Early Sacral Neuromodulation Prevented Detrusor Overactivity in Rats With Spinal Cord Injury

Sacral neuromodulation (SNM) has been shown to alleviate bladder dysfunction in patients with overactive bladder and nonobstructive urinary retention. However, the therapeutic effect and mechanism of SNM in neurogenic bladder dysfunction are still not fully understood. Using a rat model of spinal cord injury (SCI), this study aims to investigate the therapeutic effect of early SNM in the bladder-areflexia phase on neurogenic bladder dysfunction and evaluate its possible mechanism.

Basic physiological parameters such as body/bladder weight, blood pressure, and electrocardiogram results were measured to evaluate the safety of SNM. Enzyme-linked immunosorbent assays and quantitative real-time polymerase chain reaction were used to examine the expression of proinflammatory factors. Hematoxylin and eosin and Masson's trichrome staining were used to observe morphological changes, and cystometry was used to evaluate urodynamic changes after SNM treatment. Western blotting and immunofluorescence staining were used to measure the levels of transient receptor potential vanilloid 1 (TRPV1) and calcitonin gene-related peptide (CGRP) in the L6-S1 dorsal root ganglia (DRGs) and bladder. Capsaicin desensitization was used to investigate whether inhibiting TRPV1 could prevent detrusor overactivity in SCI rats.

Early SNM did not affect the body/bladder weight, heart rate, blood pressure, or the expression of proinflammatory cytokines (PGE2, IL-1, IL-2, IL-6, TGF-β, or TNF-α) in the bladders of SCI rats. Morphologically, early SNM prevented urothelial edema (p = 0.0248) but did not influence collagen/smooth muscle in the bladder. Compared with untreated rats with SCI, the rats treated with SNM exhibited increased bladder capacity (p = 0.0132) and voiding efficiency (p = 0.0179), and decreased nonvoiding contraction (NVC) frequency (p = 0.0240). The maximum pressure, basal pressure, postvoid residual, and NVC amplitude did not change significantly. After the SNM treatment, the expression of TRPV1 in the bladder and CGRP in L6-S1 DRGs weredecreased (L6, p = 0.0160; S1, p = 0.0024) in SCI rats. In capsaicin-desensitized SCI rats, urodynamic results showed an increase in bladder capacity (p = 0.0116) and voiding efficiency (p = 0.0048), and diminished NVC frequency (p = 0.0116), while other parameters did not change significantly.

Early SNM prevented urothelial edema morphologically and detrusor overactivity in SCI rats. Inhibition of TRPV1 in the bladder and DRGs may be one of the potential mechanisms for preventing detrusor overactivity by SNM.