Refractory atypical absence seizures in rat: a two hit model

Revisiting the concept of drug-resistant epilepsy: A TASK1 report of the ILAE/AES Joint Translational Task Force

Despite progress in the development of anti-seizure medications (ASMs), one third of people with epilepsy have drug-resistant epilepsy (DRE). The working definition of DRE, proposed by the International League Against Epilepsy (ILAE) in 2010, helped identify individuals who might benefit from presurgical evaluation early on. As the incidence of DRE remains high, the TASK1 workgroup on DRE of the ILAE/American Epilepsy Society (AES) Joint Translational Task Force discussed the heterogeneity and complexity of its presentation and mechanisms, the confounders in drawing mechanistic insights when testing treatment responses, and barriers in modeling DRE across the lifespan and translating across species. We propose that it is necessary to revisit the current definition of DRE, in order to transform the preclinical and clinical research of mechanisms and biomarkers, to identify novel, effective, precise, pharmacologic treatments, allowing for earlier recognition of drug resistance and individualized therapies.

Antiepileptogenic effects of rapamycin in a model of infantile spasms due to structural lesions

OBJECTIVE

Infantile spasms may evolve into persistent epilepsies including Lennox-Gastaut syndrome. We compared adult epilepsy outcomes in models of infantile spasms due to structural etiology (multiple-hit model) or focal cortical inflammation and determined the anti-epileptogenic effects of pulse-rapamycin, previously shown to stop spasms in multiple-hit rats.

METHODS

Spasms were induced in 3-day-old male rats via right intracerebral doxorubicin/lipopolysaccharide (multiple-hit model) infusions. Controls and sham rats were used. Separate multiple-hit rats received pulse-rapamycin or vehicle intraperitoneally between postnatal days 4 and 6. In adult mice, video-EEG (electroencephalography) scoring for seizures and sleep and histology were done blinded to treatment.

RESULTS

Motor-type seizures developed in 66.7% of multiple-hit rats, usually from sleep, but were reduced in the pulse-rapamycin-treated group (20%, p = .043 vs multiple-hit) and rare in other groups (0-9.1%, p < .05 vs multiple-hit). Spike-and-wave bursts had a slower frequency in multiple-hit rats (5.4-5.8Hz) than in the other groups (7.6-8.3Hz) (p < .05); pulse rapamycin had no effect on the hourly spike-and-wave burst rates in adulthood. Rapamycin, however, reduced the time spent in slow-wave-sleep (17.2%), which was increased in multiple-hit rats (71.6%, p = .003). Sham rats spent more time in wakefulness (43.7%) compared to controls (30.6%, p = .043). Multiple-hit rats, with or without rapamycin treatment, had right more than left corticohippocampal, basal ganglia lesions. There was no macroscopic pathology in the other groups.

SIGNIFICANCE

Structural corticohippocampal/basal ganglia lesions increase the risk for post-infantile spasms epilepsy, Lennox-Gastaut syndrome features, and sleep dysregulation. Pulse rapamycin treatment for infantile spasms has anti-epileptogenic effects, despite the structural lesions, and decreases the time spent in slow wave sleep.

Experimental Models of Absence Epilepsy

Introduction:

Absence epilepsy is a brief non-convulsive seizure associated with sudden abruptness in consciousness. Because of the unpredictable occurrence of absence seizures and the ethical issues of human investigation on the pathogenesis and drug assessment, researchers tend to study animal models. This paper aims to review the advantages and disadvantages of several animal models of nonconvulsive induced seizure.

Methods:

The articles that were published since 1990 were assessed. The publications that used genetic animals were analyzed, too. Besides, we reviewed possible application methods of each model, clinical types of seizures induced, purposed mechanism of epileptogenesis, their validity, and relevance to the absence epileptic patients.

Results:

The number of studies that used genetic models of absence epilepsy from years of 2000 was noticeably more than pharmacological models. Genetic animal models have a close correlation of electroencephalogram features and epileptic behaviors to the human condition.

Conclusion:

The validity of genetic models of absence epilepsy would motivate the researchers to focus on genetic modes in their studies. As there are some differences in the pathophysiology of absence epilepsy between animal models and humans, the development of new animal models is necessary to understand better the epileptogenic process and, or discover novel therapies for this disorder.

Early Chronic Carbamazepine-in-Food Administration to MAM/Pilocarpine Rats Does Not Affect Convulsive Motor Seizures

Antiepileptic drug-resistance is a major health problem in patients with cortical dysplasia (CD). Whether drug-resistant epilepsy is associated with progressive brain damage is still debated. We previously generated a rat model of acquired CD, the methylazoxymethanol-pilocarpine (MP) rat, in which the occurrence of status epilepticus and subsequent spontaneous seizures induce progressive brain damage (Nobili et al., 2015). The present study tested the outcome of early-chronic carbamazepine (CBZ) administration on both seizure activity and brain damage in MP rats. We took advantage of the non-invasive CBZ-in-food administration protocol, established by Ali (2012), which proved effective in suppressing generalized convulsive seizures in kainic acid rat model of epilepsy. MP rats were treated immediately after the onset of the first spontaneous seizure with 300 mg/kg/day CBZ formulated in pellets for a two-months-trial. CBZ-treated rats were continuously video-monitored to detect seizure activity and were compared with untreated epileptic MP rats. Despite CBZ serum levels in treated rats were within the suggested therapeutic range for humans, CBZ affected spontaneous convulsive seizures in 2 out of 10 treated rats (responders), whereas the remaining animals (non-responders) did not show any difference when compared to untreated MP rats. Histological analysis revealed cortical thinning paralleled by robust staining of Fluoro-Jade⁺ (FJ⁺) degenerating neurons and diffuse tissue necrosis in CBZ-non-responder vs CBZ-responder rats. Data reported here suggest that MP rat model represents suitable experimental setting where to investigate mechanisms of CD-related drug-resistant epilepsy and to verify if modulation of seizures, with appropriate treatment, may reduce seizure-induced brain damage.

Oscillotherapeutics - Time-targeted interventions in epilepsy and beyond

Oscillatory brain activities support many physiological functions from motor control to cognition. Disruptions of the normal oscillatory brain activities are commonly observed in neurological and psychiatric disorders including epilepsy, Parkinson's disease, Alzheimer's disease, schizophrenia, anxiety/trauma-related disorders, major depressive disorders, and drug addiction. Therefore, these disorders can be considered as common oscillation defects despite having distinct behavioral manifestations and genetic causes. Recent technical advances of neuronal activity recording and analysis have allowed us to study the pathological oscillations of each disorder as a possible biomarker of symptoms. Furthermore, recent advances in brain stimulation technologies enable time- and space-targeted interventions of the pathological oscillations of both neurological disorders and psychiatric disorders as possible targets for regulating their symptoms.

In vitro and in vivo experimental models employed in the discovery and development of antiepileptic drugs for pharmacoresistant epilepsy

Epilepsy is one of the most common chronic, recurrent and progressive neurological diseases. In spite of the large number of antiepileptic drugs currently available for the suppression of seizures, about one-third of patients develop drug-resistant epilepsy, even when they are administered the most appropriate treatment available. Thus, nonclinical models can be valuable tools for the elucidation of the mechanisms underlying the development of pharmacoresistance and also for the development of new therapeutic agents that may be promising therapeutic approaches for this unmet medical need. Up today, several epilepsy and seizure models have been developed, exhibiting similar physiopathological features of human drug-resistant epilepsy; moreover, pharmacological response to antiepileptic drugs clinically available tends to be similar in animal models and humans. Therefore, they should be more intensively used in the preclinical discovery and development of new candidates to antiepileptic drugs. Although useful, in vitro models cannot completely replicate the complexity of a living being and their potential for a systematic use in antiepileptic drug screening is limited. The whole-animal models are the most commonly employed and they can be classified as per se drug-resistant due to an inherent poor drug response or be based on the selection of subgroups of epileptic animals that respond or not to a specific antiepileptic drug. Although more expensive and time-consuming, the latter are chronic models of epilepsy that better exhibit the disease-associated alterations found in human epilepsy. Several antiepileptic drugs in development or already marketed have been already tested and shown to be effective in these models of drug-resistant epilepsy, constituting a new hope for the treatment of drug-resistant epilepsy. This review will provide epilepsy researchers with detailed information on the in vitro and in vivo nonclinical models of interest in drug-resistant epilepsy, which may enable a refined selection of most relevant models for understanding the mechanisms of the disease and developing novel antiepileptic drugs.

Acute and chronic pharmacological models of generalized absence seizures

This article reviews the contribution of pharmacologically induced acute and chronic animal models to our understanding of epilepsies featuring non-convulsive generalized seizures, the typical and atypical absence seizures. Typical absences comprise about 5% of all epilepsies regardless of age and the atypical ones are even more common. Although absence epilepsy was thought to be relatively benign, children with childhood epilepsy (CAE) turn out to have a high rate of pretreatment attention deficits that persist despite seizure freedom. The phenomenon of the absence seizure has long attracted research interest because of the clear temporal relationship of the conspicuous EEG rhythm of 3 Hz generalized spike and wave discharges (GSWD) and the parallel transient "loss of consciousness" characterizing these seizures which is time-locked with the GSWD. Indeed, clinical epileptologists, basic scientists and neurophysiologists have long recognized in GSWD a unique electrographic and behavioral marker of the genetic predisposition to most types of epilepsy. Interestingly, the subject is still controversial since it has recently been proposed that both classification terms of CAE currently in use: idiopathic and primary generalized, be abandoned - a point of debate. Both issues - underlying mechanisms and focal origin of absence seizures - may be further enlightened by observations in valid animal models.

Neurochemical and behavioral features in genetic absence epilepsy and in acutely induced absence seizures

The absence epilepsy typical electroencephalographic pattern of sharp spikes and slow waves (SWDs) is considered to be due to an interaction of an initiation site in the cortex and a resonant circuit in the thalamus. The hyperpolarization-activated cyclic nucleotide-gated cationic I h pacemaker channels (HCN) play an important role in the enhanced cortical excitability. The role of thalamic HCN in SWD occurrence is less clear. Absence epilepsy in the WAG/Rij strain is accompanied by deficiency of the activity of dopaminergic system, which weakens the formation of an emotional positive state, causes depression-like symptoms, and counteracts learning and memory processes. It also enhances GABAA receptor activity in the striatum, globus pallidus, and reticular thalamic nucleus, causing a rise of SWD activity in the cortico-thalamo-cortical networks. One of the reasons for the occurrence of absences is that several genes coding of GABAA receptors are mutated. The question arises: what the role of DA receptors is. Two mechanisms that cause an infringement of the function of DA receptors in this genetic absence epilepsy model are proposed.

Animal models

Epilepsy accounts for a significant portion of the dis-ease burden worldwide. Research in this field is fundamental and mandatory. Animal models have played, and still play, a substantial role in understanding the patho-physiology and treatment of human epilepsies. A large number and variety of approaches are available, and they have been applied to many animals. In this chapter the in vitro and in vivo animal models are discussed,with major emphasis on the in vivo studies. Models have used phylogenetically different animals - from worms to monkeys. Our attention has been dedicated mainly to rodents.In clinical practice, developmental aspects of epilepsy often differ from those in adults. Animal models have often helped to clarify these differences. In this chapter, developmental aspects have been emphasized.Electrical stimulation and chemical-induced models of seizures have been described first, as they represent the oldest and most common models. Among these models, kindling raised great interest, especially for the study of the epileptogenesis. Acquired focal models mimic seizures and occasionally epilepsies secondary to abnormal cortical development, hypoxia, trauma, and hemorrhage.Better knowledge of epileptic syndromes will help to create new animal models. To date, absence epilepsy is one of the most common and (often) benign forms of epilepsy. There are several models, including acute pharmacological models (PTZ, penicillin, THIP, GBL) and chronic models (GAERS, WAG/Rij). Although atypical absence seizures are less benign, thus needing more investigation, only two models are so far available (AY-9944,MAM-AY). Infantile spasms are an early childhood encephalopathy that is usually associated with a poor out-come. The investigation of this syndrome in animal models is recent and fascinating. Different approaches have been used including genetic (Down syndrome,ARX mutation) and acquired (multiple hit, TTX, CRH,betamethasone-NMDA) models.An entire section has been dedicated to genetic models, from the older models obtained with spontaneous mutations (GEPRs) to the new engineered knockout, knocking, and transgenic models. Some of these models have been created based on recently recognized patho-genesis such as benign familial neonatal epilepsy, early infantile encephalopathy with suppression bursts, severe myoclonic epilepsy of infancy, the tuberous sclerosis model, and the progressive myoclonic epilepsy. The contribution of animal models to epilepsy re-search is unquestionable. The development of further strategies is necessary to find novel strategies to cure epileptic patients, and optimistically to allow scientists first and clinicians subsequently to prevent epilepsy and its consequences.

EEG recording in rodents, with a focus on epilepsy

This unit describes the materials, methods, and analytical techniques available for the study of electrical activity of neural tissue in rodents in both homeostatic and disease states, with emphasis on epileptogenesis. A table containing a list of suppliers of relevant materials and equipment is also provided.

Cholesterol synthesis inhibitor U18666A and the role of sterol metabolism and trafficking in numerous pathophysiological processes

The multiple actions of U18666A have enabled major discoveries in lipid research and contributed to understanding the pathophysiology of multiple diseases. This review describes these advances and the utility of U18666A as a tool in lipid research. Harry Rudney's recognition that U18666A inhibited oxidosqualene cyclase led him to discover a pathway for formation of polar sterols that he proved to be important regulators of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase. Laura Liscum's recognition that U18666A inhibited the egress of cholesterol from late endosomes and lysosomes led to greatly improved perspective on the major pathways of intracellular cholesterol trafficking. The inhibition of cholesterol trafficking by U18666A mimicked the loss of functional Niemann-Pick type C protein responsible for NPC disease and thus provided a model for this disorder. U18666A subsequently became a tool for assessing the importance of molecular trafficking through the lysosomal pathway in other conditions such as atherosclerosis, Alzheimer's disease, and prion infections. U18666A also provided animal models for two important disorders: petite mal (absence) epilepsy and cataracts. This was the first chronic model of absence epilepsy. U18666A is also being used to address the role of oxidative stress in apoptosis. How can one molecule have so many effects? Perhaps because of its structure as an amphipathic cationic amine it can interact and inhibit diverse proteins. Restricting the availability of cholesterol for membrane formation through inhibition of cholesterol synthesis and intracellular trafficking could also be a mechanism for broadly affecting many processes. Another possibility is that through intercalation into membrane U18666A can alter membrane order and therefore the function of resident proteins. The similarity of the effects of natural and enantiomeric U18666A on cells and the capacity of intercalated U18666A to increase membrane order are arguments in favor of this possibility.

Population-based study of baseline ethanol consumption and risk of incident essential tremor

BACKGROUND

Recent postmortem studies have demonstrated pathological changes, including Purkinje cell loss, in the cerebellum in essential tremor (ET). Toxic exposures that compromise cerebellar tissue could lower the threshold for developing ET. Ethanol is a well-established cerebellar toxin, resulting in Purkinje cell loss.

OBJECTIVE

To test whether higher baseline ethanol consumption is a risk factor for the subsequent development of incident ET.

METHODS

Lifetime ethanol consumption was assessed at baseline (1994-1995) in a prospective, population-based study in central Spain of 3285 elderly participants, 76 of whom developed incident ET by follow-up (1997-1998).

RESULTS

In a Cox proportional hazards model adjusting for cigarette pack-years, depressive symptoms and community, the baseline number of drink-years was marginally associated with a higher risk of incident ET (relative risk, RR = 1.003, p = 0.059). In an adjusted Cox model, the highest baseline drink-year quartile doubled the risk of incident ET (RR = 2.29, p = 0.018), while other quartiles were associated with more modest elevations in risk (RR(3rd quartile) = 1.82 (p = 0.10), RR(2nd quartile) = 1.75 (p = 0.10), RR(1st quartile) = 1.43 (p = 0.34) vs non-drinkers (RR = 1.00)). With each higher drink-year quartile, the risk of incident ET increased an average of 23% (p = 0.01, test for trend).

CONCLUSIONS

Higher levels of chronic ethanol consumption increased the risk of developing ET. Ethanol is often used for symptomatic relief; studies should explore whether higher consumption levels are a continued source of underlying cerebellar neurotoxicity in patients who already manifest this disease.

Altered glutamate receptor - transporter expression and spontaneous seizures in rats exposed to methylazoxymethanol in utero

PURPOSE

Brain malformations are a common cause of intractable epilepsy and cognitive dysfunction in children. Prenatal exposure to the teratogen methylazoxymethanol (MAM) is a rodent model of brain malformation featuring loss of lamination, clusters of displaced hippocampal cells, and pharmaco-resistance to antiepileptic drugs. In a normotopic hippocampus, expression of postsynaptic glutamate receptors and the transporters regulating neurotransmitter reuptake are critical factors modulating excitation and synaptic communication. Alterations in this system can have profound effects on overall excitability, cognitive function, and seizure thresholds.

METHODS

Immunohistochemical techniques were used to analyze the expression of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5 methylisoxazole-4-proprionic acid (AMPA) receptor subunits in rats exposed to MAM in utero (25 mg/kg, intraperitoneal injection). We also examined the expression of several glutamate transporters (EAAC1, vGLUT1, and vGLUT2). A video-electroencephalographic (video-EEG) system was used for long-term monitoring of adult MAM-exposed rats.

RESULTS

Heterotopic hippocampal neurons exhibited striking reductions in GluR1 and EAAC1 expression; vGlut2 expression was prominent in these regions. Spontaneous electrographic seizures were verified in two animals.

CONCLUSIONS

We conclude that glutamate receptor subunit and transporter expression are altered in animals exposed to MAM in utero. Further studies in the MAM model may provide greater insight into the potential disruptions in excitatory synaptic neurotransmission that can occur in a malformed brain.