Repeated variate stress (RVS) in male rats induces increased voiding frequency, somatic sensitivity and urinary bladder NGF expression

Stress exacerbates symptoms of functional lower urinary tract disorders including interstitial cystitis (IC)/bladder pain syndrome (BPS) and overactive bladder (OAB) in humans, but mechanisms contributing to symptom worsening are unknown. These studies address stress-induced changes in the structure and function of the micturition reflex using an animal model of stress in male rats. Rats were exposed to 7 days of repeated variate stress (RVS). Target organ (urinary bladder, thymus, adrenal gland) tissues were collected and weighed following RVS. Evans blue (EB) concentration and histamine, MPO, NGF, BDNF, and CXCL12 protein content (ELISA) were measured in the urinary bladder, and somatic sensitivity of the hindpaw and pelvic regions was determined following RVS. Bladder function was evaluated using continuous, open outlet intravesical infusion of saline in conscious rats. Increases in body weight gain were significantly (p ≤ 0.01) attenuated by day 5 of RVS and adrenal weight was significantly (p ≤ 0.05) increased. Histamine, MPO, NGF, and CXCL12 protein expression was significantly (p ≤ 0.01) increased in the urinary bladder following RVS. Somatic sensitivity of the hindpaw and pelvic regions was significantly (p ≤ 0.01) increased at all monofilament forces tested (0.1 to 4 g) following RVS. Intercontraction interval, infused volume, and void volume were significantly (p ≤ 0.01) decreased following RVS. These studies demonstrate increased voiding frequency, histamine, MPO, NGF and CXCL12 bladder content and somatic sensitivity after RVS suggesting an inflammatory component to stress-induced changes in bladder function and somatic sensitivity. These studies demonstrate several findings with respect to stress-induced changes in micturition reflexes in rats, particularly regarding NGF protein expression, somatic sensitivity, and bladder function. In the present studies, we demonstrate that RVS (1) produces biological markers of stress (body and adrenal weights) similar to previous findings (30, 31, 36, 57) including a robust and reproducible reduction (10%) in body weight gain during RVS exposure; (2) increases NGF protein expression and other inflammatory markers (e.g., MPO, histamine, chemokines) in the urinary bladder; (3) increases somatic sensitivity in the hindpaw and pelvic regions; and (4) decreases bladder capacity, void volume, and intercontraction interval during conscious cystometry. Previous studies using this stress model have focused on its role in anxiety-like behavior demonstrating neurochemical plasticity (i.e. pituitary adenylate cyclase-activating polypeptide (PACAP) and its cognate receptor PAC1) in the bed nucleus of the stria terminalis (BNST), a critical structure in the brain in mediating fear- and anxiety-like behavior in humans and animals (30, 31). Furthermore, excitotoxic lesions to the BNST have been shown to attenuate the effects of RVS on weight gain by the last day of stressor exposure (56). The current studies extend the use of the RVS model to the study of micturition reflex function and demonstrate RVS-induced changes in urinary bladder function, somatic sensitivity and in the inflammatory milieu of the urinary bladder.