Presentation Authors: Bradley Potts*, Matthew Fraser, Durham, NC
Introduction: Detrusor underactivity (DU) is an important contributor to voiding dysfunction with numerous neurogenic and myogenic causes still being identified. Treatment options for DU, however, remain few. In the early 1900&[prime]s, Barrington discovered excitatory urethra-to-bladder reflexes (UBR) in cats via pudendal, hypogastric, and pelvic nerve afferents. We electrically field-stimulated nerves of the proximal urethras of spinal-intact (SI) 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.
Methods: Eight urethane-anesthetized female Sprague-Dawley rats (230-290g) received ureteral diversion and transvesical catheters via laparotomy. The ventral pubis was removed to expose the urethra. Five rats were prepped with posterior vertebral dissection to facilitate acute SCI. Following continuous cystometry, static bladder volumes were set below bladder capacity (BC) and proximal urethral electrical stimulation (PUES) was applied via two 50 Î¼m stainless steel wire electrodes placed across the rostral and caudal proximal urethra and immediate surrounding tissue. PUES was applied for 30 sec (60 sec recovery) with 0.1msec pulse, 5-250Hz and 10-50V. Following SI stimulation, SCI was performed at T9-10 (n=5). The bladder was filled to pre-SCI BC and PUES was performed from 5-250Hz and 50-75V. Extracted data included presence/absence of bladder contraction and evidence of lower extremity motor activity. Data were assigned a score of 1 if there was a bladder without motor response, 0 for no response or both bladder and motor response, and -1 for only motor response. Data were analyzed graphically and frequencies with non-negative results were further analyzed with one-way ANOVA.
Results: Overall positive responses were observed in SI for frequencies of 20Hz and 50Hz. Only 20Hz demonstrated significant differences by intensity; 30 and 40V elicited significantly higher average scores than other voltages (P=0.0213-0.0365 for 10, 20 and 50V). While 50V always elicited both a bladder and motor response in SI, only motor responses were observed after SCI.
Conclusions: In the SI rat, PUES at 20Hz and 30-40V elicited reliable bladder contraction in the absence of observable motor responses. Failure to elicit bladder responses following SCI suggests supralumbar involvement in UBR reflex arcs, as both bladder-to-urethral EUS guarding and smooth muscle relaxant reflexes have been shown to remain.
Source of Funding: Discretionary Research Funds