How human neural networks fire spiking activity and responds to electrical stimuli when they coupled to a dense multi-electrode arrays for up to 3 months
A decade ago, the landmark discovery of induced pluripotent stem cells (iPSCs) raised high hopes and opened up new avenues in the field of regenerative medicine. This success has indeed provided enormous potential to use human-iPS (hiPS) as a promising source material for accelerating in vitro human-specific-disease modeling and drug development. But this can only be successful if there is sufficient understanding of the functional properties emerging from networks derived from these hiPS ensembles. This alone is a fundamental motivation to characterize emerging network-wide functional measures from these cultures. But how long do these cells demand until they form a functional network? and what does regulate their physiological maturation and synaptic functional plasticity?
Hayder Amin and colleagues at the Neuroscience and Brain Technologies Dpt. of the Fondazione Istituto Italiano di Tecnologia (IIT) approached these points in a new original research study. Using a combination of thought experiments consisting of high spatiotemporal resolution electrical measurements and optical imaging, the researchers succeeded to provide a unified explanation of how human-derived neurons made from skin fibroblasts could resemble a complex neuronal network that fires and responds to electrical stimuli after 3 months of cellular development. Their study has now been published in the ”Journal of Frontiers in Neuroscience”. The findings may help neuroscientists to better understand how human neuronal networks could develop, mature, and process at the synaptic level, as well as giving rise to physiological responses upon intrinsic stimuli.
Amin and colleagues have now succeeded in presenting on CMOS-MEAs, the experimental characterization of the developing functional properties expressed by human-derived neuronal networks, as induced by different biochemically coated substrates, i.e. poly-dl-ornithine (PDLO), poly-l-ornithine (PLO), and polyethylenimine (PEI), which were used as adhesion promoters for the cell culture. For the first time, they were able to demonstrate that both spontaneous and evoked electrical spiking activities of these human networks can be characterized on active Multi Electrode Arrays (MEAs) by taking advantage from the spatiotemporal resolution and high-statistical significance of mean network activity parameters provided by 4096 multi-electrode array recordings. Remarkably, these arrays can simultaneously record extracellular activity from cultured networks, and also allow reliable quantification of the spiking activity of a few neurons sparse in the network, thus enabling robust insights of network formation even at early stages of network development.
The scientists extended their investigations to correlate changes of neuronal network-wide activity obtained from CMOS-MEA recordings with the maturation and formation of synapse connections as indicated by the level of PSD-95 expression. In turn, they reported that networks grown on PDLO coated substrates showed significantly higher spontaneous firing activity, reliable responses to low-frequency electrical stimuli, and an appropriate level of PSD-95 that may explain a physiological neuronal maturation profile and synapse stabilization.
Thus, this study has demonstrated a powerful tool arises from two emerging technologies (iPS and high-resolution CMOS-MEAs) to develop more physiologically relevant electrical and cell based assays for disease modeling and drug screening.
Amin H., Maccione A., Marinaro F., Zordan S., Nieus T. and Berdondini L. (2016) "Electrical Responses and Spontaneous Activity of Human iPS-Derived Neuronal Networks Characterized for 3-month Culture with 4096-Electrode Arrays". Front. Neurosci. 10:121. doi: 10.3389/fnins.2016.00121.