Role Of 5-HT_5A Receptors In Activation Of Astroglia In The Spinal Dorsal Horn In A Rat Model Of Neuropathic Pain

Objective To evaluate the role of 5-HT_5Areceptors in activation of astroglia in the spinal dorsal horn in a rat model of neuropathic pain.Methods 1. The neonatal rat brain was taken and the cortex was made into suspension with aids of enzyme-digestion and mechanical dissociation, inoculated culture 10d after sieve filter. Observed by immunofluorescence in 5-HT_5AR expression of astrocytes. Twenty adult male adult male SD rats weighing 180²00 g were randomly divided into 2 groups (n=10): group control and group model. Neuropathic pain was induced by repeated intraperitoneal injection of vincristine 0.1 mg/kg in group model. The animals were injected normal saline 1 ml intraperitoneally in group control. Mechanical pain threshold was measured 2d after intraperitoneal injection. The animals were sacrificed and spinal dorsal horn were removed for determination of 5-HT_5AR and GFAP expression. 2. Thirty adult male SD rats weighing 180²00 g were randomly divided into 3 groups (n=10):groupâ… neuropathic pain (group P), groupâ…¡Ad-X-HK (group B) and groupâ…¢Ad-5-HT_5AR-siRNA (group S). Neuropathic pain was adopted as the same way in group P,B and S. Mechanical pain threshold was measured 2 d after intraperitoneal injection. After that, group P,B and S received injection intrathecally of artificial cerebrospinal fluid, Ad-X-HK and Ad-5-HT_5AR-siRNA respectively. Mechanical pain threshold was measured again 7 d after intrathecal injection. The animals were sacrificed and spinal dorsal horn were removed for determination of 5-HT_5AR and GFAP expression. Results 1. 5-HT_5AR express in the membrane and cytoplasm of cultured astrocytes. Compared with group control, mechanical pain threshold was significantly decreased and expression of 5-HT_5AR , GFAP were significantly increased in group model and astrocytes activation was significantly. 2. Compared with group P, mechanical pain threshold 7 d after intrathecal injection and 5-HT_5AR expression were significantly decreased and GFAP expression was increased in group S , astrocytes activation was significantly (P<0.05). There was no significant difference in mechanical pain threshold and expression of 5-HT_5AR and GFAP between group P and group B (P>0.05). Conclusions 5-HT_5AR is involved inhabition of astrocytes activation, resulting in reducion of vincristine-induced neuropathic pain.