Colon and anal sphincter contractions evoked by microstimulation of the sacral spinal cord in cats

The colon and anal sphincter contractions induced by microstimulation of the S2 spinal cord were investigated by measuring the intraluminal pressure change via saline filled balloons in alpha-chlorolose anesthetized cats. Stimulation of sacral ventral roots (S1-S3) revealed that the S2 efferent outflow usually produces the largest colon response. Stimulation of the S2 ventral root or the spinal cord both indicated that 15 Hz stimulation was the optimal frequency for evoking colon contractions. Colon and anal sphincter contractions were also influenced by stimulation intensity and pulsewidth. Locations in S2 spinal cord, where microstimulation evoked a distal/proximal colon pressure response that was greater than the anal sphincter response, included the area of sacral parasympathetic nucleus (SPN), the area medial to the SPN extending to the dorsal commissure, and areas deep in the ventral horn. Anal sphincter relaxation was evoked by microstimulation in more restricted locations in S2 spinal cord, which appeared to overlap with those evoking anal sphincter contractions. These results suggest a possible method to evoke colon contraction and defecation by microstimulation of the S2 spinal cord with multiple microelectrodes.