Characterization of mouse neuro-urological dynamics in a novel decerebrate arterially perfused mouse (DAPM) preparation

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.

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.

Probabilistic, spinally-gated control of bladder pressure and autonomous micturition by Barrington's nucleus CRH neurons

Micturition requires precise control of bladder and urethral sphincter via parasympathetic, sympathetic and somatic motoneurons. This involves a spino-bulbospinal control circuit incorporating Barrington’s nucleus in the pons (Barr). Ponto-spinal glutamatergic neurons that express corticotrophin-releasing hormone (CRH) form one of the largest Barr cell populations. Barr^CRH neurons can generate bladder contractions, but it is unknown whether they act as a simple switch or provide a high-fidelity pre-parasympathetic motor drive and whether their activation can actually trigger voids. Combined opto- and chemo-genetic manipulations along with multisite extracellular recordings in urethane anaesthetised CRH^Cre mice show that Barr^CRH neurons provide a probabilistic drive that generates co-ordinated voids or non-voiding contractions depending on the phase of the micturition cycle. CRH itself provides negative feedback regulation of this process. These findings inform a new inferential model of autonomous micturition and emphasise the importance of the state of the spinal gating circuit in the generation of voiding.

Responsiveness of lumbosacral superficial dorsal horn neurons during the voiding reflex and functional loss of spinal urethral-responsive neurons in streptozotocin-induced diabetic rats

AIMS

Sensory information from the lower urinary tract (LUT) is conveyed to the spinal cord to trigger and co-ordinate micturition. However, it is not fully understood how spinal dorsal horn neurons are excited during the voiding reflex. In this study, we developed an in vivo technique allowing recording of superficial dorsal horn (SDH) neurons concurrent with intravesical pressure (IVP) during the micturition cycle in both normal and diabetic rats.

METHODS

Lumbosacral dorsal horn neuronal activity and IVP were recorded from urethane-anesthetized naive and streptozotocin (STZ)-induced diabetic rats. Saline was continuously perfused into the urinary bladder through a cannula to induce micturition.

RESULTS

We classified SDH neurons into bladder- and urethral-responsive neurons, based on their responsiveness during the voiding reflex. Bladder-responsive SDH neurons responded to the rapid increase in IVP at the start of voiding. In contrast, urethral-responsive SDH neuronal firing increased at the peak IVP and their firing lasted during the voiding phase (the high-frequency oscillations). Urethral-responsive SDH neurons were more sensitive to capsaicin, received C afferent fiber inputs, and were rarely detected in STZ-diabetes rats. Administration of a cyclohexenoic long-chain fatty alcohol (TAC-302), which is reported to promote neurite outgrowth of peripheral nerves in STZ-diabetic rats, prevented the functional loss of spinal urethral response.

CONCLUSIONS

Sensory information from the bladder and urethra is conveyed separately to different groups of SDH neurons. Functional loss of spinal urethral sensory information through unmyelinated C afferent fibers may contribute to diabetic bladder dysfunction.

Influence of sildenafil on the purinergic components of nerve-mediated and urothelial ATP release from the bladder of normal and spinal cord injured mice

Background and purpose

PDE inhibitors such as sildenafil alleviate lower urinary tract symptoms; however, a complete understanding of their action on the bladder remains unclear. We are investigating the effects of sildenafil, on post and preganglionic nerve‐mediated contractions of the mouse bladder, and neuronal and urothelial ATP release.

Experimental approach

Bladders were used from young (12 weeks), aged (24 months), and spinal cord transected (SCT), mice, for in vitro contractility experiments. An arterially perfused in situ whole mouse model was used to record bladder pressure. Nerve‐mediated contractions were generated by electrical field stimulation (EFS) of postganglionic nerve terminals or the pelvic nerve. ATP release during EFS in intact detrusor strips, and during stretch of isolated mucosa strips, was measured using a luciferin‐luciferase assay.

Key results

Sildenafil (20 μM) inhibited nerve‐mediated contractions in young mice, with an increase in f_1/2 values in force–frequency relationships, demonstrating a greater effect at low frequencies. Sildenafil reduced the atropine‐resistant, purinergic component of nerve‐mediated contractions, and suppressed neuronal ATP release upon EFS in vitro. Sildenafil reduced the preganglionic pelvic nerve stimulated bladder pressure recordings in situ; comparable to in vitro experiments. Sildenafil reduced stretch‐induced urothelial ATP release. Sildenafil also relaxed nerve‐mediated contractions in aged and SCT mice.

Conclusion and implications

Sildenafil has a greater effect on the low‐frequency, purinergic‐mediated contractions and suppresses neuronal ATP release. In addition, sildenafil reduces stretch‐induced urothelial ATP release. These results demonstrate a novel action of sildenafil to selectively inhibit ATP release from nerve terminals innervating detrusor smooth muscle and the urothelium.

Sildenafil, a phosphodiesterase type 5 inhibitor, augments sphincter bursting and bladder afferent activity to enhance storage function and voiding efficiency in mice

Objectives

To investigate the influence of low‐dose sildenafil, a phosphodiesterase type 5 inhibitor (PDE5‐I), on the function of the mouse lower urinary tract (LUT).

Materials and Methods

Adult male mice were decerebrated and arterially perfused with a carbogenated Ringer's solution to establish the decerebrate arterially perfused mouse (DAPM). To allow distinction between central neural and peripheral actions of sildenafil, experiments were conducted in both the DAPM and in a ‘pithed’ DAPM, which has no functional brainstem or spinal cord. The action of systemic and intrathecal sildenafil on micturition was assessed in urethane‐anaesthetised mice.

Results

In the DAPM, systemic perfusion of sildenafil (30 pm) decreased the voiding threshold pressure [to a mean (sem) 84.7 (3.8)% of control] and increased bladder compliance [to a mean (sem) 140.2 (8.3)% of control, an effect replicated in the pithed DAPM]. Sildenafil was without effect on most voiding variables but significantly increased the number of bursts of the external urethral sphincter (EUS) per void in DAPM [to a mean (sem) 130.1 (6.9)% of control at 30 pm] and in urethane‐anaesthetised mice [to a mean (sem) 117.5 (5.8)% of control at 14 ng/kg]. Sildenafil (10 and 30 pm) increased pelvic afferent activity during both bladder filling and the isovolumetric phase [to a mean (sem) 205.4 (30.2)% of control at 30 pm]. Intrathecal application of sildenafil (5 μL of either 150 pm or 1.5 nm) did not alter cystometry and EUS‐electromyography variables in urethane‐anaesthetised mice.

Conclusions

Low‐dose sildenafil increases bladder compliance, increases pelvic nerve afferent activity, and augments the bursting activity of the EUS. We propose that the novel actions on afferent traffic and sphincter control may contribute to its beneficial actions to restore storage and voiding efficiency in LUT dysfunction.

Modulation of Bladder Wall Micromotions Alters Intravesical Pressure Activity in the Isolated Bladder

Micromotions are phasic contractions of the bladder wall. During urine storage, such phasic activity has little effect on intravesical pressure, however, changed motile activity may underlie urodynamic observations such as detrusor overactivity. The potential for bladder motility to affect pressure reflects a summation of the overall movements, comprising the initiation, propagation, and dissipation components of micromotions. In this study, the influence of initiation of micromotions was investigated using calcium activated chloride channel blocker niflumic acid, and the effect of propagation using blockers of gap junctions. The overall bladder tone was modulated using isoprenaline. Isolated tissue strips and whole bladder preparations from juvenile rats were used. 18β-glycyrrhetinic acid was used to block gap junctions, reducing the amplitude and frequency of micromotions in in vitro and ex vivo preparations. Niflumic acid reduced the frequency of micromotions but had no effect on the amplitude of pressure fluctuations. Isoprenaline resulted in a reduction in pressure fluctuations and a decrease in pressure baseline. Using visual video data analysis, bladder movement was visible, irrespective of lack of pressure changes, which persisted during bladder relaxation. However, micromotions propagated over shorter distances and the overall bladder tone was reduced. All these results suggest that phasic activity of the bladder can be characterised by a combination of initiation and propagation of movement, and overall bladder tone. At any given moment, intravesical pressure recordings are an integration of these parameters. This synthesis gives insight into the limitations of clinical urodynamics, where intravesical pressure is the key indicator of detrusor activity.

Characterization of mouse neuro-urological dynamics in a novel decerebrate arterially perfused mouse (DAPM) preparation

AIM

To develop the decerebrate arterially perfused mouse (DAPM) preparation, a novel voiding model of the lower urinary tract (LUT) that enables in vitro-like access with in vivo-like neural connectivity.

METHODS

Adult male mice were decerebrated and arterially perfused with a carbogenated, Ringer's solution to establish the DAPM. To allow distinction between central and peripheral actions of interventions, experiments were conducted in both the DAPM and in a "pithed" DAPM which has no brainstem or spinal cord control.

RESULTS

Functional micturition cycles were observed in response to bladder filling. During each void, the bladder showed strong contractions and the external urethral sphincter (EUS) showed bursting activity. Both the frequency and amplitude of non-voiding contractions (NVCs) in DAPM and putative micromotions (pMM) in pithed DAPM increased with bladder filling. Vasopressin (>400 pM) caused dyssynergy of the LUT resulting in retention in DAPM as it increased tonic EUS activity and basal bladder pressure in a dose-dependent manner (basal pressure increase also noted in pithed DAPM). Both neuromuscular blockade (vecuronium) and autonomic ganglion blockade (hexamethonium), initially caused incomplete voiding, and both drugs eventually stopped voiding in DAPM. Intravesical acetic acid (0.2%) decreased the micturition interval. Recordings from the pelvic nerve in the pithed DAPM showed bladder distention-induced activity in the non-noxious range which was associated with pMM.

CONCLUSIONS

This study demonstrates the utility of the DAPM which allows a detailed characterization of LUT function in mice.