Intraprostatic Capsaicin Injection as a Novel Model for Nonbacterial Prostatitis and Effects of Botulinum Toxin A

Objectives: An animal model for nonbacterial prostatitis in rats was developed with the use of intraprostatic injection of capsaicin, an agent thought to excite C-afferent fibers and cause neurogenic inflammation. The analgesic and anti-inflammatory properties of botulinum toxin type A (BoNT-A) was tested in this model. Methods: Adult male Spraque-Dawley rats were injected with varying doses of capsaicin into the prostate. The nociceptive effects of capsaicin were evaluated for 30 min by using a behavior approach; then the prostate was removed for histology and cyclooxygenase (COX) 2 protein concentration measurement. Evans blue (50 mg/kg) was also injected intravenously to assess for plasma protein extravasation. A second set of animals were injected with up to 20 U of BoNT-A into the prostates 1 wk prior to intraprostatic injection of 1000 μmol/l capsaicin. Results: Capsaicin dose dependently induced modifications in pain behavior: closing of the eyes, hypolocomotion, and inflammatory changes: increase of inflammatory cell accumulation, COX2 expression, and plasma extravasation at the acute stage, but completely recovered at 1 wk. BoNT-A pretreatment dose dependently reversed pain behavior and inflammation. BoNT-A 20 U significantly decreased inflammatory cell accumulation, COX2 expression, and Evans blue extraction (82.1%, 83.0%, and 50.4%, respectively), and reduced pain behavior (66.7% for eye score and 46.5% for locomotion score). Conclusions: Intraprostatic capsaicin injection induced neurogenic prostatitis and prostatic pain, and may be a useful research model. BoNT-A produced anti-inflammatory and analgesic effects, and support clinical evaluation in prostatitis.