| Preemptive Effect of Ketamine on Inflammatory Pain and Spinal c-fos Expression Induced by Formalin in the Rat. |
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In Ho Lee, Il Ok Lee |
1Department of Anesthesiology, Sungkyunkwan University School of Medicine, Seoul, Korea.
2Department of Anesthesiology, College of Medicine, Korea University, Seoul, Korea. iloklee@hotmail.com |
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| Abstract |
BACKGROUND
Studies on the mechanism of ketamine preemption have led to conflicting results. The purpose of this study was to compare behavioral antinociceptive responses with spinal fos-like immunoreactivity (FLI) in intravenous ketamine injection between pre- versus post-formalin administration in the rat.
METHODS
Sprague-Dawley rats (250 300 g) were prepared to receive either saline or ketamine. Formalin (5%) 100mul was injected into the hindpaw. All rats were randomly divided into 4 groups; basal, control, pretreatment and posttreatment group. Pain related behavior was quantified by counting the incidence of flinches of the injected hindpaw for 60 minutes. The effect of pre- versus posttreatment with the ketamine on FLI in the lumbar spinal cord was examined by immunohistochemistry using specific antibodies.
RESULTS
Flinches of phase 2 were 0.5 +/- 0.3, 239.3 +/- 22.8, 118.6 +/- 7.5 (P < 0.05 vs. control) and 186.7 +/- 16.6 in the basal, control, and pre-, posttreatment group respectively. Similarly, the pretreatment group virtually inhibited a formalin-induced expression of FLI (P < 0.05 vs.
control, posttreatment) in the laminae I-II and III-VI ipsilateral to the formalin injection. FLI expression significantly correlated with the phase 2 flinching behavior (P < 0.001).
CONCLUSIONS
Pretreatment of intravenous ketamine inhibits inflammatory pain behavior and FLI expression in the lumbar enlargement following formalin injection in rats, suggesting that pretreatment of ketamine plays an important role in preemptive analgesia. |
| Key Words:
C-fos; formalin test; ketamine; preemptive |
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