REORGANIZATION OF SOMATO-URETHRAL REFLEXES FOLLOWING SPINAL-CORD INJURY IN THE RAT

Purpose: It is known that reflex activity of the urinary bladder can b e inhibited or facilitated by perineal cutaneous stimulation. This stu dy was undertaken to examine the urethral striated (EUS) and smooth mu scle responses evoked by perineal cutaneous stimulation in the rat. Ma terials and Methods: Urethral perfusion pressure and EUS-EMG were moni tored in urethane-anesthetized normal and chronic spinal rats (4-5 wee ks after T8-9 spinalization) of either sex. Somatic perineal stimulati on was performed by tactile or pinch stimulation to the perineum. Resu lts: In both normal and chronic spinal rats, perineal stimulation elic ited a transient increase in EUS-EMG activity which was abolished foll owing neuromuscular blockade with alpha-bungarotoxin i.v. In normal ra ts treated with alpha-bungarotoxin perineal stimulation did not elicit a detectable urethral smooth muscle response. However, in chronic spi nal rats perineal stimulation increased urethral. pressure by smooth m uscle contraction in males and decreased urethral pressure by smooth m uscle relaxation in females. The evoked urethral smooth muscle contrac tion in males was significantly reduced or abolished by atropine i.v., but not by sympathetic nerve transection or prazosin i.v., whereas th e relaxation in females was significantly reduced or abolished by N-ni tro-L-arginine methyl ester (a nitric oxide synthase inhibitor, i.v.). Conclusions: These data indicate that spinal cord injury unmasks soma to-urethral smooth muscle reflexes mediated by lumbosacral parasympath etic efferent pathways. The reflexes consist of a nitric oxide-mediate d urethral relaxation in females and an atropine-sensitive urethral co ntraction in male rats.