The effect of glucocorticoids on anxiety-induced mechanical hyperalgesia in rats

Abstract

Objective To investigate the role of glucocorticoids(GCs) in anxiety-induced mechanical hyperalgesia in rats. Methods Seventy-two rats were divided into two part of experiments. ① Behavioral test. 24 rats were randomly divided into 3 groups(n=8): control group(C group), single prolonged stress(SPS) group(A group), SPS+ metyrapone group(M group). A group and M group were exposed to SPS. Intraperitoneal injection of metyrapone(25 mg/kg) was performed 1 h before SPS procedure. Elevated plus-maze test was tested on the first day after the SPS exposure. Paw withdrawal mechanical threshold (PWMT) was test on day 1 before SPS(T0) and days 1(T1), 4(T2), 7(T3), 14(T4) after SPS. ②Western blot. 48 rats were used, glucocorticoid receptor(GR) protein expression of A group was tested by Western blot in T0, T1, T3, T4, 3 rats in each time point. GR protein expression of every group was tested by Western blot in T1, T2, T3, T4, 3 rats in each group. Results In the elevated plus-maze test, the number of entries and the percentage of time spent in open-arms of A group [(4.6±1.5), (12.0±1.9)%]was significantly decreased compared with C group [(12.3±1.8), (17.8±2.5)%]and M group [(9.9± 1.5), (16.4±3.3)% ](P<0.05). The PWMT of A group was significantly decreased on 1, 4, 7, 14 d after SPS compared with C group(P< 0.05), the PWMT of M group was significantly increased on 1, 4, 7, 14 d compared with A group(P<0.05). The expression levels of glucocorticoid receptor(GR) in the spinal cord were increased significantly after SPS exposure, and it lasted 14 days(P<0.05). The expression levels of GR of M group were significantly increased compared with A group(P<0.05). Conclusions GCs are involved in anxiety-induced hyperalgesia in rats exposed to SPS. Metyrapone can significantly inhibit anxiety-induced mechanical hyperalgesia. Key words: Glucocorticoids; Single prolonged stress; Anxiety; Hyperalgesia; Metyrapone; Rat