Direct evidence for sensory innervation of the dorsal portion of the Co5/6 coccygeal intervertebral disc in rats.
METHODS
We examined the sensory innervation of the coccygeal (Co) 5/6 intervertebral disc in rats using a retrograde neurotracing method and immunohistochemistry.


OBJECTIVE
To investigate the properties of the sensory innervation of the rat coccygeal disc.


BACKGROUND
Developing a rat disease model for degenerative intervertebral disc compression using lumbar discs is technically impractical because of their location. Coccygeal intervertebral discs are more readily accessible and several reports of morphologic evaluation of degenerative coccygeal intervertebral discs using compression devices exist. However, their sensory innervation and properties have not yet been characterized.


METHODS
FluoroGold neurotracer was applied to the Co5/6 intervertebral discs of intraperitoneally anesthetized Sprague Dawley rats (n = 10). Subsequently, the discs and the L1-S4 dorsal root ganglions (DRGs) were resected and sectioned. The discs were double-stained for immunoreactivity to the neuronal marker beta-tubulin (Tuj-1) and biotin-labeled isolectinB4 (IB4), a neuropathic pain marker, or Tuj-1 and calcitonin gene-related peptide (CGRP), an inflammatory pain marker. The DRGs were double-stained for IB4-binding and CGRP immunoreactivity (IR). The proportions of IB4-binding or CGRP-IR DRG neurons were assessed by cell counting and compared.


RESULTS
The disc immunohistochemistry showed evidence of sensory nerve fibers lying in the outermost layer of the anulus fibrosus. FluoroGold labeled DRG neurons mainly derived from S1 to S3 DRGs, especially S2 and S3. No labeled neurons were observed in the S4 DRG. The histochemistry of the DRGs showed a predominance of CGRP-IR DRG neurons (3.5 +/- 1.7% IB4-binding and 15.4 +/- 5.6% CGRP-IR on average).


CONCLUSIONS
This study showed evidence for nerve fibers in the discs and predominant innervation by CGRP-IR DRG neurons. The neurons innervating the discs mostly derived from S1 to S3 DRGs, especially S2 and S3. These findings may be useful in developing rat models of disease involving degenerative intervertebral disc compression.
Orita
Sumihisa
S
Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan. sumihisa@silver.email.ne.jp
Ohtori
Seiji
S
Taniguchi
Aya
A
Yamashita
Masaomi
M
Yamauchi
Kazuyo
K
Inoue
Gen
G
Suzuki
Munetaka
M
Eguchi
Yawara
Y
Ochiai
Nobuyasu
N
Kishida
Shunji
S
Takaso
Masashi
M
Aoki
Yasuchika
Y
Takahashi
Kazuhisa
K
Kawakami
Mamoru
M
D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000032:analysis; D003050:Coccyx; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology / Q000378:metabolism*; D006023:Glycoproteins / Q000032:analysis; D007150:Immunohistochemistry; D007403:Intervertebral Disc / Q000294:innervation*; D037102:Lectins / Q000032:analysis; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D053675:Versicans
D006023:Glycoproteins; D037102:Lectins; C508324:Vcan protein, rat; D053675:Versicans; D015740:Calcitonin Gene-Related Peptide