Effect of bladder outlet obstruction on micturition reflex pathways in the rat

The effect of outlet obstruction on neural pathways to the bladder was examined six weeks after urethral ligation in rats. Ligated rats exhibited a seven-fold increase in bladder weight, a six-fold increase in volume, and significant increases (p less than 0.001) in micturition pressure, residual volume and compliance measured under urethane anesthesia. Unanesthetized ligated rats in comparison to control rats voided smaller volumes of urine more frequently (0.7 vs 1.1 voids/hr., p less than 0.001). Electrophysiological examination of vesical afferent and efferent peripheral neural pathways in the pelvic and hypogastric nerves and sympathetic chain did not reveal any differences in thresholds, axonal conduction velocities or ganglionic transmission. A significant difference (p less than 0.05) was noted in the percentage of obstructed rats (100%) exhibiting a short latency spinal reflex as compared to controls (35%). The long latency supraspinal micturition reflex was similar in both groups. These data suggest that obstruction in rats is accompanied by some degree of neural plasticity resulting in a more prominent spinal reflex that could contribute to the development of the unstable bladder following obstruction in humans and unanesthetized animals.