Neuronal networks provide rapid neuroprotection against spreading toxicity

Andrew J Samson,Christopher N Connolly,Graham Robertson,Michele Zagnoni

doi:10.1038/srep33746

Andrew J Samson, Christopher N Connolly + Show 2 more

Open Access

https://doi.org/10.1038/srep33746

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Abstract

Acute secondary neuronal cell death, as seen in neurodegenerative disease, cerebral ischemia (stroke) and traumatic brain injury (TBI), drives spreading neurotoxicity into surrounding, undamaged, brain areas. This spreading toxicity occurs via two mechanisms, synaptic toxicity through hyperactivity, and excitotoxicity following the accumulation of extracellular glutamate. To date, there are no fast-acting therapeutic tools capable of terminating secondary spreading toxicity within a time frame relevant to the emergency treatment of stroke or TBI patients. Here, using hippocampal neurons (DIV 15–20) cultured in microfluidic devices in order to deliver a localized excitotoxic insult, we replicate secondary spreading toxicity and demonstrate that this process is driven by GluN2B receptors. In addition to the modeling of spreading toxicity, this approach has uncovered a previously unknown, fast acting, GluN2A-dependent neuroprotective signaling mechanism. This mechanism utilizes the innate capacity of surrounding neuronal networks to provide protection against both forms of spreading neuronal toxicity, synaptic hyperactivity and direct glutamate excitotoxicity. Importantly, network neuroprotection against spreading toxicity can be effectively stimulated after an excitotoxic insult has been delivered, and may identify a new therapeutic window to limit brain damage.

Highlights

During the development of the central nervous system, competition for synapse formation and early patterns of neuronal network activity are required for neurons to “fire together and wire together”, driving the formation of functional neuronal networks[1,2,3]
In order to isolate secondary spreading toxicity from the primary excitotoxic insult, we adopted the use of a microfluidic system having five cell culture chambers serially interconnected by 500 μm long microchannels (Fig. 1a)
An isolated excitotoxic insult may be delivered to a neuronal network and spreading toxicity monitored

Summary

Introduction

During the development of the central nervous system, competition for synapse formation and early patterns of neuronal network activity are required for neurons to “fire together and wire together”, driving the formation of functional neuronal networks[1,2,3]. A problem in studying spreading toxicity to naïve neurons in vivo is the difficulty in separating the initial lesion from its downstream consequences We have achieved this separation using an in vitro model based on a microfluidic channel network, where multiple neuron populations, that are environmentally isolated but synaptically connected, are cultured and their microenvironment precisely manipulated[20]. Using this approach, we can isolate activity-dependent spreading toxicity from direct glutamate excitotoxicity and use this to model and investigate potential neuroprotective network activity

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