Basic research in epilepsy and aging

Role of α-amino-3‑hydroxy-5-methyl-4-isoxazolepropionic acid receptors and the antagonist perampanel in geriatric epilepsy and status epilepticus

The α-amino-3‑hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) is an ionotropic glutamate receptor recognized for its active involvement in epilepsy. Through AMPAR functional alterations, multiple factors contribute to the increased susceptibility to seizures in the geriatric population. These factors include changes in the hippocampus, neuroinflammation, ischemic insults, amyloid deposition, previous seizures, alterations in the microenvironment, and neurovascular unit dysfunction. Perampanel, a noncompetitive AMPAR antagonist, has been approved for the treatment of focal and generalized epilepsy. However, a complete understanding of AMPAR's role in epileptogenesis and the pharmacotherapy of perampanel in the geriatric population remains elusive. To address this gap, we conducted a comprehensive literature review, screening 1557 articles and ultimately selecting 94 relevant ones. We provided insights into AMPAR functionality changes and perampanel's role in treating geriatric epilepsy. Various clinical trials and retrospective studies have demonstrated that the safety and efficacy of perampanel in the older population are comparable to those in the younger population, with overall good tolerability. It is also effective for treating focal and generalized onset seizures and possibly for managing status epilepticus. In conclusion, the existing body of evidence supports the safety and efficacy of perampanel in the geriatric population, indicating its potential as a valuable therapeutic option for focal and generalized epilepsy. Additional research is warranted to deepen our understanding of AMPAR's involvement in epileptogenesis and to refine the pharmacotherapeutic nuances in this specific demographic.

A Neuroscience Primer for Integrating Geroscience With the Neurobiology of Aging

Neuroscience has a rich history of studies focusing on neurobiology of aging. However, much of the aging studies in neuroscience occur outside of the gerosciences. The goal of this primer is 2-fold: first, to briefly highlight some of the history of aging neurobiology and second, to introduce to geroscientists the broad spectrum of methodological approaches neuroscientists use to study the neurobiology of aging. This primer is accompanied by a corresponding geroscience primer, as well as a perspective on the current challenges and triumphs of the current divide across these 2 fields. This series of manuscripts is intended to foster enhanced collaborations between neuroscientists and geroscientists with the intent of strengthening the field of cognitive aging through inclusion of parameters from both areas of expertise.

The need to incorporate aged animals into the preclinical modeling of neurological conditions

Neurological conditions such as traumatic brain injury, stroke, Parkinson's disease, epilepsy, multiple sclerosis, and Alzheimer's disease are serious clinical problems that affect millions of people worldwide. The majority of clinical trials for these common conditions have failed, and there is a critical need to understand why treatments in preclinical animal models do not translate to patients. Many patients with these conditions are middle-aged or older, however, the majority of preclinical studies have used only young-adult animals. Considering that aging involves biological changes that are relevant to the pathobiology of neurological diseases, the lack of aged subjects in preclinical research could contribute to translational failures. This paper details how aging affects biological processes involved in neurological conditions, and reviews aging research in the context of traumatic brain injury, stroke, Parkinson's disease, epilepsy, multiple sclerosis, and Alzheimer's disease. We conclude that aging is an important, but often overlooked, factor that influences biology and outcomes in neurological conditions, and provide suggestions to improve our understanding and treatment of these diseases in aged patients.

Long-Term Effects of Early Life Seizures on Endogenous Local Network Activity of the Mouse Neocortex

Understanding the long term impact of early life seizures (ELS) is of vital importance both for researchers and clinicians. Most experimental studies of how seizures affect the developing brain have drawn their conclusions based on changes detected at the cellular or behavioral level, rather than on intermediate levels of analysis, such as the physiology of neuronal networks. Neurons work as part of networks and network dynamics integrate the function of molecules, cells and synapses in the emergent properties of brain circuits that reflect the balance of excitation and inhibition in the brain. Therefore, studying network dynamics could help bridge the cell-to-behavior gap in our understanding of the neurobiological effects of seizures. To this end we investigated the long-term effects of ELS on local network dynamics in mouse neocortex. By using the pentylenetetrazole (PTZ)-induced animal model of generalized seizures, single or multiple seizures were induced at two different developmental stages (P9-15 or P19-23) in order to examine how seizure severity and brain maturational status interact to affect the brain's vulnerability to ELS. Cortical physiology was assessed by comparing spontaneous network activity (in the form of recurring Up states) in brain slices of adult (>5 mo) mice. In these experiments we examined two distinct cortical regions, the primary motor (M1) and somatosensory (S1) cortex in order to investigate regional differences in vulnerability to ELS. We find that the effects of ELSs vary depending on (i) the severity of the seizures (e.g., single intermittent ELS at P19-23 had no effect on Up state activity, but multiple seizures induced during the same period caused a significant change in the spectral content of spontaneous Up states), (ii) the cortical area examined, and (iii) the developmental stage at which the seizures are administered. These results reveal that even moderate experiences of ELS can have long lasting age- and region-specific effects in local cortical network dynamics.

Pharmacological characterization of nicotine-induced tremor: Responses to anti-tremor and anti-epileptic agents

We previously showed that nicotine evoked kinetic tremor by activating the inferior olive, which is implicated in the pathogenesis of essential tremor, via α7 nicotinic acetylcholine receptors. Here, we evaluated the effects of various anti-tremor and anti-epileptic agents on nicotine-induced tremor in mice to clarify the pharmacological characteristics of nicotine tremor. Drugs effective for essential tremor, propranolol, diazepam and phenobarbital, all significantly inhibited kinetic tremor induced by an intraperitoneal (i.p.) injection of nicotine (1 mg/kg). In contrast, none of the medications for Parkinson's disease, l-DOPA, bromocriptine or trihexyphenidyl, affected the nicotine tremor. Among the anti-epileptic agents examined, valproate, carbamazepine and ethosuximide, significantly inhibited nicotine-induced tremor. In addition, a selective T-type Ca²⁺ channel blocker, TTA-A2, also suppressed the nicotine tremor. However, neither gabapentin, topiramate, zonisamide nor levetiracetam significantly affected nicotine-induced tremor. The present results show that nicotine-induced tremor resembles essential tremor not only on the neural basis, but also in terms of the pharmacological responses to anti-tremor agents, implying that nicotine-induced tremor can serve as a model for essential tremor. In addition, it is suggested that anti-epileptic agents, which have stimulant actions on the GABAergic system or blocking actions on voltage-gated Na⁺ channels and T-type Ca²⁺ channels, can alleviate essential tremor.

Susceptibility to hippocampal kindling seizures is increased in aging C57 black mice

The incidence of seizures increases with old age. Stroke, dementia and brain tumors are recognized risk factors for new-onset seizures in the aging populations and the incidence of these conditions also increased with age. Whether aging is associated with higher seizure susceptibility in the absence of the above pathologies remains unclear. We used classic kindling to explore this issue as the kindling model is highly reproducible and allows close monitoring of electrographic and motor seizure activities in individual animals. We kindled male young and aging mice (C57BL/6 strain, 2-3 and 18-22 months of age) via daily hippocampal CA3 stimulation and monitored seizure activity via video and electroencephalographic recordings. The aging mice needed fewer stimuli to evoke stage-5 motor seizures and exhibited longer hippocampal afterdischarges and more frequent hippocampal spikes relative to the young mice, but afterdischarge thresholds and cumulative afterdischarge durations to stage 5 motor seizures were not different between the two age groups. While hippocampal injury and structural alterations at cellular and micro-circuitry levels remain to be examined in the kindled mice, our present observations suggest that susceptibility to hippocampal CA3 kindling seizures is increased with aging in male C57 black mice.

Tonic glutamate in CA1 of aging rats correlates with phasic glutamate dysregulation during seizure

OBJECTIVE

Characterize glutamate neurotransmission in the hippocampus of awake-behaving rodents during focal seizures in a model of aging.

METHODS

We used enzyme-based ceramic microelectrode array technology to measure in vivo extracellular tonic glutamate levels and real-time phasic glutamate release and clearance events in the hippocampus of awake Fischer 344 rats. Local application of 4-aminopyridine (4-AP) into the CA1 region was used to induce focal motor seizures in different animal age groups representing young, late-middle aged and elderly humans.

RESULTS

Rats with the highest preseizure tonic glutamate levels (all in late-middle aged or elderly groups) experienced the most persistent 4-AP-induced focal seizure motor activity (wet dog shakes) and greatest degree of acute seizure-associated disruption of glutamate neurotransmission measured as rapid transient changes in extracellular glutamate levels.

SIGNIFICANCE

Increased seizure susceptibility was demonstrated in the rats with the highest baseline hippocampal extracellular glutamate levels, all of which were late-middle aged or aged animals. The manifestation of seizures behaviorally was associated with dynamic changes in glutamate neurotransmission. To our knowledge, this is the first report of a relationship between seizure susceptibility and alterations in both baseline tonic and phasic glutamate neurotransmission.

Stem cell transplantation in neurological diseases: improving effectiveness in animal models

Neurological diseases afflict a growing proportion of the human population. There are two reasons for this: first, the average age of the population (especially in the industrialized world) is increasing, and second, the diagnostic tools to detect these pathologies are now more sophisticated and can be used on a higher percentage of the population. In many cases, neurological disease has a pharmacological treatment which, as in the case of Alzheimer's disease, Parkinson's disease, Epilepsy, and Multiple Sclerosis can reduce the symptoms and slow down the course of the disease but cannot reverse its effects or heal the patient. In the last two decades the transplantation approach, by means of stem cells of different origin, has been suggested for the treatment of neurological diseases. The choice of slightly different animal models and the differences in methods of stem cell preparation make it difficult to compare the results of transplantation experiments. Moreover, the translation of these results into clinical trials with human subjects is difficult and has so far met with little success. This review seeks to discuss the reasons for these difficulties by considering the differences between human and animal cells (including isolation, handling and transplantation) and between the human disease model and the animal disease model.

Clinical features of late-onset partial cryptogenic epilepsy: toward an idiopathic temporal epilepsy?

Adult-onset epilepsy is commonly thought to be secondary to a brain lesion. However, the etiology of adult-onset epilepsy remains unknown in approximately 25% of patients, despite progress in medical and diagnostic tools. In the present study, we investigated whether late-onset partial cryptogenic epilepsies could be subgrouped based on seizure semiology and clinical characteristics. A total of 41 patients with late-onset cryptogenic epilepsy were included, and the corresponding clinical and electrophysiological data were analyzed. The following three clinical subgroups were identified: 1) a group that fulfilled the diagnostic criteria of transient epileptic amnesia (TEA); 2) a group with late-onset cryptogenic epilepsies with a temporal seizure semiology; and 3) a cryptogenic extratemporal group, which was consistent with the categorization of cryptogenic epilepsies, i.e., epilepsies involving unknown lesions. The temporal group showed homogeneous clinical characteristics, especially a rapid evolution and a greater tendency toward generalization and pharmacoresistance compared with the other two groups. Transient epileptic amnesia was associated with a higher frequency of sleep disorders than either of the other groups. Our findings argue for the clinical identification of a subgroup of late-onset temporal epilepsy that might constitute an idiopathic form. The association between TEA and sleep disorders would suggest a possible pathophysiological role of sleep apnea syndromes in TEA.

The brain, seizures and epilepsy throughout life: understanding a moving target

The human brain is a tremendously complex and still enigmatic three-dimensional structure, composed of countless interconnected neurons and glia. The temporal evolution of the brain throughout life provides a fourth dimension, one that influences every element of the brain's function in health and disease. This temporal evolution contributes to the probability of seizure generation and to the type and the nature of these seizures. The age-specific properties of the brain also influence the consequences of seizures on neuronal structure and behavior. These, in turn, govern epileptic activity and cognitive and emotional functions, contributing to the diverse consequences of seizures and epilepsy throughout life.

AED Treatment Through Different Ages: As Our Brains Change, Should Our Drug Choices Also?

Patient age can impact selection of the optimal antiepileptic drug for a number of reasons. Changes in brain physiology from neonate to elderly, as well as changes in underlying etiologies of epilepsy, could potentially affect the ability of different drugs to control seizures. Unfortunately, much of this is speculative, as good studies demonstrating differences in efficacy across age ranges do not exist. Beyond the issue of efficacy, certain drugs may be more or less appropriate at different ages because of differing pharmacokinetics, including changes in hepatic metabolism, absorption, and elimination. Lack of appropriate drug formulations (such as liquid forms) may be a barrier to using drugs in the very young. Finally, some serious adverse events are seen either exclusively or preferentially at different ages.

Differential susceptibility of interneurons expressing neuropeptide Y or parvalbumin in the aged hippocampus to acute seizure activity

Acute seizure (AS) activity in old age has an increased predisposition for evolving into temporal lobe epilepsy (TLE). Furthermore, spontaneous seizures and cognitive dysfunction after AS activity are often intense in the aged population than in young adults. This could be due to an increased vulnerability of inhibitory interneurons in the aged hippocampus to AS activity. We investigated this issue by comparing the survival of hippocampal GABA-ergic interneurons that contain the neuropeptide Y (NPY) or the calcium binding protein parvalbumin (PV) between young adult (5-months old) and aged (22-months old) F344 rats at 12 days after three-hours of AS activity. Graded intraperitoneal injections of the kainic acid (KA) induced AS activity and a diazepam injection at 3 hours after the onset terminated AS-activity. Measurement of interneuron numbers in different hippocampal subfields revealed that NPY+ interneurons were relatively resistant to AS activity in the aged hippocampus in comparison to the young adult hippocampus. Whereas, PV+ interneurons were highly susceptible to AS activity in both age groups. However, as aging alone substantially depleted these populations, the aged hippocampus after three-hours of AS activity exhibited 48% reductions in NPY+ interneurons and 70% reductions in PV+ interneurons, in comparison to the young hippocampus after similar AS activity. Thus, AS activity-induced TLE in old age is associated with far fewer hippocampal NPY+ and PV+ interneuron numbers than AS-induced TLE in the young adult age. This discrepancy likely underlies the severe spontaneous seizures and cognitive dysfunction observed in the aged people after AS activity.

Vulnerability of hippocampal GABA-ergic interneurons to kainate-induced excitotoxic injury during old age

Hippocampal inhibitory interneurons expressing glutamate decarboxylase-67 (GAD-67) considerably decline in number during old age. Studies in young adult animals further suggest that hippocampal GAD-67+ interneuron population is highly vulnerable to excitotoxic injury. However, the relative susceptibility of residual GAD-67+ interneurons in the aged hippocampus to excitotoxic injury is unknown. To elucidate this, using both adult and aged F344 rats, we performed stereological counting of GAD-67+ interneurons in different layers of the dentate gyrus and CA1 & CA3 sub-fields, at 3 months post-excitotoxic hippocampal injury inflicted through an intracerebroventricular administration of kainic acid (KA). Substantial reductions of GAD-67+ interneurons were found in all hippocampal layers and sub-fields after KA-induced injury in adult animals. Contrastingly, there was no significant change in GAD-67+ interneuron population in any of the hippocampal layers and sub-fields following similar injury in aged animals. Furthermore, the stability of GAD-67+ interneurons in aged rats after KA was not attributable to milder injury, as the overall extent of KA-induced hippocampal principal neuron loss was comparable between adult and aged rats. Interestingly, because of the age-related disparity in vulnerability of interneurons to injury, the surviving GAD-67+ interneuron population in the injured aged hippocampus remained comparable to that observed in the injured adult hippocampus despite enduring significant reductions in interneuron number with aging. Thus, unlike in the adult hippocampus, an excitotoxic injury to the aged hippocampus does not result in significantly decreased numbers of GAD-67+ interneurons. Persistence of GAD-67+ interneuron population in the injured aged hippocampus likely reflects an age-related change in the response of GAD-67+ interneurons to excitotoxic hippocampal injury. These results have implications towards understanding mechanisms underlying the evolution of initial precipitating injury into temporal lobe epilepsy in the elderly population.

Vulnerability of hippocampal GABA-ergic interneurons to kainate-induced excitotoxic injury during old age

Hippocampal inhibitory interneurons expressing glutamate decarboxylase-67 (GAD-67) considerably decline in number during old age. Studies in young adult animals further suggest that hippocampal GAD-67+ interneuron population is highly vulnerable to excitotoxic injury. However, the relative susceptibility of residual GAD-67+ interneurons in the aged hippocampus to excitotoxic injury is unknown. To elucidate this, using both adult and aged F344 rats, we performed stereological counting of GAD-67+ interneurons in different layers of the dentate gyrus and CA1 & CA3 sub-fields, at 3 months post-excitotoxic hippocampal injury inflicted through an intracerebroventricular administration of kainic acid (KA). Substantial reductions of GAD-67+ interneurons were found in all hippocampal layers and sub-fields after KA-induced injury in adult animals. Contrastingly, there was no significant change in GAD-67+ interneuron population in any of the hippocampal layers and sub-fields following similar injury in aged animals. Furthermore, the stability of GAD-67+ interneurons in aged rats after KA was not attributable to milder injury, as the overall extent of KA-induced hippocampal principal neuron loss was comparable between adult and aged rats. Interestingly, because of the age-related disparity in vulnerability of interneurons to injury, the surviving GAD-67+ interneuron population in the injured aged hippocampus remained comparable to that observed in the injured adult hippocampus despite enduring significant reductions in interneuron number with aging. Thus, unlike in the adult hippocampus, an excitotoxic injury to the aged hippocampus does not result in significantly decreased numbers of GAD-67+ interneurons. Persistence of GAD-67+ interneuron population in the injured aged hippocampus likely reflects an age-related change in the response of GAD-67+ interneurons to excitotoxic hippocampal injury. These results have implications towards understanding mechanisms underlying the evolution of initial precipitating injury into temporal lobe epilepsy in the elderly population.

Senescent synapses and hippocampal circuit dynamics

Excitatory synaptic transmission is altered during aging in hippocampal granule cells, and in CA3 and CA1 pyramidal cells. These functional changes contribute to age-associated impairments in experimentally-induced plasticity in each of these primary hippocampal subregions. In CA1, plasticity evoked by stimulation shares common mechanisms with the synaptic modification observed following natural behavior. Aging results in deficits in both artificially- and behaviorally-induced plasticity, and this could in part reflect age-related changes in Ca2+ homeostasis. Other observations, however, suggest that increased intracellular Ca2+ levels are beneficial under some circumstances. This review focuses on age-associated changes in synaptic function, how these alterations might contribute to cognitive decline, and the extent to which altered hippocampal circuit properties are detrimental or reflect compensatory processes.

Epilepsy in the elderly

The elderly, often defined as those 65 years or older, are the most rapidly growing segment of the population, and onset of epilepsy is higher in this age group than in any other. This paper reviews recent developments, including a new proposed definition of epilepsy, a transgenic mouse model of Alzheimer's disease that exhibits complex partial seizures, evidence that the highest incidence of epilepsy may occur after admission to a nursing home, a challenge to the vitamin D hypothesis of osteoporosis associated with antiepileptic drugs (AEDs), evidence that the genetic complement of hepatic isoenzymes is more predictive of metabolic rate than age, and data showing that there is considerable variability in serum levels of AEDs in many nursing home residents during constant dosing conditions.

[Specificity of epileptic seizures in the elderly: A proposed electro-clinical scale]

Diagnosis of epileptic seizure may be difficult in older patients because seizure manifestations are often unusual: confusion, paresis... and because there are multiple differential diagnoses (syncope, transient ischemic attack, transient global amnesia...). To promote and facilitate the diagnosis of seizures in the elderly, neurologists and gerontologists must work together and focus their strategy on two points: firstly, the knowledge of the specific presentation of seizures in elderly patients, and secondly, the adoption of a reasoning based on seizures and not epileptic syndromes. A multidisciplinary group worked on epilepsy of the elderly to elaborate an electro-clinical score which aims to help establish the diagnosis of epilepsy in elderly patients in different clinical settings. This electro-clinical score is based on a systematic review of scientific literature and the recommendations are explicitly linked to supporting evidence. Further, clinical validation of the electro-clinical score is required.

Molecular pharmacodynamics, clinical therapeutics, and pharmacokinetics of topiramate

Topiramate (TPM; TOPAMAX) is a broad-spectrum antiepileptic drug (AED) that is approved in many world markets for preventing or reducing the frequency of epileptic seizures (as monotherapy or adjunctive therapy), and for the prophylaxis of migraine. TPM, a sulfamate derivative of the naturally occurring sugar D-fructose, possesses several pharmacodynamic properties that may contribute to its clinically useful attributes, and to its observed adverse effects. The sulfamate moiety is essential, but not sufficient, for its pharmacodynamic properties. In this review, we discuss the known pharmacodynamic and pharmacokinetic properties of TPM, as well as its various clinically beneficial and adverse effects.

Cognitive progression in epilepsy

The issue of cognitive progression in people with epilepsy is of considerable interest and has important clinical and theoretical implications. In this paper, we review recent studies in both the adult and childhood epilepsy literature which have included a longitudinal test-retest design to examine this question. Several important methodological issues of this literature are highlighted and areas which require more investigation are identified.

Domoic acid preconditioning and seizure induction in young and aged rats

Clinical reports suggest that the elderly are hypersensitive to the neurological effects of domoic acid (DOM). In the present study we assessed DOM-induced seizures in young and aged rats, and seizure attenuation following low-dose DOM pretreatment (i.e. preconditioning). Seizure behaviours following saline or DOM administration (0.5-2mg/kg i.p.) were continuously monitored for 2.5h in naïve and DOM preconditioned rats. Competitive ELISA was used to determine serum and brain DOM concentrations. Dose- and age-dependent increases in seizure activity were evident in response to DOM. Lower doses of DOM in young and aged rats promoted low level seizure behaviours. Animals administered high doses (2mg/kg in young; 1mg/kg in aged) progressed through various stages of stereotypical behaviour (e.g., head tics, scratching, wet dog shakes) before ultimately exhibiting tonic-clonic convulsions. Serum and brain DOM analysis indicated impaired renal clearance as contributory to increased DOM sensitivity in aged animals, and this was supported by seizure analysis following direct intrahippocampal administration of DOM. Preconditioning young and aged animals with low-dose DOM 45-90 min before high-dose DOM significantly reduced seizure intensity. We conclude that age-related supersensitivity to DOM is related to reduced clearance rather than increased neuronal sensitivity, and that preconditioning mechanisms underlying an inducible tolerance to excitotoxins are robustly expressed in both young and aged CNS.

Acute confusion or altered mental state: consider nonconvulsive status epilepticus

BACKGROUND

The diagnosis of nonconvulsive status epilepticus (NCSE) is particularly challenging in elderly patients. Confusion, personality change, dysphasia, subtle motor activity and nystagmus may be the only presenting signs.

OBJECTIVE

To review current knowledge about NCSE with special focus on older people.

METHODS

Systematic review of the current literature via Medline search.

CONCLUSION

Although prospective studies are still lacking, NCSE may be one of the most frequently missed diagnoses in patients presenting with altered mental status. Elderly patients are at particular risk of diagnostic errors because of the broad range of presentations of NCSE, significant comorbidities (especially cerebrovascular disease), limited awareness of this particular seizure emergency or difficulties with access to electroencephalography. Although diagnostic criteria and treatment remain controversial, the diagnosis of NCSE is important because it is potentially reversible.

Epilepsy in the older patient

The world population is aging rapidly. The post World War II ‘baby boomers’ have benefited from improved medical science, sanitation, political freedom, and social and economic development, resulting in the knock-on demographic trend of an aging population. From a health-economic perspective, this places increasing demands on society and on health services to meet evolving medical and social needs. By 2025, over 30% of the populations of developed countries will be aged over 60 years (US Bureau of Census 2004).

Mechanisms of action of antiepileptic drugs

The management of seizures in the patient with epilepsy relies heavily on antiepileptic drug (AED) therapy. Fortunately, for a large percentage of patients, AEDs provide excellent seizure control at doses that do not adversely affect normal function. At the molecular level, the majority of AEDs are thought to modify excitatory and inhibitory neurotransmission through effects on voltage-gated ion channels (e.g., sodium and calcium) and gamma-aminobutyric acid (GABA)(A) receptors, respectively. In addition to these effects, two of the "second-generation" AEDs have been found to limit glutamate-mediated excitatory neurotransmission (i.e., felbamate and topiramate). Not surprisingly, those AEDs with broad spectrum clinical activity are often found to exert an action at more than one molecular target. Emerging evidence suggests that receptor and voltage-gated subunits are modified by chronic seizures. Thus, attempts to understand the relationship between target and effect continue to provide important information about the neuropathology of the epileptic network and to facilitate the development of novel therapies for the treatment of refractory epilepsy.

Animal models of geriatric epilepsy

Geriatric epilepsy is a significant clinical problem that has not been studied adequately in animal models. This chapter will review the available literature with particular attention to models that have demonstrated how acute seizures and epilepsy in aged animals differ from those of younger animals. Studies include several strains of mice [e.g., El, DBA, senescence-accelerated mouse (SAM), Cacnb4 knockout] as well as acute seizure models in common strains of aged mice. Aged rats (including Fischer 344, Wistar, and Sprague-Dawley) have been used in acute seizure, lesion, and epilepsy models. This area of research remains largely unexplored and therefore provides numerous opportunities for new investigations.

A long-term video-EEG and behavioral follow-up after endothelin-1 induced middle cerebral artery occlusion in rats

The aim was to test the hypothesis that occlusion of the middle cerebral artery (MCA) results in the development of epilepsy in rats. Further, we investigated whether lesion volume, hippocampal pathology, early seizures, or severity of behavioral impairment is associated with the development and severity of epilepsy or interictal spiking. MCA occlusion was induced by intracerebral injection of endothelin-1 (ET; 120 pmol). One group of ET-injected rats were followed-up for 6 months (n = 15) and another for 12 months (n = 20). Sham-operated animals were injected with saline (n = 12). Occurrence of early and late seizures was monitored by intermittent video-electroencephalography. Sensorimotor function was tested with the running wheel and tapered beam-walking tests. Emotional learning and memory were assessed with the fear conditioning test and spatial learning and memory with the Morris water maze. Finally, brains were processed for histology. Only one rat developed late spontaneous seizures (i.e., epilepsy). Epileptiform interictal spiking was detected in 9 of 26 animals. Early seizures did not predict the development of epilepsy, spiking activity, or severity of behavioral impairment. Production of MCA stroke by intracerebral injection of ET was not a strong trigger of epileptogenesis in adult rats. Further studies are needed to investigate the effect of age, genetic background, and location of ET-injection on the development of hyperexcitability and the risk of post-stroke epileptogenesis.