Existence of nerve growth factor receptors, tyrosine kinase a and p75 neurotrophin receptors in intervertebral discs and on dorsal root ganglion neurons innervating intervertebral discs in rats.
METHODS
We evaluated 2 types of nerve growth factor (NGF) receptors on dorsal root ganglion (DRG) cells and nerve fibers innervating rat lumbar intervertebral discs.


OBJECTIVE
To examine the NGF receptors, tyrosine kinase A (TrkA) and p75 neurotrophin receptor (p75NTR) on DRG cells and nerve fibers innervating rat lumbar intervertebral discs using immunohistochemistry and a retrograde neurotracing method.


BACKGROUND
Nerve innervation of intervertebral discs is thought to be a pathology of discogenic low back pain. NGF is also important for mediating inflammatory pain from intervertebral discs via the high affinity receptor, TrkA. Recent research has also revealed that the low affinity NGF receptor, p75NTR plays an important role in inflammatory pain. However, the presence of TrkA and p75NTR-immunoreactive (NTR-IR) DRG neurons innervating the rat L5/6 intervertebral disc, and p75NTR-IR nerve fibers in rat intervertebral discs, has not been explored.


METHODS
The Fluoro-gold neurotracer was applied to rat L5/6 intervertebral discs to determine the DRG neurons innervating the discs (n = 20). Fourteen days after surgery, bilateral DRG from the L1-L6 levels were harvested, sectioned, and immunostained for TrkA and p75NTR. The percentages of TrkA and p75NTR-IR DRG neurons were counted, and p75NTR-IR nerve fibers in L5/6 discs evaluated.


RESULTS
p75NTR-IR nerve fibers were found in superficial layers in the annulus fibrosus in L5/6 intervertebral discs. Fluoro-gold-labeled neurons innervating the L5/6 discs were distributed throughout DRG from the L1-L6 levels. The percentage of TrkA-immunoreactive (TrkA-IR) neurons was 75.1% +/- 3.9% (mean +/- SE) and that of p75NTR-IR neurons was 75.8% +/- 5.1%. These percentages were similar for each level.


CONCLUSIONS
Rat L5/6 intervertebral discs were innervated by multisegmental levels of DRG. Most DRG neurons innervating the discs were positive for 2 types of NGF receptors.
Sugiura
Ai
A
Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
Ohtori
Seiji
S
Yamashita
Masaomi
M
Inoue
Gen
G
Yamauchi
Kazuyo
K
Koshi
Takana
T
Suzuki
Munetaka
M
Norimoto
Masaki
M
Orita
Sumihisa
S
Eguchi
Yawara
Y
Takahashi
Yuzuru
Y
Watanabe
Tomoko Saito
TS
Ochiai
Nobuyasu
N
Takaso
Masashi
M
Takahashi
Kazuhisa
K