Ice Water Testing Reveals Hypersensitivity in Adult Rats That Experienced Neonatal Bladder Inflammation: Implications for Painful Bladder Syndrome/Interstitial Cystitis

Abstract

We determined whether clinical observations of hypersensitivity to ice water testing, that is infusion of ice-cold saline into the bladder, in patients with painful bladder syndrome/interstitial cystitis have a parallel in a rat model of bladder hypersensitivity produced by neonatal inflammation. Rat pups were anesthetized as neonates (postnatal days 14 to 16). In some pups the bladder was inflamed by intravesical zymosan treatment. As adults, the rats were re-anesthetized and tested for abdominal muscle contractions to ice water testing, measured on electromyogram. Various neonatally treated groups of rats underwent bladder re-inflammation/no re-inflammation and/or bladder distention before ice water testing. Other control rats were treated only in adulthood. Rats that underwent bladder inflammation as neonates manifested bladder hypersensitivity in adulthood, as indexed by significantly greater mean electromyogram responses during ice water testing. This bladder hypersensitivity did not require adult re-inflammation to manifest. Hypersensitivity was also observed with or without prior bladder distention, although the magnitude of electromyogram responses during ice water testing significantly correlated with the magnitude of electromyogram responses to bladder distention. Neonatally induced effects were not significantly related to estrous cycle phase. Exposure to menthol did not significantly enhance the overall magnitude of the electromyogram response to ice water testing in neonatally treated rats. Current results parallel those in a recent study showing that most patients with painful bladder syndrome/interstitial cystitis experience pain when undergoing ice water testing after previous urodynamic testing. These findings suggest that this animal model may be useful for understanding the etiology of and treatment for painful bladder syndrome/interstitial cystitis.