Brainstem microstimulation activates sympathetic fibers in pudendal nerve motor branch

A bilateral spino-bulbo-spinal circuit conveys information from/to the male urogenital tract and perineal muscles. This is the first electrophysiologi cal report of another descending pathway, one which conveys output from the medullary reticular formation (MRF) to activate postganglionic sympathetic fibers contained within the motor branch of the pudendal nerve (PudM). In anesthetized rats, long latency (> 150 ms) discharges were elicited in the PudM following ipsilateral or contralateral microstimulation of the MRF. Th ese firing bursts were not observed in rats after sectioning the lower lumb ar sympathetic trunk. The most robust activation was observed when neurons in or near the lateral paragigantocellular reticular nucleus were microstim ulated bilaterally. Urogenital dysfunction that occurs following severe spi nal cord injury probably results from disrupting these and other supraspina l circuits. NeuroReport 11:379-382 (C) 2000 Lippincott Williams & Wilkins.