The Relationship Between Cortical Activation in Response to Anorectal Stimuli and Continence Behavior in Freely Behaving Rats Before and After Application of Sacral Nerve Stimulation

Abstract

Background: Changes in anorectal sensation have been reported in patients with fecal incontinence and there is limited evidence that sacral nerve stimulation can restore normal sensation. Objective: The aims of the present study were to investigate changes in transmission of sensory anorectal stimuli in a rodent model of FI and to study the effects of SNS on defecation behaviour. Design & Interventions: An established model of fecal incontinence using pudendal nerve stretch and compression was used in 16 adult female Wistar rats and followed for 3 weeks: six rats received sacral nerve stimulation for 1 week using an implantable neurostimulator and ten rats had non-functioning ‘dummy’ devices inserted. Five additional rats were sham operated. Anorectal cortical evoked potentials were used as a surrogate marker for anorectal sensory function. Main Outcome Measures: Faecal incontinence index, evoked potential amplitude and latency. Results: Fifty percent of rats showed behavioral signs of FI measured by the Fecal Incontinence Index(>0.20), calculated using the pellet distribution outside the cage’s latrine area. Anorectal evoked potential amplitude was reduced in rats with an fecal incontinence index >0.20(p=0.019). The amplitude of forepaw evoked potentials recorded as a control was not different between groups. Sacral nerve stimulation using the fully implantable device and custom rodent lead was safe and stable during this prospective study. Incontinent rats(N=3) that received sacral nerve stimulation showed an improvement of fecal incontinence indexand an increase of evoked potential amplitude to anorectal stimulation compared to the dummy implant controls (N=5). Limitations: The main limitation is the small number of animals that received sacral nerve stimulation. Conclusions: Chronic sacral nerve stimulation is feasible in rats when miniature telemetric devices are used. Behavioral signs of fecal incontinence were positively correlated with latency of anorectal evoked potentials.