Pain originating in the bile duct is common and many patients who have suffered from it report that it is one of the most intense forms of pain that they have experienced. Many uncertainties remain about the mechanisms underlying pain originating in the bile duct. For example, the dorsal root ganglion (DRG) neurons that give rise to the sensory innervation of the common bile duct (CBD) have not been identified and examined in any species. The goal of the present study was to determine the number, distribution, and size of DRG neurons that innervate the CBD in rats. Injections of WGA-HRP or CTB-HRP were restricted to the lumen of the bile duct. Injections of WGA-HRP labeled a mean number of about 500 DRG neurons bilaterally throughout all thoracic and upper lumbar levels. Injections of CTB-HRP labeled smaller numbers of DRG neurons. Application of colchicine onto the surface of the CBD reduced the number of cells labeled following injections of WGA-HRP into the lumen of the CBD by roughly 86%, suggesting that tracer had not spread in large amounts out of the CBD and labeled afferent fibers in other tissues. Approximately 85% of the neurons labeled with WGA-HRP had cell bodies that were classified as small; the remainder were medium in size. Injections of CTB-HRP labeled cell bodies of varying sizes, including a few large diameter cell bodies. These results indicate that a large number of primarily small DRG cells, located bilaterally at many segmental levels, provide a rich innervation of the common bile duct.
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Acknowledgements We thank Dr. Martin Wessendorf for critically reading an early version of this manuscript and Drs. Gary Mawe and Robert Sorenson for valuable discussions. This work was supported by NIH grant NS25932 (GJG) and DA09641 (CNH).
- Bile duct
- Dorsal horn
- Dorsal root ganglia
- Spinal cord
- Thoracic segments
- Visceral pain