Footshock-induced urinary bladder hypersensitivity: role of spinal corticotropin-releasing factor receptors

Stress-induced symptom exacerbation: Stress increases voiding frequency, somatic sensitivity, and urinary bladder NGF and BDNF expression in mice with subthreshold cyclophosphamide (CYP)

Symptom exacerbation due to stress is prevalent in many disease states, including functional disorders of the urinary bladder (e.g., overactive bladder (OAB), interstitial cystitis/bladder pain syndrome (IC/BPS)); however, the mechanisms underlying the effects of stress on micturition reflex function are unclear. In this study we designed and evaluated a stress-induced symptom exacerbation (SISE) mouse model that demonstrates increased urinary frequency and somatic (pelvic and hindpaw) sensitivity. Cyclophosphamide (CYP) (35 mg/kg; i.p., every 48 hours for a total of 4 doses) or 7 days of repeated variate stress (RVS) did not alter urinary bladder function or somatic sensitivity; however, both CYP alone and RVS alone significantly (p ≤ 0.01) decreased weight gain and increased serum corticosterone. CYP treatment when combined with RVS for 7 days (CYP+RVS) significantly (p ≤ 0.01) increased serum corticosterone, urinary frequency and somatic sensitivity and decreased weight gain. CYP+RVS exposure in mice significantly (p ≤ 0.01) increased (2.6-fold) voiding frequency as we determined using conscious, open-outlet cystometry. CYP+RVS significantly (p ≤ 0.05) increased baseline, threshold, and peak micturition pressures. We also evaluated the expression of NGF, BDNF, CXC chemokines and IL-6 in urinary bladder in CYP alone, RVS alone and CYP+RVS mouse cohorts. Although all treatments or exposures increased urinary bladder NGF, BDNF, CXC and IL-6 content, CYP+RVS produced the largest increase in all inflammatory mediators examined. These results demonstrated that CYP alone or RVS alone creates a change in the inflammatory environment of the urinary bladder but does not result in a change in bladder function or somatic sensitivity until CYP is combined with RVS (CYP+RVS). The SISE model of CYP+RVS will be useful to develop testable hypotheses addressing underlying mechanisms where psychological stress exacerbates symptoms in functional bladder disorders leading to identification of targets and potential treatments.

The Innovative Approach in Functional Bladder Disorders: The Communication Between Bladder and Brain-Gut Axis

Functional bladder disorders including overactive bladder and interstitial cystitis may induce problems in many other parts of our body such as brain and gut. In fact, diagnosis is often less accurate owing to their complex symptoms. To have correct diagnosis of these diseases, we need to understand the pathophysiology behind overlapped clinical presentation. First, we focused on reviewing literatures that have reported the link between bladder and brain, as the patients with bladder disorders frequently accompanied mood disorders such as depression and anxiety. Second, we reviewed literatures that have described the relationship between bladder and gut. There exist many evidences of patients who suffered from both bladder and intestinal diseases, such as irritable bowel syndrome and inflammatory bowel disease, at the same time. Furthermore, the interaction between brain and gut, well-known as brain-gut axis, might be a key factor that could change the activity of bladder and vice versa. For example, the affective disorders could alter the activity of efferent nerves or autonomic nervous system that modulate the gut itself and its microbiota, which might cause the destruction of homeostasis in bladder eventually. In this way, the communication between bladder and brain-gut axis might affect permeability, inflammation, as well as infectious etiology and dysbiosis in bladder diseases. In this review, we aimed to find an innovative insight of the pathophysiology in the functional bladder disorders, and we could provide a new understanding of the overlapped clinical presentation by elucidating the pathophysiology of functional bladder disorders.

The Unmet Needs for Studying Chronic Pelvic/Visceral Pain Using Animal Models

The different definitions of chronic pelvic/visceral pain used by international societies have changed over the years. These differences have a great impact on the way researchers study chronic pelvic/visceral pain. Recently, the role of systemic changes, including the role of the central nervous system, in the perpetuation and chronification of pelvic/visceral pain has gained weight. Consequently, researchers are using animal models that resemble those systemic changes rather than using models that are organ- or tissue-specific. In this review, we discuss the advantages and disadvantages of using bladder-centric and systemic models, enumerating some of the central nervous system changes and pain-related behaviors occurring in each model. We also present some drawbacks when using animal models and pain-related behavior tests and raise questions about possible, yet to be demonstrated, investigator-related bias. We also suggest new approaches to study chronic pelvic/visceral pain by refining existing animal models or using new ones.

Stress-induced bladder hypersensitivity: Effect of corticotropin releasing factor receptors assessed by spinal neurophysiology and neurochemistry

Corticotropin releasing factor (CRF) receptors have been implicated in stress-induced hyperalgesia. The present study examined the role of CRF receptors Type 1&2 (CRFR1, CRFR2) in stress-induced bladder hyperalgesia in female rats by quantifying changes in receptor and agonist content following chronic (CFS, 7 daily episodes), acute (AFS, single episode) and control (NFS, no episodes) footshock protocols. ELISAs demonstrated that CFS lead to an increase in spinal thoracolumbar and lumbosacral spinal cord CRFR2 content and a decrease in lumbosacral spinal cord CRFR1 content. Content of the endogenous CRFR2 agonist, urocortin 2, was also increased in lumbosacral spinal cord and bladder tissues of CFS-pretreated rats, but urocortin 3 was decreased. Correlative single unit studies of lumbosacral dorsal horn neurons excited by bladder distension, in anesthetized rats that had undergone CFS, AFS or NFS protocols, used a before-after methodology with administration of a CRFR1 antagonist (antalarmin, 24 μg), CRFR2 antagonist (aSVG30, 12 μg) or normal saline topically to the exposed spinal cord following primary characterization. aSVG30 produced a reduction of neuronal responses evoked by bladder distension in CFS-pretreated rats but no statistically significant effects of aSVG30, antalarmin or vehicle were noted in other groups tested with the exception that antalarmin had an inhibitory effect on spontaneous activity in NFS-pretreated rats. The present findings are consistent with previous experiments using reflex responses to bladder distension as endpoints and further support a role for CRFR2-related mechanisms in stress-induced bladder hypersensitivity. This suggests CRFR2 antagonists may have efficacy in the treatment of bladder pain.

Exploring combat stress exposure effects on burn pain in a female rodent model

In the military, constant physiological and psychological stress encountered by Soldiers can lead to development of the combat and operational stress reaction (COSR), which can effect pain management. Similar effects are seen in other populations subjected to high levels of stress. Using a model of COSR, our lab recently showed that four weeks of stress prior to an injury increases pain sensitivity in male rats. With the roles of women in the military expanding and recent studies indicating sex differences in stress and pain processing, this study sought to investigate how different amounts of prior stress exposure affects thermal injury-induced mechanosensitivity in a female rat model of COSR. Adult female Sprague Dawley rats were exposed to the unpredictable combat stress (UPCS) procedure for either 2 or 4 weeks. The UPCS procedure included exposure to one stressor each day for four days. The stressors include: (1) sound stress for 30 min, (2) restraint stress for 4 h, (3) cold stress for 4 h, and (4) forced swim stress for 15 min. The order of stressors was randomized weekly. Mechanical and thermal sensitivity was tested twice weekly. After the UPCS procedure, a sub-set of rats received a thermal injury while under anesthesia. The development of mechanical allodynia and thermal hyperalgesia was examined for 14 days post-burn. UPCS exposure increased mechanosensitivity after two weeks. Interestingly, with more stress exposure, females seemed to habituate to the stress, causing the stress-induced changes in mechanosensitivity to decrease by week three of UPCS. If thermal injury induction occurred during peak stress-induced mechanosensitivity, after two weeks, this resulted in increased mechanical allodynia in the injured hind paw compared to thermal injury alone. This data indicates a susceptibility to increased nociceptive sensitization when injury is sustained at peak stress reactivity. Additionally, this data indicates a sex difference in the timing of peak stress. Post-mortem examination of the prefrontal cortex (PFC) showed altered expression of p-TrkB in 4-week stressed animals given a thermal injury, suggesting a compensatory mechanism. Future work will examine treatment options for preventing stress-induced pain to maintain the effectiveness and readiness of the Warfighter.

Neonatal cystitis leads to alterations in spinal corticotropin releasing factor receptor-type 2 content and function in adult rats following bladder re-inflammation

Spinal mechanisms associated with visceral hypersensitivity are poorly understood. One model of bladder hypersensitivity with phenotypic features similar to the disorder interstitial cystitis/bladder pain syndrome is the neonatal bladder inflammation (NBI) model. In this model, rat pup bladders are infused with zymosan solutions on post-partum days 14-16 and then rats are retested as adults. Studies of other sites of deep tissue hypersensitivity have suggested a role for corticotropin-releasing factor (CRF) receptors type 1 and 2 (CRFR1 and CRFR2). Using neurochemical measures, pharmacological manipulations and both reflex and neuronal responses to urinary bladder distension as endpoints, the present study probed the role of CRFR2s in bladder hyperalgesia secondary to NBI and acute bladder re-inflammation as an adult (ABI). ELISA measures of the lumbosacral spinal cord demonstrated increased CRFR1s and CRFR2s following pretreatment with both NBI + ABI as well as NBI-related increases in the CRFR2 agonist urocortin 2. Intrathecal CRFR2 antagonists, but not a CRFR1 antagonist, blocked the augmentation of visceromotor responses to distension following pretreatment with both NBI + ABI. Lumbosacral dorsal horn neuronal responses to distension in rats pretreated with NBI + ABI were attenuated by the spinal topical administration of a CRFR2 antagonist. These studies suggest therapeutic value of CRFR2 antagonists in the treatment of painful bladder disorders.

Beyond depression and anxiety; a systematic review about the role of corticotropin-releasing hormone antagonists in diseases of the pelvic and abdominal organs

Evidence for beneficial effects of corticotropin releasing hormone (CRH) antagonists in abdominal and pelvic organs is emerging in preclinical studies. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement a compilation of preclinical studies using CRH receptor antagonists as a treatment for abdominal and pelvic disease was carried out. The Animal Research: Reporting of In Vivo Experiments (ARRIVE) essential 10 guidelines were used to determine quality of the included studies. A total of 40 studies from the last 15 years studying irritable bowel syndrome, inflammatory bowel disease, endometriosis, enteritis, stress impact on gastrointestinal processes and exogenous CRH administration effects were included. Blockage of the CRH receptor 1 was mainly associated with beneficial effects while that of CRH receptor 2 worsened studied effects. However, time of administration, route of administration and the animal model used, all had an impact on the beneficial outcomes. Frequency of drugs administered indicated that astressin-2B, astressin and antalarmin were among the most utilized antagonists. Of concern, studies included were predominantly carried out in male models only, representing a gender discrepancy in preclinical studies compared to the clinical scenario. The ARRIVE score average was 13 with ~60% of the studies failing to randomize or blind the experimental units. Despite the failure to date of the CRH antagonists in moving across the clinical trials pipeline, there is evidence for their beneficial effects beyond mood disorders. Future pre-clinical studies should be tailored towards effectively predicting the clinical scenario, including reduction of bias and randomization.

The Effect of Chronic Psychological Stress on Lower Urinary Tract Function: An Animal Model Perspective

Chronic psychological stress can affect urinary function and exacerbate lower urinary tract (LUT) dysfunction (LUTD), particularly in patients with overactive bladder (OAB) or interstitial cystitis–bladder pain syndrome (IC/BPS). An increasing amount of evidence has highlighted the close relationship between chronic stress and LUTD, while the exact mechanisms underlying it remain unknown. The application of stress-related animal models has provided powerful tools to explore the effect of chronic stress on LUT function. We systematically reviewed recent findings and identified stress-related animal models. Among them, the most widely used was water avoidance stress (WAS), followed by social stress, early life stress (ELS), repeated variable stress (RVS), chronic variable stress (CVS), intermittent restraint stress (IRS), and others. Different types of chronic stress condition the induction of relatively distinguished changes at multiple levels of the micturition pathway. The voiding phenotypes, underlying mechanisms, and possible treatments of stress-induced LUTD were discussed together. The advantages and disadvantages of each stress-related animal model were also summarized to determine the better choice. Through the present review, we hope to expand the current knowledge of the pathophysiological basis of stress-induced LUTD and inspire robust therapies with better outcomes.

Spinal neurochemical mechanisms of acute stress-induced visceral hypersensitivity in healthy rats

Psychological stress has been demonstrated to increase reports of pain in humans with pelvic pain of urologic origin. In rodent models, conditioning with acute footshock (AFS) has been demonstrated to increase measures of stress/anxiety as well as bladder hypersensitivity. The spinal neurochemical mechanisms of this pro-nociceptive process are unknown and so the present study administered antagonists for multiple receptors that have been associated with facilitatory mechanisms into the spinal intrathecal space. Bladder hypersensitivity was induced through use of an AFS paradigm in which female Sprague-Dawley rats received a 15-min intermittent shock treatment. Visceromotor responses (VMRs; abdominal muscle contractions) to air pressure-controlled urinary bladder distension (UBD) were used as nociceptive endpoints. Immediately following AFS treatments, rats were anesthetized (inhaled isoflurane, IP urethane) and surgically prepared. Pharmacological antagonists were administered via an intrathecal (IT) catheter onto the lumbosacral spinal cord and VMRs to graded UBD determined 15 min later. Administration of IT naloxone hydrochloride (10 μg) and IT phentolamine hydrochloride (10 μg) resulted in VMRs that were more robust than VMRs in rats that received AFS and IT normal saline whereas there was no significant effect of these drugs on VMRs in rats which underwent non-footshock procedures. In contrast, a low dose of the NMDA-receptor antagonist, MK-801 (30 μg), significantly reduced VMRs in rats made hypersensitive to UBD by AFS, but had no significant effect on rats that underwent non-footshock procedures. This study suggests that pro-nociceptive effects of AFS in otherwise healthy rats involve a spinal NMDA-linked mechanism. The effects of IT naloxone and IT phentolamine suggest the presence of inhibitory influences that are opioidergic and/or alpha-adrenergic and that are masked by the pro-nociceptive mechanisms. Other agents with no statistically significant effect on VMRs include methysergide (30 μg), ondansetron (10 μg), mecamylamine (50 μg), antalarmin (24 μg), aSVG30 (12 μg), and SSR149415 (50 μg).

Voiding and storage symptoms in depression/anxiety

We here described the frequency and nature of voiding and storage bladder symptoms in depression/anxiety, for which we propose the name "bladder somatic symptom disorder (SSD)" because such symptoms most probably have brain mechanisms. SSD was formerly called as various terms including "somatoform disorder", "medically unexplained physical symptoms", "functional somatic syndrome" and "hysterical neurosis/hysteria". Bladder SSD has the following specific features that are distinguishable from "true" neurologic/organic bladder dysfunction: 1) situation-dependence (close association with life event in some), 2) urodynamically increased bladder sensation/hypersensitivity and 3) absence of neurologic/organic diseases, in addition to 4) other stress symptoms (insomnia, etc.), are key clues to the possibility of bladder SSD. Urodynamics in these patients showed, to a lesser extent, underactive bladder without post-void residual. These findings might reflect the biological changes of the depressive brain; e.g., decreases in serotonin and GABA, and possible increases in CRH. Treatment of bladder SSD can follow that of general depression/anxiety, with the potential addition of anticholinergic or selective beta3 bladder drugs.

Preclinical models of endometriosis and interstitial cystitis/bladder pain syndrome: an Innovative Medicines Initiative-PainCare initiative to improve their value for translational research in pelvic pain

ABSTRACT

Endometriosis (ENDO) and interstitial cystitis/bladder pain syndrome (IC/BPS) are chronic pain conditions for which better treatments are urgently needed. Development of new therapies with proven clinical benefit has been slow. We have conducted a review of existing preclinical in vivo models for ENDO and IC/BPS in rodents, discussed to what extent they replicate the phenotype and pain experience of patients, as well as their relevance for translational research. In 1009 publications detailing ENDO models, 41% used autologous, 26% syngeneic, 18% xenograft, and 11% allogeneic tissue in transplantation models. Intraperitoneal injection of endometrial tissue was the subcategory with the highest construct validity score for translational research. From 1055 IC/BPS publications, most interventions were bladder centric (85%), followed by complex mechanisms (8%) and stress-induced models (7%). Within these categories, the most frequently used models were instillation of irritants (92%), autoimmune (43%), and water avoidance stress (39%), respectively. Notably, although pelvic pain is a hallmark of both conditions and a key endpoint for development of novel therapies, only a small proportion of the studies (models of ENDO: 0.5%-12% and models of IC/BPS: 20%-44%) examined endpoints associated with pain. Moreover, only 2% and 3% of publications using models of ENDO and IC/BPS investigated nonevoked pain endpoints. This analysis highlights the wide variety of models used, limiting reproducibility and translation of results. We recommend refining models so that they better reflect clinical reality, sharing protocols, and using standardized endpoints to improve reproducibility. We are addressing this in our project Innovative Medicines Initiative-PainCare/Translational Research in Pelvic Pain.

Psychological/mental stress-induced effects on urinary function: Possible brain molecules related to psychological/mental stress-induced effects on urinary function

Exposure to psychological/mental stress can affect urinary function, and lead to and exacerbate lower urinary tract dysfunctions. There is increasing evidence showing stress-induced changes not only at phenomenological levels in micturition, but also at multiple levels, lower urinary tract tissues, and peripheral and central nervous systems. The brain plays crucial roles in the regulation of the body's responses to stress; however, it is still unclear how the brain integrates stress-related information to induce changes at these multiple levels, thereby affecting urinary function and lower urinary tract dysfunctions. In this review, we introduce recent urological studies investigating the effects of stress exposure on urinary function and lower urinary tract dysfunctions, and our recent studies exploring "pro-micturition" and "anti-micturition" brain molecules related to stress responses. Based on evidence from these studies, we discuss the future directions of central neurourological research investigating how stress exposure-induced changes at peripheral and central levels affect urinary function and lower urinary tract dysfunctions. Brain molecules that we explored might be entry points into dissecting the stress-mediated process for modulating micturition.

Chronic psychological stress and lower urinary tract symptoms

It is well established that lower urinary tract symptoms (LUTS), particularly urinary urgency and incontinence, cause stress and anxiety for patients. However, there is mounting evidence that the relationship between these two factors is bidirectional and that chronic psychological stress itself can result in the development of symptoms such as urinary frequency, urgency, incontinence, and pelvic pain. This review considers the evidence that such a relationship exists and reviews the literature from clinical and animal studies to identify some of the mechanisms that might be involved. Inflammatory responses induced by chronic stress appear to offer the strongest link to bladder dysfunction. There is overwhelming evidence, both in patients and animal models, for a release of pro-inflammatory cytokines and chemokines during periods of chronic stress. Furthermore, cytokines have been shown to cause bladder dysfunction and pain via actions in the central nervous system and locally in the bladder. In the brain and spinal cord, pro-inflammatory cytokines influence the regulation of micturition pathways by corticotropin-releasing factor (CRF) and its receptors, while peripherally cytokines affect bladder function, directly causing detrusor hypertrophy and afferent nerve hypersensitivity. There is little information on which treatments may have most benefit for stressed/anxious patients with LUTS, but animal studies suggest traditional drugs for overactive bladder (solifenacin, mirabegron) are more effective on LUTS than anxiolytic drugs (fluoxetine, imipramine). The preliminary preclinical data for CRF receptor antagonists is not consistent. A clearer understanding of the mechanisms involved in stress-induced LUTS should provide a basis for improved treatment of this condition.

Foot shock stress generates persistent widespread hypersensitivity and anhedonic behavior in an anxiety-prone strain of mice

A significant subset of patients with urologic chronic pelvic pain syndrome suffer from widespread, as well as pelvic, pain and experience mood-related disorders, including anxiety, depression, and panic disorder. Stress is a commonly reported trigger for symptom onset and exacerbation within these patients. The link between stress and pain is believed to arise, in part, from the hypothalamic-pituitary-adrenal axis, which regulates the response to stress and can influence the perception of pain. Previous studies have shown that stress exposure in anxiety-prone rats can induce both pelvic and widespread hypersensitivity. Here, we exposed female A/J mice, an anxiety-prone inbred murine strain, to 10 days of foot shock stress to determine stress-induced effects on sensitivity, anhedonia, and hypothalamic-pituitary-adrenal axis regulation and output. At 1 and 28 days after foot shock, A/J mice displayed significantly increased bladder sensitivity and hind paw mechanical allodynia. They also displayed anhedonic behavior, measured as reduced nest building scores and a decrease in sucrose preference during the 10-day foot shock exposure. Serum corticosterone was significantly increased at 1 day after foot shock, and bladder mast cell degranulation rates were similarly high in both sham- and shock-exposed mice. Bladder cytokine and growth factor mRNA levels indicated a persistent shift toward a proinflammatory environment after foot shock exposure. Together, these data suggest that chronic stress exposure in an anxiety-prone mouse strain may provide a useful translational model for understanding mechanisms that contribute to widespreadness of pain and increased comorbidity in a subset of patients with urologic chronic pelvic pain syndrome.

Role of corticotropin-releasing factor on bladder function in rats with psychological stress

Stress-related peptide corticotropin-releasing factor (CRF) and CRF-related peptides are distributed in the peripheral viscera such as the bladder. We investigated the contribution of psychological stress (PS) and CRF on bladder function. Male rats received sham stress (SS) or PS using a communication box method for 120 min every day for 7 days. One group of rats received the intraperitoneal CRF-R1 antagonist antalarmin for 7 days during stress exposure. Mean voided volume per micturition was significantly lower in PS rats compared to SS rats, which was antagonized by antalarmin treatment. Increases in plasma and bladder CRF, and mRNA expressions of bladder CRF, CRF-R1, and M2/3 muscarinic receptors, were found in PS rats. CRF did not influence bladder contraction in itself; however, stress increased the response of muscarinic contraction of bladder strips. These changes were antagonized by antalarmin treatment. In conclusion, PS reinforces M3 receptor-mediated contractions via CRF-R1, resulting in bladder storage dysfunction.

Are psychological comorbidities important in the aetiology of lower urinary tract dysfunction-ICI-RS 2018?

AIMS

To review studies on the comorbid psychological symptoms and disorders in patients with lower urinary tract disorders (LUTD) over the life-span, to analyse how they contribute toward the aetiology of LUTD and to discuss optimal service implementation.

MATERIALS AND METHODS

A review of relevant literature was conducted and presented during the ICI-RS meeting in 2018. Open questions and future directions were discussed.

RESULTS

On the basis of current research, there is overwhelming evidence in all age groups that psychological comorbidities are more common in patients with LUTD. Vice versa, patients with psychiatric disorders have higher rates of LUTD. The types of LUTDs and psychiatric disorders are heterogeneous. Complex aetiological models best explain specific associations of comorbidity. Irrespective of aetiology, it is advisable to address both urological and psychological issues in patients of all age groups with LUTD.

CONCLUSIONS

Psychological symptoms and disorders play a decisive role in the development of LUTD in all age groups and need to be considered in the assessment and treatment of LUTD.

Neonatal bladder inflammation alters the role of the central amygdala in hypersensitivity produced by Acute Footshock stress in adult female rats

There is increasing evidence that chronic pain may be associated with events that occur during critical periods of development. Recent studies have identified behavioral, spinal neurophysiological and spinal/peripheral neurochemical differences in rats that have experienced neonatal bladder inflammation (NBI): a putative model of the chronically painful bladder disorder, interstitial cystitis. Stress has been shown to exacerbate symptoms of interstitial cystitis and produces bladder hypersensitivity in animal models. We recently reported that Acute Footshock-induced bladder hypersensitivity was eliminated in otherwise normal rats by prior bilateral lesions of the central nucleus of the amygdala. Since the spinal and peripheral nervous systems of NBI-treated rats are known to differ from normal rats, the present experiments sought to determine whether a supraspinal nervous system structure, the central amygdala, is still necessary for the induction of Acute Footshock-induced hypersensitivity. The effect of bilateral amygdala electrolytic lesions on Acute Footshock-induced bladder hypersensitivity in adult female rats was tested in Control rats which underwent a control protocol as neonates and in experimental rats which experienced NBI. Consistent with our previous report, in Control rats, Acute Footshock-induced bladder hypersensitivity was eliminated by bilateral Amygdala Lesions. In contrast, Acute Footshock-induced bladder hypersensitivity in NBI-treated rats was unaffected by bilateral Amygdala Lesions. These findings provide evidence that NBI results in the recruitment of substrates of bladder hypersensitivity that may differ from those of normal rats. This, in turn, suggests that unique therapeutics may be needed for painful bladder disorders like interstitial cystitis.

The Influence of Early Life Experience on Visceral Pain

Pain is the most reported and troublesome symptom of nearly all functional disorders affecting the genitourinary and gastrointestinal organs. Patients with irritable bowel syndrome (IBS), interstitial cystitis/painful bladder syndrome (IC/PBS), vulvodynia, and/or chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS; collectively termed chronic pelvic pain syndromes) report pain severe enough to impact quality of life and often suffer from symptoms of or are diagnosed with more than one of these syndromes. This increased comorbidity between chronic pelvic pain syndromes, and with pain disorders of disparate body regions, as well as with mood disorders, can be influenced by disruptions in the hypothalamic-pituitary-adrenal (HPA) axis, which regulates the response to stress and influences the perception of pain. Experiencing trauma, neglect, or abuse in early life can permanently affect the functioning of the HPA axis. As such, a significant proportion of patients suffering from comorbid chronic pelvic pain syndromes report a history of early life stress or trauma. Here we will report on how these early life experiences influence chronic pelvic pain in patients. We will also discuss various rodent models that have been developed to study this phenomenon to understand the mechanisms underlying HPA axis dysfunction, as well as potential underlying mechanisms connecting these syndromes to one another.

Periaqueductal Gray Glutamatergic Transmission Governs Chronic Stress-Induced Depression

The mechanisms underlying chronic stress-induced dysfunction of glutamatergic transmission that contribute to helplessness-associated depressive disorder are unknown. We investigated the relationship of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and stress, and the neuroplastic changes of stress-induced depression-like behavior in the ventrolateral periaqueductal gray (vlPAG). We conducted whole-cell patch-clamp electrophysiological recordings in the vlPAG neurons. Depression-like behavior was assayed using tail suspension test and sucrose preference test. Surface and cytosolic glutamate receptor 1 (GluR1) AMPA receptor expression was analyzed using western blotting. Phosphorylated GluR1 expression was quantified using western blotting and immunohistochemical analysis. Unpredictable inescapable foot shock stress caused reduction in glutamatergic transmission originating from both presynaptic and postsynaptic loci in the vlPAG that was associated with behavioral despair and anhedonia in chronic stress-induced depression. Pharmacological inhibition of GluR1 function in the vlPAG caused depression-like behavior. Diminished glutamatergic transmission was due to reduced glutamate release presynaptically and enhanced GluR1-endocytosis from the cell surface postsynaptically. Chronic stress-induced neuroplastic changes and maladaptive behavior were reversed and mimicked by administration of glucocorticoid receptor (GR) antagonist and agonist, respectively. However, chronic stress did not affect γ-aminobutyric acid (GABA)-mediated inhibitory synaptic transmission in the vlPAG. These results demonstrate that depression-like behavior is associated with remarkable reduction in glutamatergic, but not GABAergic, transmission in the vlPAG. These neuroplastic changes and maladaptive behavior are attributed to GR-dependent mechanisms. As reduced GluR1-associated responses in the vlPAG contribute to chronic stress-induced neuroplastic changes, this cellular mechanism may be a critical component in the pathogenesis of stress-associated neuropsychiatric disorders.

PACAP/Receptor System in Urinary Bladder Dysfunction and Pelvic Pain Following Urinary Bladder Inflammation or Stress

Complex organization of CNS and PNS pathways is necessary for the coordinated and reciprocal functions of the urinary bladder, urethra and urethral sphincters. Injury, inflammation, psychogenic stress or diseases that affect these nerve pathways and target organs can produce lower urinary tract (LUT) dysfunction. Numerous neuropeptide/receptor systems are expressed in the neural pathways of the LUT and non-neural components of the LUT (e.g., urothelium) also express peptides. One such neuropeptide receptor system, pituitary adenylate cyclase-activating polypeptide (PACAP; Adcyap1) and its cognate receptor, PAC1 (Adcyap1r1), have tissue-specific distributions in the LUT. Mice with a genetic deletion of PACAP exhibit bladder dysfunction and altered somatic sensation. PACAP and associated receptors are expressed in the LUT and exhibit neuroplastic changes with neural injury, inflammation, and diseases of the LUT as well as psychogenic stress. Blockade of the PACAP/PAC1 receptor system reduces voiding frequency in preclinical animal models and transgenic mouse models that mirror some clinical symptoms of bladder dysfunction. A change in the balance of the expression and resulting function of the PACAP/receptor system in CNS and PNS bladder reflex pathways may underlie LUT dysfunction including symptoms of urinary urgency, increased voiding frequency, and visceral pain. The PACAP/receptor system in micturition pathways may represent a potential target for therapeutic intervention to reduce LUT dysfunction.

Sound-stress-induced altered nociceptive behaviors are associated with increased spinal CRFR2 gene expression in a rat model of burn injury

Sound stress (SS) elicits behavioral changes, including pain behaviors. However, the neuronal mechanisms underlying SS-induced pain behaviors remain to be explored. The current study examined the effects of SS on nociceptive behaviors and changes in expression of the spinal corticotropin-releasing factor (CRF) system in male Sprague Dawley rats with and without thermal pain. We also studied the effects of SS on plasma corticosterone and fecal output. Rats were exposed to 3 days of SS protocol (n = 12/group). Changes in nociceptive behaviors were assessed using thermal and mechanical pain tests. Following the induction of SS, a subgroup of rats (n = 6/group) was inflicted with thermal injury and on day 14 postburn nociceptive behaviors were reassessed. Spinal CRF receptor mRNA expression was analyzed by semiquantitative reverse transcription polymerase chain reaction (RT-PCR). In addition, plasma corticosterone and spinal CRF concentrations were quantified using enzyme-linked immunosorbent assay (ELISA). Increased defecation was observed in SS rats. SS produced transient mechanical allodynia in naive rats, whereas it exacerbated thermal pain in thermally injured rats. Spinal CRFR2 mRNA expression was unaffected by stress or thermal injury alone, but their combined effect significantly increased its expression. SS had no effect on plasma corticosterone and spinal CRF protein in postburn rats. To conclude, SS is capable of exacerbating postburn thermal pain, which is linked to increased CRFR2 gene expression in the spinal cord. Future studies have to delineate whether attenuation of CRFR2 signaling at the spinal level prevents stress-induced exacerbation of burn pain.

Lesions of the central amygdala and ventromedial medulla reduce bladder hypersensitivity produced by acute but not chronic foot shock

Both acute and chronic stress has been shown to exacerbate symptoms of chronic visceral pain conditions such as interstitial cystitis. Studies using animal models support these findings in that both acute and chronic exposure to foot shock-induced stress (FS) augment nociceptive reflex responses to urinary bladder distension (UBD). Only a few studies have examined the neural substrates mediating these phenomena and it is not clear whether acute and chronic stress engage the same or different substrates to produce bladder hypersensitivity. The present studies examined the role of two important central nervous system structures - the amygdala (AMG) and the ventromedial medulla (VMM) - in mediating/modulating hypersensitivity evoked by acute versus chronic FS using responses to graded UBD in adult, female Sprague-Dawley rats. Bladder hypersensitivity produced by acute FS was significantly reduced by either bilateral central AMG or VMM lesions using measures generated by graded UBD, but these lesions had no significant effects using the same measures on bladder hyperalgesia produced by chronic FS. Our findings provide evidence that neural substrates underlying bladder hypersensitivity produced by chronic stress differ from those produced by acute stress. These findings suggest that while the AMG and VMM participate in pain processing during periods of limited exposure to stress, prolonged stress may recruit a new set of neural substrates not initially activated by acute exposure to stress.

The role of C-fibers in the development of chronic psychological stress induced enhanced bladder sensations and nociceptive responses: A multidisciplinary approach to the study of urologic chronic pelvic pain syndrome (MAPP) research network study

AIMS

To evaluate C fiber-mediated changes in bladder sensation and nociception in an animal model of stress induced bladder hyperalgesia and urinary frequency.

METHODS

Female Wistar-Kyoto (WKY) rats were exposed to a chronic (10 days) water avoidance stress (WAS) and compared to controls. Rats were evaluated by cystometrogram (CMG) and visceromotor reflex (VMR) to bladder infusion with room temperature (RT) or cold saline. Cold saline activates afferent C-fibers via cold bladder receptors. To further evaluate bladder hyperalgesia, CMG and VMR were also obtained during RT isometric bladder distention (RT-iBD) at variable pressures.

RESULTS

During RT infusion, WAS rats had significant decreases in pressure threshold (PT) and in the ratio of VMR threshold/maximum intravesical pressure (IVPmax), and a significant increase in VMR duration. Cold infusion also induced significant decreases in PT and in the ratio of VMR threshold/IVPmax in WAS rats. During RT-iBD, rats exposed to WAS showed a significant decrease in VMR latency and a significant increase in VMR area under the curve (AUC) compared to controls.

CONCLUSION

Chronic WAS induced bladder hypersensitivity manifested by earlier voiding with earlier VMR appearance. Chronic stress also enhanced bladder nociceptive responses. WAS leads to increase responses to ice cold water infusion, implying a role of sensitized C-fibers and mechanoreceptors in WAS-induced bladder dysfunction and hypersensitivity.

Screening and Optimization of Nerve Targets and Parameters Reveals Inhibitory Effect of Pudendal Stimulation on Rat Bladder Hypersensitivity

BACKGROUND AND OBJECTIVES

Neuromodulation has been reported to reliably improve symptoms of bladder overactivity and sometimes pain. The effect of electrical stimulation of several nerve pathways demonstrated to alter cystometric responses to bladder distension was examined on nociceptive responses in models of bladder hypersensitivity.

METHODS

Bladder hypersensitivity was produced by several published methods including neonatal inflammation, acute inflammation, and chronic stress. Effects of different sites of stimulation (L6 and T13 nerve roots, proximal and distal pudendal nerves [PNs]) on nociceptive reflex responses to urinary bladder distension in urethane-anesthetized female rats were assessed and a parametric analysis of parameters of stimulation was performed.

RESULTS

Bilateral biphasic stimulation of the proximal PNs resulted in statistically significant inhibition of visceromotor and cardiovascular responses to bladder distension in rats made hypersensitive by neonatal bladder inflammation. We found a range of optimal stimulation frequencies (5-10 Hz) which produced robust inhibitory effects when using short pulse widths (100-240 μs). Onset of inhibition was within minutes and persisted for several minutes after the stimulus was discontinued. Use of bilateral PN stimulation in acute inflammation and stress-induced hypersensitivity models as well as unilateral stimulation, very distal PN cutaneous branch stimulation, and stimulation of the T13 and L6 nerve roots all proved ineffective with the parameters used.

CONCLUSIONS

This study suggests that inhibitory effects of bilateral PN stimulation can be evoked in a rodent hypersensitivity model at relatively low frequencies with short pulse widths. The onset of effect is rapid, which suggests the potential for treating episodic pain in painful bladder disorders.

Urinary bladder hypersensitivity and dysfunction in female mice following early life and adult stress

Early adverse events have been shown to increase the incidence of interstitial cystitis/painful bladder syndrome in adulthood. Despite high clinical relevance and reports of stress-related symptom exacerbation, animal models investigating the contribution of early life stress to female urological pain are lacking. We examined the impact of neonatal maternal separation (NMS) on bladder sensitivity and visceral neuroimmune status both prior-to, and following, water avoidance stress (WAS) in adult female mice. The visceromotor response to urinary bladder distension was increased at baseline and 8d post-WAS in NMS mice, while colorectal sensitivity was transiently increased 1d post-WAS only in naïve mice. Bladder micturition rate and output, but not fecal output, were also significantly increased following WAS in NMS mice. Changes in gene expression involved in regulating the stress response system were observed at baseline and following WAS in NMS mice, and WAS reduced serum corticosterone levels. Cytokine and growth factor mRNA levels in the bladder, and to a lesser extent in the colon, were significantly impacted by NMS and WAS. Peripheral mRNA levels of stress-responsive receptors were differentially influenced by early life and adult stress in bladder, but not colon, of naïve and NMS mice. Histological evidence of mast cell degranulation was increased in NMS bladder, while protein levels of protease activated receptor 2 (PAR2) and transient receptor potential ankyrin 1 (TRPA1) were increased by WAS. Together, this study provides new insight into mechanisms contributing to stress associated symptom onset or exacerbation in patients exposed to early life stress.

Urine Trouble: Alterations in Brain Function Associated with Bladder Pain

PURPOSE

Chronic bladder pain is a debilitating condition often accompanied by alterations in affective and autonomic function. Many symptoms associated with chronic bladder pain are mediated by the central nervous system. In this review data from preclinical animal models and human neuroimaging studies were analyzed and a theoretical supraspinal bladder pain network was generated.

MATERIALS AND METHODS

We comprehensively reviewed the literature using PubMed® and Google Scholar™. Relevant reviews and original research articles, and the cited references were summarized and then organized on a neuroanatomical basis.

RESULTS

The brain loci the most predominant in the bladder pain literature are the thalamus, parabrachial nucleus, cerebral cortex, amygdala, hypothalamus, periaqueductal gray and rostral ventromedial medulla. This review highlights each of these regions, discussing the molecular and physiological changes that occur in each in the context of bladder pain.

CONCLUSIONS

A complex network of brain loci is involved in bladder pain modulation. Studying these brain regions and the changes that they undergo during the transition from acute to chronic bladder pain will provide novel therapeutic strategies for patients with chronic bladder pain diseases such as interstitial cystitis/bladder pain syndrome and chronic prostatitis/chronic pelvic pain syndrome.

Intrathecal urocortin I in the spinal cord as a murine model of stress hormone-induced musculoskeletal and tactile hyperalgesia

Stress is antinociceptive in some models of pain, but enhances musculoskeletal nociceptive responses in mice and muscle pain in patients with fibromyalgia syndrome. To test the hypothesis that urocortins are stress hormones that are sufficient to enhance tactile and musculoskeletal hyperalgesia, von Frey fibre sensitivity and grip force after injection of corticotropin-releasing factor (CRF), urocortin I and urocortin II were measured in mice. Urocortin I (a CRF1 and CRF2 receptor ligand) produced hyperalgesia in both assays when injected intrathecally (i.t.) but not intracerebroventricularly, and only at a large dose when injected peripherally, suggesting a spinal action. Morphine inhibited urocortin I-induced changes in nociceptive responses in a dose-related fashion, confirming that changes in behaviour reflect hyperalgesia rather than weakness. No tolerance developed to the effect of urocortin I (i.t.) when injected repeatedly, consistent with a potential to enhance pain chronically. Tactile hyperalgesia was inhibited by NBI-35965, a CRF1 receptor antagonist, but not astressin 2B, a CRF2 receptor antagonist. However, while urocortin I-induced decreases in grip force were not observed when co-administered i.t. with either NBI-35965 or astressin 2B, they were even more sensitive to inhibition by astressin, a non-selective CRF receptor antagonist. Together these data indicate that urocortin I acts at CRF receptors in the mouse spinal cord to elicit a reproducible and persistent tactile (von Frey) and musculoskeletal (grip force) hyperalgesia. Urocortin I-induced hyperalgesia may serve as a screen for drugs that alleviate painful conditions that are exacerbated by stress.

Serotonin enhances urinary bladder nociceptive processing via a 5-HT3 receptor mechanism

Serotonin from the descending pain modulatory pathway is critical to nociceptive processing. Its effects on pain modulation may either be inhibitory or facilitatory, depending on the type of pain and which receptors are involved. Little is known about the role of serotonergic systems in bladder nociceptive processing. These studies examined the effect of systemic administration of the serotonin precursor, 5-hydroxytryptophan (5-HTP), on normal bladder and somatic sensation in rats. ELISA was used to quantify peripheral and central changes in serotonin and its major metabolite following 5-HTP administration, and the potential role of the 5-HT3 receptor on changes in bladder sensation elicited by 5-HTP was investigated. 5-HTP produced bladder hypersensitivity and somatic analgesia. The pro-nociceptive effect of 5-HTP was attenuated by intrathecal, but not systemic, ondansetron. Peripheral increases in serotonin, its metabolism and rate of turnover were detectable within 30min of 5-HTP administration. Significant enhancement of serotonin metabolism was observed centrally. These findings suggest that 5-HTP increases serotonin, which may then affect descending facilitatory systems to produce bladder hypersensitivity via activation of spinal 5-HT3 receptors.

The amygdala central nucleus is required for acute stress-induced bladder hyperalgesia in a rat visceral pain model

Chronic stress has been implicated in the pathogenesis of chronic visceral pain conditions, such as interstitial cystitis (IC), and bouts of acute stress exacerbate clinical urological pain. Studies using animal models have shown that exposure to chronic footshock stress augments reflex responses to urinary bladder distension (UBD) in animal models, however acute effects in animal models are largely unknown, as are the central nervous system mechanisms of stress-related increases in nociception. The amygdala is a salient structure for integration of sensory and cognitive/emotional factors. The present study determined the role of the central nucleus of the amygdala (CeA) in stress-related bladder hypersensitivity. We examined the effects of CeA manipulations (lesions and chemical stimulation) on visceromotor responses (abdominal muscle contractions) to UBD in adult, female Sprague-Dawley rats. We report that acute footshock stress produces bladder hyperalgesia that can be prevented by bilateral CeA lesions, despite no effect of lesions on baseline somatic sensation, as indicated by flinch/jump thresholds to electrical shock. Further, acute glucocorticoid stimulation of the CeA recapitulated stress-induced hyperalgesia. Of note is that CeA lesions, but not chemical stimulation, significantly affected HPA axis activation, as indicated by measurements of circulating corticosterone. Our findings conclusively show that the CeA is necessary for the generation of bladder hyperalgesia in response to acute stress. The CeA may play multiple stress-related roles in nociceptive modulation, i.e., via direct facilitation of the HPA axis during acute stress, or via modulation of other systems that augment acute stress responsiveness.

Corticotropin-releasing factor family peptide signaling in feline bladder urothelial cells

Corticotropin-releasing factor (CRF) plays a central role in the orchestration of behavioral and neuroendocrine responses to stress. The family of CRF-related peptides (CRF and paralogs: urocortin (Ucn)-I, -II, and -III) and associated receptors (CRFR1 and CRFR2) are also expressed in peripheral tissues such as the skin and gastrointestinal tract. Local signaling may exert multiple effects of stress-induced exacerbation of many complex syndromes, including psoriasis and visceral hypersensitivity. Interstitial cystitis/painful bladder syndrome (IC/PBS), a chronic visceral pain syndrome characterized by urinary frequency, urgency, and pelvic pain, is reported to be exacerbated by stress. Functional changes in the epithelial lining of the bladder, a vital blood-urine barrier called the urothelium, may play a role in IC/PBS. This study investigated the expression and functional activity of CRF-related peptides in the urothelium of normal cats and cats with feline interstitial cystitis (FIC), a chronic idiopathic cystitis exhibiting similarities to humans diagnosed with IC/PBS. Western blots analysis showed urothelial (UT) expression of CRFR1 and CRFR2. Enzyme immunoassay revealed release of endogenous ligands (CRF and Ucn) by UT cells in culture. Evidence of functional activation of CRFR1 and CRFR2 by receptor-selective agonists (CRF and UCN3 respectively) was shown by i) the measurement of ATP release using the luciferin-luciferase assay and ii) the use of membrane-impermeant fluorescent dyes (FM dyes) for fluorescence microscopy to assess membrane exocytotic responses in real time. Our findings show evidence of CRF-related peptide signaling in the urothelium. Differences in functional responses between FIC and normal UT indicate that this system is altered in IC/PBS.

Vaginal hypersensitivity and hypothalamic-pituitary-adrenal axis dysfunction as a result of neonatal maternal separation in female mice

Early life stress can permanently alter functioning of the hypothalamic-pituitary-adrenal (HPA) axis, which regulates the stress response and influences the perception of pain. Chronic pelvic pain patients commonly report having experienced childhood neglect or abuse, which increases the likelihood of presenting with comorbid chronic pain and/or mood disorders. Animal models of neonatal stress commonly display enhanced anxiety-like behaviors, colorectal hypersensitivity, and disruption of proper neuro-immune interactions in adulthood. Here, we tested the hypothesis that early life stress impacts vaginal sensitivity by exposing mice to neonatal maternal separation (NMS) for 3h/day during the first two (NMS14) or three (NMS21) postnatal weeks. As adults, female mice underwent vaginal balloon distension (VBD), which was also considered an acute stress. Before or after VBD, mice were assessed for anxiety-like behavior, hindpaw sensitivity, and changes in gene and protein expression related to HPA axis function and regulation. NMS21 mice displayed significantly increased vaginal sensitivity compared to naïve mice, as well as significantly reduced anxiety-like behavior at baseline, which was heightened following VBD. NMS21 mice exhibited significant thermal and mechanical hindpaw hypersensitivity at baseline and following VBD. NMS14 mice displayed no change in anxiety-like behavior and only exhibited significantly increased hindpaw mechanical and thermal sensitivity following VBD. Centrally, a significant decrease in negative regulation of the HPA axis was observed in the hypothalamus and hippocampus of NMS21 mice. Peripherally, NMS and VBD affected the expression of inflammatory mediators in the vagina and bladder. Corticotropin-releasing factor (CRF) receptor and transient receptor potential (TRP) channel protein expression was also significantly, and differentially, affected in vagina, bladder, and colon by both NMS and VBD. Together these data indicate that NMS affects both central and peripheral aspects of the HPA axis, which may drive changes in vaginal sensitivity and the development of comorbid chronic pain and mood disorders.

Visceral pain

Modeling visceral pain requires an appreciation of the underlying neurobiology of visceral sensation, including characteristics of visceral pain that distinguish it from pain arising from other tissues, the unique sensory innervation of visceral organs, the functional basis of visceral pain, and the concept of viscero-somatic and viscero-visceral convergence. Further, stimuli that are noxious when applied to the viscera are different than stimuli noxious to skin, muscle, and joints, thus informing model development and assessment. Visceral pain remains an important and understudied area of pain research and basic science knowledge and mechanisms acquired using animal models can translate into approaches that can be applied to the study and development of future therapeutics.

Cytoskeletal protein translation and expression in the rat brain are stressor-dependent and region-specific

Stress is an integral component of life that can sometimes cause a critical overload, depending on the qualitative and quantitative natures of the stressors. The involvement of actin, the predominant component of dendritic integrity, is a plausible candidate factor in stress-induced neuronal cytoskeletal changes. The major aim of this study was to compare the effects of three different stress conditions on the transcription and translation of actin-related cytoskeletal genes in the rat brain. Male Wistar rats were exposed to one or other of the frequently used models of physical stress, i.e. electric foot shock stress (EFSS), forced swimming stress (FSS), or psychosocial stress (PSS) for periods of 3, 7, 14, or 21 days. The relative mRNA and protein expressions of β-actin, cofilin and mitogen-activated protein kinase 1 (MAPK-1) were determined by qRT- PCR and western blotting from hippocampus and frontal cortex samples. Stressor-specific alterations in both β-actin and cofilin expression levels were seen after stress. These alterations were most pronounced in response to EFSS, and exhibited a U-shaped time course. FSS led to a significant β-actin mRNA expression elevation in the hippocampus and the frontal cortex after 3 and 7 days, respectively, without any subsequent change. PSS did not cause any change in β-actin or cofilin mRNA or protein expression in the examined brain regions. EFSS, FSS and PSS had no effect on the expression of MAPK-1 mRNA at any tested time point. These findings indicate a very delicate, stress type-dependent regulation of neuronal cytoskeletal components in the rat hippocampus and frontal cortex.

Repeated variate stress in male rats induces increased voiding frequency, somatic sensitivity, and urinary bladder nerve growth factor 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, myeloperoxidase (MPO), nerve growth factor (NGF), brain-derived neurotropic factor (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 after RVS. Somatic sensitivity of the hindpaw and pelvic regions was significantly (P ≤ 0.01) increased at all monofilament forces tested (0.1-4 g) after RVS. Intercontraction interval, infused volume, and void volume were significantly (P ≤ 0.01) decreased after 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.

Forced swim-induced musculoskeletal hyperalgesia is mediated by CRF2 receptors but not by TRPV1 receptors

The exacerbation of musculoskeletal pain by stress in humans is modeled by the musculoskeletal hyperalgesia in rodents following a forced swim. We hypothesized that stress-sensitive corticotropin releasing factor (CRF) receptors and transient receptor vanilloid 1 (TRPV1) receptors are responsible for the swim stress-induced musculoskeletal hyperalgesia. We confirmed that a cold swim (26 °C) caused a transient, morphine-sensitive decrease in grip force responses reflecting musculoskeletal hyperalgesia in mice. Pretreatment with the CRF2 receptor antagonist astressin 2B, but not the CRF1 receptor antagonist NBI-35965, attenuated this hyperalgesia. Desensitizing the TRPV1 receptor centrally or peripherally using desensitizing doses of resiniferatoxin (RTX) failed to prevent the musculoskeletal hyperalgesia produced by cold swim. SB-366791, a TRPV1 antagonist, also failed to influence swim-induced hyperalgesia. Together these data indicate that swim stress-induced musculoskeletal hyperalgesia is mediated, in part, by CRF2 receptors but is independent of the TRPV1 receptor.

Sciatic nerve injury induces functional pro-nociceptive chemokine receptors in bladder-associated primary afferent neurons in the rat

Visceral sensory afferents during disease or following injury often produce vague, diffuse body sensations, and pain referred to somatic targets. Alternatively, injury due to trauma or disease of somatic nerve targets can also lead to referred pain in visceral targets via a somatovisceral reflex. Both phenomenons are thought to be due to convergence of visceral and somatic afferents within the spinal cord. To investigate a potential peripheral influence for referred pain in visceral targets following somatic nerve injury, we examined whether a sciatic nerve injury known to produce hindpaw tactile hyperalgesia alters the frequency of micturition and the sensitivity of bladder-associated sensory neurons to pro-nociceptive chemokines. Adult female Sprague-Dawley rats received injections of cholera toxin B subunit conjugated to 555 into urinary bladder wall to retrogradely label visceral primary afferent neurons. After 7 days, the right sciatic nerve of these animals was subjected to a lysophosphatidylcholine (LPC)-induced focal demyelination injury. Pre- and post-injury tactile sensitivity in the hind paw and micturition frequency were assayed. Animals were allowed to survive for 14-28 days. Lumbosacral and lumbar dorsal root ganglia (DRG) ipsilateral to the nerve injury were acutely dissociated from sham and nerve injured animals. Bladder wall-associated sensory neurons identified via the retrograde marker were assayed for fluxes in intracellular calcium following administration of pro-nociceptive chemokines. The assayed chemokines included monocyte chemoattractant protein-1 (MCP1/CCL2) and stromal cell derived factor-1 alpha (SDF1/CXCL12). LPC nerve injured animals exhibited tactile hyperalgesia and increased micturition frequency for at least 28 days. Focal demyelination of the sciatic nerve also increased the number of injured L₄L₅ and non-injured L₆-S₂ bladder-associated sensory neurons that responded to MCP1 and SDF1 when compared with sensory neurons derived from uninjured naïve and sham-injured control animals. Taken together, these data suggest that some visceral hypersensitivity states may have a somatic origin. More importantly, nociceptive somatovisceral sensation may be mediated by upregulation of chemokine signaling in visceral sensory neurons.

Footshock stress differentially affects responses of two subpopulations of spinal dorsal horn neurons to urinary bladder distension in rats

This investigation examined the effect of footshock on responses of 283 spinal dorsal horn neurons (DHNs) to urinary bladder distension (UBD). Female rats were treated with seven daily sessions of footshock (chronic footshock, CFS), six accommodation sessions followed by one exposure to footshock (acute footshock, AFS) or handled similarly without receiving any footshock (no footshock, NFS). After the final footshock or NFS session, rats were anesthetized, a laminectomy performed and extracellular single-unit recordings of L6-S1 DHNs obtained in intact or spinalized preparations. Neurons were classified as Type I-inhibited by heterotopic noxious conditioning stimuli (HNCS) or as Type II-not inhibited by HNCS-and characterized for spontaneous activity and for neuronal discharges evoked by graded UBD. A differential effect of footshock-induced stress was noted on neuronal subgroups. In intact preparations, Type I neurons were less responsive to UBD after either chronic or acute stress, while Type II neurons demonstrated significantly augmented responses to UBD. This enhanced neuronal responsiveness to UBD was present in spinalized preparations following exposure to CFS but not AFS. Type I neurons were still less responsive to stress in spinalized preparations following CFS and AFS. This study provides further evidence that (1) at least two populations of spinal neurons exist which encode for visceral stimuli and are likely to have distinct roles in visceral nociception, and that (2) the chronic stress-induced enhancement of DHN responses to UBD involves changes at the spinal level while the acute stress effects are dependent on a supraspinal substrate.

Corticotropin-releasing hormone-receptor 2 is required for acute stress-induced bladder vascular permeability and release of vascular endothelial growth factor

OBJECTIVE

To investigate the corticotropin-releasing hormone (CRH) receptor (CRH-R) requirement for the effect of acute stress on bladder vascular permeability and release of vascular endothelial growth factor (VEGF), as increasing evidence indicates that acute stress worsens certain inflammatory disorders, including interstitial cystitis/painful bladder syndrome (IC/PBlS), which is characterized by pain, variable bladder inflammation, increased expression of bladder vascular endothelial growth factor (VEGF), and many detrusor mast cells.

MATERIALS AND METHODS

Bladders of normal C57BL/6, and C57BL/6- derived CRH-R1, CRH-R2 or double CRH-R1 + 2 knockout (-/-) female mice (10-12 weeks old) were catheterized under anaesthesia. After emptying the urine, normal saline was instilled with or without intravesical CRH-R antagonists in C57BL/6 mice before they were stressed by placing them in a restrainer for 30 min. Evans blue was injected in the tail vein before stress for the permeability experiments. The bladders from C57BL/6 or CRH-R -/- mice were then removed, minced into 1 mm(2) pieces and cultured overnight. Culture media were collected 24 h later for VEGF assay. C57BL/6 bladder was processed for CRH-R immunohistochemistry.

RESULTS

Acute stress increased bladder vascular permeability in control C57BL/6 and CRH-R1 -/- mice, but not CRH-R2 -/- or CRH-R1+2 -/- mice. The CRH-R2 antagonist Astressin 2B, but not the CRH-R1 antagonist Antalarmin, inhibited stress-induced VEGF release from C57BL/6 mouse bladder explants. Stress could not induce a VEGF increase from bladder explants of CRH-R2 -/- or CRH-R1+2 -/- mice, but did so in CRH-R1 -/- mice. Bladder CRH-R2 immunoreactivity was detected in C57BL/6 bladders.

CONCLUSIONS

Acute stress induces bladder vascular permeability and VEGF release that is dependent on CRH-R2. These findings suggest that CRH and VEGF might participate in the pathogenesis of IC/PBlS and provide for new therapeutic targets.

Effects of oxytocin and prolactin on stress-induced bladder hypersensitivity in female rats

Anecdotal evidence suggests that chronic bladder pain improves while breastfeeding. The present study sought to identify potential mechanisms for such a phenomenon by investigating the effects of the lactogenic hormones prolactin (PL) and oxytocin (OXY) in a rat model of bladder nociception. Lactating rats were less sensitive to urinary bladder distension (UBD) than controls. In investigating potential antinociceptive and anxiolytic roles for these hormones, we found exposure to a footshock paradigm (STRESS groups) produced bladder hypersensitivity in saline-treated rats, manifested as significantly higher electromyographical (EMG) responses to UBD, compared to rats exposed to a nonfootshock paradigm (SHAM groups). This hypersensitivity was attenuated by the intraperitoneal administration of OXY prior to footshock in the STRESS-OXY group. The administration of PL augmented EMG responses in the SHAM-PL group but had no effect on the responses of the STRESS-PL group. In the absence of behavioral pretreatment, OXY attenuated UBD-evoked responses while PL had no effect. Moreover, OXY-treated rats spent more time in the open arm of an elevated plus maze compared to saline-treated rats suggesting anxiolysis. These studies suggest the potential for systemic OXY, but not PL, as an analgesic and anxiolytic treatment for painful bladder disorders such as interstitial cystitis.

PERSPECTIVE

This study presents evidence that systemic oxytocin has both analgesic and anxiolytic properties which may make it a potentially useful agent for patients with stress-exacerbated chronic-pain syndromes such as interstitial cystitis. These studies do not suggest a similar role for prolactin.