OBJECTIVETo observe the expressions of the substance P (SP) mRNA and neurokinin-1 receptor (NK-1R) in the posterior horn of the L5 - S2 spinal cord in the rat model of chronic prostatitis pain, and to investigate the changes in the activation of astrocytes and influence of SP on this activation in rat spinal cord astrocytes cultured in vitro.

METHODSThe rat model of chronic prostatitis pain was established by injection of complete Freund's adjuvant (CFA) and assessed by the tail flick threshold test, the control rats injected with sodium chloride and all observed at 0, 14 and 28 days. Changes in the expressions of SP mRNA, NK-1R, glial fibrillary acidic protein (GFAP), tumor necrosis factor-alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS) in the posterior horn of the L5 - S2 spinal cord were detected by RT-PCR and Western blot. Rat spinal cord astrocytes were cultured in vitro and divided into a control group, cultured with ITS cell culture fluid, and two experiment groups, with Group 1 stimulated with SP at the concentration of 10(-9) - 10(-6) mol/L for 12 hours followed by determination of the expressions of TNF-alpha, IL-1beta, NO and NOS by ELISA and nitrate reductase and colorimetric methods, and Group 2 at 10(-7) mol/L for 0, 24, 48 and 72 hours followed by detection of the GFAP expression by Western blot.

RESULTSThe expressions of SP mRNA, NK-1 R, GFAP, TNF-alpha and iNOS in the posterior horn of the L5 - S2 spinal cord were obviously higher in the rat prostatitis pain models than in the controls, successively higher at 28 than at 14 and 0 d (P < 0.01), and so was the expression of GFAP at 28 than at 14 d in the experiment groups (P < 0.05). SP induced a gradual increase at 10(-7) mol/L in the expression of GFAP in the spinal cord astrocytes at 0 -72 h, significantly different from that of the control group (P < 0.01), and it promoted the excretion of TNF-alpha and IL-1beta and the activity of NO and NOS at 10(-9) - 10(-6) mol/L at 12 h in a concentration-dependent manner, with marked differences between the experiment and control groups (P < 0.01, P < 0.05). But a decreased excretion of IL-1 beta was observed in the 10(-6) mol/L group, though with no significant difference from the control (P > 0.05).

CONCLUSIONChronic prostatitis pain could upregulate the expressions of the excitatory transmitter SP and receptor in the L5 - S2 spinal cord, and result in the activation of astrocytes and increased excretion of proinflammatory cytokines, which may be associated with the persistence and generalization of prostatitis pain.