Hypothesis / aims of study
Bladder dysfunction such as overactive bladder, incontinence and interstitial cystitis are common in the general population and even more common with age. A body of clinical evidence exists linking bladder disorders with stress, anxiety and depression, including witness trauma. Stress appears to greatly influence the development of bladder symptoms, or worsens symptom severity. In spite of this, there is little research on the precise changes and underlying mechanisms. This study investigates the hypothesis that water avoidance stress in mice causes bladder dysfunction and an overactive bladder phenotype via mechanisms including altered detrusor responses.
Study design, materials and methods
Female C57BL/6J mice (12-14 weeks) were randomly allocated to Control (n=5) or Water Avoidance Stress (WAS) (n=5) experimental groups. WAS mice were placed on a central pedestal surrounded by room temperature water for 1hr/day for 10 days. Controls were age-matched and housed normally without environmental stress exposure. Voiding pattern analysis was performed prior to (Day 0) and on days 1, 3, 5 and 10 of the stress protocol. Mice were euthanised 24 hours after the final stress exposure and bladders were removed, catheterised and intravesical pressure responses recorded during distension with saline and in response to stimulation using carbachol, ATP, isoprenaline, KCl and electrical field stimulation (EFS).
Results
WAS induced an overactive bladder phenotype in mice with a significant increase in the number of voiding events observed at all time points tested (Figure 1). Urinary frequency doubled by 24-hours following the first stress exposure (p<0.01) and increased 7-fold (p<0.001) following 10-days WAS. This increase in frequency was associated with a significant decrease in void size but no change in total voided volume. Bladder pressure responses to EFS were not altered by WAS. However, while the NO synthase inhibitor L-NNA (100μM) reduced responses, this was less in bladders from WAS mice (9.5 ± 3.1%, p<0.05) than Control mice (28.5 ± 5.1%, p<0.01), and purinergic receptor desensitisation reduced responses to EFS more in bladders from WAS mice (65.9 ± 2.0%, p<0.001) than Control mice (50.5 ± 2.4%, p<0.01). Atropine reduced neurogenic contractions similarly in Control and WAS bladders. Pressure responses to the muscarinc agonist carbachol (p<0.05), and purinergic agonists ATP (p<0.05) and alpha,beta-mATP (p<0.05) was significantly increased in bladders from WAS mice.
Interpretation of results
Repeated exposure to environmental stress through water avoidance altered voiding behaviour and enhanced contractile bladder responses to muscarinic and purinergic stimulation. In addition, the contribution of neuronal NO and ATP to efferent nerve evoked contractile responses decreased and increased respectively in bladders from WAS mice.