Do dichotomizing afferent fibers exist which supply visceral organs as well as somatic structures? A contribution to the problem or referred pain.

Fibers in the inferior splanchnic nerves were found which could be activated by electrical stimulation of one of the lumbar white rami as well as of the somatic nerve of the same spinal segment at stable latency. The responses of these fibers reliably followed high frequency stimulation (20-100 Hz) of the nerves. The axons were unmyelinated (conduction velocity 1.02 +/- 0.57 m/sec, mean +/- 1 S.D., n = 14), had no ongoing discharges and could not be excited by afferent stimuli via a spinal or supraspinal reflex pathway. Therefore, it is likely that these fibers are afferent. The findings support the hypothesis that referred pain may be produced by dichotomizing sensory fibers, one branch passing to visceral organs and the other branch to the site of reference in muscle or skin.