Chronic social defeat, but not restraint stress, alters bladder function in mice

Abstract

BACKGROUND Voiding disorders in humans, particularly in children are associated with increased incidence of behavioral issues as well as past history of childhood abuse. We hypothesized that creating stress in mice, utilizing either a chronic social defeat model (SD) or restraint stress in shallow water model (RSSW), would engender changes in bladder function, morphology, and behavior, thereby enabling us to study the resultant voiding dysfunction. METHODS For SD stress (14 days), C57BL/6 male mice were exposed daily to a larger aggressive CD-1 male for 10 minutes, followed by sensory exposure in a barrier cage for 24 hours. Control mice were similarly housed with no exposure. For RSSW (21 days), C57BL/6 mice were put in a perforated conical tube with feet immersed in water daily for 4 hours, then returned to single housing cages. Control mice were also in single housing. After the stress period, voiding patterns were obtained on filter paper, followed by behavioral tests. At necropsy, blood was taken for corticosterone analysis, and bladder and body weights measured. Bladder cryosections were stained with hematoxylin and eosin (H&E) for morphological assessment. Sequential sections were immunostained with antibodies to Ki-67 as a proliferation marker, CD31 (endothelial cell marker), and Uroplakin-II. Image J software was used to measure bladder wall thickness on blinded H&E photomicrographs as well as quantitate CD31 staining. Both Ki-67 -positive and -negative nuclei were counted with Imaris software to obtain a proliferation index. RESULTS Only SD mice had a single large void pattern. Bladder -to -body weight ratios increased in SD mice (p≤ 0.02) but not in RSSW mice. Plasma corticosterone levels were elevated in all stressed mice. SD mice exhibited lower levels of locomotor activity compared with controls; RSSW mice were hyperactive. In SD mice, bladder wall thickness was increased (p ≤ 0.003) but no change was seen in Ki-67 proliferation index, consistent with hypertrophy. No difference with control mice was seen in vascularity as visualized by CD31 staining. Uniform Uroplakin-II staining lined the urothelium of both SD and control mice. CONCLUSIONS Mice exposed to repeated SD (14 days) respond with altered voiding indicative of urine retention, and exhibit bladder wall changes consistent with hypertrophy while the urothelial barrier is maintained. These changes were not observed with repeated RSSW. SD, in contrast to RSSW, provides a model of psychological stress to further study the interplay of behavior and bladder dysfunction, enabling an improved understanding of voiding dysfunction, and the ability to create innovative and more effective management pathways for children who present with voiding dysfunction.

Voiding Behavior and Efferent Bladder Function Altered in Mice Following Social Defeat but Not Witness Trauma

“…Exposure to physical or emotional stress produced a similar hormonal stress response in both groups, confirming that the mice used in this study were stressed when compared to controls. This is consistent with other experimental studies which assessed corticosterone levels in the social defeat model (Mann et al, 2015), as well as paired social defeat/witness trauma model (Sial et al, 2016;Li et al, 2018). Interestingly, while social defeat resulted in reduced urinary frequency, which supports previous reports of voiding dysfunction in this model (Chang et al, 2009;Mann et al, 2015), voiding was not altered in witness trauma mice despite a similar hormonal stress response.…”

“…This is consistent with other experimental studies which assessed corticosterone levels in the social defeat model (Mann et al, 2015), as well as paired social defeat/witness trauma model (Sial et al, 2016;Li et al, 2018). Interestingly, while social defeat resulted in reduced urinary frequency, which supports previous reports of voiding dysfunction in this model (Chang et al, 2009;Mann et al, 2015), voiding was not altered in witness trauma mice despite a similar hormonal stress response. Mann et al (2015) similarly found that like witness trauma, chronic restraint stress did not alter bladder function, with similar voiding, bladder mass and bladder wall thickness compared to controls.…”

“…Interestingly, while social defeat resulted in reduced urinary frequency, which supports previous reports of voiding dysfunction in this model (Chang et al, 2009;Mann et al, 2015), voiding was not altered in witness trauma mice despite a similar hormonal stress response. Mann et al (2015) similarly found that like witness trauma, chronic restraint stress did not alter bladder function, with similar voiding, bladder mass and bladder wall thickness compared to controls. A recent study, that explored how social support affects stress-induced changes in social behavior produced by the social defeat/witness trauma paradigm used here, found that the social support provided by paired housing following stress exposure had protective effects in the witness but not in social defeat mice (Li et al, 2018).…”

“…Water avoidance stress caused increased urinary frequency in female rats, which was associated with increased infiltration and activation of mast cells and angiogenesis in the bladder (Smith et al, 2011). In contrast, social defeat in male rodents has been reported to alter voiding differently, with less frequent voiding events observed in mice exposed to social defeat (Chang et al, 2009) and one single large void typically observed (Mann et al, 2015). This altered voiding behavior in social defeat mice and rats is referred to in the literature as a urinary retention phenotype and is associated with bladder wall hypertrophy, urodynamic changes including increased bladder capacity and micturition volume, and upregulation of corticotropin releasing factor (CRF) in Barrington's nucleus neurons (Wood et al, 2009).…”

Effect of chronic stress on running wheel activity in mice

“…Indicators of stress : Previous research has shown that bladders from mice subjected to chronic stress undergo significant morphological change including hypertrophy and enhanced bladder-to-body weight ratios [ 20 ]. This index of stress was chosen because it demonstrates a physiological consequence to chronic stress.…”