Yonsei Med J.  2014 Nov;55(6):1600-1605. 10.3349/ymj.2014.55.6.1600.

Increase of TRPV1-Immunoreactivity in Dorsal Root Ganglia Neurons Innervating the Femur in a Rat Model of Osteoporosis

• Yoshino K
• Suzuki M
• Kawarai Y
• Sakuma Y
• Inoue G
• Orita S
• Yamauchi K
• Aoki Y
• Ishikawa T
• Miyagi M
• Kamoda H
• Kubota G
• Oikawa Y
• Inage K
• Sainoh T
• Sato J
• Nakamura J
• Toyone T
• Takahashi
• Ohtori S

• KMID: 2070208
• DOI: http://doi.org/10.3349/ymj.2014.55.6.1600

Abstract

PURPOSE
Transient receptor potential vanilloid 1 (TRPV1) is a ligand-gated nonselective cation channel, which can be activated by capsaicin and other noxious stimuli. Recently, an association between bone pain and TRPV1 has been reported. However, the influence of osteoporosis on TRPV1 in the sensory system innervating the femur has not been reported.
MATERIALS AND METHODS
TRPV1-immunoreactive (ir) in dorsal root ganglia (DRG) neurons labeled with neurotracer [Fluoro-Gold (FG)] innervating the femurs of Sprague Dawley rats were examined in control, sham, and ovariectomized (OVX) rats. We evaluated osteoporosis in the femurs and compared the proportion of TRPV1-ir DRG neurons innervating femur between the 3 groups of rats.
RESULTS
OVX rats showed osteoporotic cancellous bone in the femur. FG labeled neurons were distributed from L1 to L6 DRG, but there was no significant difference in the proportion of labeled neurons between the 3 groups (p>0.05). The proportions of FG labeled TRPV1-ir DRG neurons were 1.7%, 1.7%, and 2.8% of DRG neurons innervating the femur, in control, sham-operated, and OVX rats, respectively. The proportion of TRPV1-ir neurons in DRG innervating the femur in OVX rats was significantly higher than that in control and sham-operated rats (p<0.05).
CONCLUSION
Under physiological conditions, DRG neurons innervating femurs in rats contain TRPV1. Osteoporosis increases the numbers of TRPV1-ir neurons in DRG innervating osteoporotic femurs in rats. These findings suggest that TRPV1 may have a role in sensory perception of osteoporotic femurs.

Keyword

Osteoporosis; pain; transient receptor potential vanilloid 1; femur

MeSH Terms

Animals
Female
Femur/*innervation/*metabolism
Ganglia, Spinal/*metabolism
Lumbar Vertebrae/*innervation/physiopathology
Neurons
Osteoporosis/complications
Rats
Rats, Sprague-Dawley
Stilbamidines
TRPV Cation Channels/*metabolism
Stilbamidines
TRPV Cation Channels

Figure

• 

  Fig. 1 HE staining of control and OVX femurs. OVX femur samples showed thinner cortex and more widely separated bone trabeculae with decreased density compared with samples from the control group. (A) Control. (B) OVX. HE, hematoxylin and eosin; OVX, ovariectomized.

• 

  Fig. 2 Innervation of the left femur. FG-labeled (A, B, and C) and TRPV1 immunoreactive (ir) DRG neurons (D, E, and F) [A and D (control), B and E (sham), and C and F (OVX) are same sections. Arrows indicate double labeled neurons]. FG, Fluoro-Gold; TRPV1, transient receptor potential vanilloid 1; DRG, dorsal root ganglia; OVX, ovariectomized.

• 

  Fig. 3 Distribution and proportion of FG-labeled DRG neurons innervating the left femur. FG-labeled DRG neurons were present in DRG from L1 through L6, and there was no significant difference in the proportion of FG-labeled neurons between the 3 groups. FG, Fluoro-Gold; DRG, dorsal root ganglia; OVX, ovariectomized.

• 

  Fig. 4 Distribution and proportion of FG-labeled and TRPV1-ir DRG neurons innervating the left femur. FG-labeled and TRPV1-ir DRG neurons innervating the left femur were present in DRG from L1 through L6. The proportion of FG-labeled and TRPV1-ir DRG neurons in OVX rats was significantly higher than those in control and sham-operated rats (*p<0.05). FG, Fluoro-Gold; TRPV1, transient receptor potential vanilloid 1; DRG, dorsal root ganglia; OVX, ovariectomized; ir, immunoreactive.

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