Degenerate mapping of environmental location presages deficits in object-location encoding and memory in the 5xFAD mouse model for Alzheimer's disease

Calcium Signalling in Neurological Disorders, with Insights from Miniature Fluorescence Microscopy

Neurological disorders (NDs), such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and schizophrenia, represent a complex and multifaceted health challenge that affects millions of people around the world. Growing evidence suggests that disrupted neuronal calcium signalling contributes to the pathophysiology of NDs. Additionally, calcium functions as a ubiquitous second messenger involved in diverse cellular processes, from synaptic activity to intercellular communication, making it a potential therapeutic target. Recently, the development of the miniature fluorescence microscope (miniscope) enabled simultaneous recording of the spatiotemporal calcium activity from large neuronal ensembles in unrestrained animals, providing a novel method for studying NDs. In this review, we discuss the abnormalities observed in calcium signalling and its potential as a therapeutic target for NDs. Additionally, we highlight recent studies that utilise miniscope technology to investigate the alterations in calcium dynamics associated with NDs.

Disruption of hippocampal-prefrontal neural dynamics and risky decision-making in a mouse model of Alzheimer's disease

This study investigates how amyloid pathology influences hippocampal-prefrontal neural dynamics and decision-making in Alzheimer's disease (AD) using 5XFAD mice, a well-established model system characterized by pronounced early amyloid pathology. Utilizing ecologically-relevant "approach food-avoid predator" foraging tasks, we observed that 5XFAD mice exhibited persistent risk-taking behaviors and reduced adaptability to changing threat conditions, indicative of impaired decision-making. Multi-regional neural recordings revealed rigid hippocampal CA1 place-cell fields, decreased sharp-wave ripple (SWR) frequencies, and disrupted medial prefrontal-hippocampal connectivity, all of which corresponded with deficits in behavioral flexibility during spatial risk scenarios. These findings highlight the critical role of SWR dynamics and corticolimbic circuit integrity in adaptive decision-making, with implications for understanding cognitive decline in AD in naturalistic contexts. By identifying specific neural disruptions underlying risky decision-making deficits, this work provides insights into the neural basis of cognitive dysfunction in AD and suggests potential targets for therapeutic intervention.

Monosynaptic Rabies Tracing Reveals Sex- and Age-Dependent Dorsal Subiculum Connectivity Alterations in an Alzheimer's Disease Mouse Model

The subiculum (SUB), a hippocampal formation structure, is among the earliest brain regions impacted in Alzheimer's disease (AD). Toward a better understanding of AD circuit-based mechanisms, we mapped synaptic circuit inputs to dorsal SUB using monosynaptic rabies tracing in the 5xFAD mouse model by quantitatively comparing the circuit connectivity of SUB excitatory neurons in age-matched controls and 5xFAD mice at different ages for both sexes. Input-mapped brain regions include the hippocampal subregions (CA1, CA2, CA3), medial septum and diagonal band, retrosplenial cortex, SUB, postsubiculum (postSUB), visual cortex, auditory cortex, somatosensory cortex, entorhinal cortex, thalamus, perirhinal cortex (Prh), ectorhinal cortex, and temporal association cortex. We find sex- and age-dependent changes in connectivity strengths and patterns of SUB presynaptic inputs from hippocampal subregions and other brain regions in 5xFAD mice compared with control mice. Significant sex differences for SUB inputs are found in 5xFAD mice for CA1, CA2, CA3, postSUB, Prh, lateral entorhinal cortex, and medial entorhinal cortex: all of these areas are critical for learning and memory. Notably, we find significant changes at different ages for visual cortical inputs to SUB. While the visual function is not ordinarily considered defective in AD, these specific connectivity changes reflect that altered visual circuitry contributes to learning and memory deficits. Our work provides new insights into SUB-directed neural circuit mechanisms during AD progression and supports the idea that neural circuit disruptions are a prominent feature of AD.

Linking activity dyshomeostasis and sleep disturbances in Alzheimer disease

The presymptomatic phase of Alzheimer disease (AD) starts with the deposition of amyloid-β in the cortex and begins a decade or more before the emergence of cognitive decline. The trajectory towards dementia and neurodegeneration is shaped by the pathological load and the resilience of neural circuits to the effects of this pathology. In this Perspective, I focus on recent advances that have uncovered the vulnerability of neural circuits at early stages of AD to hyperexcitability, particularly when the brain is in a low-arousal states (such as sleep and anaesthesia). Notably, this hyperexcitability manifests before overt symptoms such as sleep and memory deficits. Using the principles of control theory, I analyse the bidirectional relationship between homeostasis of neuronal activity and sleep and propose that impaired activity homeostasis during sleep leads to hyperexcitability and subsequent sleep disturbances, whereas sleep disturbances mitigate hyperexcitability via negative feedback. Understanding the interplay among activity homeostasis, neuronal excitability and sleep is crucial for elucidating the mechanisms of vulnerability to and resilience against AD pathology and for identifying new therapeutic avenues.

Probing neural circuit mechanisms in Alzheimer's disease using novel technologies

The study of Alzheimer's Disease (AD) has traditionally focused on neuropathological mechanisms that has guided therapies that attenuate neuropathological features. A new direction is emerging in AD research that focuses on the progressive loss of cognitive function due to disrupted neural circuit mechanisms. Evidence from humans and animal models of AD show that dysregulated circuits initiate a cascade of pathological events that culminate in functional loss of learning, memory, and other aspects of cognition. Recent progress in single-cell, spatial, and circuit omics informs this circuit-focused approach by determining the identities, locations, and circuitry of the specific cells affected by AD. Recently developed neuroscience tools allow for precise access to cell type-specific circuitry so that their functional roles in AD-related cognitive deficits and disease progression can be tested. An integrated systems-level understanding of AD-associated neural circuit mechanisms requires new multimodal and multi-scale interrogations that longitudinally measure and/or manipulate the ensemble properties of specific molecularly-defined neuron populations first susceptible to AD. These newly developed technological and conceptual advances present new opportunities for studying and treating circuits vulnerable in AD and represent the beginning of a new era for circuit-based AD research.

Systematic characterization of a non-transgenic Aβ1-42 amyloidosis model: synaptic plasticity and memory deficits in female and male mice

BACKGROUND

The amyloid-β (Aβ) cascade is one of the most studied theories linked to AD. In multiple models, Aβ accumulation and dyshomeostasis have shown a key role in AD onset, leading to excitatory/inhibitory imbalance, the impairments of synaptic plasticity and oscillatory activity, and memory deficits. Despite the higher prevalence of Alzheimer's disease (AD) in women compared to men, the possible sex difference is scarcely explored and the information from amyloidosis transgenic mice models is contradictory. Thus, given the lack of data regarding the early stages of amyloidosis in female mice, the aim of this study was to systematically characterize the effect of an intracerebroventricular (icv.) injection of Aβ1-42 on hippocampal-dependent memory, and on associated activity-dependent synaptic plasticity in the hippocampal CA1-CA3 synapse, in both male and female mice.

METHODS

To do so, we evaluated long term potentiation (LTP) with ex vivo electrophysiological recordings as well as encoding and retrieval of spatial (working, short- and long-term) and exploratory habituation memories using Barnes maze and object location, or open field habituation tasks, respectively.

RESULTS

Aβ1-42 administration impaired all forms of memory evaluated in this work, regardless of sex. This effect was displayed in a long-lasting manner (up to 17 days post-injection). LTP was inhibited at a postsynaptic level, both in males and females, and a long-term depression (LTD) was induced for the same prolonged period, which could underlie memory deficits.

CONCLUSIONS

In conclusion, our results provide further evidence on the shifting of LTP/LTD threshold due to a single icv. Aβ1-42 injection, which underly cognitive deficits in the early stages of AD. These long-lasting cognitive and functional alterations in males and females validate this model for the study of early amyloidosis in both sexes, thus offering a solid alternative to the inconsistence of amyloidosis transgenic mice models.

Qi-fu-yin attenuated cognitive disorders in 5xFAD mice of Alzheimer's disease animal model by regulating immunity

Introduction

Cognitive impairment is the main symptom of Alzheimer's disease (AD). Accumulating evidence implicate that immunity plays an important role in AD. Here, we investigated the effect of Qi-fu-yin (QFY) on cognitive impairment and cytokine secretion of 5xFAD mice.

Methods

We used 2.5-month-old 5xFAD transgenic mice for behavioral tests to observe the changes in cognitive function after QFY treatment. After the behavioral experiment, the whole brain, cortex and plasma of each mouse were collected for soluble Aβ analysis, immunohistochemical experiment and cytokine analysis.

Results

Here we found that the treatment of QFY ameliorated the ability of object recognition, passive avoidance responses and the ability of spatial learning and memory in 5xFAD mice. The deposits of β_{1 - 42} and Aβ_{1 - 40} were alleviated and the ration of Aβ_{1 - 42}/Aβ_{1 - 40} was decrease in the plasma and brain of 5xFAD mice administrated with QFY. The administration of QFY promoted the secretion of anti-inflammatory cytokines, IL-5, IL-10 and G-CSF, and reduced the content of proinflammatory cytokines IFN-γ in plasma of 5xFAD mice. Notably, we found that the treatment of QFY decreased the concentration of CCL11 in the brain and plasma of 5xFAD mice.

Conclusion

This suggested that QFY improved cognition and reduced Aβ deposits in 5xFAD mice by regulating abnormal immunity in 5xFAD mice. QFY may be as a potential therapeutic agent for AD.