Buskila, Y. | Search bioRxiv

bioRxiv2024

Potassium homeostasis during disease progression of Alzheimers Disease

Alzheimers disease (AD) is an age-dependent neurodegenerative disorder characterized by neuronal loss leading to dementia and ultimately death. Whilst the loss of neurons is central to the disease, it is becoming clear that glia, specifically astrocytes, contribute to the onset and progression of neurodegeneration. Astrocytic role in retaining ion homeostasis in the extracellular milieu is fundamental for multiple brain functions, including synaptic plasticity and neuronal excitability, which are compromised during AD and affect neuronal signalling. In this study, we have measured the astrocytic K+ clearance rate in the hippocampus and somatosensory cortex of a mouse model for AD during disease progression. Our results establish that astrocytic [K+]o clearance in the hippocampus is reduced in symptomatic 5xFAD mice, and this decrease is region-specific. The decrease in the [K+]o clearance rate correlated with a significant reduction in the expression and conductivity of Kir4.1 channels and a decline in the number of primary connected astrocytes. Moreover, astrocytes in the hippocampus of symptomatic 5xFAD mice demonstrated increased reactivity which was accompanied by an increased excitability and altered spiking profile of nearby neurons. These findings indicate that the supportive function astrocytes typically provide to nearby neurons is diminished during disease progression, which affects the neuronal circuit signalling in this area and provides a potential explanation for the increased vulnerability of neurons in AD.

neuroscience↗

bioRxiv2019

Neuromodulation of astrocytic K+ clearance

Potassium homeostasis is a fundamental requirement for normal brain function. Therefore, effective removal of excessive K+ accumulation from the synaptic cleft during neuronal activity is paramount. Astrocytes, one of the most common subtype of glial cells in the brain, play a key role in K+ clearance from the extracellular milieu using various mechanisms, including uptake via Kir channels and the Na+-K+ ATPase, and spatial buffering through the astrocytic gap-junction coupled network. Recently we showed that alterations in the concentrations of extracellular potassium ([K+]{degrees}) or impairments of the astrocytic clearance mechanism effect the resonance and oscillatory behaviour of both individual and networks of neurons recorded from C57/BL6 mice of both sexes. These results indicate that astrocytes have the potential to modulate neuronal network activity, however the cellular effectors that may affect the astrocytic K+ clearance process are still unknown. In this study, we have investigated the impact of neuromodulators, which are known to mediate changes in network oscillatory behaviour, on the astrocytic clearance process. Our results suggest that some neuromodulators (5-HT; NA) affect astrocytic spatial buffering via gap-junctions, while others (DA; Histamine) affect the uptake mechanism via Kir channels. These results suggest that neuromodulators can affect network oscillatory activity through parallel activation of both neurons and astrocytes, establishing a synergistic mechanism to recruitment of neurons into ensamble of networks to maximise the synchronous network activity. Significance statementNeuromodulators are known to mediate changes in network oscillatory behaviour and thus impact on brain states. In this study we show that certain neuromodulators directly affect distinct stages of astrocytic K+ clearance, promoting neuronal excitability and network oscillations through parallel activation of both neurons and astrocytes, thus establishing a synergistic mechanism to maximise the synchronous network activity.

neuroscience↗