Rectal Distention Inhibits the Spinal Micturition Reflex via Glycinergic or GABAergic Mechanisms in Rats with Spinal Cord Injury

Abstract

Background: We examined the influence of rectal distention on the spinal micturition reflex and the mechanism underlying its inhibition of bladder contraction. Methods: Fourteen conscious female Sprague-Dawley rats were used in this study after transection of the lower thoracic cord. Isovolumetric cystometry was performed before and after distention of the rectum by inflation of a rectal balloon, followed by intrathecal injection of strychnine (a selective glycine receptor antagonist) or bicuculline (a GABA_A receptor antagonist) into the lumbosacral cord. Results: Rectal distention (1.0–3.0 cm³) prolonged the interval, decreased the amplitude, and shortened the duration of bladder contraction, and eventually almost abolished bladder activity. After intrathecal injection of strychnine (0.001–10 µg) or bicuculline (0.001–1 µg) in animals with inhibition of bladder activity by rectal distention, the interval, amplitude, and duration of bladder contraction returned to baseline. Conclusion: These results suggest that there is an inhibitory rectovesical reflex in the lumbosacral cord of rats with spinal cord injury, which modulates the spinal micturition reflex via glycinergic or GABAergic mechanisms.