Aberrant excitatory neuronal activity and compensatory remodeling of inhibitory hippocampal circuits in mouse models of Alzheimer's disease

Entrainment by transcranial alternating current stimulation: Insights from models of cortical oscillations and dynamical systems theory

Signature of neuronal oscillations can be found in nearly every brain function. However, abnormal oscillatory activity is linked with several brain disorders. Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation technique that can potentially modulate neuronal oscillations and influence behavior both in health and disease. Yet, a complete understanding of how interacting networks of neurons are affected by tACS remains elusive. Entrainment effects by which tACS synchronizes neuronal oscillations is one of the main hypothesized mechanisms, as evidenced in animals and humans. Computational models of cortical oscillations may shed light on the entrainment effects of tACS, but current modeling studies lack specific guidelines to inform experimental investigations. This study addresses the existing gap in understanding the mechanisms of tACS effects on rhythmogenesis within the brain by providing a comprehensive overview of both theoretical and experimental perspectives. We explore the intricate interactions between oscillators and periodic stimulation through the lens of dynamical systems theory. Subsequently, we present a synthesis of experimental findings that demonstrate the effects of tACS on both individual neurons and collective oscillatory patterns in animal models and humans. Our review extends to computational investigations that elucidate the interplay between tACS and neuronal dynamics across diverse cortical network models. To illustrate these concepts, we conclude with a simple oscillatory neuron model, showcasing how fundamental theories of oscillatory behavior derived from dynamical systems, such as phase response of neurons to external perturbation, can account for the entrainment effects observed with tACS. Studies reviewed here render the necessity of integrated experimental and computational approaches for effective neuromodulation by tACS in health and disease.

Reactive Astrocytes with Reduced Function of Glutamate Transporters in the AppNL-G-F Knock-in Mice

Alzheimer's disease (AD) is associated with synaptic and memory dysfunction. One of the hallmarks of AD is reactive astrogliosis, with reactive astrocytes surrounding amyloid plaques in the brain. Astrocytes have also been shown to be actively involved in disease progression, nevertheless, mechanistic information about their role in synaptic transmission during AD pathology is lacking. Astrocytes maintain synaptic transmission by taking up extracellular glutamate during synaptic activity through astrocytic glutamate transporter GLT-1, but its function has been difficult to measure in real-time in AD pathology. Here, we used an App knock-in AD model (AppNL-G-F) carrying the Swedish, Arctic and Beyreuther mutations associated with AD and exhibiting AD-like Aβ plaque deposition and memory impairment. Using immunohistochemistry, patch-clamp of astrocytes, and Western blot from tissue and FACS isolated synaptosomes, we found that AppNL-G-F mice at 6-8 months of age have astrocytes with clearly altered morphology compared to wild-type (WT). Moreover, astrocyte glutamate clearance function in AppNL-G-F mice, measured as electrophysiological recordings of glutamate transporter currents, was severely impaired compared to WT animals. The reduction of glutamate uptake by astrocytes cannot be explained by GLT-1 protein levels, which were unchanged in synaptosomes and hippocampus of AppNL-G-F mice. Our data suggest that astrocytic glutamate transporters are affected by excess Aβ42 in the brain contributing to synaptic dysfunction in the hippocampus. This data contributes to the notion of restoring astrocyte synaptic function as a potential therapeutic strategy to treat AD.

The interaction between neurotransmitter receptor activity and amyloid-β pathology in Alzheimer's disease

The accumulation of amyloid-β (Aβ) peptides is a hallmark of Alzheimer's disease (AD). Central to AD pathology is the production of Aβ peptides through the amyloidogenic processing of amyloid-β protein precursor (AβPP) by β-secretase (BACE-1) and γ-secretase. Recent studies have shifted focus from Aβ plaque deposits to the more toxic soluble Aβ oligomers. One significant way in which Aβ peptides impair neuronal information processing is by influencing neurotransmitter receptor function. These receptors, including adrenergic, acetylcholine, dopamine, 5-HT, glutamate, and gamma-aminobutyric acid (GABA) receptors, play a crucial role in regulating synaptic transmission, which underlies perceptual and cognitive functions. This review explores how Aβ interacts with these key neurotransmitter receptors and how these interactions contribute to neural dysfunction in AD. Moreover, we examine how agonists and antagonists of these receptors influence Aβ pathology, offering new perspectives on potential therapeutic strategies to curb AD progression effectively and improve patients' quality of life.

Increased excitability of dentate gyrus mossy cells occurs early in life in the Tg2576 model of Alzheimer's disease

BACKGROUND

Hyperexcitability in Alzheimer's disease (AD) is proposed to emerge early and contribute to disease progression. The dentate gyrus (DG) and its primary cell type, granule cells (GCs) are implicated in hyperexcitability in AD. Hence, we hypothesized that mossy cells (MCs), important regulators of GC excitability, contribute to early hyperexcitability in AD. Indeed, MCs and GCs are linked to hyperexcitability in epilepsy.

METHODS

Using the Tg2576 model of AD and WT mice (~ 1 month-old), we compared MCs and GCs electrophysiologically and morphologically, assessed the activity marker c-Fos, Aβ expression and a hippocampal- and MC-dependent memory task that is impaired at 3-4 months of age in Tg2576 mice.

RESULTS

Tg2576 MCs had increased spontaneous excitatory events (sEPSP/Cs) and decreased spontaneous inhibitory currents (sIPSCs), increasing the excitation/inhibition ratio. Additionally, Tg2576 MC intrinsic excitability was enhanced. Consistent with in vitro results, Tg2576 MCs showed enhanced c-Fos protein expression. Tg2576 MCs had increased intracellular Aβ expression, suggesting a reason for increased excitability. GCs showed increased excitatory and inhibitory input without changes in intrinsic properties, consistent with effects of increased MC activity. In support, increased GC activity was normalized by an antagonist of MC input to GCs. Also in support, Tg2576 MC axons showed sprouting to the area of GC dendrites. These effects occurred before an impairment in the memory task, suggesting they are extremely early alterations.

CONCLUSIONS

Alterations in Tg2576 MCs and GCs early in life suggest an early role for MCs in increased GC excitability. MCs may be a novel target to intervene in AD pathophysiology at early stages.

Chronic administration of prebiotics and probiotics prevent pathophysiological hallmarks of Alzheimer's disease in the cortex of APP/PS1 mice

Introduction

Dysbiosis is a characteristic of patients with Alzheimer's disease (AD). The disbalance between Gram-negative and Gram-positive bacteria causes increased production of beta-amyloid (Aβ) in the gut, which can contribute to brain accumulation of Aβ. Recovering microbiota composition with symbiotic administration of prebiotics and probiotics may be a strategy to prevent or reduce AD symptomathology. The aim of this research was to study whether chronic administration of pre- and probiotics modifies the histopathological signs of neurodegeneration in the cortex of APP/PS1 mice, a transgenic mouse model of AD. We focused on neuritic plaques deposition, neuronal degeneration and glia activation.

Methods

Transgenic (TG) mice and Wild type (WT) littermates were fed daily with a diet supplemented with prebiotics (a multi-extract of fibers and plant complexes, containing inulin/fruit-oligosaccharides) and probiotics (a 50%-50% mixture of Lactobacillus rhamnosus and Lactobacillus paracasei). The treatment started at 2 months of age and lasted for 6 months. Controls were WT and TG mice fed with a standard diet. All groups were evaluated qualitatively and quantitatively by immunofluorescence, confocal microscopy and digital imaging. Cortical sections were immunostained for neuritic plaques, neurons, astrocytes, microglia, and inflammatory proteins. Qualitative and quantitative analyses were carried out by immunofluorescence, confocal microscopy and digital imaging with ImageJ software.

Results

Quantitative analyses in TG mice demonstrated intense Aβ load and accumulation of neurofilament heavy polypeptide (NHP) in neuritic plaques, neuronal degeneration, shrinkage of the cortex, increase of GFAP expression, and microglia and astrocytes activation. All these effects were mainly evident in cortical Layer 5. The symbiotic treatment with pre- and probiotics decreased Aβ deposition and neuritic plaques in the frontoparietal cortex. In addition, the treatment decreased the degeneration of neurons, the cortical shrinkage, increased GFAP expression, and modified microglia phenomic, decreasing significantly microglia activation. The abovementioned effects of the treatment were mostly evident in cortical Layer 5.

Discussion

These data confirm that prolonged dietary regimen enriched with pre- and probiotics counteracts many of the histopathological hallmarks of AD, and poses the bases for a simple, affordable treatment that may help prevent AD.

An AAV capsid proposed as microglia-targeting directs genetic expression in forebrain excitatory neurons

A newly developed capsid AAV-MG1.2 was reported to mediate specific microglial transduction. However, we find that AAV-MG1.2 actually enables specific genetic access to excitatory neurons in forebrain regions including hippocampal formation and visual cortex but does not confer expression in microglia or astrocytes in vivo. Furthermore, we find that AAV-MG1.2 specifically labels the deep layer of the CA1 pyramidal layer in a titer-dependent manner. We show that AAV-MG1.2-Cre can be used to genetically target excitatory neurons for cell-type-specific neural circuit mapping studies. We also find that AAV-MG1.2 conserves specificity for excitatory neurons in rat hippocampus. Thus, the AAV-MG1.2 presents a useful viral-genetic tool for targeting excitatory neurons in the forebrain across different species.

Microglial MS4A4A Protects against Epileptic Seizures in Alzheimer's Disease

Alzheimer's disease (AD) is a predominant neurodegenerative disorder worldwide, with epileptic seizures being a common comorbidity that can exacerbate cognitive deterioration in affected individuals, thus highlighting the importance of early therapeutic intervention. It is determined that deletion of Ms4a4a, an AD-associated gene, exacerbates seizures in amyloid β (Aβ)-driven AD mouse model. MS4A4A is significantly upregulated in brain lesions in patients with epilepsy. Single-cell sequencing reveals that MS4A4A is highly expressed in microglia within these lesions, linked to enhanced phagocytic activity. Mechanistic investigation delineates that deletion of Ms4a4a impairs microglial phagocytosis, accompanied by diminished calcium influx and disruptions in mitochondrial metabolic fitness. The cytosolic fragment of Ms4a4a is anchored to the cytoskeletal components, supporting its critical role in mediating phagocytosis. Induction of Ms4a4a through central delivery of LNP-Il4 alleviates seizure conditions. Collectively, these findings identify Ms4a4a as a potential therapeutic target for managing seizures in AD treatment.

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).

G protein-gated inwardly rectifying K+ (GIRK/Kir3) channels: Molecular, cellular, and subcellular diversity

G protein-gated inwardly rectifying K+ (GIRK/Kir3) channels are mainly expressed in excitable cells such as neurons and atrial myocytes, where they can respond to a wide variety of neurotransmitters. Four GIRK subunits have been found in mammals (GIRK1-4) and act as downstream targets for various Gαi/o-linked G protein-coupled receptors (GPCRs). Activation of GIRK channels produces a postsynaptic efflux of potassium from the cell, responsible for hyperpolarization/inhibition of the neuron. A growing body of evidence suggests that dysregulation of GIRK signalling can lead to excessive or deficient neuronal excitability, which contributes to neurological diseases and disorders. Therefore, GIRK channels are proposed as new pharmacological targets. The function of GIRK channels in neurons is not only determined by their biophysical properties but also by their cellular and subcellular localization patterns and densities on the neuronal surface. GIRK channels can be located within several subcellular compartments, where they have many different functional implications. This subcellular localization changes dynamically along the neuronal surface in response to drug intake. Ongoing research is focusing on determining the proteins that form macromolecular complexes with GIRK channels and are responsible for fast and precise signalling under physiological conditions, and how their alteration is implicated in pathological conditions. In this review, the distinct regional, cellular, and subcellular distribution of GIRK channel subunits in the brain will be discussed in view of their possible functional and pathological implications.

Cannabidiol ameliorates cognitive decline in 5×FAD mouse model of Alzheimer's disease through potentiating the function of extrasynaptic glycine receptors

Emerging evidence supports the therapeutic potential of cannabinoids in Alzheimer's disease (AD), but the underlying mechanism upon how cannabinoids impact brain cognition and AD pathology remains unclear. Here we show that chronic cannabidiol (CBD) administration significantly mitigates cognitive deficiency and hippocampal β-amyloid (Aβ) pathology in 5×FAD mouse model of AD. CBD achieves its curative effect mainly through potentiating the function of inhibitory extrasynaptic glycine receptor (GlyR) in hippocampal dentate gyrus (DG). Based on the in vitro and in vivo electrophysiological recording and calcium imaging, CBD mediated anti-AD effects via GlyR are mainly accomplished by decreasing neuronal hyperactivity of granule cells in the DG of AD mice. Furthermore, the AAV-mediated ablation of DG GlyRα1, or the GlyRα1S296A mutation that exclusively disrupts CBD binding, significantly intercepts the anti-AD effect of CBD. These findings suggest a GlyR dependent mechanism underlying the therapeutic potential of CBD in the treatment of AD.

Unraveling the mystery of citrate transporters in Alzheimer's disease: An updated review

A key molecule in cellular metabolism, citrate is essential for lipid biosynthesis, energy production, and epigenetic control. The etiology of Alzheimer's disease (AD), a progressive neurodegenerative illness marked by memory loss and cognitive decline, may be linked to dysregulated citrate transport, according to recent research. Citrate transporters, which help citrate flow both inside and outside of cells, are becoming more and more recognized as possible participants in the molecular processes underlying AD. Citrate synthase (CS), a key enzyme in the tricarboxylic acid (TCA) cycle, supports mitochondrial function and neurotransmitter synthesis, particularly acetylcholine (ACh), essential for cognition. Changes in CS activity affect citrate availability, influencing energy metabolism and neurotransmitter production. Choline, a precursor for ACh, is crucial for neuronal function. Lipid metabolism, oxidative stress reactions, and mitochondrial function can all be affected by aberrant citrate transport, and these changes are linked to dementia. Furthermore, the two main pathogenic characteristics of AD, tau hyperphosphorylation and amyloid-beta (Aβ) aggregation, may be impacted by disturbances in citrate homeostasis. The goal of this review is to clarify the complex function of citrate transporters in AD and provide insight into how they contribute to the development and course of the illness. We aim to provide an in-depth idea of which particular transporters are dysregulated in AD and clarify the functional implications of these dysregulated transporters in brain cells. To reduce neurodegenerative processes and restore metabolic equilibrium, we have also discussed the therapeutic potential of regulating citrate transport. Gaining insight into the relationship between citrate transporters and the pathogenesis of AD may help identify new indicators for early detection and creative targets for treatment. This study offers hope for more potent ways to fight this debilitating illness and is a crucial step in understanding the metabolic foundations of AD.

Elevated pyramidal cell firing orchestrates arteriolar vasoconstriction through COX-2-derived prostaglandin E2 signaling

Neurovascular coupling, linking neuronal activity to cerebral blood flow, is essential for brain function and underpins functional brain imaging. Whereas mechanisms involved in vasodilation are well-documented, those controlling vasoconstriction remain overlooked. This study unravels the mechanisms by which pyramidal cells elicit arteriole vasoconstriction. Using patch-clamp recording, vascular and Ca2+ imaging in mouse cortical slices, we show that strong optogenetic activation of layer II/III pyramidal cells induces vasoconstriction, correlating with firing frequency and somatic Ca2+ increase. Ex vivo and in vivo pharmacological investigations indicate that this vasoconstriction predominantly recruits prostaglandin E2 through the cyclooxygenase-2 pathway, and activation of EP1 and EP3 receptors. We also present evidence that specific interneurons releasing neuropeptide Y, and astrocytes, through 20-hydroxyeicosatetraenoic acid, contribute to this process. By revealing the mechanisms by which pyramidal cells lead to vasoconstriction, our findings shed light on the complex regulation of neurovascular coupling.

CaV2.1 mediates presynaptic dysfunction induced by amyloid β oligomers

Synaptic dysfunction is an early pathological phenotype of Alzheimer's disease (AD) that is initiated by oligomers of amyloid β peptide (Aβos). Treatments aimed at correcting synaptic dysfunction could be beneficial in preventing disease progression, but mechanisms underlying Aβo-induced synaptic defects remain incompletely understood. Here, we uncover an epithelial sodium channel (ENaC) - CaV2.3 - protein kinase C (PKC) - glycogen synthase kinase-3β (GSK-3β) signal transduction pathway that is engaged by Aβos to enhance presynaptic CaV2.1 voltage-gated Ca2+ channel activity, resulting in pathological potentiation of action-potential-evoked synaptic vesicle exocytosis. We present evidence that the pathway is active in human APP transgenic mice in vivo and in human AD brains, and we show that either pharmacological CaV2.1 inhibition or genetic CaV2.1 haploinsufficiency is sufficient to restore normal neurotransmitter release. These findings reveal a previously unrecognized mechanism driving synaptic dysfunction in AD and identify multiple potentially tractable therapeutic targets.

Prefrontal cortex excitatory neurons show distinct response to heroin-associated cue and social stimulus after prolonged heroin abstinence in mice

Substance use disorder (SUD) has been linked with social impairments. The social cognitive dysfunctions can further increase the risk of the development of SUD or relapse. Therefore, understanding the neural mechanism of substance exposure-associated social impairments is beneficial for the development of novel prevention or treatment strategies for SUD. The prefrontal cortex (PFC) is a key brain region involved in both social cognition and drug addiction. Specifically, the prelimbic part of PFC (PrL) regulates social interaction and heroin-seeking behavior. Therefore, in this study, we explored how PFC excitatory neurons respond to social stimuli after prolonged abstinence from heroin self-administration (SA). Using fiber photometry calcium imaging, we monitored calcium-dependent fluorescent signals in PrL CaMKII-expressing neurons during drug seeking and social interaction tests following 14 days of abstinence from heroin SA. We found that GCaMP6f signals in PrL CaMKII-expressing neurons were increased when heroin-associated cues were presented during drug-seeking tests in both male and female mice after prolonged heroin abstinence, although the baseline neuronal activity in home cage is lower in the heroin group. Conversely, the calcium signals in PrL CaMKII-expressing neurons during social investigation were decreased after heroin abstinence in both sexes, along with reduced total social interaction time. In addition, drug-seeking behavior is partially negatively correlated with social investigation time. These findings provide direct evidence showing that opioid exposure impairs the PFC functional response to social stimuli, which may potentially increase the risk for opioid relapse.

GRAMD1B is a regulator of lipid homeostasis, autophagic flux and phosphorylated tau

Lipid dyshomeostasis and tau pathology are present in frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD). However, the relationship between lipid dyshomeostasis and tau pathology remains unclear. We report that GRAM Domain Containing 1B (GRAMD1B), a nonvesicular cholesterol transporter, is increased in excitatory neurons of human neural organoids (HNOs) with the MAPT R406W mutation. Human FTLD, AD cases, and PS19 tau mice also have increased GRAMD1B expression. We show that overexpression of GRAMD1B increases levels of free cholesterol, lipid droplets, and impairs autophagy flux. Modulating GRAMD1B in iPSC-derived neurons also alters key autophagy-related components such as PI3K, phospho-AKT, and p62, as well as phosphorylated tau, and CDK5R1. Blocking GRAMD1B function decreases free cholesterol and lipid droplets. Knocking down GRAMD1B additionally reduces phosphorylated tau, and CDK5R1 expression. Our findings elucidate the role of GRAMD1B in the nervous system and highlight its relevance to FTLD and AD.

Fueling Brain Inhibition: Integrating GABAergic Neurotransmission and Energy Metabolism

Despite decades of research in brain energy metabolism and to what extent different cell types utilize distinct substrates for their energy metabolism, this topic remains a vibrant area of neuroscience research. In this review, we focus on the substrates utilized by the inhibitory GABAergic neurons, which has been less explored than glutamatergic neurons. First, we discuss how GABAergic neurons may utilize both glucose, lactate, or ketone bodies under different functional conditions, and provide some preliminary data suggesting that unlike glutamatergic neurons, GABAergic neurons work well when substrate supply is restricted to lactate. We end by discussing the role of GABAergic neuron energy metabolism in pathologies where failure of inhibitory function play a central role, namely epilepsy, hepatic encephalopathy, and Alzheimer's disease.

Circadian rhythm disturbances in Alzheimer's disease: insights from plaque-free and plaque-burdened stages in APPSWE/PS1dE9 mice

BACKGROUND

Disruptions in circadian rhythms are commonly observed in patients with Alzheimer's disease (AD) and could potentially accelerate the progression of the condition. However, the relationship between circadian rhythm disruptions and AD development, as well as the mechanisms involved, remain poorly understood.

METHODS

This study investigated the circadian behavior, rhythmic gene expression in multiple brain regions, and its correlation with sleep architecture of AD mice at two disease stages: plaque-free stage (2-month-old) and plaque-burdened stage (10-month-old) as compared to age-matched wild-type (WT) mice.

RESULTS

Two-month-old AD mice already displayed alteration in the activity patterns compared to WT mice, showing increased activity during the light phase and decreased activity during the dark phase, and the change in the activity pattern of 10-month-old AD mice was more significant. Further, electroencephalogram (EEG) examination showed increased wakefulness and reduced non-rapid eye movement (NREM) sleep in 2- and 10-month-old AD mice. In addition, we documented a significant change in circadian core clock genes in the suprachiasmatic nucleus (SCN), hippocampus, and cortex of 2- and 10-month-old AD mice. Correlation analyses demonstrated the close relationship between circadian clock gene expression level and specific sleep-wake parameters, especially within the SCN and hippocampus.

CONCLUSIONS

These findings revealed that circadian rhythm disturbances in AD mice preceded Aβ deposition. The circadian rhythm disturbances observed in the early AD might be attributed to the abnormal expression of core clock genes in the brain regions involved in circadian rhythm regulation.

Mettl3 regulates the pathogenesis of Alzheimer's disease via fine-tuning Lingo2

Alzheimer's disease (AD) is the most common neurodegenerative disease, and diverse factors contribute to its pathogenesis. Previous studies have suggested the dysregulation of m6A modification involves in AD, but the underlying mechanism and targets remain largely unknown. In the present study, we have shown that the levels of Mettl3 and m6A modification are increased in specific brain regions of 5xFAD mice and post-mortem AD patients, respectively. Heterozygous deletion of neuronal Mettl3 (AD::Mettl3+/-) reduced Aβ plaques and inflammation, and improved learning and memory of AD mice, and vice versa for Mettl3 knock in (AD::Mettl3-KI). Mechanistically, we observed that the level of m6A modification of Lingo2 increased in 5xFAD mice and AD patients, which promoted the binding of Ythdf2 and enhanced the degradation of Lingo2 mRNA. The decreased level of Lingo2 promoted the interaction between APP and β-site amyloid precursor protein cleaving enzyme (Bace1), and subsequently enhanced Aβ production in AD mice, which can be inhibited by Mettl3 depletion. Both ectopic Lingo2 and the administration of Mettl3 inhibitor STM2457 significantly alleviated the neuropathology and behavioral deficits of AD mice. In summary, our study has revealed the important function of Mettl3 and m6A in the pathogenesis of AD and provided novel insight for the underlying mechanisms. Our study also suggests that m6A and Lingo2 could be potential therapeutic targets for AD.

Cellular expression of low-density lipoprotein receptor-related protein 1 and amyloid beta deposition in human and rat epileptogenic brain

Decreased capillary expression of low-density lipoprotein receptor-related protein 1 (LRP1) has been linked to increased brain amyloid beta (Aβ) accumulation in Alzheimer's disease (AD). Aβ accumulation has also been observed in (a subset of) temporal lobe epilepsy (TLE) patients, suggesting a potential link between epilepsy and AD. This study examines cellular LRP1 expression in human and rat epileptogenic brain tissue to explore LRP1's role in epilepsy. LRP1 expression and localization were analyzed in hippocampal sections from patients with status epilepticus (SE, n = 12), TLE (n = 12), autopsy controls (n = 20), and AD (n = 10) using immunohistochemistry. Soluble Aβ levels and deposits were compared across TLE, AD, and control tissues. LRP1 expression was also studied in an electrical post-SE rat model of TLE. Decreased capillary LRP1 expression was found in both human and rat brain tissue (SE and TLE). Higher LRP1 expression was detected in CA1 neurons (only in human TLE) and glial cells (SE and TLE). Aβ deposits were observed in only one out of 12 TLE patients, and soluble Aβ levels were not significantly elevated. In contrast, AD patients showed decreased capillary LRP1 expression accompanied by Aβ plaques and increased soluble Aβ40/42 levels. The significant reduction in LRP1 expression in brain capillaries in both adult human and rat TLE was not clearly associated with notable Aβ accumulation implying that alternative amyloid clearance mechanisms beyond LRP1 in blood vessels might be at play. It also supports previous findings indicating that Aβ pathology may be less prominent in adult TLE than some studies suggest.

Neurotrophic factor alpha 1 gene therapy in Alzheimer's disease: scope and advancements

Alzheimer's disease (AD) is the leading cause of dementia, accounting for 60-80% of all cases globally. Hallmark pathologies of AD include the accumulation of amyloid β peptide and phosphorylated tau, leading to neuronal circuit dysfunction, defective axonal transport, and neurotransmitter system (NTS) abnormalities. Disruptions in acetylcholine, GABA, dopamine, serotonin, and glutamate levels, as well as the loss of cholinergic, GABAergic, and monoaminergic neurons, contribute to the progression of AD. Additionally, neurotrophic factors like brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) are significantly reduced in AD, impacting neuronal health and synaptic integrity. This review highlights the emerging role of neurotrophic factor alpha 1 (NF-α1), also known as carboxypeptidase E, in AD. NF-α1 shows neuroprotective and neurogenesis-promoting properties, offering potential for therapeutic interventions. The review compares NF-α1 gene therapy with other neurotrophin-based treatments, providing insights into its efficacy in AD management.

NPTX2 transfection improves synaptic E/I balance and performance in learning impaired aged rats

Excessive neural activity in the medial temporal lobe commonly associates with cognitive decline in elderly humans and also in rodents.An attractive model pathway to study synaptic mechanisms underlying age-dependent circuit hyperexcitability is the connection made by lateral entorhinal cortex cells onto the dentate gyrus (LEC→DG). Both structures are particularly affected by age and, importantly, in behaviorally characterized aged rats, learning impairment correlates with diminished feedforward inhibition of granule cells recruited by LEC inputs. In this rat model of aging, we evaluated how overexpression of Neuronal Pentraxin 2 (NPTX2) in the LEC, essential for stabilizing excitatory inputs onto fast-spiking inhibitory interneurons (FS-INs), enhances feedforward inhibition and improves spatial memory in impaired individuals. In addition, we found that FS-INs from unimpaired aged individuals have an increased excitatory drive compared to young individuals. These findings support the notion that NPTX2-mediated compensatory mechanisms to enhance the recruitment of FS-INs are crucial to maintaining proficient memory performance during aging.

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.

Teucrium Polium ameliorates amyloid β-induced brain network disorders in rats: electrophysiological and behavioral studies

Synaptic failure in specific cholinergic networks in rat brains has been implicated in amyloid β-induced neurodegeneration. Teucrium polium is a promising candidate for drug development against Alzheimer's disease (AD) and similar disorders. However, the protective effect of Teucrium polium against amyloid β-induced impairment of short-term synaptic plasticity is still poorly understood. In this study, we used in vivo extracellular single-unit recordings to investigate the preventive efficacy of Teucrium polium on Aβ(25-35)-induced aberrant neuronal activity in the hippocampus and basolateral amygdala of rats, in response to high-frequency stimulation of the cholinergic nucleus basalis magnocellularis (NBM). After 12 weeks of intracerebroventricular administration of Aβ(25-35), alterations such as decreased excitatory responses and increased inhibitory synaptic activity were observed in the NBM-hippocampus and NBM-basolateral amygdala cholinergic circuits. Treatment with Teucrium polium improved the balance of excitatory and inhibitory responses by modulating synaptic transmission strength and restoring short-term plasticity. Acute injection of a therapeutic dose of Teucrium temporarily inhibited spiking activity in single NBM neurons. Open field tests revealed that amyloid-injected rats displayed anxiety and reduced exploratory drive. Treatment with Teucrium polium improved these behaviors, reducing anxiety and increasing exploration. Teucrium polium mitigated amyloid β-induced alterations in cholinergic circuits by enhancing the adaptive capacity of short-term synaptic plasticity. These findings suggest that Teucrium polium could serve as a preventive strategy to delay the progression of cholinergic neurodegeneration.

KAT6B overexpression in mice causes aggression, anxiety, and epilepsy

Loss of the gene encoding the histone acetyltransferase KAT6B (MYST4/MORF/QKF) causes developmental brain abnormalities as well as behavioral and cognitive defects in mice. In humans, heterozygous variants in the KAT6B gene cause two cognitive disorders, Say-Barber-Biesecker-Young-Simpson syndrome (SBBYSS; OMIM:603736) and genitopatellar syndrome (GTPTS; OMIM:606170). Although the effects of KAT6B homozygous and heterozygous mutations have been documented in humans and mice, KAT6B gain-of-function effects have not been reported. Here, we show that overexpression of the Kat6b gene in mice caused aggression, anxiety, and spontaneous epilepsy. Kat6b overexpression led to an increase in histone H3 lysine 9 acetylation and upregulation of genes driving nervous system development and neuronal differentiation. Kat6b overexpression additionally promoted neural stem cell proliferation and favored neuronal over astrocyte differentiation in vivo and in vitro. Our results suggest that, in addition to loss-of-function alleles, gain-of-function KAT6B alleles may be detrimental for brain development.

Prevalence and factors associated with seizures among patients with dementia: A retrospective clinic-based study

OBJECTIVE

Chronic diseases associated with aging, such as dementia and seizures, are expected to rise significantly in the Philippines' growing elderly population. This study aims to determine the frequency, demographic characteristics, and clinical profile of dementia patients who developed new-onset seizures in an outpatient setting.

METHODS

This descriptive, retrospective, cumulative prevalence study included 245 patients diagnosed with dementia at a tertiary hospital in Manila from February 2010 to February 2020, according to DSM-5 criteria. Patients were stratified into those who developed seizures and those who did not. Data on demographics, type, dementia severity, comorbidities, and seizure characteristics were collected and analyzed using descriptive statistics, bivariate, and multivariate logistic regression analyses.

RESULTS

The study included 245 dementia patients, of whom 10 (4.1%) developed seizures, with a higher likelihood observed in those with severe dementia. Most patients were diagnosed with Alzheimer's disease, and seizures were mostly seen in individuals between the ages of 65 and 79. The majority of the seizures were classified as generalized (50%). Compared to mild cases, patients with moderate dementia are about 1.5 times more likely to experience seizures, whereas patients with severe dementia are about 10 times more likely to experience seizures compared to patients with mild dementia. The association is statistically significant for severe cases of dementia.

SIGNIFICANCE

This study revealed that 4.1% of Filipino patients diagnosed with dementia in an outpatient setting at a tertiary hospital developed new-onset seizures. Seizures were mostly reported in patients with severe Alzheimer's disease. Conventional understanding of seizures among patients with dementia is important to identify features and predictors to provide efficient management among these patients to possibly improve their quality of life.

PLAIN LANGUAGE SUMMARY

With the aging Filipino population, there is an expected rise in chronic diseases such as dementia and seizures. This study looked at dementia patients in an outpatient setting over 10 years and found that 4.1% developed seizures. Most patients had Alzheimer's disease, and seizures were more common in severe dementia cases.

Preclinical insights into gamma-tACS: foundations for clinical translation in neurodegenerative diseases

Gamma transcranial alternating current stimulation (gamma-tACS) represents a novel neuromodulation technique with promising therapeutic applications across neurodegenerative diseases. This mini-review consolidates recent preclinical and clinical findings, examining the mechanisms by which gamma-tACS influences neural oscillations, enhances synaptic plasticity, and modulates neuroimmune responses. Preclinical studies have demonstrated the capacity of gamma-tACS to synchronize neuronal firing, support long-term neuroplasticity, and reduce markers of neuroinflammation, suggesting its potential to counteract neurodegenerative processes. Early clinical studies indicate that gamma-tACS may improve cognitive functions and network connectivity, underscoring its ability to restore disrupted oscillatory patterns central to cognitive performance. Given the intricate and multifactorial nature of gamma oscillations, the development of tailored, optimized tACS protocols informed by extensive animal research is crucial. Overall, gamma-tACS presents a promising avenue for advancing treatments that support cognitive resilience in a range of neurodegenerative conditions.

Neuromorphic deviations associated with transcriptomic expression and specific cell type in Alzheimer's disease

Alzheimer's disease (AD) is known to be associated with cortical anatomical atrophy and neurodegeneration across various brain regions. However, the relationships between brain structural changes in AD and gene expression remain unclear. We perform the morphometric similarity network (MSN) analysis to reveal the consistent cortical structural differences in individuals with AD compared to controls, and investigate the associations between brain-wide gene expression and morphometric changes. Furthermore, we identify abnormally MSN-related genes linked to specific cell types as the major contributors to transcriptomic relationships. MSN-related structural changes are located in the lateral ventral prefrontal cortex, temporal pole and medial prefrontal lobe, which are highly associated with the AD's cognitive decline. Analysis of gene expression shows the spatial correlations between AD-related genes and MSN differences. Examination of cell type-specific signature genes indicates that changes in microglia and neuronal transcriptional profiles largely contribute to AD-specific MSN differences. The study map the disease-specific structural alterations in AD down to the cellular level, offering a novel perspective on the linking surface-level changes to molecular mechanisms.

Forty-hertz sensory entrainment impedes kindling epileptogenesis and reduces amyloid pathology in an Alzheimer disease mouse model

OBJECTIVE

The 5xFAD mouse model of Alzheimer disease (AD) recapitulates amyloid-beta (Aβ) deposition and pronounced seizure susceptibility observed in patients with AD. Forty-hertz audiovisual stimulation is a noninvasive technique that entrains gamma neural oscillations and can reduce Aβ pathology and modulate glial expression in AD models. We hypothesized that 40-Hz sensory stimulation would improve seizure susceptibility in 5xFAD mice and this would be associated with reduction of plaques and modulation of glial phenotypes.

METHODS

5xFAD mice and wild-type (WT) littermates received 1 h/day 40-Hz audiovisual stimulation or sham (n = 7-11/group), beginning 2 weeks before and continuing throughout amygdala kindling epileptogenesis. Postmortem analyses included Aβ pathology and morphology of astrocytes and microglia.

RESULTS

5xFAD mice exhibited enhanced susceptibility to seizures compared to WT, evidenced by fewer stimulations to reach kindling endpoint (incidence rate ratio [IRR] = 1.46, p < .0001) and a trend to higher seizure severity (odds ratio [OR] = .34, p = .059). Forty-hertz stimulation reduced the behavioral severity of the first seizure (OR = 4.04, p = .02) and delayed epileptogenesis, increasing the number of stimulations required to reach kindling endpoint (IRR = .82, p = .01) compared to sham, regardless of genotype. 5xFAD mice receiving sensory stimulation exhibited ~50% reduction in amyloid pathology compared to sham. Furthermore, markers of astrocytes and microglia were upregulated in both genotypes receiving 40-Hz stimulation.

SIGNIFICANCE

Forty-hertz sensory entrainment slows epileptogenesis in the mouse amygdala kindling model. Although this intervention improves Aβ pathology in 5xFAD mice, the observed antiepileptogenic effect may also relate to effects on glia, because mice without Aβ plaques (i.e., WT) also experienced antiepileptogenic effects of the intervention.

Periodontitis associated with brain function impairment in middle-aged and elderly individuals with normal cognition

BACKGROUND

The present study aimed to investigate changes in intranetwork functional connectivity (FC) and internetwork FC in middle-aged and elderly individuals with normal cognition (NC) and varying degrees of periodontitis to determine the effects of periodontitis on brain function.

METHODS

Periodontal findings and resting-state functional magnetic resonance imaging data were acquired from 51 subjects with NC. Independent component analysis and correlation analysis were used for the statistical analysis of the data.

RESULTS

Differences in intranetwork FC were observed among groups in the anterior default-mode network (aDMN), dorsal attention network and dorsal sensorimotor network (dSMN). Compared with the nonperiodontitis (NP) group or the mild-periodontitis group, the analysis of internetwork FC showed increased FC between the auditory network and the ventral attention network (VAN), between the aDMN and the salience network (SN), and between the SN and the VAN and decreased FC between the posterior default-mode network and the right frontoparietal network in the moderate-to-severe periodontitis group. Additionally, internetwork FC between the dSMN and the VAN was also increased in the moderate-to-severe periodontitis group compared to the NP group. The altered intra- and internetwork FC were significantly correlated with the periodontal clinical index.

CONCLUSION

Our results confirmed that periodontitis was associated with both intra- and internetwork FC changes even in NC. The present study indicates that periodontitis might be a potential risk factor for brain damage and provides a theoretical clue and a new treatment target for the early prevention of Alzheimer disease.

PLAIN LANGUAGE SUMMARY

Recent research has proposed that periodontitis is a potential risk factor for Alzheimer disease (AD). However, the relationship between periodontitis and the brain function of middle-aged and elderly individuals with normal cognition (NC) remains unclear. Analyzing the effect of periodontitis on brain function in the NC stage can provide clues to AD development and help achieve early prevention of dementia. The present study aimed to investigate changes in brain functional connectivity (FC) in NC with different severity of periodontitis to determine the effects of periodontitis on brain function. Both changed intranetwork FC and internetwork FC were found in the moderate-to-severe periodontitis group, and periodontitis was associated with brain network function impairment in NC. The present study indicates that periodontitis might be a potential risk factor for brain damage even in NC stage, and provides a theoretical clue and a new treatment target for the early prevention of AD.

HCN2 deficiency correlates with memory deficits and hyperexcitability of dCA1 pyramidal neurons in Alzheimer's disease

BACKGROUND

Abnormal excitability of hippocampal neurons may lead to dysfunction of neural circuits and then causes cognitive impairments in Alzheimer's disease (AD). However, the underlying mechanisms remain to be fully elucidated.

METHODS

Electrophysiology was performed to examine the intrinsic excitability of CA1 neurons and the activity of the hyperpolarization-activated cyclic nucleotide-gated ion channels (HCNs) of CA1 neurons in wild type (WT) and hAPP-J20 mice. The activity of CA1 pyramidal neurons (PNs) was modulated with chemogenetics. The activity of HCNs was regulated with nonselective facilitator (cAMP) or inhibitor (ZD7288) of HCNs. Immunohistochemical staining or western blotting were performed to examine the expression of HCN1 and HCN2 in the hippocampus of WT and hAPP-J20 mice, or AD patients and non-AD controls. AAVs were injected to specifically modulate the expression of HCN2 in dorsal CA1 (dCA1) PNs. Cognitive performance of mice was assessed with behavioral tests.

RESULTS

dCA1 PNs were more excitable in hAPP-J20 mice, but the excitability of PNs in the ventral CA1 (vCA1) or PV neurons was comparable between WT and hAPP-J20 mice. The activity of the HCNs was reduced in dCA1 PNs of hAPP-J20 mice, and pharmacologically increasing the activity of HCNs attenuated the hyperexcitability of dCA1 PNs in hAPP-J20 mice, suggesting that the reduced activity of HCNs is associated with the hyperexcitability of dCA1 PNs in hAPP-J20 mice. The expression of HCN2 but not HCN1 was reduced in the hippocampus of hAPP-J20 mice, and the expression of HCN2 was also reduced in the hippocampus of AD patients, suggesting that dysregulation of HCN2 is associated with the reduced activity of HCNs in AD. Overexpressing HCN2 rescued the activity of HCNs, attenuated the hyperexcitability of dCA1 PNs and improved memory of hAPP-J20 mice, and knocking down HCN2 impaired the function of HCNs, increased the excitability of dCA1 PNs and led to memory deficits in WT mice.

CONCLUSIONS

Our data suggest that dysregulation of HCNs, particularly HCN2, contributes to the abnormal excitability of CA1 PNs in AD mice and probably in AD patients as well, and thus provide new insights into the mechanisms underlying the aberrant activity or excitability of hippocampal neurons in AD.

Pharmacological reduction of reverse-translated hippocampal hyperactivity in mouse: relevance for psychosis

Hippocampal hyperactivity (HH) is a potential biomarker in schizophrenia psychosis, which also appears in several other brain disorders, compromising specificity. We hypothesized that the reversal of HH in an established, reverse-translational animal preparation, coupled with a behavioral marker of psychosis may be a predictor of antipsychotic efficacy of a medication. We used a chemogenetic reverse-translational mouse preparation relevant to schizophrenia psychosis which shows HH and aberrant psychosis-relevant behaviors, specifically disrupted social recognition memory (SRM). Mice with and without HH were treated with three drugs; two known antipsychotics and one HH-reducing anticonvulsant, to assess their effects on both HH and SRM performance. All animals received one of the four treatments: vehicle (N = 15-24), haloperidol (N = 8-15), xanomeline (N = 8-13) or levetiracetam (N = 6-15) and were subsequently tested for baseline c-Fos protein expression within the hippocampal subfields (CA3 and CA1) as a measure of neuronal activity, or tested with the SRM task as a measure of social memory. All three drugs acutely reduced baseline HH compared to vehicle treatment. Subacute administration of haloperidol or xanomeline, the two drugs known to have antipsychotic activity, but not levetiracetam, normalized the SRM behavior to control levels. These results suggest that the reversal of HH alone cannot be a predictor of antipsychotic efficacy of an experimental drug and HH as a biomarker could benefit from a more sensitive readout approach.

Advances in the study of apathy related to cerebral small vessel disease

Cerebral small vessel disease (CSVD) is a complex clinical-imaging pathological syndrome caused by small vessel lesions in the brain, which is characterized by aging-related, insidious onset and slow progression. Apathy is a key component of the common neuropsychiatric symptoms among CSVD patients, severely affecting their daily lives and social functioning. Moreover, there are fewer studies on CSVD-related apathy, and greater attention should be paid to this condition in clinical practice. This article describes the latest research advances in the concept, epidemiological features, pathogenesis, assessment and diagnosis, imaging and biomarkers, and treatment of CSVD-related apathy, aiming to serve as a reference for the clinical diagnosis and prevention of CSVD-related apathy.

Quantification and correlation of amyloid-β plaque load, glial activation, GABAergic interneuron numbers, and cognitive decline in the young TgF344-AD rat model of Alzheimer's disease

Background

Animal models of Alzheimer's disease (AD) are essential tools for investigating disease pathophysiology and conducting preclinical drug testing. In this study, we examined neuronal and glial alterations in the hippocampus and medial prefrontal cortex (mPFC) of young TgF344-AD rats and correlated these changes with cognitive decline and amyloid-β plaque load.

Methods

We compared TgF344-AD and non-transgenic littermate rats aged 7-8 months of age. We systematically quantified β-amyloid plaques, astrocytes, microglia, four different subtypes of GABAergic interneurons (calretinin-, cholecystokinin-, parvalbumin-, and somatostatin-positive neurons), and newly generated neurons in the hippocampus. Spatial learning and memory were assessed using the Barnes maze test.

Results

Young TgF344-AD rats had a large number of amyloid plaques in both the hippocampus and mPFC, together with a pronounced increase in microglial cell numbers. Astrocytic activation was significant in the mPFC. Cholecystokinin-positive cell numbers were decreased in the hippocampus of transgenic rats, but calretinin-, parvalbumin-, and somatostatin-positive cell numbers were not altered. Adult neurogenesis was not affected by genotype. TgF344-AD rats had spatial learning and memory impairments, but this cognitive deficit did not correlate with amyloid plaque number or cellular changes in the brain. In the hippocampus, amyloid plaque numbers were negatively correlated with cholecystokinin-positive neuron and microglial cell numbers. In the mPFC, amyloid plaque number was negatively correlated with the number of astrocytes.

Conclusion

Pronounced neuropathological changes were found in the hippocampus and mPFC of young TgF344-AD rats, including the loss of hippocampal cholecystokinin-positive interneurons. Some of these neuropathological changes were negatively correlated with amyloid-β plaque load, but not with cognitive impairment.

The effects of amyloidosis and aging on glutamatergic and GABAergic synapses, and interneurons in the barrel cortex and non-neocortical brain regions

Previous studies on changes in the distribution of GABAergic interneurons and excitation/inhibition (E/I) balance in Alzheimer's disease (AD) and aging were mainly conducted in the neocortex and hippocampus. However, the limbic system is the primary and crucial location for AD progression. Therefore, in this study, we utilized AD and aging mouse models to investigate the E/I balance and the distribution of parvalbumin (PV)- and somatostatin (SST)-expressing cells in S1BF (barrel field of primary somatosensory cortex, barrel cortex), CA1 hippocampal area and brain regions beyond the neocortex and hippocampus, including retrosplenial cortex (RSC, which is composed of RSG and RSA), piriform cortex (Pir), amygdala (BMA), and hypothalamus (DM). We discovered that amyloidosis may disrupt the alignment of excitatory pre- and postsynaptic quantities. Amyloidosis reduces the quantity of synapses and SST cells, but does not impact the counts of PV cells. By contrast, aging is linked to a decline in synapses, I/E ratios, SST and PV cells. Amyloidosis affects the S1BF and BMA, while aging may harm all studied regions, including the S1BF, RSC, hippocampus, Pir, BMA, and DM. Aging mostly affects synapses and I/E ratios in Pir, BMA, and DM, and PV and SST interneurons in the hippocampus.

Tau pathology in the dorsal raphe may be a prodromal indicator of Alzheimer's disease

Protein aggregation in brainstem nuclei is thought to occur in the early stages of Alzheimer's disease (AD), but its specific role in driving prodromal symptoms and disease progression is largely unknown. The dorsal raphe nucleus (DRN) contains a large population of serotonin (5-hydroxytryptamine; 5-HT) neurons that regulate mood, reward-related behavior, and sleep, which are all disrupted in AD. We report here that tau pathology is present in the DRN of individuals 25-80 years old without a known history of dementia, and its prevalence was comparable to the locus coeruleus (LC). By comparison, fewer cases were positive for other pathological proteins including α-synuclein, β-amyloid, and TDP-43. To evaluate how early tau pathology impacts behavior, we overexpressed human P301L-tau in the DRN of mice and observed depressive-like behaviors and hyperactivity without deficits in spatial memory. Tau pathology was predominantly found in neurons relative to glia and colocalized with a significant proportion of Tph2-expressing neurons in the DRN. 5-HT neurons were also hyperexcitable in P301L-tauDRN mice, and there was an increase in the amplitude of excitatory post-synaptic currents (EPSCs). Moreover, astrocytic density was elevated in the DRN and accompanied by an increase in IL-1α and Frk expression, which suggests increased inflammatory signaling. Additionally, tau pathology was detected in axonal processes in the thalamus, hypothalamus, amygdala, and caudate putamen. A significant proportion of this tau pathology colocalized with the serotonin reuptake transporter (SERT), suggesting that tau may spread in an anterograde manner to regions outside the DRN. Together these results indicate that tau pathology accumulates in the DRN in a subset of individuals over 50 years and may lead to behavioral dysregulation, 5-HT neuronal dysfunction, and activation of local astrocytes which may be prodromal indicators of AD.

Seizing the opportunity to therapeutically address neuronal hyperexcitability in Alzheimer's disease

Seizures in people with Alzheimer's disease are increasingly recognized to worsen disease burden and accelerate functional decline. Harnessing established antiseizure medicine discovery strategies in rodents with Alzheimer's disease associated risk genes represents a novel way to uncover disease modifying treatments that may benefit these Alzheimer's disease patients. This commentary discusses the recent evaluation by Dejakaisaya and colleagues to assess the antiseizure and disease-modifying potential of the repurposed cephalosporin antibiotic, ceftriaxone, in the Tg2576 mouse model. The use of established epilepsy models in Alzheimer's disease research carries the potential to advance novel disease-modifying treatments.

Electrophysiological insights into Alzheimer's disease: A review of human and animal studies

This review highlights the crucial role of neuroelectrophysiology in illuminating the mechanisms underlying Alzheimer's disease (AD) pathogenesis and progression, emphasizing its potential to inform the development of effective treatments. Electrophysiological techniques provide unparalleled precision in exploring the intricate networks affected by AD, offering insights into the synaptic dysfunction, network alterations, and oscillatory abnormalities that characterize the disease. We discuss a range of electrophysiological methods, from non-invasive clinical techniques like electroencephalography and magnetoencephalography to invasive recordings in animal models. By drawing on findings from these studies, we demonstrate how electrophysiological research has deepened our understanding of AD-related network disruptions, paving the way for targeted therapeutic interventions. Moreover, we underscore the potential of electrophysiological modalities to play a pivotal role in evaluating treatment efficacy. Integrating electrophysiological data with clinical neuroimaging and longitudinal studies holds promise for a more comprehensive understanding of AD, enabling early detection and the development of personalized treatment strategies. This expanded research landscape offers new avenues for unraveling the complexities of AD and advancing therapeutic approaches.

Targeting high-affinity nicotinic receptors protects against the functional consequences of β-amyloid in mouse hippocampus

The accumulation of β-amyloid oligomers is a hallmark of Alzheimer's disease, inducing neural and network dysfunction in the early stages of pathology. The hippocampus is affected early in the pathogenesis of AD, however the impact of soluble β-amyloid on the dentate gyrus (DG) subregion of the hippocampus and its interaction with nicotinic acetylcholine receptors (nAChRs) within this region are not known. Using a localized model of over-expression, we show that β-amyloid induces early-onset neuronal hyperactivity and hippocampal-dependent memory deficits in mice. Further, we find the DG region to be under potent and sub-type specific nicotinic control in both healthy and pathophysiological conditions, with targeted receptor inhibition leading to a mnemonic rescue against localized amyloidosis. We show that while neurogenesis and synaptic functions are not severely affected in our model, reducing β2-containing nAChR function is associated with the promotion of young adult-born neurons within the pathological network, suggesting a possible protective mechanism. Our data thus reveal the DG network level changes which occur in the early-stages of β-amyloid accumulation and highlight the downstream consequences of targeted nicotinic neuromodulation.

Neural circuit mechanisms underlying aberrantly prolonged functional hyperemia in young Alzheimer's disease mice

Neurovascular defects are one of the most common alterations in Alzheimer's disease (AD) pathogenesis, but whether these deficits develop before the onset of amyloid beta (Aβ) accumulation remains to be determined. Using in vivo optical imaging in freely moving mice, we explored activity-induced hippocampal microvascular blood flow dynamics in AppSAA knock-in and J20 mouse models of AD at early stages of disease progression. We found that prior to the onset of Aβ accumulation, there was a pathologically elevated blood flow response to context exploration, termed functional hyperemia. After the onset of Aβ accumulation, this context exploration-induced hyperemia declined rapidly relative to that in control mice. Using in vivo electrophysiology recordings to explore the neural circuit mechanism underlying this blood flow alteration, we found that hippocampal interneurons before the onset of Aβ accumulation were hyperactive during context exploration. Chemogenetic tests suggest that hyperactive activation of inhibitory neurons accounted for the elevated functional hyperemia. The suppression of nitric oxide (NO) produced from hippocampal interneurons in young AD mice decreased the accumulation of Aβ. Together, these findings reveal that neurovascular coupling is aberrantly elevated before Aβ deposition, and this hyperactive functional hyperemia declines rapidly upon Aβ accumulation.

Regulation of GABAergic neurotransmission by purinergic receptors in brain physiology and disease

Purinergic receptors regulate the processing of neural information in the hippocampus and cerebral cortex, structures related to cognitive functions. These receptors are activated when astrocytic and neuronal populations release adenosine triphosphate (ATP) in an autocrine and paracrine manner, following sustained patterns of neuronal activity. The modulation by these receptors of GABAergic transmission has only recently been studied. Through their ramifications, astrocytes and GABAergic interneurons reach large groups of excitatory pyramidal neurons. Their inhibitory effect establishes different synchronization patterns that determine gamma frequency rhythms, which characterize neural activities related to cognitive processes. During early life, GABAergic-mediated synchronization of excitatory signals directs the experience-driven maturation of cognitive development, and dysfunctions concerning this process have been associated with neurological and neuropsychiatric diseases. Purinergic receptors timely modulate GABAergic control over ongoing neural activity and deeply affect neural processing in the hippocampal and neocortical circuitry. Stimulation of A2 receptors increases GABA release from presynaptic terminals, leading to a considerable reduction in neuronal firing of pyramidal neurons. A1 receptors inhibit GABAergic activity but only act in the early postnatal period when GABA produces excitatory signals. P2X and P2Y receptors expressed in pyramidal neurons reduce the inhibitory tone by blocking GABAA receptors. Finally, P2Y receptor activation elicits depolarization of GABAergic neurons and increases GABA release, thus favoring the emergence of gamma oscillations. The present review provides an overall picture of purinergic influence on GABAergic transmission and its consequences on neural processing, extending the discussion to receptor subtypes and their involvement in the onset of brain disorders, including epilepsy and Alzheimer's disease.

Amyloid-β deposition predicts oscillatory slowing of magnetoencephalography signals and a reduction of functional connectivity over time in cognitively unimpaired adults

With the ongoing developments in the field of anti-amyloid therapy for Alzheimer's disease, it is crucial to better understand the longitudinal associations between amyloid-β deposition and altered network activity in the living human brain. We included 110 cognitively unimpaired individuals (67.9 ± 5.7 years), who underwent [18F]flutemetamol (amyloid-β)-PET imaging and resting-state magnetoencephalography (MEG) recording at baseline and 4-year follow-up. We tested associations between baseline amyloid-β deposition and MEG measures (oscillatory power and functional connectivity). Next, we examined the relationship between baseline amyloid-β deposition and longitudinal MEG measures, as well as between baseline MEG measures and longitudinal amyloid-β deposition. Finally, we assessed associations between longitudinal changes in both amyloid-β deposition and MEG measures. Analyses were performed using linear mixed models corrected for age, sex and family. At baseline, amyloid-β deposition in orbitofrontal-posterior cingulate regions (i.e. early Alzheimer's disease regions) was associated with higher theta (4-8 Hz) power (β = 0.17, P < 0.01) in- and lower functional connectivity [inverted Joint Permutation Entropy (JPEinv) theta, β = -0.24, P < 0.001] of these regions, lower whole-brain beta (13-30 Hz) power (β = -0.13, P < 0.05) and lower whole-brain functional connectivity (JPEinv theta, β = -0.18, P < 0.001). Whole-brain amyloid-β deposition was associated with higher whole-brain theta power (β = 0.17, P < 0.05), lower whole-brain beta power (β = -0.13, P < 0.05) and lower whole-brain functional connectivity (JPEinv theta, β = -0.21, P < 0.001). Baseline amyloid-β deposition in early Alzheimer's disease regions also predicted future oscillatory slowing, reflected by increased theta power over time in early Alzheimer's disease regions and across the whole brain (β = 0.11, β = 0.08, P < 0.001), as well as decreased whole-brain beta power over time (β = -0.04, P < 0.05). Baseline amyloid-β deposition in early Alzheimer's disease regions also predicted a reduction in functional connectivity between these regions and the rest of the brain over time (JPEinv theta, β = -0.07, P < 0.05). Baseline whole-brain amyloid-β deposition was associated with increased whole-brain theta power over time (β = 0.08, P < 0.01). Baseline MEG measures were not associated with longitudinal amyloid-β deposition. Longitudinal changes in amyloid-β deposition in early Alzheimer's disease regions were associated with longitudinal changes in functional connectivity of early Alzheimer's disease regions (JPEinv theta, β = -0.19, P < 0.05) and the whole brain [corrected amplitude envelope correlations alpha (8-13 Hz), β = -0.22, P < 0.05]. Finally, longitudinal changes in whole-brain amyloid-β deposition were associated with longitudinal changes in whole-brain relative theta power (β = 0.21, P < 0.05). Disruptions of oscillatory power and functional connectivity appear to represent early functional consequences of emerging amyloid-β deposition in cognitively unimpaired individuals. These findings suggest a role for neurophysiology in monitoring disease progression and potential treatment effects in pre-clinical Alzheimer's disease.

Adenosine deficiency facilitates CA1 synaptic hyperexcitability in the presymptomatic phase of a knockin mouse model of Alzheimer disease

The disease's trajectory of Alzheimer disease (AD) is associated with and negatively correlated to hippocampal hyperexcitability. Here, we show that during the asymptomatic stage in a knockin (KI) mouse model of Alzheimer disease (APPNL-G-F/NL-G-F; APPKI), hippocampal hyperactivity occurs at the synaptic compartment, propagates to the soma, and is manifesting at low frequencies of stimulation. We show that this aberrant excitability is associated with a deficient adenosine tone, an inhibitory neuromodulator, driven by reduced levels of CD39/73 enzymes, responsible for the extracellular ATP-to-adenosine conversion. Both pharmacologic (adenosine kinase inhibitor) and non-pharmacologic (ketogenic diet) restorations of the adenosine tone successfully normalize hippocampal neuronal activity. Our results demonstrated that neuronal hyperexcitability during the asymptomatic stage of a KI model of Alzheimer disease originated at the synaptic compartment and is associated with adenosine deficient tone. These results extend our comprehension of the hippocampal vulnerability associated with the asymptomatic stage of Alzheimer disease.

Medial entorhinal-hippocampal desynchronization parallels the emergence of memory impairment in a mouse model of Alzheimer's disease pathology

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive impairments in episodic and spatial memory, as well as circuit and network-level dysfunction. While functional impairments in medial entorhinal cortex (MEC) and hippocampus (HPC) have been observed in patients and rodent models of AD, it remains unclear how communication between these regions breaks down in disease, and what specific physiological changes are associated with the onset of memory impairment. We used silicon probes to simultaneously record neural activity in MEC and hippocampus before or after the onset of spatial memory impairment in the 3xTg mouse model of AD pathology. We found that reduced hippocampal theta power, reduced MEC-CA1 theta coherence, and altered phase locking of MEC and hippocampal neurons all coincided with the emergence of spatial memory impairment in 3xTg mice. Together, these findings indicate that disrupted temporal coordination of neural activity in the MEC-hippocampal system parallels the emergence of memory impairment in a model of AD pathology.

Revealing excitation-inhibition imbalance in Alzheimer's disease using multiscale neural model inversion of resting-state functional MRI

BACKGROUND

Alzheimer's disease (AD) is a serious neurodegenerative disorder without a clear understanding of pathophysiology. Recent experimental data have suggested neuronal excitation-inhibition (E-I) imbalance as an essential element of AD pathology, but E-I imbalance has not been systematically mapped out for either local or large-scale neuronal circuits in AD, precluding precise targeting of E-I imbalance in AD treatment.

METHOD

In this work, we apply a Multiscale Neural Model Inversion (MNMI) framework to the resting-state functional MRI data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) to identify brain regions with disrupted E-I balance in a large network during AD progression.

RESULTS

We observe that both intra-regional and inter-regional E-I balance is progressively disrupted from cognitively normal individuals, to mild cognitive impairment (MCI) and to AD. Also, we find that local inhibitory connections are more significantly impaired than excitatory ones and the strengths of most connections are reduced in MCI and AD, leading to gradual decoupling of neural populations. Moreover, we reveal a core AD network comprised mainly of limbic and cingulate regions. These brain regions exhibit consistent E-I alterations across MCI and AD, and thus may represent important AD biomarkers and therapeutic targets. Lastly, the E-I balance of multiple brain regions in the core AD network is found to be significantly correlated with the cognitive test score.

CONCLUSIONS

Our study constitutes an important attempt to delineate E-I imbalance in large-scale neuronal circuits during AD progression, which may facilitate the development of new treatment paradigms to restore physiological E-I balance in AD.

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).

Mass spectrometry identifies tau C-terminal phosphorylation cluster during neuronal hyperexcitation

Tau is a microtubule-associated protein implicated in Alzheimer's disease (AD) and other neurodegenerative disorders termed tauopathies. Pathological, aggregated forms of tau form neurofibrillary tangles (NFTs), impairing its ability to stabilize microtubules and promoting neurotoxicity. Indeed, NFTs correlate with neuronal loss and cognitive impairment. Hyperphosphorylation of tau is seen in all tauopathies and mirrors disease progression, suggesting an essential role in pathogenesis. However, hyperphosphorylation remains a generic and ill-defined term, obscuring the functional importance of specific sites in different physiological or pathological settings. Here, we focused on global mapping of tau phosphorylation specifically during conditions of neuronal hyperexcitation. Hyperexcitation is a property of AD and other tauopathies linked to human cognitive deficits and increased risk of developing seizures and epilepsy. Moreover, hyperexcitation promotes extracellular secretion and trans-synaptic propagation of tau. Using unbiased mass spectrometry, we identified a novel phosphorylation signature in the C-terminal domain of tau detectable only during neuronal hyperactivity in primary cultured rat hippocampal neurons. These sites influenced tau localization to dendrites as well as the size of excitatory postsynaptic sites. These results demonstrate novel physiological tau functions at synapses and the utility of comprehensive analysis of tau phosphorylation during specific signaling contexts.

Astrocyte-derived MFG-E8 facilitates microglial synapse elimination in Alzheimer's disease mouse models

Region-specific synapse loss is an early pathological hallmark in Alzheimer's disease (AD). Emerging data in mice and humans highlight microglia, the brain-resident macrophages, as cellular mediators of synapse loss; however, the upstream modulators of microglia-synapse engulfment remain elusive. Here, we report a distinct subset of astrocytes, which are glial cells essential for maintaining synapse homeostasis, appearing in a region-specific manner with age and amyloidosis at onset of synapse loss. These astrocytes are distinguished by their peri-synaptic processes which are 'bulbous' in morphology, contain accumulated p62-immunoreactive bodies, and have reduced territorial domains, resulting in a decrease of astrocyte-synapse coverage. Using integrated in vitro and in vivo approaches, we show that astrocytes upregulate and secrete phagocytic modulator, milk fat globule-EGF factor 8 (MFG-E8), which is sufficient and necessary for promoting microglia-synapse engulfment in their local milieu. Finally, we show that knocking down Mfge8 specifically from astrocytes using a viral CRISPR-saCas9 system prevents microglia-synapse engulfment and ameliorates synapse loss in two independent amyloidosis mouse models of AD. Altogether, our findings highlight astrocyte-microglia crosstalk in determining synapse fate in amyloid models and nominate astrocytic MFGE8 as a potential target to ameliorate synapse loss during the earliest stages of AD.

Regulation of presynaptic homeostatic plasticity by glial signalling in Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia among the elderly, affects numerous individuals worldwide. Despite advances in understanding the molecular underpinnings of AD pathology, effective treatments to prevent or cure the disease remain elusive. AD is characterized not only by pathological hallmarks such as amyloid plaques and neurofibrillary tangles but also by impairments in synaptic physiology, circuit activity and cognitive function. Synaptic homeostatic plasticity plays a vital role in maintaining the stability of synaptic and neural functions amid genetic and environmental disturbances. A key component of this regulation is presynaptic homeostatic potentiation, where increased presynaptic neurotransmitter release compensates for reduced postsynaptic glutamate receptor functionality, thereby stabilizing neuronal excitability. The role of presynaptic homeostatic plasticity in synapse stabilization in AD, however, remains unclear. Moreover, recent advances in transcriptomics have illuminated the complex roles of glial cells in regulating synaptic function in ageing brains and in the progression of neurodegenerative diseases. Yet, the impact of AD-related abnormalities in glial signalling on synaptic homeostatic plasticity has not been fully delineated. This review discusses recent findings on how glial dysregulation in AD affects presynaptic homeostatic plasticity. There is increasing evidence that disrupted glial signalling, particularly through aberrant histone acetylation and transcriptomic changes in glia, compromises this plasticity in AD. Notably, the sphingosine signalling pathway has been identified as being protective in stabilizing synaptic physiology through epigenetic and homeostatic mechanisms, presenting potential therapeutic targets for treating neurodegenerative disorders.

Structural and functional alterations of neurons derived from sporadic Alzheimer's disease hiPSCs are associated with downregulation of the LIMK1-cofilin axis

BACKGROUND

Alzheimer's Disease (AD) is a neurodegenerative disorder characterized by the accumulation of pathological proteins and synaptic dysfunction. This study aims to investigate the molecular and functional differences between human induced pluripotent stem cells (hiPSCs) derived from patients with sporadic AD (sAD) and age-matched controls (healthy subjects, HS), focusing on their neuronal differentiation and synaptic properties in order to better understand the cellular and molecular mechanisms underlying AD pathology.

METHODS

Skin fibroblasts from sAD patients (n = 5) and HS subjects (n = 5) were reprogrammed into hiPSCs using non-integrating Sendai virus vectors. Through karyotyping, we assessed pluripotency markers (OCT4, SOX2, TRA-1-60) and genomic integrity. Neuronal differentiation was evaluated by immunostaining for MAP2 and NEUN. Electrophysiological properties were measured using whole-cell patch-clamp, while protein expression of Aβ, phosphorylated tau, Synapsin-1, Synaptophysin, PSD95, and GluA1 was quantified by western blot. We then focused on PAK1-LIMK1-Cofilin signaling, which plays a key role in regulating synaptic structure and function, both of which are disrupted in neurodegenerative diseases such as AD.

RESULTS

sAD and HS hiPSCs displayed similar stemness features and genomic stability. However, they differed in neuronal differentiation and function. sAD-derived neurons (sAD-hNs) displayed increased levels of AD-related proteins, including Aβ and phosphorylated tau. Electrophysiological analyses revealed that while both sAD- and HS-hNs generated action potentials, sAD-hNs exhibited decreased spontaneous synaptic activity. Significant reductions in the expression of synaptic proteins such as Synapsin-1, Synaptophysin, PSD95, and GluA1 were found in sAD-hNs, which are also characterized by reduced neurite length, indicating impaired differentiation. Notably, sAD-hNs demonstrated a marked reduction in LIMK1 phosphorylation, which could be the underlying cause for the changes in cytoskeletal dynamics that we found, leading to the morphological and functional modifications observed in sAD-hNs. To further investigate the involvement of the LIMK1 pathway in the morphological and functional changes observed in sAD neurons, we conducted perturbation experiments using the specific LIMK1 inhibitor, BMS-5. Neurons obtained from healthy subjects treated with the inhibitor showed similar morphological changes to those observed in sAD neurons, confirming that LIMK1 activity is crucial for maintaining normal neuronal structure. Furthermore, administration of the inhibitor to sAD neurons did not exacerbate the morphological alterations, suggesting that LIMK1 activity is already compromised in these cells.

CONCLUSION

Our findings demonstrate that although sAD- and HS-hiPSCs are similar in their stemness and genomic stability, sAD-hNs exhibit distinct functional and structural anomalies mirroring AD pathology. These anomalies include synaptic dysfunction, altered cytoskeletal organization, and accumulation of AD-related proteins. Our study underscores the usefulness of hiPSCs in modeling AD and provides insights into the disease's molecular underpinnings, thus highlighting potential therapeutic targets.

Enhanced prefrontal nicotinic signaling as evidence of active compensation in Alzheimer's disease models

BACKGROUND

Cognitive reserve allows for resilience to neuropathology, potentially through active compensation. Here, we examine ex vivo electrophysiological evidence for active compensation in Alzheimer's disease (AD) focusing on the cholinergic innervation of layer 6 in prefrontal cortex. Cholinergic pathways are vulnerable to neuropathology in AD and its preclinical models, and their modulation of deep layer prefrontal cortex is essential for attention and executive function.

METHODS

We functionally interrogated cholinergic modulation of prefrontal layer 6 pyramidal neurons in two preclinical models: a compound transgenic AD mouse model that permits optogenetically-triggered release of endogenous acetylcholine and a transgenic AD rat model that closely recapitulates the human trajectory of AD. We then tested the impact of therapeutic interventions to further amplify the compensated responses and preserve the typical kinetic profile of cholinergic signaling.

RESULTS

In two AD models, we found potentially compensatory upregulation of functional cholinergic responses above non-transgenic controls after onset of pathology. To identify the locus of this enhanced cholinergic signal, we dissected key pre- and post-synaptic components with pharmacological strategies. We identified a significant and selective increase in post-synaptic nicotinic receptor signalling on prefrontal cortical neurons. To probe the additional impact of therapeutic intervention on the adapted circuit, we tested cholinergic and nicotinic-selective pro-cognitive treatments. Inhibition of acetylcholinesterase further enhanced endogenous cholinergic responses but greatly distorted their kinetics. Positive allosteric modulation of nicotinic receptors, by contrast, enhanced endogenous cholinergic responses and retained their rapid kinetics.

CONCLUSIONS

We demonstrate that functional nicotinic upregulation occurs within the prefrontal cortex in two AD models. Promisingly, this nicotinic signal can be further enhanced while preserving its rapid kinetic signature. Taken together, our work suggests that compensatory mechanisms are active within the prefrontal cortex that can be harnessed by nicotinic receptor positive allosteric modulation, highlighting a new direction for cognitive treatment in AD neuropathology.