Behavioral and urological evaluation of a testicular pain model

To develop an animal model of testicular pain to examine the hypothesis that neural crosstalk between testicular nociceptors and bladder reflex pathways may underlie bladder overactivity. In chronic pelvic pain disorders, neural crosstalk is thought to underlie referred pain and functional interaction in pelvic organs, and patients with chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) suffer from pain in multiple organs, including the testes and perineum, as well as increased urinary frequency.

In male Wistar rats, acetic acid was injected into the testes, and behaviors and bladder functions with conscious cystometry were examined. The effects of indomethacin and capsaicin pretreatment on both behaviors and bladder functional changes induced by acetic acid injection were examined. The weight of the testes and bladder after the testicular injection were measured.

Injection of acetic acid (1% and 3%) induced pain behaviors and bladder overactivity proportional to the concentration. Indomethacin reduced, and capsaicin pretreatment almost completely abolished, both pain behavior and bladder overactivity induced by acetic acid injection. Administration of acetic acid increased testis weight and blanched the tissue, but no apparent changes were observed in the bladder.

Injection of dilute acetic acid into the testes produces a reproducible testicular pain model involving testicular inflammation and activation of primary afferent C fibers and suggests a neural pathway for interaction between testicular pain and bladder overactivity. This study may provide a simple method to evaluate testicular pain, related bladder overactivity, and insight into the pathophysiology of bladder overactivity in patients with CP/CPPS.