Silencing of Activity During Hypoxia Improves Functional Outcomes in Motor Neuron Networks in vitro

Abstract

The effects of hypoxia, or reduced oxygen supply, to brain tissue can be disastrous, leading to extensive loss of function. Deoxygenated tissue becomes unable to maintain healthy metabolism, which leads to increased production of reactive oxygen species (ROS) and loss of calcium homoeostasis, with damaging downstream effects. Neurons are a highly energy demanding cell type, and as such they are highly sensitive to reductions in oxygenation and some types of neurons such as motor neurons are even more susceptible to hypoxic damage. In addition to the immediate deleterious effects hypoxia can have on neurons, there can be delayed effects which lead to increased risk of developing neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), even if no immediate consequences are apparent. Furthermore, impairment of the function of various hypoxia-responsive factors has been shown to increase the risk of developing several neurodegenerative disorders. Longitudinal assessment of electrophysiological network activity is underutilised in assessing the effects of hypoxia on neurons and how their activity and communication change over time following a hypoxic challenge. This study utilised multielectrode arrays and motor neuron networks to study the response to hypoxia and the subsequent development of the neuronal activity over time, as well as the effect of silencing network activity during the hypoxic challenge. We found that motor neuron networks exposed to hypoxic challenge exhibited a delayed fluctuation in multiple network activity parameters compared to normoxic networks. Silencing of activity during the hypoxic challenge leads to maintained bursting activity, suggesting that functional outcomes are better maintained in these networks and that there are activity-dependent mechanisms involved in the network damage following hypoxia.

Evolving alterations of structural organization and functional connectivity in feedforward neural networks after induced P301L tau mutation

“…As shown in Figure 2 , our engineered neural networks expressed both the excitatory neuronal marker CaMKIIa, and the inhibitory neuronal marker GAD65/67 in conjunction with the neuronal marker MAP2 by 21 DIV, strongly indicating the capacity for excitatory – inhibitory synaptic transmission within the maturing networks. This was further verified through recordings of electrophysiological activity, which showed that in healthy conditions, networks developed highly dynamic and complex age-dependent firing activity and network bursts over time, in line with previous studies by us and others (Chiappalone et al, 2006; Chiappalone et al, 2007; Fiskum et al, 2021; van de Wijdeven et al, 2018; Weir et al, 2023).…”

Microdissection and culturing of adult lateral entorhinal cortex layer II neurons from APP/PS1 Alzheimer model mice

“…The timing of media change relative to the time of recording is also likely to affect network activity. For example, human motor neurons were found to have a higher firing frequency 24 hours after media change compared to 48 hours after media change (Fiskum et al, 2021). The fact that we recorded activity 72 hours after media change may thus contribute to the very low burst propensity exhibited in our networks.…”

“…A signal was defined and recorded as a spike when reaching beyond a differential threshold of 7.5 times the standard deviation of the background activity. Firing rate and burst propensity (a measure of fraction of spikes in networks bursts) were analysed using an in-house made MATLAB script, reported previously (Fiskum et al, 2021). A network burst was identified when a binned spike distribution of 50ms bins exceeded a threshold of firing rate of 7.5 standard deviations and more than 20% of all active electrodes in the recording fired.…”

Digitoids: a novel computational platform for mimicking oxygen-dependent firing dynamics inin vitroneuronal networks

“…For further information see S3 Table It should also be noted that the rate of membrane depolarization increases as the available oxygen concentration at the neuron decreases. This behaviour was reported in both brain slices and in vitro cultures exposed to hypoxia [64,[67][68][69][70], and can be explained by the fact that a reduced availability of oxygen causes a break in the homeostatic maintenance of ion concentrations between inner and outer neuron environments, which is responsible for sustaining the electrical activity of the neuron. Essentially, when oxygen levels are reduced, the Na + -K + -ATP pump lacks resources for fuelling ion transport.…”