First Demonstration of Nociceptive and Non-Nociceptive Responses from Spinal Neurons in a Porcine Model

The spinal cord plays a key role in pain processing, but it remains unexplored in large animal models. We have developed a methodology to record from spinal neurons using three pigs. Here we aim to determine (1) at which rostro-caudal level ulnar nerve evoked responses can be recorded and (2) at which depth distinctly different responses can be recorded after noxious and non-noxious stimulation. Neural signals were evoked by ulnar nerve stimulation and recorded at different levels of the spinal cord in anesthetized pigs. Event-related potentials and peri-stimulus histograms showed that most activity was recorded at the C7 level, which diminished when the electrodes were moved towards C6 or C8. At 1 mm depth, spinal neurons responded primarily to noxious stimulation, which is typical for nociceptive specific neurons. While at 2 mm depth, neurons showed responses typical for wide dynamic range neurons by responding differently to noxious and non-noxious stimulation. Histological analysis showed that these signals may indeed have been recorded from lamina I/II and IV/V, respectively. This method opens new possibilities for studying pain and other spinal mechanisms in large animals and can be combined with peripheral and brain recordings to provide a more integrated picture of (chronic) pain mechanisms.