Development of a Drosophila seizure model for in vivo high-throughput drug screening

An important application of model organisms in neurological research has been to identify and characterise therapeutic approaches for epilepsy, a recurrent seizure disorder that affects > 1% of the human population. Proconvulsant-treated rodent models have been widely used for antiepileptic drug discovery and development, but are not suitable for high-throughput screening. To generate a genetically tractable model that would be suitable for large-scale, high-throughput screening for antiepileptic drug candidates, we characterized a Drosophila chemical treatment model using the GABA(A) receptor antagonist picrotoxin. This proconvulsant, delivered to Drosophila larvae via simple feeding methods suitable for automated screening, generated robust generalised seizures with lethality occurring at doses between 0.3 and 0.5 mg/mL. Electrophysiological analysis of CNS motor neuron output in picrotoxin-treated larvae revealed generalised seizures within minutes of drug exposure. At subthreshold doses for seizure induction, picrotoxin produced an increased frequency of motor neuron action potential bursting, indicating that CNS GABAergic transmission regulates patterned activity. Mutants in the Drosophila Rdl GABA(A) receptor are resistant to picrotoxin, confirming that seizure induction occurs via a conserved GABA(A) receptor pathway. To validate the usefulness of this model for in vivo drug screening, we identified several classes of neuroactive antiepileptic compounds in a pilot screen, including phenytoin and nifedipine, which can rescue the seizures and lethal neurotoxicity induced by picrotoxin. The well-defined actions of picrotoxin in Drosophila and the ease with which compounds can be assayed for antiseizure activity makes this genetically tractable model attractive for high-throughput in vivo screens to identify novel anticonvulsants and seizure susceptibility loci.     

The neuropharmacology of the ketogenic diet

The ketogenic diet is a valuable therapeutic approach for epilepsy, one in which most clinical experience has been with children. Although the mechanism by which the diet protects against seizures is unknown, there is evidence that it causes effects on intermediary metabolism that influence the dynamics of the major inhibitory and excitatory neurotransmitter systems in brain. The pattern of protection of the ketogenic diet in animal models of seizures is distinct from that of other anticonvulsants, suggesting that it has a unique mechanism of action. During consumption of the ketogenic diet, marked alterations in brain energy metabolism occur, with ketone bodies partly replacing glucose as fuel. Whether these metabolic changes contribute to acute seizure protection is unclear; however, the ketone body acetone has anticonvulsant activity and could play a role in the seizure protection afforded by the diet. In addition to acute seizure protection, the ketogenic diet provides protection against the development of spontaneous recurrent seizures in models of chronic epilepsy, and it has neuroprotective properties in diverse models of neurodegenerative disease.     

Neonatal seizures: diagnosis and treatment

Neonatal seizures are a frequent problem encountered in neonatal nurseries, but their significance is controversial. Some investigators regard newborn seizures as simply epiphenomena and reflective of brain injury, whereas others note associated metabolic and physiologic aberrations suggesting that seizures per se are injurious to the central nervous system. The proper approach to the treatment of neonatal seizures depends on the etiology because treatment differs if seizures are of metabolic, toxic, or structural origin. Most studies reporting the efficacy of anticonvulsant agents neither define the seizure characteristics being treated nor use electroencephalographic documentation of seizure activity. The choice of anticonvulsants has been based on tradition rather than on the proven superiority of one agent over another. Although several anticonvulsants are available, phenobarbital remains the drug most frequently chosen as the initial agent in treatment. The important pharmacologic considerations of anticonvulsants include route of administration, ability to achieve therapeutically efficacious and predictable plasma levels rapidly, drug distribution, the availability and affinity of receptor sites, protein-binding characteristics, effects on brain growth, and cardiovascular toxicities. At the present time, critical questions remain regarding the effects of both seizures and anticonvulsants on the developing central nervous system.     

Implementing a bioassay to screen molecules for antiepileptogenic activity: chronic pilocarpine versus subdudral haematoma models.

BACKGROUND: There is a need to discover novel chemical compounds that will inhibit the pathological process of epileptogenesis (i.e. agents that will prevent the long-term formation of an active seizure focus following a brain insult). The goal of this paper is to identify a bioassay of value in drug design when screening new chemical entities as putative antiepileptogenic agents. METHODS: We focused on two models: the pilocarpine chronic seizure model of spontaneous recurrent seizures (SRSs) and a chronic subdural haematoma model of SRSs. Both models were evaluated using more than 20 Sprague-Dawley rats for each model. RESULTS: In the pilocarpine-induced model of SRSs, 80% of animals went on to develop SRSs when the dose of pilocarpine was 380 mg/kg i.p. In 50 animals that developed SRSs, the average number of seizures per 15 days of observation was 3.8 seizures with a range of 2-23 seizures per 15-day period. The chronic subdural model was inefficient in producing SRSs. CONCLUSIONS: A pilocarpine-induced SRS model of epilepsy affords a reliable model of epileptogenesis suitable for evaluating new chemical entities as putative antiepileptogenics.     

The role of technical, biological and pharmacological factors in the laboratory evaluation of anticonvulsant drugs. III. Pentylenetetrazole seizure models

Although seizure models using systemic administration of the chemoconvulsant pentylenetetrazol (PTZ) for induction of generalized clonic seizures in rodents are widely employed to identify potential anticonvulsants, the important role of diverse technical, biological and pharmacological factors in interpretation of results obtained with these models is often not recognized. The aim of this study was to delineate factors other than sex, age, diet, climate, and circadian rhythms, which are generally known. For this purpose, experiments with 8 clinically established antiepileptic drugs were undertaken in the following PTZ models: (1) the threshold for different types of PTZ seizures, i.e., initial myoclonic twitch, generalized clonus with loss of righting reflexes, and tonic backward extension of forelimbs (forelimb tonus), in mice; (2) the traditional PTZ seizure test with s.c. injection of the CD97 for generalized clonic seizures in mice; and (3) the s.c. PTZ seizure test in rats. In rats, in addition to evaluating drug effects on generalized clonic seizures, a ranking system was used to determine drug effects on other seizure types. When drugs were dissolved in vehicles which themselves did not exert effects on seizure susceptibility, the most important factors which influenced drug potencies were: (1) bishaped dose-response curves, i.e., a decline in anticonvulsant dose-response at high doses of some drugs, leading to misinterpretations of drug efficacy if only a single high drug dosage is tested; (2) effects of route of PTZ administration (i.v. infusion vs. s.c. injection) on estimation of anticonvulsant potency; (3) species differences in drug metabolism; (4) differences in drug potencies calculated on the basis of administered doses compared to potency calculations based on 'active' drug concentrations in plasma; (5) qualitative and quantitative species differences in drug actions; (6) endpoints used for PTZ tests; (7) misleading predictions from PTZ seizure models. Analysis of anticonvulsant drug actions indicated that myoclonic or clonic seizures induced by i.v. or s.c. PTZ might be suitable for predicting efficacy against myoclonic petit mal seizures in humans, but certainly not to predict efficacy against absence seizures. Tonic seizures induced by PTZ were blocked by drugs, such as ethosuximide, which exert no effect on tonic seizures in humans. In order to reduce the variability among estimates of anticonvulsant activity in PTZ seizure models, the various factors delineated in this study should be rigidly controlled in experimental situations involving assay of anticonvulsant agents.     

The role of technical, biological and pharmacological factors in the laboratory evaluation of anticonvulsant drugs. II. Maximal electroshock seizure models

Although seizure models using electrical stimulation for the induction of generalized tonic-clonic seizures in rodents are widely employed to identify potential anticonvulsants, the important role of various technical, biological and pharmacological factors in the interpretation of results obtained with these models is often not recognized. The aim of this study was to delineate factors other than sex, age, diet, climate and circadian rhythms, which are generally known. For this purpose, experiments with 8 clinically established antiepileptic drugs were undertaken in the following electroshock seizure models: (1) the maximal (tonic extensor) electroshock seizure threshold (MEST) in mice; (2) the traditional maximal electroshock seizure (MES) test with supra-threshold stimulation in mice; and (3) the MES test with suprathreshold stimulation in rats. When drugs were dissolved in vehicles which did not themselves exert effects on seizure susceptibility, the most important factors which influenced drug potencies were (1) marked differences between drugs and species in terms of peak drug effect, duration of action and the formation of active metabolites; (2) differences in drug potencies calculated on the basis of administered doses compared to potency calculations based on active drug concentrations; (3) the equipment used for seizure induction; (4) marked effects of current strength on results obtained in electroshock seizure models; (5) site of application of the electrical stimulus (transcorneal vs. transauricular). In order to reduce the variability among estimates of anticonvulsant activity, the various factors delineated in this study should be rigidly controlled in experimental situations involving assay of anticonvulsant agents.     

Outcomes of 32 hemispherectomies for Sturge-Weber syndrome worldwide

BACKGROUND: Epilepsy affects 80% of patients with Sturge-Weber syndrome; the majority of seizures begin before the age of 1. When seizures are intractable to medications and unihemispheric, hemispherectomy is often advised. OBJECTIVE: To examine the natural history of patients who underwent hemispherectomy and identify the outcomes in terms of seizure reduction, cognition, and motor deficits. METHODS: A questionnaire was mailed to the parents of patients identified by the Sturge-Weber Foundation as having had a hemispherectomy between 1979 and 2001. Forty-six percent (32/70) of the parents responded. RESULTS: The mean age at onset of seizures was 4 months, and the median age at surgery was 1.2 years. Children had failed to respond to 3.7 anticonvulsants prior to surgery and averaged 387 seizures/month. Forty-seven percent had complications (e.g., hemorrhage and hypertension) in the perioperative period; however, 81% are currently seizure-free, with 53% off anticonvulsants. Hemispherectomy type (anatomic versus functional versus hemidecortication) did not influence outcome. Age at onset of seizures did not predict seizure freedom; however, an older age at hemispherectomy was positively correlated. Postoperative hemiparesis was not more severe than before surgery. Cognitive outcome was not related to the age at operation, side of operation, or seizure freedom. CONCLUSIONS: Children undergoing hemispherectomy presented at a young age and had frequent seizures for approximately 1 year but are now mostly seizure-free. Age at surgery did not have an adverse effect on either seizure or cognitive outcomes.     

Should alcohol withdrawal seizures be treated with anti-epileptic drugs?

Seizures and delirium tremens were recorded among 292 randomly selected patients admitted to an in-patient alcoholism program. Despite the almost routine prophylactic use of anticonvulsant and sedative drugs the incidence of seizures and delirium tremens during detoxification in hospital was 3%. However, as most alcohol withdrawal seizures occurred immediately before admission, the overall seizure incidence was higher (10%). Those patients who developed seizures during detoxification admitted previous abuse of benzodiazepines or erratic use of phenytoin. The results suggest that prescribing of anticonvulsants to alcoholics may increase their seizure problems, because they are prone to erratic drug taking, and because of drug-alcohol interactions, increased drug metabolism and abuse of the sedative anticonvulsants.     

Dramatic Effect of Lamotrigine in Young Adults Suffering from Intractable Absences and Generalized Tonic–Clonic Seizures Since Childhood

The purpose of this study was to evaluate the efficacy of adding lamotrigine to valproic acid in patients with refractory absence seizures starting in childhood and persisting into adulthood. Lamotrigine was added to previous anticonvulsants (always including valproic acid) in 10 patients aged 23–44 years, with intractable absence and generalized tonic–clonic seizures. Seven patients became seizure free, three patients had > 75% reduction in seizure frequency. The patients have remained on comedication with valproic acid and lamotrigine, after gradually discontinuing most other anticonvulsants, for a follow-up period ranging from 1–4 years. There has been no increase in seizure frequency during this period. None of the patients reported any side effects. This study supports the growing evidence of therapeutic synergy between lamotrigine and valproic acid. This combination may be the therapy of choice for refractory absence and generalized tonic–clonic seizures both in children and adults.     

Amygdala Kindling of Forebrain Seizures and the Occurrence of Brainstem Seizures in Genetically Epilepsy-Prone Rats

Forebrain seizures were kindled in rats by daily electrical stimulation of the amygdala. Genetically epilepsy-prone rats scoring 9 (GEPR-9s) on the seizure severity scale during audiogenic seizure (AGS) screening (“brainstem seizure-experienced”) required fewer stimulations to achieve fully kindled seizures (forelimb clonus with rearing and falling) than control rats. AGS-naive GEPR-9s required an intermediate number of stimulations, indicating a role for both genetic predisposition and previous acoustically evoked brainstem seizure experience. Other forebrain kindling indices such as afterdischarge thresholdlduration and seizure latencylduration also involved genetic as well as phenotypic (previous seizure experience) factors. In most GEPR-9s in both groups, severe brainstem seizures occurred after forebrain stimulation. The occurrence of brainstem seizures had a random nature and was not related to the sequence of kindling-dependent forebrain seizure progression. The lack of a difference in the occurrence of brainstem seizures between seizure-experienced and AGS-naïve GEPR-9s suggest that genetic predisposition is the major factor in forebrain seizure-induced activation of brainstem seizure circuitry. This brainstem seizure activity appears to model pertinent aspects of secondary generalization observed in human partial seizures.     

Antiepileptic therapy in patients with central nervous system malignancies

More than 200,000 patients are diagnosed with primary or metastatic brain tumors each year in the United States. Of these patients, 20% to 40% will develop seizures at presentation, and another 20% to 40% will require treatment for seizures during their illness. Although the use of antiepileptic drugs (AEDs) in patients who have had seizures seems reasonable, the issue of prophylactic AED use for patients who have not had a seizure is an intensely debated subject. The American Academy of Neurology released a position statement in May 2000 addressing the use of anticonvulsants in newly diagnosed brain tumor patients who have never had a seizure. After a review of the literature, including all trials showing class I evidence, multivariate analysis using calculated odds ratios failed to show a prophylactic benefit of preventing a first seizure versus the risk of side effects and recommended not using prophylactic anticonvulsants in newly diagnosed patients with brain tumor. Despite this recommendation, a recent survey of the American Association of Neurologic Surgeons revealed that most neurosurgeons still use anticonvulsants prophylactically in patients with brain tumor. This review mainly includes primary brain tumors, but most of the concepts are transferable to patients with metastatic tumors.     

Seizures after Spontaneous Intracerebral Hemorrhage

Objective

In patients with spontaneous intracerebral hemorrhage (ICH), the risk factors for seizure and the effect of prophylactic anticonvulsants are not well known. This study aimed to determine the risk factor for seizures and the role for prophylactic anticonvulsants after spontaneous ICH.

Methods

Between 2005 and 2010, 263 consecutive patients with spontaneous ICH were retrospectively assessed with a mean follow-up of 19.5 months using medical records, updated clinical information and, when necessary, direct patient contact. The seizures were classified as early (within 1 week of ICH) or late (more than 1 week after ICH). The outcomes were measured with the Glasgow Outcome Scale at discharge and the modified Rankin Scale (mRS) at both 2 weeks and discharge.

Results

Twenty-two patients (8.4%; 9 patients with early seizures and 13 patients with late seizures) developed seizures after spontaneous ICH. Out of 263 patients, prophylactic anticonvulsants were administered in 216 patients. The prophylactic anticonvulsants were not associated with a reduced risk of early (p=0.094) or late seizures (p=0.326). Instead, the factors associated with early seizure were cortical involvement (p<0.001) and younger age (60 years or less) (p=0.046). The risk of late seizure was increased by cortical involvement (p<0.001) and communicating hydrocephalus (p=0.004). The prophylactic anticonvulsants were associated with a worse mRS at 2 weeks (p=0.024) and at last follow-up (p=0.034).

Conclusion

Cortical involvement may be a factor for provoked seizures. Although the incidence of early seizures tended to decrease in patients prescribed prophylactic anticonvulsants, no statistical difference was found.     

Seizures in children with congenital hydrocephalus: long-term outcome.

We documented seizures in 33 of 68 (48.5%) children with congenital hydrocephalus not associated with myelomeningocele. Mental retardation (MR) and CNS malformations correlated with seizure occurrence; age at shunt insertion and number of shunt revisions and infections were not significant variables in predicting seizures. Of 11 patients seizure free for 2 or more years on medication, six had therapy discontinued without seizure recurrence. Among those 33 children with seizures, 14 (42.4%), including five who had failed withdrawal of medication, have adequately controlled seizures on anticonvulsants. Frequent convulsions despite treatment occur in 13 (39.4%) of the 33 children with seizures. Absence of MR, older age and nonparoxysmal EEG at seizure onset, and absence of CNS malformation correlated with seizure remission. Longer time without seizures while on medication did not predict successful discontinuation of therapy. In contrast, MR correlated significantly with seizure recurrence following cessation of treatment. Our study indicates that medication can be safely discontinued in children with congenital hydrocephalus who are of normal intelligence and have been seizure free on anticonvulsants for 3 years.     

Epileptic spasms: a variety of etiologies and associated syndromes

Epileptic spasms have been described as a paroxysmal epileptic seizure type that consists of a series of motor movements, involving sudden flexion or extension predominantly of axial and/or proximal limb muscles, occurring with a noticeable periodicity, outside the age of infantile spasms, but have otherwise not been well characterized or described. The purpose of this study was to evaluate patients with epileptic spasms to describe the etiology and best treatment regimen for this seizure type. Twenty-eight children fit the selection criteria for this study, and their charts and electroencephalography (EEG) results were reviewed. Data regarding onset of seizures, characteristics of seizures, duration of seizures, activity at onset, treatments tried and/or failed, genetic or metabolic workup, and results of any imaging studies were collected. The results indicate that the genetic and metabolic workups that were done were most often negative or unrevealing. In addition, treatment regimens varied greatly from patient to patient, and it is evident that these seizures are refractory to many standard anticonvulsants, as well as the ketogenic diet. The results of imaging from this series point to a variety of structural abnormalities that could possibly explain a structural versus metabolic etiology for epileptic spasms. In conclusion, epileptic spasms remain an elusive seizure type to classify, diagnose, and treat. The results of the current series show a relationship between structural abnormalities on magnetic resonance imaging (MRI) and resultant epileptic spasms, which has further implications regarding surgical treatment of these seizures as opposed to the traditional treatment with anticonvulsants, to which epileptic spasms remain refractory.     

Effects of piracetam alone and in combination with antiepileptic drugs in rodent seizure models

Summary. The nootropic drug piracetam was investigated in various experimental models of epilepsy. Generally, piracetam exhibits no or only moderate anticonvulsant properties against generalized tonic or clonic seizures. However, in many cases it did increase the anticonvulsant effectiveness of conventional antiepileptics, as shown in the maximal electroshock seizure (MES) threshold test, the traditional MES test or in DBA/2 mice. A pharmacokinetic interaction does not seem to be responsible for this effect. In lethargic mice, a model of absence seizures, piracetam significantly decreased the incidence and duration of spike-wave discharges. Furthermore, in the cobalt-induced focal epilepsy model piracetam reduced the number of spikes/min and in the hippocampal stimulation model it increased the anticonvulsant potency of phenobarbital and phenytoin after single and repeated administration. In conclusion, the well tolerated piracetam itself did not show marked anticonvulsant effects in most screening tests, however, its co-medication with antiepileptic drugs improved seizure protection in various models which may bear potential clinical significance.     

Cannabidiol exerts anti-convulsant effects in animal models of temporal lobe and partial seizures

Cannabis sativa has been associated with contradictory effects upon seizure states despite its medicinal use by numerous people with epilepsy. We have recently shown that the phytocannabinoid cannabidiol (CBD) reduces seizure severity and lethality in the well-established in vivo model of pentylenetetrazole-induced generalised seizures, suggesting that earlier, small-scale clinical trials examining CBD effects in people with epilepsy warrant renewed attention. Here, we report the effects of pure CBD (1, 10 and 100mg/kg) in two other established rodent seizure models, the acute pilocarpine model of temporal lobe seizure and the penicillin model of partial seizure. Seizure activity was video recorded and scored offline using model-specific seizure severity scales. In the pilocarpine model CBD (all doses) significantly reduced the percentage of animals experiencing the most severe seizures. In the penicillin model, CBD (≥ 10 mg/kg) significantly decreased the percentage mortality as a result of seizures; CBD (all doses) also decreased the percentage of animals experiencing the most severe tonic-clonic seizures. These results extend the anti-convulsant profile of CBD; when combined with a reported absence of psychoactive effects, this evidence strongly supports CBD as a therapeutic candidate for a diverse range of human epilepsies.     

Screening electroencephalograms in autism spectrum disorders: evidence-based guideline

The purpose of this study was to establish guidelines for the use of screening electroencephalograms (EEGs) in autism spectrum disorders to identify subclinical epileptiform activity. MEDLINE and EMBASE were searched for relevant articles. The evidence was reviewed using the methodology of the Canadian Task Force on Preventive Health Care. A priori criteria were established for article selection and for grading the quality and strength of the evidence. Seizures are common, occurring in 20 to 30% of patients based on the majority of studies. Epileptiform EEG abnormalities are present in 10.3% to 72.4% of patients and subclinical abnormalities in 6.1% to 31%. Evidence for the effectiveness of anticonvulsants and corticosteroids in reducing seizures and/or autistic symptoms is based primarily on case series and case reports, with only one published randomized trial. There is currently insufficient evidence to recommend for or against the use of screening EEGs in autistic patients. Given the frequency of seizure disorders in this patient population, a high index of clinical suspicion should be maintained for subtle symptoms of seizures.     

NMDA receptor antagonists and limbic status epilepticus: a comparison with standard anticonvulsants

Status epilepticus (SE) evolves through several stages when untreated. The later stages of SE are less responsive to standard anticonvulsants and may require general anesthesia to suppress seizures. Antagonists acting at the N-methyl-D-aspartate (NMDA) subclass of glutamate (excitatory) receptors have been demonstrated to exert antiepileptic activity in some seizure models. We report experiments performed to determine if NMDA receptor antagonists are effective in stopping seizures in the late stages of SE. A model of limbic SE induced by 90 min of 'continuous' electrical stimulation of the hippocampus in rats was employed. Three NMDA receptor antagonists, one 'competitive' (CPP) and two 'non-competitive' (ketamine and MK-801), were compared to 3 standard antiepileptic drugs (diazepam, phenobarbital, and phenytoin) for their ability to suppress seizures at a physiologically defined stage of SE. All NMDA receptor antagonists, diazepam and phenobarbital were effective in suppressing behavioral and electrographic seizures for varying periods of time. Phenytoin had no effect on SE. Ketamine and MK-801 induced a paradoxical enhancement of electrographic seizures that preceded SE suppression. We believe that NMDA-receptor antagonists offer a novel approach for treating the late stages of SE.     

Seizure precipitants and perceived self-control of seizures in adults with poorly-controlled epilepsy

This study was set up in order to investigate the prevalence and nature of seizure precipitants and self-control behaviours in adults with intractable seizures. A semi-structured interview was conducted with 100 patients attending neurology or neuropsychiatry epilepsy out-patient clinics. The interview included six questions regarding seizure precipitants, the extent to which the patients seek and avoid precipitants, and their ability to induce or abort seizures. The study revealed that over 90% of the participants could identify at least one seizure precipitant. Stress, depression, tiredness and the menstrual cycle were the most common precipitants reported. In addition, 65% of the participants could identify at least one 'low-risk' situation in which seizures were unlikely to occur. Fifteen percent reported they could induce a seizure, 52% said that they consciously try to avoid seizure precipitants and 47% said they could sometimes stop their seizures from happening. These results indicate that the majority of the sample could identify factors which trigger their seizures, and that some of the participants engage in attempts to reduce their seizure frequency by avoiding these factors and by controlling the onset of their seizures. The possible mechanisms involved in the relationship between precipitants and seizure genesis are discussed.     

Effects of seizures and carbamazepine on interictal spiking in amygdala kindled cats

We examined the influence of seizures and carbamazepine (CBZ) on spiking rates in kindled cats. In the first experiment, spiking rates were measured before and after seizures, with and without CBZ. CBZ was administered immediately after seizures in order not to affect them. Spiking rates were measured over 9 h during the different sleep stages. In a second experiment, CBZ was administered before and after seizures so as to affect seizure strength and thus measure its effect on spiking. Results confirmed earlier findings of a large increase in spiking following a stage 6 seizure in fully kindled animals. We also established that: (1) repeated daily seizures caused a further increase in spiking until a ceiling was reached; (2) increased spiking was not a direct effect of postictal alterations in sleep stages; (3) CBZ, despite its effectiveness as an anticonvulsant, did not reduce spiking but rather increased it; (4) postictal increases in spiking were related to seizure 'strength'. These findings support the hypothesis that spiking rates are primarily influenced by seizure occurrence, as was found in patients with temporal lobe seizures, and that anticonvulsants act differently on seizures and spikes. This emphasizes the possibility of distinct pathophysiological mechanisms for interictal spikes and seizures.