Intrathecal administration of metabotropic glutamate receptor subtype 5 antagonist on pain behavior and spinal astrocytes activation in mouse mod of bone cancer pain

Abstract

Objective To investigate effects of metabotropic glutamate receptor subtype 5 (mGluR5) antagonist MTEP on the nociceptive behavior and the expression of glial fibrillary acidic protein (GFAP) in spinal cord associated with bone cancer pain. Methods C3H/HeNCrlVr 60 male mice were randomly divided into 5 groups: ( 1 ) normal control group: the mice were given food and water ad libitum; ( 2 ) MTEP + Tumor group: the mice were treated by intrathecal gdministration ( once daily on the days 14 ～20 after inoculation of tumor cells)with MTEP (150 nmol); (3) physiological saline + Tumor group:the tumor mice were treated with the same volume of physiological saline; (4) MTEP + Sham group: the sham mice were treated with the same dose of MTEP;(5) physiological saline + Sham group: the sham mice were treated with the same volume of physiological saline.the mice pain behaviors were assessed with the paw withdrawal thermal latency (PWTL) at the corresponding time points, then the mice were killed and the samples of spinal cord were used to real-time PCR and western blot detection of GFAP mRNA and protein expression. Results The basic values of PWTL had no significant differences among all groups (P＜0.05). At day 14 after operation,no significant difference was found in the PWTL value between normal control group and the sham operation group. But in tumor group, the PWTL value was significantly lower than in the normal control group (P＜ 0.05 ). At day 21 after operation,the PWTL and the level of GFAP expression in the spinal cord had no significant differences among normal control group, MTEP + Sham group and physiological saline + Sham group (P ＞ 0.05 ); the PWTL ( (6. 18 ± 1.29 ) s) in physiological saline + Tumor group was significantly lower than in normal control group ( ( 15.91 ± 1.65 )s), physiological saline + Sham group ( ( 16.57 ± 1.86) s) and MTEP + Sham group ( ( 17.05 ± 2.43 ) s) (P ＜ 0.05 ), but the level of GFAP expression was higher than in the above three groups. In MTEP +Tumor group ,the PWTL (9.39 ± 1.94s) was higher than in physiological saline + Tumor group, and the level of GFAP expression was lower than in physiological saline +Tumor group (P ＜ 0.05 ). Conclusion Inhibiting spinal activation of astrocytes may be one of the MTEP anticancer pain mechanisms. Key words: Bone cancer pain; Metabotropic glutamate receptors; Astrocytes; Glial fibrillary acidic protein