Psychological stress and recovery: compensation to overcome bladder overactivity in mice

Introduction: Numerous clinical studies have linked bladder disorders with stress, anxiety and depression. Stress appears to greatly influence the development of bladder symptoms or worsens the severity of symptoms. Little is understood about the precise changes and underlying mechanisms. This study investigates the hypothesis that psychological stress (environmental) in mice causes an overactive bladder phenotype, via altered contractile mechanisms. We also present preliminary findings on how a period of stress-free recovery affects bladder function. Materials & methods: Female mice (C57BL/6J, 12-14 weeks old) were randomly allocated to control, stress or recovery experimental groups. In the stress and recovery group, mice were placed on a central pedestal surrounded by room temperature water for 1hr/day for 10 days, to induce environmental stress due to water avoidance (WAS). Controls were age-matched and housed normally without exposure to environmental stress. Recovery mice were maintained in normal housing for a further 10 days (recovery period). Voiding frequency was measured periodically throughout the stress and recovery protocol. Mice were euthanised 24-hours after the final stress exposure or following 10 days recovery. Whole bladders were removed, catheterised and intravesical pressure recorded during bladder distension following filling of bladders with saline. In addition, the contraction of bladders following stimulation of nerves, and the neurotransmitters involved, were studied, along with contractions caused by addition of drugs acting at muscarinic, adrenergic and purinergic receptors. AREC: BOND/536/17, Bond University. Results: Environmental stress induced a hormonal stress response, with a significant increase in plasma corticosterone levels in the WAS group compared to control (Figure 1A). An overactive bladder phenotype was observed in WAS mice, causing a significant increase in the number of voiding events observed from as early as day-3, and a 7-fold increase following 10-days’ stress (Figure 1B). This increase in voiding frequency was associated with a significant decrease in void size but no change in total voided volume. Bladders from stressed mice showed greater contractility in response to the muscarinic agonist carbachol (p<0.05), and also to the purinergic agonists adenosine triphosphate (ATP) (p<0.05) and alpha,beta-mATP (p<0.05) compared to controls. Preliminary results indicate that following 10-days’ stress-free recovery, there is a decrease in voiding frequency (Figure 1B). This is accompanied by an increase in bladder compliance (Figure 1C), which was unchanged initially during the stress protocol.Conclusions: Repeated exposure to environmental stress produced a hormonal stress response and an overactive bladder phenotype, confirmed by increased voiding frequency and enhanced bladder contractile responses to muscarinic and purinergic stimulation. Preliminary findings indicate that following a period of stress-free recovery, there is a decrease in voiding frequency which may be due to compensation through increased bladder compliance, rather than a reversal of the stress-induced changes.Competing interest statement: This study was supported by an Australian Bladder Foundation Grant - Richard Millard Award.