Correlation of pain with Substance P and neurokinin-1 receptor in the L5-S2 spinal cord in rats with chronic nonbacterial prostatitis

Background: To investigate the correlation of the pain with the expression of SP and NK-1R in the posterior horn of the L5-S2 spinal cord in a rat model of chronic nonbacterial prostatitis (CNP) at different time points of modeling. MethodsForty adult male SD rats were randomly divided into four equal groups: control group, 45 day (d) group, 60 d group, and 90 d group, and proteins were obtained from the prostatic tissue of another 30 rats. The CNP model was established by intraperitoneal injection of 0.5 mL diazepam vaccine and intradermal injection of a mixed solution of 1 mL prostatein extract and complete adjuvant at a 1:1 ratio. The control group rats were injected with the same volume of normal saline. At 45, 60, and 90 days after modeling, we measured the paw withdrawal threshold (PWT) of the rats, detected the level of TNF-α, IL-1ß, IL-2, and IL-10 in the prostate tissues by ELISA, observed the histomorphological changes in the prostate by transmission electron and light microscopy, and detected the expression of SP and NK1-R in the L5-S2 spinal cord by immunohistochemistry. ResultsThe levels of TNF-α, IL-1ß, IL-2, and IL-10 in the prostate tissue were markedly higher in the CNP models than those in the control group(all P<0.05); this difference was Most significant at 90 days (all P<0.05). Immunohistochemistry showed that the expressions of SP and NK-1R were remarkably higher in the CNP model groups than in the control (all P<0.05), with the highest expression found at 90 days. Light microscopy revealed no inflammatory cell infiltration in the prostate tissue of the control rats, and obvious edema and increased lymphocyte count were observed as the duration of modeling increased. Transmission electron microscopy showed inflammatory changes in the prostate tissue of the model rats; peritubular interstitial edema was most obvious at 90 days, with widened gaps between the peritubular cells and epithelial base and increased numbers of fibroblasts and collagen fibrils. ConclusionThere was a correlation between the pain and the expressions of SP and the NK-1R in the L5-S2 spinal cord of the rats.