi-target, this feature having occurred just because those drugs were selected by phenotypic screening in vivo, or emerged from serendipitous clinical observations. The novel systems pharmacology aims, however, to devise ab initio multi-target drugs that will appropriately act on multiple molecular entities. Though this is a task much more complex than the single-target strategy, major informatics resources and computational tools for the systemic approach of drug discovery are already set forth and their rapid progress forecasts promising outcomes for neuropharmacology.

Systems biology, complexity, and the impact on antiepileptic drug discovery.

The number of available anticonvulsant drugs increased in the period spanning over more than a century, amounting to the current panoply of nearly two dozen so-called antiepileptic drugs (AEDs). However, none of them actually prevents/reduces the post-brain insult development of epilepsy in man, and in no less than a third of patients with epilepsy, the seizures are not drug-controlled. Plausibly, the enduring limitation of AEDs' efficacy derives from the insufficient understanding of epileptic pathology. This review pinpoints the unbalanced reductionism of the analytic approaches that overlook the intrinsic complexity of epilepsy and of the drug resistance in epilepsy as the core conceptual flaw hampering the discovery of truly antiepileptogenic drugs. A rising awareness of the complexity of epileptic pathology is, however, brought about by the emergence of nonreductionist systems biology (SB) that considers the networks of interactions underlying the normal organismic functions and of SB-based systems (network) pharmacology that aims to restore pathological networks. By now, the systems pharmacology approaches of AED discovery are fairly meager, but their forthcoming development is both a necessity and a realistic prospect, explored in this review.

Systems biology impact on antiepileptic drug discovery.

Systems biology (SB), a recent trend in bioscience research to consider the complex interactions in biological systems from a holistic perspective, sees the disease as a disturbed network of interactions, rather than alteration of single molecular component(s). SB-relying network pharmacology replaces the prevailing focus on specific drug-receptor interaction and the corollary of rational drug design of "magic bullets", by the search for multi-target drugs that would act on biological networks as "magic shotguns". Epilepsy being a multi-factorial, polygenic and dynamic pathology, SB approach appears particularly fit and promising for antiepileptic drug (AED) discovery. In fact, long before the advent of SB, AED discovery already involved some SB-like elements. A reported SB project aimed to find out new drug targets in epilepsy relies on a relational database that integrates clinical information, recordings from deep electrodes and 3D-brain imagery with histology and molecular biology data on modified expression of specific genes in the brain regions displaying spontaneous epileptic activity. Since hitting a single target does not treat complex diseases, a proper pharmacological promiscuity might impart on an AED the merit of being multi-potent. However, multi-target drug discovery entails the complicated task of optimizing multiple activities of compounds, while having to balance drug-like properties and to control unwanted effects. Specific design tools for this new approach in drug discovery barely emerge, but computational methods making reliable in silico predictions of poly-pharmacology did appear, and their progress might be quite rapid. The current move away from reductionism into network pharmacology allows expecting that a proper integration of the intrinsic complexity of epileptic pathology in AED discovery might result in literally anti-epileptic drugs.

Epileptic hypersynchrony revisited.

Synchronization of neuronal responses, which allows coordination of distributed activity patterns, is instrumental in brain functioning, as altered neuronal synchronization is involved in a variety of brain pathologies. Epileptic hypersynchrony chiefly relies on brain wiring, which, in a broader sense, means including astrocytic release of gliotransmitters and electrotonic coupling through gap junctions, beyond classical synaptic connections. Epileptic hypersynchrony also relies on electrical field effects and ion concentration changes in the extracellular space, and it relates to intracellular mechanisms underlying neuronal hyperexcitability. The current lack of a specific impact of hypersynchrony on antiepileptic drug development might be next surpassed, as hypersynchrony seems to be a worthy and approachable, though challenging target of antiepileptic pharmacology.

Brivaracetam (ucb 34714) inhibits Na(+) current in rat cortical neurons in culture.

Brivaracetam (ucb 34714; BRV), a new antiepileptic drug (AED) candidate, is a pyrrolidone derivative displaying a markedly higher affinity than levetiracetam (LEV; Keppra) to the synaptic vesicle protein SV2A, shown to be the brain-specific binding site of LEV. The higher affinity for SV2A correlates significant antiepileptic activity in animal epilepsy models in vitro and in vivo. Since many AEDs act upon inhibiting neuronal Na(+) currents, this study explored putative activity of BRV on the properties of these currents. Voltage-activated Na(+) currents were recorded by whole-cell patch-clamp on neuronal somas of rat neocortical neurons, grown in dissociated cell culture for up to 12 days. BRV, dissolved at the desired final concentration (between 0.2microM and 1mM) was applied by a multi-barrel pipette system near the soma of the recorded neuron. BRV produced a concentration-dependent inhibition of voltage-dependent Na(+) currents with IC(50) values of 41microM at the holding potential of -100mV, and of 6.5microM at the holding potential of -60mV. The voltage-dependence of activation and the kinetics of fast inactivation were not modified in the presence of BRV (30microM). Conversely, the recovery from fast inactivation was significantly slower and the voltage of half-maximal inactivation was shifted toward hyperpolarized value after BRV perfusion in a concentration-dependent manner. Furthermore, BRV (30microM) induced a significant use-dependent block at 50Hz stimulation frequency. These results indicate that BRV is able to modulate the voltage-activated Na(+) inflow in cortical neurons, which conceivably might contribute to the antiepileptic activity of this drug.

Profile of the new pyrrolidone derivative seletracetam (ucb 44212) in animal models of epilepsy.

Seletracetam is a pyrrolidone derivative with a one-log-unit higher affinity for the synaptic vesicle protein 2A (SV2A) than levetiracetam (Keppra). This study explored its anticonvulsant properties in animal models of epilepsy. Seletracetam reduced both the amplitude and repetitive firing of population spikes induced by a high K(+)/low Ca(2+) concentration fluid (HKLCF) in rat hippocampal slices. The reduction of HKLCF-induced increases in population spike amplitude was particularly pronounced, and occurred at approximately 10 times lower seletracetam concentrations than previously observed for levetiracetam. These invitro data suggest that desynchronisation of epileptiform activity may contribute significantly to the antiepileptic properties of seletracetam. Seletracetam also showed a potent anti-seizure activity in animal models mimicking partial-onset (kindled animals) and generalized epilepsy (audiogenic seizure susceptible mice and genetic absence epilepsy rats from Strasbourg (GAERS)). In amygdala-kindled rats, seletracetam increased the generalized seizure threshold current and decreased the duration of the after-discharge and the seizure severity observed at the after-discharge threshold current, and generally had a much more potent effect than previously observed for levetiracetam. Seletracetam showed no psychomimetic effects and a very high central nervous system (CNS) tolerability in both kindled and GAERS rats, markedly superior to that of levetiracetam and other antiepileptic drugs. These results suggest that seletracetam may represent an effective and very well tolerated broad-spectrum agent for the symptomatic treatment of epilepsy.

Brivaracetam inhibits spreading depression in rat neocortical slices in vitro.

Epilepsy and migraine are episodic neurological disorders with marked co-morbidity, making migraine common among epileptic patients. Conversely, several antiepileptic drugs (AEDs) are used as migraine-preventive medication. Cortical spreading depression (CSD) represents a transient suppression of bioelectric activity and is considered a key event in migraine and stroke. This study assessed the novel AED candidate brivaracetam (BRV) vs. the chemically related AED levetiracetam in a rat neocortical slice model allowing consistent quantification of drug effects on CSD. CSD episodes were regularly elicited on slices upon delivery of calibrated KCl drops and were recorded via two micropipette electrodes. After control CSDs, the drug was added to the perfusion and five subsequent CSDs were elicited during drug perfusion. Effects were assessed via CSD amplitude (Ampl) and duration at half-amplitude (D(1/2)). BRV, 10 and 32 microM reduced the Ampl and transiently the D(1/2). Levetiracetam, 32 and 100 microM had no effect on either Ampl or D(1/2). The anti-CSD effect of BRV in this in vitro model might suggest a potential anti-migraine activity of this compound, which warrants further investigation.

Mechanisms of drug resistance in epilepsy: relevance for antiepileptic drug discovery.

BACKGROUND: Epilepsy, the most common chronic neurological pathology, is symptomatically treated by present antiepileptic drugs (AEDs) in about two-thirds of the cases. Unfortunately, this proportion has not been significantly reduced despite the introduction of several new-generation AEDs. OBJECTIVE: This review challenges the utility of the paradigm of the excitation-inhibition imbalance for AED discovery and review mechanisms, presumed to be involved in drug-resistant epilepsy, with the purpose of discussing their relevance as targets for future AED discovery. CONCLUSION: Considering epilepsy as a mere imbalance between excitation and inhibition seems incapable of providing any proper basis for enabling future AED discovery to combat drug-resistant epilepsy as it oversimplifies a complex pathology, yet insufficiently understood. Two current hypotheses on the mechanisms of drug resistance in epilepsy highlight the roles of increased activity of blood-brain barrier multidrug transporter proteins and of alterations in the drug targets rendering them drug-insensitive. Both mechanisms are relevant but seem insufficient to account for the complexity of brain changes involved in drug-resistant epilepsy. Recent studies of drug-resistant epilepsy have revealed the involvement of inflammation processes, functional glia changes and altered intercellular communication related to gap junctions. This provides further, albeit not exhaustive, examples of targets to consider for future AED discovery. A successful strategy aimed at overcoming resistance to AEDs necessitates an integrated vision encompassing the basic features of intractable epilepsies.

Effects of chronic treatment with levetiracetam on hippocampal field responses after pilocarpine-induced status epilepticus in rats.

Levetiracetam (Keppra) is a new generation antiepileptic drug characterized by a unique profile of activity in experimental models of epilepsy. It also has a distinct binding site in the brain, i.e. the synaptic vesicle protein type 2 (SV2A). Levetiracetam has been reported to have antiepileptogenic and disease-modifying properties. In the present study the effects of chronic treatment with levetiracetam were assessed in rats that sustained pilocarpine-induced status epilepticus (SE). Hippocampal field potentials were recorded in vivo in anesthetized animals after 3-day washout period that followed 21-day treatment with different doses of levetiracetam (50, 150 or 300 mg/kg/day) administered via ALZET osmotic mini-pumps. Vehicle treated rats together with naive animals (not subjected to SE) were used as control groups. Chronic treatment with levetiracetam yielded clinically relevant plasma concentrations throughout the experiment with complete washout of the drug 3 days after treatment cessation. At this point in time post-SE rats chronically treated with vehicle developed clear signs of hippocampal hyperexcitability, i.e. increased amplitude of population spike (PS) recorded in the dentate gyrus and reduced paired-pulse inhibition in the CA1 area. Levetiracetam treatment dose-dependently counteracted these long-term effects of pilocarpine-induced SE. Furthermore, at the dose of 300 mg/kg/day levetiracetam restored these parameters back to control level. The present results indicate that chronic treatment with levetiracetam completely inhibits the development of hippocampal hyperexcitability following pilocarpine-induced SE.

The connexin 36 blockers quinine, quinidine and mefloquine inhibit cortical spreading depression in a rat neocortical slice model in vitro.

A protocol for inducing cortical spreading depression (SD) on rat neocortical slices in vitro, upon local application of calibrated approximately nl drops of KCl, 3M was used to elicit SD events, recorded at two different points on the slice. This in vitro model was validated by the inhibition of SD episodes by the NMDA antagonist MK-801 (20 microM), the reference SD blocker. Quinine, its stereoisomer quinidine, and mefloquine consistently inhibited the SD episodes. Quinine and quinidine, 100 and 200 microM reduced the duration, while mefloquine, 100 and 200 microM reduced the amplitude of SD events, all in a concentration-dependent manner. These compounds have been reported to block gap junctions, specifically the neuronal connexin (Cx) 36, but they also exert other cellular effects. While further investigation is warranted to settle whether SD inhibition in vitro by quinine, quinidine and mefloquine reflects an involvement of neuronal Cx36 channels in SD generation/propagation, these results bear potential drug-discovery relevance for the migraine with aura.

Differential effects of cation-chloride co-transport-blocking diuretics in a rat hippocampal slice model of epilepsy.

The cation-Cl- co-transport-blocking loop diuretics have clinically known anticonvulsant activity, though they can also induce seizures. We explored the effects of ethacrynic acid (ETA), furosemide (FUR) and bumetanide (BUM), prototypical blockers of cation-Cl- co-transport, on the epileptiform field potentials induced in CA3 area of hippocampal slices from 5-weeks-old rats by a high K+-low Ca2+ perfusion fluid. That milieu induces frequent spontaneous field bursts, making single fimbrial stimuli to evoke several repetitive population spikes, of increased amplitude. ETA (0.25-1 mM) concentration-dependently reduced spontaneous field bursting, up to terminating it. FUR, 5 mM also inhibited spontaneous field bursting, while BUM (12.5-100 microM) only presented an inconsistent tendency. Both ETA and FUR showed a less marked ability to depress the evoked responses, but approximately mM concentrations significantly reduced the number of repetitive population spikes and their amplitude. BUM only modestly reduced population spike amplitude, without concentration-dependence. This study shows that K+-Cl- co-transport-blocking diuretics ETA and FUR inhibit high K+-induced epileptiform activity in hippocampal slices from (nearly) adult rats, while the Na+-K+-2Cl- co-transport-preferring diuretic BUM had only negligible activity. These results support that neuronal K+-Cl- co-transport-blockade provides antiepileptic effects.

Caffeine-induced epileptiform field potentials in rat hippocampal slices: a pharmacological characterization.

Pharmacological modulation of the epileptiform electric activity induced by caffeine, 10 mM (CAF) on rat hippocampal slices was studied upon field potential recordings in CA3 area of the slices. This concentration of CAF, reportedly releasing Ca2+ ions from the endoplasmic reticulum, led single fimbrial stimuli to evoke repetitive population spikes (PSs) and induced periodic spontaneous field bursts. Carbamazepine, 50 microM reduced (by <40%) the number of repetitive PSs and the rate of spontaneous bursting, with no significant effect on the amplitude of evoked and spontaneous bursts. Valproate, 1 mM reduced only the number (by approximately 25%), but not the amplitudes, of repetitive PSs. Clonazepam, 1 microM consistently reduced the number of repetitive PSs (by approximately 45%), their amplitudes (by 30-60%), and the amplitude of spontaneous bursts (by approximately 70%). The adenosine receptor agonists 2-chloroadenosine, 5 microM and R(-) N6-(2-phenylisopropyl)adenosine, 1 microM had only scanty anti-CAF activity. The depletor of intracellular Ca2+ stores, thapsigargin, 2 microM transiently inhibited the number of evoked PSs and spontaneous bursting. The blocker of ryanodine receptor opening, ruthenium red had an anti-CAF effect, modest at 30 microM, but very strong at 40 microM. Nifedipine, 20 microM opposed CAF-induced spontaneous bursting, but not the evoked PSs. Flunarizine, 50 microM presented only a transient tendency to delay spontaneous bursting. In conclusion, this in vitro slice model appears readily able to reveal antiepileptic properties, though it does not support unequivocal mechanistic interpretation. Nevertheless, anti-CAF activity in this model would suggest the likely involvement of the neuronal ryanodine receptor-related traffic of calcium.

Is the persistent sodium current a specific target of anti-absence drugs?

The persistent Na+ current (INaP) has been proposed as the putative target of the anti-absence antiepileptic drugs. Accordingly, the effect of reference anti-absence drugs ethosuximide (ESM) and valproate (VPA), and of the new antiepileptic drug levetiracetam (LEV), on INaP have been tested in CA1 hippocampal neurons and compared to the classic anticonvulsant phenytoin (PHT) and the neuroprotective agent riluzole (RIL). Whole-cell patch-clamp recordings of the slowly inactivating current, fully characterized as INaP, were performed with a standard voltage-step protocol on thin hippocampal slices prepared from rat brain. Both PHT (100 microM) and RIL (10 microM) strongly depressed INaP, whereas ESM (1 mM) induced a slight decrease of INaP and VPA (1 mM) had no effect. Likewise, 60-min perfusion with relevant concentrations of LEV (10, 32 or 100 microM) did not modify INaP. In conclusion, these data question the impact of INaP depression as an anti-absence mechanism, and also disclaim the involvement of INaP in the antiepileptic mechanism of LEV.

Reduction of voltage-operated potassium currents by levetiracetam: a novel antiepileptic mechanism of action?

Levetiracetam (ucb L059; Keppra) is a novel antiepileptic drug. Its effects on action potential generation and voltage-operated potassium currents were studied in acutely isolated hippocampal CA1 neurones from rat and guinea pig, using the patch-clamp technique in the whole-cell configuration. (i) Levetiracetam reduced repetitive action potential generation and affected the single action potential. Levetiracetam, 100 microM, decreased the total number of action potentials and reduced the total depolarisation area of repetitive action potentials by 21%. Furthermore, levetiracetam increased the duration of the first action potential slightly, prolonged that of the second action potential by 13% and decreased the slope of rise by 23%. (ii) Levetiracetam decreased the voltage-operated potassium current. Without effect on sodium and A-type potassium currents, levetiracetam, 100 microM, reduced the delayed rectifier current by 26%. The concentration of half-maximal block was 47 microM for guinea pig and 6 microM for rat neurones. Thus, the reduction of repetitive action potential generation by levetiracetam can be attributed, unexpectedly, to a moderate reduction of the delayed rectifier potassium current, as supported by a simulation of action potential generation. This suggests that a reduction of potassium currents may contribute to the antiepileptic effect(s) of levetiracetam.

Desynchronizing effect of levetiracetam on epileptiform responses in rat hippocampal slices.

The effect of levetiracetam on neuronal hypersynchrony and hyperexcitability was examined using simultaneous extra- and intracellular recordings in rat brain slices perfused with a high K+/low Ca2+ (HKLC) fluid. These findings were compared to results obtained with carbamazepine, valproate and clonazepam. The HKLC milieu induces in hippocampal CA3 area, spontaneous interictal bursts and epileptiform responses. Levetiracetam decreased the number of population spikes per extracellular response but did not affect the number of action potentials per intracellular burst. This contrasts the effects of the reference antiepileptic drugs, which depressed both the extracellular and the intracellular bursts. These results indicate that levetiracetam is distinct from classical antiepileptic drugs by a relatively selective effect on collective neuronal responses, rather than on single neuron activity and suggests a potentially novel desynchronizing effect that probably contributes to its antiepileptic action.

H3 agonist immepip markedly reduces cortical histamine release, but only weakly promotes sleep in the rat.

Presynaptic H3 receptors exert negative control on brain histamine synthesis and release and may thereby play a key role in the control of the sleep/wake cycle. This suggests that pharmacological stimulation by H3 receptor agonists may potentially decrease wakefulness and induce sleep. This study reports the effect of a potent and selective H3 agonist, immepip, on EEG assessed sleep/wake phases in Sprague-Dawley rats at doses that significantly modulate brain histamine release. Immepip injected intraperitoneally (i.p.) at 5 or 10 mg kg(-1) induced a sustained decrease in cortical histamine efflux as measured by in vivo microdialysis. In a separate experiment, rats were prepared for EEG/EMG recording and evaluated during the dark phase of their light/dark cycle. The results showed that the same i.p. doses of 5 and 10 mg kg(-1) of immepip was devoid of any significant impact on the sleep/wake phases (active awake, drowsiness and slow wave sleep), except for a slight, albeit significant, decrease in sleep onset latency. These results reveal that a marked H3 receptor agonist-mediated reduction in cortical histamine release is not corroborated by a significant sleep promoting effect and therefore question the hypnotic potential of H3 agonists.

Levetiracetam has no significant gamma-aminobutyric acid-related effect on paired-pulse interaction in the dentate gyrus of rats.

Gamma-aminobutyric acid (GABA)ergic mechanisms of the novel antiepileptic drug, levetiracetam (Keppra), have been both favored and rejected. Since paired-pulse interaction is accepted in functionally assessing GABAergic mechanisms, we investigated whether levetiracetam affects the paired-pulse inhibition/facilitation of the field potentials, evoked in the dentate gyrus of urethane-anesthesized rats. This model revealed a strong paired-pulse inhibition at 20-ms interstimulus interval, a noteworthy paired-pulse facilitation at 80-ms interstimulus interval, and a moderate paired-pulse inhibition at 500-ms interstimulus interval. Bicuculline (3 mg/kg/h, i.v.) and baclofen (10 mg/kg, i.v.) markedly depressed paired-pulse inhibition at 20-ms interstimulus interval, while clonazepam (1 mg/kg, i.p.), diazepam (10 mg/kg, i.v.), and phenobarbital (40 mg/kg, i.v.) enhanced it. Bicuculline also depressed paired-pulse inhibition at 500-ms interstimulus interval. Bicuculline, baclofen, and diazepam reduced paired-pulse facilitation at 80-ms interstimulus interval. Distinct from these GABA(A) receptor- and GABA(B) receptor-related drugs, levetiracetam (17 and 540 mg/kg, i.v.) had no significant effect on either paired-pulse interaction in this model, a result not favoring any major role of GABAergic mechanisms in its antiseizure action.

Levetiracetam reduces caffeine-induced Ca2+ transients and epileptiform potentials in hippocampal neurons.

The effect of the novel antiepileptic drug levetiracetam on caffeine (10 mM)-induced intracellular calcium ([Ca2+]i) response was investigated in rat hippocampal neurons in culture, with the aim of exploring the cellular mechanisms of this new drug. Levetiracetam significantly reduced caffeine-induced [Ca2+]i) response, with maximum inhibition at 32 microM. The R-enantiomer of levetiracetam, ucb L060, which is devoid of anticonvulsant activity, at 32 microM had no effect on caffeine-induced [Ca2+]i) response. Caffeine 10 mM also induced epileptiform field potentials in rat hippocampal slices : single stimuli evoked repetitive population spikes and spontaneous field bursts regularly occurred. Levetiracetam (32 microM) significantly inhibited the amplitudes and the number of caffeine-induced repeated population spikes and delayed the appearance of spontaneous bursts, while ucb L060 (32 microM) completely lacked anti-caffeine activity. These results suggest that the inhibition of caffeine-induced Ca release from intra-neuronal stores might be an excitability-reducing effect of levetiracetam, contributing to its antiepileptic activity.

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.

Pilocarpine-induced epileptogenesis in the rat: impact of initial duration of status epilepticus on electrophysiological and neuropathological alterations.

This study characterized the electrophysiological and neuropathological changes in rat brains caused by pilocarpine (PILO)-induced status epilepticus (SE) of different duration. SE induced by PILO (375 mg/kg, i.p. adm.) were terminated with a bolus dose of diazepam (10 mg/kg, i.v. adm.) injected 7.5, 15, 30, 60 or 120 min after initiation of the secondary generalization of the SE. Three weeks later, the gain in body weight was significantly reduced in the rats exposed to PILO-induced SE lasting 30 min or more, when compared to controls. Spontaneous seizures were not detected in rats with PILO-induced SE of 7.5 min duration whereas 50 and 25% of the rats exposed to seizure durations of 30 and 120 min expressed motor seizures. Significant alterations reflecting hyperexcitability (increased number of population spikes (PSs)) and reduced paired-pulse inhibition were observed in recordings of hippocampal field potentials from rats with PILO-induced SE of at least 30 min duration. This was substantiated by brain lesions (necrosis in olfactory cortex, hippocampus, amygdala and thalamus) in all rats manifesting a SE of at least 30 min duration. Thus, the results of the present study demonstrate that rats exposed to PILO-induced SE of at least 30 min duration manifest an epileptogenic process, revealed 3 weeks later by several parameters. Among these, hippocampal field potentials appear to represent the most sensitive marker, potentially useful for pharmacological evaluation of drugs with putative antiepileptogenic properties.