Recto-anal motility responses in the Göttingen minipig by selective stimulation of the ventral sacral nerve roots

Electrical stimulation of sacral roots for electrodefecation results in simultaneous activation of the rectum and the external anal sphincter. The sphincter contraction hinders evacuation of the rectum. In this study anodal blocking has been used to reduce the activation of the external anal sphincter. Using a tripolar cuff electrode and monophasic rectangular current pulses in 7 acute minipigs experiments the pressure response in the anal canal was reduced more than 80 % in all animals compared to stimulation without blocking. The result confirms previous results from the bladder, in other species, in that selective small fibre activation can be obtained using an anodal block.