Long-term functional consequences of transient occlusion of the middle cerebral artery in rats: a 1-year follow-up of the development of epileptogenesis and memory impairment in relation to sensorimotor deficits

Animal models of epilepsy after ischemic stroke

Stroke ranks among the foremost causes of disability and mortality globally, with ischemic stroke (IS) being the most prevalent subtype. Post-stroke epilepsy (PSE) represents a significant and common complication following a stroke, imposing substantial burdens on patients, their families, and society at large. Establishing a reliable animal model is crucial for investigating the mechanisms and potential treatments for PSE. This article offers a review of studies pertaining to animal models of epilepsy subsequent to ischemic stroke.

Role of blood-brain barrier dysfunction in the development of poststroke epilepsy

Stroke is a major contributor to mortality and morbidity worldwide and the most common cause of epilepsy in the elderly in high income nations. In recent years, it has become increasingly evident that both ischemic and hemorrhagic strokes induce dysfunction of the blood-brain barrier (BBB), and that this impairment can contribute to epileptogenesis. Nevertheless, studies directly comparing BBB dysfunction and poststroke epilepsy (PSE) are largely absent. Therefore, this review summarizes the role of BBB dysfunction in the development of PSE in animal models and clinical studies. There are multiple mechanisms whereby stroke induces BBB dysfunction, including increased transcytosis, tight junction dysfunction, spreading depolarizations, astrocyte and pericyte loss, reactive astrocytosis, angiogenesis, matrix metalloproteinase activation, neuroinflammation, adenosine triphosphate depletion, oxidative stress, and finally cell death. The degree to which these effects occur is dependent on the severity of the ischemia, whereby cell death is a more prominent mechanism of BBB disruption in regions of critical ischemia. BBB dysfunction can contribute to epileptogenesis by increasing the risk of hemorrhagic transformation, increasing stroke size and the amount of cerebral vasogenic edema, extravasation of excitatory compounds, and increasing neuroinflammation. Furthermore, albumin extravasation after BBB dysfunction contributes to epileptogenesis primarily via increased transforming growth factor β signaling. Finally, seizures themselves induce BBB dysfunction, thereby contributing to epileptogenesis in a cyclical manner. In repairing this BBB dysfunction, pericyte migration via platelet-derived growth factor β signaling is indispensable and required for reconstruction of the BBB, whereby astrocytes also play a role. Although animal stroke models have their limitations, they provide valuable insights into the development of potential therapeutics designed to restore the BBB after stroke, with the ultimate goal of improving outcomes and minimizing the occurrence of PSE. In pursuit of this goal, rapamycin, statins, losartan, semaglutide, and metformin show promise, whereby modulation of pericyte migration could also be beneficial.

A Look at the Etiology of Alzheimer's Disease based on the Brain Ischemia Model

Alzheimer's disease (AD) is the frequent form of dementia in the world. Despite over 100 years of research into the causes of AD, including amyloid and tau protein, the research has stalled and has not led to any conclusions. Moreover, numerous projects aimed at finding a cure for AD have also failed to achieve a breakthrough. Thus, the failure of anti-amyloid and anti-tau protein therapy to treat AD significantly influenced the way we began to think about the etiology of the disease. This situation prompted a group of researchers to focus on ischemic brain episodes, which, like AD, mostly present alterations in the hippocampus. In this context, it has been proposed that cerebral ischemic incidents may play a major role in promoting amyloid and tau protein in neurodegeneration in AD. In this review, we summarized the experimental and clinical research conducted over several years on the role of ischemic brain episodes in the development of AD. Studies have shown changes typical of AD in the course of brain neurodegeneration post-ischemia, i.e., progressive brain and hippocampal atrophy, increased amyloid production, and modification of tau protein. In the post-ischemic brain, the diffuse and senile amyloid plaques and the development of neurofibrillary tangles characteristic of AD were revealed. The above data evidently showed that after brain ischemia, there are modifications in protein folding, leading to massive neuronal death and damage to the neuronal network, which triggers dementia with the AD phenotype.

Preventing development of post-stroke hyperexcitability by optogenetic or pharmacological stimulation of cortical excitatory activity

Stroke is the most common cause of acquired epilepsy, but treatment for preventing the development of post-stroke epilepsy is still unavailable. Since stroke results in neuronal damage and death as well as initial loss of activity in the affected brain region, homeostatic plasticity may be trigged and contribute to an increase in network hyperexcitability that underlies epileptogenesis. Correspondingly, enhancing brain activity may inhibit hyperexcitability from enhanced homeostatic plasticity and prevent post-stroke epileptogenesis. To test these hypotheses, we first used in vivo two-photon and mesoscopic imaging of activity of cortical pyramidal neurons in Thy1-GCaMP6 transgenic mice to determine longitudinal changes in excitatory activity after a photothrombotic ischemic stroke. At 3-days post-stroke, there was a significant loss of neuronal activity in the peri-injury area as indicated by reductions in the frequency of calcium spikes and percentage of active neurons, which recovered to baseline level at day 7, supporting a homeostatic activity regulation of the surviving neurons in the peri-injury area. We further used optogenetic stimulation to specifically stimulate activity of pyramidal neurons in the peri-injury area of Thy-1 channelrhodopsin transgenic mice from day 5 to day 15 after stroke. Using pentylenetetrazole test to evaluate seizure susceptibility, we showed that stroke mice are more susceptible to Racine stage V seizures (time latency 54.3 ± 12.9 min) compared to sham mice (107.1 ± 13.6 min), but optogenetic stimulation reversed the increase in seizure susceptibility (114.0 ± 9.2 min) in mice with stroke. Similarly, administration of D-cycloserine, a partial N-methyl-d-aspartate (NMDA) receptor agonist that can mildly enhance neuronal activity without causing post-stroke seizure, from day 5 to day 15 after a stroke significantly reversed the increase in seizure susceptibility. The treatment also resulted in an increased survival of glutamic acid decarboxylase 67 (GAD67) positive interneurons and a reduced activation of glial fibrillary acidic protein (GFAP) positive reactive astrocytes. Thus, this study supports the involvement of homeostatic activity regulation in the development of post-stroke hyperexcitability and potential application of activity enhancement as a novel strategy to prevent post-stroke late-onset seizure and epilepsy through regulating cortical homeostatic plasticity.

Pathological changes of brain oscillations following ischemic stroke

Brain oscillations recorded in the extracellular space are among the most important aspects of neurophysiology data reflecting the activity and function of neurons in a population or a network. The signal strength and patterns of brain oscillations can be powerful biomarkers used for disease detection and prediction of the recovery of function. Electrophysiological signals can also serve as an index for many cutting-edge technologies aiming to interface between the nervous system and neuroprosthetic devices and to monitor the efficacy of boosting neural activity. In this review, we provided an overview of the basic knowledge regarding local field potential, electro- or magneto- encephalography signals, and their biological relevance, followed by a summary of the findings reported in various clinical and experimental stroke studies. We reviewed evidence of stroke-induced changes in hippocampal oscillations and disruption of communication between brain networks as potential mechanisms underlying post-stroke cognitive dysfunction. We also discussed the promise of brain stimulation in promoting post stroke functional recovery via restoring neural activity and enhancing brain plasticity.

Post-Ischemic Neurodegeneration of the Hippocampus Resembling Alzheimer's Disease Proteinopathy

In this review, we summarize, inter alia, the protein and gene changes associated with Alzheimer’s disease and their role in post-ischemic hippocampal neurodegeneration. In the hippocampus, studies have revealed dysregulation of the genes for the amyloid protein precursor metabolism and tau protein that is identical in nature to Alzheimer’s disease. Data indicate that amyloid and tau protein, derived from brain tissue and blood due to increased permeability of the blood–brain barrier after ischemia, play a key role in post-ischemic neurodegeneration of the hippocampus, with concomitant development of full-blown dementia. Thus, the knowledge of new neurodegenerative mechanisms that cause neurodegeneration of the hippocampus after ischemia, resembling Alzheimer’s disease proteinopathy, will provide the most important therapeutic development goals to date.

NgR1 pathway expression in cerebral ischemic Sprague-Dawley rats with cognitive impairment

Objective(s):

This study aimed to determine the effect of ischemic occlusion duration and recovery time course on motor and cognitive function, identify optimal conditions for assessing cognitive function with minimal interference from motor deficits, and elucidate the underlying mechanism of axonal inhibitors.

Materials and Methods:

Sprague-Dawley (SD) rats were randomly allocated to the transient middle cerebral artery occlusion (tMCAO) 60-min (tMCAO60min), tMCAO90min, tMCAO120min, and sham groups. We conducted forelimb grip strength, two-way shuttle avoidance task, and novel object recognition task (NORT)tests at three time points (14, 21, and 28 days). Expression of Nogo receptor-1 (NgR1), the endogenous antagonist lateral olfactory tract usher substance, ras homolog family member A (Rho-A), and RhoA-activated Rho kinase (ROCK) was examined in the ipsilateral thalamus.

Results:

There was no difference in grip strength between sham and tMCAO_90min rats at 28 days. tMCAO_90min and tMCAO_120min rats showed lower discrimination indices in the NORT than sham rats on day 28. Compared with that in sham rats, the active avoidance response rate was lower in tMCAO_90min rats on days 14, 21, and 28 and in tMCAO_120min rats on days 14 and 21. Furthermore, 50-54% of rats in the tMCAO_90min group developed significant cognitive impairment on day 28, and thalamic NgR1, RhoA, and ROCK expression were greater in tMCAO_90min rats than in sham rats.

Conclusion:

Employing 90-min tMCAO in SD rats and assessing cognitive function 28 days post-stroke could minimize motor dysfunction effects in cognitive function assessments. Axonal inhibitor deregulation could be involved in poststroke cognitive impairment.

Rodent models used in preclinical studies of deep brain stimulation to rescue memory deficits

Deep brain stimulation paradigms might be used to treat memory disorders in patients with stroke or traumatic brain injury. However, proof of concept studies in animal models are needed before clinical translation. We propose here a comprehensive review of rodent models for Traumatic Brain Injury and Stroke. We systematically review the histological, behavioral and electrophysiological features of each model and identify those that are the most relevant for translational research.

Participation of Amyloid and Tau Protein in Post-Ischemic Neurodegeneration of the Hippocampus of a Nature Identical to Alzheimer's Disease

Recent evidence suggests that amyloid and tau protein are of vital importance in post-ischemic death of CA1 pyramidal neurons of the hippocampus. In this review, we summarize protein alterations associated with Alzheimer's disease and their gene expression (amyloid protein precursor and tau protein) after cerebral ischemia, as well as their roles in post-ischemic hippocampus neurodegeneration. In recent years, multiple studies aimed to elucidate the post-ischemic processes in the development of hippocampus neurodegeneration. Their findings have revealed the dysregulation of genes for amyloid protein precursor, β-secretase, presenilin 1 and 2, tau protein, autophagy, mitophagy, and apoptosis identical in nature to Alzheimer's disease. Herein, we present the latest data showing that amyloid and tau protein associated with Alzheimer's disease and their genes play a key role in post-ischemic neurodegeneration of the hippocampus with subsequent development of dementia. Therefore, understanding the underlying process for the development of post-ischemic CA1 area neurodegeneration in the hippocampus in conjunction with Alzheimer's disease-related proteins and genes will provide the most important therapeutic development goals to date.

Modeling poststroke epilepsy and preclinical development of drugs for poststroke epilepsy

Stroke is a severe clinical issue for global public health, representing the third leading cause of death and a major cause of disability in developed countries. Progresses in the pharmacological treatment of the acute stroke have given rise to a significant decrease in its mortality rate. However, as a result, there has been an increasing number of stroke survivors living with disability worldwide. Poststroke epilepsy (PSE) is a common clinical complication following stroke. Seizures can arise in close temporal association with stroke damage and/or after a variably longer interval. Overall, PSE have a good prognosis; in fact, its responding rate to antiepileptic drugs (AEDs) is higher than other types of epilepsy. However, regarding pharmacological treatment, some issues are still unresolved. To this aim, a deeper understanding of mechanisms underlying the transformation of infarcted tissue into an epileptic focus or better from a nonepileptic brain to an epileptic brain is also mandatory for PSE. However, studying epileptogenesis in patients with PSE clearly has several limitations and difficulties; therefore, modeling PSE is crucial. Until now, different experimental models have been used to study the etiopathology of cerebrovascular stroke with or without infarction, but few studies focused on poststroke epileptogenesis and PSE. In this review, we show a brief overview on the features emerging from preclinical research into experimental PSE, which could affect the discovery of biomarkers and therapy strategies for poststroke epileptogenesis. This article is part of the Special Issue "Seizures & Stroke".

Effects of dietary 5-methoxyindole-2-carboxylic acid on brain functional recovery after ischemic stroke

Stroke leads to devastating outcomes including impairments of sensorimotor and cognitive function that may be long lasting. New intervention strategies are needed to overcome the long-lasting effects of ischemic injury. Previous studies determined that treatment with 5-methoxyindole-2-carboxylic acid (MICA) conferred chemical preconditioning and neuroprotection against stroke. The purpose of the current study was to determine whether the preconditioning can lead to functional improvements after stroke (done by transient middle cerebral artery occlusion). After 4 weeks of MICA feeding, half the rats underwent ischemic injury, while the other half remained intact. After one week recovery, all the rats were tested for motor and cognitive function (rotorod and water maze). At the time of euthanasia, measurements of long-term potentiation (LTP) were performed. While stroke injury led to motor and cognitive dysfunction, MICA supplementation did not reverse these impairments. However, MICA supplementation did improve stroke-related impairments in hippocampal LTP. The dichotomy of the outcomes suggest that more studies are needed to determine optimum duration and dosage for MICA to lead to substantial motor and cognitive improvements, along with LTP change and neuroprotection.

Lateral fluid-percussion injury leads to pituitary atrophy in rats

Traumatic brain injury (TBI) causes neuroendocrine dysregulation in up to 40% of humans, which is related to impaired function of the hypothalamo-hypophyseal axis and contributes to TBI-related co-morbidities. Our objective was to investigate whether hypophyseal atrophy can be recapitulated in rat lateral fluid-percussion injury model of human TBI. High-resolution structural magnetic resonance images (MRI) were acquired from rats at 2 days and 5 months post-TBI. To measure the lobe-specific volumetric changes, manganese-enhanced MRI (MEMRI) scans were acquired from rats at 8 months post-TBI, which also underwent the pentylenetetrazol (PTZ) seizure susceptibility and Morris water-maze spatial memory tests. MRI revealed no differences in the total hypophyseal volume between TBI and controls at 2 days, 5 months or 8 months post-TBI. Surprisingly, MEMRI at 8 months post-TBI indicated a 17% reduction in neurohypophyseal volume in the TBI group as compared to controls (1.04 ± 0.05 mm3 vs 1.25 ± 0.05 mm3, p < 0.05). Moreover, neurohypophyseal volume inversely correlated with the number of PTZ-induced epileptiform discharges and the mean latency to platform in the Morris water-maze test. Our data demonstrate that TBI leads to neurohypophyseal lobe-specific atrophy and may serve as a prognostic biomarker for post-TBI outcome.

Neuroprotective and Neurological/Cognitive Enhancement Effects of Curcumin after Brain Ischemia Injury with Alzheimer's Disease Phenotype

In recent years, ongoing interest in ischemic brain injury research has provided data showing that ischemic episodes are involved in the development of Alzheimer's disease-like neuropathology. Brain ischemia is the second naturally occurring neuropathology, such as Alzheimer's disease, which causes the death of neurons in the CA1 region of the hippocampus. In addition, brain ischemia was considered the most effective predictor of the development of full-blown dementia of Alzheimer's disease phenotype with a debilitating effect on the patient. Recent knowledge on the activation of Alzheimer's disease-related genes and proteins-e.g., amyloid protein precursor and tau protein-as well as brain ischemia and Alzheimer's disease neuropathology indicate that similar processes contribute to neuronal death and disintegration of brain tissue in both disorders. Although brain ischemia is one of the main causes of death in the world, there is no effective therapy to improve the structural and functional outcomes of this disorder. In this review, we consider the promising role of the protective action of curcumin after ischemic brain injury. Studies of the pharmacological properties of curcumin after brain ischemia have shown that curcumin has several therapeutic properties that include anti-excitotoxic, anti-oxidant, anti-apoptotic, anti-hyperhomocysteinemia and anti-inflammatory effects, mitochondrial protection, as well as increasing neuronal lifespan and promoting neurogenesis. In addition, curcumin also exerts anti-amyloidogenic effects and affects the brain's tau protein. These results suggest that curcumin may be able to serve as a potential preventive and therapeutic agent in neurodegenerative brain disorders.

Transient and permanent arterial occlusions modeling poststroke epilepsy in aging rats

The pathophysiological mechanisms of epileptogenesis following ischemic stroke in the aged brain are not well understood, largely due to limited developments in animal modeling of poststroke epilepsy (PSE). A recent study in our laboratory (Kelly et al., 2018) using transient (3 h) unilateral middle cerebral artery (MCA) and common carotid artery (CCA) occlusion (MCA/CCAo) in 4- and 20-month-old Fischer (F344) rats resulted in epileptic seizures in both age groups; age and infarction factors independently had effects on seizure frequency. We hypothesized that permanent unilateral MCA/CCAo, a simpler model, was capable of producing results comparable to those of transient MCA/CCAo. In this study, we performed permanent MCA/CCAo and compared it to transient MCA/CCAo in 76 4-, 12-, and 20-month-old F344 rats; 41 (54%) animals experienced early, unexpected mortality. The remaining 35 (46%) animals had depth electrodes implanted. Prior to implantation of depth electrodes, 9 (26%) of these 35 animals (26%) were monitored periodically by video alone before video-EEG monitoring (17,837 h total) to assess the potential development of PSE. No EEG recordings were obtained from 12- or 20-month-old transient occlusion or 20-month-old permanent occlusion animals due to premature deaths. Five animals (14%) demonstrated epileptic seizure activity after MCA/CCAo: one 4-month-old transient occlusion animal, one 4-month-old permanent occlusion animal, and three 12-month-old permanent occlusion animals. Of these 5 animals, all but the 4-month-old permanent animal demonstrated 1-4 Hz spike-wave discharges variably associated with inactivity or frank motor arrest, and 2 animals (4- and 12-month-old permanent) demonstrated generalized ictal EEG discharges associated with grade 5 convulsive activity. All animals monitored with video-EEG demonstrated generalized 7-9 Hz spike-wave discharges, innate in F344 animals and distinct from lesion-induced epileptic seizures. Gross inspection of brains revealed variability in lesion presence and size among age groups and occlusion types. Comparison of infarct volumes of permanent MCA/CCAo animals (2.9 ± 1.29 mm³, n = 6) with those of transient MCA/CCAo animals (1.7 ± 0.31 mm³, n = 3) was not significant (p = 0.44) due to the small sample size. Timm staining revealed no evidence of mossy fiber sprouting in 7 animals tested, only one of which was known to be epileptic (4-month-old transient). These results provide evidence of focal nonconvulsive electrographic ictal discharges and behavioral seizures in both permanent and transient MCA/CCAo animals lesioned at 4- or 12-months-of-age and support the use of arterial ligation as a viable method for modeling PSE.

Poststroke epilepsy following transient unilateral middle cerebral and common carotid artery occlusion in young adult and aged F344 rats

The mechanisms of injured brain that establish poststroke seizures and epilepsy are not well understood, largely because animal modeling has had limited development. The main objective of this study was to determine whether an arterial occlusion model of cortical stroke in young adult and aged rats was capable of generating either focal or generalized epileptic seizures within 2 months of lesioning. Four- and 20-month-old male Fischer 344 (F344) sham-operated controls and those lesioned by transient (3 h) unilateral middle cerebral artery (MCA) and common carotid artery (CCA) occlusion (MCA/CCAo) were studied by video-EEG recordings up to 2 months post-procedure. The main findings were: 1) seizures (grade 3 and above) were recorded within 2 months in both young (4-month; 0.23/h) and aged (20-month; 1.93/h) MCA/CCAo rat groups; both MCA/CCAo rat groups had more seizures recorded than the respective control groups, i.e., no seizures in young controls and 0.52/h in old controls; 2) both age and infarction independently had effects on seizure frequency; however, there was no demonstrated interaction between the two factors; and 3) there was no difference in infarct volumes comparing 4- to 20-month-old MCA/CCAo animals. In addition, all lesioned and sham-operated animals demonstrated intermittent solitary myoclonic convulsions arising out of sleep. Morbidity and mortality of animals limited the extent to which the animals could be evaluated, especially 20-month-old animals. These results suggest that transient unilateral MCA/CCAo can result in poststroke epileptic seizures in both young adult and aged F344 rats within a relatively brief period of time following lesioning.

Prospects of modeling poststroke epileptogenesis

This Review describes the current status of poststroke epilepsy (PSE) with an emphasis on poststroke epileptogenesis modeling for testing new therapeutic agents. Stroke is a leading cause of epilepsy in an aging population. Late-onset "epileptic" seizures have been reported in up to 30% cases after stroke. Nevertheless, the overall prevalence of PSE is 2-4%. Rodent models of stroke have contributed to our understanding of the relationship between seizures and the underlying ischemic damage to neurons. To understand whether acutely generated stroke events lead to a chronic phenotype more closely resembling PSE with recurrent seizures, a limited variety of approaches emerged in early 2000s. These limited methods of causing an occlusion in mice and rats show different infarct size and neurological deficits. The most often employed procedure for inducing focal ischemia is the middle cerebral artery occlusion. This mimics the pathophysiology seen in humans in terms of extent of damage to cortex and striatum. Photothrombosis and endothelin-1 models can similarly evoke episodes of ischemic stroke. These models are well suited to studying mechanisms and biomarkers of epileptogenesis or optimizing novel drug discoveries. However, modeling of PSE is tedious, is highly variable, and lacks validity; therefore, it is not widely implemented in epilepsy research. Moreover, the relevance of ischemic models to specific forms of human stroke remains unclear. Stroke modeling in young male rodents lacks clinical relevance to elderly populations and especially to women, likely as a result of sex differences. Nevertheless, because of the neuronal damage and epileptogenic insult that these models trigger, they are helpful tools in studying acquired epilepsy and prophylactic drug therapy. © 2016 Wiley Periodicals, Inc.

Protective efficacy of a single salvianolic acid A treatment on photothrombosis-induced sustained spatial memory impairments

With respect to the high burden of ischemic stroke and the absence of pharmacological treatment for promoting rehabilitation, promising candidates with specific effects on long-term functional recovery are highly desired. Candidates need reasonable experimental paradigms to evaluate the long-term functional outcome focused on ischemia-induced sensorimotor and memory deficits. "Danshen", a traditional Chinese herb, has long been used to treat coronary and cerebral vascular diseases as well as dementia. Salvianolic acid A (SAA), one of the major active ingredients of Danshen, was demonstrated to be effective in protecting against cerebral ischemic injury. Here, employing an experimental stroke model induced by photothrombosis in the unilateral frontal cortex of rats, we investigated whether SAA has long-term protective effects on ischemia-induced sensorimotor and memory deficits in our behavioral tests. The results indicated that a single SAA treatment improved the cortical ischemia-induced sensorimotor deficits during 15 days' cylinder test period, and alleviated ischemia-induced sustained spatial memory impairments during the 2 months' dependent Morris Water Maze (MWM) tests. In addition, either ischemic injury or SAA treatment did not show any changes compared with sham group in other behavioral tests including rotarod tests, swimming speed in MWM tests, open field tests, elevated plus maze tests, treadmill tests and forced swimming tests. The results reveal that the cognitive deficits are not the results of animal's anxiety or confounding motor impairments. Overall, the present paradigm appears suitable for the preclinical evaluation of the long-term effects of pharmacological treatments on ischemic stroke. Meanwhile, SAA might have therapeutic potential for the treatment of memory deficits associated with ischemic stroke.

Development of epilepsy after ischaemic stroke

For about 30% of patients with epilepsy the cause is unknown. Even in patients with a known risk factor for epilepsy, such as ischaemic stroke, only a subpopulation of patients develops epilepsy. Factors that contribute to the risk for epileptogenesis in a given individual generally remain unknown. Studies in the past decade on epilepsy in patients with ischaemic stroke suggest that, in addition to the primary ischaemic injury, existing difficult-to-detect microscale changes in blood vessels and white matter present as epileptogenic pathologies. Injury severity, location and type of pathological changes, genetic factors, and pre-injury and post-injury exposure to non-genetic factors (ie, the exposome) can divide patients with ischaemic stroke into different endophenotypes with a variable risk for epileptogenesis. These data provide guidance for animal modelling of post-stroke epilepsy, and for laboratory experiments to explore with increased specificity the molecular 'mechanisms, biomarkers, and treatment targets of post-stroke epilepsy in different circumstances, with the aim of modifying epileptogenesis after ischaemic stroke in individual patients without compromising recovery.

Epileptogenesis

Epileptogenesis is a chronic process that can be triggered by genetic or acquired factors, and that can continue long after epilepsy diagnosis. In 2015, epileptogenesis is not a treatment indication, and there are no therapies available in clinic to treat individuals at risk of epileptogenesis. However, thanks to active research, a large number of animal models have become available for search of molecular mechanisms of epileptogenesis. The first glimpses of treatment targets and biomarkers that could be developed to become useful in clinic are in sight. However, the heterogeneity of the epilepsy condition, and the dynamics of molecular changes over the course of epileptogenesis remain as challenges to overcome.

Complex assessment of distinct cognitive impairments following ouabain injection into the rat dorsoloateral striatum

A stroke in humans may induce focal injury to the brain tissue resulting in various disabilities. Although motor deficits are the most discernible, cognitive impairments seem to be crucial for patients mental well-being. The current lack of effective treatments encourages scientists and clinicians to develop novel approaches. Before applying them in clinic, testing for safety and effectiveness in non-human models is necessary. Such animal model should include significant cognitive impairments resulting from brain lesion. We used ouabain stereotactic injection into the right dorsolateral striatum of male Wistar rats, and enriched environment housing. To confirm the brain injury before cognitive testing, rats were given a beam-walking task to evaluate the level of sensorimotor deficits. To determine the cognitive impairment after focal brain damage, rats underwent a set of selected tasks over an observation period of 30 days. Brain injury induced by ouabain significantly impaired the acquisition of the T-maze habit learning task, where 'win-stay' strategy rules were applied. The injured rats also showed significant deficits in the performance of the T-maze switching task, which involved shifting from multiple clues previously relevant to the only one important clue. Focal brain injury also significantly changed 'what--where' memory, tested in the object exploration task, in which a novel object consecutively appeared in the same place while the location of a familiar item was continuously changed. In conclusion, we developed an animal model of distinct cognitive impairments after focal brain injury that provides a convenient method to test the effectiveness of restorative therapies.

Present status and future challenges of electroencephalography- and magnetic resonance imaging-based monitoring in preclinical models of focal cerebral ischemia

Animal models are useful tools for better understanding the mechanisms underlying neurological deterioration after an ischemic insult as well as subsequent evolution of changes and recovery of functions. In response to the updated requirements for preclinical investigations of stroke to include relevant functional measurement techniques and biomarker endpoints, we here review the state of knowledge on application of some translational electrophysiological and neuroimaging methods, and in particular, electroencephalography monitoring and magnetic resonance imaging in rodent models of ischemic stroke. This may lead to improvement of diagnostic methods and identification of new therapeutic targets, which would considerably advance the translational value of preclinical stroke research.

Assessment of behavioral flexibility after middle cerebral artery occlusion in mice

Middle cerebral artery occlusion (MCAO) is the most common animal model of cerebral ischemia and induces various functional impairments. Long-lasting deficits resulting from MCAO however, remain insufficiently characterized, especially regarding cognition. Yet, behavioral flexibility, a prominent cognitive process is found impaired after stroke in humans. We thus used an operant-based task to assess behavioral flexibility in mice after MCAO. Three weeks after 30 min MCAO surgery, mice were subjected to a battery of sensorimotor tests (rotarod, vertical pole test, spontaneous locomotion and grip-strength test). Behavioral flexibility was then assessed in an operant task, in which mice, rewarded according to a FR5 schedule of reinforcement, had to alternate their operant responses between two levers from trial to trial. Regarding sensory and motor functioning, only the pole test yielded a significant difference between MCAO and sham mice. In the operant flexibility task, results showed a behavioral flexibility deficit in MCAO mice; neither the operant response acquisition nor the appeal for food rewards was altered. In conclusion, our operant-based task revealed a long-lasting behavioral flexibility deficit after MCAO in mice.

Transient focal cerebral ischemia induces long-term cognitive function deficit in an experimental ischemic stroke model

Vascular dementia ranks as the second leading cause of dementia in the United States. However, its underlying pathophysiological mechanism is not fully understood and no effective treatment is available. The purpose of the current study was to evaluate long-term cognitive deficits induced by transient middle cerebral artery occlusion (tMCAO) in rats and to investigate the underlying mechanism. Sprague-Dawley rats were subjected to tMCAO or sham surgery. Behavior tests for locomotor activity and cognitive function were conducted at 7 or 30days after stroke. Hippocampal long term potentiation (LTP) and involvement of GABAergic neurotransmission were evaluated at 30days after sham surgery or stroke. Immunohistochemistry and Western blot analyses were conducted to determine the effect of tMCAO on cell signaling in the hippocampus. Transient MCAO induced a progressive deficiency in spatial performance. At 30days after stroke, no neuron loss or synaptic marker change in the hippocampus were observed. LTP in both hippocampi was reduced at 30days after stroke. This LTP impairment was prevented by blocking GABAA receptors. In addition, ERK activity was significantly reduced in both hippocampi. In summary, we identified a progressive decline in spatial learning and memory after ischemic stroke that correlates with suppression of hippocampal LTP, elevation of GABAergic neurotransmission, and inhibition of ERK activation. Our results indicate that the attenuation of GABAergic activity or enhancement of ERK/MAPK activation in the hippocampus might be potential therapeutic approaches to prevent or attenuate cognitive impairment after ischemic stroke.

Sporadic Alzheimer's disease begins as episodes of brain ischemia and ischemically dysregulated Alzheimer's disease genes

The study of sporadic Alzheimer’s disease etiology, now more than ever, needs an infusion of new concepts. Despite ongoing interest in Alzheimer’s disease, the basis of this entity is not yet clear. At present, the best-established and accepted “culprit” in Alzheimer’s disease pathology by most scientists is the amyloid, as the main molecular factor responsible for neurodegeneration in this disease. Abnormal upregulation of amyloid production or a disturbed clearance mechanism may lead to pathological accumulation of amyloid in brain according to the “amyloid hypothesis.” We will critically review these observations and highlight inconsistencies between the predictions of the “amyloid hypothesis” and the published data. There is still controversy over the role of amyloid in the pathological process. A question arises whether amyloid is responsible for the neurodegeneration or if it accumulates because of the neurodegeneration. Recent evidence suggests that the pathophysiology and neuropathology of Alzheimer’s disease comprises more than amyloid accumulation, tau protein pathology and finally brain atrophy with dementia. Nowadays, a handful of researchers share a newly emerged view that the ischemic episodes of brain best describe the pathogenic cascade, which eventually leads to neuronal loss, especially in hippocampus, with amyloid accumulation, tau protein pathology and irreversible dementia of Alzheimer type. The most persuasive evidences come from investigations of ischemically damaged brains of patients and from experimental ischemic brain studies that mimic Alzheimer-type dementia. This review attempts to depict what we know and do not know about the triggering factor of the Alzheimer’s disease, focusing on the possibility that the initial pathological trigger involves ischemic episodes and ischemia-induced gene dysregulation. The resulting brain ischemia dysregulates additionally expression of amyloid precursor protein and amyloid-processing enzyme genes that, in addition, ultimately compromise brain functions, leading over time to the complex alterations that characterize advanced sporadic Alzheimer’s disease. The identification of the genes involved in Alzheimer’s disease induced by ischemia will enable to further define the events leading to sporadic Alzheimer’s disease-related abnormalities. Additionally, knowledge gained from the above investigations should facilitate the elaboration of the effective treatment and/or prevention of Alzheimer’s disease.

Neuroprotection targeting ischemic penumbra and beyond for the treatment of ischemic stroke

Neuroprotection to attenuate or block the ischemic cascade and salvage neuronal damage has been extensively explored for the treatment of ischemic stroke. In the last two decades, neuroprotective strategy has been evolving from targeting a signal pathway in neurons to protecting all neurovascular components and improving cell-cell and cell-extracellular matrix interaction that ultimately benefits the brain recovery after ischemic stroke. The progression from potentially reversible to irreversible injury in the ischemic penumbra has provided the opportunity to develop therapies to attenuate the ischemic stroke damage. Thus, the ischemic penumbra has been the main target for the current neuroprotective intervention. However, despite our increasing knowledge of the physiologic, mechanistic, and imaging characterizations of the ischemic penumbra, no effective neuroprotective therapy has been found so far for the treatment of ischemic stroke. The current acute neuroprotective approach focusing on the damaging mechanisms at the ischemic penumbra is greatly limited by the rapid evolution of the deleterious cascades in the ischemic penumbra. Neuroprotective intervention attempts to promote endogenous repairing in the transition zone of the penumbra for the therapeutic purposes may overcome the unrealistic therapeutic windows under the current neuroprotective strategy. In addition, increasing evidence has indicated ischemic stroke could induce long-lasing cellular and hemodynamic changes beyond the ischemic territory. It is unclear whether and how the global responses induced by the ischemic cascade contribute to the progression of cognitive impairment after ischemic stroke. The prolonged pathophysiological cascades induced by ischemic stroke beyond the ischemic penumbra might provide novel therapeutic opportunities for the neuroprotective intervention, which could prevent or slow down the progression of vascular dementia after ischemic stroke.

The potential for estrogens in preventing Alzheimer's disease and vascular dementia

Estrogens are the best-studied class of drugs for potential use in the prevention of Alzheimer's disease (AD). These steroids have been shown to be potent neuroprotectants both in vitro and in vivo, and to exert effects that are consistent with their potential use in prevention of AD. These include the prevention of the processing of amyloid precursor protein (APP) into beta-amyloid (Aß), the reduction in tau hyperphosphorylation, and the elimination of catastrophic attempts at neuronal mitosis. Further, epidemiological data support the efficacy of early postmenopausal use of estrogens for the delay or prevention of AD. Collectively, this evidence supports the further development of estrogen-like compounds for prevention of AD. Several approaches to enhance brain specificity of estrogen action are now underway in an attempt to reduce the side effects of chronic estrogen therapy in AD.

Experimental approaches to study functional recovery following cerebral ischemia

Valid experimental models and behavioral tests are indispensable for the development of therapies for stroke. The translational failure with neuroprotective drugs has forced us to look for alternative approaches. Restorative therapies aiming to facilitate the recovery process by pharmacotherapy or cell-based therapy have emerged as promising options. Here we describe the most common stroke models used in cell-based therapy studies with particular emphasis on their inherent complications, which may affect behavioral outcome. Loss of body weight, stress, hyperthermia, immunodepression, and infections particularly after severe transient middle cerebral artery occlusion (filament model) are recognized as possible confounders to impair performance in certain behavioral tasks and bias the treatment effects. Inherent limitations of stroke models should be carefully considered when planning experiments to ensure translation of behavioral data to the clinic.

Association of chronic vascular changes with functional outcome after traumatic brain injury in rats

We tested the hypothesis that vascular remodeling in the cortex, hippocampus, and thalamus is associated with long-term functional recovery after traumatic brain injury (TBI). We induced TBI with lateral fluid-percussion (LFP) injury in adult rats. Animals were followed-up for 9 months, during which we tested motor performance using a neuroscore test, spatial learning and memory with a Morris water maze, and seizure susceptibility with a pentylenetetrazol (PTZ) test. At 8 months, they underwent structural MRI, and cerebral blood flow (CBF) was assessed by arterial spin labeling (ASL) MRI. Then, rats were perfused for histology to assess the density of blood vessels. In the perilesional cortex, the CBF decreased by 56% (p < 0.01 compared to controls), and vessel density increased by 28% (p < 0.01). There was a negative correlation between CBF in the perilesional cortex and vessel density (r = -0.75, p < 0.01). However, in the hippocampus, we found a 13% decrease in CBF ipsilaterally (p < 0.05) and 20% contralaterally (p < 0.01), and no change in vessel number. In the ipsilateral thalamus, the increase in CBF (34%, p < 0.01) was associated with a remarkable increase in vessel density (78%, p < 0.01). Animals showed motor impairment that was not associated with vascular changes. Instead, poor performance in the Morris water maze correlated with enhanced thalamic vessel density (r = -0.81, p < 0.01). Finally, enhanced seizure susceptibility was associated with reduced CBF in the ipsilateral hippocampus (r = 0.78, p < 0.05) and increased vascular density in the thalamus (r = 0.69, p < 0.05). There was little interaction between the behavioral measures. The present study demonstrates that each of the investigated brain areas has a unique pattern of vascular abnormalities. Chronic alterations in CBF could not be attributed to changes in vascular density. Association of thalamic hypervascularity to epileptogenesis warrants further studies. Finally, hippocampal hypoperfusion may predict later seizure susceptibility in the LFP injury model of TBI, which could be of value for pre-clinical antiepileptogenesis trials.

Animal modeling of poststroke seizures and epilepsy: 5-year update

Poststroke seizures and epilepsy have been described in numerous clinical and epidemiological studies over many years. In contrast, the pathophysiological events occurring in injured brain that establish poststroke epileptogenesis and epilepsy are not known. However, in the last several years, animal modeling has made significant inroads toward an improved understanding of the progressive biochemical, anatomical, and physiological changes associated with both early and late seizures following stroke. A review of animal studies of poststroke seizures and epilepsy is presented.

Alzheimer's mechanisms in ischemic brain degeneration

There is increasing evidence for influence of Alzheimer's proteins and neuropathology on ischemic brain injury. This review investigates the relationships between beta-amyloid peptide, apolipoproteins, presenilins, tau protein, alpha-synuclein, inflammation factors, and neuronal survival/death decisions in brain following ischemic episode. The interactions of these molecules and influence on beta-amyloid peptide synthesis and contribution to ischemic brain degeneration and finally to dementia are reviewed. Generation and deposition of beta-amyloid peptide and tau protein pathology are important key players involved in mechanisms in ischemic neurodegeneration as well as in Alzheimer's disease. Current evidence suggests that inflammatory process represents next component, which significantly contribute to degeneration progression. Although inflammation was initially thought to arise secondary to ischemic neurodegeneration, recent studies present that inflammatory mediators may stimulate amyloid precursor protein metabolism by upregulation of beta-secretase and therefore are able to establish a vicious cycle. Functional brain recovery after ischemic lesion was delayed and incomplete by an injury-related increase in the amount of the neurotoxic C-terminal of amyloid precursor protein and beta-amyloid peptide. Moreover, ischemic neurodegeneration is strongly accelerated with aging, too. New therapeutic alternatives targeting these proteins and repairing related neuronal changes are under development for the treatment of ischemic brain consequences including memory loss prevention.

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.

Seizure activity in the rat hippocampus, perirhinal and prefrontal cortex associated with transient global cerebral ischemia

Epileptiform EEG activity associated with ischemia can contribute to early damage of hippocampal neurons, and seizure activity may also lead to dysfunction in extrahippocampal regions. In this study, seizure activity associated with the four-vessel occlusion model of cerebral ischemia was monitored using chronically implanted electrodes in the CA1/subicular region, the perirhinal cortex, and the prefrontal cortex of the rat. Background EEG amplitude was reduced in all recording sites during occlusion, but spiking and bursting activity was also observed. Seizure activity occurred in most animals during the first several hours of reperfusion, but was not observed on subsequent days. Epileptiform spikes and bursts were often synchronous between two or three recording sites, and spikes in the CA1 region also often occurred just prior to spikes in other sites. These results demonstrate that the four-vessel occlusion model can lead to patterns of seizure activity in the hippocampus, prefrontal and perirhinal cortices.

A chronic histopathological and electrophysiological analysis of a rodent hypoxic-ischemic brain injury model and its use as a model of epilepsy

Ischemic brain injury is one of the leading causes of epilepsy in the elderly, and there are currently no adult rodent models of global ischemia, unilateral hemispheric ischemia, or focal ischemia that report the occurrence of spontaneous motor seizures following ischemic brain injury. The rodent hypoxic-ischemic (H-I) model of brain injury in adult rats is a model of unilateral hemispheric ischemic injury. Recent studies have shown that an H-I injury in perinatal rats causes hippocampal mossy fiber sprouting and epilepsy. These experiments aimed to test the hypothesis that a unilateral H-I injury leading to severe neuronal loss in young-adult rats also causes mossy fiber sprouting and spontaneous motor seizures many months after the injury, and that the mossy fiber sprouting induced by the H-I injury forms new functional recurrent excitatory synapses. The right common carotid artery of 30-day old rats was permanently ligated, and the rats were placed into a chamber with 8% oxygen for 30 min. A quantitative stereologic analysis revealed that the ipsilateral hippocampus had significant hilar and CA1 pyramidal neuronal loss compared with the contralateral and sham-control hippocampi. The septal region from the ipsilateral and contralateral hippocampus had small but significantly increased amounts of Timm staining in the inner molecular layer compared with the sham-control hippocampi. Three of 20 lesioned animals (15%) were observed to have at least one spontaneous motor seizure 6-12 months after treatment. Approximately 50% of the ipsilateral and contralateral hippocampal slices displayed abnormal electrophysiological responses in the dentate gyrus, manifest as all-or-none bursts to hilar stimulation. This study suggests that H-I injury is associated with synaptic reorganization in the lesioned region of the hippocampus, and that new recurrent excitatory circuits can predispose the hippocampus to abnormal electrophysiological activity and spontaneous motor seizures.

Late-onset epileptogenesis and seizure genesis: lessons from models of cerebral ischemia

Patients surviving ischemic stroke often express delayed epileptic syndromes. Late poststroke seizures occur after a latency period lasting from several months to years after the insult. These seizures might result from ischemia-induced neuronal death and associated morphological and physiological changes that are only partly elucidated. This review summarizes the long-term morphofunctional alterations observed in animal models of both focal and global ischemia that could explain late-onset seizures and epileptogenesis. In particular, this review emphasizes the change in GABAergic and glutamatergic signaling leading to hyperexcitability and seizure genesis.

Early motherhood in rats is associated with a modification of hippocampal function

The transition to motherhood results in a number of hormonal, neurological and behavioral changes necessary to ensure offspring survival. However, little attention has been paid to changes not directly linked to reproductive function in the early mother. In this study, we demonstrate that spatial performances during the learning phase were impaired after the delivery in rats, while spatial retention ability was improved 2 weeks later. In addition, we also report that early motherhood reduced the cell proliferation in the dentate gyrus of the hippocampus without inducing a decrease in the newborn cells 2 weeks later. The decrease of estradiol levels and high levels of glucocorticoids after delivery could in part explain the changes in the hippocampal function. In summary, our findings suggest that early postpartum period is associated with a modification of hippocampal function. This may reflect a homeostatic form of hippocampal plasticity in response to the onset of the maternal experience.

Epileptogenesis after cortical photothrombotic brain lesion in rats

We investigated epileptogenesis after cortical photothrombotic stroke induced with Rose Bengal dye in adult Sprague-Dawley rats. To detect spontaneous seizures, video-electroencephalograms were recorded at 2, 4, 6, 8, and 10 months for 7-14 days (24 h/day). At the end, spatial and emotional learning and memory were assessed using the Morris water-maze and fear-conditioning test, respectively, and the brains were processed for histologic analysis. Seizures were detected in 18% of rats that received photothrombosis. The average seizure frequency was 0.39 seizures per recording day and mean seizure duration was 117 s. Over 60% of seizures occurred during the dark hours. Rats with photothrombotic lesions were impaired in the water-maze (P<0.05) but not in the fear-conditioning test as compared with controls. Histology revealed that lesion depth varied from cortical layers I to VI in photothrombotic rats with epilepsy. Epileptic rats had light mossy fiber sprouting in the inner molecular layer of the dentate gyrus both ipsilateral and contralateral to the lesion. This study extends the current understanding of epileptogenesis and functional impairment after cortical lesions induced by photothrombosis. Our observations support the hypothesis that photothrombotic stroke in rats is a useful animal model for investigating the mechanisms of post-stroke epileptogenesis.

Behavioral tests for preclinical intervention assessment

Select functional outcome tests commonly used for evaluating sensorimotor and cognitive capacity in rodents with focal intracerebral ischemic or hemorrhagic injury are described, along with upgrades and issues of concern for translational research. An emphasis is placed on careful quantitative and qualitative assessment of acute and long-term behavioral deficits, and on avoidance of frequent pitfalls. Methods for detecting different degrees of injury and treatment-related improvements are included. Determining the true potential of an intervention requires a set of behavioral analyses that can monitor compensatory learning. In a number of preclinical outcome tests, animals can develop remarkably effective "tricks" that are difficult to detect but frequently lead to dramatic improvements in performance, particularly with repeated practice. However, some interventions may facilitate learning without promoting brain repair, but these may not translate into a meaningful level of benefit in the clinic. Additionally, it is important to determine whether there are any preinjury functional asymmetries in order to accurately assess damage-related changes in behavior. This is illustrated by the fact that some animals have chronic endogenous asymmetries and that others, albeit infrequently, can sustain a spontaneous cerebral stroke, without any experimental induction, that can lead to chronic deficits as reflected by behavioral, imaging, and histological analyses. Finally, a useful new modification of the water maze that involves moving the platform from trial to trial within the target quadrant is reviewed, and its advantages over the standard version are discussed.

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.

Endovascular middle cerebral artery occlusion in rats as a model for studying vascular dementia

Vascular dementia (VaD), incorporating cognitive dysfunction with vascular disease, ranks as the second leading cause of dementia in the United States, yet no effective treatment is currently available. The challenge of defining the pathological substrates of VaD is complicated by the heterogeneous nature of cerebrovascular disease and coexistence of other pathologies, including Alzheimer's disease (AD) types of lesion. The use of rodent models of ischemic stroke may help to elucidate the type of lesions that are responsible for cognitive impairment in humans. Endovascular middle cerebral artery (MCA) occlusion in rats is considered to be a convenient and reliable model of human cerebral ischemia. Both sensorimotor and cognitive dysfunction can be induced in the rat endovascular MCA occlusion model, yet sensorimotor deficits induced by endovascular MCA occlusion may improve with time, whereas data presented in this review suggest that in rats this model can result in a progressive course of cognitive impairment that is consistent with the clinical progression of VaD. Thus far, experimental studies using this model have demonstrated a direct interaction of cerebral ischemic damage and AD-type neuropathologies in the primary ischemic area. Further, coincident to the progressive decline of cognitive function, a delayed neurodegeneration in a remote area, distal to the primary ischemic area, the hippocampus, has been demonstrated in a rat endovascular MCA occlusion model. We argue that this model could be employed to study VaD and provide insight into some of the pathophysiological mechanisms of VaD.

A simple modification of the water maze test to enhance daily detection of spatial memory in rats and mice

The water maze is one of the most frequently used tools in behavioral neuroscience. Many variations of the water maze task have been used; however, established water maze protocols have several disadvantages. Notably, these protocols demand considerable time to perform reference and probe tests separately. Here, we suggest a modified protocol, which is rapidly performed, is sensitive to cognitive deficits, and can assay reference as well as strategy-switching ability. The platform is relocated randomly within the target quadrant with each training trial. Because the rodents must spend more time searching within the target quadrant, every trial effectively becomes a probe trial. The rodents are then run in the switching strategy test, where the platform is randomly placed along the wall of the pool. The best new strategy would thus be to search along the walls of the pool systematically. The percent distance traveled and time spent near the wall is evaluated across trials, as is the distance traveled and time spent in the previously correct quadrant. In this way one can assess whether the rodent is continuing to search in the older platform location (i.e., displaying a strategy-switching problem) or whether it has successfully adopted a new search strategy.

Epileptogenesis after experimental focal cerebral ischemia

Cerebrovascular diseases are one of the most common causes of epilepsy in adults, and the incidence of stroke-induced epileptogenesis is increasing as the population ages. The mechanisms that lead to stroke-induced epileptogenesis in a subpopulation of patients, however, are still poorly understood. Recent advances in inducing epileptogenesis in rodent focal ischemia models have provided tools that can be used to identify the risk factors and neurobiologic changes leading to development of epilepsy after stroke. Here we summarize data from models in which epileptogenesis has been studied after focal ischemia; photothrombosis, middle cerebral artery (MCA) occlusion with filament, and endothelin-1-induced MCA occlusion. Analysis of the data indicates that neurobiologic changes occurring during stroke-induced epileptogenesis share some similarities to those induced by status epilepticus or traumatic brain injury.

Basic research in epilepsy and aging

A PubMed search of the years 1965 to 2003 found only 30 articles that were directly related to modeling seizures or epilepsy in aged animals. This lack of research is disturbing but explainable because of the high cost of aged animals and their increasing infirmity. Many changes occur in the older brain: cell loss in the hippocampal formation, changes in long-term potentiation maintenance, alteration in kindling, increased susceptibility to status epilepticus, and neuronal damage from stroke. The effect of aging on voltage-gated sodium and calcium channels has not been studied sufficiently. With increasing numbers of elderly persons with epilepsy needing appropriate treatment, the need to better understand the basic mechanisms of epilepsy is crucial.

Electrobehavioral characteristics of epileptic rats following photothrombotic brain infarction

The goal of this study was to characterize the electroencephalographic (EEG) and behavioral properties of young adult rats during extended video-EEG monitoring following photothrombotic brain infarction. Two-month-old male Sprague-Dawley rats underwent photothrombotic brain infarction of the left sensorimotor cortex with the photosensitive dye rose bengal (n=10) or were used as controls (n=9). Qualitative and quantitative EEG analysis was performed on digital video-EEG records obtained during 6 months of recording. The main finding of this study was that 5/10 (50%) lesioned animals developed focal epileptic seizures ipsilateral to the cortical infarct characterized by rhythmic spike-wave discharges with or without behavioral change. Epileptic animals demonstrated increased delta, theta, and low beta-range power ipsilateral to the infarct that reliably distinguished them from lesioned nonepileptic and control animals. Lesioned animals (epileptic and nonepileptic) also demonstrated a distinct pattern of focal rhythmic theta activity before or after generalized high beta-range discharges. Electrical and behavioral characteristics common to both lesioned and control animals included: (1) focal rhythmic theta activity in either hemisphere; (2) focal low beta-range discharges in either hemisphere; (3) generalized high beta-range discharges; (4) absence seizures; (5) generalized pseudoperiodic spike discharges associated with mild multifocal body jerks; (6) tonic-clonic seizures (one nai;ve control; one lesioned animal). Cresyl violet staining of lesioned animals' brains showed consistent infarcts of the sensorimotor cortex extending to the subcortical white matter. These results provide an expanded electrobehavioral description of young adult rats following photothrombotic brain infarction and augment further investigation into the molecular, cellular, and network alterations that contribute to the establishment of post-stroke epilepsy.