J Korean Neurosurg Soc.  2018 Mar;61(2):186-193. 10.3340/jkns.2017.0404.019.

Cold Allodynia after C2 Root Resection in Sprague-Dawley Rats

• Chung D
• Cho DC
• Park SH
• Kim KT
• Sung JK
• Jeon Y

• KMID: 2408019
• DOI: http://doi.org/10.3340/jkns.2017.0404.019

Abstract

OBJECTIVE
The purpose of this study was to evaluate pain-related behaviors after bilateral C2 root resection and change in pain patterns in the suboccipital region in rats.
METHODS
Male Sprague-Dawley rats were randomly assigned to three groups (n=25/group); näive, sham, and C2 resection. Three, 7, 10, and 14 days after surgery, cold allodynia was assessed using 20 μL of 99.7% acetone. c-Fos and c-Jun were immunohistochemically stained to evaluate activation of dorsal horn gray matter in C2 segments of the spinal cord 2 hours, 1 day, 7 days, and 14 days after surgery.
RESULTS
Three days after surgery, the response to acetone in the sham group was significantly greater than in the näive group, and this significant difference between the näive and sham groups was maintained throughout the experimental period (p < 0.05 at 3, 7, 10, and 14 days). Seven, 10, and 14 days after surgery, the C2 root resection group exhibited a significantly greater response to acetone than the näive group (p < 0.05), and both the sham and C2 resection groups exhibited significantly greater responses to acetone compared with 3 days after surgery. No significant difference in cold allodynia was observed between the sham and C2 root resection groups throughout the experimental period. Two hours after surgery, both the sham and C2 root resection groups exhibited significant increases in c-Fos- and c-Jun-positive neurons compared with the naive group (p=0.0021 and p=0.0358 for the sham group, and p=0.0135 and p=0.014 for the C2 root resection group, respectively). One day after surgery, both the sham and C2 root resection groups exhibited significant decreases in c-Fos -positive neurons compared with two hours after surgery (p=0.0169 and p=0.0123, respectively), and these significant decreases in c-Fos immunoreactivity were maintained in both the sham and C2 root resection groups 7 and 14 days after surgery. The sham and C2 root resection groups presented a tendency toward a decrease in c-Jun-positive neurons 1, 7, and 14 days after surgery, but the decrease did not reach statistical significance.
CONCLUSION
We found no significant difference in cold allodynia and the early expression of c-Fos and c-Jun between the sham and C2 resection groups. Our results may support the routine resection of the C2 nerve root for posterior C1-2 fusion, but, further studies are needed.

Keyword

Cold allodynia; C2 root resection; Neuropathic pain; Posterior atlantoaxial fusion

MeSH Terms

Acetone
Animals
Gray Matter
Humans
Hyperalgesia*
Male
Neuralgia
Neurons
Rats
Rats, Sprague-Dawley*
Spinal Cord
Spinal Cord Dorsal Horn
Acetone

Figure

• 

  Fig. 1 After careful dissection of the posterior neck muscle, the C2 root ganglion was revealed just below the C1 posterior arch. A : The white arrow indicates the C2 root ganglion. The asterisk indicates the posterior C1 arch. B : Once exposed, the bilateral C2 roots were completely transected using microscissor in an area just proximal to the dorsal root ganglion.

• 

  Fig. 2 Illustration of cold allodynia testing. A volume of 20 μL of 99.7% acetone was dropped onto the glabrous surface below the ears. The acetone percolated through the suboccipital area, not cross the midline suture site.

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  Fig. 3 Evaluation pain-related behavior (cold allodynia) for 2 weeks after surgery. The data are expressed means±standard error of mean. *p <0.05, compared with naive group. †p <0.05, compared with sham group 3 days after surgery. ‡p<0.05, compared with C2 root resection group 3 days after surgery. No significant difference in cold allodynia was found between the sham and C2 root resection groups at each time point throughout the experimental period.

• 

  Fig. 4 Representative spinal cord sections stained with hematoxylin and eosin at C2 segment of spinal cord at 1 day after experiment. Black box shows the area for quantification of c-Fos- and c-Jun-positive nuclei in dorsal horn gray matter of Fig. 5. Scale bar=500 μm; 20×magnification.

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  Fig. 5 Immunohistochemical staining of c-Fos and c-Jun. Representative photographs of c-Fos- and c-Jun-postive immunoreactivity cells from dorsal horn gray matter of C2 segments of spinal cord at 1 day after experiment. 100×magnification.

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  Fig. 6 Immunohistochemical staining of c-Fos (A) and c-Jun (B) in C2 segments of the spinal cord. *p <0.05, compared with naive group. †p <0.05, compared with sham group 2 hours after surgery. ‡p <0.05, compared with C2 root resection group 2 hours after surgery.

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