Epilepsy and epileptiform activity in late-onset Alzheimer disease: clinical and pathophysiological advances, gaps and conundrums

Role of Ion Channels in Alzheimer's Disease Pathophysiology

Ion channels play an integral role in the normal functioning of the brain. They regulate neuronal electrical properties like synaptic activity, generation of action potentials, maintenance of resting membrane potential and neuronal plasticity, and modulate the physiology of non-neuronal cells like astrocytes and microglia. Dysregulation of ionic homeostasis and channelopathies are associated with various neurological disorders, including Alzheimer's disease (AD). Several families of ion channels are associated with AD pathophysiology and progression. In this review, we outline the current research centered around ion channel dysregulation during AD and discuss briefly the possibility of using ion channels as therapeutic targets.

Epileptic variant in the spectrum of Alzheimer's disease - practical implications

Alzheimer's disease (AD) is known to be associated with an increased risk of epilepsy, which is not exclusively related to the late stage of the disease - when a major cognitive impairment is observed, previously known as the dementia stage - but also to its prodromal stage (mild cognitive impairment). Moreover, published case reports and cohorts have shown that epilepsy may occur even earlier, at the preclinical stage of AD: Epileptic seizures may therefore be the sole objective manifestation of the disease. Such a situation is called the epileptic variant of AD (evAD). EvAD is one of the etiologies of late-onset epilepsy, which means that it carries a risk of later progression to dementia and that it can only be diagnosed by assessing amyloid and tau biomarkers. However, evAD is a window of therapeutic opportunity that is probably optimal for preventing, through antiseizure medication treatment, the accelerated cognitive decline associated with AD-related brain hyperexcitability (manifested by seizures or interictal epileptiform activities).

Epilepsy and Alzheimer disease: New insights and perspectives

Numerous epidemiological and pathophysiological arguments suggest a bidirectional link between late-onset epilepsy and Alzheimer's disease. However, the temporal and causal relationship between the pathophysiological processes underlying these two conditions remains unclear. It is likely that these connections are complex, requiring consideration of various scenarios of causality and reciprocity. In the absence of targeted therapies that effectively address the progression of both diseases, specific measures can be taken to improve patient care. These include screening for cognitive disorders in patients with late-onset epilepsy, detecting subclinical EEG activity in patients with Alzheimer's disease, and identifying and managing cardiovascular risk factors in both populations. Looking ahead, it is evident that global population aging and the potential demographic surge in these two patient groups will necessitate greater efforts to raise awareness and enhance the training of physicians and healthcare professionals in the emerging field of "epileptogeriatrics".

Functional imaging in late-onset epilepsy: A focused review

INTRODUCTION

About 25 % of new-onset epilepsies are diagnosed after age 65. Late-onset epilepsy (LOE) is predicted to become a major healthcare problem in the next 15 years as the global population increases and ages. Neurodegenerative disorders account for 10-20 % of LOE, while over 20 % of these patients have an unknown etiology. Established diagnostic tools such as FDG-PET and novel biomarkers of neurodegeneration including amyloid and tau PET hold a lot of promise in diagnosing and ruling out neurodegenerative disorders in these patients.

METHODS

We conducted a literature search to identify articles involving LOE populations and using one or more functional neuroimaging techniques.

RESULTS

A total of 5 studies were identified through Boolean searching and snowballing. These were highly heterogenous with respect to operational definitions of LOE, analyses and interpretation pipelines.

CONCLUSION

While there is some evidence for feasibility and usefulness of FDG- and Amyloid PET in LOE, methodological heterogeneities in the available literature preclude any notable conclusions. Future research in this field will benefit from a consensus on epilepsy-specific analysis and interpretation guidelines for amyloid and tau PET.

Cleavage of the TrkB-FL receptor during epileptogenesis: insights from a kainic acid-induced model of epilepsy and human samples

Brain-derived neurotrophic factor (BDNF) is essential for neuronal survival, differentiation, and plasticity. In epilepsy, BDNF exhibits a dual role, exerting both antiepileptic and pro-epileptic effects. The cleavage of its main receptor, full-length tropomyosin-related kinase B (TrkB-FL), was suggested to occur in status epilepticus (SE) in vitro. Moreover, under excitotoxic conditions, TrkB-FL was found to be cleaved, resulting in the formation of a new intracellular fragment, TrkB-ICD. Thus, we hypothesized that TrkB-FL cleavage and TrkB-ICD formation could represent an uncovered mechanism in epilepsy. We used a rat model of mesial temporal lobe epilepsy (mTLE) induced by kainic acid (KA) to investigate TrkB-FL cleavage and TrkB-ICD formation during SE (∼3 h after KA) and established epilepsy (EE) (4-5 weeks after KA). Animals treated with 10 mg/kg of KA exhibited TrkB-FL cleavage during SE, with hippocampal levels of TrkB-FL and TrkB-ICD correlating with seizure severity. Notably, TrkB-FL cleavage and TrkB-ICD formation were also detected in animals with EE, which exhibited spontaneous recurrent convulsive seizures, neuronal death, mossy fiber sprouting, and long-term memory impairment. Importantly, hippocampal samples from patients with refractory epilepsy also showed TrkB-FL cleavage with increased TrkB-ICD levels. Additionally, lentiviral-mediated overexpression of TrkB-ICD in the hippocampus of healthy mice and rats resulted in long-term memory impairment. Our findings suggest that TrkB-FL cleavage and the subsequent TrkB-ICD production occur throughout epileptogenesis, with the extent of cleavage correlating positively with seizure occurrence. Moreover, we found that TrkB-ICD overexpression impairs memory. This work uncovers a novel mechanism in epileptogenesis that could serve as a potential therapeutic target in mTLE, with implications for preserving cognitive function.

Astrocyte-synapse structural plasticity in neurodegenerative and neuropsychiatric diseases

Synaptic dysfunction is a common feature across a broad spectrum of brain diseases, spanning from psychopathologies such as post-traumatic stress disorder (PTSD) and substance use disorders (SUD) to neurodegenerative diseases like Alzheimer's and Parkinson's disease (AD and PD). While neuroscience research aiming to understand the mechanisms underlying synaptic dysfunction has traditionally focused on the neuronal elements of the synapse, recent research increasingly acknowledges the contribution of astrocytes as a third element controlling synaptic transmission. This also sparked interest to investigate the tripartite synapse and its role in the etiology of neurological diseases. According to recent evidence, changes in the structural interaction between astrocytes and synapses not only play a pivotal role in modulating synaptic function and behavioral states, but are also implicated in the initiation and progression of various brain diseases. This review aims to integrate recent findings that provide insight into the molecular mechanisms underpinning astrocytic structural changes at the synapse. We offer a comprehensive discussion of the potential implications of compromised astrocyte-synapse interactions, and put forward that astrocytic synaptic coverage is generally reduced in numerous neurological disorders, with the extent of it being disease- and stage- specific. Finally, we propose outstanding questions on astrocyte-synapse structural plasticity that are relevant for future therapeutic strategies to tackle neurodegenerative and neuropsychiatric diseases.

Do Seizures Damage the Brain?-Cumulative Effects of Seizures and Epilepsy: A 2025 Perspective

In 1885, William Gowers proposed that epilepsy is a progressive disease, based on clinical evidence before any effective treatments were available. His long-standing hypothesis has been summarized with the statement "seizures beget seizures." Whether this is the case and related questions about seizure-induced modification and damage of brain circuits are of fundamental importance for neurobiological understanding of epilepsy, development of effective treatment strategies, clinical management, and prognostication. Consensus about progression and seizure-induced damage has remained controversial. Here, we critically review these long-standing questions, incorporating perspectives about perceived inconsistencies in past studies, potential implications of recent longitudinal imaging and cognitive studies, and emphasize experimental and clinical gaps that have proved challenging. Answers to these questions are important for development of management strategies to achieve prompt effective acute control of seizures and prevention of their potential recurrence and long-term comorbidities.

Polygenic score analysis identifies distinct genetic risk profiles in Alzheimer's disease comorbidities

Alzheimer's disease (AD) is usually accompanied by comorbidities such as type 2 diabetes (T2D), epilepsy, major depressive disorder (MDD), and migraine headaches (MH) that can significantly affect patient management and progression. As AD, these comorbidities have their own cumulative common genetic risk component that can be explored in a single individual through polygenic scores. Utilizing data from the UK Biobank, we investigated the correlation between polygenic scores (PGS) for these comorbidities and their actual presentation in AD patients. We show that individuals with higher PGS values showed an elevated risk of developing T2D (OR 2.1, p = 1.07 × 10-11) and epilepsy (OR 1.5, p = 0.0176). High T2D-PGS is also associated with an earlier AD onset in individuals at high genetic risk for AD (AD-PGS). In contrast, no significant genetic associations were found for MDD and MH. Our findings show distinct common genetic risk factors for T2D and epilepsy carried by AD patients that are associated with increased prevalence and earlier disease onset. These results highlight the contribution of common genetic variation to the broader clinical landscape of AD and will contribute to future tailored patient management strategies for individuals at high genetic risk.

Alpha rhythm and Alzheimer's disease: Has Hans Berger's dream come true?

In this "centenary" paper, an expert panel revisited Hans Berger's groundbreaking discovery of human restingstate electroencephalographic (rsEEG) alpha rhythms (8-12 Hz) in 1924, his foresight of substantial clinical applications in patients with "senile dementia," and new developments in the field, focusing on Alzheimer's disease (AD), the most prevalent cause of dementia in pathological aging. Clinical guidelines issued in 2024 by the US National Institute on Aging-Alzheimer's Association (NIA-AA) and the European Neuroscience Societies did not endorse routine use of rsEEG biomarkers in the clinical workup of older adults with cognitive impairment. Nevertheless, the expert panel highlighted decades of research from independent workgroups and different techniques showing consistent evidence that abnormalities in rsEEG delta, theta, and alpha rhythms (< 30 Hz) observed in AD patients correlate with wellestablished AD biomarkers of neuropathology, neurodegeneration, and cognitive decline. We posit that these abnormalities may reflect alterations in oscillatory synchronization within subcortical and cortical circuits, inducing cortical inhibitory-excitatory imbalance (in some cases leading to epileptiform activity) and vigilance dysfunctions (e.g., mental fatigue and drowsiness), which may impact AD patients' quality of life. Berger's vision of using EEG to understand and manage dementia in pathological aging is still actual.

Predictors of status epilepticus among older adults - a prospective real-world study

Data on status epilepticus (SE) in older inpatients is limited.

AIM

To assess SE characteristics and etiologies, and identify risk factors for SE in a cohort of hospitalized patients.

METHODS

We selected patients aged ≥ 60 years with late-onset seizures from a tertiary center. We analyzed demographics, clinical characteristics, etiology of seizures, neurological diseases, and comorbidities. We performed the Kaplan-Meier analysis to examine acute symptomatic and unprovoked seizures and multivariate logistic regression to identify risk factors for SE.

RESULTS

We enrolled 236 patients (mean age: 77.1 ± 9.7 years [SD]) with acute symptomatic seizures, unprovoked seizures and both. SE occurred in 61 (25.8 %) patients. The mean age at the first-ever seizure was 76.5 ± 9.8 years. Females comprised 62.3 % of the patients in the SE group. Convulsive SE was the most common presentation (80.3 %). Cerebrovascular disorders were the most common etiology (27.9 %) among patients with SE. The likelihood of SE occurring was similar between patients with acute symptomatic seizures alone or in combination with unprovoked seizures (118/50 %), and those with unprovoked seizures (118/50 %). Dyslipidemia negatively correlated with SE (OR 0.45 [95 % CI, 0.24-0.85]; p = 0.014), perhaps due to statin use. Psychiatric disorders (OR 2.76 [95 % CI, 1.45-5.24]; p = 0.002;), sepsis (OR 2.33 [95 % CI, 1.13-4.79]; p = 0.021), and congestive heart failure (OR 2.95 [95 % CI,1.07-8.12]; p = 0.036) were risk factors for SE.

CONCLUSION

We identified older inpatients who developed SE, their characteristics, and the risk factors for developing SE.

Disrupted astrocyte-neuron signaling reshapes brain activity in epilepsy and Alzheimer's disease

Astrocytes establish dynamic interactions with surrounding neurons and synchronize neuronal networks within a specific range. However, these reciprocal astrocyte-neuronal interactions are selectively disrupted in epilepsy and Alzheimer's disease (AD), which contributes to the initiation and progression of network hypersynchrony. Deciphering how disrupted astrocyte-neuronal signaling reshapes brain activity is crucial to prevent subclinical epileptiform activity in epilepsy and AD. In this review, we provide an overview of the diverse astrocyte-neuronal crosstalk in maintaining of network activity via homeostatic control of extracellular ions and transmitters, synapse formation and elimination. More importantly, since AD and epilepsy share the common symptoms of neuronal hyperexcitability and astrogliosis, we then explore the crosstalk between astrocytes and neurons in the context of epilepsy and AD and discuss how these disrupted interactions reshape brain activity in pathological conditions. Collectively, this review sheds light on how disrupted astrocyte-neuronal signaling reshapes brain activity in epilepsy and AD, and highlights that modifying astrocyte-neuronal signaling could be a therapeutic approach to prevent epileptiform activity in AD.

Association between glymphatic system function and cognitive impairment in elderly patients with late-onset epilepsy

PURPOSE

Recent studies have shown that late-onset epilepsy (LOE) is accompanied with cognitive decline and increased risk of dementia, particularly Alzheimer's disease (AD). However, the pathophysiological mechanism underlying the cognitive decline in LOE remains unclear. The aim of current study was to evaluate the relationship between glymphatic system (GS) function and cognitive decline in LOE patients using the diffusion tensor imaging (DTI) analysis along the perivascular space (DTI-ALPS).

METHODS

Medical records and neuro-imaging data were obtained from 21 LOE patients with cognitive decline, 14 LOE patients without cognitive decline, and 20 age- and sex-matched healthy controls (HCs). Plasma biomarkers including Aβ42 and Aβ40 were examined using single-molecule array (Simoa) assays. The DTI-ALPS parameter was calculated and correlated with the clinical characteristics of LOE, including age, seizure frequency, duration of epilepsy, Mini-Mental State Examination (MMSE), and Aβ42/40. Regression models were used to evaluate the influencing factors of DTI-ALPS index.

RESULTS

LOE patients exhibited a decreased ALPS index and Aβ42/40 compared with the HCs. Post-hoc analysis indicated that the DTI-ALPS index and Aβ42/40 in LOE patients with cognitive decline was significantly lower in relative to LOE patients without cognitive decline and HCs. Spearman correlations showed a negative correlation between DTI-ALPS index and age, seizure frequency and disease duration while a positive correlations between the DTI-ALPS index and Aβ42/40 and MMSE scores in LOE patients. Linear regression analysis suggested that the DTI-ALPS index was independently related to age, Aβ42/40 and MMSE score after correcting for gender, education, and vascular risk factors.

CONCLUSION

Our findings using DTI-ALPS method found a positive correlation between cognitive decline and GS dysfunction in LOE patients, and may indicate a potential internal link between age-related LOEU and dementia formation. Therefore, the DTI-ALPS index may serve as a potential imaging marker for diagnosing and monitoring the GS function in LOE patients.

Clinical features and outcomes of late-onset epilepsy of unknown etiology: A retrospective study in West China

PURPOSE

Late-onset epilepsy (LOE) usually refers to the development of epilepsy at the age of 50 years or older. Approximately 20 % of LOE cases are diagnosed as late-onset epilepsy of unknown etiology (LOUE) due to a lack of an identifiable cause. The aim of this study was to investigate the clinical features, seizure and cognitive outcomes of patients with LOUE in West China.

METHODS

Patients diagnosed with LOUE at West China Hospital between January 2015 and December 2022 were retrospectively recruited. The seizure and cognitive outcome were followed up for at least 1 year after discharge. Logistic regression models were applied to investigate the risk factors of recurrent seizure and cognitive impairment in patients with LOUE.

RESULTS

We included 286 LOUE patients with a median seizure onset age of 59 years. The most common seizure types were focal to bilateral tonic-clonic seizure (61.9 %) and focal non-motor seizure (37.0 %). Two-hundred and seventy-seven (96.9 %) patients underwent video electroencephalography (VEEG), with seizures recorded in 11.9 % of patients and interictal epileptiform discharges in 58.2 % cases. Majority of the patients (73.4 %) received monotherapy, with levetiracetam, oxcarbazepine and valproate being the most commonly prescribed anti-seizure medications. During the follow-up, 69.1 % of patients achieved seizure-free. Multivariate analysis identified ictal event recorded during VEEG monitoring (OR:0.205, 95 % CI: 0.045-0.932, p = 0.040) and memory impairment (OR:2. 470, 95 % CI: 1.181-5.167, p = 0.016) as significant factors associated with recurrent seizure. Twenty-two patients were classified as cognitive impairment. The onset age (OR:1.095, 95 % CI:1.032-1.162, p = 0.003) and total Fazekas score (OR = 6.770, 95 % CI:1.972-23.241, p = 0.002) were significant risk factors associated with cognitive dysfunction.

CONCLUSION

LOUE is generally a benign form of epilepsy with a high percentage of patients achieving seizure-free status. However, these patients are at a higher risk of memory decline and cognitive dysfunction.

The Bidirectional Relationship Between Epilepsy and Alzheimer's Disease

PURPOSE OF REVIEW

Epilepsy has long been considered a late-stage consequence of Alzheimer's Disease (AD), but recent studies highlight its role early in the disease process, even preceding cognitive symptoms. Population studies reveal a two- to fourfold increased epilepsy risk in AD, particularly in early-onset cases, with seizures clustering around diagnosis. Furthermore, individuals with late-onset unexplained epilepsy have an elevated risk of developing mild cognitive impairment and dementia, underscoring a bidirectional relationship between AD and epilepsy.

RECENT FINDINGS

Experimental models support this connection, demonstrating amyloid and tau pathology-induced hyperexcitability at pre-symptomatic stages, implicating soluble Aβ oligomers and inhibitory interneuron dysfunction in excitatory/inhibitory imbalance. Subclinical or clinical epileptiform activity, detectable in 20-50% of AD patients, is associated with cognitive decline, possibly due to sleep-related memory consolidation disruption. Emerging biomarkers, such as TIRDA and high-frequency oscillations, show promise for early detection and intervention. Anti-seizure medications (ASMs), particularly low-dose levetiracetam, show potential not only for seizure control but also for mitigating amyloid deposition, tau hyperphosphorylation, and cognitive decline. However, treatment complexities remain due to variable ASM efficacy, age-related side effects, and limited clinical trials. The bidirectional nature of AD and epilepsy emphasizes the need for integrated diagnostics, including EEG and biomarker assessments, to guide early intervention and targeted therapies. Future research should focus on the mechanistic interplay between amyloid, tau, and hyperexcitability, alongside trials of ASM regimens, to refine therapeutic strategies and improve outcomes in this population.

Timing of risk factors, prodromal features, and comorbidities of dementia from a large health claims case-control study

BACKGROUND

Many risk factors for dementia have been identified, but the timing of risk is less well understood. Here, we analyzed risk factors in a case-control study covering 10 years before an incident dementia diagnosis.

METHODS

We designed a case-control study using insurance claims of outpatient consultations of patients with German statutory health insurance between January 1, 2012, and December 31, 2022. We included patients with an incident diagnosis of dementia and controls without a diagnosis of dementia matched 1:2 for age, sex, region, and earliest year of outpatient encounter. We selected exposures based on previous systematic reviews, case-control and cohort studies reporting on risk factors, comorbidities, and prodromal features of dementia. We calculated the prevalence of risk factors in cases and controls and odds ratios for each year before the index date, along with Bonferroni-corrected confidence intervals, using conditional logistic regression.

RESULTS

We identified a total of 1,686,759 patients with incident dementia (mean (SD) age, 82.15 (6.90) years; 61.70% female) and 3,373,518 matched controls (mean (SD) age, 82.15 (6.90) years; 61.70% female). Study participants were followed up for a mean (SD) of 6.6 (2.3) years. Of the 63 risk factors and prodromal features examined, 56 were associated with an increased risk of dementia in all years during the 10th and the 1st year before the index date. These included established risk factors, such as depression, hypertension, hearing impairment, nicotine and alcohol abuse, obesity, hypercholesterolaemia, traumatic brain injury, and diabetes. The greatest risk, with odds ratios greater than 2.5, was conferred by delirium, memory impairment, mental retardation, personality and behavioral disorders, sensory disorders, schizophrenia, and psychosis. Cancer was associated with a reduced risk of dementia.

CONCLUSIONS

This large case-control study confirmed established risk factors of dementia. In addition, the study identified non-specific diagnoses that showed a steep increase in risk close to the index date, such as psychosis, conduct disorder, and other sensory disorders. Consideration of these diagnoses, which may represent prodromal features rather than risk factors for dementia, may help to identify people with dementia in routine care.

Late-onset temporal lobe epilepsy: insights from brain atrophy and Alzheimer's disease biomarkers

Considering the growing age of the world population, the incidence of epilepsy in older adults is expected to increase significantly. It has been suggested that late-onset temporal lobe epilepsy (LO-TLE) may be neurodegenerative in origin and overlap with Alzheimer's disease (AD). Herein, we aimed to characterize the pattern of cortical atrophy and CSF biomarkers of AD (total and phosphorylated tau and amyloid-β) in a selected population of LO-TLE of unknown origin. We prospectively enrolled individuals with temporal lobe epilepsy onset after the age of 50 and no cognitive impairment. They underwent a structural MRI scan and CSF biomarkers measurement. Imaging and biomarkers data were compared to three retrospectively collected groups: (i) age-sex-matched healthy controls; (ii) patients with mild cognitive impairment (MCI) and abnormal CSF AD biomarkers (MCI-AD); and (iii) patients with MCI and normal CSF AD biomarkers (MCI-noAD). From a pool of 52 patients, 20 consecutive eligible LO-TLE patients with a mean disease duration of 1.8 years were recruited. As control populations, 25 patients with MCI-AD, 25 patients with MCI-noAD and 25 healthy controls were enrolled. CSF biomarkers returned normal values in LO-TLE, significantly different from patients with MCI due to AD. There were no differences in cortico-subcortical atrophy between epilepsy patients and healthy controls, while patients with MCI demonstrated widespread injuries of cortico-subcortical structures. Individuals with LO-TLE, characterized by short disease duration and normal CSF amyloid-β and tau protein levels, showed patterns of cortical thickness and subcortical volumes not significantly different from healthy controls, but highly different from patients with MCI, either due to AD or not.

Cerebrospinal fluid cytokine levels affect electroencephalographic activity in Alzheimer's disease

To investigate the role of neuroinflammation as mediator of amyloid-β-induced cortical activity changes in Alzheimer's disease (AD), we examined the relationship between cerebrospinal fluid (CSF) inflammatory cytokines (IL-1β, IL-2, IL-4, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13, IL-17, TNF-α, IFN-γ, GM-CSF, G-CSF, MIP-1α, MCP-1) and electroencephalographic (EEG) abnormalities in a cohort of biologically defined AD patients (n = 55, M:F = 19:36, median age 73, Mini-Mental State Examination ≥ 22). We retrieved a positive association between IL-4 CSF levels and EEG background activity frequency; IL-7, IL-8, and IL-12 CSF levels were positively associated with the presence of interictal epileptiform discharges. Neuroinflammation accompanying AD pathology may enhance the amyloid's epileptogenic potential while also counteracting neurodegenerative damage.

Excessive Alcohol Use as a Risk Factor for Alzheimer's Disease: Epidemiological and Preclinical Evidence

Alcohol use has recently emerged as a modifiable risk factor for Alzheimer's disease (AD). However, the neurobiological mechanisms by which alcohol interacts with AD pathogenesis remain poorly understood. In this chapter, we review the epidemiological and preclinical support for the interaction between alcohol use and AD. We hypothesize that alcohol use increases the rate of accumulation of specific AD-relevant pathologies during the prodromal phase and exacerbates dementia onset and progression. We find that alcohol consumption rates are increasing in adolescence, middle age, and aging populations. In tandem, rates of AD are also on the rise, potentially as a result of this increased alcohol use throughout the lifespan. We then review the biological processes in common between alcohol use disorder and AD as a means to uncover potential mechanisms by which they interact; these include oxidative stress, neuroimmune function, metabolism, pathogenic tauopathy development and spread, and neuronal excitatory/inhibitory balance (EIB). Finally, we provide some forward-thinking suggestions we believe this field should consider. In particular, the inclusion of alcohol use assessments in longitudinal studies of AD and more preclinical studies on alcohol's impacts using better animal models of late-onset Alzheimer's disease (LOAD).

Bursts of brain erosion: seizures and age-dependent neurological vulnerability

Hypersynchronous and exaggerated neuronal firing, exemplified by epileptiform activity and seizures, are disruptors of brain function across acute and chronic neuropathological conditions. Here, we focus on how seizure activity, whether as a primary symptom or a secondary comorbid event within a complex pathological setting, adversely impacts neurological trajectories. We discuss experimental and clinical evidence illustrating the participation of neurodegenerative and senescence-like adaptations. Paroxysmal neuronal events, through bidirectional causality, are linked with immune and microvascular changes, disrupting cellular homeostasis and creating a feed-forward loop that intertwines with age-related frailty to deteriorate mental health. We emphasize the clinical significance of early detection of these brain vulnerabilities through biomarkers, monitoring neurodevelopmental risks in children, and tracking neurodegenerative disease progression in aging populations.

The role of parvalbumin interneuron dysfunction across neurodegenerative dementias

Parvalbumin-positive (PV+) basket neurons are fast-spiking, non-adapting inhibitory interneurons whose oscillatory activity is essential for regulating cortical excitation/inhibition balance. Their dysfunction results in cortical hyperexcitability and gamma rhythm disruption, which have recently gained substantial traction as contributing factors as well as potential therapeutic targets for the treatment of Alzheimer's Disease (AD). Recent evidence indicates that PV+ cells are also impaired in Frontotemporal Dementia (FTD) and Dementia with Lewy bodies (DLB). However, no attempt has been made to integrate these findings into a coherent pathophysiological framework addressing the contribution of PV+ interneuron dysfunction to the generation of cortical hyperexcitability and gamma rhythm disruption in FTD and DLB. To fill this gap, we epitomized the most recent evidence on PV+ interneuron impairment in AD, FTD, and DLB, focusing on its contribution to the generation of cortical hyperexcitability and gamma oscillatory disruption and their interplay with misfolded protein accumulation, neuronal death, and clinical symptoms' onset. Our work deepens the current understanding concerning the role of PV+ interneuron dysfunction across neurodegenerative dementias, highlighting commonalities and differences among AD, FTD, and DLB, thus paving the way for identifying novel biomarkers and potential therapeutic targets for the treatment of these diseases.

Amino Acid Compound 2 (AAC2) Treatment Counteracts Insulin-Induced Synaptic Gene Expression and Seizure-Related Mortality in a Mouse Model of Alzheimer's Disease

Diabetes is a major risk factor for Alzheimer's disease (AD). Amino acid compound 2 (AAC2) improves glycemic and cognitive functions in diabetic mouse models through mechanisms distinct from insulin. Our goal was to compare the effects of AAC2, insulin, and their nanofiber-forming combination on early asymptomatic AD pathogenesis in APP/PS1 mice. Insulin, but not AAC2 or the combination treatment (administered intraperitoneally every 48 h for 120 days), increased seizure-related mortality, altered the brain fat-to-lean mass ratio, and improved specific cognitive functions in APP/PS1 mice. NanoString and pathway analysis of cerebral gene expression revealed dysregulated synaptic mechanisms, with upregulation of Bdnf and downregulation of Slc1a6 in insulin-treated mice, correlating with insulin-induced seizures. In contrast, AAC2 promoted the expression of Syn2 and Syp synaptic genes, preserved brain composition, and improved survival. The combination of AAC2 and insulin counteracted free insulin's effects. None of the treatments influenced canonical amyloidogenic pathways. This study highlights AAC2's potential in regulating synaptic gene expression in AD and insulin-induced contexts related to seizure activity.

Neuropsychiatry revisited: epilepsy as the borderland between neurology and psychiatry

Since epilepsy is often complicated by psychiatric symptoms, the contributions of psychiatry are indispensable for the care and improvement of the quality of life of individuals with epilepsy. Moreover, the existence of a bidirectional relationship between epilepsy and psychiatric symptoms was recently proposed, based on the evidence that not only are some psychiatric symptoms more likely than others to follow epilepsy, but also that psychiatric symptoms may precede the onset of epilepsy and the presence of psychiatric symptoms may influence the outcome of treatment for seizures. There has also been a gradual accumulation of neurobiological findings related to psychosis, depressive, and anxiety symptoms that are associated with epilepsy with respect to abnormalities in brain networks and neurotransmission. This mini-review focuses on the neuropsychiatric aspects of epilepsy and proposes that a reconsideration of neuropsychiatry in light of epilepsy findings could serve as a bridge between psychiatry and neurology.

The Crossroads Between Alzheimer's Disease Pathophysiology and Epilepsy

Association of Plasma Aβ42/Aβ40 Ratio and Late-Onset Epilepsy: Results From the Atherosclerosis Risk in Communities Study Johnson EL, Sullivan KJ, Schneider ALC, Simino J, Mosley TH, Kucharska-Newton A, Knopman DS, Gottesman RF. Neurology . 2023 Sep 26;101(13):e1319-e1327. doi:10.1212/WNL.0000000000207635 . Epub 2023 Aug 4. PMID: 37541842 Background and Objectives: The objective of this study was to determine the relationship between plasma β-amyloid (Aβ), specifically the ratio of 2 Aβ peptides (the Aβ42/Aβ40 ratio, which correlates with increased accumulation of Aβ in the central nervous system [CNS]), and late-onset epilepsy (LOE). Methods: We used Medicare fee-for-service claims codes from 1991 to 2018 to identify cases of LOE among 1424 Black and White men and women enrolled in the Atherosclerosis Risk in Communities (ARIC) study cohort. The Aβ42/Aβ40 ratio was calculated from plasma samples collected from ARIC participants from 1993 to 1995 (age 50-71 years) and 2011 to 2013 (age 67-90 years). We used survival analysis accounting for the competing risk of death to determine the relationship between late-life plasma Aβ42/Aβ40, and its change from midlife to late life, and the subsequent development of epilepsy. We adjusted for demographics, the apolipoprotein e4 genotype, and comorbidities, including stroke, dementia, and head injury. A low plasma ratio of 2 Aβ peptides, the Aβ42/Aβ40 ratio, correlates with low CSF Aβ42/Aβ40 and with increased accumulation of Aβ in the CNS. Results: A decrease in plasma Aβ42/Aβ40 ratio from midlife to late life, but not an isolated measurement of Aβ42/Aβ40, was associated with the development of epilepsy in later life. For every 50% reduction in Aβ42/Aβ40, there was a 2-fold increase in the risk of epilepsy (adjusted subhazard ratio 2.30, 95% CI: 1.27-4.17). Discussion: A reduction in plasma Aβ42/Aβ40 is associated with an increased risk of subsequent epilepsy. Our observations provide a further validation of the link between Aβ, hyperexcitable states, and LOE. Similar Brain Proteomic Signatures in Alzheimer's Disease and Epilepsy Leitner D, Pires G, Kavanagh T, Kanshin E, Askenazi M, Ueberheide B, Devinsky O, Wisniewski T, Drummond E. Acta Neuropathol . 2024 Jan 30;147(1):27. doi:10.1007/s00401-024-02683-4 . PMID: 38289539 The prevalence of epilepsy is increased among Alzheimer's disease (AD) patients and cognitive impairment is common among people with epilepsy. Epilepsy and AD are linked but the shared pathophysiological changes remain poorly defined. We aim to identify protein differences associated with epilepsy and AD using published proteomics datasets. We observed a highly significant overlap in protein differences in epilepsy and AD: 89% (689/777) of proteins altered in the hippocampus of epilepsy patients were significantly altered in advanced AD. Of the proteins altered in both epilepsy and AD, 340 were altered in the same direction, while 216 proteins were altered in the opposite direction. Synapse and mitochondrial proteins were markedly decreased in epilepsy and AD, suggesting common disease mechanisms. In contrast, ribosome proteins were increased in epilepsy but decreased in AD. Notably, many of the proteins altered in epilepsy interact with tau or are regulated by tau expression. This suggests that tau likely mediates common protein changes in epilepsy and AD. Immunohistochemistry for Aβ and multiple phosphorylated tau species (pTau396/404, pTau217, and pTau231) showed a trend for increased intraneuronal pTau217 and pTau231 but no phosphorylated tau aggregates or amyloid plaques in epilepsy hippocampal sections. Our results provide insights into common mechanisms in epilepsy and AD and highlight the potential role of tau in mediating common pathological protein changes in epilepsy and AD.

Microglial purinergic signaling in Alzheimer's disease

Alzheimer's disease (AD) is a progressive and fatal neurodegenerative disease. The prevalent features of AD pathogenesis are the appearance of β-amyloid (Aβ) plaques and neurofibrillary tangles, which cause microglial activation, synaptic deficiency, and neuronal loss. Microglia accompanies AD pathological processes and is also linked to cognitive deficits. Purinergic signaling has been shown to play a complex and tight interplay with the chemotaxis, phagocytosis, and production of pro-inflammatory factors in microglia, which is an important mechanism for regulating microglia activation. Here, we review recent evidence for interactions between AD, microglia, and purinergic signaling and find that the purinergic P2 receptors pertinently expressed on microglia are the ionotropic receptors P2X4 and P2X7, and the subtypes of P2YRs expressed by microglia are metabotropic receptors P2Y2, P2Y6, P2Y12, and P2Y13. The adenosine P1 receptors expressed in microglia include A1R, A2AR, and A2BR. Among them, the activation of P2X4, P2X7, and adenosine A1, A2A receptors expressed in microglia can aggravate the pathological process of AD, whereas P2Y2, P2Y6, P2Y12, and P2Y13 receptors expressed by microglia can induce neuroprotective effects. However, A1R activation also has a strong neuroprotective effect and has a significant anti-inflammatory effect in chronic neuroinflammation. These receptors regulate a variety of pathophysiological processes in AD, including APP processing, Aβ production, tau phosphorylation, neuroinflammation, synaptic dysfunction, and mitochondrial dysfunction. This review also provides key pharmacological advances in purinergic signaling receptors.

Targeting excitatory:inhibitory network imbalance in Alzheimer's disease

This scientific commentary refers to ‘Seizures exacerbate excitatory: inhibitory imbalance in Alzheimer’s disease and 5XFAD mice’ by Barbour et al. (https://doi.org/10.1093/brain/awae126).

Persistent ∆FosB expression limits recurrent seizure activity and provides neuroprotection in the dentate gyrus of APP mice

Recurrent seizures lead to accumulation of the activity-dependent transcription factor ∆FosB in hippocampal dentate granule cells in both mouse models of epilepsy and mouse models of Alzheimer's disease (AD), which is also associated with increased incidence of seizures. In patients with AD and related mouse models, the degree of ∆FosB accumulation corresponds with increasing severity of cognitive deficits. We previously found that ∆FosB impairs spatial memory in mice by epigenetically regulating expression of target genes such as calbindin that are involved in synaptic plasticity. However, the suppression of calbindin in conditions of neuronal hyperexcitability has been demonstrated to provide neuroprotection to dentate granule cells, indicating that ∆FosB may act over long timescales to coordinate neuroprotective pathways. To test this hypothesis, we used viral-mediated expression of ∆JunD to interfere with ∆FosB signaling over the course of several months in transgenic mice expressing mutant human amyloid precursor protein (APP), which exhibit spontaneous seizures and develop AD-related neuropathology and cognitive deficits. Our results demonstrate that persistent ∆FosB activity acts through discrete modes of hippocampal target gene regulation to modulate neuronal excitability, limit recurrent seizure activity, and provide neuroprotection to hippocampal dentate granule cells in APP mice.

Parvalbumin Interneuron Dysfunction in Neurological Disorders: Focus on Epilepsy and Alzheimer's Disease

Parvalbumin expressing (PV+) GABAergic interneurons are fast spiking neurons that provide powerful but relatively short-lived inhibition to principal excitatory cells in the brain. They play a vital role in feedforward and feedback synaptic inhibition, preventing run away excitation in neural networks. Hence, their dysfunction can lead to hyperexcitability and increased susceptibility to seizures. PV+ interneurons are also key players in generating gamma oscillations, which are synchronized neural oscillations associated with various cognitive functions. PV+ interneuron are particularly vulnerable to aging and their degeneration has been associated with cognitive decline and memory impairment in dementia and Alzheimer's disease (AD). Overall, dysfunction of PV+ interneurons disrupts the normal excitatory/inhibitory balance within specific neurocircuits in the brain and thus has been linked to a wide range of neurodevelopmental and neuropsychiatric disorders. This review focuses on the role of dysfunctional PV+ inhibitory interneurons in the generation of epileptic seizures and cognitive impairment and their potential as targets in the design of future therapeutic strategies to treat these disorders. Recent research using cutting-edge optogenetic and chemogenetic technologies has demonstrated that they can be selectively manipulated to control seizures and restore the balance of neural activity in the brains of animal models. This suggests that PV+ interneurons could be important targets in developing future treatments for patients with epilepsy and comorbid disorders, such as AD, where seizures and cognitive decline are directly linked to specific PV+ interneuron deficits.