120mea100 30ir ti gr

Primary cortical neurons were cultured on MEAs containing 120 planar extracellular titanium nitrite electrodes with four internal references (120MEA100/30iR-Ti-gr, Multi Channel Systems) for 14–16 DIV. For the recordings, signals from 120 recording electrodes were collected with MCRack software in a MEA 2100 system (Multi Channel Systems) at a sampling rate of 50 kHz and high-pass filtered at 200 Hz. Spikes were detected using a threshold-based detector set to a threshold of seven times the standard deviation of the noise level (MC_Rack, Multi Channel Systems). Electrophysiological recordings were performed in culture medium and temperature was maintained at 37°C by a temperature controller (TC02, Multi Channel Systems). Spike datasets from all electrodes were imported into Matlab 7.7 (Mathworks, Natick, MA, USA) for analysis of single units using a custom written routine. Spike sorting was carried out as described previously [44 (link)]. Autocorrelation functions were applied to confirm spike sorting. If single units fired at least twice within the recording period, units were counted as active neurons. Average firing frequencies were calculated as arithmetic mean of individual firing frequencies of all identified units and number of active neurons was defined as number of individual single units with at least two action potentials per recording.

Cell cultures were established on MEAs containing 120 planar extracellular titanium nitrite electrodes with four internal references (120MEA100/30iR-Ti-gr, Multi Channel Systems, Reutlingen, Germany). MEAs had an electrode diameter of 30 μm and an interelectrode spacing of 100 μm. Signals from 120 recording electrodes were recorded with MC_RACK software (Multi Channel Systems) in a MEA 2100 system (Multi Channel Systems) at a sampling rate of 50 kHz and high-pass filtered at 200 Hz. Cultures were recorded after 14–16 DIV. A subset of recordings was performed after 7–8 DIV and 21–22 DIV. Spikes were detected using a threshold-based detector set to a threshold of 7× the SD of the noise level (MC_RACK, Multi Channel Systems). All electrophysiological recordings were performed in artificial cerebrospinal fluid (aCSF) that resembled the culture medium (Cohen et al., 2008 (link)) (in mM): 129 NaCl, 5.3 KCl, 2 CaCl₂, 1 MgCl₂, 10 D(+)-glucose, 26 NaHCO₃ and gassed with 95% O₂/5% CO₂. ACSF was perfused at a rate of 1 ml/min and temperature was maintained at 32°C by a temperature controller (TC02, Multi Channel Systems). Spike datasets from all electrodes were imported into Matlab 7.7 (Mathworks, Natick, MA, USA) for analysis using a custom written routine.