Motor evoked potentials induced by electrical stimulation of the spine in dogs: which structures are involved?

A minimally invasive method for the stimulation of the spinal cord in dogs was developed. Electrical stimuli were delivered to the spine at the T8 vertebral level through partially insulated needles and under ketamine anesthesia. This allowed the recording of reproducible responses in hind limb muscles of intact dogs. Chronic unilateral deafferentation suppressed the muscle responses on the operated side. A cordotomy sparing the dorsal columns at the L1 level did not completely suppress the muscle responses. It was concluded that motoneuron activation through antidromic conduction in first-order sensory neurons was possible with thoracic spine stimulation and that the recording of muscle responses did not necessarily assess central motor pathways.