Temporal parameters of desensitization to intravesical resiniferatoxin in the rat

Temporal factors affecting desensitization of bladder sensory afferents to the capsaicin-like irritant resiniferatoxin (RTX) were studied, to determine optimal treatment parameters for clinical application of such substances. Four days after implantation of a chronic cannula into the bladder dome, vehicle or RTX (0.1-10 nmol) was injected into the bladders of awake, freely moving rats four times at 60-min intervals for exposure durations of 5, 15, or 45 min, or at intervals of 15, 60, or 120 min (duration 5 min). The first RTX injection dose-dependently increased time spent engaged in abdominal licking. Regardless of exposure interval and duration, time spent licking increased to a lesser extent with each subsequent injection, indicating desensitization of sensory afferents. Magnitude and duration of desensitization were dose dependent for all exposure regimens, and there were few differences between groups. Desensitization at 24 h was also greater in rats exposed four times compared to rats exposed once. Following four exposures to RTX, nearly complete recovery occurred within 7-14 days, in a dose-dependent manner. Thus, magnitude and duration of desensitization to locally administered RTX depend primarily on dose and number of exposures to RTX; duration of exposure and interval between exposures within the ranges studied were less important determinants.