Effect of preemptive treatment of capsaicin or resiniferatoxin on the development of pre-micturition contractions after partial urethral obstruction in the rat.

PURPOSE: Neuroplasticity in afferent pathways, including C-fiber bladder afferents, is believed to be one of the major causes of changes in bladder function after partial urethral obstruction. We determined if capsaicin sensitive C-fiber bladder afferents are involved in the development of pre-micturition contractions after partial urethral obstruction in the rat.
MATERIALS AND METHODS: Female Wistar rats were preemptively treated with capsaicin (100 mg/kg subcutaneously) or resiniferatoxin (0.3 mg/kg subcutaneously) prior to the creation of obstruction. Before and 6 weeks after obstruction micturition profiles were compared among the 3 groups, including obstructed rats preemptively treated with capsaicin (BO/CAP) or resiniferatoxin (BO/RTX) and untreated obstructed rats (BO/-). In addition, conscious filling cystometry was performed after obstruction.
RESULTS: Instillation of capsaicin solutions into the eye or bladder induced significant irritative reactions in BO/- but not in BO/CAP or BO/RTX, indicating that the effect of pretreatment with capsaicin or resiniferatoxin lasted 6 weeks. Voided volume per micturition on micturition profiles was decreased after partial urethral obstruction in all 3 groups. On conscious filling cystometry a significant increase in bladder capacity, voided volume and micturition threshold pressure was noted in BO/CAP but not in BO/RTX compared with BO/-. In contrast, there was no significant change in residual volume, voiding efficiency or micturition pressure among the 3 groups. The prevalence of pre-micturition contractions was 100% in BO/CAP and BO/RTX, and 83% in BO/-.
CONCLUSIONS: Capsaicin sensitive C-fiber afferents are not essential to induce pre-micturition contractions but they are involved in functional alterations in bladder afferent pathways after partial urethral obstruction in rats.