Reliable visceromotor responses are evoked by noxious bladder distention in mice.

PURPOSE: A mouse model of bladder distension (UBD) induced acute visceral nociception was characterized. Murine models of nociception may allow for the investigation of mechanisms of pain and analgesia through the use of genetic models.
MATERIALS AND METHODS: Isoflurane anesthetized, spontaneously breathing female C3H/J mice had 24 gauge intravesical catheters transurethrally placed and electrodes implanted in the abdominal musculature and in upper limbs for electromyograms and electrocardiograms.
RESULTS: UBD (10 to 80 mm Hg for 20 seconds, phasic air distention) produced reliable, reproducible visceromotor responses (VMRs), that is increased abdominal muscle activity, which were graded with graded UBD. Heart rate and respiratory responses were reliable but not reproducible. Subcutaneous morphine (1 to 4 mg/kg) and intravesical lidocaine (500 microg) produced reversible VMR inhibition. Inflammation produced by intravesical mustard oil (2.5% for 15 minutes with an olive oil control) produced a marked increase in sensitivity to UBD with more robust responses evoked by lower UBD intensities. VMRs were present in decerebrate but not in spinal cord transected mice. Unanesthetized mice had similar responses to UBD but with lower pressure thresholds for VMRs.
CONCLUSIONS: These findings suggest the usefulness of the current model system for the study of bladder nociception. In mice UBD evoked VMRs are spinobulbospinal reflexes that are reliable and reproducible, graded in relation to the stimulus, inhibited by analgesics and augmented by the presence of inflammation. Together these data strongly support the use of this model because it may allow the assessment of pharmacogenetic differences among murine strains and the use of transgenic technologies.