Yonsei Med J.  2014 Nov;55(6):1631-1639. 10.3349/ymj.2014.55.6.1631.

Epidural Dexamethasone Decreased Inflammatory Hyperalgesia and Spinal cPLA2 Expression in a Rat Formalin Test

• Min SH
• Soh JS
• Park JY
• Choi SU
• Lee HW
• Lee JJ
• Kim JH

• KMID: 2070213
• DOI: http://doi.org/10.3349/ymj.2014.55.6.1631

Abstract

PURPOSE
The aim of this study was to investigate the effect of epidural dexamethasone on analgesia and cytosolic phospholipase A2 (cPLA2) expression in the spinal cord in a rat formalin test.
MATERIALS AND METHODS
Epidural dexamethasone injection was performed to Sprague-Dawley rats with a 25 gauge needle under fluoroscopy. Following the epidural injection, a formalin induced pain behavior test was performed. Next, the spinal cords corresponding to L4 dorsal root ganglion was extracted to observe the cPLA2 expression.
RESULTS
There were no differences in pain response during phase I among the groups. The phase II pain response in 300 microg of epidural dexamethasone group decreased as compared to control, 30 microg of epidural dexamethasone, 100 microg of epidural dexamethasone, and 300 microg of systemic dexamethasone groups. The expression of cPLA2 decreased in Rexed laminae I-II in 300 microg of the epidural dexamethasone group compared with the ones in the control group.
CONCLUSION
Taken together, these results suggest that 300 microg of epidural dexamethasone has an attenuating effect on the peripheral inflammatory tissue injury induced hyperalgesia and this effect is mediated through the inhibition of intraspinal cPLA2 expression and the primary site of action is the laminae I-II of the spinal cord.

Keyword

Cytosolic phospholipase A2; dexamethasone; epidural injections; formalin test

MeSH Terms

Animals
Anti-Inflammatory Agents/*pharmacology
Dexamethasone/*pharmacology
Formaldehyde/*adverse effects
Group IV Phospholipases A2/*metabolism
Hyperalgesia/*drug therapy
Injections, Epidural
Male
Pain/chemically induced/*metabolism
Pain Measurement
Rats
Rats, Sprague-Dawley
Spinal Cord/*metabolism
Anti-Inflammatory Agents
Dexamethasone
Formaldehyde
Group IV Phospholipases A2

Figure

• 

  Fig. 1 Schematic diagram of the bent needle.

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  Fig. 2 Confirmation of an epidural injection using contrast dye under fluoroscopic guidance. (A) The needle was directed to the ligamentum flavum. (B) The bevel of the needle was turned parallel to the dura. (C) The needle approached the epidural space using the loss of resistance technique. (D) Contrast dye (arrows) was injected to confirm the position of the needle. (E) The epidural space was filled with contrast dye (arrows). (F) After the epidural drug injection, the contrast dye was washed out.

• 

  Fig. 3 Anteroposterior (A) and lateral (B) radiographs after contrast dye injection. The needle was positioned centrally within the dorsal epidural space. The contrast material was seen circumferentially within the epidural space and along the proximal nerve sheaths (arrows). (C) Schematic representation of lateral radiograph depicts needle placement and orientation relative to structures. ES, epidural space; IT, intrathecal space; LF, ligamentum flavum; S, spinous process; VB, vertebral body.

• 

  Fig. 4 Dose-dependent response of epidural dexamethasone on formalin induced pain behaviors. (A) Time course of pain behaviors. The numbers of flinches were used as an index of pain response. (B) Bar graphs show the total sum of flinches during phase I (0-10 min) and phase II (11-60 min). *p<0.005 vs. control, †p<0.005 vs. D30, ‡p<0.05 vs. D100. Symbols and error bars represent the mean±SEM (n=10). SEM, standard error of mean.

• 

  Fig. 5 Effect of epidural and systemic dexamethasone on formalin induced pain behaviors. (A) Time course of pain behaviors. The numbers of flinches were used as an index of pain response. (B) Bar graphs show the total sum of flinches during phase I (0-10 min) and phase II (11-60 min). *p<0.001 vs. control, †p<0.001 vs. vehicle, ‡p<0.005 vs. S300. Symbols and error bars represent the mean±SEM (n=10). SEM, standard error of mean.

• 

  Fig. 6 Microscopic view of cytoplasmic staining for cPLA2 in the ipsilateral spinal cord dorsal horn. Three sections shown within the dotted lines represented the ipsilateral Rexed laminae I-II, III-IV, V-VI each. 40× magnified image of dorsal horn in naive (A), control (B), and D300 groups (C). (D, E, and F) are the 10× magnified image of each quadrangle in naive (A), control (B), and D300 groups (C). Scale bar=100 µm (A, B, and C). cPLA2, cytosolic phospholipase A2 (arrows).

• 

  Fig. 7 The area of ASI of the ipsilateral Rexed laminae I-II analyzed by ImageJ. Data are expressed as box (median and 25% and 75% IQR) and whisker (maximum and minimum) plots. *p<0.001 vs. naive, †p<0.001 vs. D300. ASI, anti-cytosolic phospholipase A2 antibody specific immunoreacitivity (n=10).

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