Excitatory and inhibitory A- and C-reflexes in pelvic parasympathetic efferent nerves elicited by single shock to A and C afferent fibers of perineal and limb somatic nerves in anesthetized rats.

The effects of single electrical shocks to myelinated A and unmyelinated C afferent fibers of perineal and limb somatic nerves on the reflex discharges in pelvic parasympathetic (L6/S1) efferent nerves to the bladder were examined in anesthetized central nervous system (CNS)-intact and acute spinal rats. When the bladder was empty, stimulation of perineal somatic inputs to the L6 and S1 segments from the perineo-femoral branch of a pudendal nerve produced excitatory A- and C-reflex discharge components in postganglionic parasympathetic efferent nerve branches on the bladder surface. When the bladder was expanded and pelvic efferent neurons were rhythmically active, additional inhibitory A- and C-reflex components could be seen. After acute spinal transection, the same stimuli elicited excitatory A- and C-reflex discharges of similar latency as those observed before the spinal transection, but were of larger amplitude and longer duration; resting activity in the pelvic nerve was low, and no evoked inhibitory reflex components could be observed. Electrical stimulation of afferents in the tibial nerve had no effect when the bladder pressure was low, but when the bladder was distended, early and late components of reflex inhibition and excitation of parasympathetic activity were visible in CNS-intact rats; these reflex responses were abolished following spinalization.