Effect of intrathecal injection of tumor necrosis factor-alpha on pain threshold in rats

Objective To investigate the effect of intrathecal injection of different doses of tumor necrosis factor-alpha(TNF-α) on hindpaw withdrawal mechanical threshold(HWMT) and hindpaw withdrawal thermal latency(HWTL) in rats.Methods Twenty-four health adult male Sprague-Dawley rats weighing 200-250 g were randomly divided into 4 groups(n=6 each): group C receiving saline(10 μl) via intrathecal injection;groups T1,T5 and T10 receiving TNF-α 1 ng(10 μl),5 ng(10 μl) and 10 ng(10 μl) via intrathecal injection respectively after anesthesia.HWMT was assessed using a Dynamic Plantar Aesthesiometer(UGO BASILE,Italy) and HWTL by using a Plantar test respectively,The tests were performed at-1,4,8,16 and 24 h after intrathecal injection.Results 4-8 h after intrathecal injection,HWMT and HWTL were decreased significantly(P0.05 or P0.01) in groups T1,T5 and T10;16 h after intrathecal injection,HWMT and HWTL decreased significantly(P0.05 or P0.01) in group T5 and group T10;24 h after intrathecal injection,HWMT and HWTL were decreased significantly(P0.05) in group T10.Conclusion Intrathecal injection of TNF-α contributes to central hyperalgesia.