An electrically resistive sheet of glial cells for amplifying signals of neuronal extracellular recordings

Abstract

Electrical signals of neuronal cells can be recorded non-invasively and with a high degree of temporal resolution using multielectrode arrays (MEAs). However, signals that are recorded with these devices are small, usually 0.01%-0.1% of intracellular recordings. Here, we show that the amplitude of neuronal signals recorded with MEA devices can be amplified by covering neuronal networks with an electrically resistive sheet. The resistive sheet used in this study is a monolayer of glial cells, supportive cells in the brain. The glial cells were grown on a collagen-gel film that is permeable to oxygen and other nutrients. The impedance of the glial sheet was measured by electrochemical impedance spectroscopy, and equivalent circuit simulations were performed to theoretically investigate the effect of covering the neurons with such a resistive sheet. Finally, the effect of the resistive glial sheet was confirmed experimentally, showing a 6-fold increase in neuronal signals. This technique feasibly amplifies signals of MEA recordings. V C 2016 AIP Publishing LLC. Microelectrode array (MEA) technology is widely used to record trains of action potentials from cultured neurons, cardiomyocytes, or brain slice preparations. [1][2][3][4] The major advantage of this method lies in its high temporal resolution (>10 kHz) and non-invasiveness. MEA recordings have been used both in fundamental studies, e.g., to analyse activity patterns of cultured neuronal networks, 5,6 and in pharmacological research, for screening lead compounds in vitro. 7,8 However, small signals that can be detected through extracellularly positioned microelectrodes inhibit MEAs from being used in further applications such as studies of subthreshold activity. The amplitude of extracellularly recorded signals is usually in the order of ten to a hundred microvolts, which is 3-4 orders of magnitude lower than the intracellular change of membrane potential in an action potential ($100 mV).Various attempts have been made to overcome this issue. One approach involves increasing the seal resistance between the cell and the electrode. This can be achieved by using nanostructured electrodes instead of planar electrodes that become engulfed by overlying cells. 1,9 A second approach is to decrease the electrode impedance. To record activity from single cells, the use of a smaller electrode is preferable, but this comes at the cost of increased electrode impedance, which decreases the signal. Wolfrum et al. overcame this dilemma by creating micropores that interface the cells to larger electrodes. 10,11 A third approach involves decreasing the membrane impedance at the cell-electrode junction. In practice, this involves transiently rapturing the cell membrane by applying a zap voltage to a nanostructured electrode, thus allowing the electrodes to enter the cell and perform pseudo-intracellular recording until the raptured membrane reorganizes. 1,12,13 In this letter, we propose an alternative approach to increase the neuron-electrode seal for amplifying signals in ex...

Action potential propagation recorded from single axonal arbors using multielectrode arrays

“…A confluent glial bed could create a permissive environment for growth of axons closer to MEA electrodes than they might otherwise grow. Alternatively, glia could be an electrically resistive sheet that increases eAP amplitude across all electrodes by effectively decreasing the size of the electric field (Matsumura et al 2016). In neuronal cultures not grown on glia, we observed that neuronal processes tended to avoid the area around the electrodes, that the signal-to-noise ratio was lower than in neurons plated on a glial bed, and that propagation signals were not as notable in cultures lacking glia (data not shown).…”

“…This observation is consistent with physical elimination, or withdrawal, of the axonal process. In contrast, a decrease in spike-coupled transmembrane current in the axon at that electrode would not be expected to affect the size of the capacitive component of the eAP waveform at this site, although other explanations, such as withdrawal of glial processes leading to decreases in apparent signal size, cannot be ruled out (Matsumura et al 2016). Our data show that significant changes in axonal excitability can occur over several hours and imply that distinct portions of single axons can Decreases in the delays between the peak-scaled negative peak (arrowhead) and subsequent positive repolarization peaks (arrows) are consistent with a developmental decrease in spike width of the eAP at D6 between 11 and 26 DIV.…”

Recording action potential propagation in single axons using multi-electrode arrays

“…This could create a permissive environment for growth of axons closer to MEA electrodes than they might otherwise grow. Alternatively, glia could act as a resistive sheet that increases eAP amplitude across all electrodes (Matsumura et al, 2016). On bare arrays we observed that neuronal processes tend to avoid the area around the electrodes, that the signal-to-noise ratio was lower than in neurons plated on a glial bed and propagation signals were not as notable (data not shown).…”

Chip‐Based Heat Stimulation for Modulating Signal Propagation in HL‐1 Cell Networks

“…Recently, microsystems have created new opportunities for applying spatially and temporally controlled stimuli and recording cellular activity . Examples demonstrate the application of microchip devices for electrical stimulation and studies of signal propagation in cardiac myocyte networks .…”