Changes in micturition after spinal cord injury in conscious rats

To determine the feasibility of urodynamic monitoring of voiding function in conscious, female spinal cord-injured (SCI) rats and to compare the voiding function in SCI rats and those with normal spinal cord (NSC).

Cystometrograms were performed on conscious, female Sprague-Dawley rats. Parameters measured included voided volume, residual volume, volume threshold for inducing micturition, voiding efficiency, micturition pressure, pressure threshold for inducing micturition, and bladder contraction duration. SCI animals were studied 2 to 3 weeks after T8-T10 spinal cord transection.

Approximately one half of SCI rats exhibited uninhibited bladder contractions before voiding. These contractions were not observed in NSC rats. Compared with NSC rats, SCI rats had larger volume thresholds (1.43 versus 0.34 mL, P <0.001) and voided volumes (0.72 versus 0.31 mL, P <0.01). Although SCI rats had larger micturition pressures (65 versus 35 cm H2O, P <0.001), residual volumes were increased (0.71 versus 0.03 mL, P <0.001) and voiding efficiency was decreased (50% versus 92%, P <0.001) compared with the measurements in NSC rats. The micturition pressure threshold was slightly lower (23%, P <0.05) and the bladder contraction duration was longer (33%, P <0.05) in SCI rats than in NSC rats.

Cystometric studies in conscious female SCI and NSC rats revealed significant changes in the activity of the lower urinary tract after spinal cord transection. Fifty-five percent of SCI rats exhibited detrusor hyperreflexia during bladder filling and decreased voiding efficiency compared with NSC animals. This method of cystometric evaluation in the conscious animal is likely to be useful for evaluating new pharmacologic treatments for neurogenic bladder dysfunction.