Spinal evoked potential P2 wave elicited by C fiber input and depressed by analgesic factors

Spinal cord potentials were recorded from the surface of the spinal cord of rats. The effects of various treatments on a positive wave following the original P wave, which was evoked by strong electrical stimulation and named the P2 wave, were investigated. The results of this study demonstrate that capsaicin applied on to the sciatic nerve, intrathecal injection of morphine, electroacupuncture and noxious heat applied to the hindpaw contralateral to the recording side could suppress the P2 wave. These data suggest that P2 is mediated by C afferents and might be useful as a new indicator of spinal nociception.