Presentation Authors: Yan Zheng, Shun Li, Todd Yecies*, Tara Nikonow, Haotian Cai, Bing Shen, Nathalie Pace, Jicheng Wang, James Roppolo, William de Groat, Changfeng Tai, Pittsburgh, PA
Introduction: The normal micturition reflex in cats is mediated by AÎ´-afferents in the pelvic nerve, while pelvic C-fiber afferents do not respond to bladder distension in normal physiological conditions, However, bladder irritation can sensitize these silent C-fibers, so that they can respond to bladder distension causing urinary urgency, frequency, and bladder pain. Little is known about the function of hypogastric afferents in nociceptive bladder activity. We aimed to determine if hypogastric afferents play a role in the generation of nociceptive bladder activity induced by bladder irritation.
Methods: The hypogastric nerves were exposed in Î±-chloralose anesthetized cats. Electrodes were placed at the central end of the hypogastric nerves for stimulation. The stimulation threshold for activation of C-fiber axons was identified. Bladder irritation was performed via infusion of 0.25% acetic acid (AA). Bladder capacity prior to triggering reflex bladder contraction was measured under control (saline) and AA conditions, with hypogastric nerves intact and transected, and with and without hypogastric nerve stimulation (HGNS).
Results: In cats with an intact hypogastric nerves, AA irritation significantly reduced bladder capacity to 45.0Â±5.7% of the control capacity. In cats with the hypogastric nerves transected bilaterally, AA irritation also significantly (p < 0.05) reduced bladder capacity but the change was significantly smaller (capacity reduced to 71.5Â±10.6% of saline control, p < 0.05). Application of HGNS (20 Hz, 0.2 ms) to the central end of the transected nerves at an intensity (16 V) strong enough to activate C-fiber afferents facilitated the effect of AA irritation and further reduced bladder capacity to 48.4Â±7.4% of the control. This facilitation by HGNS was effective only at selected frequencies (1, 20, and 30 Hz) when the stimulation intensity was above the threshold for activating C-fibers. Tramadol at 3 mg/kg (i.v.) completely blocked the nociceptive bladder activity and eliminated the facilitation by HGNS. HGNS did not alter non-nociceptive bladder activity induced by saline distention of the bladder.
Conclusions: These results indicate that sympathetic afferents in the hypogastric nerve play an important role in the facilitation of the nociceptive bladder activity induced by bladder irritation.
Source of Funding: National Institute of Diabetes and Kidney Disease Grants DK094905, DK102427, and DK111382