[Evaluation of the lower urinary tract function using voiding spot assay in mice]

The objective of present study was to develop a simple and reliable voiding spot assay (VSA) system to evaluate the lower urinary tract function of mice, and to establish it as a standardized protocol. Ultraviolet (UV) light was used to screen out the filter paper without autofluorescence and with optimal urine diffusion properties. Next, the appropriate wavelength of UV was determined based on the quality of the photographic image of urine spots on the filter paper. To confirm that the urine stain area on the filter paper was correlated with the amount of urine, a volume-area standard curve was constructed. The utility of this VSA system was validated using female wild-type C57BL/6J mice aged 12-13 weeks, and the data generated under identical procedural settings were compared among laboratories. Furthermore, this VSA system was employed to analyze the changes in voiding patterns in mice with urinary tract infections or transportation stress. No. 4 filter paper with a thickness of 0.7 mm was identified as the most suitable material for VSA, exhibiting no autofluorescence and facilitating optimal urine diffusion. The filter paper retained its integrity during the assay, and there was a linear correlation between urine volume and stained area under 365 nm UV light. Utilizing this VSA system, we determined that female wild-type C57BL/6J mice produced approximately 695.8 μL total urine and 5.5 primary voiding spots (PVS) with an average size of 126.4 μL/spot within 4-h period. Over 84% of PVS volumes ranged from 20 to 200 μL. Notably, PVS volumes of mice were similar across different laboratories. Mice with urinary tract infections or transportation stress exhibited significant changes in VSA parameters, including increased voiding frequency, PVS number, and decreased PVS volume. Therefore, this VSA system can be used to evaluate the urinary function of normal mice, as well as those with urinary tract infection or transportation stress.