Reorganization of somato-urethral reflexes following spinal cord injury in the rat

Purpose: It is known that reflex activity of the urinary bladder can be inhibited or facilitated by perineal cutaneous stimulation. This study was undertaken to examine the urethral striated (EUS) and smooth muscle responses evoked by perineal cutaneous stimulation in the rat. Materials and Methods: Urethral perfusion pressure and EUS-EMG were monitored in urethane-anesthetized normal and chronic spinal rats (4-5 weeks after T8-9 spinalization) of either sex. Somatic perineal stimulation was performed by tactile or pinch stimulation to the perineum. Results: In both normal and chronic spinal rats, perineal stimulation elicited a transient increase in EUS-EMG activity which was abolished following neuromuscular blockade with alpha-bungarotoxin i.v. In normal rats treated with alpha-bungarotoxin perineal stimulation did not elicit a detectable urethral smooth muscle response. However, in chronic spinal rats perineal stimulation increased urethral. pressure by smooth muscle contraction in males and decreased urethral pressure by smooth muscle relaxation in females. The evoked urethral smooth muscle contraction in males was significantly reduced or abolished by atropine i.v., but not by sympathetic nerve transection or prazosin i.v., whereas the relaxation in females was significantly reduced or abolished by N-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor, i.v.). Conclusions: These data indicate that spinal cord injury unmasks somato-urethral smooth muscle reflexes mediated by lumbosacral parasympathetic efferent pathways. The reflexes consist of a nitric oxide-mediated urethral relaxation in females and an atropine-sensitive urethral contraction in male rats.