Detrusor underactivity (DU) is an important contributor to voiding dysfunction and is commonly discovered in patients undergoing pressure-flow urodynamics for lower urinary tract symptoms. Numerous neurogenic and myogenic causes are still being identified but few reliable treatment options exist. In the early 1900’s, Barrington mechanically manipulated cat urethras with a catheter and discovered three excitatory urethra-to-bladder reflexes. These are shown to work via pudendal, hypogastric, and pelvic nerve afferents. We hypothesized that these reflexes may provide a therapeutic target for the treatment of DU. We electrically field-stimulated nerves of the proximal urethras of spinal-intact rats before and, in some, subsequent to acute suprasacral spinal cord injury (SCI) to determine if we could elicit these reflexes in normal and acute spinal shock conditions.

The current study was approved by our Institutional Animal Care and Use Committee and carried out in accordance with institutional guidelines. We performed experiments using eight female Sprague-Dawley rats (230 – 290 g). Under urethane anesthesia, surgical preparation via laparotmy included placement of bilateral ureteral diversion catheters and a transvesical catheter for bladder infusion during cystometry. The ventral pubis was removed to expose the proximal urethra. Five rats were also prepped with posterior vertebral exposure to facilitate later acute SCI. In the supine position, continuous cystometry (≥20 min) was performed to ensure spontaneous reflex bladder activity; the infusion was stopped immediately following a voiding contraction and if no further contractions were observed within a 5 minute period, bladder volume was considered stable and we proceeded to proximal urethral electrical stimulation (PUES). PUES was applied via two ~0.6 cm long, 50 µm diameter electrodes placed orthogonally across the proximal urethra and immediate surrounding tissue (~0.3 cm apart). PUES was performed for 30 seconds with a 60 second recovery in between stimulation periods. Stimulation parameters were 0.1 msec pulse and frequencies and intensities were systematically varied (5 -100 hz in 1/3 log steps and 10 to 50 V in decade steps). Following stimulation under spinal-intact conditions, spinal cord transection (SCI) was performed at T9-10 via a laminectomy in the vertebral-exposed rats. The bladder was filled to pre-SCI bladder capacity and PUES was again performed. Extracted data included presence/absence of bladder contractions and/or lower extremity motor activity. Stimulation responses were assigned a score of 1 if bladder only response, 0 for no response or both bladder and motor response, and -1 for only motor response. Data were analyzed graphically and stimulation frequencies with non-negative results across the voltage ranges were further analyzed with one-way ANOVA with Tukey’s MCT.

Overall positive responses were observed in the spinal-intact rats at 20 hz (0-86% positive score across intensities) and 50 hz (0-75% positive score across intensities). The rate of isolated bladder contraction by PUES at 20 hz was significantly greater at 30 V and 40 V (P<0.03 and <0.04, respectively). For stimulation at 50 hz, 40 V produced the highest positive score rate but ANOVA did not detect significance. No bladder responses to PUES were seen post-SCI, even in the presence of lower extremity motor activity.

In the spinal-intact rat, PUES at 20 Hz and 30 - 40 V elicited reliable bladder contractions in the absence of motor responses. Failure to elicit bladder responses following SCI suggests suprasacral involvement in excitatory urethra-to-bladder reflex arcs. This is unique as both bladder-to-urethral external urethral sphincter guarding and smooth muscle relaxant reflexes have been previously shown to remain after suprasacral SCI.

Based on reliable bladder response to PUES in a spinal-intact rodent model, the proximal urethra offers a potential target for the treatment of DU. Although PUES was unsuccessful in eliciting reflex bladder contractions under acute spinal shock conditions, we hope to assess bladder response using this approach in other DU rodent models.