PURPOSE:This study investigated the role of the sacral nerves in the mechanism of defecation using adult mongrel dogs. The possibility of designing a colonic pacemaker as a new therapeutic device to treat defecation disturbances, such as fecal incontinence and severe constipation, is also discussed.METHODS:Colorectal motility during spontaneous defecation was monitored with force strain‐gauge transducers implanted in the proximal, distal, and sigmoid colon, rectum, and internal anal sphincter. Under general anesthesia, the sacral nerve was stimulated electrically, and the colorectal motility response was examined.RESULTS:During spontaneous defecation, three characteristic motility patterns were observed: 1) giant migrating contractions of the colon were propagated to the rectum or anus; 2) the rectum relaxed before the giant migrating contractions were propagated; and 3) the internal anal sphincter was relaxed during the propagation of the giant migrating contraction. Sacral nerve stimulation elicited the following three unique responses: 1) contractile movements were propagated from the distal colon to the rectum; 2) a relaxation response was noted in the rectum; and 3) the internal anal sphincter exhibited a relaxation response. The duration and propagation velocity of the contractile responses and the duration of relaxation responses elicited by electrical stimulation of the sacral nerve were similar to those that occurred during spontaneous defecation, but their amplitudes were smaller.CONCLUSION:The coordinated processes of the colon and anorectum during defecation were affected by the sacral nerves. This suggests that it is possible to design a colonic pacemaker to control lower colonic and rectal movements.