Bladder sensation evaluation of a carrageenan‐induced chronic prostatitis model using a direct measurement of the bladder mechanosensitive single‐unit afferent nerve activity

Aims Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) causes long‐standing pain and/or storage symptoms. This study aimed to evaluate the likelihood of deterioration of bladder sensation in a carrageenan‐induced CP/CPPS model by direct measurement of the bladder mechanosensitive single‐unit afferent nerve activity. Methods In this study, male adult Sprague‐Dawley rats were used. They were injected 50 µL of 3% λ‐carrageenan or its vehicle (saline) into both lobes of the ventral prostate. Seven days following injection, the pain behavior at the pelvic‐perineal area (using von Frey filaments), prostatic blood flow (using a laser blood flowmeter), and histology were examined along with cystometry (under conscious free‐moving condition) and mechanosensitive single‐unit afferent nerve activity (under urethane anesthesia). Results The prostate showed increased tissue weight and decreased blood flow and inflammatory cell infiltration in the carrageenan group compared to the control group. Consequently, the threshold of the pain behavior was decreased, and the basal and threshold pressures of the bladder were increased in the carrageenan group. In contrast, no significant differences of bladder histology and other cystometric parameters were found between the groups. Regarding Aδ‐ or C‐fibers, the mechanosensitive afferent nerve activities revealed no differences in either group. Conclusions The carrageenan‐induced CP/CPPS rat model showed edema, ischemia, and inflammatory pain in the prostate, whereas a little change was detected in bladder sensation. These findings, which were evaluated using a direct measurement of the mechanosensitive single‐unit afferent nerve activity, suggest that the bladder sensation is unlikely deteriorated in this model.