Int J Oral Biol.  2018 Sep;43(3):155-160. 10.11620/IJOB.2018.43.3.155.

Ultrastructure of Substance P Immunopositive Axons in the Human Dental Pulp

Affiliations
  • 1Department of Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu 41940, Republic of Korea. ycbae@knu.ac.kr
  • 2Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu 41940, Republic of Korea.
  • 3Department of Dental Hygiene, Taegu Science University, Daegu 41453, Republic of Korea.

Abstract

There exists very little information on the ultrastructure of substance P immunopositive (+) fibers in the human dental pulp, which may help in understanding the mechanism for substance P associated pulpal inflammatory pain. To address this issue, we investigated the presence of substance P+ fibers in the human dental pulp by light- and electron-microscopic immunohistochemistry. Light microscopy revealed that substance P+ fibers ran within neurovascular bundles in the radicular pulp and in the core of coronal pulp. They were also frequently present in the peripheral pulp. Substance P+ fibers showed beads like swellings interconnected by thin axonal strand, in a manner similar to bouton en passants and interconnecting axonal strand in the spinal cord. Electron microscopy revealed that almost all the substance P+ axons were unmyelinated. The axonal swellings of the substance P+ contained numerous clear round vesicles (40-50 nm in diameter) and many large dense-cored vesicles (80-110 nm in diameter) as well as many mitochondria. The vesicles and mitochondria were rarely observed in the thin axonal strand interconnecting the swellings. Intimate interrelationship or synaptic structure between the swellings of substance P+ axon and nearby pulpal cells or axons was not found. These findings suggest co-release of substance P and glutamate from the substance P+ pulpal axons and its action on nearby structures in a paracrine manner.

Keyword

dental pulp; substance P; nerve fiber; ultrastructure; immunohistochemistry

MeSH Terms

Axons*
Dental Pulp*
Glutamic Acid
Humans*
Immunohistochemistry
Microscopy
Microscopy, Electron
Mitochondria
Nerve Fibers
Spinal Cord
Substance P*
Glutamic Acid
Substance P
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