Can Urinary Bladder Innervation Be Restored After Outlet Obstruction and Denervation?

Article information

Int Neurourol J. 2024;28(2):75-82
Publication date (electronic) : 2024 June 30
doi : https://doi.org/10.5213/inj.2448134.067
1Department of Urology, Skåne University Hospital, Malmö, Sweden
2Department of Clinical Sciences, Lund University, Lund, Sweden
3Department of Laboratory Medicine, Lund University, Lund, Sweden
4Wake Forest Institute for Regenerative Medicine, Winston Salem, NC, USA
Corresponding author: Bengt Uvelius Department of Urology, Skåne University Hospital, Jan Waldenströms gata 7, SE-21421 Malmö, Sweden Email: bengt.uvelius@med.lu.se
Received 2024 March 8; Accepted 2024 May 27.

Abstract

Transurethral resection of the prostate, or other methods to decrease outlet resistance usually leads to relief of symptoms in patients with bladder outlet obstruction (BOO). If symptoms of underactivity persist after normalization of outflow conditions, treatment options are limited. In this review, we hypothesize, based on results from basic research, what might become treatment options for such patients in the future. The primary local treatment will still aim at reducing outlet obstruction. We speculate that local secondary treatment in the future might include transplantation of stem cells or mature bladder ganglion cells into the bladder wall. There has been some success in transplanting ganglion cells into the rat bladder. The ganglion cells will sprout into the surrounding tissue but functional connections between the axons of the transplanted neurons, and the detrusor smooth muscle have so far not been demonstrated. Neurotrophins or neurotrimin might be injected into the bladder wall to increase the sprouting of existing or transplanted neurons. Stem cell transplantation has been performed and improves detrusor function, but it has so far, been difficult to demonstrate transplanted stem cells. BOO, persisting detrusor underactivity, and decreased nerve density are often combined with inflammatory activity of the lower urinary tract. NLR family pyrin domain containing 3 (NLRP3) and its messenger RNA (mRNA) as well as cyclooxygenase-2 (Cox-2) mRNA are increased in obstructed bladders. Systemic treatment with the NLRP3 inhibitor glyburide normalized nerve density in rat bladder, and, to some extent, bladder function. It is unclear whether Cox-2 is involved in the decreased nerve density following obstruction, but Cox-2 mRNA increases 5-fold in obstructed bladder. Future therapy against bladder underactivity remaining following relief of obstruction includes either systemic treatment, perhaps by anti-inflammatory drugs, or local treatment by injection of stem cells, mature ganglion cells, and/or neurotrophins or neurotrimin into the bladder wall.

INTRODUCTION

The motor innervation of the human urinary bladder is mainly by postganglionic parasympathetic axons. The ganglion cells are situated in ganglia both along the parasympathetic nerves and in the bladder itself (intramural ganglia). Such intramural ganglion cells are also found in e.g., guinea pig bladders [1]. The sensory input to the spinal cord is via afferent axons with their perikarya situated in the dorsal root ganglia. The adrenergic innervation is sparse except in the bladder neck and urethral sphincter. The parasympathetic innervation of the bladder is very dense, each detrusor muscle cell is reached by at least one nerve terminal [2]. The innervation of the human bladder is a resilient system. Lesions will affect a mixture of preganglionic (decentralization) and postganglionic (postganglionic denervation) axons, and probably the intramural ganglion cells. Nerve damage of clinical importance might occur e.g., after pelvic organ surgery, pelvic fractures, bladder outlet obstruction, diabetes mellitus, and acrylamide intoxication. In the bladders subjected to outlet obstruction, the lesions are mostly postganglionic but might also affect the intramural ganglion cells. Injury of the afferent nerves might also contribute to bladder dysfunction and is a major cause of bladder dysfunction in diabetes mellitus and acrylamide intoxication.

Denervated and obstructed bladders have similarities. The detrusor muscle cells hypertrophy in both, and the bladder weight increases. Array data show that the hypertrophic response to denervation and obstruction are quite similar. One example is that the messenger RNA (mRNA) for the gap junction protein connexin 43 increases in both (by 2.63 in 10-day obstructed bladder, and by 3.30 in 10-day denervated bladder) [3]. An increased number of connexons between the smooth muscle cells might be a compensatory mechanism counteracting the decrease or absence of motor nerve terminals. A consequence of this is a higher amplitude of the spontaneous contractions in the bladder wall during filling. This overactivity is most pronounced in the denervated bladder, where the tetrodotoxin-resistant phasic contractions can reach almost 60% of the maximal contractile amplitude [4]. Another example of a similar hypertrophic response in the denervated and obstructed bladder is the significantly increased mRNA for (basal lamina) collagen 4 (10 days obstructed 2.9, 10 days denervated 2.8) and elastin (10 days obstructed 4.1, 10 days denervated 6.5) in the obstructed and denervated bladders. In our arrays, there was no difference in mRNA levels for muscarinic receptors in denervated, and obstructed bladders, and their respective controls. Others have, however, found an increased number of muscarinic receptors in obstructed [5] and denervated bladders [6]. In the latter study, the increase was partly due to an upregulation of the M2 receptor [7].

It may be questioned if the hypertrophy of the denervated bladders is due to the denervation as such, or if it is secondary to the stretch of the smooth muscle cells caused by the distension of the paralyzed bladder. Nilvebrant et al. [6] found that bladder denervation led to increased bladder weight and increased number of muscarinic receptors. If the urinary flow was diverted to avoid bladder distension, bladder weight, and muscarinic receptor density remained normal. Thus, the hypertrophic response and the increased density of M receptors were secondary to the stretch of the bladder wall, and not a direct effect of the denervation.

The rat bladder also hypertrophies in response to diabetes mellitus. Whether this hypertrophy is similar to that of denervated or obstructed bladders is somewhat unclear. Earlier studies have interpreted diabetes hypertrophy as a response to the increased functional demand (increased diuresis) of the diabetic bladder [8]. It has recently been suggested that the hypertrophy is a direct effect of the diabetic state on the detrusor smooth muscle cells [9]. Bladder arrays suggest differences between bladder hypertrophy caused by diabetes and polyuria caused by sucrose feeding [10]. Hindi et al. [10] found e.g., a sevenfold increase in brain-derived neurotrophic factor (BDNF) mRNA in diabetic bladders but no effect by sucrose feeding. We have previously reported a 2-fold increase of BDNF mRNA in obstructed bladders [3]. BDNF stimulates sprouting of parasympathetic axons from the pelvic ganglia [11]. Taken together, this might indicate denervation and reinnervation processes in both diabetic and obstructed bladders. This is supported by the observations that neurotrimin mRNA is increased both in 10-day obstructed and 10-day denervated bladder ( ×3.5 for both, present study), and in diabetic bladders [10]. Neurotrimin is known to stimulate axonal growth, guidance of nerves to their targets, and be involved in synaptogenesis.

In recent years many studies have been published attempting to restore nerve function in urinary bladders with various lesions to the innervation. There has been some but limited success. In the following, we will review and reassess methods and approaches in the literature to restore bladder innervation after outlet obstruction and denervation. We intend to identify new directions for research and targets for therapeutic interventions.

MATERIALS AND METHODS

The present review is mainly a literature survey but contains also previously unpublished results from our bank of electron microscopy plates of obstructed and denervated female rat bladders, and bladder wholemounts stained for detection of acetylcholinesterase. We also have used unpublished microarray data from control, obstructed, and denervated rat bladders. These arrays have been used to characterize what happens at the molecular level during the growth of the obstructed bladder or denervated bladder and to check, in a systematic manner, the effect of obstruction and denervation for the mRNA expression of around 15,000 proteins. The microarrays have been used in other publications [3, 12, 13] and are publicly available (GEO accession numbers GSE47080 and 104540).

PREVIOUS RESULTS, NEW RESULTS, AND DISCUSSION

The symptoms of bladder innervation injury are secondary to either an increased spontaneous activity of the detrusor muscle cells causing an increased stiffness or overactivity of the bladder, or the contrary, an underactive bladder (UAB) with a large residual urine, and a decreased bladder sensitivity. It has been well demonstrated in different animal species that the obstructed bladder will show an increase in sensitivity to exogenously applied agonists and a reduction in sensitivity to intramural nerve stimulation (postjunctional supersensitivity). Morphological studies have shown an inverse correlation between nerve density and the duration of obstruction [14], leading to a dramatically decreased density of synapses in the long-term obstructed detrusor [15]. In animals [16, 17], but also in man [18, 19] the nerve damage is inhomogeneous. Urinary outlet obstruction can elicit a partial (patchy) denervation of the bladder, probably caused by e.g., ischemia in the bladder wall and stretch of the intramural nerves caused by the development of residual urine [16, 17, 19, 20]. Fusco et al. [21] summarized available evidence about BOO-induced morphological and molecular alterations occurring in the various compartments of the human bladder and concluded that the remodeling process involved multiple cellular compartments including not only detrusor muscle and nerves but also the urothelium, lamina propria, and detrusor extracellular medium, thus confirming what has been found in numerous animal studies.

In a series of acetylcholinesterase-stained wholemounts of the rat bladder the major nerve pattern of the obstructed bladders was found to be the same as in the control bladders (Fig. 1). The nerves were thicker, but the anatomical pattern of intramural nerves was the same as in the controls. No new nerves were observed in any of the obstructed bladders, and there were no intramural ganglia.

Fig. 1.

Wholemounts of acetylcholinesterase-stained ventral segment of a control bladder (A), and a 6-week obstructed bladder (B). Urethral orifice at the midbottom. The weight of the control and obstructed bladder was 70 mg, and 700 mg, respectively. The picture with the obstructed bladder is diminished 90% to give the same size as that of the control. No new nerves have developed in the obstructed bladder. Instead, there seems to be fewer nerves. No intramural ganglion cells can be seen. When the different magnifications are considered, it is obvious that the muscle bundles in the obstructed bladder are much larger than in the control. The amount of muscle in relation to the visible nerves is considerably higher in the obstructed bladder. The base of the left and right picture corresponds to 8.2 and 15.8 mm, respectively. The equatorial circumference was 36 mm (control), and 98 mm (obstructed). Both pictures are from the left side of the bladder. The photo of the control bladder is reversed to simplify the comparison.

Compensatory Mechanisms

Restoration of nerve function after injury can occur spontaneously or as the result of different types of intervention. The bladder innervation has a high degree of plasticity. This means that after a nerve lesion, surviving axons can sprout and take over the innervation from those axons that have degenerated [22]. This indicates that the capacity for restitution is high. There is also a high safety margin. Every muscle cell has at least one motor synapse, and there is connexion-dependent coupling between the cells making it possible for one active muscle cell to activate its neighbors. The bladder can lose up to 50% of its motor and sensory innervations without the development of residual urine [23].

Relief of Obstruction

The most obvious way of restoring nerve function of the obstructed bladder is of course to relieve the obstruction. After obstruction relief, there was a return toward control values of the physiological responses to exogenously applied agonists (acetylcholine and potassium) and electrical field stimulation [24]. There was also an increase in neuronal innervation which was more marked in the animals with a shorter period of obstruction. However, this relief of obstruction does not normalize the structural changes. Deobstructed bladders have characteristic gene expressions, structural morphologies, and functional properties that make them distinctly different from both control and obstructed bladders [3].

Ganglion Cell Differentiation

If the rat pelvic ganglia are removed or destroyed, the postganglionic parasympathetic axons in the bladder wall disappear completely causing a postganglionic denervation of the bladder. If the preganglionic nerves are cut, a decentralization of the bladder will occur but the ganglion cells and the postganglionic axons are left intact. The sensory axons from the bladder pass through the pelvic ganglia on their way to the spinal cord. Pelvic ganglionectomy thus also elicits a sensory denervation.

The nerves in the bladder wall contain axons and their supporting Schwann cells, surrounded by a fibrous sheath with collagen and fibroblasts. After unilateral ganglionectomy, the axons of the ipsilateral bladder nerves degenerate and disappear. The fibrous sheath and the Schwann cells do not degenerate, so the pattern of the distribution of the axon-free nerves is the same as in the normal bladder. If axons sprout, they can be led by the nerves to more distally located detrusor muscle cells. Fig. 2 shows a control ventral nerve and a corresponding nerve 3 months after ipsilateral ganglionectomy.

Fig. 2.

A ventral longitudinal nerve from a control bladder (A) and from a bladder 3 months after ipsilateral excision of the pelvic ganglion (B). The control nerve contains many Schwann cells, and unmyelinated axons to the detrusor muscle cells. A limited number of myelinated axons are sensory. In the lower panel the nerve still contains many Schwann cells after 3 months, but there is no sign of axonal sprouting. The surviving “axon-free” nerves probably have an important role in guiding the sprouting axons to their target, the smooth muscle cells. Calibration bar is 5 μm.

New ganglion cells can differentiate (Fig. 3) in the bladder wall from precursor cells along the intramural nerves [25]. A female rat pelvic ganglion contains about 2,600 ganglion cells [26]. If one pelvic ganglion is removed [25] about 50 new intramural ganglion cells seem to develop. This corresponds to about 1.9% of the number in the remaining ganglion. Whether the number of ganglion cells also increases in the remaining ganglion is not known. It is, however, known that the number of ganglion cells has increased to 3,995 [26] in adult female Brattleboro rats with hereditary diabetes insipidus. This suggests that the increased functional demand of the detrusor has led to the development of an increased number of ganglion cells. It can, however, not be ruled out that there is an age-dependent decrease in the number of pelvic ganglion neurons, and that this decrease is slowed down by the increased functional demand [27].

Fig. 3.

Ipsilaterally ganglionectomized bladder wall. New ganglion cells. Acetylcholinesterase staining. Panel A shows 2 axonfree (“denervated”) nerves coming from the bladder base and running distally (upwards). A newly developed cluster of ganglion cells is situated where these “empty” nerves coalesce, and the single nerve running distally (upwards) is filled with acetylcholinesterase staining axons. (B) An axon-free nerve is running in a distal direction (upwards). Axons from a nearby cluster of ganglion cells send 2 axon bundles to the nerve. The upper bundle then runs distally along the nerve. The size of the ganglion cells is about 25 μm.

Neurotrophin Stimulation

The axonal sprouting from cultured mouse pelvic ganglia in vitro is stimulated by the neurotrophins BDNF and neurotrophin-3 (NT3) whereas nerve growth factor (NGF) has little effect [11]. We have previously reported an increased level of BDNF mRNA in the obstructed bladder wall [3]. This increases BDNF level which then stimulates the axonal sprouting of parasympathetic intramural axons, and perhaps also the development of new ganglion cells. Preliminary experiments (Uvelius and Gabella) suggest that superior cervical ganglion (SCG) neurons (transmitter noradrenaline) do not sprout when transplanted into the bladder wall. The SCG neurons have TrkA receptors, instead of TrkB and C as the pelvic ganglion cells and would therefore need NGF, which is low in the bladder, as its neurotrophin. Neurotrimin, although not a neurotrophin [10] has an increased mRNA in obstructed bladders. If it was possible to increase the concentration of BDNF, NT3, or neurotrimin in the wall of the obstructed bladder one would expect more sprouting axons from pelvic ganglion neurons.

Ganglion Cell Transplantation

An interesting approach to the restoration of damaged bladder denervation was described by Gabella and Uvelius [28] who transplanted a large portion of the pelvic ganglion of adult female rats into the wall of the urinary bladder of the same animals. Since the rat urinary bladder does not normally contain any intramural ganglion cells this makes it a good model to study bladder denervation and decentralization, giving experimental advantages over bladders that, like the human, have intramural ganglia. Gabella and Uvelius [28] found that the general architecture of all the transplanted ganglia was preserved, and that the vascularization was re-established. The nerves grew out of the transplant and connections with the original intramural nerves. All the synapses degenerated at the time of transplantation, but new synapses began to reappear on the ganglion neurons and most neurons survived for the full length of the experiments (4 months). The authors suggested that their results showed that homotransplants of pelvic neurons into the bladder have a high rate of success, in terms of survival, maintenance of fine structure, growth, and reconnections. In addition, these neurons of adult organisms display plastic and regenerative abilities. The bladder innervation has a high degree of plasticity. This means that surviving axons can sprout and take over the innervation from those nerves that have degenerated. Gabella and Uvelius [28] did not investigate the functional status of the bladders after transplantation. If bladder function can be restored, this approach may be possible to apply in humans: parasympathetic ganglion cells could be injected into the bladder wall through a cystoscope in the same manner as Botox injections. A future possibility would be to use ganglion cells with different transmitters.

Stem Cell Therapy

An attractive way to improve function in an obstructed and or denervated bladder would be stem cell therapy [29-33]. Studies of stem cells injected into the bladder have demonstrated positive effects in experimental voiding dysfunctions such as detrusor overactivity with or without bladder outflow obstruction (BOO). Most studies on the effects of stem cells on bladder dysfunction have been performed on the rat BOO model [31, 34, 35].

It is obvious that stem cell treatment can affect the remodeling of the bladder that occurs after the initiation of obstruction in the rat BOO model, and that this treatment may have a beneficial effect against both morphological and functional changes. In many of the animal studies performed, the authors speculated on the use of mesenchymal stem cells (MSCs) as a new treatment to prevent the morphological and functional effects of BOO in humans. However, if MSC treatment has positive effects also in human BOO, relevant questions are (1) When should treatment be instituted?, (2) can cell therapy reverse established morphological changes? In most of the BOO studies cited above, stem cells were given early in the remodeling process initiated by the urethral obstruction, i.e., at times points when the process is still dynamic. Studies on the clinical application of MSCs in humans with various diseases are available. However, the effects of stem cell therapy for bladder dysfunction, e.g., in patients with OAB, BOO-associated detrusor overactivity, or patients with UAB have so far not been published.

Anti-Inflammatory Therapy

The progressive urinary dysfunction associated with BOO has been known for over a decade to be the result of an ongoing inflammatory response triggered by at least 3 interrelated insults: (1) high pressure, (2) excessive stretch, and (3) hypoxia/reperfusion (oxidative stress), all of which occur repeatedly with each micturition cycle as the bladder contracts with greater force to overcome the outflow resistance [21]. Of particular interest in this context are the nucleotide-binding oligomerization domain-like receptors, especially the best-studied family member, NLR family pyrin domain containing 3 (NLRP3). Hughes et al. [36] studied the importance of NLRP3 in a chronic setting to determine whether the NLRP3 inhibitor glyburide, affected inflammation, voiding dysfunction, bladder decompensation, and nerve density in long-term obstruction. The nerves they measured were identical to those seen in Fig. 1 but with the bladders cut at a right angle to their long axis. Note that they did not measure the density of synapses in their light microscopy study, and a decreased nerve density does not necessarily indicate a decrease in the density of synapses, i.e., denervation.

Hughes et al. [36] found 7 nerves per 106 μm2 in their control rat bladders. Sadegh et al. [15] found, in similar bladders, 1 synapse per 100 μm2 (104 synapses per 106 μm2). They used electron microscopy which has a much higher resolution and makes it possible to directly count synapses. In the obstructed bladders Hughes et al. [36] found 2 nerves per 106 μm2, whereas Sadegh et al. [15] found 0.1 synapse per 100 μm2 (103 synapses per 106 μm2). This means that obstruction decreases nerve density by a factor 3.5, and synapse density by a factor of 10. As Hughes et al. [36] defined nerves this means that there are about 1,400 synapses per nerve in control bladders and 500 in the obstructed. The measurements of nerve densities are thus not a direct function of the synapse densities but relative comparisons between nerve densities seem possible.

Hughes et al. [36] noted functional improvement after glyburide treatment, e.g., the decrease in voiding efficiency in the chronic BOO rats was prevented. Of particular interest was that the reduction in nerve density apparent with BOO was attenuated with glyburide. The authors concluded that their results suggested a critical role for NLRP3 in mediating bladder decompensation and nerve density during chronic BOO. It is not known, however, if glyburide has any effect on the density of synapses. We found in our arrays that NLRP3 mRNA increased by 90 percent in 10-day denervated bladders but was unaffected by obstruction.

It is unclear whether Cox-2 is involved in the changed nerve density following obstruction. Cox-2 mRNA is, however, increased almost 5 times in 10-day obstructed bladders but was unaffected by 10-day denervation. This fits well with the results in the study by Park et al. [37]. They studied the effect of acute total obstruction in the mouse bladder and found that 6 hours of obstruction induced a pronounced increase of Cox-2 mRNA caused by the stretch of the detrusor smooth muscle cells. NS-398, a Cox-2 inhibitor could prevent this increase.

We speculate that NLRP3 is increased in the denervated bladders by neurogenic inflammation caused by the degenerating intramural axons, whereas the increased Cox-2 mRNA is caused by the stretch of the bladder wall in our partially obstructed bladders.

SUMMARY

Relief of obstruction, e.g., transurethral resection of the prostate (TURP) usually leads to relief of symptoms, and the patient feels cured. If symptoms of underactivity persist after the normalization of outflow conditions, the treatment options are limited, and include both re-TURP and clean intermittent catheterization. In the present review, we speculate what will become the future options.

There will be both local and systemic treatment. As of today, the standard local treatment will aim at reducing outlet obstruction. Other local treatments might be transplanting stem cells or mature bladder ganglion cells into the bladder wall. The literature shows that there has been some progress. It is possible to transplant ganglion cells experimentally into the bladder. The ganglion cells survive and sprout into the surrounding tissue. So far, it is not known if there are functional connections (synapses) between the axons of the transplanted ganglion cells, and the detrusor smooth muscle cells. Stem cell transplantation has been performed successfully but with a result opposite to that of ganglion cell transplantation. Transplantation of stem cells improves the function of the detrusor, but it has been difficult to demonstrate the transplanted stem cells, or the cells derived from them.

Neurotrophins or neurotrimin might be injected in the bladder wall to increase the sprouting of existing ganglion cells, or cells that have been injected into the bladder wall.

Bladder outlet obstruction, persisting underactivity, and decreased nerve density are often combined with inflammatory activity of the lower urinary tract. NLRP3 and its mRNA as well as Cox-2 mRNA are increased in obstructed bladders. Systemic treatment with the NLRP3 inhibitor glyburide normalized nerve density, and, to some extent, bladder function. It is unclear whether Cox-2 is involved in the changed nerve density following obstruction, but Cox-2 mRNA increases almost 5-fold in the obstructed bladder.

CONCLUSIONS

Without being too speculative future therapy against bladder underactivity remaining following relief of outlet obstruction could be either a systemic therapy, perhaps by anti-inflammatory drug treatment, or a local using neurotrophins, ganglionic or stem cells, perhaps by injection into the bladder wall as Botulinum toxin is injected today.

Notes

Grant/Fund Support

This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Research Ethics

The study does not contain any new animal experiments. Ethical permits for the original experiments were applied for at the Swedish Board of Agriculture and approved by the Malmo/Lund Ethical Committee for animal experiments (approval numbers M 4–16, M 104–15, and M 40–13).

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

AUTHOR CONTRIBUTION STATEMENT

· Conceptualization: BU, KEA

· Data curation: BU, KEA

· Formal analysis: BU, KEA

· Funding acquisition: BU, KEA

· Methodology: BU, KEA

· Project administration: BU, KEA

· Visualization: BU, KEA

· Writing: BU, KEA

Acknowledgements

We acknowledge the long-lasting cooperation with Professor Giorgio Gabella.

References

1. Gabella G. Intramural neurons in the urinary bladder of the guinea-pig. Cell Tissue Res 1990;261:231–7.
2. Gabella G. The structural relations between nerve fibres and muscle cells in the urinary bladder of the rat. J Neurocytol 1995;24:159–87.
3. Uvelius B, Andersson KE. Molecular and morphological characteristics of the de-obstructed rat urinary bladder - an update. Int J Mol Sci 2022;23:11330.
4. Ekström J, Uvelius B. Length-tension relations of smooth muscle from normal and denervated rat urinary bladders. Acta Physiol Scand 1981;112:443–7.
5. Shakirova Y, Swärd K, Uvelius B, Ekman M. Biochemical and functional correlates of an increased membrane density of caveolae in hypertrophic rat urinary bladder. Eur J Pharmacol 2010;649:362–8.
6. Nilvebrant L, Ekström J, Malmberg L. Muscarinic receptor density in the rat urinary bladder after denervation, hypertrophy and urinary diversion. Acta Pharmacol Toxicol (Copenh) 1986;59:306–14.
7. Braverman AS, Doumanian LR, Ruggieri MR Sr. M2 and M3 muscarinic receptor activation of urinary bladder contractile signal transduction. II. Denervated rat bladder. J Pharmacol Exp Ther 2006;316:875–80.
8. Andersson PO, Malmgren A, Uvelius B. Cystometrical and in vitro evaluation of urinary bladder function in rats with streptozotocininduced diabetes. J Urol 1988;139:1359–62.
9. Arioglu Inan E, Ellenbroek JH, Michel MC. A systematic review of urinary bladder hypertrophy in experimental diabetes: part I. Streptozotocin-induced rat models. Neurourol Urodyn 2018;37:1212–9.
10. Hindi EA, Williams CJ, Zeef LAH, Lopes FM, Newman K, Davey MMM, et al. Experimental long-term diabetes mellitus alters the transcriptome and biomechanical properties of the rat urinary bladder. Sci Rep 2021;11:15529.
11. Ekman M, Zhu B, Swärd K, Uvelius B. Neurite outgrowth in cultured mouse pelvic ganglia - Effects of neurotrophins and bladder tissue. Auton Neurosci 2017;205:41–9.
12. Zhu B, Ekman M, Svensson D, Lindvall JM, Nilsson BO, Uvelius B, et al. Array profiling reveals contribution of Cthrc1 to growth of the denervated rat urinary bladder. Am J Physiol Renal Physiol 2018;314:F893–905.
13. Zhu B, Daoud F, Zeng S, Matic L, Hedin U, Uvelius B, et al. Antagonistic relationship between the unfolded protein response and myocardin-driven transcription in smooth muscle. J Cell Physiol 2020;235:7370–82.
14. Barendrecht MM, Chichester P, Michel MC, Levin RM. Effect of short-term outlet obstruction on rat bladder nerve density and contractility. Auton Autacoid Pharmacol 2007;27:47–53.
15. Sadegh MK, Ekman M, Krawczyk K, Svensson D, Göransson O, Dahan D, et al. Detrusor induction of miR-132/212 following bladder outlet obstruction: association with MeCP2 repression and cell viability. PLoS One 2015;10:e0116784.
16. Speakman MJ, Brading AF, Gilpin CJ, Dixon JS, Gilpin SA, Gosling JA. Bladder outflow obstruction - a cause of denervation supersensitivity. J Urol 1987;138:1461–6.
17. Pandita RK, Fujiwara M, Alm P, Andersson KE. Cystometric evaluation of bladder function in non-anesthetized mice with and without bladder outlet obstruction. J Urol 2000;164:1385–9.
18. Drake MJ, Gardner BP, Brading AF. Innervation of the detrusor muscle bundle in neurogenic detrusor overactivity. BJU Int 2003;91:702–10.
19. Brading A, Pessina F, Esposito L, Symes S. Effects of metabolic stress and ischaemia on the bladder, and the relationship with bladder overactivity. Scand J Urol Nephrol Suppl 2004;(215):84–92.
20. de Jongh R, Dambros M, Haenen GR, den Hartog GJ, Bast A, van Kerrebroeck PE, et al. Partial bladder outlet obstruction reduces the tissue antioxidant capacity and muscle nerve density of the guinea pig bladder. Neurourol Urodyn 2009;28:461–7.
21. Fusco F, Creta M, De Nunzio C, Iacovelli V, Mangiapia F, Li Marzi V, et al. Progressive bladder remodeling due to bladder outlet obstruction: a systematic review of morphological and molecular evidences in humans. BMC Urol 2018;18:15.
22. Uvelius B, Gabella G. The distribution of intramural nerves in urinary bladder after partial denervation in the female rat. Urol Res 1998;26:291–7.
23. Berggren T, Gabella G, Malmgren A, Uvelius B. Effects of unilateral pelvic ganglionectomy on urinary bladder function in the male rat. Scand J Urol Nephrol 1993;27:181–8.
24. Speakman MJ, Brading AF, Dixon JS, Gilpin SA, Gilpin CJ, Gosling JA. Cystometric, physiological and morphological studies after relief of bladder outflow obstruction in the pig. Br J Urol 1991;68:243–7.
25. Uvelius B, Gabella G. Intramural neurones appear in the urinary bladder wall following excision of the pelvic ganglion in the rat. Neuroreport 1995;6:2213–6.
26. Kayanja D, Gabella G. Pelvic ganglion neurons in rats with familial diabetes insipidus (Brattleboro strain) [abstract]. J Auton Nerv Sys 1993;43 Suppl:88–9.
27. Malmgren A, Uvelius B, Andersson KE, Andersson PO. Urinary bladder function in rats with hereditary diabetes insipidus; a cystometrical and in vitro evaluation. J Urol 1992;148:930–4.
28. Gabella G, Uvelius B. Homotransplant of pelvic ganglion into bladder wall in adult rats. Neuroscience 1998;83:645–53.
29. Andersson KE. Potential of stem cell treatment in detrusor dysfunction. Adv Drug Deliv Rev 2015;82-83:117–22.
30. Shin JH, Ryu CM, Yu HY, Shin DM, Choo MS. Current and future directions of stem cell therapy for bladder dysfunction. Stem Cell Rev Rep 2020;16:82–93.
31. Kim JH, Yang HJ, Choi SS, Kim SU, Lee HJ, Song YS. Improved bladder contractility after transplantation of human mesenchymal stem cells overexpressing hepatocyte growth factor into underactive bladder from bladder outlet obstruction models of rats. PLoS One 2021;16:e0261402.
32. Yu HY, Shin JH, Yun H, Ryu CM, Lee S, Heo J, et al. A preclinical study of human embryonic stem cell-derived mesenchymal stem cells for treating detrusor underactivity by chronic bladder ischemia. Stem Cell Rev Rep 2021;17:2139–52.
33. Shen Z, Ge Q, Shen D, Xia K, Xiao J. Bone marrow mesenchymal stem cells therapy on bilateral pelvic nerve crush-induced voiding dysfunction in rats. Int Urogynecol J 2022;33:2485–92.
34. Woo LL, Tanaka ST, Anumanthan G, Pope JC 4th, Thomas JC, Adams MC, et al. Mesenchymal stem cell recruitment and improved bladder function after bladder outlet obstruction: preliminary data. J Urol 2011;185:1132–8.
35. Song M, Heo J, Chun JY, Bae HS, Kang JW, Kang H, et al. The paracrine effects of mesenchymal stem cells stimulate the regeneration capacity of endogenous stem cells in the repair of a bladder-outletobstruction-induced overactive bladder. Stem Cells Dev 2014;23:654–63.
36. Hughes FM Jr, Sexton SJ, Ledig PD, Yun CE, Jin H, Purves JT. Bladder decompensation and reduction in nerve density in a rat model of chronic bladder outlet obstruction are attenuated with the NLRP3 inhibitor glyburide. Am J Physiol Renal Physiol 2019;316:F113–20.
37. Park JM, Yang T, Arend LJ, Schnermann JB, Peters CA, Freeman MR, et al. Obstruction stimulates COX-2 expression in bladder smooth muscle cells via increased mechanical stretch. Am J Physiol 1999;276:F129–36.

Article information Continued

Fig. 1.

Wholemounts of acetylcholinesterase-stained ventral segment of a control bladder (A), and a 6-week obstructed bladder (B). Urethral orifice at the midbottom. The weight of the control and obstructed bladder was 70 mg, and 700 mg, respectively. The picture with the obstructed bladder is diminished 90% to give the same size as that of the control. No new nerves have developed in the obstructed bladder. Instead, there seems to be fewer nerves. No intramural ganglion cells can be seen. When the different magnifications are considered, it is obvious that the muscle bundles in the obstructed bladder are much larger than in the control. The amount of muscle in relation to the visible nerves is considerably higher in the obstructed bladder. The base of the left and right picture corresponds to 8.2 and 15.8 mm, respectively. The equatorial circumference was 36 mm (control), and 98 mm (obstructed). Both pictures are from the left side of the bladder. The photo of the control bladder is reversed to simplify the comparison.

Fig. 2.

A ventral longitudinal nerve from a control bladder (A) and from a bladder 3 months after ipsilateral excision of the pelvic ganglion (B). The control nerve contains many Schwann cells, and unmyelinated axons to the detrusor muscle cells. A limited number of myelinated axons are sensory. In the lower panel the nerve still contains many Schwann cells after 3 months, but there is no sign of axonal sprouting. The surviving “axon-free” nerves probably have an important role in guiding the sprouting axons to their target, the smooth muscle cells. Calibration bar is 5 μm.

Fig. 3.

Ipsilaterally ganglionectomized bladder wall. New ganglion cells. Acetylcholinesterase staining. Panel A shows 2 axonfree (“denervated”) nerves coming from the bladder base and running distally (upwards). A newly developed cluster of ganglion cells is situated where these “empty” nerves coalesce, and the single nerve running distally (upwards) is filled with acetylcholinesterase staining axons. (B) An axon-free nerve is running in a distal direction (upwards). Axons from a nearby cluster of ganglion cells send 2 axon bundles to the nerve. The upper bundle then runs distally along the nerve. The size of the ganglion cells is about 25 μm.