How important is the α1-adrenoceptor in primate and rodent proximal urethra? Sex differences in the contribution of α1-adrenoceptor to urethral contractility

Cells and ionic conductances contributing to spontaneous activity in bladder and urethral smooth muscle

Smooth muscle organs of the lower urinary tract comprise the bladder detrusor and urethral wall, which have a reciprocal contractile relationship during urine storage and micturition. As the bladder fills with urine, detrusor smooth muscle cells (DSMCs) remain relaxed to accommodate increases in intravesical pressure while urethral smooth muscle cells (USMCs) sustain tone to occlude the urethral orifice, preventing leakage. While neither organ displays coordinated regular contractions as occurs in small intestine, lymphatics or renal pelvis, they do exhibit patterns of rhythmicity at cellular and tissue levels. In rabbit and guinea-pig urethra, electrical slow waves are recorded from USMCs. This activity is linked to cells expressing vimentin, c-kit and Ca2+-activated Cl- channels, like interstitial cells of Cajal in the gastrointestinal tract. In mouse, USMCs are rhythmically active (firing propagating Ca2+ waves linked to contraction), and this cellular rhythmicity is asynchronous across tissues and summates to form tone. Experiments in mice have failed to demonstrate a voltage-dependent mechanism for regulating this rhythmicity or contractions in vitro, suggesting that urethral tone results from an intrinsic ability of USMCs to 'pace' their own Ca2+ mobilization pathways required for contraction. DSMCs exhibit spontaneous transient contractions, increases in intracellular Ca2+ and action potentials. Consistent across numerous species, including humans, this activity relies on voltage-dependent Ca2+ influx in DSMCs. While interstitial cells are present in the bladder, they do not 'pace' the organ in an excitatory manner. Instead, specialized cells (PDGFRα+ interstitial cells) may 'negatively pace' DSMCs to prevent bladder overexcitability.

Human HPSE2 gene transfer ameliorates bladder pathophysiology in a mutant mouse model of urofacial syndrome

Rare early-onset lower urinary tract disorders include defects of functional maturation of the bladder. Current treatments do not target the primary pathobiology of these diseases. Some have a monogenic basis, such as urofacial, or Ochoa, syndrome (UFS). Here, the bladder does not empty fully because of incomplete relaxation of its outflow tract, and subsequent urosepsis can cause kidney failure. UFS is associated with biallelic variants of HPSE2, encoding heparanase-2. This protein is detected in pelvic ganglia, autonomic relay stations that innervate the bladder and control voiding. Bladder outflow tracts of Hpse2 mutant mice display impaired neurogenic relaxation. We hypothesized that HPSE2 gene transfer soon after birth would ameliorate this defect and explored an adeno-associated viral (AAV) vector-based approach. AAV9/HPSE2, carrying human HPSE2 driven by CAG, was administered intravenously into neonatal mice. In the third postnatal week, transgene transduction and expression were sought, and ex vivo myography was undertaken to measure bladder function. In mice administered AAV9/HPSE2, the viral genome was detected in pelvic ganglia. Human HPSE2 was expressed and heparanase-2 became detectable in pelvic ganglia of treated mutant mice. On autopsy, wild-type mice had empty bladders, whereas bladders were uniformly distended in mutant mice, a defect ameliorated by AAV9/HPSE2 treatment. Therapeutically, AAV9/HPSE2 significantly ameliorated impaired neurogenic relaxation of Hpse2 mutant bladder outflow tracts. Impaired neurogenic contractility of mutant detrusor smooth muscle was also significantly improved. These results constitute first steps towards curing UFS, a clinically devastating genetic disease featuring a bladder autonomic neuropathy.

Sex differences in lower urinary tract function in mice with or without spinal cord injury

OBJECTIVES

We examined sex differences of lower urinary tract function and molecular mechanisms in mice with and without spinal cord injury (SCI).

METHODS

SCI was induced by Th8-9 spinal cord transection in male and female mice. We evaluated cystometrograms (CMG) and electromyography (EMG) of external urethral sphincter (EUS) at 6 weeks after SCI in spinal intact (SI) and SCI mice. The mRNA levels of Piezo2 and TRPV1 were measured in L6-S1 dorsal root ganglia (DRG). Protein levels of nerve growth factor (NGF) in the bladder mucosa was evaluated using an enzyme-linked immunosorbent assay.

RESULTS

Sex differences were found in the EUS behavior during voiding as voiding events in female mice with or without SCI occurred during EUS relaxation periods without EUS bursting activity whereas male mice with or without SCI urinated during EUS bursting activity in EMG recordings. In both sexes, SCI decreased voiding efficiency along with increased tonic EUS activities evident as reduced EUS relaxation time in females and longer active periods of EUS bursting activity in males. mRNA levels of Piezo2 and TRPV1 of DRG in male and female SCI mice were significantly upregulated compared with SI mice. NGF in the bladder mucosa showed a significant increase in male and female SCI mice compared with SI mice. However, there were no significant differences in Piezo2 or TRPV1 levels in DRG or NGF protein levels in the bladder mucosa between male and female SCI mice.

CONCLUSIONS

We demonstrated that female and male mice voided during EUS relaxation and EUS bursting activity, respectively. Also, upregulation of TRPV1 and Piezo2 in L6-S1 DRG and NGF in the bladder could be involved in SCI-induced lower urinary tract dysfunction in both sexes of mice.

Neurogenic Defects Occur in LRIG2-Associated Urinary Bladder Disease

Introduction

Urofacial, or Ochoa, syndrome (UFS) is an autosomal recessive disease featuring a dyssynergic bladder with detrusor smooth muscle contracting against an undilated outflow tract. It also features an abnormal grimace. Half of individuals with UFS carry biallelic variants in HPSE2, whereas other rare families carry variants in LRIG2.LRIG2 is immunodetected in pelvic ganglia sending autonomic axons into the bladder. Moreover, Lrig2 mutant mice have abnormal urination and abnormally patterned bladder nerves. We hypothesized that peripheral neurogenic defects underlie LRIG2-associated bladder dysfunction.

Methods

We describe a new family with LRIG2-associated UFS and studied Lrig2 homozygous mutant mice with ex vivo physiological analyses.

Results

The index case presented antenatally with urinary tract (UT) dilatation, and postnatally had urosepsis and functional bladder outlet obstruction. He had the grimace that, together with UT disease, characterizes UFS. Although HPSE2 sequencing was normal, he carried a homozygous, predicted pathogenic, LRIG2 stop variant (c.1939C>T; p.Arg647∗). Lrig2 mutant mice had enlarged bladders. Ex vivo physiology experiments showed neurogenic smooth muscle relaxation defects in the outflow tract, containing the urethra adjoining the bladder, and in detrusor contractility. Moreover, there were nuanced differences in physiological outflow tract defects between the sexes.

Conclusion

Putting this family in the context of all reported UT disease-associated LRIG2 variants, the full UFS phenotype occurs with biallelic stop or frameshift variants, but missense variants lead to bladder-limited disease. Our murine observations support the hypothesis that UFS is a genetic autonomic neuropathy of the bladder affecting outflow tract and bladder body function.

The differences in the adrenergic receptors of proximal urethra between sexes

Objectives

The bladder and urethra work as a physiologically functional unit to facilitate continence in the storage and voiding phase. Sex differences have been found in the urethral contraction in response to α-adrenergic receptor activation. This study aimed to investigate the role of adrenergic receptors in the proximal urethra of male and female mice.

Materials and Methods

Urinary bladder and proximal urethral smooth muscle (USM) samples from male and female C57BL/6 mice were isolated and mounted in an organ bath.

Results

Acetylcholine-induced contraction of the urinary bladder was compared in male and female mice. Phenylephrine and norepinephrine (NE) induced little contraction at a lower concentration, but a relaxing phase of female proximal USM was observed at a higher concentration. This contraction profile was inhibited by NG-nitro-L-arginine, lidocaine, and capsaicin. In addition, the NE-induced contraction was greater in the incubation of propranolol than that of L-NNA or lidocaine. These results suggested that the β-adrenoceptor may be the dominant receptor of female proximal USM, and the activity of calcitonin gene-related peptide sensory nerves and nitrergic nerves may pose an anti-contraction effect on the proximal urethra in female mice.

Conclusion

β-adrenoceptor may be the dominant receptor of female proximal USM. The use of β-adrenergic receptor blocker agents might have the potential for the treatment of female voiding dysfunction.

Control of rat bladder neck relaxation with NORD-1, a red light-reactive nitric oxide releaser: In vitro study

We aimed to control the relaxation of rat bladder neck specimens by using NORD-1, a red light-reactive nitric oxide (NO) releaser. Female and male 10-11-week-old Wistar/ST rats were divided into three groups: NORD-1, vehicle, and NORD-1+[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; a soluble guanylyl cyclase inhibitor). We infused 10-4 M NORD-1 into the bladders of NORD-1 and NORD-1+ODQ group rats and the vehicle into those of vehicle group rats. Isometric tension was analyzed using circular bladder neck specimens with 10-5 M NG-nitro-l-arginine methyl ester, an NO synthase inhibitor. Moreover, 10-5 M ODQ was added into the NORD-1+ODQ group bath. After precontraction with 10-5 M carbachol, the specimens were irradiated with red light and their relaxation responses were measured. We evaluated NORD-1 tissue permeability by observing the sliced bladder neck specimens. The NORD-1 group specimens relaxed during red light irradiation; the relaxation response increased with the increase in light intensity. The vehicle and NORD-1+ODQ group specimens did not respond to irradiation. Sex-related differences in responsiveness were not noted. NORD-1 permeated into the urothelium of NORD-1 group specimens. Rat bladder neck relaxation was controlled by NORD-1 and light irradiation in vitro. NORD-1 might be a novel therapeutic agent for voiding dysfunction.

Age-associated bladder and urethral coordination impairment and changes in urethral oxidative stress in rats

AIMS

We examined age-associated changes in bladder and urethral coordination involving the nitric oxide (NO)/soluble guanylyl cyclase (sGC) system, which induces urethral smooth muscle relaxation, and urethral ischemic/oxidative stress changes in rats.

MAIN METHODS

Sixteen female Sprague-Dawley rats were divided into young (3 months old) and middle-aged (12-15 months old) groups. Urethral activity was evaluated by simultaneously recording intravesical pressure under isovolumetric conditions and urethral perfusion pressure (UPP) under urethane anesthesia. Sodium nitroprusside (SNP, 0.1 mg/kg), an NO donor, and BAY 41-2272, a novel NO-independent stimulator of sGC (0.1 mg/kg), were administered intravenously to both groups. N-nitro-l-arginine methyl ester hydrochloride (l-NAME, 100 mg/kg) was also injected intravenously, to inhibit NO synthase activity in both groups. Staining for the ischemic marker, hypoxia-inducible factor-1α (HIF-1α), and the oxidative stress markers, 8-hydroxy-2'-deoxyguanosine (8-OHdG) and malondialdehyde (MDA), was performed on tissue sections of the urethra, in both groups.

KEY FINDINGS

Baseline UPP and UPP changes were significantly lower in middle-aged rats than in young rats. After administration of SNP and BAY 41-2272, baseline UPP and UPP nadir were significantly decreased in both groups. After administration of l-NAME, UPP change/bladder contraction amplitude in young rats was still lower than at baseline but was completely restored to control levels in middle-aged rats. Immunoreactivity of HIF-1α, 8-OHdG, and MDA was higher in middle-aged rats than in young rats.

SIGNIFICANCE

Age-associated ischemic and oxidative stress in the urethra might be correlated with impairment of the NO/sGC system and with coordination of the bladder and urethra.

Role of Ano1 Ca2+-activated Cl- channels in generating urethral tone

Urinary continence is maintained in the lower urinary tract by the contracture of urethral sphincters, including smooth muscle of the internal urethral sphincter. These contractions occlude the urethral lumen, preventing urine leakage from the bladder to the exterior. Over the past 20 years, research on the ionic conductances that contribute to urethral smooth muscle contractility has greatly accelerated. A debate has emerged over the role of interstitial cell of Cajal (ICC)-like cells in the urethra and their expression of Ca²⁺-activated Cl^- channels encoded by anoctamin-1 [Ano1; transmembrane member 16 A (Tmem16a) gene]. It has been proposed that Ano1 channels expressed in urethral ICC serve as a source of depolarization for smooth muscle cells, increasing their excitability and contributing to tone. Although a clear role for Ano1 channels expressed in ICC is evident in other smooth muscle organs, such as the gastrointestinal tract, the role of these channels in the urethra is unclear, owing to differences in the species (rabbit, rat, guinea pig, sheep, and mouse) examined and experimental approaches by different groups. The importance of clarifying this situation is evident as effective targeting of Ano1 channels may lead to new treatments for urinary incontinence. In this review, we summarize the key findings from different species on the role of ICC and Ano1 channels in urethral contractility. Finally, we outline proposals for clarifying this controversial and important topic by addressing how cell-specific optogenetic and inducible cell-specific genetic deletion strategies coupled with advances in Ano1 channel pharmacology may clarify this area in future studies.NEW & NOTEWORTHY Studies from the rabbit have shown that anoctamin-1 (Ano1) channels expressed in urethral interstitial cells of Cajal (ICC) serve as a source of depolarization for smooth muscle cells, increasing excitability and tone. However, the role of urethral Ano1 channels is unclear, owing to differences in the species examined and experimental approaches. We summarize findings from different species on the role of urethral ICC and Ano1 channels in urethral contractility and outline proposals for clarifying this topic using cell-specific optogenetic approaches.

ANO1 in urethral SMCs contributes to sex differences in urethral spontaneous tone

Stress urinary incontinence (SUI) is more common in women than in men, and sex differences in anatomic structure and physiology have been suggested as causes; however, the underlying cellular and molecular mechanisms remain unclear. The spontaneous tone (STT) of the urethra has been shown to have a fundamental effect on preventing the occurrence of SUI. Here, we investigated whether the urethral STT exhibited sex differences. First, we isolated urethral smooth muscle (USM) and detected STT in female mice and women. No STT was found in male mice or men. Furthermore, caffeine induced increased contractility and intracellular Ca²⁺ concentration in urethrae from female mice compared with male mice. EACT [an N-aroylaminothiazole, anoctamin-1 (ANO1) activator] elicited increased intracellular Ca²⁺ concentration and stronger currents in female mice than in male mice. Moreover, ANO1 expression in single USM cells from women and female mice was almost twofold higher than that found in cells from men and male mice. In summary, ANO1 in USM contributes to sex differences in urethral spontaneous tone. This finding may provide new guidance for the treatment of SUI in women and men.

Urethral dysfunction and alterations of nitric oxide mechanisms in streptozotocin-induced diabetic rats with or without low-dose insulin treatment

AIMS

To establish an animal model of diabetes mellitus (DM) with moderately elevated blood glucose levels, and to examine the nitric oxide (NO) mechanism controlling urethral function in streptozotocin (STZ)-induced DM rats.

MAIN METHODS

Female Sprague-Dawley rats were used. DM was induced by intraperitoneal injection of STZ (65 mg/kg) and some of them received subcutaneous implantation of a low-dose insulin pellet. Voiding behavior was evaluated in metabolic cages. Isovolumetric cystometry and urethral perfusion pressure (UPP) were then evaluated under urethane anesthesia, during which L-arginine (100 mg/kg) and N-nitro-L-arginine methyl ester hydrochloride (L-NAME) (50 mg/kg) were administered intravenously. In vitro urethral activity was also tested by organ bath muscle strip studies.

KEY FINDINGS

UPP changes and high-frequency oscillation (HFO) were significantly (P < 0.05) smaller in 8-weeks DM rats vs. normal control (NC) rats or insulin-treated DM rats, which showed reductions in urine overproduction and voided volume per micturition vs. untreated DM rats. UPP nadir was decreased by L-arginine in NC and insulin-treated DM groups, and decreased by L-NAME in all groups. Five of 6 untreated DM rats showed a detrusor-sphincter dyssynergia pattern after L-NAME. In in vitro studies, the relative ratio of L-NAME-induced reductions of urethral relaxation against pre-drug urethral relaxation was significantly smaller in DM vs. NC rats (P < 0.05).

SIGNIFICANCE

Low-dose insulin-treated DM rats would be a useful model for studying natural progression of DM-induced lower urinary tract dysfunction. The impaired NO-mediated urethral relaxation mechanisms play an important role in DM-induced urethral dysfunction, which could contribute to DM-induced inefficient voiding.

Urethral dysfunction in a rat model of chemically induced prostatic inflammation: potential involvement of the MRP5 pump

Prostate inflammation (PI) is a clinical condition associated with infection and/or inflammation of the prostate. It is a common disease frequently associated to lower urinary tract (LUT) symptoms. The urethra is an understudied structure in the LUT and plays a fundamental role in the urinary cycle. Here, we proposed to evaluate the effect of PI on the urethra tissue. Male Sprague-Dawley rats were used, and PI was induced by formalin injection into the ventral lobes of the prostate. The pelvic urethra at the prostatic level was harvested for histological analysis, contraction (electrical field stimulation and phenylephrine), and relaxation (sodium nitroprusside/MK-571) experiments. Various gene targets [cytochrome c oxidase subunit 2, transforming growth factor-β₁, interleukin-1β, hypoxia-inducible factor-1α, α_1A-adrenoceptor, inositol 1,4,5-trisphosphate receptor type 1, voltage-gated Ca²⁺ channel subunit-α_1D, neuronal nitric oxide synthase, soluble guanylyl cyclase, phosphodiesterase 5A, protein kinase CGMP-dependent 1, and multidrug resistance-associated protein 5 (MRP5; ATP-binding cassette subfamily C member 5)] were quantified, and cGMP levels were measured. No histological changes were detected, and functional assays revealed decreased contraction and increased relaxation of urethras from the PI group. The addition of MK-571 to functional assays increased urethral relaxation. Genes associated with inflammation were upregulated in urethras from the PI group, such as cytochrome oxidase c subunit 2, transforming growth factor-β₁, interleukin-1β, and hypoxia-inducible factor-1α. We also found increased expression of L-type Ca²⁺ channels and the neuronal nitric oxide synthase enzyme and decreased expression of the MRP5 pump. Finally, cGMP production was enhanced in urethral tissue of PI animals. The results indicate that PI is associated with proinflammatory gene expression in the urethra without histologically evident inflammation and that PI produces a dysfunctional urethra and MRP5 pump downregulation, which results in cGMP accumulation inside the cell. These findings would help to better understand LUT dysfunctions associated with PI and the role of MRP pumps in the control of LUT function.

Impact of sex, androgens, and prostate size on C57BL/6J mouse urinary physiology: urethral histology

The National Institutes of Health leveled new focus on sex as a biological variable with the goal of understanding sex-specific differences in health and physiology. We previously published a functional assessment of the impact of sex, androgens, and prostate size on C57BL/6J mouse urinary physiology (Ruetten H, Wegner KA, Zhang HL, Wang P, Sandhu J, Sandhu S, Mueller B, Wang Z, Macoska J, Peterson RE, Bjorling DE, Ricke WA, Marker PC, Vezina CM. Am J Physiol Renal Physiol 317: F996-F1009, 2019). Here, we measured and compared five characteristics of urethral histology (urethral lumen diameter and area, epithelial cell count, epithelial and rhabdosphincter thickness, epithelial cell area, and total urethral area) in male and female 9-wk-old C57BL/6J mice using hematoxylin and eosin staining. We also compared male mice with castrated male mice, male and female mice treated with the steroid 5α-reductase inhibitor finasteride or testosterone, or male mice harboring alleles (Pbsn4^cre/+; R26R^Dta/+) that reduce prostate lobe mass. The three methods used to reduce prostate mass (castration, finasteride, and Pbsn4^cre/+; R26R^Dta/+) changed urethral histology, but none feminized male urethral histology (increased urethral epithelial area). Exogenous testosterone caused increased epithelial cell count in intact females but did not masculinize female urethral histology (decrease epithelial area). Our results lay a critical foundation for future studies as we begin to parse out the influence of hormones and cellular morphology on male and female urinary function.

Trends in the use of antimuscarinics and alpha-adrenergic blockers in women with lower urinary tract symptoms in Taiwan: A nationwide, population-based study, 2007-2012

BACKGROUND

We aim to examine the trend in the use of antimuscarinics and off-label alpha-adrenergic blockers for treatment of lower urinary tract symptoms (LUTS) in a Taiwanese Women Cohort between 2007 and 2012.

METHODS

This population-based National Health Insurance Research Database (NHIRD) was used to examine the trends in the use of antimuscarinics or off-label alpha-adrenergic blockers in Taiwan. A sample of 1,000,000 individuals randomly drawn from the whole population of 23 million individuals who were registered in the NHI in 2005. From 2007 through 2012, women aged over 18 years whose claim record contained prescriptions of either of the two drugs for treatment of any of the LUTS-related diagnoses were identified and analyzed. The annual usage of the two drug classes were calculated by defined daily dose (DDD).

RESULTS

From 2007-2012, there was a 0.80 fold (69676.8 to 125104.3) increase in DDD of antimuscarinics in our cohort. The overall healthcare seeking prevalence of LUTS was 7.33% in 2007 and 12.38% in 2012, in a rising trend. The prevalence of antimuscarinics-treated LUTS in our cohort increased from 2.53 in 2007 to 3.41 per 1000 women in 2012. The prevalence of LUTS treated by antimuscarinics increased especially for those older than 60 years during the study period.

CONCLUSIONS

This 6-year observational study provided the epidemiologic information of clinically significant LUTS of Asian female population. Moreover, there was a rising trend in the use of antimuscarinics and off-label alpha-adrenergic blockers in the population-based cohort.

Pupo A. Updates in the function and regulation of α1 -adrenoceptors

α1 -Adrenoceptors are seven transmembrane domain GPCRs involved in numerous physiological functions controlled by the endogenous catecholamines, noradrenaline and adrenaline, and targeted by drugs useful in therapeutics. Three separate genes, whose products are named α1A -, α1B -, and α1D - adrenoceptors, encode these receptors. Although the existence of multiple α1 -adrenoceptors has been acknowledged for almost 25 years, the specific functions regulated by each subtype are still largely unknown. Despite the limited comprehension, the identification of a single class of subtype-selective ligands for the α1A - adrenoceptors, the so-called α-blockers for prostate dysfunction, has led to major improvement in therapeutics, demonstrating the need for continued efforts in the field. This review article surveys the tissue distribution of the three α1 -adrenoceptor subtypes in the cardiovascular system, genitourinary system, and CNS, highlighting the functions already identified as mediated by the predominant activation of specific subtypes. In addition, this review covers the recent advances in the understanding of the molecular mechanisms involved in the regulation of each of the α1 -adrenoceptor subtypes by phosphorylation and interaction with proteins involved in their desensitization and internalization. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Autonomic dysregulation at multiple sites is implicated in age-associated underactive bladder in female mice

AIMS

To evaluate the functional and molecular alterations of contractile and relaxant machinery in the bladder and urethra that lead to the underactive bladder (UAB) in old female mice.

METHODS

Female young (3-months) and old (18-months) C57BL/6 mice were used. Urodynamic was assessed in awake and anaesthetized mice. Electrical-field stimulation (EFS) and concentration-response curves to contractile and relaxing agents in isolated bladders and urethras were performed. Messenger RNA (mRNA) expressions of muscarinic, adrenergic, and transient receptor potential vanilloid-4 (TRPV4), and of the enzymes tyrosine hydroxylase and neuronal nitric oxide synthase (nNOS) were determined. Bladder cyclic adenosine monophosphate (cAMP) levels were measured.

RESULTS

Cystometry in old mice showed incapacity to produce bladder emptying. On filter paper, old mice showed reduced urinary spots. Compared to the young group, bladder contractions induced by EFS and carbachol were lower in old mice. The β₃ -adrenoceptor agonist mirabegron promoted higher bladder relaxation and elevation of cAMP levels in old mice. In old mice urethras, the α_1a -adrenoceptor agonist phenylephrine produced higher contractions, but no differences were found for the NO donor sodium nitroprusside-induced relaxations. In old mice, increased mRNA expressions of β₃ - and α_1a -adrenoceptors in bladder and urethra were found, respectively, whereas the muscarinic M₂ and M₃ receptors and β₂ -adrenoceptors did not change between groups. Reduced mRNA expressions of tyrosine hydroxylase and nNOS were found in old mouse urethras. Additionally, TRPV4 expression was reduced in bladder urothelium from old mice.

CONCLUSION

Age-associated mouse UAB is the result of autonomic dysfunction at multiple levels leading to the less sensitive and overrelaxed bladder, along with urethral hypercontractility.

Sex differences in lower urinary tract biology and physiology

Females and males differ significantly in gross anatomy and physiology of the lower urinary tract, and these differences are commonly discussed in the medical and scientific literature. However, less attention is dedicated to investigating the varied development, function, and biology between females and males on a cellular level. Recognizing that cell biology is not uniform, especially in the lower urinary tract of females and males, is crucial for providing context and relevance for diverse fields of biomedical investigation. This review serves to characterize the current understanding of biological sex differences between female and male lower urinary tracts, while identifying areas for future research. First, the differences in overall cell populations are discussed in the detrusor smooth muscle, urothelium, and trigone. Second, the urethra is discussed, including anatomic discussions of the female and male urethra followed by discussions of cellular differences in the urothelial and muscular layers. The pelvic floor is then reviewed, followed by an examination of the sex differences in hormonal regulation, the urinary tract microbiome, and the reticuloendothelial system. Understanding the complex and dynamic development, anatomy, and physiology of the lower urinary tract should be contextualized by the sex differences described in this review.

A cautionary note for researchers treating mice with the neurotransmitter norepinephrine

The sympathetic nervous system plays a crucial role in metabolic function and glucose homeostasis. Norepinephrine is the main neurotransmitter released from sympathetic neurons. The major goal of our studies was to examine the impact of norepinephrine on metabolism related gene expression in obesity in vivo. Interestingly, we discovered that norepinephrine had a detrimental effect in our studies. C57BL6/J mice fed a high fat diet were intraperitoneally injected with 0.2 or 2 mg/kg/day norepinephrine. These doses of norepinephrine have been used previously by other researchers. Survival of the mice was documented. Kidney and bladder tissues were excised and fixed for histological studies. A subset of norepinephrine treated mice experienced unexpected adverse events which included bladder distension and reduced kidney perfusion as suggested by kidney discolouration. This eventuated in the mice having to be sacrificed or the mice succumbed to the pathological condition. To our knowledge, such an effect of norepinephrine has not been previously reported in mice. Morphological examination of kidney and bladder indicated marked detrimental architectural changes, which we postulate is associated with norepinephrine induced vasoconstriction, urinary retention and renal impairment. Our studies highlight that administration of norepinephrine to mice may trigger adverse effects relating predominantly to the urogenital tract which can result in decline in a subpopulation of these mice. Researchers administering norepinephrine in mouse models should be aware and look out for these unexpected adverse events associated with the use of norepinephrine.

Laboratory practical to study the differential innervation pathways of urinary tract smooth muscle

In the mammalian lower urinary tract, there is a reciprocal relationship between the contractile state of the bladder and urethra. As the bladder fills with urine, it remains relaxed to accommodate increases in volume, while the urethra remains contracted to prevent leakage of urine from the bladder to the exterior. Disruptions to the normal contractile state of the bladder and urethra can lead to abnormal micturition patterns and urinary incontinence. While both the bladder and urethra are smooth-muscle organs, they are differentially contracted by input from cholinergic and sympathetic nerves, respectively. The laboratory practical described here provides an experiential approach to understanding the anatomy of the lower urinary tract. Several key factors in urinary tract physiology are outlined, e.g., the bladder is contracted by activation of the parasympathetic pathway via cholinergic stimulation on muscarinic receptors, whereas the urethra is contracted by activation of the sympathetic pathway via adrenergic stimulation on α₁-adrenoceptors. This is achieved by measuring the force generated by bladder and urethra smooth muscle to demonstrate that acetylcholine contracts the smooth muscle of the bladder, whereas adrenergic agonists contract the urethral smooth muscle. An inhibition of these effects is also demonstrated by application of the muscarinic receptor antagonist atropine and the α₁-adrenergic receptor blocker phentolamine. A list of suggested techniques and exam questions to evaluate student understanding on this topic is also provided.

Deletion or pharmacological blockade of TLR4 confers protection against cyclophosphamide-induced mouse cystitis

Interstitial Cystitis/Bladder Pain Syndrome (IC/BPS) is a chronic inflammatory disease without consistently effective treatment. We investigate the role of toll-like receptor 4 (TLR4) on voiding dysfunction and inflammation in the cyclophosphamide (CYP)-induced mouse cystitis. Male C57BL/6 [wild-type, (WT)] and/or TLR4 knockout (TLR4^-/-) mice were treated with an injection of CYP (300 mg/kg, 24 h) or saline (10 ml/kg). The pharmacological blockade of the TLR4 by resatorvid (10 mg/kg) was also performed 1 h prior CYP-injection in WT mice. Urodynamic profiles were assessed by voiding stain on filter paper and filling cystometry. Contractile responses to carbachol were measured in isolated bladders. In CYP-exposed WT mice, mRNA for TLR4, myeloid differentiation primary response 88, and TIR-domain-containing adapter-inducing interferon-β increased by 45%, 72%, and 38%, respectively ( P < 0.05). In free-moving mice, CYP-exposed mice exhibited a higher number of urinary spots and smaller urinary volumes. Increases of micturition frequency and nonvoiding contractions, concomitant with decreases of intercontraction intervals and capacity, were observed in the filling cystometry of WT mice ( P < 0.05). Carbachol-induced bladder contractions were significantly reduced in the CYP group, which was paralleled by reduced mRNA for M2 and M3 muscarinic receptors. These functional and molecular alterations induced by CYP were prevented in TLR4^-/- and resatorvid-treated mice. Additionally, the increased levels of inflammatory markers induced by CYP exposure, myeloperoxidase activity, interleukin-6, and tumor necrosis factor-alpha were significantly reduced by resatorvid treatment. Our findings reveal a central role for the TLR4 signaling pathway in initiating CYP-induced bladder dysfunction and inflammation and thus emphasize that TLR4 receptor blockade may have clinical value for IC/BPS treatment.