is unclear. This study aims to investigate the direct effects of BoNT/A on sensory afferent firing in an ex vivo mouse bladder preparation. METHODS: Adult male mice were sacrificed humanely according to UK legislation. The whole pelvic region was dissected out and placed in a recording chamber superfused with oxygenated Krebs-bicarbonate solution (95% O2, 5% CO2) at 35°C. The urethra and dome were catheterised. Recording of afferent nerve firing was performed by placing a pelvic sensory nerve bundle into a suction electrode, as previously described (Daly et al, 2007). This preparation enabled simultaneous sampling of intravesical pressure and multiunit afferent nerve firing. Ramp distension (100μl.min-1) of the bladder with saline (NaCl, 0.9%) up to 40 mmHg was repeated at 10 minute intervals. To determine the effect of BoNT/A, 2U (BOTOX®) was applied to the bladder lumen during distension, preceded and followed by the control (saline) distension protocol. The effects of BoNT/A was monitored for over 2 hours post application. Data are presented as normalised to the response prior to application of BoNT/A and presented as mean ± S.E.M. Statistical analysis was carried out using either a 2-way ANOVA followed by a Bonferroni post test or paired Students t-test. RESULTS: Ramp distension of the bladder evoked a graded increase in afferent firing with increasing intravesical pressure, which was reproducible following repeated distensions with saline. Following addition of BoNT/A, the afferent response was significantly attenuated after 1 hour. At 2 hours, the maximum afferent firing at 40 mmHg was reduced by 75.9 ± 12.2% (control: 116 ± 13.6 vs. BoNT/A: 24.1 ± 12.2, P=0.0016, n=5). A 2-way ANOVA revealed statistically different afferent responses > 15 mmHg. Interestingly, bladder compliance was not affected after application of BoNT/A (P=0.38). CONCLUSIONS: These results indicate that intravesical BoNT/A directly attenuated distension evoked sensory afferent nerve firing in vitro. BoNT/A application did not affect bladder compliance. Further studies are required to determine how BoNT/A affects mechano-sensory pathways in the bladder. Daly D et al. J Physiol 2007 Sep;583(2):663-674