Convergence of visceral and somatic sensory information in the sacral cord: morphologic evidence for referred pain

Abstract

The somatic foci of pelvic organs referred pain are often and mainly distributed along the anteriolateral aspect of the lower limbs. Our study was designed to investigate the neural pathways and their transmitters for the pelvic visceral referred pain. By using tracing techniques, we observed that neurons in the sacral dorsal commissural nucleus (SDCN) innervated by primary afferents originated from both pelvic nerve and sciatic nerve and projected to parabrachial nucleus (PBN). Excitatory postsynaptic potentials (EPSPs) were elicited by the electrical stimulation of the pelvic or sciatic nerves in the SDCN neurons tested by patch clamp recording. After visceral noxious stimulation, there were more Fos‐immunopositive (Fos‐ip) neurons in the SDCN than that in the dorsal horn. SPR‐ip neurons with FOS‐ip nuclei projected to the PBN and contacted with SP‐ip terminals. Under electron microscope, we found that SP‐ip terminals or ENK‐, GABA‐, Gly‐ip terminals to make synapses with SDCN neurons projected to the PBN. These results indicated that: (1) SDCN might be the convergence point of the referred pain associated with pelvic visceral organs to lower limbs; (2) The projection from the SDCN to the PBN might contribute to the pelvic visceral information transmission; (3) SP, ENK, GABA and Gly are important for the pelvic visceral information transmission and regulation.National Natural Science Foundation of China