Effect of applying p75NTR saporin to a punctured intervertebral disc on calcitonin gene-related peptide expression in rat dorsal root ganglion neurons.
BACKGROUND
Recent studies have revealed that the low-affinity nerve growth factor receptor, p75 neurotrophin receptor (p75NTR), is important in inflammatory pain. Moreover, p75NTR immunoreactive sensory nerve and dorsal root ganglion (DRG) neurons have been found to innervate lumbar intervertebral discs. The purpose of the current study was to investigate the effect of p75NTR saporin, a toxin used to destroy p75NTR, on calcitonin gene-related peptide (CGRP), an inflammatory neuropeptide associated with pain, in DRG neurons innervating punctured intervertebral discs in rats.


METHODS
The neurotracer fluorogold (FG) was applied to the surfaces of L5/6 discs to label their innervating DRG neurons (n = 30). Of 30 rats, 10 were in a nonpunctured disc sham surgery control group (nonpuncture group), and the other 20 were in experimental groups in which intervertebral discs were punctured with a 23-gauge needle. p75NTR saporin was applied to the discs of 10 rats (puncture + p75NTR saporin group) and the other 10 received the same volume of saline (puncture + saline group). At 14 days after surgery, DRGs from L1 to L6 were harvested, sectioned, and immunostained for CGRP, and the proportions of CGRP-immunoreactive DRG neurons was evaluated.


RESULTS
Of the FG-labeled neurons innervating the L5/6 disc, the proportion of CGRP-immunoreactive neurons was 32% +/- 6% (mean +/- SE) in the nonpuncture group, 47.2% +/- 8% in the puncture + saline group, and 34.6% +/- 9% in the puncture + p75NTR saporin group. The proportion of CGRP-immunoreactive neurons was significantly greater in the puncture + saline group compared with the nonpuncture and puncture + p75NTR saporin groups (P < 0.01).


CONCLUSIONS
Half of the DRG neurons innervating the discs were positive for CGRP in the puncture + saline group. CGRP is important for mediating inflammatory and nerve-injured pain and may be important in discogenic pain. However, p75NTR saporin suppressed CGRP expression in DRG neurons. Therefore, p75NTR may be an important receptor for mediating discogenic pain via CGRP expression.
Sugiura
Ai
A
Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chuo-ku, Chiba, Japan.
Ohtori
Seiji
S
Yamashita
Masaomi
M
Yamauchi
Kazuyo
K
Inoue
Gen
G
Suzuki
Munetaka
M
Norimoto
Masaki
M
Orita
Sumihisa
S
Eguchi
Yawara
Y
Kuniyoshi
Kazuki
K
Ochiai
Nobuyasu
N
Kishida
Shunji
S
Takaso
Masashi
M
Aoki
Yasuchika
Y
Ishikawa
Tetsuhiro
T
Arai
Gen
G
Miyagi
Masayuki
M
Kamoda
Hiroto
H
Nakamura
Junichi
J
Takahashi
Kazuhisa
K
D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000378:metabolism*; D007403:Intervertebral Disc / Q000293:injuries*; D008159:Lumbar Vertebrae / Q000294:innervation*; D008297:Male; D009419:Nerve Tissue Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley; D017978:Receptors, Growth Factor; D017475:Receptors, Nerve Growth Factor / Q000502:physiology*; D054789:Ribosome Inactivating Proteins, Type 1; D000076985:Saporins; D013266:Stilbamidines
C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D009419:Nerve Tissue Proteins; D017978:Receptors, Growth Factor; D017475:Receptors, Nerve Growth Factor; D054789:Ribosome Inactivating Proteins, Type 1; D013266:Stilbamidines; C068313:Ngfr protein, rat; D000076985:Saporins; D015740:Calcitonin Gene-Related Peptide