| Objective The purpose of this study was to determine if intrathecal esmolol can modulate formalin-induced nociception and spinal c-Fos,COX-2 mRNA expression in dorsal horn of spinal cord in the mouse formalin test.Methods The experiment was performed in 2 parts. In part one,we determine if intrathecal esmolol can modulate formalin-induced nociception ,if so ,the median effective dose of intrathecal esmolol was obtained.In part two, sixty-four rats were randomly assigned to one of four groups: the control group (n = 8) received intrathecal normal saline 10μL, while the other three groups (n =8 for each) received intrathecal esmolol at doses of 700μg·kg-1, 500μg·kg-1 and 300μg·kg-1(according to the ED50 and 95% CI), respectively, immediately after induction of anesthesia with isoflurane. After awakening, inflammatory pain was induced by 50μL of 5% formalin solution injected into the dorsal surface of the right hind paw. The nociceptive behaviours including licking, biting and lifting of the injected paw were cumulatively recorded during phase I (0–5 min) and phase II (15–50 min),and then we score it by Dubuisson's method. The c-fos protein expressions in the spinal dorsal horn were detected with immunohistochemical techniques,and the COX-2 mRNA expressions in the spinal dorsal horn were detected with RT-PCR technique.Results The median effective analgesic dose(median value and 95% confidence interval) of intrathecal injection esmolol after peripheral was 453μg·kg-1;Compared to the NS group, all the rats of A,B,C group significantly decreased pain-related behaviours in phase II during the formalin test. spinal c-Fos and COX-2 mRNA expression in the spinal dorsal horn were significantly lower in A,B,C group compared to the NS group (P < 0.01).Conclusion: The present study indicates that intrathecally administered esmolol produces significant antinociceptive effects in the formalin test. And these data suggest a potential role ofβ?1-adrenoreceptors in spinal nociceptive processing. |
