Localized transmeningeal muscimol prevents neocortical seizures in rats and nonhuman primates: Therapeutic implications

Classics in Chemical Neuroscience: Muscimol

Muscimol (3) is a psychoactive isoxazole present in various Amanita mushrooms, along with ibotenic acid and muscarine. It is structurally related to GABA and acts as a GABAA agonist with great affinity. Muscimol use dates back to Siberian shamanic cultures as an entheogen, where it was ingested orally to exert psychoactive effects. Although not approved for clinical use, its potential and use as a research tool in neuroscience is of immense value, with 3H-muscimol being used as a radioligand in GABA receptor research. Since its discovery in the early 60s, many research groups have worked on the synthesis of the compound. Recent research suggests the potential use of muscimol in neuropathic pain relief and other potential uses are also being studied. In this review, we will cover the history, chemistry, pharmacology and overall importance of the compound.

Acute and chronic convection-enhanced muscimol delivery into the rat subthalamic nucleus induces antiseizure effects associated with high responder rates

Intracerebral drug delivery is an emerging treatment strategy aiming to manage seizures in patients with systemic drug-resistant epilepsies. In rat seizure and epilepsy models, the GABA_A receptor agonist muscimol has shown powerful antiseizure potential when injected acutely into the subthalamic nucleus (STN), known for its capacity to provide remote control of different seizure types. However, chronic intrasubthalamic muscimol delivery required for long-term seizure suppression has not yet been investigated. We tested the hypothesis that chronic convection-enhanced delivery (CED) of muscimol into the STN produces long-lasting antiseizure effects in the intravenous pentylenetetrazole seizure threshold test in female rats. Acute microinjection was included to verify efficacy of intrasubthalamic muscimol delivery in this seizure model and caused significant antiseizure effects at 30 and 60 ng per hemisphere with a dose-dependent increase of responders and efficacy and only mild adverse effects compared to controls. For the chronic study, muscimol was bilaterally infused into the STN over three weeks at daily doses of 60, 300, or 600 ng per hemisphere using an implantable pump and cannula system. Chronic intrasubthalamic CED of muscimol caused significant long-lasting antiseizure effects for up to three weeks at 300 and 600 ng daily. Drug responder rate increased dose-dependently, as did drug tolerance rates. Transient ataxia and body weight loss were the main adverse effects. Drug distribution was comparable (about 2-3 mm) between acute and chronic delivery. This is the first study providing proof-of-concept that not only acute, but also chronic, continuous CED of muscimol into the STN raises seizure thresholds.

An On-Demand Drug Delivery System for Control of Epileptiform Seizures

Drug delivery systems have the potential to deliver high concentrations of drug to target areas on demand, while elsewhere and at other times encapsulating the drug, to limit unwanted actions. Here we show proof of concept in vivo and ex vivo tests of a novel drug delivery system based on hollow-gold nanoparticles tethered to liposomes (HGN-liposomes), which become transiently permeable when activated by optical or acoustic stimulation. We show that laser or ultrasound simulation of HGN-liposomes loaded with the GABA_A receptor agonist, muscimol, triggers rapid and repeatable release in a sufficient concentration to inhibit neurons and suppress seizure activity. In particular, laser-stimulated release of muscimol from previously injected HGN-liposomes caused subsecond hyperpolarizations of the membrane potential of hippocampal pyramidal neurons, measured by whole cell intracellular recordings with patch electrodes. In hippocampal slices and hippocampal–entorhinal cortical wedges, seizure activity was immediately suppressed by muscimol release from HGN-liposomes triggered by laser or ultrasound pulses. After intravenous injection of HGN-liposomes in whole anesthetized rats, ultrasound stimulation applied to the brain through the dura attenuated the seizure activity induced by pentylenetetrazol. Ultrasound alone, or HGN-liposomes without ultrasound stimulation, had no effect. Intracerebrally-injected HGN-liposomes containing kainic acid retained their contents for at least one week, without damage to surrounding tissue. Thus, we demonstrate the feasibility of precise temporal control over exposure of neurons to the drug, potentially enabling therapeutic effects without continuous exposure. For future application, studies on the pharmacokinetics, pharmacodynamics, and toxicity of HGN-liposomes and their constituents, together with improved methods of targeting, are needed, to determine the utility and safety of the technology in humans.

Bypassing the Blood-Brain Barrier: Direct Intracranial Drug Delivery in Epilepsies

Epilepsies are common chronic neurological diseases characterized by recurrent unprovoked seizures of central origin. The mainstay of treatment involves symptomatic suppression of seizures with systemically applied antiseizure drugs (ASDs). Systemic pharmacotherapies for epilepsies are facing two main challenges. First, adverse effects from (often life-long) systemic drug treatment are common, and second, about one-third of patients with epilepsy have seizures refractory to systemic pharmacotherapy. Especially the drug resistance in epilepsies remains an unmet clinical need despite the recent introduction of new ASDs. Apart from other hypotheses, epilepsy-induced alterations of the blood-brain barrier (BBB) are thought to prevent ASDs from entering the brain parenchyma in necessary amounts, thereby being involved in causing drug-resistant epilepsy. Although an invasive procedure, bypassing the BBB by targeted intracranial drug delivery is an attractive approach to circumvent BBB-associated drug resistance mechanisms and to lower the risk of systemic and neurologic adverse effects. Additionally, it offers the possibility of reaching higher local drug concentrations in appropriate target regions while minimizing them in other brain or peripheral areas, as well as using otherwise toxic drugs not suitable for systemic administration. In our review, we give an overview of experimental and clinical studies conducted on direct intracranial drug delivery in epilepsies. We also discuss challenges associated with intracranial pharmacotherapy for epilepsies.

Epidural focal brain cooling abolishes neocortical seizures in cats and non-human primates

Focal brain cooling (FBC) is under investigation in preclinical trials of intractable epilepsy (IE), including status epilepticus (SE). This method has been studied in rodents as a possible treatment for epileptic disorders, but more evidence from large animal studies is required. To provide evidence that FBC is a safe and effective therapy for IE, we investigated if FBC using a titanium cooling plate can reduce or terminate focal neocortical seizures without having a significant impact on brain tissue. Two cats and two macaque monkeys were chronically implanted with an epidural FBC device over the somatosensory and motor cortex. Penicillin G was delivered via the intracranial cannula for induction of local seizures. Repetitive FBC was performed using a cooling device implanted for a medium-term period (FBC for 30min at least twice every week; 3 months total) in three of the four animals. The animals exhibited seizures with repetitive epileptiform discharges (EDs) after administration of penicillin G, and these discharges decreased at less than 20°C cooling with no adverse histological effects. The results of this study suggest that epidural FBC is a safe and effective potential treatment for IE and SE.

Differential contribution of COX-1 and COX-2 derived prostanoids to cortical spreading depression-Evoked cerebral oligemia

Cortical spreading depression (CSD) is considered a significant phenomenon for human neurological conditions and one of its key signatures is the development of persistent cortical oligemia. The factors underlying this reduction in cerebral blood flow (CBF) remain incompletely understood but may involve locally elaborated vasoconstricting eicosanoids. We employed laser Doppler flowmetry in urethane-anesthetized rats, together with a local pharmacological blockade approach, to test the relative contribution of cyclooxygenase (COX)-derived prostanoids to the oligemic response following CSD. Administration of the non-selective COX inhibitor naproxen completely inhibited the oligemic response. Selective inhibition of COX-1 with SC-560 preferentially reduced the early reduction in CBF while selective COX-2 inhibition with NS-398 affected only the later response. Blocking the action of thromboxane A2 (TXA2), using the selective thromboxane synthase inhibitor ozagrel, reduced only the initial CBF decrease, while inhibition of prostaglandin F2alpha action, using the selective FP receptor antagonist AL-8810, blocked the later phase of the oligemia. Our results suggest that the long-lasting oligemia following CSD consists of at least two distinct temporal phases, mediated by preferential actions of COX-1- and COX-2-derived prostanoids: an initial phase mediated by COX-1 that involves TXA2 followed by a later phase, mediated by COX-2 and PGF2alpha.

Equivalent intraperitoneal doses of ibuprofen supplemented in drinking water or in diet: a behavioral and biochemical assay using antinociceptive and thromboxane inhibitory dose-response curves in mice

Background. Ibuprofen is used chronically in different animal models of inflammation by administration in drinking water or in diet due to its short half-life. Though this practice has been used for years, ibuprofen doses were never assayed against parenteral dose–response curves. This study aims at identifying the equivalent intraperitoneal (i.p.) doses of ibuprofen, when it is administered in drinking water or in diet.

Methods. Bioassays were performed using formalin test and incisional pain model for antinociceptive efficacy and serum TXB₂ for eicosanoid inhibitory activity. The dose–response curve of i.p. administered ibuprofen was constructed for each test using 50, 75, 100 and 200 mg/kg body weight (b.w.). The dose–response curves were constructed of phase 2a of the formalin test (the most sensitive phase to COX inhibitory agents), the area under the ‘change in mechanical threshold’-time curve in the incisional pain model and serum TXB₂ levels. The assayed ibuprofen concentrations administered in drinking water were 0.2, 0.35, 0.6 mg/ml and those administered in diet were 82, 263, 375 mg/kg diet.

Results. The 3 concentrations applied in drinking water lay between 73.6 and 85.5 mg/kg b.w., i.p., in case of the formalin test; between 58.9 and 77.8 mg/kg b.w., i.p., in case of the incisional pain model; and between 71.8 and 125.8 mg/kg b.w., i.p., in case of serum TXB₂ levels. The 3 concentrations administered in diet lay between 67.6 and 83.8 mg/kg b.w., i.p., in case of the formalin test; between 52.7 and 68.6 mg/kg b.w., i.p., in case of the incisional pain model; and between 63.6 and 92.5 mg/kg b.w., i.p., in case of serum TXB₂ levels.

Discussion. The increment in pharmacological effects of different doses of continuously administered ibuprofen in drinking water or diet do not parallel those of i.p. administered ibuprofen. It is therefore difficult to assume the equivalent parenteral daily doses based on mathematical calculations.

Future of epilepsy treatment: integration of devices

ABSTRACT 

The use of devices in the treatment of epilepsy is an emerging therapy for those patients whose seizures are not controlled by medications. This article will discuss current treatment options with devices for vagus nerve stimulation, deep brain stimulation and responsive neurostimulation. Emerging therapies in noninvasive neurostimulation such as with trigeminal nerve stimulation, transcranial magnetic stimulation and transcranial direct current stimulation may prove to be promising solutions. Finally, new and enhanced techniques of drug delivery are discussed as well as other devices with potential use in the study and treatment of epilepsy.

Anticonvulsant and behavioral effects of muscimol in immature rats

Potentiation of GABAergic inhibition is a mechanism of action of many antiepileptic drugs. The potential use of an agonist of GABAA receptors, muscimol, as an antiepileptic drug was studied in immature rats by assessing anticonvulsant activity and side effects on motor activities. Anticonvulsant action was tested in two models of seizures (pentetrazol-induced convulsions and cortical epileptic afterdischarges). Off target effect on motor performance was assessed in a battery of tests and in the open field in three age groups (12-, 18- and 25-day-old rats). Muscimol was administered in doses from 0.1 to 1mg/kg i.p. Only the 1 mg/kg dose exhibited marked anticonvulsant effect against pentetrazol-induced convulsions in 12- and 18-day-old rats, proconvulsant effect was observed in the second model in 18- and 25-day-old rats as prolongation of afterdischarges. Even the 0.5 mg/kg dose suppressed spontaneous locomotion and heavily compromised motor performance. The effect on motor activity was marked in the youngest group and decreased with age. Due to the low anticonvulsant potency and serious side effects, systemic administration of a competitive agonist of GABAA receptors in immature animals is not a promising strategy for new anticonvulsants.

Meningeal and choroid plexus cells--novel drug targets for CNS disorders

The meninges and choroid plexus perform many functions in the developing and adult human central nervous system (CNS) and are composed of a number of different cell types. In this article I focus on meningeal and choroid plexus cells as targets for the development of drugs to treat a range of traumatic, ischemic and chronic brain disorders. Meningeal cells are involved in cortical development (and their dysfunction may be involved in cortical dysplasia), fibrotic scar formation after traumatic brain injuries (TBI), brain inflammation following infections, and neurodegenerative disorders such as Multiple Sclerosis (MS) and Alzheimer's disease (AD) and other brain disorders. The choroid plexus regulates the composition of the cerebrospinal fluid (CSF) as well as brain entry of inflammatory cells under basal conditions and after injuries. The meninges and choroid plexus also link peripheral inflammation (occurring in the metabolic syndrome and after infections) to CNS inflammation which may contribute to the development and progression of a range of CNS neurological and psychiatric disorders. They respond to cytokines generated systemically and secrete cytokines and chemokines that have powerful effects on the brain. The meninges may also provide a stem cell niche in the adult brain which could be harnessed for brain repair. Targeting meningeal and choroid plexus cells with therapeutic agents may provide novel therapies for a range of human brain disorders.

Long-term behavioral, electrophysiological, and neurochemical monitoring of the safety of an experimental antiepileptic implant, the muscimol-delivering Subdural Pharmacotherapy Device in monkeys

Object

The authors evaluated the extent to which the Subdural Pharmacotherapy Device (SPD), chronically implanted over the frontal cortex to perform periodic, localized muscimol-delivery/CSF removal cycles, affects overall behavior, motor performance, electroencephalography (EEG) activity, and blood and CSF neurochemistry in macaque monkeys.

Methods

Two monkeys were used to adjust methodology and 4 monkeys were subjected to comprehensive testing. Prior to surgery, the animals' behavior in a large test chamber was monitored, and the motor skills required to remove food pellets from food ports located on the walls of the chamber were determined. The monkeys underwent implantation of the subdural and extracranial SPD units. The subdural unit, a silicone strip integrating EEG electrodes and fluid-exchange ports, was positioned over the right frontal cortex. The control unit included a battery-powered, microprocessor-regulated dual minipump and radiofrequency module secured to the cranium. After implantation, the SPD automatically performed periodic saline or muscimol (1.0 mM) deliveries at 12-hour intervals, alternating with local CSF removals at 6-hour intervals. The antiepileptic efficacy of this muscimol concentration was verified by demonstrating its ability to prevent focal acetylcholine-induced seizures. During SPD treatment, the monkeys' behavior and motor performance were again monitored, and the power spectrum of their radiofrequency-transmitted EEG recordings was analyzed. Serum and CSF muscimol levels were measured with high-performance liquid chromatography electrochemical detection, and CSF protein levels were measured with turbidimetry.

Results

The SPD was well tolerated in all monkeys for up to 11 months. The behavioral study revealed that during both saline and muscimol SPD treatment, the monkeys could achieve the maximum motor performance of 40 food-pellet removals per session, as before surgery. The EEG study showed that local EEG power spectra were not affected by muscimol treatment with SPD. The neurochemical study demonstrated that the administration of 1.0 mM muscimol into the neocortical subarachnoid space led to no detectable levels of this compound in the blood and cisternal CSF, as measured 1–125 minutes after delivery. Total protein levels were within the normal range in the cisternal CSF, but protein levels in the cortical-site CSF were significantly higher than normal: 361 ± 81.6 mg/dl. Abrupt discontinuation of 3-month, periodic, subdural muscimol treatments induced withdrawal seizures, which could be completely prevented by gradually tapering off the subdural muscimol concentration from 1.0 mM to 0.12–0.03 mM over a period of 2 weeks. The monkeys' general health and weight were maintained. Infection occurred only in one monkey 9 months after surgery.

Conclusions

Long-term, periodic, transmeningeal muscimol delivery with the SPD is essentially a safe procedure. If further improved and successfully adapted for use in humans, the SPD can be used for the treatment of intractable focal neocortical epilepsy affecting approximately 150,000 patients in the US.

Therapeutic devices for epilepsy

Therapeutic devices provide new options for treating drug-resistant epilepsy. These devices act by a variety of mechanisms to modulate neuronal activity. Only vagus nerve stimulation (VNS), which continues to develop new technology, is approved for use in the United States. Deep brain stimulation of anterior thalamus for partial epilepsy recently was approved in Europe and several other countries. Responsive neurostimulation, which delivers stimuli to 1 or 2 seizure foci in response to a detected seizure, recently completed a successful multicenter trial. Several other trials of brain stimulation are in planning or underway. Transcutaneous magnetic stimulation (TMS) may provide a noninvasive method to stimulate cortex. Controlled studies of TMS are split on efficacy, which may depend on whether a seizure focus is near a possible region for stimulation. Seizure detection devices in the form of shake detectors via portable accelerometers can provide notification of an ongoing tonic-clonic seizure, or peace of mind in the absence of notification. Prediction of seizures from various aspects of electroencephalography (EEG) is in early stages. Prediction appears to be possible in a subpopulation of people with refractory seizures, and a clinical trial of an implantable prediction device is underway. Cooling of neocortex or hippocampus reversibly can attenuate epileptiform EEG activity and seizures, but engineering problems remain in its implementation. Optogenetics is a new technique that can control excitability of specific populations of neurons with light. Inhibition of epileptiform activity has been demonstrated in hippocampal slices, but use in humans will require more work. In general, devices provide useful palliation for otherwise uncontrollable seizures, but with a different risk profile than with most drugs. Optimizing the place of devices in therapy for epilepsy will require further development and clinical experience.

Optical control of focal epilepsy in vivo with caged γ-aminobutyric acid

OBJECTIVE

There is enormous clinical potential in exploiting the spatial and temporal resolution of optical techniques to modulate pathophysiological neuronal activity, especially intractable focal epilepsy. We have recently utilized a new ruthenium-based caged compound, ruthenium-bipyridine-triphenylphosphine-γ-aminobutyric acid (RuBi-GABA), which releases GABA when exposed to blue light, to rapidly terminate paroxysmal activity in vitro and in vivo.

METHODS

The convulsant 4-aminopyridine was used to induce interictal activity and seizures in rat neocortical slices and anesthetized rats. We examined the effect of blue light, generated by a small, light-emitting diode (LED), on the frequency and duration of ictal activity in the presence and absence of RuBi-GABA.

RESULTS

Neither blue light alone, nor low concentrations of RuBi-GABA, affected interictal activity or baseline electrical activity in neocortical slices. However, brief, blue illumination of RuBi-GABA, using our LED, dramatically reduced extracellular spikes and bursts. More impressively, illumination of locally applied RuBi-GABA rapidly terminated in vivo seizures induced by topical application of 4-aminopyridine. The RuBi-GABA effect was blocked by the GABA(A) antagonist picrotoxin, but not duplicated by direct application of GABA.

INTERPRETATION

This is the first example of optical control of in vivo epilepsy, proving that there is sufficient cortical light penetration from an LED and diffusion of caged GABA to quickly terminate intense focal seizures. We are aware that many obstacles need to be overcome before this technique can be translated to patients, but at the moment, this represents a feasible method for harnessing optical techniques to fabricate an implantable device for the therapy of neocortical epilepsy.

Autoradiographic evidence for the transmeningeal diffusion of muscimol into the neocortex in rats

Electrophysiological and behavioral studies have demonstrated that muscimol administered through the cranial meninges can prevent focal neocortical seizures. It was proposed that transmeningeal muscimol delivery can be used for the treatment of intractable focal neocortical epilepsy. However, it has not been proved that muscimol administered via the transmeningeal route can penetrate into the neocortex. The purpose of the present study was to solve this problem by using combined autoradiography-histology methods. Four rats were implanted with epidural cups over the parietal cortices. A 50 μL mixture of [³H] muscimol and unlabeled muscimol with a final concentration of 1.0mM was delivered through each cup on the dura mater. After a 1-hour exposure, the muscimol solution was removed and replaced with formalin to trap the transmeningeally diffused molecules. Then the whole brain was fixed transcardially, sectioned, with the sections subjected to autoradiography and thionine counterstaining. Results showed that (1) [³H] muscimol diffused through the meninges into the cortical tissue underlying the epidural cup in all rats. (2) [³H] muscimol-related autoradiography grains were distributed in all six neocortical layers. (3) [³H] muscimol-related autoradiography grains were localized to the cortical area underneath the epidural delivery site and were absent in the cerebral cortical white matter and other brain structures. This study provided evidence that muscimol can be delivered via the transmeningeal route into the neocortical tissue in a spatially controlled manner. The finding further supports the rationale of using transmeningeal muscimol for the treatment of intractable focal neocortical epilepsy.

Neuromodulation in Epilepsy

Neuromodulation strategies have been proposed to treat a variety of neurological disorders, including medication-resistant epilepsy. Electrical stimulation of both central and peripheral nervous systems has emerged as a possible alternative for patients who are not deemed to be good candidates for resective procedures. In addition to well-established treatments such as vagus nerve stimulation, epilepsy centers around the world are investigating the safety and efficacy of neurostimulation at different brain targets, including the hippocampus, thalamus, and subthalamic nucleus. Also promising are the preliminary results of responsive neuromodulation studies, which involve the delivery of stimulation to the brain in response to detected epileptiform or preepileptiform activity. In addition to electrical stimulation, novel therapeutic methods that may open new horizons in the management of epilepsy include transcranial magnetic stimulation, focal drug delivery, cellular transplantation, and gene therapy. We review the current strategies and future applications of neuromodulation in epilepsy.

A high-performance transcutaneous battery charger for medical implants

As new functionality is added to the implantable devices, their power requirements also increase. Such power requirements make it hard for keeping such implants operational for long periods by non-rechargeable batteries. This result in a need for frequent surgeries to replace these batteries. Rechargeable batteries can satisfy the long-term power requirements of these new functions. To minimize the discomfort to the patients, the recharging of the batteries should be as infrequent as possible. Traditional battery charging methods have low battery charging efficiency. This means they may limit the amount of charge that can be delivered to the device, speeding up the depletion of the battery and forcing frequent recharging. In this paper, we evaluate the suitability of a state-of-the-art general purpose charging method called current-pumped battery charger (CPBC) for implant applications. Using off-the-shelf components and with minimum optimization, we prototyped a proof-of-concept transcutaenous battery charger based on CPBC and show that the CPBC can charge a 100 mAh battery transcutaneously within 137 minutes with at most 2.1°C increase in tissue temperature even with a misalignment of 1.3 cm in between the coils, while keeping the battery charging efficiency at 85%.

Evolution and prospects for intracranial pharmacotherapy for refractory epilepsies: the subdural hybrid neuroprosthesis

Intracranial pharmacotherapy is a novel strategy to treat drug refractory, localization-related epilepsies not amenable to resective surgery. The common feature of the method is the use of some type of antiepileptic drug (AED) delivery device placed inside the cranium to prevent or stop focal seizures. This distinguishes it from other nonconventional methods, such as intrathecal pharmacotherapy, electrical neurostimulation, gene therapy, cell transplantation, and local cooling. AED-delivery systems comprise drug releasing polymers and neuroprosthetic devices that can deliver AEDs into the brain via intraparenchymal, ventricular, or transmeningeal routes. One such device is the subdural Hybrid Neuroprosthesis (HNP), designed to deliver AEDs, such as muscimol, into the subdural/subarachnoid space overlaying neocortical epileptogenic zones, with electrophysiological feedback from the treated tissue. The idea of intracranial pharmacotherapy and HNP treatment for epilepsy originated from multiple sources, including the advent of implanted medical devices, safety data for intracranial electrodes and catheters, evidence for the seizure-controlling efficacy of intracerebral AEDs, and further understanding of the pathophysiology of focal epilepsy. Successful introduction of intracranial pharmacotherapy into clinical practice depends on how the intertwined scientific, engineering, clinical, neurosurgical and regulatory challenges will be met to produce an effective and commercially viable device.

Advances in the application of technology to epilepsy: the CIMIT/NIO Epilepsy Innovation Summit

In 2008, a group of clinicians, scientists, engineers, and industry representatives met to discuss advances in the application of engineering technologies to the diagnosis and treatment of patients with epilepsy. The presentations also provided a guide for further technological development, specifically in the evaluation of patients for epilepsy surgery, seizure onset detection and seizure prediction, intracranial treatment systems, and extracranial treatment systems. This article summarizes the discussions and demonstrates that cross-disciplinary interactions can catalyze collaborations between physicians and engineers to address and solve many of the pressing unmet needs in epilepsy.

Convection-enhanced delivery in the treatment of epilepsy

Convection-enhanced delivery (CED) is a novel drug-delivery technique that uses positive hydrostatic pressure to deliver a fluid containing a therapeutic substance by bulk flow directly into the interstitial space within a localized region of the brain parenchyma. CED circumvents the blood-brain barrier and provides a wider, more homogenous distribution than bolus deposition (focal injection) or other diffusion-based delivery approaches. A potential use of CED is for the local delivery of antiseizure agents, which would provide an epilepsy treatment approach that avoids the systemic toxicities of orally administered antiepileptic drugs and bystander effects on nonepileptic brain regions. Recent studies have demonstrated that brief CED infusions of nondiffusible peptides that inhibit the release of excitatory neurotransmitters, including omega-conotoxins and botulinum neurotoxins, can produce long-lasting (weeks to months) seizure protection in the rat amygdala-kindling model. Seizure protection is obtainable without detectable neurological or behavioral side effects. Although conventional diffusible antiepileptic drugs do confer seizure protection when administered locally by CED, the effect is transitory. CED is a potential approach for seizure protection that could represent an alternative to resective surgery in the treatment of focal epilepsies that are resistant to orally-administered antiepileptic drugs. The prolonged duration of action of nondiffusible toxins would allow seizure protection to be maintained chronically with infrequent reinfusions.