Iranian Journal of Medical Sciences

Document Type: Review Article

Authors

1 Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran

2 Research Center for Evidence Based-Medicine, Iranian EBM Centre: A Joanna Briggs Institute Affiliated Group, Tabriz University of Medical Sciences, Tabriz, Iran; Department of Urology, Imam Reza Teaching Hospital, Tabriz University of Medical Sciences, Tabriz, Ira

3 Department of Neurosciences and Cognitive, School of Advanced Medical Sciences, Tabriz University of Medical Sciences, Tabriz, Iran

4 Department of Tissue Engineering, School of Advanced Medical Sciences, Tabriz University of Medical Sciences, Tabriz, Iran

5 Research Center for Evidence Based-Medicine, Iranian EBM Centre: A Joanna Briggs Institute Affiliated Group, Tabriz University of Medical Sciences, Tabriz, Iran; Neurosciences Research Center, Tabriz University of Medical Sciences, Tabriz, Iran

Abstract

Neurogenic bladder (NGB) secondary to spinal cord injury (SCI) is accompanied with several complications such as urinary tract deterioration, urinary incontinence, and consequently lower quality of life (QoL), significant morbidities, and occasionally death. Current therapeutic methods have some side effects and there is no treatment for the upper urinary tract injuries. Stem cell therapy is a promising method for treating this condition. However, the best timing and the best route of its transplantation have not yet been determined. Animal models of SCI, especially in rats, are the most commonly used method for evaluating the efficacy of cell therapy in NGB improvement, and the most common assessment method is the urodynamic studies (UDS). However, there are variations in the range of UDS parameters among the published studies. The current review aimed to discuss the effect of stem cell transplantation on bladder dysfunction recovery based on urodynamic parameters after SCI in rats. For this purpose, the cell source, doses, the route of administration, and the complete UDS equipment and its parameters were summarized in SCI models in rats. In some urodynamic test results, to some extent, an improvement in the lower urinary system function was observed in each treatment group. However, this improvement was far from full functional recovery. The average cell dose was about 1 million cells in every injected site. In most studies, the stem cells (SCs) were transplanted 9 days after the injury using PE-50 and PE-60. Many researchers have recommended further experimental and clinical studies to confirm this treatment modality.

Keywords

What’s Known

Animal models of spinal cord injury, especially rats, are the most commonly used method to evaluate the efficacy of cell therapy in neurogenic bladder improvement and the most common assessment method is urodynamic studies. There are variations in the range of urodynamic parameters among the published studies.

What’s New

Contusion injury is the most common spinal cord injury model. The average cell dose is about 1 million cells, transplanted 9 days after injury. In some urodynamic test results, to some extent, improvement in the function of the lower urinary system was observed. However, this improvement is far from full functional recovery.

Introduction

Neurogenic bladder (NGB) is a common condition in most neurological diseases such as spinal cord injury (SCI), 1 Parkinson’s disease, 2 multiple sclerosis, 3 and cerebral vascular accident/stroke, 4 which has a negative impact on quality of life (QoL). 5 The International Continence Society (ICS) has defined overactive bladder (OAB) symptoms as urgency (with or without urge incontinence), daytime frequency, and nocturia. In the presence of a neurological condition, this problem is called neurogenic OAB. 6 Urine stasis and upper urinary tract injury following NGB arises from high detrusor pressure during the filling phase (poor compliance) and additional contraction of the detrusor against the closed sphincter (detrusor sphincter dyssynergia). 7 , 8 The prevalence of NGB in patients with SCI is 70% to 84%. 9 NGB secondary to SCI is accompanied with several complications such as urinary tract deterioration, 10 , 11 urinary incontinence 12 and consequently lower QoL, 13 significant morbidities and occasionally death. 14 Numerous therapies for NGB including physical and psychological methods, 15 electrical stimulation, 16 medication, 17 and surgery 18 have been developed. However, these methods have some side effects and sometimes resulted in incomplete recovery. 8

Stem cell transplantation and tissue engineering are the two important options that may overcome the limitations of the current therapies. 19 - 21 Cell therapy is a sub-type of regenerative medicine. In this process, SCs are introduced into the tissue to treat a disease with or without gene therapy. 22 The main SCs used for cell therapy are multipotent mesenchymal stem cells (MSCs) 23 , 24 with two important abilities, namely self-renewing and differentiation into various cell types. 25 MSCs are derived from bone marrow (BM-MSCs), 26 skeletal muscle (Sk-MSCs), 27 umbilical cord (UC-MSCs), 28 and adipose tissue. 29 , 30 Another source is adult tissue such as oral mucosa. 31 For bladder regeneration, MSCs showed better results in comparison with using differentiated SCs. 32 While numerous reports have shown the potential of these cells to replace or transplant in the lungs, liver, heart, and brain, data on improved bladder function is scarce. 33 - 35 Some researches focused on the role of neural progenitor SCs, as multipotent adult SCs, which exist in the central nervous system, in the regeneration of animal models. 36 The self-renewal potency and formation of new neurons and glial cells led researchers to use these cells. 37

Bladder substitutes, using synthetic or natural materials, have been developed in recent years. However, despite numerous attempts, it is still an immature process because of mechanical, structural, functional, or biocompatibility problems. Bladder acellular matrix (BAM)-based scaffold obtained from donor’s bladders may overcome these problems. In this process, the cell and its components are removed from the bladder and then the tissue matrix with collagen, elastin, fibronectin, glycosaminoglycans, proteoglycans, and growth factors contents are placed. 38

The current review aimed to discuss the effect of stem cell transplantation on bladder dysfunction recovery based on urodynamic parameters after SCI in rats. For this purpose, the cell source, doses, the route of administration, and the complete UDS equipment and its parameters were summarized in SCI models in rats.

Diagnosis of NGB

UDS is an important factor in the diagnosis of urethral and bladder dysfunction. 39 According to the definition of ICS, UDS is the study of lower urinary tract physiology and the urinary hydrodynamic transmission. 6 Rodents, most commonly rats, are widely used to show urinary storage and voiding function both in normal conditions and in disease models 40 using cystomery as a common methodology. cystometry in rodents gives important information about the physiology and pharmacology of the bladder. 41

Cystometry in Rodents

There are morphological and functional differences between the bladder of humans and rats. 41 In rats, bladder contraction is mediated by ATP, whereas in humans it is contracted by the mediation of acetylcholine. 40 - 42 Cystometric parameters in rodents are poorly defined and the used criteria are different from humans. Therefore, it is important to define the terminology on what is measured and avoid using the terminology for human cystometry. 41

The reviewed articles had considered two different methods for urodynamic testing in rats. The first method was performed by using a cystometry catheter (PE-50) “Y” connected to a continuous infusion system and to a polygraph. In this method, vesical pressure during the filling and voiding phase is determined and the maximum urethral closure pressure is calculated with an indirect method. 40 The second method is performed using a catheter (external diameter of 0.64 mm and internal diameter of 0.5 mm) with two orifices inserted via the urethra to the bladder and “Y” connected to the infusion pump and polygraph. In this method, the behavior of the bladder during urination is determined. 43

Anderson reported on a rodent UDS model 40 and noted that a control or sham group should be present in every cystometric study. 40 The common parameters that are usually reported in UDS include pressure parameters such as the baseline pressure or minimum pressure between two micturitions (usually between 10 to 20 cmH2O), intermicturition pressure or mean pressure between two micturitions (related to the occurrence of non-voiding contractions), threshold pressure or intravesical pressure (immediately before micturition, maximum pressure during a micturition cycle or peak pressure, maximum voiding pressure, or maximum intravesical pressure), micturition frequency (the number of micturitions per hour), bladder capacity (determined as infused volume divided by the number of micturitions, provided there is no residual volume), and ICI (defined as the time period between two maximum voiding pressures). Volume parameters are the other cystometric parameters in the evaluation of the rodent bladder. It includes micturition volume (volume after a micturition minus volume before a micturition) and residual volume (the volume remaining in the bladder after voiding). Another important parameter of rodent UDS is bladder compliance (bladder capacity divided by threshold minus basal pressure). 40

Models of SCI to Induce NGB

The contusion model of SCI is reported in some articles at the T10-T12 vertebral level, 44 T8-T9 level of the spinal cord, 23 at mid-thoracic level of T9, 45 at the 10th thoracic level of the spinal cord segment, 46 with the NYU impactor (10 g, 25 mm) 47 injury at the T9 vertebral level of the spinal cord 48 or laminectomy of the T10 spinal vertebrae, and complete transection at the lower thoracic level of the spinal cord. 49 Temeltas and others performed a laminectomy, following anesthesia, at the T9-T10 level and induced a hemisection SCI model via dura incision above the dorsal root entry zone and cutting with micro-scissors at the rostral and caudal extents of the injury. Then, aspiration was done to ablate only the lateral white matter tracts and a minimal portion of the dorsal and ventral gray matter. 50

The contusion injury model is the most common SCI model. In this model, the dorsal region of the spinal cord is damaged or destroyed. Rostral to the lumbosacral level of SCI leads to bladder hyperreflexia, detrusor sphincter dyssynergia, and finally bladder hypertrophy. 49 Complete deterioration of bladder compliance, function, infection, and lower urinary tract complications are the other sequels of SCI. 51 In these studies, the mechanism of bladder dysfunction induced by SCI reported overactivity.

The Timing of SCs Transplantation After Injury

Different studies used different timings for the transplantation of SCs. It ranged from the immediate transplantation of cells after SCI 44 to 8 weeks after SCI. 49 However, in most studies, the SCs were transplanted nine days after injury. Cho and others 44 infused 100 μl of oral mucosa SCs immediately after SCI. Park and others 23 used the timing of nine days after injury in which human MSCs were placed in the contusion site of the spinal cord. Sandner 45 injected bone marrow stromal cells three days after inducing SCI in the center of the lesion. Obara 46 grafted BAM 2-3 weeks after SCI in rats that had undergone partial cystectomy 13 weeks after contusion. Jin 47 transplanted neural progenitor cells by using a 10-ul NanoFil™ syringe (World Precision Instruments, USA) with a 33-gauge needle. In their process, the dura in the center of the lesion was not opened and remained for one minute after the injection.

In a study conducted by Lee, 48 human bone marrow MSCs labeled with magnetic nanoparticles were transplanted into six areas of the bladder muscle of rats four weeks after the SCI operation. Urakami 49 performed bladder replacement surgery eight weeks post-injury. The urinary bladder was exposed via a small suprapubic incision and partial cystectomy (50%), then BAM graft was anastomosed to the host bladder with running and interlocking 7-0 absorbable sutures. Temeltas and others 50 implanted a mixed population of neuronal restricted precursors (NRP)/glial restricted precursors (GRP) or culture medium transplantation, into the injury cavity nine days after hemisection.

The best route of administration and site of transplantation for different diseases and the possible contraindication of clinical usage are still unknown. 32 Moreover, the time of cell transplantation is very important 52 for the therapeutic effect. 32 The characteristics of the reviewed studies are described in table 1.

Reference SCI type Device name for injury The number of rodents in each group Cell type for transplantation Cell labeling Time of transplantation after SCI Route of transplantation Cell count Injured vertebrate segment
Cho44 Needle-stick injury 22-gauge needle 10 Oral mucosa stem cells Just after SCI Stem cells were infused over the course of 1 min by using a 22-gauge insert vein (IV) catheter intrathecal 100 μl T11
Park23 Contusion Multicenter animal SCI study (MASCIS) impactor (Rutgers, The State University of New Jersey, Newark, NJ), a 10-gram rod was dropped from a vertical distance of 25 mm 6-11 hMSCs 9 days after injury Into the injured spinal cord via Hamilton syringe 5 μL T9
Obara46 Compression Compression with a 40-gram rod (tip area: 3.0-2.2 mm) placed on the exposed dura for 30 minutes 5 and 15 BAM grafting 2 to 3 weeks after BAM grafting A BAM was firmly anastomosed to the host bladder with running and interlocking 7-0 absorbable sutures. T10
Sander45 Contusion Infinite Horizon (IH) impactor SCI device (Precision Systems and Instrumentation, Lexington, KY, USA) with an impact force of 200 kilodynes (kdyn) 6-8 BMSCs 3 days postinjury Into the center of the lesion at a maximum depth of 1.5 mm using a pulled glass pipette (100 μm internal diameter) and a Picospritzer II 1×105 T9
Urakami49 Transection Micro scissors BAM grafting 8 weeks after SCI (bladder replacement) The BAMG was anastomosed to the host bladder with running and interlocking 7–0 absorbable sutures T10
Temeltas50 Hemisection Micro scissors 6-10 NRP/GRP 9 days after hemisection Into the injury cavity 1×106 T9-T10
JIN47 Contusion NYU impactor (10 g, 25 mm) 9-10 NPCs 13 weeks after SCI Using a 10-ul NanoFil syringe with a 33-gauge needle, 1×105 cell/µl were injected into the lesion center along the midline (4 µl) and rostral and caudal to the lesion along the midline (3 µl/each). T10
Lee48 Contusion Chung-Ang University Hospital Model 2.0 (CAUH-2) pneumatic impactor (3 mm depth) 10 BM3.B10 Fluorescent MNPs 4 weeks after SCI Into the bladder muscle of the rats in six areas 1×106 T9
Table1. Characteristic of SCI and stem cell types in the reviewed studies

The Methods and Time of Catheterization to Perform Cystometry after SCI

In a study by Cho and others, 44 after anesthesia, a sterile polyethylene catheter (PE50) was inserted into the bladder connected to a pressure transducer (Harvard Apparatus Inc., USA) to record the intravesical pressure as well as a syringe pump to infuse saline into the bladder. After emptying the bladder, cystometry was performed. Park and others 23 conducted cystometry at 28 days and 56 days after transplantation. Sandner 45 catheterized the bladder 3-4 days prior to urodynamic measurements. After anesthesia, the bladder was exposed by a midline incision in the low abdominal wall and a PE catheter with a cuff was inserted into the bladder dome and secured by a purse-string suture and externalized through the skin in the back of the neck. The external tip of the catheter was closed thermally, to prevent leakage and infection, and sutured to the skin until the urodynamic measurements. Urodynamic measurements were performed 8.5 weeks post-injury in conscious rats.

In a study by Obara, 46 cystometry was performed at 5, 7, and 15 weeks in the intact-BAM and SCI-BAM rats. A polyethylene catheter was placed via the urethra into the bladder and was connected to the pressure transducers and then the pressure signals were recorded. Jin 47 performed cystometry in conscious rats eight weeks after transplantation (22 weeks after initial injury) by using a polyethylene catheter. After catheterization, the rats recovered for 1-2 hours and were then placed in a restraining cage (KN-326, Japan). A pressure transducer (Bladder pressure transducer, Germany) and infusion pump (STC-523, Japan) were used in this procedure. In a study by Lee, 48 voiding response was assessed at four weeks after transplantation. After anesthesia, the bladder was exposed via a midline abdominal incision and a catheter was inserted through a small incision in the bladder dome. After passing the other end of the catheter subcutaneously, its end was exited through the skin. Urakami 49 performed cystometry before grafting and repeated eight weeks after bladder replacement. After anesthesia, cystometry was performed after emptying the bladder. In a study by Temeltas and others, 50 UDS was conducted four weeks after transplantation similar to the previously mentioned method.

The time of catheterization to perform UDS varied among different studies. However, the timing was in the range of 2 to 8 weeks after transplantation. The catheter was inserted via the urethra or the bladder, usually in the dome, secured by a purse-string suture, tunneled subcutaneously, and externalized through the skin at the back of the neck. In these studies, PE-50 and PE-60 were used. However, in other UDS in rats, PE-10, 53 PE-50, 54 - 57 PE-60, 58 PE-90, 59 , 60 and PE-100 61 were used.

The Rate of Infusion into the Bladder to Induce Micturition to Perform Cystometry and Measure Parameters

Cho and others 44 infused 0.5 ml normal saline and conducted cystometry. Park and others 23 infused 10 ml/hour normal saline at room temperature into the bladder. Then, the rate was reduced to 5 ml/hour. For stabilizing the micturition cycles, after the first void, the infusion was stopped every 30 minutes. Detrusor pressure, timing, and frequency of voiding were recorded. It should be noted that the cystometry in their study was conducted under the anesthetic vapor with low level (0.5%) to reduce the effect of anesthesia on the micturition cycle.

In a study by Sander, 45 to measure repeated micturition cycles, the bladder was filled via the implanted catheter with saline for 30-45 minutes at a rate of 6 ml/h. During UDS, the bladder pressure and urine volume were recorded. To measure micturition volume, released fluid was collected through a funnel into a cup connected to a force transducer. For pressure measurements, the bladder catheter was connected via a three-way stopcock to a pressure transducer and to a syringe pump. Both transducers were connected to an amplifier and a data acquisition system. The measured parameters were micturition volume (MV), micturition frequency (MF per hour), basal pressure (Pbase: minimum pressure between two micturition events), maximum voiding pressure (Pmax: maximum bladder pressure during a micturition cycle), and pressure difference (Pdiff: Pmax-Pbase).

In a study by Obara, 46 saline 0.9% at room temperature was infused into the bladder continuously at a constant rate of 0.1ml/min. They only checked the leak-point volume and pressure when saline leaked from the meatus around the tube in anesthetic rats. Jin 47 performed UDS by infusion saline with a rate of 0.1 ml/min. Lee 45 recorded UDS by infusion of physiological saline at room temperature into the bladder at a rate of 0.04 ml/min. Urakami 49 performed a cystometry with saline infusion into the bladder at the rate of 0.2 ml/min. The measured parameters were bladder pressure during the filling phase, bladder capacity, threshold voiding pressure, bladder compliance (by dividing the bladder capacity by the threshold voiding pressure), voided volume, post-void residual volume, uninhibited detrusor contractions (UIC), maximal amplitude of UIC, and infused saline volume at the first UIC (table 2).

Temeltas and others, 50 4-6 hours after rat recovery from anesthesia, infused saline at room temperature at the rate of 0.2 ml per minute and monitored the intravesical pressure. The saline infusion was halted during the micturition process. The voiding saline from the rat’s urethral meatus was measured to a designated voided volume and post-void residual urine volume was then measured. The residual saline amount was withdrawn via an intravesical catheter and the bladder of the rats was squeezed manually on the abdominal wall and the remaining intravesical amount was collected. Voided volume and post-void residual volume was calculated as the bladder capacity. Different infusion rates have been described for rat urodynamics from 2.4 ml/hr to 11 ml/hr. 40 , 53 - 62 In these studies, the rate of saline infusion was in the range of 0.04 ml/min to 0.1 ml/min or 6 ml/h. The characteristics of urodynamics of the studies are described in table 2.

Reference The time of cystometry after bladder catheterization Time of catheterization to perform cystometry after SCI The type of catheter used for cystometry Animals status in cystometry (conscious or anesthetized) The type of anesthetic drug for catheterization Cystometry set-up The rate of infusion into bladder
Cho44 Just before cystometry 21 days after SCI PE-50 Anesthetized Zoletil Pressure transducer and a syringe pump (Harvard Apparatus, Holliston, MA, USA) monitored using LabScribe (iWork System, Inc., Dover, NH, USA). 0.50 ml/min
Park23 Just before cystometry 28 and 56 days after injury Double lumen polyethylene catheter (PE-160 and PE-50; Clay Adams, Parsippany, NJ, USA) anesthetized Isoflurane Pressure transducer by polygraph (Grass polygraph model 7E, Quincy, MA, USA) and infusion pump (Baxter, Deerfield, IL, USA). First 10 ml/hour and then 5 ml/hour
Obara46 Just before cystometry 5, 7, and 15 weeks after SCI PE-60 (Clay Adams, Parsippany, NJ, USA) Anesthetized Pentobarbital sodium Pressure transducers (Statham P-23, Gulton-Statham Transducers, CA, USA) and recorded by (Menuet Compact, Dantec Medical A/S, Denmark). 0.10 ml/min
Sander45 3 to 4 days prior to urodynamic measurements 8.5 weeks post injury PE catheter (diameter 2.1 mm, PE-50 (Schubert Medizinprodukte, Wackersdorf, Germany) Conscious Ketamine, xylazine, and acepromazine Force transducer (MLT1030/D wide range force transducer; AD Instruments, Oxford, UK), pressure transducer (MLT0699 disposable BP transducer; AD Instruments, New Zealand) and to a syringe pump (KR Analytical, Cheshire, UK), data acquisition system (PowerLab 8/35; AD Instruments, New Zealand) 6 ml/h
Urakami49 Just before cystometry Before grafting, 8 and 16 weeks after SCI and bladder replacement 22-gauge catheter Anesthetized Ketamine 0.20 ml/min
Temeltas50 4 to 6 hours after recovery 4 weeks after transplantation PE-50 ketamine+xylazine Biopac Systems™ device 0.20 ml/min
JIN47 1-2 hour before urodynamic measurements 22 weeks after SCI and 8 weeks after transplantation PE-60 (Clay Adams, Parsippany, NJ, USA) Conscious Isoflurane Pressure transducer (BLPR; World Precision Instruments) (BLPR; Bladder pressure transducer, Germany) and infusion pump (STC-523; Terumo, Tokyo, Japan) 0.10 ml/min
Lee48 5-6 hour before urodynamic measurements 4 weeks after cell transplantation and 8 weeks after injury PE-50 (Harvard Clinical Technology, Inc., South Natick, MA, USA) Conscious Isoflurane 0.04 ml/min
Table2. Characteristic of UDS in the reviewed studies

The Results of UDS

Cho 44 determined the contraction pressure 2.55±0.22 cmH2O in the sham-operation group, 6.49±0.77 cmH2O in the SCI-induced group, and 3.05±0.14 cmH2O in the SCI-induced and oral mucosa stem cell transplantation group. The results showed that bladder contraction pressure and contraction time were increased in the SCI group, whereas they were improved after the transplantation of oral mucosa SCs.

Park and others 23 showed that the voiding frequency (time/min) was 0.80±0.09 and 0.82±0.16 in the two control groups and 0.79±0.11 in an experimental group at 28 days after injury. Sandner 45 observed a similar baseline bladder pressure, a slightly increased maximal voiding pressure, and a significantly increased pressure difference. In addition, spinal cord-injured animals frequently showed non-voiding contractions, which was not observed in naive animals. In treated animals, a tendency toward a decrease of the micturition frequency was reported compared to non-injected injured rats; although this difference was not statistically significant using ANOVA analysis (P=0.0535 comparing all injured groups). The voided volume per micturition of all injured animals was decreased compared to intact animals, but was not significant using ANOVA analysis (P=0.06). In both fibroblast-grafted and BMSC grafted animals compared to the injured control animals, the voided volume per micturition was slightly high and the difference among the injured group and control group was not statistically significant using ANOVA analysis (P=0.28).

In a study by Obara, 46 due to the phenobarbital anesthesia effect on suppressing the neural circuit of the micturition reflex, the intravesical pressure rose gradually until voiding was initiated. The leak point volume of the SCI rats was significantly higher than that of the intact rats, and the leak-point pressure of the SCI rats was significantly lower than the intact rats.

Jin 47 observed bladder deficiency in all experimental groups in comparison with the intact group. As shown in table 3, these values increased in all experimental groups compared to the intact group (P<0.05). Non-voiding contractions in the intact group were zero, while in other groups were 7.4±3.1, 6.0±0.6, 7.0±1.2 and 7.8±1.5, respectively. The voided volume (ml) ranged between 0.3 in the intact group to 4.13 in the group of NPCs+lentivirus vectors expressing chondroitinase and neurotrophic factors (N/C/G group). The bladder contraction duration and amplitude of micturition were also high in three of the four experimental groups compared to the intact animals, except for the N/C/G group, which was similar to normal values. After combined treatment, bladder function improvement was observed. The interaction intervals (seconds) were 148.9±10.5 in the intact group, 214±40.9 in medium (control) group, 289.8±78.8 in neural progenitor cells transplants (NPCs) group, 258.2±38.4 in NPC+lentivirus vector expressing chondroitinase group, and 230.5±69.2 in NPC+lentivirus vectors expressing chondroitinase and neurotrophic factors. Bladder contraction duration (seconds) was 19.1±2.5, 28.6±3.9, 28.2±6.2, 31.8±4.6, and 18.9±3.5, respectively. The amplitude of micturition (cmH2O) was 35.0±6.3, 44.3±7.8, 42.3±6.3, 47.9±7.2, and 34.7±2.5, respectively. Residual volume (ml) was zero in the intact group, 0.177 in medium group, 0.1 in NPC group, 0.05 in N/C, and 0.05 in N/C/G group.

Lee and others 48 showed that following SCI, the inter-contraction interval (ICI: the interval between voids or reflex bladder contractions) was low. However, after cell transplantation, the inter-contraction interval was increased. According to their figures, the ICI (seconds) was about 340 in normal rats, 370 in the sham group, 50 in the SCI group, and about 160 in the SCI+B10 cell group. The pressure threshold (PT) was similar between the groups. The amount of PT (cmH2O) in the control group was about 8, 9 in the sham group, 7 in the SCI group, and about 9 in the SCI+B10 cell group. After SCI, the amount of maximum voiding pressure was increased, but it decreased after B10 cell transplantation.

In a study by Urakami, 49 eight weeks after spinalization, 22 rats (71.0%) had hyperreflexic bladders with UIC and nine rats (29.0%) had underactive bladders with no UIC. The mean bladder capacity and RUV of SCI rats (4.2±2.3, 1.5±1.6 ml, respectively) were remarkably higher than normal rats (0.5±0.1, 0.05±0.02 ml, respectively). Similar urodynamic results were seen in SCI-control rats (with no bladder replacement) eight weeks and 16 weeks after spinalization. No uninhibited contraction was observed in all ten normal rats. The bladder capacity was 1.0 ml and the maximum amplitude of the voiding contractions was 31.0 cm/H2O.

A typical cystometrogram in spinalized rat showed many large uninhibited non-voiding contractions (more than 15 cm/H2O) during saline infusion. The size of the contractions increased with time. Bladder capacity was approximately 2.5 ml, threshold pressure was 33.5 cm/H2O, and bladder compliance was 0.075. No uninhibited contractions during saline infusion were seen in a typical cystometrogram of SCI-induced underactive-bladder (areflexia). The bladder capacity exceeded 4.0 ml and bladder compliance was very high.

Temeltas 50 reported that the mean±SD of baseline pressure (cmH2O) in the sham operation group was 2.15±0.54, in the SCI group that received NRP/GRP was 3.38±0.30, in the SCI group that received bone marrow stromal cell transplantation 5.16±0.55, and in the SCI control group 8.78±0.55. The mean±SD of maximum bladder capacity (ml) was 0.57±0.13, 1.64±0.13, 1.70±0.10, and 1.89±0.18, respectively. The frequency of uninhibited detrusor contractions per minute was in the range of 0.20±0.44 to 5.80±2.58 and the amplitude (cmH2O) was in the range of 1.20±2.68 to 32.01±10.19. The mean±SD of voiding pressure (cmH2O) was 24.90±4.03 in the sham operation group, 43.40±5.71 in group 2, 53.10±7.88 in group 3, and 61.80±9.41 in the SCI control group. The mean±SD of voided volume (ml) was 0.56±0.12 in group 1, 1.02±0.08 in group 2, 0.90±0.18 in group 3, and 0.27±0.05 in group 4. Post-void residual volume (ml) was in the range of 0.05±0.07 to 1.61±0.23. Urodynamic parameters were poor in all other groups compared to the sham operation group (P=0.0001). After treatment, the level of baseline pressure, maximum capacity, and amplitude of involuntary contraction during the filling phase were improved (P=0.0001, P=0.001, and P=0.001, respectively). The number of involuntary contractions was not significantly different between the treatment groups and group 4. Mean voiding pressure and post-void residual urine volume in the treatment groups were lower than the control group (P=0.0001 and P=0.001, respectively), while voiding volume was greater (P=0.001).

In the reviewed articles, several cystometric parameters such as cystometric pressure parameters (baseline, intermicturition, threshold, maximal, voiding and non-voiding pressure), micturition frequency, volume parameters (voided volume, post-void residual volume), and bladder compliance were measured. In some studies, only contraction pressure and time with a range of 2-6 cmH2O and 8-15 seconds, respectively, were measured. 44 In another study, only maximal pressure was measured. 23 Three studies reported bladder capacity 45 , 49 , 50 with a minimum range of 0.3 to a maximum range of 5.3 ml. 44 , 46 , 47 Some important results of UDS in the above-mentioned studies are summarized in table 3.

Reference Groups Contraction pressure (cmH2O) (mean±SD) Contraction time (seconds) (mean±SD) Voiding pressure (mean±SD) Voided volume (mean±SD) Voiding frequency (time/min) (mean±SD) Maximal pressure (mean±SD) Voiding pressure (VP) (mean±SD) Pressure threshold (PT) (mean±SD) Bladder capacity (mean±SD) Bladder compliance (mean±SD) Post-void residual volume (mean±SD) Baseline pressure (cmH2O) (mean±SD)
Cho44 Control 2.55±0.22 8.09±0.43
Negative control 6.49±0.77 15.29±1.65
Experimental *3.05±0.14 *13.36±0.40
Park23 Control 1 PBS (n=7) 0.80±0.09 9.21±5.30 1345.25±1206.27 mm3
Control 2 hFb (n=11) 0.82±0.16 9.60±4.20 1263.75±838.05 mm3
Experimental hMSC (n=9) 0.76±0.32 9.70±4.11 1279.57±1310.69 mm3
Lee48 Control 39.24±2.64 8.18±0.77
Sham 43.77±1.50 8.50±0.54
SCI 77.73±2.64 7.13±0.72
SCI+B10 57.35±4.15* 8.54±0.31*
*Sander45 SCI 23.00±2.25 72.60±9.56 26.38±6.38
BMSC-grafted 19.75±1.87 81.73±9.13 29.36±3.82
Fibroblast-grafted 15.50±1.12* 65.65±6.52* 19.57±2.55*
Urakam49 Control 0.50±0.10
Before graft 0.37±0.07 1.38±0.20
After BAM-grafted *P<0.0001
Temeltas50 Sham 24.90±4.03 0.56 24.90 0.57±0.13 0.05±0.07 2.15±0.54
SCI+neuronal restricted precursor/glial restricted precursor *43.40±5.71 1.02 *43.40 *1.64±0.13 *0.64± 0.12 3.38±0.30
SCI+BM-SCs *53.10±7.88 0.90 *53.10 *1.70±0.10 *0.79±0.20 *5.16±1.03
SCI control 61.80±9.41 0.27 61.80 1.89±0.18 1.61±0.23 8.78±0.55
JIN47 Intact 0.30 0.3±0.00 0.00
Medium (control) 3.63 3.8±0.90 0.17
NPC transplant *5.20 *5.3±1.20 *0.10
NPC transplant with Chase/LV (N/C) *4.05 *4.1±0.80 *0.05
NPC transplant with Chase/LV+BDNF/NT-3/LV (N/C/G) *4.13 *4.2±1.30 *0.05
Table3. Measured urodynamic parameters in SCI-induced neurogenic bladder in the reviewed studies

Discussion

SCI-induced bladder dysfunction is one of the most debilitating functional deficits. 63 , 64 Among different treatment methods, stem cell transplantation is promising. In some urodynamic test results, to some extent, improvement in the function of the lower urinary system in each treatment group was observed. However, this improvement was far from full functional recovery. The remaining unknowns for the best therapeutic effect are the route of administration, cell doses, timing, the site of cell transplantation for different diseases, and possible contraindication of clinical usage. 32 , 46 Another concern in the field of stem cell therapy is the diminishing regenerative potential of aged SCs. Thus, the success of future clinical trials will depend on experimental investigations. 65 There were different timings for stem cell transplantation among the reviewed studies, ranging from immediate transplantation of cells after SCI 44 to several weeks after SCI. 49 The average cell dose was about one million cells in every injected site and, in most studies, the SCs were transplanted nine days after injury. Transplanted cell survival is still another significant challenge that limits further recovery in SCI. In this regard, the main limitation is the high post-transplantation cell mortality. 66 Various strategies for improving the survival of SCs have been proposed. 67 However, none of the reviewed studies had mentioned such strategies.

To examine voiding functions, an implanted catheter into the bladder dome (by avoiding bladder outlet obstruction and providing the ability to perform urodynamic measurements in conscious rats) was preferred. Different infusion rates from 2.4 ml/hr to 11 ml/hr have been described for rat urodynamics. In the reviewed studies, the rate of saline infusion ranged from 0.04 ml/min to 0.1 ml/min or 6 ml/hr. PE-50 and PE-60 were also used; however, PE-10, 53 PE-50, 54 - 57 PE-60, 58 PE-90, 59 , 60 and PE-100 61 were used in other urodynamic studies in rats. It was assumed that the thinner tubes (PE 10) had a higher resistance. 68

Several cystometric parameters such as pressure parameters, volume parameters, and bladder compliance were measured. Some studies only measured the contraction pressure and time with a range of 2 to 6 cmH2O and 8 to 15 seconds, respectively. In another study, only the maximal pressure was measured. Three studies reported bladder capacity with a minimum range of 0.3 to a maximum range of 5.3 ml. Moreover, conscious rats had different bladder behavior compared to anesthetized rats. In the present review, approximately 50% of the studies were conducted on conscious rats and some others used common drugs such as isoflurane and/or ketamine for anesthesia. Ozkurkcugil surveyed the effect of different anesthetic drugs on cystometric parameters in comparison with the conscious condition. The effect of ether and midazolam on the parameters were similar in both conditions. Propofol altered these parameters but was not statistically significant. 69

Despite the claim that ketamine has no effect on cystometric parameters, Ozkurkcugil reported that it had a high depressant effect on micturition. Therefore, it may be not suitable for experimental studies using urodynamic parameters in rats. 69 Isoflurane may be the best choice for small surgical procedures, because it has a short half-life. However, in a study by Chang and others, isoflurane led to the prolongation of bladder inter-contractile intervals. 70 Hence, anesthetic properties should be taken into account in the experimental design and interpretation of urodynamic findings in rodent models.

Conclusion

In the present study, the effect of stem cell transplantation on bladder dysfunction recovery based on urodynamic parameters after SCI in rats was reviewed. For this purpose, the cell source, doses, route of administration, and the complete UDS equipment and its parameters were summarized in SCI models in rodents. Among the reviewed studies, the contusion injury model was the most common SCI model. The average cell dose was about one million cells in every injected site. Additionally, the SCs were transplanted into the lesion cavity nine days after injury.

In some urodynamic test results, to some extent, an improvement in the function of the lower urinary system in each treatment group was observed. However, this improvement was far from full functional recovery. Since we did not assess its effect on the other neurological conditions, it cannot be generalized to other neurological diseases. Hence, it is recommended to conduct a comprehensive review of all neurological conditions that lead to NGB and to compare urodynamic parameters between treated and control groups.

References

  1. Linder A, Leach GE, Raz S. Augmentation cystoplasty in the treatment of neurogenic bladder dysfunction. J Urol. 1983; 129:491-3. PubMed
  2. Palma JA, Kaufmann H. Treatment of autonomic dysfunction in Parkinson disease and other synucleinopathies. Mov Disord. 2018; 33:372-90. Publisher Full Text | DOI | PubMed
  3. Stoffel JT. Chronic Urinary Retention in Multiple Sclerosis Patients: Physiology, Systematic Review of Urodynamic Data, and Recommendations for Care. Urol Clin North Am. 2017; 44:429-39. DOI | PubMed
  4. Son SB, Chung SY, Kang S, Yoon JS. Relation of Urinary Retention and Functional Recovery in Stroke Patients During Rehabilitation Program. Ann Rehabil Med. 2017; 41:204-10. Publisher Full Text | DOI | PubMed
  5. Lima DX, Pires CR, Santos AC, Mendes RG, Fonseca CE, Zocratto OB. Quality of life evaluation of patients with neurogenic bladder submitted to reconstructive urological surgeries preserving the bladder. Int Braz J Urol. 2015; 41:542-6. Publisher Full Text | DOI | PubMed
  6. Abrams P, Cardozo L, Fall M, Griffiths D, Rosier P, Ulmsten U. The standardisation of terminology in lower urinary tract function: report from the standardisation sub-committee of the International Continence Society. Urology. 2003; 61:37-49. PubMed
  7. de Seze M, Ruffion A, Denys P, Joseph PA, Perrouin-Verbe B, Genulf The neurogenic bladder in multiple sclerosis: review of the literature and proposal of management guidelines. Mult Scler. 2007; 13:915-28. DOI | PubMed
  8. Benevento BT, Sipski ML. Neurogenic bladder, neurogenic bowel, and sexual dysfunction in people with spinal cord injury. Phys Ther. 2002; 82:601-12. PubMed
  9. Esclarin De Ruz A, Garcia Leoni E, Herruzo Cabrera R. Epidemiology and risk factors for urinary tract infection in patients with spinal cord injury. J Urol. 2000; 164:1285-9. PubMed
  10. Gormley EA. Urologic complications of the neurogenic bladder. Urol Clin North Am. 2010; 37:601-7. DOI | PubMed
  11. Hackler RH, Dalton JJ, Bunts RC. Changing Concepts in the Preservation of Renal Function in the Paraplegic. J Urol. 1965; 94:107-11. PubMed
  12. Sakalis VI, Floyd MS, Jr*Caygill P, Price C, Hartwell B, Guy PJ. Management of stress urinary incontinence in spinal cord injured female patients with a mid-urethral tape - a single center experience. J Spinal Cord Med. 2018; 41:703-9. Publisher Full Text | DOI | PubMed
  13. Westgren N, Levi R. Quality of life and traumatic spinal cord injury. Arch Phys Med Rehabil. 1998; 79:1433-9. PubMed
  14. Biering-Sorensen F, Nielans HM, Dorflinger T, Sorensen B. Urological situation five years after spinal cord injury. Scand J Urol Nephrol. 1999; 33:157-61. PubMed
  15. Gormley EA, Lightner DJ, Burgio KL, Chai TC, Clemens JQ, Culkin DJ. Diagnosis and treatment of overactive bladder (non-neurogenic) in adults: AUA/SUFU guideline. J Urol. 2012; 188:2455-63. DOI | PubMed
  16. Van Kerrebroeck PE, Koldewijn EL, Rosier PF, Wijkstra H, Debruyne FM. Results of the treatment of neurogenic bladder dysfunction in spinal cord injury by sacral posterior root rhizotomy and anterior sacral root stimulation. J Urol. 1996; 155:1378-81. PubMed
  17. Verpoorten C, Buyse GM. The neurogenic bladder: medical treatment. Pediatr Nephrol. 2008; 23:717-25. Publisher Full Text | DOI | PubMed
  18. Linder A, Leach GE, Raz S. Augmentation cystoplasty in the treatment of neurogenic bladder dysfunction. J Urol. 1983; 129:491-3. PubMed
  19. Jack GS, Almeida FG, Zhang R, Alfonso ZC, Zuk PA, Rodriguez LV. Processed lipoaspirate cells for tissue engineering of the lower urinary tract: implications for the treatment of stress urinary incontinence and bladder reconstruction. J Urol. 2005; 174:2041-5. DOI | PubMed
  20. Atala A, Bauer SB, Soker S, Yoo JJ, Retik AB. Tissue-engineered autologous bladders for patients needing cystoplasty. Lancet. 2006; 367:1241-6. DOI | PubMed
  21. Lewis JM, Cheng EY. Non-traditional management of the neurogenic bladder: tissue engineering and neuromodulation. ScientificWorldJournal. 2007; 7:1230-41. Publisher Full Text | DOI | PubMed
  22. Yoo JJ, Olson J, Atala A, Kim B. Regenerative medicine strategies for treating neurogenic bladder. Int Neurourol J. 2011; 15:109-19. Publisher Full Text | DOI | PubMed
  23. Park WB, Kim SY, Lee SH, Kim HW, Park JS, Hyun JK. The effect of mesenchymal stem cell transplantation on the recovery of bladder and hindlimb function after spinal cord contusion in rats. BMC Neurosci. 2010; 11:119. Publisher Full Text | DOI | PubMed
  24. Jack GS, Zhang R, Lee M, Xu Y, Wu BM, Rodriguez LV. Urinary bladder smooth muscle engineered from adipose stem cells and a three dimensional synthetic composite. Biomaterials. 2009; 30:3259-70. Publisher Full Text | DOI | PubMed
  25. Strauer BE, Kornowski R. Stem cell therapy in perspective. Circulation. 2003; 107:929-34. PubMed
  26. Pham PV, Vu NB, Pham VM, Truong NH, Pham TL, Dang LT. Good manufacturing practice-compliant isolation and culture of human umbilical cord blood-derived mesenchymal stem cells. J Transl Med. 2014; 12:56. Publisher Full Text | DOI | PubMed
  27. Pham PV, Vu NB, Pham VM, Truong NH, Pham TL, Dang LT. Good manufacturing practice-compliant isolation and culture of human umbilical cord blood-derived mesenchymal stem cells. J Transl Med. 2014; 12:56. Publisher Full Text | DOI | PubMed
  28. Sibov TT, Severino P, Marti LC, Pavon LF, Oliveira DM, Tobo PR. Mesenchymal stem cells from umbilical cord blood: parameters for isolation, characterization and adipogenic differentiation. Cytotechnology. 2012; 64:511-21. Publisher Full Text | DOI | PubMed
  29. Van Pham P, Vu NB, Phan NK. Umbilical cord-derived stem cells (MODULATISTTM) show strong immunomodulation capacity compared to adipose tissue-derived or bone marrow-derived mesenchymal stem cells. Biomedical Research and Therapy. 2016; 3:687-96. DOI
  30. Zuk PA, Zhu M, Mizuno H, Huang J, Futrell JW, Katz AJ. Multilineage cells from human adipose tissue: implications for cell-based therapies. Tissue Eng. 2001; 7:211-28. DOI | PubMed
  31. Zhang QZ, Nguyen AL, Yu WH, Le AD. Human oral mucosa and gingiva: a unique reservoir for mesenchymal stem cells. J Dent Res. 2012; 91:1011-8. Publisher Full Text | DOI | PubMed
  32. Wei X, Yang X, Han ZP, Qu FF, Shao L, Shi YF. Mesenchymal stem cells: a new trend for cell therapy. Acta Pharmacol Sin. 2013; 34:747-54. Publisher Full Text | DOI | PubMed
  33. Li JH, Zhang N, Wang JA. Improved anti-apoptotic and anti-remodeling potency of bone marrow mesenchymal stem cells by anoxic pre-conditioning in diabetic cardiomyopathy. J Endocrinol Invest. 2008; 31:103-10. DOI | PubMed
  34. Sakaida I, Terai S, Yamamoto N, Aoyama K, Ishikawa T, Nishina H. Transplantation of bone marrow cells reduces CCl4-induced liver fibrosis in mice. Hepatology. 2004; 40:1304-11. DOI | PubMed
  35. Zhao DC, Lei JX, Chen R, Yu WH, Zhang XM, Li SN. Bone marrow-derived mesenchymal stem cells protect against experimental liver fibrosis in rats. World J Gastroenterol. 2005; 11:3431-40. Publisher Full Text | DOI | PubMed
  36. Smalley E. Neural stem cell trailblazer StemCells folds. Nat Biotechnol. 2016; 34:677-8. DOI | PubMed
  37. Mitsui T, Kakizaki H, Tanaka H, Shibata T, Matsuoka I, Koyanagi T. Immortalized neural stem cells transplanted into the injured spinal cord promote recovery of voiding function in the rat. J Urol. 2003; 170:1421-5. DOI | PubMed
  38. Song L, Murphy SV, Yang B, Xu Y, Zhang Y, Atala A. Bladder acellular matrix and its application in bladder augmentation. Tissue Eng Part B Rev. 2014; 20:163-72. DOI | PubMed
  39. Wein AJ. Neuromuscular dysfunction of the lower urinary tract. Campbell’s urology. 1992;573-642.
  40. Andersson KE, Soler R, Fullhase C. Rodent models for urodynamic investigation. Neurourol Urodyn. 2011; 30:636-46. DOI | PubMed
  41. Suaid H, Martins A, Rock J, Cologna A, Tucci JS. Comparison of urethral function after simple cystectomy in female rats and cystoprostatectomy in male rats. Acta Cir Bras. 1998; 13:25-9.
  42. Elneil S, Skepper JN, Kidd EJ, Williamson JG, Ferguson DR. Distribution of P2X(1) and P2X(3) receptors in the rat and human urinary bladder. Pharmacology. 2001; 63:120-8. DOI | PubMed
  43. Resplande J, Graziottin T, Gholami S, Nunes L, Lue T. Urethral pressure profile in female rats. Morphologic and functional aspects. Braz J Urol 2001; 27:158.
  44. Cho YS, Ko IG, Kim SE, Lee SM, Shin MS, Kim CJ. Oral mucosa stem cells alleviates spinal cord injury-induced neurogenic bladder symptoms in rats. J Biomed Sci. 2014; 21:43. Publisher Full Text | DOI | PubMed
  45. Sandner B, Ciatipis M, Motsch M, Soljanik I, Weidner N, Blesch A. Limited Functional Effects of Subacute Syngeneic Bone Marrow Stromal Cell Transplantation After Rat Spinal Cord Contusion Injury. Cell Transplant. 2016; 25:125-39. DOI | PubMed
  46. Obara T, Matsuura S, Narita S, Satoh S, Tsuchiya N, Habuchi T. Bladder acellular matrix grafting regenerates urinary bladder in the spinal cord injury rat. Urology. 2006; 68:892-7. DOI | PubMed
  47. Jin Y, Bouyer J, Shumsky JS, Haas C, Fischer I. Transplantation of neural progenitor cells in chronic spinal cord injury. Neuroscience. 2016; 320:69-82. Publisher Full Text | DOI | PubMed
  48. Lee HJ, An J, Doo SW, Kim JH, Choi SS, Lee SR. Improvement in Spinal Cord Injury-Induced Bladder Fibrosis Using Mesenchymal Stem Cell Transplantation Into the Bladder Wall. Cell Transplant. 2015; 24:1253-63. DOI | PubMed
  49. Urakami S, Shiina H, Enokida H, Kawamoto K, Kikuno N, Fandel T. Functional improvement in spinal cord injury-induced neurogenic bladder by bladder augmentation using bladder acellular matrix graft in the rat. World J Urol. 2007; 25:207-13. DOI | PubMed
  50. Temeltas G, Dagci T, Kurt F, Evren V, Tuglu I. Bladder function recovery in rats with traumatic spinal cord injury after transplantation of neuronal-glial restricted precursors or bone marrow stromal cells. J Urol. 2009; 181:2774-9. DOI | PubMed
  51. Yoshiyama M, Nezu FM, Yokoyama O, de Groat WC, Chancellor MB. Changes in micturition after spinal cord injury in conscious rats. Urology. 1999; 54:929-33. PubMed
  52. Ren G, Zhao X, Zhang L, Zhang J, L’Huillier A, Ling W. Inflammatory cytokine-induced intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in mesenchymal stem cells are critical for immunosuppression. J Immunol. 2010; 184:2321-8. Publisher Full Text | DOI | PubMed
  53. Pehrson R, Stenman E, Andersson KE. Effects of tramadol on rat detrusor overactivity induced by experimental cerebral infarction. Eur Urol. 2003; 44:495-9. PubMed
  54. Persson K, Pandita RK, Spitsbergen JM, Steers WD, Tuttle JB, Andersson KE. Spinal and peripheral mechanisms contributing to hyperactive voiding in spontaneously hypertensive rats. Am J Physiol. 1998; 275:R1366-73. DOI | PubMed
  55. Cannon TW, Damaser MS. Effects of anesthesia on cystometry and leak point pressure of the female rat. Life Sci. 2001; 69:1193-202. PubMed
  56. Lee T, Andersson KE, Streng T, Hedlund P. Simultaneous registration of intraabdominal and intravesical pressures during cystometry in conscious rats--effects of bladder outlet obstruction and intravesical PGE2. Neurourol Urodyn. 2008; 27:88-95. DOI | PubMed
  57. Masuda H, Ogawa T, Kihara K, Chancellor MB, de Groat WC, Yoshimura N. Effects of anaesthesia on the nitrergic pathway during the micturition reflex in rats. BJU Int. 2007; 100:175-80. DOI | PubMed
  58. Yokoyama O, Yoshiyama M, Namiki M, de Groat WC. Influence of anesthesia on bladder hyperactivity induced by middle cerebral artery occlusion in the rat. Am J Physiol. 1997; 273:R1900-7. DOI | PubMed
  59. Matsuura S, Downie JW. Effect of anesthetics on reflex micturition in the chronic cannula-implanted rat. Neurourol Urodyn. 2000; 19:87-99. PubMed
  60. Huang YC, Shindel AW, Ning H, Lin G, Harraz AM, Wang G. Adipose derived stem cells ameliorate hyperlipidemia associated detrusor overactivity in a rat model. J Urol. 2010; 183:1232-40. Publisher Full Text | DOI | PubMed
  61. Yaksh TL, Durant PA, Brent CR. Micturition in rats: a chronic model for study of bladder function and effect of anesthetics. Am J Physiol. 1986; 251:R1177-85. DOI | PubMed
  62. Streng T, Santti R, Andersson KE, Talo A. The role of the rhabdosphincter in female rat voiding. BJU Int. 2004; 94:138-42. DOI | PubMed
  63. Hagen EM. Acute complications of spinal cord injuries. World J Orthop. 2015; 6:17-23. Publisher Full Text | DOI | PubMed
  64. Johnson RT, Joy JE, Altevogt BM, Liverman CT. Spinal cord injury: progress, promise, and priorities. National Academies Press: Washington ; 2005.
  65. Roh JK, Jung KH, Chu K. Adult stem cell transplantation in stroke: its limitations and prospects. Curr Stem Cell Res Ther. 2008; 3:185-96. PubMed
  66. Adamowicz J, Pokrywczynska M, Van Breda SV, Kloskowski T, Drewa T. Concise Review: Tissue Engineering of Urinary Bladder; We Still Have a Long Way to Go?. Stem Cells Transl Med. 2017; 6:2033-43. Publisher Full Text | DOI | PubMed
  67. Li L, Chen X, Wang WE, Zeng C. How to Improve the Survival of Transplanted Mesenchymal Stem Cell in Ischemic Heart?. Stem Cells Int. 2016; 2016:9682757. Publisher Full Text | DOI | PubMed
  68. Uvin P, Everaerts W, Pinto S, Alpizar YA, Boudes M, Gevaert T. The use of cystometry in small rodents: a study of bladder chemosensation. J Vis Exp. 2012;e3869. Publisher Full Text | DOI | PubMed
  69. Ozkurkcugil C, Ozkan L. Effects of anesthetics on cystometric parameters in female rats. Int Urol Nephrol. 2010; 42:909-13. DOI | PubMed
  70. Chang HY, Havton LA. Differential effects of urethane and isoflurane on external urethral sphincter electromyography and cystometry in rats. Am J Physiol Renal Physiol. 2008; 295:F1248-53. Publisher Full Text | DOI | PubMed