To investigate the role of interleukin-17(IL-17)in spinal dorsal horns in neuropathic pain(NP)in rats and its effect on activation of astrocytes.

In vivo experiment Sixty-four male SPF Sprague-Dawley rats, aged 6-8 weeks, weighing 180-200 g, were randomly divided into 3 groups using a random number table: control group(group C, n=16), sham operation group(group S, n=24)and group NP(n=24). The animals were anesthetized with intraperitoneal pentobarbital sodium, the L_{5, 6} spinal nerves of the left side of the rat were gently separated and exposed, tightly ligated with 5-0 silk suture and transected.In group S, the L_{5, 6} spinal nerves of the left side of the rat were only exposed.In group C, no operation was performed.Mechanical pain threshold was measured at day 1 before operation and days 1, 3, 5, 7, 10 and 14 after operation.The expression of IL-17, IL-6, IL-1β and tumor necrosis factor-alpha(TNF-α)mRNA in the spinal dorsal horn was determined using quantitative real-time PCR at day 7 and day 14 after operation.At day 7 after operation, the activation of astrocytes in the spinal dorsal horn was detected.In vitro experiment Primarily cultured astrocytes of neonatal rats were randomly divided into 4 groups using a random number table: control group(group C, n=22), 10 ng/ml IL-17 group(I₁₀ group, n=18), 50 ng/ml IL-17 group(I₅₀ group, n = 18)and 100 ng/ml IL-17 group(I₁₀₀ group, n=22). In I₁₀, I₅₀ and I₁₀₀ groups, the astrocytes were incubated with the culture medium containing 10, 50 and 100 ng/ml IL-17, respectively.The proliferation of astrocytes was detected by MTT at 24, 48 and 72 h of incutation or culture.The expression of IL-6, IL-1β and TNF-α mRNA was determined using quantitative real-time PCR.

In vivo experiment Compared with group C, the mechanical pain threshold was significantly decreased at 3-14 days after operation, the expression of IL-17, IL-6 and IL-1β mRNA in the spinal dorsal horn was up-regualted at 7 days after operation, and the activation of astrocytes was increased in group NP, and no significant change was detected in the mechanical pain threshold at each time point after operation in group S. In vitro experiment Compared with group C, the proliferation of astrocytes was significantly increased at 48 h of incubation in I₁₀ and I₅₀ groups, the proliferation of astrocytes was significantly increased at 48 and 72 h of incubation, and the expression of IL-6 and IL-1β mRNA was up-regulated in I₁₀₀ group, and no significant change was found in the proliferation of astrocytes in group S.

Up-regulated expression of IL-17 in spinal dorsal horns may be involved in the maintenance of NP, and the mechanism is related to promoted activation of astrocytes and induced inflammatory responses in rats.

Interleukin-17; Neuralgia; Astrocytes; Spinal cord