Neonatal bladder inflammation produces functional changes and alters neuropeptide content in bladders of adult female rats

Adult zymosan re-exposure exacerbates the molecular alterations in the brainstem rostral ventromedial medulla of rats with early life zymosan-induced cystitis

Recent evidence suggests that the descending modulatory pathways from the brainstem rostral ventromedial medulla (RVM) are important for bladder inflammatory pain. This study aimed to identify the long-term molecular changes in RVM neurons due to early life cystitis during neuronal development and the effect of reexposure later in adulthood. RVM tissues from two treatment protocols were used: (1) neonatal zymosan exposures with acute adult rechallenge (RC) and (2) only neonatal zymosan exposures (NRC). RNAseq analysis showed upregulation of several genes associated with synaptic plasticity (Grin1, Grip2, Notch1, Arc, and Scn2b) in the cystitis groups compared to controls in both protocols. The RC protocol exhibited a stronger treatment effect with significantly higher fold differences between the groups compared to the NRC protocol (p < 0.001, fold differences RC vs NRC). In microarrays, miR-34a-5p showed cystitis-induced downregulation in both protocols. Bioinformatics analysis identified multiple 3'UTRs complementary binding sites for miR-34a-5p on Grin2b, Notch1, Grip2, Scn2b, and Arc genes. The enhanced response in the RC protocol indicates a possible priming effect of early life cystitis on rechallenge in adulthood. These long-term molecular alterations may play a critical role in the development of chronic bladder pain conditions as seen in patients with Interstitial Cystitis/Bladder pain syndrome.

Neonatal Cystitis Makes Adult Female Rat Urinary Bladders More Sensitive to Low Concentration Microbial Antigens

Purpose

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic pain disorder. Patients with IC/BPS often experience "flares" of symptom exacerbation throughout their lifetime, initiated by triggers, such as urinary tract infections. This study sought to determine whether neonatal bladder inflammation (NBI) alters the sensitivity of adult rat bladders to microbial antigens.

Methods

Female NBI rats received intravesical zymosan treatments on postnatal days P14-P16 while anesthetized; Neonatal Control Treatment (NCT) rats were anesthetized. In adults, bladder and spinal cord Toll-like receptor type 2 and 4 (TLR2, TLR4) contents were determined using ELISAs. Other rats were injected intravesically with lipopolysaccharide (LPS; mimics an E. coli infection; 25, 50, 100, or 200 μg/mL) or Zymosan (mimics yeast infection; 0.01, 0.1, 1, and 10 mg/mL) solutions on the following day. Visceromotor responses (VMRs; abdominal contractions) to graded urinary bladder distention (UBD, 10-60 mm Hg, 20s) were quantified as abdominal electromyograms (EMGs).

Results

Bladder TLR2 and TLR4 protein levels increased in NBI rats. These rats displayed statistically significant, dose-dependent, robustly augmented VMRs following all but the lowest doses of LPS and Zymosan tested, when compared with their adult treatment control groups. The NCT groups showed minimal responses to LPS in adults and minimally increased EMG measurements following the highest dose of Zymosan.

Conclusion

The microbial antigens LPS and Zymosan augmented nociceptive VMRs to UBD in rats that experienced NBI but had little effect on NCT rats at the doses tested. The greater content of bladder TLR2 and TLR4 proteins in the NBI group was consistent with increased responsiveness to their agonists, Zymosan and LPS, respectively. Given that patients with IC/BPS have a higher incidence of childhood urinary tract infections, this increased responsiveness to microbial antigens may explain the flares in symptoms following "subclinical" tract infections.

Animal models of interstitial cystitis/bladder pain syndrome

Interstitial Cystitis/Bladder Pain Syndrome (IC/BPS) is a chronic disorder characterized by pelvic and/or bladder pain, along with lower urinary tract symptoms that have a significant impact on an individual's quality of life. The diverse range of symptoms and underlying causes in IC/BPS patients pose a significant challenge for effective disease management and the development of new and effective treatments. To facilitate the development of innovative therapies for IC/BPS, numerous preclinical animal models have been developed, each focusing on distinct pathophysiological components such as localized urothelial permeability or inflammation, psychological stress, autoimmunity, and central sensitization. However, since the precise etiopathophysiology of IC/BPS remains undefined, these animal models have primarily aimed to replicate the key clinical symptoms of bladder hypersensitivity and pain to enhance the translatability of potential therapeutics. Several animal models have now been characterized to mimic the major symptoms of IC/BPS, and significant progress has been made in refining these models to induce chronic symptomatology that more closely resembles the IC/BPS phenotype. Nevertheless, it's important to note that no single model can fully replicate all aspects of the human disease. When selecting an appropriate model for preclinical therapeutic evaluation, consideration must be given to the specific pathology believed to underlie the development of IC/BPS symptoms in a particular patient group, as well as the type and severity of the model, its duration, and the proposed intervention's mechanism of action. Therefore, it is likely that different models will continue to be necessary for preclinical drug development, depending on the unique etiology of IC/BPS being investigated.

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.

Clinical Review of Neuromusculoskeletal Complementary and Alternative Approaches for the Treatment of Chronic Pelvic Pain Syndrome

Chronic pelvic pain syndrome (CPPS) is a functional pain disorder characterized by ongoing pain in the apparent absence of clinically identifiable causes. The prevalence of functional pain disorders demonstrates the importance of adequate management of ongoing symptomatology, but due to the uncertain etiology and myriad patient presentation phenotypes, reliable treatment options are difficult to implement. New interventions involving non-pharmacological approaches to pain management have been investigated across a spectrum of clinical and pre-clinical studies. Given that conservative care such as exercise, counseling, and musculoskeletal therapy is widely recommended as first-line treatment for CPPS, an updated review of these and related methodologies are needed. Familiarizing physicians and the public with the newest evidence for complementary and alternative medicine (CAM) and other conservative care treatments will assist with the promotion of evidence-based practices in a safe and reliable manner. This review aimed to summarize the current evidence and proposed mechanisms for non-pharmacological treatment specific to CAM and management of chronic pelvic pain centered on neuromusculoskeletal focused intervention such as acupuncture, auriculotherapy, manipulation, manual therapy, myofascial release, and phototherapy. The discussion suggests that reported improvements in pelvic pain or related symptomatology may be attributed to changes in the peripheral inflammasome and somatic origins of peripheral sensitization. Robustness of the included clinical studies is discussed throughout the review, and attention is paid to delineating inclusion criteria of formally diagnosed CPPS compared to general pelvic or abdominal pain. Overall, this review consolidates the current state of evidence regarding the utilization of non-traditional interventions using CAM techniques for the management of chronic pelvic pain and recommends a future direction for the field.

Identification and characterization of rostral ventromedial medulla neurons synaptically connected to the urinary bladder afferents in female rats with or without neonatal cystitis

The neurons in the rostral ventromedial medulla (RVM) play a major role in pain modulation. We have previously shown that early-life noxious bladder stimuli in rats resulted in an overall spinal GABAergic disinhibition and a long-lasting bladder/colon sensitization when tested in adulthood. However, the neuromolecular alterations within RVM neurons in the pathophysiology of early life bladder inflammation have not been elucidated. In this study, we have identified and characterized RVM neurons that are synaptically linked to the bladder and colon and examined the effect of neonatal bladder inflammation on molecular expressions of these neurons. A transient bladder inflammation was induced by intravesicular instillation of protamine sulfate and zymosan during postnatal days 14 through 16 (P14-16) followed by pseudorabies virus PRV-152 and PRV-614 injections into the bladder and colon, respectively, on postnatal day P60. Tissues were examined 96 h postinoculation for serotonergic, GABAergic, and enkephalinergic expressions using in situ hybridization and/or immunohistochemistry techniques. The results revealed that > 50% of RVM neurons that are synaptically connected to the bladder (i.e., PRV-152+) were GABAergic, 40% enkephalinergic, and about 14% expressing serotonergic marker tryptophan hydroxylase 2 (TpH2). Neonatal cystitis resulted in a significant increase in converging neurons in RVM receiving dual synaptic inputs from the bladder and colon. In addition, neonatal cystitis significantly downregulated vesicular GABA transporter (VGAT) with a concomitant increase in TpH2 expression in bladder-linked RVM neurons, suggesting an alteration in supraspinal signaling. These alterations of synaptic connectivity and GABAergic/serotonergic expressions in RVM neurons may contribute to bladder pain modulation and cross-organ visceral sensitivity.

Neonatal Bladder Inflammation Results in Adult Female Mouse Phenotype With Increased Frequency and Nociceptive Responses to Bladder Filling

Bladder pain and hypersensitivity to bladder filling are clinically common, but animal models examining syndromes with these features are limited. A rat model of bladder hypersensitivity produced by neonatal bladder inflammation (NBI) has been reported to have many of the clinical features of bladder pain syndromes. The present study sought to determine whether similar hypersensitivity might be induced by NBI in mice. Female C57BL6/J mice had NBI induced on postnatal days P12-14 by the intravesical administration of zymosan. As adults (12–14 weeks of age), the mice were examined for hypersensitivity of their bladders as: spontaneous voiding and evoked cystometrograms at baseline, and visceromotor responses (VMRs) to urinary bladder distension (UBD) following a secondary insult (either repeated bladder inflammation or acute stress induced by footshock). Mice that experienced NBI demonstrated hypersensitivity, when compared with control mice, manifested as increased spontaneous voiding, increased frequency of evoked voids during intravesical saline infusion, and increased vigor of VMRs to UBD following either acute bladder inflammation or acute stress. This recapitulates the hallmark features of clinical painful bladder disorders and suggest utility of this murine model for the study of these disorders while allowing methodological expansion into well-established genetic and immunological models.

A Model in Female Rats With Phenotypic Features Similar to Interstitial Cystitis/Bladder Pain Syndrome

This report describes methodological and exploratory investigations of the zymosan-induced neonatal bladder inflammation (NBI) model of interstitial cystitis/bladder pain syndrome (IC/BPS) in female rats. These results validate and extend the currently employed model by evaluating critical timepoints for obtaining treatment effects and identified that a second insult as an adult including repeat intravesical zymosan, intravesical lipopolysaccharide, acute footshock stress, neuropathic nociception (facial) or somatic inflammation (hindpaw) all resulted in magnified visceromotor responses to urinary bladder distension (UBD) in rats which had experienced NBI when compared with their controls. NBI also resulted in increased tone and reactivity of pelvic floor musculature to UBD, as well as increased responsiveness to intravesical potassium chloride solutions, abnormal anxiety measures (elevated plus maze) and an increased number of submucosal petechial hemorrhages following 30 min of hydrodistension of the bladder. These phenotypic findings have correlates to the clinical features of IC/BPS in humans and so support use of this model system to examine mechanisms of and treatments for IC/BPS.

Systemic and intrathecal baclofen produce bladder antinociception in rats

BACKGROUND

Baclofen, a clinically available GABAB receptor agonist, produces non-opioid analgesia in multiple models of pain but has not been tested for effects on bladder nociception.

METHODS

A series of experiments examined the effects of systemic and spinally administered baclofen on bladder nociception in female anesthetized rats. Models of bladder nociception included those which employed neonatal and adult bladder inflammation to produce bladder hypersensitivity.

RESULTS

Cumulative intraperitoneal dosing (1-8 mg/kg IP) and cumulative intrathecal dosing (10-160 ng IT) of baclofen led to dose-dependent inhibition of visceromotor responses (VMRs) to urinary bladder distension (UBD) in all tested models. There were no differences in the magnitude of the analgesic effects of baclofen as a function of inflammation versus no inflammation treatments. Hemodynamic (pressor) responses to UBD were similarly inhibited by IT baclofen as well as UBD-evoked excitatory responses of spinal dorsal horn neurons. The GABAB receptor antagonist, CGP 35,348, antagonized the antinociceptive effects of IT baclofen on VMRs in all tested models but did not affect the magnitude of the VMRs by itself suggesting no tonic GABAB activity was present in this preparation. Tolerance to a seven day continuous IT infusion of baclofen was not observed.

CONCLUSIONS

These data provide support for a clinical trial of baclofen as a non-opioid treatment of human bladder pain.

Medications used to treat bladder disorders may alter effects of neuromodulation

AIMS

Neuromodulation (nerve stimulation) can produce analgesia. One form, bilateral pudendal nerve stimulation (bPNS), suppresses responses to urinary bladder distension (UBD) in hypersensitive rats. Drugs can modify this effect (eg, benzodiazepines, but not opioids, suppress bPNS effects). Prior to a clinical trial of bPNS effects on bladder pain, we felt it was prudent to survey the effects of medications commonly used in patients with bladder disorders.

METHODS

Bladder hypersensitivity was produced by neonatal bladder inflammation in rat pups coupled with a second inflammatory insult as an adult. Antimuscarinic (oxybutynin), β₃ -adrenoceptor agonist (mirabegron, CL316243), α₁ -adrenoceptor antagonist (tamsulosin), antidepressant (amitriptyline), muscle relaxing (baclofen), and sedative (propofol) agents were administered and effects of bPNS on responses to UBD assessed. bPNS consisted of bilateral biphasic electrical stimulation of the mixed motor/sensory component of the pudendal nerves. Visceromotor responses (VMRs; abdominal muscle contractile responses) were used as nociceptive endpoints.

RESULTS

Many of these drugs directly inhibited the VMRs to UBD, but only mirabegron, at the doses employed, significantly reduced inhibitory effects of bPNS. In the presence of the other drugs, bPNS continued to produce statistically significant inhibition of VMRs to UBD.

CONCLUSIONS

This study suggests that concurrent therapy with drugs used to treat bladder disorders could affect assessment of the effects of bPNS on bladder hypersensitivity. This study gives guidance to clinical trials using bPNS for the treatment of painful bladder syndromes and suggests potential clinical use of some of these medications in the treatment of these same disorders.

Benzodiazepines Suppress Neuromodulatory Effects of Pudendal Nerve Stimulation on Rat Bladder Nociception

BACKGROUND

Neuromodulation, as a therapeutic modality for pain treatment, is an alternative to opioid therapies and therefore receiving increased interest and use. Neuromodulation at a peripheral nerve target, in the form of bilateral electrical pudendal nerve stimulation (bPNS), has been shown to reduce bladder hypersensitivity in rats and anecdotally reduces pain in humans with pelvic pain of urological origin. Recent studies have identified a role for spinal γ-aminobutyric acid (GABA) receptors in this effect. Concomitant medication use, such as benzodiazepines, could alter responses to neuromodulation, and so before the development of a clinical trial to confirm translation of this potential therapy, the potential interactions between acute and chronic use of benzodiazepines and bPNS were examined in a preclinical model.

METHODS

Bladder hypersensitivity was produced by neonatal bladder inflammation in rat pups coupled with a second inflammatory insult as an adult. Diazepam (1-5 mg/kg intraperitoneal [i.p.]) or vehicle was administered acutely (with or without bPNS) and chronically (5 mg/kg subcutaneous [s.c.] daily for 2 weeks before the final experiment). bPNS was delivered as bilateral biphasic electrical stimulation of the mixed motor/sensory component of the pudendal nerves. Visceromotor responses (VMRs; abdominal muscle contractile responses to urinary bladder distension [UBD]) were used as nociceptive end points. Due to the profound effects of diazepam, the effect of midazolam (0.5-1.0 mg/kg i.p.) on VMRs and bPNS effects was also studied.

RESULTS

Diazepam and midazolam both produced a dose-dependent, flumazenil-reversible inhibition of VMRs to UBD. bPNS resulted in statistically significant inhibition of VMRs to UBD in hypersensitive rats that had received vehicle injections. Select doses of diazepam and midazolam suppressed the inhibitory effect of bPNS on VMRs.

CONCLUSIONS

This study suggests that inhibitory effects of bPNS on bladder pain could be suppressed in subjects receiving benzodiazepine therapy, suggesting that potential clinical testing of pudendal nerve stimulation for the treatment of painful bladder syndromes may be confounded by the use of benzodiazepines. Clinical assessment of other forms of neuromodulation should also be screened for impacts of benzodiazepines.

Neuromodulatory effects of pudendal nerve stimulation on bladder hypersensitivity are present in opioid-pretreated rats

BACKGROUND AND OBJECTIVES

Bilateral electrical pudendal nerve stimulation (bPNS) reduces bladder hypersensitivity in rat models and anecdotally reduces pain in humans with pelvic pain of urologic origin. Concomitant opioids are known to alter responses to neuromodulation in some systems. So prior to the development of a clinical trial for purposes of regulatory approval, the preclinical interaction between opioids and stimulation effectiveness was examined.

METHODS

Bladder hypersensitivity was produced by neonatal bladder inflammation in rat pups coupled with a second inflammatory insult as an adult. Morphine was administered acutely (1-4 mg/kg intraperitoneal) or chronically (5 mg/kg subcutaneously daily for 2 weeks prior to the terminal experiment). bPNS consisted of bilateral biphasic electrical stimulation of the mixed motor/sensory component of the pudendal nerves. Visceromotor responses (VMR; abdominal muscle contractile responses to urinary bladder distension (UBD)) were used as nociceptive endpoints.

RESULTS

Morphine produced a dose-dependent inhibition of VMRs to UBD that was naloxone reversible. bPNS resulted in statistically significant inhibition of VMRs to UBD in hypersensitive rats that had received acute or chronic subcutaneous morphine injections.

CONCLUSIONS

This study suggests that inhibitory effects of bPNS can still be evoked in subjects who are receiving opioid therapy, thus giving guidance to potential clinical trials seeking regulatory approval for the treatment of chronic bladder pain.

Mechanisms Underlying Overactive Bladder and Interstitial Cystitis/Painful Bladder Syndrome

The bladder is innervated by extrinsic afferents that project into the dorsal horn of the spinal cord, providing sensory input to the micturition centers within the central nervous system. Under normal conditions, the continuous activation of these neurons during bladder distension goes mostly unnoticed. However, for patients with chronic urological disorders such as overactive bladder syndrome (OAB) and interstitial cystitis/painful bladder syndrome (IC/PBS), exaggerated bladder sensation and altered bladder function are common debilitating symptoms. Whilst considered to be separate pathological entities, there is now significant clinical and pre-clinical evidence that both OAB and IC/PBS are related to structural, synaptic, or intrinsic changes in the complex signaling pathways that mediate bladder sensation. This review discusses how urothelial dysfunction, bladder permeability, inflammation, and cross-organ sensitisation between visceral organs can regulate this neuroplasticity. Furthermore, we discuss how the emotional affective component of pain processing, involving dysregulation of the HPA axis and maladaptation to stress, anxiety and depression, can exacerbate aberrant bladder sensation and urological dysfunction. This review reveals the complex nature of urological disorders, highlighting numerous interconnected mechanisms in their pathogenesis. To find appropriate therapeutic treatments for these disorders, it is first essential to understand the mechanisms responsible, incorporating research from every level of the sensory pathway, from bladder to brain.

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.

Spinal mechanisms of pudendal nerve stimulation-induced inhibition of bladder hypersensitivity in rats

Bilateral electrical pudendal nerve stimulation (bPNS) reduces bladder hypersensitivity in rat models of bladder pain and anecdotally reduces pain in humans with pelvic pain of urologic origin. The spinal neurochemical mechanisms of this antinociception are unknown. In the present study, bladder hypersensitivity was produced by neonatal bladder inflammation in rat pups coupled with a second inflammatory insult as an adult. Visceromotor responses (VMRs; abdominal muscle contractions) to urinary bladder distension (UBD) were used as a nociceptive endpoint under urethane-isoflurane anesthesia. bPNS consisted of bilateral biphasic electrical stimulation of the mixed motor/sensory component of the pudendal nerves. Following determination of the inhibitory effect of bPNS on VMRs, pharmacological antagonists were administered via an intrathecal catheter onto the lumbosacral spinal cord and bPNS effects on VMRs redetermined. bPNS resulted in statistically significant inhibition of VMRs to UBD in hypersensitive rats that was statistically reduced by the intrathecal administration of methysergide, WAY100636, CGP35348 and strychnine but was unaffected by naloxone, bicuculline, phentolamine, ondansetron and normal saline. This study suggests that inhibitory effects of bPNS may include serotonergic, GABA-B-ergic and glycinergic mechanisms suggesting the potential for interaction of the neuromodulatory effect with concommitant drug therapies.

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.

Neonatal bladder inflammation induces long-term visceral pain and altered responses of spinal neurons in adult rats

Painful events early in life have been shown to increase the incidence of interstitial cystitis/painful bladder syndrome in adulthood. However, the intrinsic mechanism is not well studied. We previously reported that neonatal bladder inflammation causes chronic visceral hypersensitivity along with molecular disruption of spinal GABAergic system in rats. The present study investigates whether these molecular changes affect the integrative function and responses of bladder-sensitive primary afferent and spinal neurons. Neonatal bladder inflammation was induced by intravesicular injection of zymosan during postnatal (P) days 14-16. In adulthood (P60), the viscero-motor response (VMR) to visceral stimuli was significantly inhibited by intrathecal (i.t) HZ166 (GABA_Aα-2 agonist) only in neonatally saline-treated, but not in neonatally zymosan-treated rats. HZ166 significantly inhibited the responses of bladder-responsive lumbosacral (LS) spinal neurons to urinary bladder distension (UBD) and slow infusion (SI) in neonatally saline-treated rats. Similar results were also observed in naïve adult rats where HZ166 produced significant inhibition of bladder-responsive spinal neurons. However, HZ166 did not inhibit responses of UBD-responsive spinal neurons from neonatally zymosan-treated rats. The drug did not attenuate the responses of UBD-sensitive pelvic nerve afferent (PNA) fibers to UBD and SI in either group of rats tested. Immunohistochemical studies showed a significantly lower level of GABA_Aα-2 receptor expression in the LS spinal cord of neonatally zymosan-treated rats compared to saline-treated rats. These findings indicate that neonatal bladder inflammation leads to functional and molecular alteration of spinal GABA_Aα-2 receptor subtypes, which may result in chronic visceral hyperalgesia in adulthood.

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.

Neonatal vaginal irritation results in long-term visceral and somatic hypersensitivity and increased hypothalamic-pituitary-adrenal axis output in female mice

Neonatal irritation of the vagina permanently sensitizes the vagina and distant somatic structures in a corticotrophin-releasing factor-dependent manner.

Experiencing early life stress or injury increases a woman's likelihood of developing vulvodynia and concomitant dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis. To investigate the outcome of neonatal vaginal irritation (NVI), female mouse pups were administered intravaginal zymosan on postnatal days 8 and 10 and were assessed as adults for vaginal hypersensitivity by measuring the visceromotor response to vaginal balloon distension (VBD). Western blotting and calcium imaging were performed to measure transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1) in the vagina and innervating primary sensory neurons. Serum corticosterone (CORT), mast cell degranulation, and corticotropin-releasing factor receptor 1 (CRF₁) expression were measured as indicators of peripheral HPA axis activation. Colorectal and hind paw sensitivity were measured to determine cross-sensitization resulting from NVI. Adult NVI mice had significantly larger visceromotor response during VBD than naive mice. TRPA1 protein expression was significantly elevated in the vagina, and calcium transients evoked by mustard oil (TRPA1 ligand) or capsaicin (TRPV1 ligand) were significantly decreased in dorsal root ganglion from NVI mice, despite displaying increased depolarization-evoked calcium transients. Serum CORT, vaginal mast cell degranulation, and CRF₁ protein expression were all significantly increased in NVI mice, as were colorectal and hind paw mechanical and thermal sensitivity. Neonatal treatment with a CRF₁ antagonist, NBI 35965, immediately before zymosan administration largely attenuated many of the effects of NVI. These results suggest that NVI produces chronic hypersensitivity of the vagina, as well as of adjacent visceral and distant somatic structures, driven in part by increased HPA axis activation.

The consequences of pain in early life: injury-induced plasticity in developing pain pathways

Pain in infancy influences pain reactivity in later life, but how and why this occurs is poorly understood. Here we review the evidence for developmental plasticity of nociceptive pathways in animal models and discuss the peripheral and central mechanisms that underlie this plasticity. Adults who have experienced neonatal injury display increased pain and injury-induced hyperalgesia in the affected region but mild injury can also induce widespread baseline hyposensitivity across the rest of the body surface, suggesting the involvement of several underlying mechanisms, depending upon the type of early life experience. Peripheral nerve sprouting and dorsal horn central sensitization, disinhibition and neuroimmune priming are discussed in relation to the increased pain and hyperalgesia, while altered descending pain control systems driven, in part, by changes in the stress/HPA axis are discussed in relation to the widespread hypoalgesia. Finally, it is proposed that the endocannabinoid system deserves further attention in the search for mechanisms underlying injury-induced changes in pain processing in infants and children.

Tachykinins and their receptors: contributions to physiological control and the mechanisms of disease

The tachykinins, exemplified by substance P, are one of the most intensively studied neuropeptide families. They comprise a series of structurally related peptides that derive from alternate processing of three Tac genes and are expressed throughout the nervous and immune systems. Tachykinins interact with three neurokinin G protein-coupled receptors. The signaling, trafficking, and regulation of neurokinin receptors have also been topics of intense study. Tachykinins participate in important physiological processes in the nervous, immune, gastrointestinal, respiratory, urogenital, and dermal systems, including inflammation, nociception, smooth muscle contractility, epithelial secretion, and proliferation. They contribute to multiple diseases processes, including acute and chronic inflammation and pain, fibrosis, affective and addictive disorders, functional disorders of the intestine and urinary bladder, infection, and cancer. Neurokinin receptor antagonists are selective, potent, and show efficacy in models of disease. In clinical trials there is a singular success: neurokinin 1 receptor antagonists to treat nausea and vomiting. New information about the involvement of tachykinins in infection, fibrosis, and pruritus justifies further trials. A deeper understanding of disease mechanisms is required for the development of more predictive experimental models, and for the design and interpretation of clinical trials. Knowledge of neurokinin receptor structure, and the development of targeting strategies to disrupt disease-relevant subcellular signaling of neurokinin receptors, may refine the next generation of neurokinin receptor antagonists.

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.

MicroRNA-mediated GABA Aα-1 receptor subunit down-regulation in adult spinal cord following neonatal cystitis-induced chronic visceral pain in rats

The nociceptive transmission under pathological chronic pain conditions involves transcriptional and/or translational alteration in spinal neurotransmitters, receptor expressions, and modification of neuronal functions. Studies indicate the involvement of microRNA (miRNA) - mediated transcriptional deregulation in the pathophysiology of acute and chronic pain. In the present study, we tested the hypothesis that long-term cross-organ colonic hypersensitivity in neonatal zymosan-induced cystitis is due to miRNA-mediated posttranscriptional suppression of the developing spinal GABAergic system. Cystitis was produced by intravesicular injection of zymosan (1% in saline) into the bladder during postnatal (P) days P14 through P16 and spinal dorsal horns (L6-S1) were collected either on P60 (unchallenged groups) or on P30 after a zymosan re-challenge on P29 (re-challenged groups). miRNA arrays and real-time reverse transcription-polymerase chain reaction (RT-PCR) revealed significant, but differential, up-regulation of mature miR-181a in the L6-S1 spinal dorsal horns from zymosan-treated rats compared with saline-treated controls in both the unchallenged and re-challenged groups. The target gene analysis demonstrated multiple complementary binding sites in miR-181a for GABA(A) receptor subunit GABA(Aα-1) gene with a miRSVR score of -1.83. An increase in miR-181a concomitantly resulted in significant down-regulation of GABA(Aα-1) receptor subunit gene and protein expression in adult spinal cords from rats with neonatal cystitis. Intrathecal administration of the GABA(A) receptor agonist muscimol failed to attenuate the viscero-motor response (VMR) to colon distension in rats with neonatal cystitis, whereas in adult zymosan-treated rats the drug produced significant decrease in VMR. These results support an integral role for miRNA-mediated transcriptional deregulation of the GABAergic system in neonatal cystitis-induced chronic pelvic pain.

VEGF induces sensory and motor peripheral plasticity, alters bladder function, and promotes visceral sensitivity

BACKGROUND

This work tests the hypothesis that bladder instillation with vascular endothelial growth factor (VEGF) modulates sensory and motor nerve plasticity, and, consequently, bladder function and visceral sensitivity.In addition to C57BL/6J, ChAT-cre mice were used for visualization of bladder cholinergic nerves. The direct effect of VEGF on the density of sensory nerves expressing the transient receptor potential vanilloid subfamily 1 (TRPV1) and cholinergic nerves (ChAT) was studied one week after one or two intravesical instillations of the growth factor.To study the effects of VEGF on bladder function, mice were intravesically instilled with VEGF and urodynamic evaluation was assessed. VEGF-induced alteration in bladder dorsal root ganglion (DRG) neurons was performed on retrogradly labeled urinary bladder afferents by patch-clamp recording of voltage gated Na+ currents. Determination of VEGF-induced changes in sensitivity to abdominal mechanostimulation was performed by application of von Frey filaments.

RESULTS

In addition to an overwhelming increase in TRPV1 immunoreactivity, VEGF instillation resulted in an increase in ChAT-directed expression of a fluorescent protein in several layers of the urinary bladder. Intravesical VEGF caused a profound change in the function of the urinary bladder: acute VEGF (1 week post VEGF treatment) reduced micturition pressure and longer treatment (2 weeks post-VEGF instillation) caused a substantial reduction in inter-micturition interval. In addition, intravesical VEGF resulted in an up-regulation of voltage gated Na(+) channels (VGSC) in bladder DRG neurons and enhanced abdominal sensitivity to mechanical stimulation.

CONCLUSIONS

For the first time, evidence is presented indicating that VEGF instillation into the mouse bladder promotes a significant increase in peripheral nerve density together with alterations in bladder function and visceral sensitivity. The VEGF pathway is being proposed as a key modulator of neural plasticity in the pelvis and enhanced VEGF content may be associated with visceral hyperalgesia, abdominal discomfort, and/or pelvic pain.

Early in life bladder inflammation alters opioid peptide content in the spinal cord and bladder of adult female rats

PURPOSE

Previous research suggests that a failure of opioid inhibition may contribute to chronic bladder pain. We determined how acute adult and/or prior early in life exposure to bladder inflammation alters the adult content of endogenous opioid peptides in the bladder, spinal cord and blood.

MATERIALS AND METHODS

Inflammation was induced by intravesical administration of zymosan. Female Sprague-Dawley® rats were exposed to anesthesia only or zymosan early in life (postnatal days 14 to 16) and anesthesia only or zymosan as adults (ages 12 to 17 weeks). Thoracolumbar and lumbosacral segments of the spinal cord, and blood and bladders were collected 24 hours after adult treatment. Opioid peptide content was measured using enzyme-linked immunosorbent assay.

RESULTS

Early in life bladder inflammation alone produced a chronic increase in dynorphin A (1-17) in the lumbosacral spinal cord. When early in life inflammation was followed by adult re-inflammation, spinal cord dynorphin remained unchanged but bladder dynorphin was decreased. In addition, early in life inflammation combined with adult bladder inflammation decreased endomorphin-2 content in the thoracolumbar spinal cord. Neither early in life nor adult bladder inflammation affected thoracolumbar dynorphin, serum dynorphin, lumbosacral endomorphin-2 or plasma β-endorphin.

CONCLUSIONS

Several opioid peptides were measured using enzyme-linked immunosorbent assay following early in life and adult bladder inflammation. The changes observed are consistent with the view that early in life bladder inflammation alone can chronically alter spinal cord peptide content. When coupled with adult re-inflammation, these changes could set the neurochemical stage to support bladder hypersensitivity.

O-antigen modulates infection-induced pain states

The molecular initiators of infection-associated pain are not understood. We recently found that uropathogenic E. coli (UPEC) elicited acute pelvic pain in murine urinary tract infection (UTI). UTI pain was due to E. coli lipopolysaccharide (LPS) and its receptor, TLR4, but pain was not correlated with inflammation. LPS is known to drive inflammation by interactions between the acylated lipid A component and TLR4, but the function of the O-antigen polysaccharide in host responses is unknown. Here, we examined the role of O-antigen in pain using cutaneous hypersensitivity (allodynia) to quantify pelvic pain behavior and using sacral spinal cord excitability to quantify central nervous system manifestations in murine UTI. A UPEC mutant defective for O-antigen biosynthesis induced chronic allodynia that persisted long after clearance of transient infections, but wild type UPEC evoked only acute pain. E. coli strains lacking O-antigen gene clusters had a chronic pain phenotype, and expressing cloned O-antigen gene clusters altered the pain phenotype in a predictable manner. Chronic allodynia was abrogated in TLR4-deficient mice, but inflammatory responses in wild type mice were similar among E. coli strains spanning a wide range of pain phenotypes, suggesting that O-antigen modulates pain independent of inflammation. Spinal cords of mice with chronic allodynia exhibited increased spontaneous firing and compromised short-term depression, consistent with centralized pain. Taken together, these findings suggest that O-antigen functions as a rheostat to modulate LPS-associated pain. These observations have implications for an infectious etiology of chronic pain and evolutionary modification of pathogens to alter host behaviors.

Effects of acute adult and early-in-life bladder inflammation on bladder neuropeptides in adult female rats

Background

The purpose of the present study was to determine how acute adult and/or prior early-in life (EIL; P14-P16) exposure to bladder inflammation affects bladder content of calcitonin gene related peptide (CGRP) and substance P (SP). Estrous cycle influences were also studied in the adult-treatment conditions.

Methods

In Experiment 1, intravesical zymosan or isoflurane anesthesia alone was administered to adult female rats. Bladders and serum were collected 24 hours later during each phase of the estrous cycle. In Experiment 2, zymosan or anesthesia alone was administered EIL and as adults, with bladder tissue collection 24 h later.

Results

In general, Experiment 1 showed that bladder content of both CGRP and SP was increased by inflammation. This effect was significant when data were collapsed across all phases of the estrous cycle, but was only significant during proestrus when individual comparisons were made during each phase of estrous. Also, adult bladder inflammation significantly reduced estradiol levels. In Experiment 2, bladder content of CGRP and SP was significantly increased in rats receiving EIL and/or adult inflammation. Bladder weights were also significantly increased by inflammation.

Conclusions

These data indicate that bladder CGRP and SP are maximally increased during the proestrus phase of the estrous cycle in inflamed adult female rats. EIL exposure to bladder inflammation alone can also produce an increase in CGRP and SP lasting into adulthood. Therefore, EIL experience with bladder inflammation may predispose an organism to experience a painful bladder disorder as an adult by increasing primary afferent content of CGRP and/or SP.

Neonatal cystitis-induced colonic hypersensitivity in adult rats: a model of viscero-visceral convergence

BACKGROUND

The objective of this study was to determine if neonatal cystitis alters colonic sensitivity later in life and to investigate the role of peripheral mechanisms.

METHODS

Neonatal rats received intravesical zymosan, normal saline, or anesthesia only for three consecutive days [(postnatal (PN) days 14-16)]. The estrous cycle phase was determined prior to recording the visceromotor response (VMR) to colorectal distension (CRD) in adult rats. Eosinophils and mast cells were examined from colon and bladder tissues. CRD- or urinary bladder distension (UBD)-sensitive pelvic nerve afferents (PNAs) were identified and their responses to distension were examined. The relative expression of N-methyl-d-aspartic acid (NMDA)-NR1 subunit in the lumbo-sacral (L6-S1) spinal cord was examined using Western blot.

KEY RESULTS

The VMR to CRD (≥10mmHg) in the neonatal zymosan group was significantly higher than control in both the diestrus, estrus phase and in all phases combined. There was no difference in the total number of eosinophils, mast cells or number of degranulated mast cells between groups. The spontaneous firing of UBD, but not CRD-sensitive PNAs from the zymosan-treated rats was significantly higher than the saline-treated control. However, the mechanosensitive properties of PNAs to CRD or UBD were no different between groups (P>0.05). The expression of spinal NR1 subunit was significantly higher in zymosan-treated rats compared with saline-treated rats (P<0.05).

CONCLUSIONS & INFERENCES

Neonatal cystitis results in colonic hypersensitivity in adult rats without changing tissue histology or the mechanosensitive properties of CRD-sensitive PNAs. Neonatal cystitis does result in overexpression of spinal NR1 subunit in adult rats.

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.