Network abnormalities and interneuron dysfunction in Alzheimer disease

An emerging role of STriatal-enriched protein tyrosine phosphatase in hyperexcitability-associated brain disorders

STriatal-Enriched protein tyrosine Phosphatase (STEP) is a brain-specific tyrosine phosphatase that is associated with numerous neurological and neuropsychiatric disorders. STEP dephosphorylates and inactivates various kinases and phosphatases critical for neuronal function and health including Fyn, Pyk2, ERK1/2, p38, and PTPα. Importantly, STEP dephosphorylates NMDA and AMPA receptors, two major glutamate receptors that mediate fast excitatory synaptic transmission. This STEP-mediated dephosphorylation leads to their internalization and inhibits both Hebbian synaptic potentiation and homeostatic synaptic scaling. Hence, STEP has been widely accepted to weaken excitatory synaptic strength. However, emerging evidence implicates a novel role of STEP in neuronal hyperexcitability and seizure disorders. Genetic deletion and pharmacological blockade of STEP reduces seizure susceptibility in acute seizure mouse models and audiogenic seizures in a mouse model of Fragile X syndrome. Pharmacologic inhibition of STEP also decreases hippocampal activity and neuronal intrinsic excitability. Here, we will highlight the divergent roles of STEP in excitatory synaptic transmission and neuronal intrinsic excitability, present the potential underlying mechanisms, and discuss their impact on STEP-associated neurologic and neuropsychiatric disorders.

Impairment of brain function in a mouse model of Alzheimer's disease during the pre-depositing phase: The role of α7 nicotinic acetylcholine receptors

Alzheimer's disease (AD) is an age-dependent incurable neurodegenerative disorder accompanied by neuroinflammation, amyloid accumulation, and memory impairment. It begins decades before the first clinical symptoms appear, and identifying early biomarkers is key for developing disease-modifying therapies. We show now in a mouse model of AD that before any amyloid deposition the brains of 1.5-month-old mice contain increased levels of pro-inflammatory cytokines IL-1β and IL-6, decreased levels of nicotinic acetylcholine receptors (nAChRs) in the brain and brain mitochondria and increased amounts of α7 nAChR-bound Aβ1-42, along with impaired episodic memory and increased risk of apoptosis. Both acute (1-week-long) and chronic (4-month-long) treatments with α7-selective agonist PNU282987, starting at 1.5 months of age, were well tolerated. The acute treatment did not affect the levels of soluble Aβ1-42 but consistently upregulated the α7 nAChR expression, decreased the level of α7-Aβ1-42 complexes, and improved episodic memory of 1.5-month-old mice. The chronic treatment, covering the disease development phase, strongly upregulated the expression of all abundant brain nAChRs, reduced both free and α7-coupled Aβ1-42 within the brain, had anti-inflammatory and antiapoptotic effects, and potently upregulated cognition, thus identifying α7 nAChRs as both early biomarker and potent therapeutic target for fighting this devastating disease.

Single-Cell Patch-Clamp/Proteomics of Human Alzheimer's Disease iPSC-Derived Excitatory Neurons Versus Isogenic Wild-Type Controls Suggests Novel Causation and Therapeutic Targets

Standard single-cell (sc) proteomics of disease states inferred from multicellular organs or organoids cannot currently be related to single-cell physiology. Here, a scPatch-Clamp/Proteomics platform is developed on single neurons generated from hiPSCs bearing an Alzheimer's disease (AD) genetic mutation and compares them to isogenic wild-type controls. This approach provides both current and voltage electrophysiological data plus detailed proteomics information on single-cells. With this new method, the authors are able to observe hyperelectrical activity in the AD hiPSC-neurons, similar to that observed in the human AD brain, and correlate it to ≈1400 proteins detected at the single neuron level. Using linear regression and mediation analyses to explore the relationship between the abundance of individual proteins and the neuron's mutational and electrophysiological status, this approach yields new information on therapeutic targets in excitatory neurons not attainable by traditional methods. This combined patch-proteomics technique creates a new proteogenetic-therapeutic strategy to correlate genotypic alterations to physiology with protein expression in single-cells.

Amygdala neuronal dyshomeostasis via 5-HT receptors mediates mood and cognitive defects in Alzheimer's disease

Behavioral changes or neuropsychiatric symptoms (NPSs) are common features in dementia and are associated with accelerated cognitive impairment and earlier deaths. However, how NPSs are intertwined with cognitive decline remains elusive. In this study, we identify that the basolateral amygdala (BLA) is a key brain region that is associated with mood disorders and memory decline in the AD course. During the process from pre- to post-onset in AD, the dysfunction of parvalbumin (PV) interneurons and pyramidal neurons in the amygdala leads to hyperactivity of pyramidal neurons in the basal state and insensitivity to external stimuli. We further demonstrate that serotonin (5-HT) receptors in distinct neurons synergistically regulate the BLA microcircuit of AD rather than 5-HT levels, in which both restrained inhibitory inputs by excessive 5-HT1AR signaling in PV interneurons and depolarized pyramidal neurons via upregulated 5-HT2AR contribute to aberrant neuronal hyperactivity. Downregulation of these two 5-HT receptors simultaneously enables neurons to resist β-amyloid peptides (Aβ) neurotoxicity and ameliorates the mood and cognitive defects. Therefore, our study reveals a crucial role of 5-HT receptors for regulating neuronal homeostasis in AD pathogenesis, and this would provide early intervention and potential targets for AD cognitive decline.

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.

Synaptic signaling modeled by functional connectivity predicts metabolic demands of the human brain

PURPOSE

The human brain is characterized by interacting large-scale functional networks fueled by glucose metabolism. Since former studies could not sufficiently clarify how these functional connections shape glucose metabolism, we aimed to provide a neurophysiologically-based approach.

METHODS

51 healthy volunteers underwent simultaneous PET/MRI to obtain BOLD functional connectivity and [18F]FDG glucose metabolism. These multimodal imaging proxies of fMRI and PET were combined in a whole-brain extension of metabolic connectivity mapping. Specifically, functional connectivity of all brain regions were used as input to explain glucose metabolism of a given target region. This enabled the modeling of postsynaptic energy demands by incoming signals from distinct brain regions.

RESULTS

Functional connectivity input explained a substantial part of metabolic demands but with pronounced regional variations (34 - 76%). During cognitive task performance this multimodal association revealed a shift to higher network integration compared to resting state. In healthy aging, a dedifferentiation (decreased segregated/modular structure of the brain) of brain networks during rest was observed. Furthermore, by including data from mRNA maps, [11C]UCB-J synaptic density and aerobic glycolysis (oxygen-to-glucose index from PET data), we show that whole-brain functional input reflects non-oxidative, on-demand metabolism of synaptic signaling. The metabolically-derived directionality of functional inputs further marked them as top-down predictions. In addition, the approach uncovered formerly hidden networks with superior efficiency through metabolically informed network partitioning.

CONCLUSIONS

Applying multimodal imaging, we decipher a crucial part of the metabolic and neurophysiological basis of functional connections in the brain as interregional on-demand synaptic signaling fueled by anaerobic metabolism. The observed task- and age-related effects indicate promising future applications to characterize human brain function and clinical alterations.

Optimal gamma-band entrainment of visual cortex

Visual entrainment is a powerful and widely used research tool to study visual information processing in the brain. While many entrainment studies have focused on frequencies around 14-16 Hz, there is renewed interest in understanding visual entrainment at higher frequencies (e.g., gamma-band entrainment). Notably, recent groundbreaking studies have demonstrated that gamma-band visual entrainment at 40 Hz may have therapeutic effects in the context of Alzheimer's disease (AD) by stimulating specific neural ensembles, which utilize GABAergic signaling. Despite such promising findings, few studies have investigated the optimal parameters for gamma-band visual entrainment. Herein, we examined whether visual stimulation at 32, 40, or 48 Hz produces optimal visual entrainment responses using high-density magnetoencephalography (MEG). Our results indicated strong entrainment responses localizing to the primary visual cortex in each condition. Entrainment responses were stronger for 32 and 40 Hz relative to 48 Hz, indicating more robust synchronization of neural ensembles at these lower gamma-band frequencies. In addition, 32 and 40 Hz entrainment responses showed typical patterns of habituation across trials, but this effect was absent for 48 Hz. Finally, connectivity between visual cortex and parietal and prefrontal cortices tended to be strongest for 40 relative to 32 and 48 Hz entrainment. These results suggest that neural ensembles in the visual cortex may resonate at around 32 and 40 Hz and thus entrain more readily to photic stimulation at these frequencies. Emerging AD therapies, which have focused on 40 Hz entrainment to date, may be more effective at lower relative to higher gamma frequencies, although additional work in clinical populations is needed to confirm these findings. PRACTITIONER POINTS: Gamma-band visual entrainment has emerged as a therapeutic approach for eliminating amyloid in Alzheimer's disease, but its optimal parameters are unknown. We found stronger entrainment at 32 and 40 Hz compared to 48 Hz, suggesting neural ensembles prefer to resonate around these relatively lower gamma-band frequencies. These findings may inform the development and refinement of innovative AD therapies and the study of GABAergic visual cortical functions.

Early oxidative stress and DNA damage in Aβ-burdened hippocampal neurons in an Alzheimer's-like transgenic rat model

Oxidative stress is a key contributor to AD pathology. However, the earliest role of pre-plaque neuronal oxidative stress, remains elusive. Using laser microdissected hippocampal neurons extracted from McGill-R-Thy1-APP transgenic rats we found that intraneuronal amyloid beta (iAβ)-burdened neurons had increased expression of genes related to oxidative stress and DNA damage responses including Ercc2, Fancc, Sod2, Gsr, and Idh1. DNA damage was further evidenced by increased neuronal levels of XPD (Ercc2) and γH2AX foci, indicative of DNA double stranded breaks (DSBs), and by increased expression of Ercc6, Rad51, and Fen1, and decreased Sirt6 in hippocampal homogenates. We also found increased expression of synaptic plasticity genes (Grin2b (NR2B), CamkIIα, Bdnf, c-fos, and Homer1A) and increased protein levels of TOP2β. Our findings indicate that early accumulation of iAβ, prior to Aβ plaques, is accompanied by incipient oxidative stress and DSBs that may arise directly from oxidative stress or from maladaptive synaptic plasticity.

Co-activation of selective nicotinic acetylcholine receptor subtypes is required to reverse hippocampal network dysfunction and prevent fear memory loss in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia with no known cause and cure. Research suggests that a reduction of GABAergic inhibitory interneurons' activity in the hippocampus by beta-amyloid peptide (Aβ) is a crucial trigger for cognitive impairment in AD via hyperexcitability. Therefore, enhancing hippocampal inhibition is thought to be protective against AD. However, hippocampal inhibitory cells are highly diverse, and these distinct interneuron subtypes differentially regulate hippocampal inhibitory circuits and cognitive processes. Moreover, Aβ unlikely affects all subtypes of inhibitory interneurons in the hippocampus equally. Hence, identifying the affected interneuron subtypes in AD to enhance hippocampal inhibition optimally is conceptually and practically challenging. We have previously found that Aβ selectively binds to two of the three major hippocampal nicotinic acetylcholine receptor (nAChR) subtypes, α7- and α4β2-nAChRs, but not α3β4-nAChRs, and inhibits these two receptors in cultured hippocampal inhibitory interneurons to decrease their activity, leading to hyperexcitation and synaptic dysfunction in excitatory neurons. We have also revealed that co-activation of α7- and α4β2-nAChRs is required to reverse the Aβ-induced adverse effects in hippocampal excitatory neurons. Here, we discover that α7- and α4β2-nAChRs predominantly control the nicotinic cholinergic signaling and neuronal activity in hippocampal parvalbumin-positive (PV+) and somatostatin-positive (SST+) inhibitory interneurons, respectively. Furthermore, we reveal that co-activation of these receptors is necessary to reverse hippocampal network dysfunction and fear memory loss in the amyloid pathology model mice. We thus suggest that co-activation of PV+ and SST+ cells is a novel strategy to reverse hippocampal dysfunction and cognitive decline in AD.

β-amyloid monomer scavenging by an anticalin protein prevents neuronal hyperactivity in mouse models of Alzheimer's Disease

Hyperactivity mediated by synaptotoxic β-amyloid (Aβ) oligomers is one of the earliest forms of neuronal dysfunction in Alzheimer's disease. In the search for a preventive treatment strategy, we tested the effect of scavenging Aβ peptides before Aβ plaque formation. Using in vivo two-photon calcium imaging and SF-iGluSnFR-based glutamate imaging in hippocampal slices, we demonstrate that an Aβ binding anticalin protein (Aβ-anticalin) can suppress early neuronal hyperactivity and synaptic glutamate accumulation in the APP23xPS45 mouse model of β-amyloidosis. Our results suggest that the sole targeting of Aβ monomers is sufficient for the hyperactivity-suppressing effect of the Aβ-anticalin at early disease stages. Biochemical and neurophysiological analyses indicate that the Aβ-anticalin-dependent depletion of naturally secreted Aβ monomers interrupts their aggregation to neurotoxic oligomers and, thereby, reverses early neuronal and synaptic dysfunctions. Thus, our results suggest that Aβ monomer scavenging plays a key role in the repair of neuronal function at early stages of AD.

Neuronal APOE4-induced Early Hippocampal Network Hyperexcitability in Alzheimer's Disease Pathogenesis

The full impact of apolipoprotein E4 (APOE4), the strongest genetic risk factor for Alzheimer's disease (AD), on neuronal and network function remains unclear. We found hippocampal region-specific network hyperexcitability in young APOE4 knock-in (E4-KI) mice which predicted cognitive deficits at old age. Network hyperexcitability in young E4-KI mice was mediated by hippocampal region-specific subpopulations of smaller and hyperexcitable neurons that were eliminated by selective removal of neuronal APOE4. Aged E4-KI mice exhibited hyperexcitable granule cells, a progressive inhibitory deficit, and E/I imbalance in the dentate gyrus, exacerbating hippocampal hyperexcitability. Single-nucleus RNA-sequencing revealed neuronal cell type-specific and age-dependent transcriptomic changes, including Nell2 overexpression in E4-KI mice. Reducing Nell2 expression in specific neuronal types of E4-KI mice with CRISPRi rescued their abnormal excitability phenotypes, implicating Nell2 overexpression as a cause of APOE4-induced hyperexcitability. These findings highlight the early transcriptomic and electrophysiological alterations underlying APOE4-induced hippocampal network dysfunction and its contribution to AD pathogenesis with aging.

FGFR3 drives Aβ-induced tau uptake

The amyloid cascade hypothesis suggests that amyloid beta (Aβ) contributes to initiating subsequent tau pathology in Alzheimer's disease (AD). However, the underlying mechanisms through which Aβ contributes to tau uptake and propagation remain poorly understood. Here, we show that preexisting amyloid pathology accelerates the uptake of extracellular tau into neurons. Using quantitative proteomic analysis of endocytic vesicles, we reveal that Aβ induces the internalization of fibroblast growth factor receptor 3 (FGFR3). Extracellular tau binds to the extracellular domain of FGFR3 and is internalized by the FGFR3 ligand, fibroblast growth factor 2 (FGF2). Aβ accelerates FGF2 secretion from neurons, thereby inducing the internalization of tau-attached FGFR3. Knockdown of FGFR3 in the hippocampus reduces tau aggregation by decreasing tau uptake and improving memory function in AD model mice. These data suggest FGFR3 in neurons as a novel tau receptor and a key mediator of Aβ-induced tau uptake in AD.

Three dimensional and four dimensional live imaging to study mechanisms of progressive neurodegeneration

Neurodegenerative diseases are complex and progressive, posing challenges to their study and understanding. Recent advances in microscopy imaging technologies have enabled the exploration of neurons in three spatial dimensions (3D) over time (4D). When applied to 3D cultures, tissues, or animals, these technologies can provide valuable insights into the dynamic and spatial nature of neurodegenerative diseases. This review focuses on the use of imaging techniques and neurodegenerative disease models to study neurodegeneration in 4D. Imaging techniques such as confocal microscopy, two-photon microscopy, miniscope imaging, light sheet microscopy, and robotic microscopy offer powerful tools to visualize and analyze neuronal changes over time in 3D tissue. Application of these technologies to in vitro models of neurodegeneration such as mouse organotypic culture systems and human organoid models provide versatile platforms to study neurodegeneration in a physiologically relevant context. Additionally, use of 4D imaging in vivo, including in mouse and zebrafish models of neurodegenerative diseases, allows for the investigation of early dysfunction and behavioral changes associated with neurodegeneration. We propose that these studies have the power to overcome the limitations of two-dimensional monolayer neuronal cultures and pave the way for improved understanding of the dynamics of neurodegenerative diseases and the development of effective therapeutic strategies.

Transcranial alternating current stimulation (tACS) at gamma frequency: an up-and-coming tool to modify the progression of Alzheimer's Disease

The last decades have witnessed huge efforts devoted to deciphering the pathological mechanisms underlying Alzheimer's Disease (AD) and to testing new drugs, with the recent FDA approval of two anti-amyloid monoclonal antibodies for AD treatment. Beyond these drug-based experimentations, a number of pre-clinical and clinical trials are exploring the benefits of alternative treatments, such as non-invasive stimulation techniques on AD neuropathology and symptoms. Among the different non-invasive brain stimulation approaches, transcranial alternating current stimulation (tACS) is gaining particular attention due to its ability to externally control gamma oscillations. Here, we outline the current knowledge concerning the clinical efficacy, safety, ease-of-use and cost-effectiveness of tACS on early and advanced AD, applied specifically at 40 Hz frequency, and also summarise pre-clinical results on validated models of AD and ongoing patient-centred trials.

Nr4a1 regulates cell-specific transcriptional programs in inhibitory GABAergic interneurons

The patterns of synaptic connectivity and physiological properties of diverse neuron types are shaped by distinct gene sets. Our study demonstrates that, in the mouse forebrain, the transcriptional profiles of inhibitory GABAergic interneurons are regulated by Nr4a1, an orphan nuclear receptor whose expression is transiently induced by sensory experiences and is required for normal learning. Nr4a1 exerts contrasting effects on the local axonal wiring of parvalbumin- and somatostatin-positive interneurons, which innervate different subcellular domains of their postsynaptic partners. The loss of Nr4a1 activity in these interneurons results in bidirectional, cell-type-specific transcriptional switches across multiple gene families, including those involved in surface adhesion and repulsion. Our findings reveal that combinatorial synaptic organizing codes are surprisingly flexible and highlight a mechanism by which inducible transcription factors can influence neural circuit structure and function.

Auditory gamma-band entrainment enhances default mode network connectivity in dementia patients

Dementia, and in particular Alzheimer's disease (AD), can be characterized by disrupted functional connectivity in the brain caused by beta-amyloid deposition in neural links. Non-pharmaceutical treatments for dementia have recently explored interventions involving the stimulation of neuronal populations in the gamma band. These interventions aim to restore brain network functionality by synchronizing rhythmic energy through various stimulation modalities. Entrainment, a newly proposed non-invasive sensory stimulation method, has shown promise in improving cognitive functions in dementia patients. This study investigates the effectiveness of entrainment in terms of promoting neural synchrony and spatial connectivity across the cortex. EEG signals were recorded during a 40 Hz auditory entrainment session conducted with a group of elderly participants with dementia. Phase locking value (PLV) between different intraregional and interregional sites was examined as an attribute of network synchronization, and connectivity of local and distant links were compared during the stimulation and rest trials. Our findings demonstrate enhanced neural synchrony between the frontal and parietal regions, which are key components of the brain's default mode network (DMN). The DMN operation is known to be impacted by dementia's progression, leading to reduced functional connectivity across the parieto-frontal pathways. Notably, entrainment alone significantly improves synchrony between these DMN components, suggesting its potential for restoring functional connectivity.

Seizures exacerbate excitatory: inhibitory imbalance in Alzheimer's disease and 5XFAD mice

Approximately 22% of Alzheimer's disease (AD) patients suffer from seizures, and the co-occurrence of seizures and epileptiform activity exacerbates AD pathology and related cognitive deficits, suggesting that seizures may be a targetable component of AD progression. Given that alterations in neuronal excitatory:inhibitory (E:I) balance occur in epilepsy, we hypothesized that decreased markers of inhibition relative to those of excitation would be present in AD patients. We similarly hypothesized that in 5XFAD mice, the E:I imbalance would progress from an early stage (prodromal) to later symptomatic stages and be further exacerbated by pentylenetetrazol (PTZ) kindling. Post-mortem AD temporal cortical tissues from patients with or without seizure history were examined for changes in several markers of E:I balance, including levels of the inhibitory GABAA receptor, the sodium potassium chloride cotransporter 1 (NKCC1) and potassium chloride cotransporter 2 (KCC2) and the excitatory NMDA and AMPA type glutamate receptors. We performed patch-clamp electrophysiological recordings from CA1 neurons in hippocampal slices and examined the same markers of E:I balance in prodromal 5XFAD mice. We next examined 5XFAD mice at chronic stages, after PTZ or control protocols, and in response to chronic mTORC1 inhibitor rapamycin, administered following kindled seizures, for markers of E:I balance. We found that AD patients with comorbid seizures had worsened cognitive and functional scores and decreased GABAA receptor subunit expression, as well as increased NKCC1/KCC2 ratios, indicative of depolarizing GABA responses. Patch clamp recordings of prodromal 5XFAD CA1 neurons showed increased intrinsic excitability, along with decreased GABAergic inhibitory transmission and altered glutamatergic neurotransmission, indicating that E:I imbalance may occur in early disease stages. Furthermore, seizure induction in prodromal 5XFAD mice led to later dysregulation of NKCC1/KCC2 and a reduction in GluA2 AMPA glutamate receptor subunit expression, indicative of depolarizing GABA receptors and calcium permeable AMPA receptors. Finally, we found that chronic treatment with the mTORC1 inhibitor, rapamycin, at doses we have previously shown to attenuate seizure-induced amyloid-β pathology and cognitive deficits, could also reverse elevations of the NKCC1/KCC2 ratio in these mice. Our data demonstrate novel mechanisms of interaction between AD and epilepsy and indicate that targeting E:I balance, potentially with US Food and Drug Administration-approved mTOR inhibitors, hold therapeutic promise for AD patients with a seizure history.

Sleep functional connectivity, hyperexcitability, and cognition in Alzheimer's disease

INTRODUCTION

Sleep disturbances are common in Alzheimer's disease (AD) and may reflect pathologic changes in brain networks. To date, no studies have examined changes in sleep functional connectivity (FC) in AD or their relationship with network hyperexcitability and cognition.

METHODS

We assessed electroencephalogram (EEG) sleep FC in 33 healthy controls, 36 individuals with AD without epilepsy, and 14 individuals with AD and epilepsy.

RESULTS

AD participants showed increased gamma connectivity in stage 2 sleep (N2), which was associated with longitudinal cognitive decline. Network hyperexcitability in AD was associated with a distinct sleep connectivity signature, characterized by decreased N2 delta connectivity and reversal of several connectivity changes associated with AD. Machine learning algorithms using sleep connectivity features accurately distinguished diagnostic groups and identified "fast cognitive decliners" among study participants who had AD.

DISCUSSION

Our findings reveal changes in sleep functional networks associated with cognitive decline in AD and may have implications for disease monitoring and therapeutic development.

HIGHLIGHTS

Brain functional connectivity (FC) in Alzheimer's disease is altered during sleep. Sleep FC measures correlate with cognitive decline in AD. Network hyperexcitability in AD has a distinct sleep connectivity signature.

Electroacupuncture Ameliorates Cognitive Impairment by Regulating γ-Amino Butyric Acidergic Interneurons in the Hippocampus of 5 Familial Alzheimer's Disease Mice

OBJECTIVES

γ-amino butyric acid (GABA)-ergic dysfunction in excitatory and inhibitory (E/I) imbalance drives the pathogenesis of Alzheimer's disease (AD). Inhibitory interneurons play an important role in the regulation of E/I balance, synaptic transmission, and network oscillation through manipulation of GABAergic functions, showing positive outcomes in AD animal models. Mice expressing 5 familial AD mutation (5xFAD) exhibited a series of AD-like pathology and learning and memory deficits with age. Because electroacupuncture (EA) treatment has been used for a complementary alternative medicine therapy in patients with AD, we aimed to examine any usefulness of EA therapy in GABA interneuron function and its associated synaptic proteins, to determine whether EA could effectively improve inhibitory transmission and network oscillation and eventually alleviate cognitive impairments in 5xFAD mice, and to further elucidate the GABAergic system function underlying the antidementia response of EA.

MATERIALS AND METHODS

5xFAD mice were used to evaluate the potential neuroprotective effect of electroacupuncture at Baihui (DU 20) and Dazhui (DU 14) through behavioral testing, immunofluorescence staining, electrophysiology recording, and molecular biology analysis.

RESULTS

First, we observed that EA improved memory deficits and inhibitory synaptic protein expression. Second, EA treatment alleviated the decrease of somatostatin-positive interneurons in the dorsal hippocampus. Third, EA attenuated E/I imbalance in 5xFAD mice. Last, EA treatment enhanced theta and gamma oscillation in the hippocampus of 5xFAD mice.

CONCLUSIONS

EA stimulation at DU20 and DU14 acupoints may be a potential alternative therapy to ameliorate cognitive deficits in AD through the regulation of the function of the GABAergic interneuron.

Synaptic adhesion molecule protocadherin-γC5 mediates β-amyloid-induced neuronal hyperactivity and cognitive deficits in Alzheimer's disease

Neuronal hyperactivity induced by β-amyloid (Aβ) is an early pathological feature in Alzheimer's disease (AD) and contributes to cognitive decline in AD progression. However, the underlying mechanisms are still unclear. Here, we revealed that Aβ increased the expression level of synaptic adhesion molecule protocadherin-γC5 (Pcdh-γC5) in a Ca2+-dependent manner, associated with aberrant elevation of synapses in both Aβ-treated neurons in vitro and the cortex of APP/PS1 mice in vivo. By using Pcdhgc5 gene knockout mice, we demonstrated the critical function of Pcdh-γC5 in regulating neuronal synapse formation, synaptic transmission, and cognition. To further investigate the role of Pcdh-γC5 in AD pathogenesis, the aberrantly enhanced expression of Pcdh-γC5 in the brain of APP/PS1 mice was knocked down by shRNA. Downregulation of Pcdh-γC5 efficiently rescued neuronal hyperactivity and impaired cognition in APP/PS1 mice. Our findings revealed the pathophysiological role of Pcdh-γC5 in mediating Aβ-induced neuronal hyperactivity and cognitive deficits in AD and identified a novel mechanism underlying AD pathogenesis.

Impairment of entorhinal cortex network activity in Alzheimer's disease

The entorhinal cortex (EC) stands out as a critical brain region affected in the early phases of Alzheimer's disease (AD), with some of the disease's pathological processes originating from this area, making it one of the most crucial brain regions in AD. Recent research highlights disruptions in the brain's network activity, characterized by heightened excitability and irregular oscillations, may contribute to cognitive impairment. These disruptions are proposed not only as potential therapeutic targets but also as early biomarkers for AD. In this paper, we will begin with a review of the anatomy and function of EC, highlighting its selective vulnerability in AD. Subsequently, we will discuss the disruption of EC network activity, exploring changes in excitability and neuronal oscillations in this region during AD and hypothesize that, considering the advancements in neuromodulation techniques, addressing the disturbances in the network activity of the EC could offer fresh insights for both the diagnosis and treatment of AD.

Ferroptosis: A double-edged sword

Ferroptosis represents a form of programmed cell death that is propelled by iron-dependent lipid peroxidation, thereby being distinguished by the prominent features of iron accumulation and lipid peroxidation. Ferroptosis has been implicated in numerous physiological and pathological phenomena, with mounting indications that it holds significant implications for cancer and other medical conditions. On one side, it demonstrates anti-cancer properties by triggering ferroptosis within malignant cells, and on the other hand, it damages normal cells causing other diseases. Therefore, in this paper, we propose to review the paradoxical regulation of ferroptosis in tumors and other diseases. First, we introduce the development history, concept and mechanism of ferroptosis. The second part focuses on the methods of inducing ferroptosis in tumors. The third section emphasizes the utilization of ferroptosis in different medical conditions and strategies to inhibit ferroptosis. The fourth part elucidates the key contradictions in the control of ferroptosis. Finally, potential research avenues in associated domains are suggested.

A nonlinear meccano for Alzheimer's emergence by amyloid β-mediated glutamatergic hyperactivity

The pathophysiological process of Alzheimer's disease (AD) is believed to begin many years before the formal diagnosis of AD dementia. This protracted preclinical phase offers a crucial window for potential therapeutic interventions, yet its comprehensive characterization remains elusive. Accumulating evidence suggests that amyloid-β (Aβ) may mediate neuronal hyperactivity in circuit dysfunction in the early stages of AD. At the same time, neural activity can also facilitate Aβ accumulation through intricate feed-forward interactions, complicating elucidating the conditions governing Aβ-dependent hyperactivity and its diagnostic utility. In this study, we use biophysical modeling to shed light on such conditions. Our analysis reveals that the inherently nonlinear nature of the underlying molecular interactions can give rise to the emergence of various modes of hyperactivity. This diversity in the mechanisms of hyperactivity may ultimately account for a spectrum of AD manifestations.

Dopamine neuron degeneration in the Ventral Tegmental Area causes hippocampal hyperexcitability in experimental Alzheimer's Disease

Early and progressive dysfunctions of the dopaminergic system from the Ventral Tegmental Area (VTA) have been described in Alzheimer's Disease (AD). During the long pre-symptomatic phase, alterations in the function of Parvalbumin interneurons (PV-INs) are also observed, resulting in cortical hyperexcitability represented by subclinical epilepsy and aberrant gamma-oscillations. However, it is unknown whether the dopaminergic deficits contribute to brain hyperexcitability in AD. Here, using the Tg2576 mouse model of AD, we prove that reduced hippocampal dopaminergic innervation, due to VTA dopamine neuron degeneration, impairs PV-IN firing and gamma-waves, weakens the inhibition of pyramidal neurons and induces hippocampal hyperexcitability via lower D2-receptor-mediated activation of the CREB-pathway. These alterations coincide with reduced PV-IN numbers and Perineuronal Net density. Importantly, L-DOPA and the selective D2-receptor agonist quinpirole rescue p-CREB levels and improve the PV-IN-mediated inhibition, thus reducing hyperexcitability. Moreover, similarly to quinpirole, sumanirole - another D2-receptor agonist and a known anticonvulsant - not only increases p-CREB levels in PV-INs but also restores gamma-oscillations in Tg2576 mice. Conversely, blocking the dopaminergic transmission with sulpiride (a D2-like receptor antagonist) in WT mice reduces p-CREB levels in PV-INs, mimicking what occurs in Tg2576. Overall, these findings support the hypothesis that the VTA dopaminergic system integrity plays a key role in hippocampal PV-IN function and survival, disclosing a relevant contribution of the reduced dopaminergic tone to aberrant gamma-waves, hippocampal hyperexcitability and epileptiform activity in early AD.

Unraveling brain diseases: The promise of brain-on-a-chip models

Brain disorders, encompassing a wide spectrum of neurological and psychiatric conditions, present a formidable challenge in modern medicine. Despite decades of research, the intricate complexity of the human brain still eludes comprehensive understanding, impeding the development of effective treatments. Recent advancements in microfluidics and tissue engineering have led to the development of innovative platforms known as "Brain-on-a-Chip" (BoC) i.e., advanced in vitro systems that aim to replicate the microenvironment of the brain with the highest possible fidelity. This technology offers a promising test-bed for studying brain disorders at the cellular and network levels, providing insights into disease mechanisms, drug screening, and, in perspective, the development of personalized therapeutic strategies. In this review, we provide an overview of the BoC models developed over the years to model and understand the onset and progression of some of the most severe neurological disorders in terms of incidence and debilitation (stroke, Parkinson's, Alzheimer's, and epilepsy). We also report some of the cutting-edge therapeutic approaches whose effects were evaluated by means of these technologies. Finally, we discuss potential challenges, and future perspectives of the BoC models.

[Paradoxical lucidity and personal identity in patients with advanced dementia: change of paradigm?]

In this article we approach the concept of paradoxical lucidity (LP) (an unexpected, spontaneous, significant and relevant episode of communication or connection) in persons with advanced dementia. The existence of LP could change the paradigm of dementia as a degenerative, chronic, progressive and irreversible disease (where neuronal death plays the leading role), towards a model where functional deficits of neuronal networks acquire importance, which raises new potentially reversible therapeutic and rehabilitative possibilities. We analyze the ethical consequences that these episodes may have with respect to the implicated persons (patients, caregivers and professionals in charge of their care) and try to answer the following question: Do persons with advanced dementia continue to maintain their personal identity despite suffering cognitive impairment so severe?. The LP indicates that this is possible. In this work we make a transversal outline of the different concepts and theories of personal identity in these patients, from different areas of knowledge (philosophy, psychology, neuroscience).

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

The disease's trajectory of Alzheimer's disease (AD) is associated with and worsened by hippocampal hyperexcitability. Here we show that during the asymptomatic stage in a knock in mouse model of Alzheimer's 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's 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's disease.

GSDMD/Drp1 signaling pathway mediates hippocampal synaptic damage and neural oscillation abnormalities in a mouse model of sepsis-associated encephalopathy

BACKGROUND

Gasdermin D (GSDMD)-mediated pyroptotic cell death is implicated in the pathogenesis of cognitive deficits in sepsis-associated encephalopathy (SAE), yet the underlying mechanisms remain largely unclear. Dynamin-related protein 1 (Drp1) facilitates mitochondrial fission and ensures quality control to maintain cellular homeostasis during infection. This study aimed to investigate the potential role of the GSDMD/Drp1 signaling pathway in cognitive impairments in a mouse model of SAE.

METHODS

C57BL/6 male mice were subjected to cecal ligation and puncture (CLP) to establish an animal model of SAE. In the interventional study, mice were treated with the GSDMD inhibitor necrosulfonamide (NSA) or the Drp1 inhibitor mitochondrial division inhibitor-1 (Mdivi-1). Surviving mice underwent behavioral tests, and hippocampal tissues were harvested for histological analysis and biochemical assays at corresponding time points. Haematoxylin-eosin staining and TUNEL assays were used to evaluate neuronal damage. Golgi staining was used to detect synaptic dendritic spine density. Additionally, transmission electron microscopy was performed to assess mitochondrial and synaptic morphology in the hippocampus. Local field potential recordings were conducted to detect network oscillations in the hippocampus.

RESULTS

CLP induced the activation of GSDMD, an upregulation of Drp1, leading to associated mitochondrial impairment, neuroinflammation, as well as neuronal and synaptic damage. Consequently, these effects resulted in a reduction in neural oscillations in the hippocampus and significant learning and memory deficits in the mice. Notably, treatment with NSA or Mdivi-1 effectively prevented these GSDMD-mediated abnormalities.

CONCLUSIONS

Our data indicate that the GSDMD/Drp1 signaling pathway is involved in cognitive deficits in a mouse model of SAE. Inhibiting GSDMD or Drp1 emerges as a potential therapeutic strategy to alleviate the observed synaptic damages and network oscillations abnormalities in the hippocampus of SAE mice.

Overexpression of the schizophrenia risk gene C4 in PV cells drives sex-dependent behavioral deficits and circuit dysfunction

Fast-spiking parvalbumin (PV)-positive cells are key players in orchestrating pyramidal neuron activity, and their dysfunction is consistently observed in myriad brain diseases. To understand how immune complement dysregulation - a prevalent locus of brain disease etiology - in PV cells may drive disease pathogenesis, we have developed a transgenic mouse line that permits cell-type specific overexpression of the schizophrenia-associated complement component 4 (C4) gene. We found that overexpression of mouse C4 (mC4) in PV cells causes sex-specific behavioral alterations and concomitant deficits in synaptic connectivity and excitability of PV cells of the prefrontal cortex. Using a computational network, we demonstrated that these microcircuit deficits led to hyperactivity and disrupted neural communication. Finally, pan-neuronal overexpression of mC4 failed to evoke the same deficits in behavior as PV-specific mC4 overexpression, suggesting that C4 perturbations in fast-spiking neurons are more harmful to brain function than pan-neuronal alterations. Together, these results provide a causative link between C4 and the vulnerability of PV cells in brain disease.

Another Use for a Proven Drug: Experimental Evidence for the Potential of Artemisinin and Its Derivatives to Treat Alzheimer's Disease

Plant-derived multitarget compounds may represent a promising therapeutic strategy for multifactorial diseases, such as Alzheimer's disease (AD). Artemisinin and its derivatives were indicated to beneficially modulate various aspects of AD pathology in different AD animal models through the regulation of a wide range of different cellular processes, such as energy homeostasis, apoptosis, proliferation and inflammatory pathways. In this review, we aimed to provide an up-to-date overview of the experimental evidence documenting the neuroprotective activities of artemi-sinins to underscore the potential of these already-approved drugs for treating AD also in humans and propose their consideration for carefully designed clinical trials. In particular, the benefits to the main pathological hallmarks and events in the pathological cascade throughout AD development in different animal models of AD are summarized. Moreover, dose- and context-dependent effects of artemisinins are noted.

Abnormal gamma phase-amplitude coupling in the parahippocampal cortex is associated with network hyperexcitability in Alzheimer's disease

While animal models of Alzheimer's disease (AD) have shown altered gamma oscillations (∼40 Hz) in local neural circuits, the low signal-to-noise ratio of gamma in the resting human brain precludes its quantification via conventional spectral estimates. Phase-amplitude coupling (PAC) indicating the dynamic integration between the gamma amplitude and the phase of low-frequency (4-12 Hz) oscillations is a useful alternative to capture local gamma activity. In addition, PAC is also an index of neuronal excitability as the phase of low-frequency oscillations that modulate gamma amplitude, effectively regulates the excitability of local neuronal firing. In this study, we sought to examine the local neuronal activity and excitability using gamma PAC, within brain regions vulnerable to early AD pathophysiology-entorhinal cortex and parahippocampus, in a clinical population of patients with AD and age-matched controls. Our clinical cohorts consisted of a well-characterized cohort of AD patients (n = 50; age, 60 ± 8 years) with positive AD biomarkers, and age-matched, cognitively unimpaired controls (n = 35; age, 63 ± 5.8 years). We identified the presence or the absence of epileptiform activity in AD patients (AD patients with epileptiform activity, AD-EPI+, n = 20; AD patients without epileptiform activity, AD-EPI-, n = 30) using long-term electroencephalography (LTM-EEG) and 1-hour long magnetoencephalography (MEG) with simultaneous EEG. Using the source reconstructed MEG data, we computed gamma PAC as the coupling between amplitude of the gamma frequency (30-40 Hz) with phase of the theta (4-8 Hz) and alpha (8-12 Hz) frequency oscillations, within entorhinal and parahippocampal cortices. We found that patients with AD have reduced gamma PAC in the left parahippocampal cortex, compared to age-matched controls. Furthermore, AD-EPI+ patients showed greater reductions in gamma PAC than AD-EPI- in bilateral parahippocampal cortices. In contrast, entorhinal cortices did not show gamma PAC abnormalities in patients with AD. Our findings demonstrate the spatial patterns of altered gamma oscillations indicating possible region-specific manifestations of network hyperexcitability within medial temporal lobe regions vulnerable to AD pathophysiology. Greater deficits in AD-EPI+ suggests that reduced gamma PAC is a sensitive index of network hyperexcitability in AD patients. Collectively, the current results emphasize the importance of investigating the role of neural circuit hyperexcitability in early AD pathophysiology and explore its potential as a modifiable contributor to AD pathobiology.

MODERATE ALCOHOL CONSUMPTION INDUCES LASTING IMPACTS ON PREFRONTAL CORTICAL SIGNALING IN MICE

Both alcohol use disorder (AUD) and Alzheimer's Disease and Related Dementias (ADRD) appear to include disruption in the balance of excitation and inhibition in the cortex, but their potential interactions are unclear. We examined the effect of moderate voluntary binge alcohol consumption on the aged, pre-disease neuronal environment by measuring intrinsic excitability and spontaneous neurotransmission on prefrontal cortical pyramidal (excitatory, glutamatergic) and non-pyramidal (inhibitory, GABAergic) neurons following a prolonged period of abstinence from alcohol in mice. Results highlight that binge alcohol consumption has lasting impacts on the electrophysiological properties of prefrontal cortical neurons. A profound increase in excitatory events onto layer 2/3 non-pyramidal neurons following alcohol consumption was seen, along with altered intrinsic excitability of pyramidal neurons, which could have a range of effects on Alzheimer's Disease progression in humans. These results indicate that moderate voluntary alcohol influences the pre-disease environment in aging and highlight the need for further mechanistic investigation into this risk factor.

Astrocytes in selective vulnerability to neurodegenerative disease

Selective vulnerability of specific brain regions and cell populations is a hallmark of neurodegenerative disorders. Mechanisms of selective vulnerability involve neuronal heterogeneity, functional specializations, and differential sensitivities to stressors and pathogenic factors. In this review we discuss the growing body of literature suggesting that, like neurons, astrocytes are heterogeneous and specialized, respond to and integrate diverse inputs, and induce selective effects on brain function. In disease, astrocytes undergo specific, context-dependent changes that promote different pathogenic trajectories and functional outcomes. We propose that astrocytes contribute to selective vulnerability through maladaptive transitions to context-divergent phenotypes that impair specific brain regions and functions. Further studies on the multifaceted roles of astrocytes in disease may provide new therapeutic approaches to enhance resilience against neurodegenerative disorders.

Identification of PS1/gamma-secretase and glutamate transporter GLT-1 interaction sites

The recently discovered interaction between Presenilin 1 (PS1), a catalytic subunit of γ-secretase responsible for generating amyloid-β peptides, and GLT-1, a major glutamate transporter in the brain (EAAT2), provides a mechanistic link between these two key factors involved in Alzheimer's disease (AD) pathology. Modulating this interaction can be crucial to understand the consequence of such crosstalk in AD context and beyond. However, the interaction sites between these two proteins are unknown. Herein, we utilized an alanine scanning approach coupled with FRET-based fluorescence lifetime imaging microscopy to identify the interaction sites between PS1 and GLT-1 in their native environment within intact cells. We found that GLT-1 residues at position 276 to 279 (TM5) and PS1 residues at position 249 to 252 (TM6) are crucial for GLT-1-PS1 interaction. These results have been cross validated using AlphaFold Multimer prediction. To further investigate whether this interaction of endogenously expressed GLT-1 and PS1 can be prevented in primary neurons, we designed PS1/GLT-1 cell-permeable peptides (CPPs) targeting the PS1 or GLT-1 binding site. We used HIV TAT domain to allow for cell penetration which was assayed in neurons. First, we assessed the toxicity and penetration of CPPs by confocal microscopy. Next, to ensure the efficiency of CPPs, we monitored the modulation of GLT-1-PS1 interaction in intact neurons by fluorescence lifetime imaging microscopy. We saw significantly less interaction between PS1 and GLT-1 with both CPPs. Our study establishes a new tool to study the functional aspect of GLT-1-PS1 interaction and its relevance in normal physiology and AD models.

Native-state proteomics of Parvalbumin interneurons identifies unique molecular signatures and vulnerabilities to early Alzheimer's pathology

Dysfunction in fast-spiking parvalbumin interneurons (PV-INs) may represent an early pathophysiological perturbation in Alzheimer's Disease (AD). Defining early proteomic alterations in PV-INs can provide key biological and translationally-relevant insights. We used cell-type-specific in-vivo biotinylation of proteins (CIBOP) coupled with mass spectrometry to obtain native-state PV-IN proteomes. PV-IN proteomic signatures include high metabolic and translational activity, with over-representation of AD-risk and cognitive resilience-related proteins. In bulk proteomes, PV-IN proteins were associated with cognitive decline in humans, and with progressive neuropathology in humans and the 5xFAD mouse model of Aβ pathology. PV-IN CIBOP in early stages of Aβ pathology revealed signatures of increased mitochondria and metabolism, synaptic and cytoskeletal disruption and decreased mTOR signaling, not apparent in whole-brain proteomes. Furthermore, we demonstrated pre-synaptic defects in PV-to-excitatory neurotransmission, validating our proteomic findings. Overall, in this study we present native-state proteomes of PV-INs, revealing molecular insights into their unique roles in cognitive resiliency and AD pathogenesis.

Deep brain stimulation for Alzheimer's disease - current status and next steps

INTRODUCTION

Alzheimer's disease (AD) requires novel therapeutic approaches due to limited efficacy of current treatments.

AREAS COVERED

This article explores AD as a manifestation of neurocircuit dysfunction and evaluates deep brain stimulation (DBS) as a potential intervention. Focusing on fornix-targeted stimulation (DBS-f), the article summarizes safety, feasibility, and outcomes observed in phase 1/2 trials, highlighting findings such as cognitive improvement, increased metabolism, and hippocampal growth. Topics for further study include optimization of electrode placement, and the role of stimulation-induced autobiographical-recall. Nucleus basalis of Meynert (DBS-NBM) DBS is also discussed and compared with DBS-f. Challenges with both DBS-f and DBS-NBM are identified, emphasizing the need for further research on optimal stimulation parameters. The article also reviews alternative DBS targets, including medial temporal lobe structures and the ventral capsule/ventral striatum.

EXPERT OPINION

Looking ahead, a phase-3 DBS-f trial, and the prospect of closed-loop stimulation using EEG-derived biomarkers or hippocampal theta activity are highlighted. Recent FDA-approved therapies and other neuromodulation techniques like temporal interference and low-intensity ultrasound are considered. The article concludes by underscoring the importance of imaging-based diagnosis and staging to allow for circuit-targeted therapies, given the heterogeneity of AD and varied stages of neurocircuit dysfunction.

Local signal variability and functional connectivity: Sensitive measures of the excitation-inhibition ratio?

A novel network version of permutation entropy, the inverted joint permutation entropy (JPEinv), holds potential as non-invasive biomarker of abnormal excitation-inhibition (E-I) ratio in Alzheimer's disease (AD). In this computational modelling study, we test the hypotheses that this metric, and related measures of signal variability and functional connectivity, are sensitive to altered E-I ratios. The E-I ratio in each neural mass of a whole-brain computational network model was systematically varied. We evaluated whether JPEinv, local signal variability (by permutation entropy) and functional connectivity (by weighted symbolic mutual information (wsMI)) were related to E-I ratio, on whole-brain and regional level. The hub disruption index can identify regions primarily affected in terms of functional connectivity strength (or: degree) by the altered E-I ratios. Analyses were performed for a range of coupling strengths, filter and time-delay settings. On whole-brain level, higher E-I ratios were associated with higher functional connectivity (by JPEinv and wsMI) and lower local signal variability. These relationships were nonlinear and depended on the coupling strength, filter and time-delay settings. On regional level, hub-like regions showed a selective decrease in functional degree (by JPEinv and wsMI) upon a lower E-I ratio, and non-hub-like regions showed a selective increase in degree upon a higher E-I ratio. These results suggest that abnormal functional connectivity and signal variability, as previously reported in patients across the AD continuum, can inform us about altered E-I ratios.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11571-023-10003-x.

Diagnosing epileptic seizures in patients with Alzheimer's disease and deciding on the appropriate treatment plan

INTRODUCTION

Alzheimer's disease (AD) is the predominant cause of dementia and a significant contributor to morbidity among the elderly. Patients diagnosed with AD face an increased risk of epileptic seizures.

AREAS COVERED

Herein, the authors review the challenges in the diagnosis of seizures in patients with AD, the risks of seizures related to medications used in AD and the pharmacological treatment of seizures in AD. The authors also provide the reader with their expert opinion on the subject matter and future perspectives.

EXPERT OPINION

Healthcare professionals should maintain a vigilant approach to suspecting seizures in AD patients. Acute symptomatic seizures triggered by metabolic disturbances, infections, toxins, or drug-related factors often have a low risk of recurrence. In such cases, addressing the underlying cause may suffice without initiating antiseizure medications (ASMs). However, unprovoked seizures in certain AD patients carry a higher risk of recurrence over time, warranting the use of ASMs. Although data is limited, both lamotrigine and levetiracetam appear to be reasonable choices for controlling seizures in elderly AD patients. Decisions should be informed by the best available evidence, the treating physician's clinical experience, and the patient's preferences.

Altered patterning of neural activity in a tauopathy mouse model

Alzheimer's disease (AD) is a complex neurodegenerative condition that manifests at multiple levels and involves a spectrum of abnormalities ranging from the cellular to cognitive. Here, we investigate the impact of AD-related tau-pathology on hippocampal circuits in mice engaged in spatial navigation, and study changes of neuronal firing and dynamics of extracellular fields. While most studies are based on analyzing instantaneous or time-averaged characteristics of neuronal activity, we focus on intermediate timescales-spike trains and waveforms of oscillatory potentials, which we consider as single entities. We find that, in healthy mice, spike arrangements and wave patterns (series of crests or troughs) are coupled to the animal's location, speed, and acceleration. In contrast, in tau-mice, neural activity is structurally disarrayed: brainwave cadence is detached from locomotion, spatial selectivity is lost, the spike flow is scrambled. Importantly, these alterations start early and accumulate with age, which exposes progressive disinvolvement the hippocampus circuit in spatial navigation. These features highlight qualitatively different neurodynamics than the ones provided by conventional analyses, and are more salient, thus revealing a new level of the hippocampal circuit disruptions.

The "psychiatric" neuron: the psychic neuron of the cerebral cortex, revisited

Nearly 25 years ago, Dr. Patricia Goldman-Rakic published her review paper, "The 'Psychic' Neuron of the Cerebral Cortex," outlining the circuit-level dynamics, neurotransmitter systems, and behavioral correlates of pyramidal neurons in the cerebral cortex, particularly as they relate to working memory. In the decades since the release of this paper, the existing literature and our understanding of the pyramidal neuron have increased tremendously, and research is still underway to better characterize the role of the pyramidal neuron in both healthy and psychiatric disease states. In this review, we revisit Dr. Goldman-Rakic's characterization of the pyramidal neuron, focusing on the pyramidal neurons of the prefrontal cortex (PFC) and their role in working memory. Specifically, we examine the role of PFC pyramidal neurons in the intersection of working memory and social function and describe how deficits in working memory may actually underlie the pathophysiology of social dysfunction in psychiatric disease states. We briefly describe the cortico-cortical and corticothalamic connections between the PFC and non-PFC brain regions, as well the microcircuit dynamics of the pyramidal neuron and interneurons, and the role of both these macro- and microcircuits in the maintenance of the excitatory/inhibitory balance of the cerebral cortex for working memory function. Finally, we discuss the consequences to working memory when pyramidal neurons and their circuits are dysfunctional, emphasizing the resulting social deficits in psychiatric disease states with known working memory dysfunction.

Probing cerebellar circuit dysfunction in rodent models of spinocerebellar ataxia by means of in vivo two-photon calcium imaging

Purkinje neuron degeneration characterizes spinocerebellar ataxia type 1, yet the comprehension of the impact on the broader cerebellar circuit remains incomplete. We here detail simultaneous in vivo two-photon calcium imaging of diverse neuronal populations in the cerebellar cortex of Sca1 mice while they are navigating a virtual environment. We outline surgical procedures and protocols to chronically record from identical neurons, and we detail data post-processing and analysis to delineate disease-related alterations in neuronal activity and sensorimotor-driven response properties. For complete details on the use and execution of this protocol, please refer to Pilotto et al.1.

Safety, tolerability, and efficacy estimate of evoked gamma oscillation in mild to moderate Alzheimer's disease

Background

Alzheimer's Disease (AD) is a multifactorial, progressive neurodegenerative disease that disrupts synaptic and neuronal activity and network oscillations. It is characterized by neuronal loss, brain atrophy and a decline in cognitive and functional abilities. Cognito's Evoked Gamma Therapy System provides an innovative approach for AD by inducing EEG-verified gamma oscillations through sensory stimulation. Prior research has shown promising disease-modifying effects in experimental AD models. The present study (NCT03556280: OVERTURE) evaluated the feasibly, safety and efficacy of evoked gamma oscillation treatment using Cognito's medical device (CogTx-001) in participants with mild to moderate AD.

Methods

The present study was a randomized, double blind, sham-controlled, 6-months clinical trial in participants with mild to moderate AD. The trial enrolled 76 participants, aged 50 or older, who met the clinical criteria for AD with baseline MMSE scores between 14 and 26. Participants were randomly assigned 2:1 to receive self-administered daily, one-hour, therapy, evoking EEG-verified gamma oscillations or sham treatment. The CogTx-001 device was use at home with the help of a care partner, over 6 months. The primary outcome measures were safety, evaluated by physical and neurological exams and monthly assessments of adverse events (AEs) and MRI, and tolerability, measured by device use. Although the trial was not statistically powered to evaluate potential efficacy outcomes, primary and secondary clinical outcome measures included several cognitive and functional endpoints.

Results

Total AEs were similar between groups, there were no unexpected serious treatment related AEs, and no serious treatment-emergent AEs that led to study discontinuation. MRI did not show Amyloid-Related Imaging Abnormalities (ARIA) in any study participant. High adherence rates (85-90%) were observed in sham and treatment participants. There was no statistical separation between active and sham arm participants in primary outcome measure of MADCOMS or secondary outcome measure of CDR-SB or ADAS-Cog14. However, some secondary outcome measures including ADCS-ADL, MMSE, and MRI whole brain volume demonstrated reduced progression in active compared to sham treated participants, that achieved nominal significance.

Conclusion

Our results demonstrate that 1-h daily treatment with Cognito's Evoked Gamma Therapy System (CogTx-001) was safe and well-tolerated and demonstrated potential clinical benefits in mild to moderate AD.Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT03556280.

Selective Medial Septum Lesions in Healthy Rats Induce Longitudinal Changes in Microstructure of Limbic Regions, Behavioral Alterations, and Increased Susceptibility to Status Epilepticus

Septo-hippocampal pathway, crucial for physiological functions and involved in epilepsy. Clinical monitoring during epileptogenesis is complicated. We aim to evaluate tissue changes after lesioning the medial septum (MS) of normal rats and assess how the depletion of specific neuronal populations alters the animals' behavior and susceptibility to establishing a pilocarpine-induced status epilepticus. Male Sprague-Dawley rats were injected into the MS with vehicle or saporins (to deplete GABAergic or cholinergic neurons; n = 16 per group). Thirty-two animals were used for diffusion tensor imaging (DTI); scanned before surgery and 14 and 49 days post-injection. Fractional anisotropy and apparent diffusion coefficient were evaluated in the fimbria, dorsal hippocampus, ventral hippocampus, dorso-medial thalamus, and amygdala. Between scans 2 and 3, animals were submitted to diverse behavioral tasks. Stainings were used to analyze tissue alterations. Twenty-four different animals received pilocarpine to evaluate the latency and severity of the status epilepticus 2 weeks after surgery. Additionally, eight different animals were only used to evaluate the neuronal damage inflicted on the MS 1 week after the molecular surgery. Progressive changes in DTI parameters in both white and gray matter structures of the four evaluated groups were observed. Behaviorally, the GAT1-saporin injection impacted spatial memory formation, while 192-IgG-saporin triggered anxiety-like behaviors. Histologically, the GABAergic toxin also induced aberrant mossy fiber sprouting, tissue damage, and neuronal death. Regarding the pilocarpine-induced status epilepticus, this agent provoked an increased mortality rate. Selective septo-hippocampal modulation impacts the integrity of limbic regions crucial for certain behavioral skills and could represent a precursor for epilepsy development.

A Comprehensive Overview of the Neural Mechanisms of Light Therapy

Light is a powerful environmental factor influencing diverse brain functions. Clinical evidence supports the beneficial effect of light therapy on several diseases, including depression, cognitive dysfunction, chronic pain, and sleep disorders. However, the precise mechanisms underlying the effects of light therapy are still not well understood. In this review, we critically evaluate current clinical evidence showing the beneficial effects of light therapy on diseases. In addition, we introduce the research progress regarding the neural circuit mechanisms underlying the modulatory effects of light on brain functions, including mood, memory, pain perception, sleep, circadian rhythm, brain development, and metabolism.

Novel avenues of tau research

INTRODUCTION

The pace of innovation has accelerated in virtually every area of tau research in just the past few years.

METHODS

In February 2022, leading international tau experts convened to share selected highlights of this work during Tau 2022, the second international tau conference co-organized and co-sponsored by the Alzheimer's Association, CurePSP, and the Rainwater Charitable Foundation.

RESULTS

Representing academia, industry, and the philanthropic sector, presenters joined more than 1700 registered attendees from 59 countries, spanning six continents, to share recent advances and exciting new directions in tau research.

DISCUSSION

The virtual meeting provided an opportunity to foster cross-sector collaboration and partnerships as well as a forum for updating colleagues on research-advancing tools and programs that are steadily moving the field forward.

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

A growing body of evidence has demonstrated a link between Alzheimer disease (AD) and epilepsy. Late-onset epilepsy and epileptiform activity can precede cognitive deterioration in AD by years, and its presence has been shown to predict a faster disease course. In animal models of AD, amyloid and tau pathology are linked to cortical network hyperexcitability that precedes the first signs of memory decline. Thus, detection of epileptiform activity in AD has substantial clinical importance as a potential novel modifiable risk factor for dementia. In this Review, we summarize the epidemiological evidence for the complex bidirectional relationship between AD and epilepsy, examine the effect of epileptiform activity and seizures on cognition in people with AD, and discuss the precision medicine treatment strategies based on the latest research in human and animal models. Finally, we outline some of the unresolved questions of the field that should be addressed by rigorous research, including whether particular clinicopathological subtypes of AD have a stronger association with epilepsy, and the sequence of events between epileptiform activity and amyloid and tau pathology.

A multi-looping chromatin signature predicts dysregulated gene expression in neurons with familial Alzheimer's disease mutations

Mammalian genomes fold into tens of thousands of long-range loops, but their functional role and physiologic relevance remain poorly understood. Here, using human post-mitotic neurons with rare familial Alzheimer's disease (FAD) mutations, we identify hundreds of reproducibly dysregulated genes and thousands of miswired loops prior to amyloid accumulation and tau phosphorylation. Single loops do not predict expression changes; however, the severity and direction of change in mRNA levels and single-cell burst frequency strongly correlate with the number of FAD-gained or -lost promoter-enhancer loops. Classic architectural proteins CTCF and cohesin do not change occupancy in FAD-mutant neurons. Instead, we unexpectedly find TAATTA motifs amenable to binding by DLX homeodomain transcription factors and changing noncoding RNAPolII signal at FAD-dynamic promoter-enhancer loops. DLX1/5/6 mRNA levels are strongly upregulated in FAD-mutant neurons coincident with a shift in excitatory-to-inhibitory gene expression and miswiring of multi-loops connecting enhancers to neural subtype genes. DLX1 overexpression is sufficient for loop miswiring in wildtype neurons, including lost and gained loops at enhancers with tandem TAATTA arrays and singular TAATTA motifs, respectively. Our data uncover a genome structure-function relationship between multi-loop miswiring and dysregulated excitatory and inhibitory transcriptional programs during lineage commitment of human neurons homozygously-engineered with rare FAD mutations.

The roles of RACK1 in the pathogenesis of Alzheimer's disease

The receptor for activated C kinase 1 (RACK1) is a protein that plays a crucial role in various signaling pathways and is involved in the pathogenesis of Alzheimer's disease (AD), a prevalent neurodegenerative disease. RACK1 is highly expressed in neuronal cells of the central nervous system and regulates the pathogenesis of AD. Specifically, RACK1 is involved in regulation of the amyloid-β precursor protein processing through α- or β-secretase by binding to different protein kinase C isoforms. Additionally, RACK1 promotes synaptogenesis and synaptic plasticity by inhibiting N-methyl-D-aspartate receptors and activating gamma-aminobutyric acid A receptors, thereby preventing neuronal excitotoxicity. RACK1 also assembles inflammasomes that are involved in various neuroinflammatory pathways, such as nuclear factor-kappa B, tumor necrosis factor-alpha, and NOD-like receptor family pyrin domain-containing 3 pathways. The potential to design therapeutics that block amyloid-β accumulation and inflammation or precisely regulate synaptic plasticity represents an attractive therapeutic strategy, in which RACK1 is a potential target. In this review, we summarize the contribution of RACK1 to the pathogenesis of AD and its potential as a therapeutic target.

Impairments of GABAergic transmission in hippocampus mediate increased susceptibility of epilepsy in the early stage of Alzheimer's disease

BACKGROUND

Patients with Alzheimer's disease (AD) are often co-morbid with unprovoked seizures, making clinical diagnosis and management difficult. Although it has an important role in both AD and epilepsy, abnormal γ-aminobutyric acid (GABA)ergic transmission is recognized only as a compensative change for glutamatergic damage. Neuregulin 1 (NRG1)-ErbB4 signaling can promote GABA release and suppress epileptogenesis, but its effects on cognition in AD are still controversial.

METHODS

Four-month-old APPswe/PS1dE9 mice (APP mice) were used as animal models in the early stage of AD in this study. Acute/chronic chemical-kindling epilepsy models were established with pentylenetetrazol. Electroencephalogram and Racine scores were performed to assess seizures. Behavioral tests were used to assess cognition and emotion. Electrophysiology, western blot and immunofluorescence were performed to detect the alterations in synapses, GABAergic system components and NRG1-ErbB4 signaling. Furthermore, NRG1 was administrated intracerebroventricularly into APP mice and then its antiepileptic and cognitive effects were evaluated.

RESULTS

APP mice had increased susceptibility to epilepsy and resulting hippocampal synaptic damage and cognitive impairment. Electrophysiological analysis revealed decreased GABAergic transmission in the hippocampus. This abnormal GABAergic transmission involved a reduction in the number of parvalbumin interneurons (PV+ Ins) and decreased levels of GABA synthesis and transport. We also found impaired NRG1-ErbB4 signaling which mediated by PV+ Ins loss. And NRG1 administration could effectively reduce seizures and improve cognition in four-month-old APP mice.

CONCLUSION

Our results indicated that abnormal GABAergic transmission mediated hippocampal hyperexcitability, further excitation/inhibition imbalance, and promoted epileptogenesis in the early stage of AD. Appropriate NRG1 administration could down-regulate seizure susceptibility and rescue cognitive function. Our study provided a potential direction for intervening in the co-morbidity of AD and epilepsy.