Early Life Adverse Events Cause Long Lasting Voiding Dysfunction in a Murine Model of Maternal Separation
Nao Iguchi, PhD1, Anna P. Malykhina, PhD1, Duncan T. Wilcox, MD2.
1University of Colorado AMC, Aurora, CO, USA, 2Children's Hospital Colorado, Aurora, CO, USA.
Background
Disturbance of bladder function in early life can contribute to lifelong bladder dysfunctions and kidney failure. Although it is well recognized, the underlying mechanism was not well understood. Voiding in neonatal mice depends on the perigenital-bladder reflex triggered by their mother licking the perineum until voluntary bladder control emerges around 3 week-old. Therefore urinary retention and disturbing normal voiding cycle can be induced by separation of neonatal and/or infantile animals from their dam. The objective of this study was to examine the effects of early life voiding perturbation on bladder function using a maternal separation protocol in mice.
Materials and Methods
Newborn mouse pups were divided into control and maternal separation (M-Sep) groups after birth. M-Sep pups were removed from their dam and housed individually for 6 h per day from postnatal day 2 to 14 days. Pups in the control group stayed with their dam all the time. Long-term effects of M-Sep on bladder function were assessed in vivo by void spot assay at 15 day-, 3, 4, and 5 week-old, and in vitro by detrusor contractility studies at 6 week-old.
Results
In vitro studies of detrusor contractility in response to potassium chloride (KCl) and carbachol (CCh), an agonist of muscarinic receptors, established that detrusor contractions were significantly decreased in M-Sep female mice when compared to control mice (56 ± 5% for KCl, and 57 ± 6% for CCh, responses in control group were taken as 100%, p<0.001 to control group). Male mice showed the similar trend, but the results did not reach the level of statistical significance (Fig 1). The average of voided volume in large micturition spots (≥25 μl) was decreased in M-Sep mice in comparison to control mice at all tested time points (56-84 % to baseline, Fig. 2 left graph). The frequency of small voids (<25μl) was significantly increased by 2-5 fold in M-Sep mice at 3 to 5 weeks of age in comparison to control mice of both gender (Fig 2, right panel).
Conclusions
Our results provide evidence that maternal separation experienced during the neonatal period, delays the development of the normal micturition cycle and establishment of regular voiding habits in young mice. Animal models with maternal separation protocol can provide a better understanding of mechanisms underlying bladder reflex maturation, which could be used in the future studies for the development of novel therapies to treat voiding dysfunction in children.
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