Development of diurnal micturition pattern in mice after weaning.

[Purpose] The development of micturition in mice has been poorly studied because of the minute urine volume voided per micturition. We characterized development of the micturition pattern in young mice. [Materials and Methods] Micturition in young and adult C57BL/6 strain mice, including 5 males and 4 females at age 3 weeks immediately after weaning, and 5 of each gender at ages 9 to 10 weeks, respectively, was recorded by the automated voided stain on paper method. Micturition data were obtained under 12-hour light/dark cycles in young mice for 16 days and in adult mice for 4 days. Diurnal variations were assessed during 8 hours until the first void after lights off and those until lights on. The 24-hour rhythmicity of urinary frequency was calculated for 4-day data at the beginning and at the end on young mice, and for 4-day data on adult mice using a chi-square periodogram and relative power spectral density. [Results] Mean frequency was 20 to 30 times per day. Total daily urine volume and mean daily urine volume voided per micturition increased with age. The diurnal rhythm of frequency matured to adult levels with development, which was primarily achieved by maturation of the diurnal variation of urine volume in male mice, followed by female mice. Diurnal variation of urine volume voided per micturition was indistinct at the initial stage and gradually matured toward adult levels. [Conclusions] The automated voided stain on paper method was used to record micturition development in young mice. This generated data corresponding to frequency-volume charts in humans. Our findings could lead to the establishment of a mouse model of developmental micturition disorders, such as nocturnal enuresis