A possible new reflex pathway for micturition after spinal cord injury

In order to restore bladder function after spinal cord injury, a controllable new reflex pathway has been established in rats. It involves a somatic reflex arc with an artificially modified efferent branch which passes the somatic motor impulses to the bladder. This is achieved by intradural microanastomosis of the left L4 ventral root to L6 ventral root, while leaving the L4 dorsal root intact as a starter of micturition. The 'skin-CNS-bladder' reflex pathway is designed to initiate voiding by scratching the skin. After axonal regeneration, 15 of the 24 rats with the new pathway underwent electrophysiological study. Single stimuli (0.3-3 mA, 0.02-0.2 ms duration) to the left L4 nerve resulted in evoked potentials (0.5-1 mV) recorded from the left L6 nerve distal to the anastomosis. The bladder detrusor contraction was very quickly initiated by trains of the stimuli and bladder pressures increased rapidly to levels similar to controls. Neural tracing study with horseradish peroxidase (HRP) on six rats with the pathway demonstrated that the somatic motor axons regenerated successfully into the pelvic nerve, and the bladder was reinnervated by the L4 somatic motor neurons. The bladder contraction can also be initiated by electrostimulation of left sciatic nerve as well as scratching the L4 related skin. A new concept may be derived from the skin-CNS-bladder reflex pathway: the impulses delivered from the efferent neurons of a somatic reflex arc can be transferred to initiate responses of an autonomic effector.