Effects of Unilateral and Bilateral Sacral Nerve Stimulation on Defecation and Microbiota in Constipated Dogs

Objectives This study aims to explore potential differences in therapeutic efficacy and impact on intestinal microbiota between unilateral and bilateral sacral nerve stimulation (uSNS and bSNS) in the treatment of constipation. Materials and Methods Dual-channel sacral nerve stimulators were implanted in six beagles, while constipation was induced using compound diphenoxylate and alosetron hydrochloride. Using a randomized crossover design, dogs (total n = 6) underwent uSNS and bSNS interventions sequentially, with ten-day washout periods. Data collection spanned four stages: baseline, constipation, uSNS treatment, and bSNS treatment. Measured parameters included the number of defecations, Bristol Stool Form Scale (BSFS) scores, total gastrointestinal transit time (TGTT), short-chain fatty acid concentrations (quantified via liquid chromatography–tandem mass spectrometry), and intestinal microbiota levels (assessed by 16S ribosomal RNA [rRNA] V3–V4 region sequencing). Results Compared with the baseline stage, the constipation stage showed a reduced number of defecations, lower BSFS scores, and prolonged TGTT ( p < 0.05). Sacral nerve stimulation (SNS) improved BSFS scores and shortened TGTT in constipated dogs, but only bSNS showed statistically significant changes relative to the constipation stage ( p < 0.05). Moreover, bSNS shortened TGTT significantly more than uSNS ( p < 0.05). 16S rRNA sequencing revealed that constipation altered the intestinal microbiota composition. In constipated dogs, Blautia abundance and the concentrations of butyrate and valerate were lower than those at baseline ( p < 0.05). After SNS treatment, these measures increased without reaching statistical significance ( p > 0.05). Conclusions bSNS improved BSFS scores and TGTT in constipated dogs and was superior to uSNS for TGTT. SNS may also beneficially modulate intestinal microbiota, which warrants confirmation in larger studies. © 2025 International Neuromodulation Society.