Development and Validation of an Animal Model of Prostate Inflammation-Induced Chronic Pelvic Pain: Evaluating from Inflammation of the Prostate to Pain Behavioral Modifications

Background: Chronic prostatitis/Chronic pelvic pain syndrome (CP/CPPS) is the most common type of prostatitis. Due to the lack of a suitable animal model partly, the pathogenesis for this condition is obscure. In the current study we developed and validated an animal model for nonbacterial prostatitis and prostate inflammation-induced chronic pelvic pain in rats with the use of intraprostatic injection of lambda-carrageenan. Methods: Male Sprague-Dawley rats weighing 250-350 g were used for the experiments. After intraprostatic injection of 3% l-carrageenan, at different time points(after 24 h, 7d, 14d and 30d of injection), radiant heat and von Frey filaments were applied to the scrotum of rats to measure the heat and mechanical thresholds respectively. Then the prostate was removed for histology, and cyclooxygenase (COX) 2 protein expression was determined by Western-blot. Evans blue(50 mg/kg) was also injected intravenously to assess for plasma protein extravasation at different time points after injection of lambda-carrageenan. Results: Compared to control group, inflamed animals showed a significant reduction in mechanical threshold (mechanical allodynia) at 24 h and 7d(p = 0.022,0.046, respectively), and a significant reduction in heat threshold (thermal hyperalgesia) at 24 h, 7d and 14d(p = 0.014, 0.018, 0.002, respectively) in the scrotal skin. Significant increase of inflammatory cell accumulation, COX2 expression and Evans blue extravasation were observed at 24 h, 7d and 14d after injection. Conclusions: Intraprostatic l-carrageenan injection induced neurogenic prostatitis and prostate inflammation pain, which lasted at least 2 weeks. The current model is expected to be a valuable preclinical tool to study the neurobiological mechanisms of male chronic pelvic pain.