Inflammation and enhanced nociceptive responses to bladder distension produced by intravesical zymosan in the rat

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.

TRPV1 and TRPM8 antagonists reduce cystitis-induced bladder hypersensitivity via inhibition of different sensitised classes of bladder afferents in guinea pigs

BACKGROUND AND PURPOSE

Interstitial cystitis (=painful bladder syndrome) is a chronic bladder syndrome characterised by pelvic and bladder pain, urinary frequency and urgency, and nocturia. Transient receptor potential (TRP) channels are an attractive target in reducing the pain associated with interstitial cystitis. The current study aims to determine the efficacy of combination of TRP vanilloid 1 (TRPV1) and TRP melastatin 8 (TRPM8) channel inhibition in reducing the pain associated with experimental cystitis in guinea pigs.

EXPERIMENTAL APPROACH

A novel animal model of non-ulcerative interstitial cystitis has been developed using protamine sulfate/zymosan in female guinea pigs. Continuous voiding cystometry was performed in conscious guinea pigs. Ex vivo "close-to-target" single unit extracellular recordings were made from fine branches of pelvic nerves entering the guinea pig bladder. Visceromotor responses in vivo were used to determine the effects of TRP channel antagonists on cystitis-induced bladder hypersensitivity.

KEY RESULTS

Protamine sulfate/zymosan treatment evoked mild inflammation in the bladder and increased micturition frequency in conscious animals. In cystitis, high threshold muscular afferents were sensitised via up-regulation of TRPV1 channels, high threshold muscular-mucosal afferents were sensitised via TRPM8 channels, and mucosal afferents by both. Visceromotor responses evoked by noxious bladder distension were significantly enhanced in cystitis and were returned to control levels upon administration of combination of low doses of TRPV1 and TRPM8 antagonists.

CONCLUSIONS AND IMPLICATIONS

The data demonstrate the therapeutic promises of combination of TRPV1 and TRPM8 antagonists for the treatment of bladder hypersensitivity in cystitis.

Parametric Assessment of Spinal Cord Stimulation on Bladder Pain-Like Responses in Rats

OBJECTIVES

Spinal cord stimulation (SCS) for the treatment of pelvic visceral pains has been understudied and underused. The goal of the current study was to examine multiple stimulation parameters of SCS to determine optimal settings for the inhibition of responses to urinary bladder distension (UBD) in animal models of bladder pain as a guide for human studies.

MATERIALS AND METHODS

Adult, female isoflurane/urethane-anesthetized rats underwent a T13/L1 mini-laminectomy sufficient to implant an SCS paddle lead for neuromodulation. Silver wire electrodes were inserted into the external oblique musculature. A 22-gauge angiocatheter was placed transurethrally into the bladder and used to deliver phasic, air UBDs at pressures of 10 to 60 mm Hg and visceromotor (abdominal contractile) electromyographic responses to UBD measured in the presence and absence of SCS. Electromyographic activity was quantified using standard differential amplification and rectification. Parameter settings for SCS included both conventional (10, 50, 100 Hz) and high frequency (1,000, 5,000, and 10,000 Hz) biphasic square wave pulses with 50 to 200 μs durations. To create states of hypersensitivity, pretreatment of adult rats included an intravesical zymosan infusion 24 hours before testing with and without a preceding episode of neonatal bladder inflammation.

RESULTS

Low frequency (10, 50, and 100 Hz) 200 μs biphasic pulses at submotor thresholds demonstrated inhibition of visceromotor responses (VMRs) to UBD in rats made hypersensitive to UBD by a protocol that included neonatal cystitis. Onset of inhibitory effects occurred within 20 minutes of beginning SCS. Otherwise, SCS at all other parameters studied and in other tested rat models produced either no significant effect or augmentation of VMRs.

CONCLUSIONS

Demonstration of inhibitory effects of SCS in a clinically relevant model of bladder pain suggests the potential utility of this therapy in patients with painful bladder disorders.

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.

Beneficial effect of Bletilla striata extract solution on zymosan-induced interstitial cystitis in rat

AIMS

Interstitial cystitis (IC) is a chronic pain syndrome that is characterized by suprapubic pain upon bladder filling. Bletilla striata, a well-known traditional Chinese herb with established efficacy in wound healing and anti-inflammation, was hypothesized to improve the symptoms of IC possibly though forming a physical barrier that could isolate the bladder tissue from irritants. This study was conducted to evaluate the beneficial effects of intravesical treatment with B. striata extract solution (BSES) on visceral pain and bladder function of rats with zymosan-induced IC.

METHODS

Thirty female rats were randomly divided into control group, zymosan-induced cystitis rats treated with normal saline (Z + NS), and zymosan-induced cystitis rats treated with BSES (Z + BSES). All rats underwent evaluation for abdominal withdrawal reflex (AWR) scores to assess visceral hypersensitivity, cystometrography, and electromyogram (EMG) of both external urethral sphincter and bladder detrusor. Data were analyzed by one way analysis of variance.

RESULTS

The Z + NS group had an increased visceral hypersensitivity as compared to control group. Rats treated with BSES (Z + BSES group) had decreased AWR scores and amplitude of bladder detrusor-EMG. Besides, BSES treatment improved overactive bladder with significant effects on the extend of micturition interval and increase of storage of urine.

CONCLUSIONS

Intravesical instillation of BSES can significantly alleviate zymosan-induced visceral hypersensitivity and bladder overactivity associated with IC. This study suggested that intravesical instillation with BSES might be a promising treatment for IC.

Functional activities of beta-glucans in the prevention or treatment of cervical cancer

Cervical cancer is the fourth-ranked cancer in the world and is associated with a large number of deaths annually. Chemotherapy and radiotherapy are known as the common therapeutic approaches in the treatment of cervical cancer, but because of their side effects and toxicity, researchers are trying to discovery alternative therapies. Beta-glucans, a group of glucose polymers that are derived from the cell wall of fungi, bacteria, and etc. it has been showed that beta-glucans have some anti-cancer properties which due to their impacts on adaptive and innate immunity. Along to these impacts, these molecules could be used as drug carriers. In this regard, the application of beta-glucans is a promising therapeutic option for the cancer prevention and treatment especially for cervical cancer. Herein, we have summarized the therapeutic potential of beta-glucans alone or as adjuvant therapy in the treatment of cervical cancer. Moreover, we highlighted beta-glucans as drug carriers for preventive and therapeutic purposes.

Functional activities of beta-glucans in the prevention or treatment of cervical cancer

Cervical cancer is the fourth-ranked cancer in the world and is associated with a large number of deaths annually. Chemotherapy and radiotherapy are known as the common therapeutic approaches in the treatment of cervical cancer, but because of their side effects and toxicity, researchers are trying to discovery alternative therapies. Beta-glucans, a group of glucose polymers that are derived from the cell wall of fungi, bacteria, and etc. it has been showed that beta-glucans have some anti-cancer properties which due to their impacts on adaptive and innate immunity. Along to these impacts, these molecules could be used as drug carriers. In this regard, the application of beta-glucans is a promising therapeutic option for the cancer prevention and treatment especially for cervical cancer. Herein, we have summarized the therapeutic potential of beta-glucans alone or as adjuvant therapy in the treatment of cervical cancer. Moreover, we highlighted beta-glucans as drug carriers for preventive and therapeutic purposes.

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.

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.

Intrathecal oxytocin inhibits visceromotor reflex and spinal neuronal responses to noxious distention of the rat urinary bladder

BACKGROUND AND OBJECTIVES

Oxytocin (OXY) is a neuropeptide that has recently been recognized as an important component of descending analgesic systems. The present study sought to determine if OXY produces antinociception to noxious visceral stimulation.

METHODS

Urethane-anesthetized female rats had intrathecal catheters placed acutely, and the effect of intrathecal OXY on visceromotor reflexes (VMRs; abdominal muscular contractions quantified using electromyograms) to urinary bladder distension (UBD; 10-60 mm Hg, 20 seconds; transurethral intravesical catheter) was determined. The effect of OXY applied to the surface of exposed spinal cord was determined in lumbosacral dorsal horn neurons excited by UBD using extracellular recordings.

RESULTS

Oxytocin doses of 0.15 or 1.5 μg inhibited VMRs to UBD by 37% ± 8% and 68% ± 10%, respectively. Peak inhibition occurred within 30 minutes and was sustained for at least 60 minutes. The effect of OXY was both reversed and prevented by the intrathecal administration of an OXY-receptor antagonist. Application of 0.5 mM OXY to the dorsum of the spinal cord inhibited UBD-evoked action potentials by 76% ± 12%. Consistent with the VMR studies, peak inhibition occurred within 30 minutes and was sustained for greater than 60 minutes.

CONCLUSIONS

These results argue that intrathecal OXY produces an OXY receptor-specific antinociception to noxious UBD, with part of this effect due to inhibition of spinal dorsal horn neurons. To our knowledge, these studies provide the first evidence that intrathecal OXY may be an effective pharmacological treatment for visceral pain.

Visceral pain: the ins and outs, the ups and downs

PURPOSE OF REVIEW

Visceral pain represents a major clinical problem, yet far less is known about its mechanisms compared with somatic pains, for example, from cutaneous and muscular structures.

RECENT FINDINGS

In this review, we describe the neuroanatomical bases of visceral pain signalling in the peripheral and central nervous system, comparing to somatic pains and also the channels and receptors involved in these events. We include an overview of potential new targets in the context of mechanisms of visceral pain and hypersensitivity.

SUMMARY

This review should inform on the recognition of what occurs in patients with visceral pain, why comorbidities are common and how analgesic treatments work.

Activation of spinal extracellular signal-regulated kinases (ERK) 1/2 is associated with the development of visceral hyperalgesia of the bladder

Activation of extracellular signal-regulated kinases (ERK) 1/2 in dorsal horn neurons is important for the development of somatic hypersensitivity and spinal central sensitization after peripheral inflammation. However, data regarding the roles of spinal ERK1/2 in the development of visceral hyperalgesia are sparse. Here we studied the activation of ERK1/2 in the lumbosacral spinal cord after innocuous and noxious distention of the inflamed (cyclophosphamide-treated) and noninflamed urinary bladder in mice. We also correlated the spinal ERK1/2 activation to distention-evoked bladder nociception as quantified by the abdominal visceromotor response (VMR). Cyclophosphamide treatment (bladder inflammation) evoked increased bladder hyperalgesia and allodynia to bladder distention, as evident from an upward and leftward shift of the VMR stimulus-response curve compared with that of noninflamed mice. Development of bladder hyperalgesia was associated with robust enhancement of ERK1/2 activation in the dorsal horn and deeper laminae bilaterally in the L6-S1 spinal cord. Functional blockade of spinal ERK1/2 activity via intrathecal administration of the upstream MEK inhibitor U0126 attenuated distention-evoked bladder nociception and caused a significant downward shift of the VMR stimulus-response curve. In summary, we have provided functional and immunohistochemical evidence that activation of lumbosacral spinal ERK1/2 is associated with the development of primary visceral (bladder) hyperalgesia. Our results suggest that aberrant processing of visceral nociceptive information at the level of the lumbosacral spinal cord via activation of ERK1/2 signaling may contribute to chronic bladder pain in the context of inflammation.

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.

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.

All-trans-retinoic acid and Erk1/2 signaling synergistically regulate the expression of CD300B in human monocytic cells

The regulation of the cell-surface receptors that constitute the gene cluster, CD300, also known as the Myeloid Activating/Inhibitory Receptor (MAIR) family, is poorly understood. In the present study, we tested the hypothesis that all-trans-RA (RA), a bioactive form of vitamin A long recognized for its role in regulation of immune cell activities, may be a potent regulator of the expression of human CD300B. In monocytic THP-1 cells, RA (20nM) alone significantly increased CD300B mRNA within 2h and up to 20-fold after 24h; however, CD300B protein determined by flow cytometry and confocal microscopy showed little change. A search for coactivating molecules revealed that phorbol myristyl acetate (PMA), a mimetic of diacylglycerol, alone increased CD300B mRNA by less than 5-fold; however, the combination of at-RA and PMA increased CD300B mRNA nearly 60-fold. Moreover, CD300B protein was increased. CD300B molecules were mainly located on the plasma membrane and in the endosomal compartment, sharing a distribution/recycling pattern similar to transferrin receptor CD71. The induction of CD300B mRNA by PMA required signaling through the MEK/ERK branch of the MAP kinase pathway, as PD98059, a MEK1/2 inhibitor, abrogated this response, while SB203580, an inhibitor of the p38 pathway, had no effect. Our data suggest a model in which RA alone induces a CD300B mRNA response in which transcripts accumulate but remain untranslated and therefore "sterile," whereas RA combined with signals from the ERK1/2 pathway results in both increased CD300B transcription and protein expression on the cell surface and in endocytic vesicles.

Neonatal bladder inflammation alters activity of adult rat spinal visceral nociceptive neurons

PURPOSE

This investigation examined the effect of inflammation produced by intravesical zymosan during the neonatal period on spinal dorsal horn neuronal responses to urinary bladder distension (UBD) as adults.

METHODS

Female rat pups (P14-P16) were treated with intravesical zymosan or with anesthesia-only. These groups of rats were subdivided forming four groups: half received intravesical zymosan as adults and half received anesthesia-only. One day later, rats were anesthetized, the spinal cord was transected at a cervical level and extracellular single-unit recordings of L6-S1 dorsal horn neurons were obtained. Neurons were classified as Type I--inhibited by heterotopic noxious conditioning stimuli (HNCS) or as Type II--not inhibited by HNCS--and were characterized for Spontaneous Activity and responses to graded UBD (20-60 mm Hg).

RESULTS

227 spinal dorsal horn neurons excited by UBD were characterized. In rats treated as neonates with anesthesia-only, Type II neurons demonstrated increased spontaneous and UBD-evoked activity following adult intravesical zymosan treatment whereas Type I neurons demonstrated decreased spontaneous and UBD-evoked activity relative to controls. In rats treated as neonates with intravesical zymosan, the spontaneous and UBD-evoked activity of both Type I and Type II neurons increased following adult intravesical zymosan treatment relative to controls.

CONCLUSIONS

Neonatal bladder inflammation alters subsequent effects of acute bladder inflammation on spinal dorsal horn neurons excited by UBD such that overall there is greater sensory neuron activation. This may explain the visceral hypersensitivity noted in this model system and suggest that impaired inhibitory systems may be responsible.

Effect of estrogen on bladder nociception in rats

PURPOSE

We assessed the effect of ovariectomy and estrogen replacement on nociceptive responses to bladder distention in a rat model.

MATERIALS AND METHODS

Female Sprague-Dawley rats (Harlan) underwent ovariectomy or sham surgery. Visceromotor responses (abdominal contractions) to bladder distention were determined 3 to 4 weeks later under isoflurane anesthesia. In rat subsets estrogen was chronically replaced with a subcutaneous estrogen pellet vs a placebo pellet or acutely replaced by subcutaneous injection 24 hours before testing. Effects of estrogen withdrawal were examined in another group of rats by implanting a pellet and explanting the pellet 24 hours before testing. Uterine weight was measured to assess the estrogen dose.

RESULTS

Visceromotor responses to bladder distention were significantly less vigorous in ovariectomized rats vs controls. Acute estrogen replacement increased visceromotor responses in these rats but chronic estrogen replacement did not. Sudden chronic estrogen withdrawal resulted in increased visceromotor responses. Uterine weight was consistent with the physiological estrogen dose.

CONCLUSIONS

Estrogen alone was not sufficient to produce increased nociceptive responses but an acute decrease in estrogen resulted in increased visceromotor responses. These data suggest that the pronociceptive effects of estrogen may be due to a mismatch between peripheral vs central and/or genomic vs nongenomic effects of the hormone, which occur during rapidly decreasing estrogen levels.

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

Neonatal bladder inflammation has been demonstrated to produce hypersensitivity to bladder re-inflammation as an adult. The purpose of this study was to investigate the effects of neonatal urinary bladder inflammation on adult bladder function and structure. Female Sprague-Dawley rats were treated on postnatal days 14 to 16 with intravesical zymosan or anesthesia alone. At 12 to 16 weeks of age, micturition frequency and cystometrograms were measured. Similarly treated rats had their bladders removed for measurement of plasma extravasation after intravesical mustard oil, for neuropeptide analysis (calcitonin gene-related peptide or Substance P) or for detailed histological examination. Rats treated with zymosan as neonates exhibited increased micturition frequency, reduced micturition volume thresholds, greater extravasation of Evans blue after intravesical mustard oil administration, and greater total bladder content of calcitonin gene-related peptide and Substance P. In contrast, there were no quantitative histological changes in the thickness, fibrosis, or mast cells of bladder tissue due to neonatal zymosan treatments. Functional changes in urologic systems observed in adulthood, coupled with the increased neuropeptide content and neurogenic plasma extravasation in adult bladders, suggest that the neonatal bladder inflammation treatment enhanced the number, function, and/or neurochemical content of primary afferent neurons. These data support the hypothesis that insults to the urologic system in infancy may contribute to the development of adult bladder hypersensitivity.

PERSPECTIVE

Inflammation of the bladder early in life in the rat has multiple sequelae, including laboratory measures that suggest an alteration of the neurophysiological substrates related to the bladder. Some painful bladder syndromes in humans have similar characteristics and so may be due to similar mechanisms.

Visceral pain: the neurophysiological mechanism

The mechanism of visceral pain is still less understood compared with that of somatic pain. This is primarily due to the diverse nature of visceral pain compounded by multiple factors such as sexual dimorphism, psychological stress, genetic trait, and the nature of predisposed disease. Due to multiple contributing factors there is an enormous challenge to develop animal models that ideally mimic the exact disease condition. In spite of that, it is well recognized that visceral hypersensitivity can occur due to (1) sensitization of primary sensory afferents innervating the viscera, (2) hyperexcitability of spinal ascending neurons (central sensitization) receiving synaptic input from the viscera, and (3) dysregulation of descending pathways that modulate spinal nociceptive transmission. Depending on the type of stimulus condition, different neural pathways are involved in chronic pain. In early-life psychological stress such as maternal separation, chronic pain occurs later in life due to dysregulation of the hypothalamic-pituitary-adrenal axis and significant increase in corticotrophin releasing factor (CRF) secretion. In contrast, in early-life inflammatory conditions such as colitis and cystitis, there is dysregulation of the descending opioidergic system that results excessive pain perception (i.e., visceral hyperalgesia). Functional bowel disorders and chronic pelvic pain represent unexplained pain that is not associated with identifiable organic diseases. Often pain overlaps between two organs and approximately 35% of patients with chronic pelvic pain showed significant improvement when treated for functional bowel disorders. Animal studies have documented that two main components such as (1) dichotomy of primary afferent fibers innervating two pelvic organs and (2) common convergence of two afferent fibers onto a spinal dorsal horn are contributing factors for organ-to-organ pain overlap. With reports emerging about the varieties of peptide molecules involved in the pathological conditions of visceral pain, it is expected that better therapy will be achieved relatively soon to manage chronic visceral pain.

Acute bladder inflammation differentially affects rat spinal visceral nociceptive neurons

The present investigation examined the effect of inflammation produced by intravesical zymosan on spinal dorsal horn neuronal responses to urinary bladder distension (UBD). Extracellular single-unit recordings of neurons excited by UBD were obtained in spinalized female Sprague-Dawley rats. Neurons were classified as Type I-inhibited by heterotopic noxious conditioning stimuli (HNCS) or as Type II-not inhibited by a HNCS. In Experiment 1-following neuronal characterization, 1% zymosan was infused into the bladder and after 2h spinal units were recharacterized. Control rats received intravesical saline or subcutaneous zymosan. In Experiment 2-rats were pretreated with intravesical zymosan 24h prior to surgical preparation. Control rats received anesthesia only. 137 spinal dorsal horn neurons excited by UBD were characterized. In comparison with controls, Type II neurons demonstrated increased spontaneous and UBD-evoked activity following intravesical zymosan treatment (both Experiments 1 and 2) whereas Type I neurons demonstrated either no change (Experiment 1) or decreased activity (Experiment 2) following bladder inflammation. No significant changes were noted in neuronal activity in control experiments. Inflammation differentially affects subpopulations of spinal dorsal horn neurons excited by UBD that can be differentiated according to the effect of HNCS. This results in an altered pattern of spinal sensory transmission that may serve as the mechanism for the generation of visceral nociception.

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

Stress-induced hyperalgesia (SIH), a common clinical observation associated with multiple painful diseases including functional urinary disorders, presently has no mechanistic explanation. Using a footshock treatment, a classic stressor, to magnify physiological responses in a model of urinary bladder pain, we examined one potential group of mediators of SIH, the corticotropin-releasing factor (CRF)-related neuropeptides. Exposure to a footshock treatment produced bladder hypersensitivity in female Sprague-Dawley rats, manifested as significantly more vigorous visceromotor responses (VMRs) to urinary bladder distension (UBD) compared with rats that were exposed to a non-footshock treatment. This bladder hypersensitivity was significantly attenuated by blocking spinal CRF(2) receptors but not CRF(1) receptors. Furthermore, spinal administration of urocortin 2, a CRF(2) receptor agonist, augmented UBD-evoked VMRs in a way similar to what was observed after exposure to Footshock, an effect significantly attenuated by pretreatment with spinal aSVG30, a CRF(2) receptor antagonist. Surprisingly, neither spinal administration of CRF nor the CRF(1) receptor antagonist antalarmin had an effect on bladder nociceptive responses. The results of the present study not only provide further support for a role of stress in the exacerbation of bladder pain but also implicate spinal urocortins and their endogenous receptor, the CRF(2) receptor, as potential mediators of this effect.

PERSPECTIVE

This study presents evidence that spinal urocortins and CRF(2) receptors are involved in stress-induced hypersensitivity related to the urinary bladder. This provides a basis for investigating how urocortins mediate SIH, ultimately leading to more effective treatment options for patients with painful bladder syndromes as well as stress-exacerbated chronic pain.

Serotonergic and noradrenergic facilitation of the visceromotor reflex evoked by urinary bladder distension in rats with inflamed bladders

Bladder inflammation resulting from intravesical administration of zymosan significantly enhances the visceromotor reflex (VMR) evoked by urinary bladder distension (UBD). The present study examined whether intrathecal (i.t.) administration of receptor antagonists to either norepinephrine (NE) or serotonin (5-HT) altered this enhancement effect. I.t. administration of the non-specific 5-HT receptor antagonist methysergide (30 microg), the 5-HT(3) receptor antagonist ondansetron, or the 5-HT(1A) receptor antagonist WAY 100635 eliminated the enhancement effect produced by intravesical zymosan and also tended to reduce electromyographic (EMG) responses to UBD in non-inflamed rats. I.t. administration of either the non-specific NE receptor antagonist phentolamine (30 microg) or the alpha(1) antagonist WB 4101 also eliminated the enhancement effect, whereas i.t. administration of the alpha(2) antagonist yohimbine failed to significantly affect the enhancement effect. The effects of phentolamine and methysergide were not mediated by changes in bladder compliance. This is the first study to demonstrate that bladder hypersensitivity resulting from bladder inflammation is partly mediated by 5-HT and NE facilitatory effects. Based on these and previous findings we conclude that the net nociceptive response to bladder distension under conditions of bladder inflammation represents a complex interaction of facilitatory influences of spinal 5-HT and NE, and inhibitory influences of spinal opioids.

Rostral ventral medulla modulation of the visceromotor reflex evoked by urinary bladder distension in female rats

The present studies examined the involvement of the rostral ventral medulla (RVM) in modulating the visceromotor response (VMR) evoked by urinary bladder distension (UBD) in adult female rats. The VMR was indexed by electromyographic (EMG) responses of the abdominal external oblique muscle to UBD. Experiment 1 showed that the predominant effect of electrical stimulation of the RVM in normal rats was to produce intensity-dependent inhibition of the VMR (54% of sites sampled). Facilitatory, biphasic, or no effects were obtained at the remaining sites. Experiment 2 showed that RVM-induced inhibition of the VMR was significantly attenuated by intraperitoneal (i.p.) administration of naloxone but not saline vehicle. In experiment 3, we examined the effect of lesions of the RVM in rats with inflamed bladders because previous research has shown that an endogenous opioid inhibitory system is engaged by bladder inflammation. Electrolytic lesions of the RVM but not sham lesions of the RVM significantly increased the VMR to graded UBD in rats with augmented VMRs induced by prior inflammation of the bladder. The present data suggest that the RVM can inhibit the VMR to UBD, acting in part via an opioid-inhibitory system, and that bladder inflammation can recruit the RVM to produce a net inhibitory effect on the VMR to UBD.

PERSPECTIVE

Stimulation of the RVM resulted in inhibitory, facilitatory, and biphasic modulation of the visceromotor reflex to urinary bladder distension. Inhibitory effects of stimulation were attenuated by naloxone, and lesions of the RVM enhanced the VMR in rats with inflamed bladders. These data indicate an important role of the RVM in modulating bladder pain.

Pharmacologic evaluation of pressor and visceromotor reflex responses to bladder distension

AIMS

Several mechanisms that are involved in acute rat bladder nociception were examined. The nociceptive response was measured by analyzing both cardiovascular and visceromotor reflex responses to urinary bladder distension. The contributions of micro-opioid receptor, kappa-opioid receptor, sodium channels, muscarinic receptors, and cyclooxygenase, were explored with morphine, U50,488, mexiletine, oxybutynin, and naproxen, respectively.

METHODS

Female Sprague-Dawley rats were acutely instrumented with jugular venous, carotid arterial, and bladder cannulas. Needle electrodes were placed directly into the abdominal musculature to measure myoelectrical activity subsequent to repeated phasic urinary bladder distension (60 mmHg for 20 sec in 3 min intervals) under 1% isoflurane. Drugs were administered by i.v. bolus injection 2 min prior to distension.

RESULTS

The analgesics morphine (ID50 0.69 mg/kg), U50,488 (1.34 mg/kg), and mexiletine (2.60 mg/kg) significantly inhibited the visceromotor reflex response to noxious urinary bladder distension. Oxybutynin also attenuated reflex responses to noxious urinary bladder distension to 41% of the maximal pressor response and 32% of the control visceromotor reflex response (3.01 and 5.05 mg/kg), respectively, indicating a role of muscarinic receptors in bladder nociception. Naproxen did not attenuate the pressor response, but moderately inhibited visceromotor reflex to 45% of control at 30 mg/kg (P < 0.05).

CONCLUSIONS

Current results using the rat urinary bladder distension model are consistent with previous research demonstrating a role of the analgesics (morphine, U50,488, and mexiletine) in the inhibition of visceral nociceptive transmission. The utility of the reflex responses to urinary bladder distension may provide a method useful to examine mechanisms which target the bladder sensory pathway.

Inflammation-induced enhancement of the visceromotor reflex to urinary bladder distention: modulation by endogenous opioids and the effects of early-in-life experience with bladder inflammation

Abdominal electromyographic (EMG) responses to noxious intensities of urinary bladder distention (UBD) are significantly enhanced 24 hours after zymosan-induced bladder inflammation in adult female rats. This inflammation-induced hypersensitivity is concomitantly inhibited by endogenous opioids because intraperitoneal (i.p.) naloxone administration before testing significantly increases EMG response magnitude to UBD. This inhibitory mechanism is not tonically active because naloxone does not alter EMG response magnitude to UBD in rats without inflammation. At the dose tested, naloxone does not affect bladder compliance in rats with or without inflammation. The effects of i.p. naloxone probably result from blockade of a spinal mechanism because intrathecal naloxone also significantly enhances EMG responses to UBD in rats with inflammation. Rats exposed to bladder inflammation from P90-P92 before reinflammation at P120 show similar hypersensitivity and concomitant opioid inhibition, with response magnitudes being no different from that produced by inflammation at P120 alone. In contrast, rats exposed to bladder inflammation from P14-P16 before reinflammation at P120 show markedly enhanced hypersensitivity and no evidence of concomitant opioid inhibition. These data indicate that bladder inflammation in adult rats induces bladder hypersensitivity that is inhibited by an endogenous opioidergic mechanism. This mechanism can be disrupted by neonatal bladder inflammation.

PERSPECTIVE

The present study observed that bladder hypersensitivity resulting from acute bladder inflammation is suppressed by an opioid-inhibitory mechanism. Experiencing bladder inflammation during the neonatal period can impair the expression of this opioid inhibitory mechanism in adulthood. This suggests that bladder insults during development may permanently alter visceral sensory systems and may represent 1 cause of painful bladder disorders.

Neonatal Urinary Bladder Inflammation Produces Adult Bladder Hypersensitivity

Inflammatory events experienced during early development may permanently alter sensory processing. Because urinary tract infections frequently occur during early development in females and painful bladder disorders have a high female prevalence, the present studies were undertaken to determine whether inflammation of the bladder in female rats could lead to altered sensory processing later in life. Female rat pups were anesthetized and treated as neonates (14th-16th days of life) or as adolescents (28th-30th days of life) with either intravesical zymosan (yeast cell wall component that produces robust inflammation), intravesical normal saline, or only with anesthesia. As adults, rats that had their bladders inflamed as neonates exhibited increased spontaneous micturition frequency and, after reinflammation of the bladder, increased cardiovascular and abdominal muscle contractile responses to urinary bladder distension when compared with controls. Similar effects were not observed in rats which did not experience inflammation of the bladder until adolescence. Evan's blue extravasation, a measure of the magnitude of inflammatory changes, was also greater in rats treated as neonates with intravesical zymosan. Thermal and mechanical hindpaw sensitivity was not altered by bladder inflammation. Altogether, this suggests that neonatal bladder inflammation increases bladder sensitivity and may be a cause of the hypersensitivity of painful bladder syndromes.

PERSPECTIVE

The present study observed that bladder inflammation experienced in a neonatal rat led to accentuated responses to urinary bladder distension when tested as adults. This suggests that events experienced during development may permanently sensitize visceral sensory systems and so represent one of the causes of painful bladder disorders.