Orientation of spiral ganglion neurite extension in electrical fields of charge-balanced biphasic pulses and direct current in vitro

Cochlear implants function by stimulating residual spiral ganglion neurons (SGNs) with electric current. Promoting the neurites of SGNs to grow towards an electrode array could improve the outcome of cochlear implantation. Several studies have suggested that DC electrical fields (EFs) can affect the direction of neurite extension. To investigate the impact of steady DC EFs, pulsed DC EFs and charge-balanced biphasic pulsed EFs on the direction of SGN neurite extension, we established an SGN culturing and imaging system. SGN explants of newborn Sprague-Dawley rats were cultured on slides. Slides were positioned into the monitoring system with neurite terminals in a certain orientation and location, while the migration of SGN growth cones was monitored by taking serial photos. Deflection angles of neurites at a certain period were measured. In steady or pulsed DC EFs, neurites on laminin-coated slides turned towards the cathode, while those on PDL-coated slides turned towards the anode. The neurites in charge-balanced biphasic pulsed EFs had an obvious orientation of turning away from the electrode rings. This orientation diminished with increasing distance from the electrode rings and followed the nonuniform characteristics of charge-balanced biphasic pulsed EFs.