Barbed channels enhance unidirectional connectivity between neuronal networks cultured on multi electrode arrays

Cultured neurons on multi electrode arrays (MEAs) have been widely used to study various as-pects of neuronal (network) functioning. A possible drawback of this approach is the lack of struc-ture in these networks. At the single cell level, several solutions have been proposed to enable di-rected connectivity, and promising results were obtained. At the level of connected sub-populations, a few attempts have been made with promising results. First assessment of the de-signs’ functionality, however, suggested room for further improvement. We designed a two chamber MEA aiming to create a unidirectional connection between the net-works in both chambers (‘emitting’ and ‘receiving’). To achieve this unidirectionality, all intercon-necting channels contained barbs that hindered axon growth in the opposite direction (from receiv-ing to emitting chamber). Visual inspection showed that axons predominantly grew through the channels in the promoted direction. This observation was confirmed by spontaneous activity re-cordings. Cross-correlation between the signals from two electrodes inside the channels suggested signal propagation at ≈2 m/s from emitting to receiving chamber. Cross-correlation between the fir-ing patterns in both chambers indicated that most correlated activity was initiated in the emitting chamber, which was also reflected by a significantly lower fraction of partial bursts (e. a one-chamber-only burst) in the emitting chamber. Finally, electrical stimulation in the emitting chamber induced a fast response in that chamber, and a slower response in the receiving chamber. Stimula-tion in the receiving chamber evoked a fast response in that chamber, but no response in the emit-ting chamber. These results confirm the predominantly unidirectional nature of the connecting channels from emitting to receiving chamber.