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

Preclinical examination of early-onset thalamic-cortical seizures after hemispheric stroke

OBJECTIVE

Ischemic stroke is one of the main causes of death and disability worldwide and currently has limited treatment options. Electroencephalography (EEG) signals are significantly affected in stroke patients during the acute stage. In this study, we preclinically characterized the brain electrical rhythms and seizure activity during the hyperacute and late acute phases in a hemispheric stroke model with no reperfusion.

METHODS

EEG signals and seizures were studied in a model of hemispheric infarction induced by permanent occlusion of the middle cerebral artery (pMCAO), which mimics the clinical condition of stroke patients with permanent ischemia. Electrical brain activity was also examined using a photothrombotic (PT) stroke model. In the PT model, we induced a similar (PT group-1) or smaller (PT group-2) cortical lesion than in the pMCAO model. For all models, we used a nonconsanguineous mouse strain that mimics human diversity and genetic variation.

RESULTS

The pMCAO hemispheric stroke model exhibited thalamic-origin nonconvulsive seizures during the hyperacute stage that propagated to the thalamus and cortex. The seizures were also accompanied by progressive slowing of the EEG signal during the acute phase, with elevated delta/theta, delta/alpha, and delta/beta ratios. Cortical seizures were also confirmed in the PT stroke model of similar lesions as in the pMCAO model, but not in the PT model of smaller injuries.

SIGNIFICANCE

In the clinically relevant pMCAO model, poststroke seizures and EEG abnormalities were inferred from recordings of the contralateral hemisphere (noninfarcted hemisphere), emphasizing the reciprocity of interhemispheric connections and that injuries affecting one hemisphere had consequences for the other. Our results recapitulate many of the EEG signal hallmarks seen in stroke patients, thereby validating this specific mouse model for the examination of the mechanistic aspects of brain function and for the exploration of the reversion or suppression of EEG abnormalities in response to neuroprotective and anti-epileptic therapies.

Can Old Animals Reveal New Targets? The Aging and Degenerating Brain as a New Precision Medicine Opportunity for Epilepsy

Older people represent the fastest growing group with epilepsy diagnosis. For example, cerebrovascular disease may underlie roughly 30-50% of epilepsy in older adults and seizures are also an underrecognized comorbidity of Alzheimer's disease (AD). As a result, up to 10% of nursing home residents may take antiseizure medicines (ASMs). Despite the greater incidence of epilepsy in older individuals and increased risk of comorbid seizures in people with AD, aged animals with seizures are strikingly underrepresented in epilepsy drug discovery practice. Increased integration of aged animals into preclinical epilepsy drug discovery could better inform the potential tolerability and pharmacokinetic interactions in aged individuals as the global population becomes increasingly older. Quite simply, the ASMs on the market today were brought forth based on efficacy in young adult, neurologically intact rodents; preclinical information concerning the efficacy and safety of promising ASMs is not routinely evaluated in aged animals. Integrating aged animals more often into basic epilepsy research may also uncover novel treatments for hyperexcitability. For example, cannabidiol and fenfluramine demonstrated clear efficacy in syndrome-specific pediatric models that led to a paradigm shift in the perceived value of pediatric models for ASM discovery practice; aged rodents with seizures or rodents with aging-related neuropathology represent an untapped resource that could similarly change epilepsy drug discovery. This review, therefore, summarizes how aged rodent models have thus far been used for epilepsy research, what studies have been conducted to assess ASM efficacy in aged rodent seizure and epilepsy models, and lastly to identify remaining gaps to engage aging-related neurological disease models for ASM discovery, which may simultaneously reveal novel mechanisms associated with epilepsy.

Seizures and Interictal Epileptiform Activity in the Rat Collagenase Model for Intracerebral Hemorrhage

Aims

Intracerebral hemorrhage (ICH) is a known risk factor for the development of acute symptomatic as well as late unprovoked seizures. The underlying pathophysiology of post-ICH seizures is incompletely understood and there are no reliable predictive biomarkers. An animal model to study post-ICH seizures is currently lacking. The aim of this study was to investigate (1) the occurrence of seizures and interictal epileptiform activity in the ICH rat collagenase model using long-term video-EEG monitoring (VEM) and (2) whether seizure occurrence was associated with interictal epileptiform activity and histological features.

Methods

Male Sprague-Dawley rats were implanted with epidural electrodes. After 1 week of baseline VEM, collagenase was injected in left striatum to induce an ICH. VEM was continued for 180 days to assess the occurrence of post-ICH seizures and interictal epileptiform activity (spikes and epileptiform discharges). At the end of the experiment, animals were euthanized for histological characterization of the hemorrhagic lesion, using cresyl violet, Prussian blue and immunofluorescence staining.

Results

Acute symptomatic seizures occurred in 4/12 animals between 46 and 80 h after ICH induction. Late unprovoked seizures were present in 2/12 animals and started at 90 and 103 days post-ICH. Animals with late unprovoked seizures did not have acute symptomatic seizures. All electrographic seizures were accompanied by clear behavioral changes. Interictal spikes and epileptiform discharges were observed in all animals but occurred more frequently in rats with late seizures (p = 0.019 and p < 0.001, respectively). Animals with acute symptomatic seizures had more extended hemorrhagic lesions and hemosiderin deposits in the piriform cortex.

Conclusion

Both acute symptomatic and late unprovoked seizures were observed in the rat collagenase model. Interictal epileptiform activity was more frequently seen in animals with late seizures. Rats with acute symptomatic seizures showed more extensive lesions and hemosiderin deposits in the piriform cortex. This model could be used to further explore possible biomarkers for epileptogenesis.

Abnormalities of Cortical Sources of Resting State Delta Electroencephalographic Rhythms Are Related to Epileptiform Activity in Patients With Amnesic Mild Cognitive Impairment Not Due to Alzheimer's Disease

In the present exploratory and retrospective study, we hypothesized that cortical sources of resting state eyes-closed electroencephalographic (rsEEG) rhythms might be more abnormal in patients with epileptiform EEG activity (spike-sharp wave discharges, giant spikes) and amnesic mild cognitive impairment not due to Alzheimer's disease (noADMCI-EEA) than matched noADMCI patients without EEA (noADMCI-noEEA). Clinical, neuroimaging, neuropsychological, and rsEEG data in 32 noADMCI and 30 normal elderly (Nold) subjects were available in a national archive. Age, gender, and education were carefully matched among them. No subject had received a clinical diagnosis of epilepsy. Individual alpha frequency peak (IAF) was used to determine the delta, theta, and alpha frequency bands of rsEEG rhythms. Fixed beta and gamma bands were also considered. Regional rsEEG cortical sources were estimated by eLORETA freeware. Area under receiver operating characteristic (AUROC) curves indexed the accuracy of eLORETA solutions in the classification between noADMCI-EEA and noADMCI-noEEA individuals. As novel findings, EEA was observed in 41% of noADMCI patients. Furthermore, these noADMCI-EEA patients showed higher temporal delta source activities as compared to noADMCI-no EEA patients and Nold subjects. Those activities discriminated individuals of the two NoADMCI groups with an accuracy of about 70%. The significant percentage of noADMCI-EEA patients showing EEA and marked abnormalities in temporal rsEEG rhythms at delta frequencies suggest a substantial role of underlying neural hypersynchronization mechanisms in their brain dysfunctions.

Modulation of TRPV4 and BKCa for treatment of brain diseases

As a member of transient receptor potential family, the transient receptor potential vanilloid 4 (TRPV4) is a kind of nonselective calcium-permeable cation channel, which belongs to non-voltage gated Ca²⁺ channel. Large-conductance Ca²⁺-activated K⁺ channel (BKCa) represents a unique superfamily of Ca²⁺-activated K⁺ channel (KCa) that is both voltage and intracellular Ca²⁺ dependent. Not surprisingly, aberrant function of either TRPV4 or BKCa in neurons has been associated with brain disorders, such as Alzheimer's disease, cerebral ischemia, brain tumor, epilepsy, as well as headache. In these diseases, vascular dysfunction is a common characteristic. Notably, endothelial and smooth muscle TRPV4 can mediate BKCa to regulate cerebral blood flow and pressure. Therefore, in this review, we not only discuss the diverse functions of TRPV4 and BKCa in neurons to integrate relative signaling pathways in the context of cerebral physiological and pathological situations respectively, but also reveal the relationship between TRPV4 and BKCa in regulation of cerebral vascular tone as an etiologic factor. Based on these analyses, this review demonstrates the effective mechanisms of compounds targeting these two channels, which may be potential therapeutic strategies for diseases in the brain.

Younger age at stroke onset but not thrombolytic treatment predicts poststroke epilepsy: An updated meta-analysis

AIMS

Stroke is the most commonly identified cause of late-onset epilepsy. Risk factors for poststroke epilepsy (PSE) are partially elucidated, and many studies have been performed in recent years. We aimed to update our previous systematic review and meta-analysis on risk factors for PSE.

METHODS

PubMed, Google Scholar, and Scopus databases were searched. Articles published in English (1987-2019) were included. Odds ratios (OR) and mean values were calculated for examined variables.

RESULTS

Thirty studies with different designs were included, enrolling 26,045 patients who experienced stroke, of whom 1800 had PSE, corresponding to a prevalence of 7%. Cortical lesions (OR: 3.58, 95% confidence interval (CI): 2.35-5.46, p < 0.001), hemorrhagic component (OR: 2.47, 95% CI: 1.68-3.64, p < 0.001), early seizures (ES) (OR: 4.88, 95% CI: 3.08-7.72, p < 0.001), and younger age at stroke onset (difference in means: 2.97 years, 95% CI: 0.78 to 5.16, p = 0.008) favor PSE. Sex and acute treatment with recombinant tissue plasminogen activator (rtPA) do not predict the occurrence of PSE.

CONCLUSION

Despite limitations due to the uneven quality and design of the studies, the present meta-analysis confirms that cortical involvement, hemorrhagic component, and ES are associated with a higher risk of PSE. In this update, younger age at stroke onset but not thrombolytic treatment seems to increase the risk for PSE. This article is part of the Special Issue "Seizures & Stroke".

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".

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.

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.