Zvarova K, Zvara P. Urinary bladder function in conscious rat pups: a developmental study. Am J Physiol Renal Physiol 302: F1563-F1568, 2012. First published April 25, 2012 doi:10.1152 doi:10. /ajprenal.00567.2011metric studies of bladder function in anesthetized neonatal rats have suggested specific changes in urodynamic parameters that coincide with the development of a mature bladder-to-bladder micturition reflex. Here, we used a conscious cystometry model that avoids the potentially confounding effects of anesthesia to characterize voiding patterns and urodynamic parameters during early postnatal development in healthy rat pups. Cystometry was performed on postnatal day (P)0, 3, 7, 14, and 21 rats with continuous intravesical instillation of NaCl via a bladder catheter. Micturition cycles were analyzed with respect to voiding pattern, nonvoiding contractions, infused volume, and basal, filling, threshold, and micturition pressures. Reproducible micturition patterns were obtained from all age groups. The time from stimulation to contraction was significantly longer (P Յ 0.001) in Յ1-wk-old rats (ϳ10 s) than that in older rats (ϳ3 s). An interrupted voiding pattern was observed in Յ10-day-old subgroups. Micturition pressure progressively increased with age (from 21.77 Ϯ 1.92 cmH2O at P0 to 35.47 Ϯ 1.28 cmH2O at P21, P Յ 0.001), as did bladder capacity. Nonvoiding contractions were prominent in the P3 age group (amplitude: 4.6 Ϯ 1.3 cmH2O, frequency: ϳ4.0 events/100 s). At P7, the pattern of spontaneous contractions became altered, acquiring a volume-related character that persisted in a less prominent manner through P21. Bladder compliance increased with age, i.e., maturation. In conclusion, conscious cystometry in rat pups resulted in reproducible micturition cycles that yielded consistent data. Our results revealed immature voiding and prolonged micturition contractions during the first 10 neonatal days and provide evidence for age-related changes in urodynamic parameters. postnatal development; cystometry MICTURITION is under the control of a highly complex system that integrates neural and smooth muscle components to produce coordinated and effective bladder performance (13). During development, an immature reflex precedes voluntary bladder control. The "rationale" for the switch in regulation is not exactly known, but continuing development of the central and peripheral neural pathways involved in the regulation of micturition is believed to underlie reorganization of the reflex (9,19,23,28). Maturation occurs in an ordered fashion such that children first achieve awareness of bladder fullness, then daytime urine control, and finally nighttime urine control. The time period of postnatal "tuning" varies among species, requiring 2-5 yr in humans and generally 2-3 wk in rats. By the end of this period, the sacral/perigenital bladder reflex that prevails during ontogeny is downregulated, and a mature supraspinal micturition reflex is established/activated, allowing voluntary/ spontaneous voiding (10,21,29). ...