Comparison of the effects of complete and incomplete spinal cord injury on lower urinary tract function as evaluated in unanesthetized rats

In rats, phasic external urethral sphincter (EUS) activity (bursting) is postulated to be crucial for efficient voiding. This has been reported to be lost after spinal cord transection (txSCI), contributing to impaired function. However, anesthesia may confound evaluating EUS activity. We therefore evaluated urodynamic parameters in unanesthetized, restrained rats and compared the effects of txSCI to that of a clinically relevant, incomplete, contusive injury (iSCI) on lower urinary tract function. Adult female rats were subjected to txSCI or standardized iSCI at the T8 vertebral level. As expected, all injured rats were initially unable to void but developed a reflex bladder with time, with iSCI rats recovering more rapidly than txSCI rats. LUT function was evaluated urodynamically at 2 and 6 weeks after injury. In response to infusion of saline into the bladder, controls consistently exhibited coordinated contraction of the bladder and activation of the EUS in a phasic pattern and had a high voiding efficiency (86.4 ± 2.5%). Voiding efficiency of iSCI rats was reduced to approximately 57% and txSCI rats to approximately 32%. However, two different patterns of EUS activity during voiding were present in both txSCI and iSCI groups at both time points: (1) rats with phasic EUS activity, similar to controls and (2) those that only exhibited tonic EUS activity during voiding. The former had more normal voiding efficiencies. Thus, phasic EUS activity and the improved voiding efficiency associated with it can occur and can be detected in unanesthetized rats after both incomplete and complete SCI.