Detection of spinal action potentials with subdural electrodes in freely moving rodents

Recording directly from the spinal cord surface in freely behaving animals provides a promising means to investigate spinal electrophysiology, typically examined in stimulation experiments or during controlled behaviour. In a two-week experiment, we extract high-frequency spiking activity in control and spinal cord injured rats during freely behaving, open-field recording sessions. Electrical signals were recorded using sputtered iridium oxide (SIROF) electrodes on a polyimide-based, flexible probe surgically inserted beneath the dura of the spinal column, with electrodes in direct contact with the thoracic and lumbar spinal cord. The propagation of neural spikes was investigated following bandpass filtering in the high-frequency range (300-3000 Hz). A large, slow-travelling ascending and descending cluster was identified (< 15 ms^- 1) in both injured and non-injured animals. The amplitude of spikes detected for injured animals was significantly lower than in non-injured animals. Spike velocities remained stable during the two weeks. This study is the first to validate the neural origin of recorded electrical activity from the spinal cord in freely behaving animals without the application of any external stimulus. Metrics identified and evaluated can inform the development of injury biomarkers and recovery tracking following spinal cord injury.