Abstract
Due to their small dimensions, electrophysiology on thin and intricate axonal branches in support of understanding their role in normal and diseased brain function poses experimental challenges. To reduce experimental complexity, we coupled microelectrode arrays (MEAs) to bi-level microchannel devices for the long-term in vitro tracking of axonal morphology and activity with high spatiotemporal resolution. Our model allowed the long-term multisite recording from pure axonal branches in a microscopy-compatible environment. Compartmentalizing the network structure into interconnected subpopulations simplified access to the locations of interest. Electrophysiological data over 95 days in vitro (DIV) showed an age-dependent increase of axonal conduction velocity, which was positively correlated with, but independent of evolving burst activity over time. Conduction velocity remained constant at chemically increased network activity levels. In contrast, low frequency (1 Hz, 180 repetitions) electrical stimulation of axons or network subpopulations evoked amplitude-dependent direct (5–35 ms peri-stimulus) and polysynaptic (35–1,000 ms peri-stimulus) activity with temporarily (<35 ms) elevated propagation velocities along the perisomatic branches. Furthermore, effective stimulation amplitudes were found to be significantly lower (>250 mV) in microchannels when compared with those reported for unconfined cultures (>800 mV). The experimental paradigm may lead to new insights into stimulation-induced axonal plasticity.
Highlights
High-level brain functions emerge from the real-time interaction of interconnected neural networks
The concept of studying axonal biology in an isolated microchannel environment was introduced by Taylor et al.[13] and later exploited in other contexts in different configurations[24]
The first 200–400 μm of the microchannels were occupied by a mixture of dendrites and axons, which interfered with axonal electrophysiology or molecular studies
Summary
High-level brain functions emerge from the real-time interaction of interconnected neural networks. Recent studies of axonal biophysics aligned polydimethylsiloxane (PDMS) microchannel devices with electrodes of commercial or custom-made MEAs8, 9 or CMOS-based MEAs10, 11 to both guide axons and to create an electrically isolated and more stable cellular microenvironment. This strategy, which was previously exploited for the comprehensive analysis of axonal biology[12, 13], increases the extracellular sealing www.nature.com/scientificreports/. Multisite recording or stimulation with paired devices allowed studying axonal signal properties and activity-dependent changes in axonal signal conduction velocities under normal and chemically or electrically stimulated conditions[10, 11, 16, 17]. The described platform and results may provide the basis for gaining new insights into how axonal activity processes and controls neural output
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