Functional and molecular characterisation of the bilateral pelvic nerve crush injury rat model for neurogenic detrusor underactivity

Statin administration ameliorates ischemia-induced overactive bladder with improvement of blood flow and anti-inflammatory effects in rats

AIMS

Statins are widely used to treat dyslipidemia and have been shown to reduce the risk of ischemic heart disease and cerebrovascular disease. The effects of statins on ischemia-induced overactive bladder (OAB) and the associated mechanisms were investigated in a rat model of chronic pelvic ischemia.

METHODS

A pelvic ischemia model was created by iliac arterial injury (AI) and a high-fat diet using male Sprague-Dawley rats. Rats were assigned to 3 groups: control group, AI group, and AI + statin group. The control group underwent sham operation and was fed a normal diet. The AI group underwent AI surgery and was fed a high-cholesterol diet. The AI + statin group was administered a statin for 4 weeks. Cystometry was performed for 8 weeks after surgery. Blood flow was evaluated by laser meter. Thickness of the iliac arteries was measured, and microvascular density in the lamina propria was evaluated by immunostaining for CD31. Expressions of inflammatory cytokines in the bladder were measured by real-time PCR.

RESULTS

Cystometry showed a significantly shorter voiding interval and lower bladder capacity in the AI group than in the control group. The AI + statin group showed improvement of these findings. The AI group showed decreased bladder blood flow, increased iliac arterial wall thickening, and decreased microvascular density compared to the control group. Statin administration improved blood flow. Iliac arterial wall thickening was suppressed, and microvascular density was increased by statin administration, though not significantly. Real-time PCR showed significantly higher expressions of inflammatory cytokines (IL-6, IL-8, and TNF-α) in the AI group than in the control group, and IL-6 and IL-8 expressions were lower in the AI + statin group than in the AI group.

CONCLUSIONS

The present results suggest that statins are effective in OAB caused by arteriosclerosis and ischemia. The mechanism of their effects involves improved bladder blood flow and decreased bladder inflammation.

Transcriptomics Reveals Molecular Features of the Bilateral Pelvic Nerve Injury Rat Model of Detrusor Underactivity

The pathogenesis of detrusor underactivity (DU) is unclear, and the available therapeutic effects are unsatisfactory. We propose to find key molecules and pathways related to DU based on transcriptome sequencing. A rat model of bilateral pelvic nerve injury (BPNI) was established. Bladder tissues from the sham-operated group, 3 and 28 days after BPNI mapping, were taken for urodynamics, histopathology, and RNA-seq. An enrichment analysis of the screened differential expression genes was performed. Three days after BPNI, the results showed urodynamic features of overflow incontinence, while there was a recovery at 28 days after the operation. Masson staining revealed collagen deposition accompanied by progressive thickening of the smooth muscle layer as DU progressed. RNA-seq results suggested that a total of 1808 differentially expressed genes (DEGs) differed among the groups. RNA-seq and subsequent analysis confirmed that the cell cycle and immune response were significantly activated 3 days after BPNI, while extracellular matrix remodeling occurred 28 days after BPNI. Partial DEGs and pathways were verified by qRT-PCR. Validation of key proteins involved in cell cycle, inflammation, and fibrosis was performed by immunohistochemical staining and western blot, respectively. These molecular expression patterns at different time points after BPNI injury provide valuable insights into the search for therapeutic targets for DU.

Effect of β3-adrenoceptor agonist on the micromotion of bilateral major pelvic ganglion-excised rat bladder

AIMS

Micromotion is an autonomous intramural movement of the bladder, and is believed to be an initial step in the generation of urinary urgency. Therefore, controlling micromotion may be a novel target in overactive bladder (OAB) treatment. However, developing micromotion treatment has been limited by the absence of a standardized animal model. We attempted to create a micromotion animal model and investigated the effectiveness of a β₃ -adrenoceptor agonist (CL316,243) on micromotion.

METHODS

Bilateral major pelvic ganglia (MPGs) were excised in 18 male Sprague-Dawley rats, resulting in an almost completely denervated bladder. On postoperative Day 7, cystometry was performed. Rats were divided into three treatment groups: CL316,243; β_3- adrenoceptor antagonist (SR59230A) pretreated CL316,243; and a nonselective antimuscarinic agent (oxybutynin). Changes in micromotion were evaluated after the intra-arterial administration of each agent.

RESULTS

Low-amplitude oscillations in intravesical pressure (micromotion) were observed 1 week after MPGs excision. Micromotion frequency significantly (p = 0.003) decreased (2.17 ± 3.54 times/5 min) with CL316,243 compared with vehicle (6.33 ± 1.97 times/5 min). Micromotion amplitude also decreased with CL316,243 (1.15 ± 1.93 cmH₂ O) compared with vehicle (5.96 ± 5.12 cmH₂ O), approaching conventional significance (p = 0.090). No significant decreases in frequency or amplitude were observed with oxybutynin treatment.

CONCLUSIONS

Systemic administration of the β₃ -adrenoceptor agonist CL316,243 effectively controlled micromotion in bilateral MPGs-excised, almost completely denervated rat bladders. This result indicates that β₃ -adrenoceptor agonist may affect the bladder directly, suggesting that it might be effective for overall OAB, regardless of the presence or level of neurological deficits. Bilateral MPGs-excised rats are considered a plausible micromotion animal model suitable for future research.

Effects of Intravesical Electrical Stimulation on Urinary Adenosine Triphosphate and Nitric Oxide in Rats With Detrusor Underactivity Induced By Bilateral Pelvic Nerve Crush Injury: The Possible Underlying Mechanism

PURPOSE

To explore the effect of intravesical electrical stimulation (IVES) on urinary adenosine triphosphate (ATP) and nitric oxide (NO) in rats with detrusor underactivity (DU) induced by bilateral pelvic nerve crush (bPNC), and to determine the underlying peripheral mechanism.

METHODS

Twenty-four female Sprague-Dawley rats were equally divided into 3 groups: sham; bPNC; and IVES. Rats in the IVES group began to receive IVES treatment 10 days after bPNC (20 minutes per day for 14 consecutive days). After the 14th IVES, rat urine was collected and cystometry was performed. The serum creatinine, blood urea nitrogen, and urinary ATP and NO levels were measured, and a routine urinalysis was performed.

RESULTS

The maximum cystometric capacity (MCC), maximum changes in bladder pressure during filling (∆FP), and postvoid residual urine (PVR) in the IVES group were significantly lower than the bPNC group, and the maximum changes in bladder pressure during voiding (∆VP) was significantly higher than the bPNC group. Compared with the sham group, the MCC, ∆FP and PVR were significantly increased, and the maximum voiding pressure (MVP) and ∆VP were significantly decreased in the bPNC group. After bPNC, urinary ATP was significantly decreased, and urinary NO was significantly increased. In IVES-treated rats, urinary ATP was significantly higher than the bPNC group, and NO was significantly lower than the bPNC group. In addition, the ATP-to-NO ratio of the rats in the bPNC group was significantly lower than the sham and IVES groups. Correlation analysis showed that the ATP and NO were not correlated with the MCC, ∆FP, MVP, ∆VP, and PVR.

CONCLUSION

Promoting the release of urothelial ATP and inhibiting the release of urothelial NO may be one of the peripheral mechanisms underlying IVES in the treatment of DU. Specifically, IVES may shift the balance between excitation and inhibition toward excitation.

Functional, morphological and molecular characteristics in a novel rat model of spinal sacral nerve injury-surgical approach, pathological process and clinical relevance

Spinal sacral nerve injury represents one of the most serious conditions associated with many diseases such as sacral fracture, tethered cord syndrome and sacral canal tumor. Spinal sacral nerve injury could cause bladder denervation and detrusor underactivity. There is limited clinical experience resolving spinal sacral nerve injury associated detrusor underactivity patients, and thus the treatment options are also scarce. In this study, we established a spinal sacral nerve injury animal model for deeper understanding and further researching of this disease. Forty 8 w (week) old Sprague Dawley rats were included and equally divided into sham (n = 20) and crush group (n = 20). Bilateral spinal sacral nerves of rats were crushed in crush group, and sham group received same procedure without nerve crush. Comprehensive evaluations at three time points (1 w, 4 w and 6 w) were performed to comprehend the nature process of this disease. According to urodynamic test, ultrasonography and retrograde urography, we could demonstrate severe bladder dysfunction after spinal sacral nerve injury along the observation period compared with sham group. These functional changes were further reflected by histological examination (hematoxylin-eosin and Masson's trichrome staining) of microstructure of nerves and bladders. Immunostaining of nerve/bladder revealed schwann cell death, axon degeneration and collagen remodeling of bladder. Polymerase Chain Reaction results revealed vigorous nerve inflammation and bladder fibrosis 1 week after injury and inflammation/fibrosis returned to normal at 4 w. The CatWalk gait analysis was performed and there was no obvious difference between two groups. In conclusion, we established a reliable and reproducible model for spinal sacral nerve injury, this model provided an approach to evaluate the treatment strategies and to understand the pathological process of spinal sacral nerve injuries. It allowed us to understand how nerve degeneration and bladder fibrosis changed following spinal sacral nerve injury and how recovery could be facilitated by therapeutic options for further research.

Clinical Correlation of Bladder Electron Microscopic Characteristics in Patients with Detrusor Underactivity of Various Etiologies

This study aimed to investigate the ultrastructural characteristics of the bladder of patients with detrusor underactivity (DU) of various etiologies. Twenty-five patients with DU and control subjects underwent urodynamic testing and transmission electron microscopic examination of bladder specimens. The epithelium, lamina propria, and muscle layers were analyzed separately. The DU bladders exhibited total epithelial denudation (52%). In the bladders with remaining epithelium, apical cell uroplakins (44.4%) and tight junction complexes (77.8%) were also noted. The lamina propria was characterized by loose extracellular connective tissue (48%) and a lack of nerve terminals (76%). Smooth muscle shrinkage and a loss of their regular spindle shape (91.6%) were also noted in the detrusor layer. Patients with DU with intact epithelial cell layers had significantly larger void volumes and maximal flow rates than those with mild or severe epithelial denudation. Patients with remaining nerve terminals in lamina propria had a stronger first sensation of filling and smaller residual urine volume than those without nerve terminals. The proportion of ultrastructural defects of the bladder was not significantly different among patients with DU of various etiologies and treatment outcomes. DU bladders were characterized by ultrastructural defects in the entire bladder, and the defects were correlated to clinical parameters.

Bone marrow mesenchymal stem cells therapy on bilateral pelvic nerve crush-induced voiding dysfunction in rats

INTRODUCTION AND HYPOTHESIS

Neurogenic voiding dysfunction can be induced after radical pelvic surgery and severely affects patients' quality of life. This study aims to investigate the effects of bone marrow mesenchymal stem cells (BMSCs) on neurogenic voiding dysfunction in male rats and explore the underlying mechanisms.

METHODS

Thirty 4-week-old male Sprague-Dawley rats were randomly divided into three groups: (1) sham-operated (sham, n = 10), (2) intrabladder wall injection of phosphate buffer solution (PBS) after bilateral pelvic nerve crush (BPNC+PBS, n = 10), and (3) intrabladder wall injection of BMSCs after bilateral pelvic nerve crush (BPNC+BMSCs, n = 10). Four weeks postoperatively, functional and morphological examinations were performed.

RESULTS

Compared to the sham group, BPNC rats manifested significant augmentation in the frequency of non-voiding contractions and postvoid residual and bladder capacity, and they had decreases in intravesical pressure and voiding efficiency. However, they were markedly improved after BMSC injection. Masson's trichrome staining showed that the ratio of collagen area in bladder wall tissue significantly increased in the BPNC+PBS group but was reduced following BMSC injection. BPNC increased the protein expression of TGF-β1, Smad2/3, and collagen I/III but decreased the expression of α-SMA. BMSC injection stimulated higher expression levels of α-SMA and lower expression levels of the other target proteins. The expression levels of vesicular acetylcholine transporters were reduced at 4 weeks post-BPNC, whereas injection of BMSCs boosted the expression quantity.

CONCLUSIONS

BMSC therapy suppressed detrusor fibrosis, improved intravesical pressure and voiding efficiency, and partially restored voiding function in male rats after BPNC.

Effects of losartan on bladder dysfunction due to aging-related severe hypertension in rats

Aging is a major risk factor for bladder dysfunction. Anti-hypertensive drugs, angiotensin II type 1 receptor blockers (ARBs), are reported to ameliorate lower urinary tract dysfunction in rodent models and humans. We aimed to examine the preventive effect of an ARB, losartan, against bladder dysfunction due to aging-related severe hypertension. Male spontaneously hypertensive rats (SHRs) (36-week-old) were administered losartan (0, 3, or 10 mg/kg, p.o.) for 18 weeks. Age-matched, vehicle-treated Wistar Kyoto rats (WKYs) were used as controls. After the treatments, bladder and renal weight, mean blood pressure, and voiding parameters were measured. Additionally, detrusor thickness and bladder arterial wall thickness were evaluated using hematoxylin and eosin staining. Renal morphology was also assessed using periodic acid-Schiff staining. Compared to WKYs, SHRs demonstrated significantly higher bladder weight/body weight ratio (BBR), renal weight/body weight ratio, mean blood pressure, detrusor thickness, bladder arterial wall thickness, urine output, water intake, post-voiding residual urine volume, bladder capacity, intercontraction interval, and rate of glomerular and tubular injury and a lower urine osmolality. A low dose of losartan decreased the urine output, post-voiding residual urine volume, and bladder capacity in SHRs but not mean blood pressure in SHRs. A high dose of losartan decreased the BBR, mean blood pressure, detrusor thickness, bladder arterial wall thickness, post-voiding residual urine volume, bladder capacity, intercontraction interval, and glomerular and tubular injury in SHRs. Losartan inhibits bladder dysfunction in aged SHRs. The ARB losartan might be a preventive drug for bladder dysfunction due to aging-related severe hypertension.

Aging-related severe hypertension induces detrusor underactivity in rats

AIMS

Aging is an obvious risk factor for detrusor underactivity. We investigated the effects of aging on bladder function in spontaneously hypertensive rats.

MAIN METHODS

Male spontaneously hypertensive rats and Wistar Kyoto rats (used as normotensive controls) at the ages of 18, 36, 54, or 72 weeks were used. Bladder weight, blood pressure, bladder blood flow, and urodynamic and renal parameters were measured. Additionally, detrusor thickness and renal histology were evaluated.

KEY FINDINGS

In spontaneously hypertensive rats, significant increases were observed in bladder weight/body weight ratio, blood pressure, detrusor thickness, intercontraction interval, urine output, serum creatinine, and renal glomerular and tubular scores, and decreases in bladder blood flow and urine osmolality at 72 weeks as compared to those at 18 weeks. In spontaneously hypertensive rats, significant increases were observed in single voided volume, post voiding residual urine volume, and bladder capacity, with decrease in voiding efficiency were observed at 54 or 72 weeks than at 18 weeks. However, there were no significant differences in blood pressure, urodynamic and renal parameters, detrusor thickness and renal histology among Wistar Kyoto rats of different ages.

SIGNIFICANCE

In spontaneously hypertensive rats, aging induces significant increases in blood pressure, single voided volume, post voiding residual urine volume, intercontraction intervals and urine output, and decreases in voiding efficiency and bladder blood flow indicative of detrusor underactivity. Aging-related severe hypertension could induce voiding dysfunction such as detrusor underactivity via severe bladder ischemia and polyuria. Aged spontaneously hypertensive rats may be useful animal models for detrusor underactivity.

Impairment of accessory nerves around major pelvic ganglion leading to overflow urinary incontinence in rats

AIMS

To investigate the relationship between lower urinary tract function and the accessory nerve (ACN) arising from the major pelvic ganglion (MPG).

METHODS

Ten-week-old male Wistar/ST rats were randomly divided into eight groups according to the type of treatment (sham or bilateral accessory nerve injury [BACNI]) and the duration of observation (3 days, 1 week, 2 weeks, or 4 weeks: Sham-3d, Sham-1w, Sham-2w, Sham-4w, BACNI-3d, BACNI-1w, BACNI-2ws, and BACNI-4w. BACNI was induced in the following manner: the ACN was crushed for 1 min (2 mm away from the MPG) using reverse-action tweezers. The same procedure was performed on both sides. On the last day of each observation period, the bladder function was measured by awake cystometry, and histological evaluation was performed.

RESULTS

All rats in the Sham groups micturated normally. In the BACNI-3d and BACNI-1w groups, all rats showed symptoms of overflow urinary incontinence (OUI). This OUI improved gradually over time. The bladder's size in the BACNI group was significantly larger than that in the Sham group (p < .01). In addition, fibrosis was observed in the subserosa of the bladder of rats in BACNI groups.

CONCLUSION

The BACNI model rats exhibited OUI, suggesting that ACN is involved in the lower urinary tract function. It might be possible that ACN controls the function of either the bladder, the urethra, or both.

Pathogenesis evidence from human and animal models of detrusor underactivity

Detrusor underactivity (DU) is a common urodynamic diagnosis in patients with lower urinary tract symptoms and large post-voiding residual volume. Animal and human studies showed the possible etiologies of DU include central or peripheral nerve injury, bladder outlet obstruction, chronic ischemia, aging, diabetes mellitus, and sympathetic inhibition of micturition reflex. Evidence from animal and human DU studies with various etiologies revealed highly similar gross and histological characteristics in the bladders, including increased bladder weight, bladder wall thickening, inflammation, collagen deposition, and fibrosis. In electron microscopy, smooth muscle destruction, swollen mitochondria, decreased nerve innervation, caveolae, and umbrella cell fusiform vesicles were noted in the DU bladders. Most animal DU models demonstrate detrusor contractility changes from compensatory to the decompensatory stage, and the change was compatible with human DU observation. The cystometry in the DU animal studies is characterized by impaired contractility, prolong intercontraction interval, and hyposensation, while in vitro bladder muscle strips experiment may exhibit normal detrusor contractility. Decreased bladder blood flow and increased oxidative stress in bladders had been proved in different animal DU models, suggesting they should be important in the DU pathogenesis pathway. Sensory receptors mRNA and protein expression changes in DU bladders had been observed in both animal and human studies, including muscarinic receptors M2, M3, adrenergic receptor β3, purinergic receptor P2X1, P2X3, and transient receptor potential vanilloid (TRPV) 1 and TRPV4. Although some of the sensory receptors changes remain controversial, it might be the target for further pharmacologic treatments.

Establishment of animal model manifested as bladder neurogenic changes generated by bilateral pelvic nerve injury in male rats

PURPOSE

To establish a male rat model of neurogenic bladder after bilateral pelvic nerve injury (BPNI) and investigate the factors associated with onset of neurogenic bladder.

METHODS

Twenty-four 8-week-old male Sprague-Dawley rats were randomly divided into three groups (n = 8 rats per group). Rats in 4-week and 8-week nerve injury group underwent BPNI, while rats in the sham group underwent a sham operation. Bladder functional analysis were performed and then bladders tissues were harvested for morphological examination and investigating the mRNA expression levels of target genes in all rats.

RESULTS

The bladder weight significantly increased in rats following BPNI. Functional analysis revealed non-voiding contractions and decreased detrusor contractility following BPNI, manifested as elevated post-void residual and bladder capacity while reduced maximum voiding pressure and voiding efficiency. The collagen area in bladder tissue and mRNA expression levels of target genes significantly increased at 4 or 8 weeks post-BPNI except Smad3. At 4 weeks post-BPNI, expression levels of vesicular acetylcholine transporter were reduced, then returned to baseline at 8 weeks. Expression levels of tyrosine hydroxylase were reduced at both 4 and 8 weeks post-BPNI.

CONCLUSIONS

A neurogenic bladder animal model was successfully established by performing BPNI in male rats, characterized by impaired voiding function, bladder detrusor fibrosis, and reduced neurotransmitter release.

Simulated vaginal delivery causes transients vaginal smooth muscle hypersensitivity and urethral sphincter dysfunction

BACKGROUND

Although pelvic floor dysfunction (PFD) has a multifactorial etiology, pregnancy and childbirth are considered crucial events predisposing to urinary incontinence as well as pelvic organ prolapse, which are highly prevalent. Rats are the most frequently used animal model and pudendal nerve crush (PNC) and vaginal distension (VD) are often used to mimic vaginal delivery.

OBJECTIVE

To document the time course of events after simulated vaginal delivery (SVD) on the urethral sphincter and the vaginal smooth muscle layer.

MATERIALS AND METHODS

Virgin female Sprague-Dawley rats were subjected to SVD (PNC + VD) or sham surgery and evaluated at 7, 14, 21, and 42 days after the injury. Urethral function was determined in vivo by microultrasound during cystometry and vaginal smooth muscle layer was harvested for in vitro pharmacologic investigation by isometric tension recording. Furthermore, vaginal and urethral samples were investigated by immunohistochemistry and real-time quantitative polymerase chain reaction.

RESULTS

Microultrasound showed no bursting of the urethral sphincter in the SVD group at 7 days with a functional recovery starting at 14 days, and normal bursting at 21 and 42 days. Vaginal smooth muscle showed higher sensitivity to carbachol at 14 and 21 days after injury; however, at 42 days, its sensitivity decreased when compared with sham.

CONCLUSION

SVD induces urethral dysfunction and a shift in vaginal smooth muscle contractile responses to carbachol.