Psychological stess plays an important role in the induction of frequent urination and exacerbation of bladder dysfunction including overactive bladder (OAB) and bladder pain syndrome/interstitial cystitis (BPS/IC).  Psychological stress-related information is conveyed to the brain, and then the brain recruits neuronal and neuroendocrine systems for adaptation to stressful conditions.  However, the brain pathophysiological mechanisms underlying psychological stress-induced effects on bladder function are still unclear.  Recently, we reported that bombesin (BB)-like peptides, which are stress-related neuropeptides, centrally induces facilitation of the rat micturition reflex [1].  Central BB-like peptides are reported to induce activation of the hypothalamo-pituitary-adrenal axis and sympathetic nerves, as representative responses to stressful conditions, through brain corticotropin-releasing factor (CRF) [2], another stress-related neuropeptide.  In this study, therefore, we examined whether brain CRF is involved in BB-induced frequent urination in rats.

(1) In urethane anesthetized (0.8 g/kg, ip) male Sprague-Dawley (SD) rats (300-350 g), a catheter was inserted into the bladder from the dome to perform cystometry (CMG, 12 ml/h saline infusion).  Three hours after the surgery, astressin (a non-selective antagonist of CRF receptors, 1 or 3 nmol/rat, intracerebroventricular [icv]) was administered 60 min before BB administration (0.03 nmol/rat, icv).  Saline infusion into the bladder and evaluation of intercontraction intervals (ICI) and maximal voiding pressure (MVP) were started 60 min before the first icv administration.
  (2) By using urethane anesthetized (0.8 g/kg, ip) male Wistar rats (300-350 g), similar surgery and CMG experiments described above were performed.  Three hours after the surgery, CP154526 (a selective antagonist of CRF receptor type 1 (CRF1 receptor), 3 or 10 nmol/rat, icv) or K41498 (a selective antagonist of CRF receptor type 2 (CRF2 receptor), 10 nmol/rat, icv) was administered 30 min before BB administration (0.03 nmol/rat, icv).

Centrally administered BB significantly reduced ICI compared to pre-treatment values before BB (-10~0 min) (Figs. 1-2) without affecting MVP (data not shown) in both SD and Wistar rats in line with our previous report [1].
  (1) Central pretreatment with astressin significantly suppressed the central BB-induced reduction in ICI (Fig. 1).  There were no significant effects on the treatment with astressin alone (3 nmol/rat, icv) withoug BB on ICI or MVP (data not shown).
  (2) Central pretreatment with CP154526 significantly suppressed the central BB-induced reduction in ICI (Fig. 2A), but K41498 had no significant effect on the central BB-induced response (Fig. 2B).  There were no significant effects of the treatment with CP154526 alone (10 nmol/rat, icv) withoug BB on ICI or MVP (data not shown).

(1) Although we used SD and Wistar rats, centrally administered BB induced similar effects on bladder activity by reducing ICI.  Because our previous report confirmed that centrally administered BB reduced single-voided volume and bladder capacity without altering post-voiding residual urine volume or voiding efficiency [1], it is suggested that central BB-like peptides induce frequent urination in rats regardless of their strains (SD or Wistar). 
  (2) The results of experiments using astressin, CP154526 and K41498 suggest that brain CRF1, but not CRF2, receptors are involved in the brain BB-like peptides-induced frequent urination in rats.  CRF1 receptors are highly expressed in the forebrain and amygdala, whereas the expression in the hypothalamus is low under basal conditions but markedly up-regulated by stress exposure [3].  In these brain regions, BB-like peptides are released by stress exposure.  Because the hypothalamus, forebrain and amygdala are known to innervate the midbrain periaqueductal gray matter (PAG), a site coordinating activity of the pontine micturition center, brain BB-like peptides might stimulate these pathways to the PAG through  CRF1 receptors, thereby inducing frequent urination in stressful conditions.  In addition, centrally administered astressin or CP154526 by itself had no effect on ICI or MVP, indicating that endogenous CRF in the brain do not seem to affect bladder function in the normal conditions.

Brain BB system is involved in facilitation of the rat micturition reflex through brain CRF1 receptor subtypes.  These findings would be useful for understanding the underlying brain mechanisms of psychological stress-related exacerbation of lower urinary tract symptoms in OAB and BPS/IC, for which brain CRF1 receptors could be a new therapeutic target.

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