• Xu Chen, Yong Yang, Hui Liu, Hong Xiao, and Bang-xiang Yang.
• Laboratory of Anesthesiology and Critical Disease, West China Hospital, Sichuan University, Chengdu 610041, China.
• Sichuan Da Xue Xue Bao Yi Xue Ban. 2008 Jan 1;39(1):89-93.

ObjectiveThe objective of this study was to investigate an antinociceptive effect of preemptive intrathecal lornoxicam on behavior and expression of c-Fos protein in the spinal cord of the formalin hurting rats.MethodsForty-two healthy male adult SD rats (200-250 g) were randomized into 7 groups. In the normal saline control group (group NS), 20 microL of normal saline was injected intrathecally, which was followed by a subcutaneous administration of 100 microL of normal saline into the hind plantar skin of rats 10 min later. In the formalin control group (group FOR), 20 microL of normal saline was injected intrathecally, and followed by rat intraplantar administration of 100 microL of 5% formalin. In the intrathecal lornoxicam experiment groups (groups L60-300), lornoxicam 60, 120, 180, 240, and 300 micdrog were administered intrathecally, respectively, and followed by rat intra-plantar administration of 100 microL of 5% formalin. The graded pain behavior was observed and the nociceptive behavior index (NBI) was calculated per 5 min during one hour immediately after the intra-plantar injection. At the 2-hour time point, all the rats were deeply anesthetized and perfused intracardially; and then, the spinal cord was removed for analysis of c-Fos protein-like immunoreactive neurons (FLIN) at the dorsal horn in the L4-L6 segments. The Student-Newman-Keuls test was used to identify the differences between groups,and correlation analysis was used to demonstrate the relationship between rat behavior and c-Fos expression.ResultsAlmost no pain response was observed in group NS. The typical biphasic pain response was observed in the formalin-injected groups. In phase I, no difference in the NBI was found between the formalin-injected groups except group L240 and group L300 in which NBI were significantly smaller than that in other formalin-injected groups. In phase II, the cumulative NBI in phase II decreased with the increase in lornoxicam dosage, but the difference was not significant when the dosage above 180 microg. (2) Both in the superficial and deep laminae at the dorsal horn, the amount of FLIN of group NS was much less than that of the remaining groups. The amount of FLIN decreased with the increase in the lornoxicam dosage, but the difference was not significant when the dosage above 180 microg in the superficial lamina and above 240 microg in the deep lamina. (3) Correlation analysis showed that the correlation coefficient between the sum of NBI in one hour and the expression of c-Fos in the superfacial or deep lamina of dorsal horn was positive.ConclusionPre-intrathacal lornoxicam can successfully inhibit nociceptive behavior and c-Fos expression in spinal dorsal horn of formalin test rats. This effect is correlated with the dosage of lornoxicam and has ceiling phenomenon.

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