A rat model for studying effects of sacral neuromodulation on the contractile activity of a chronically inflamed bladder

Closed-loop sacral neuromodulation for bladder function using dorsal root ganglia sensory feedback in an anesthetized feline model

Overactive bladder patients suffer from a frequent, uncontrollable urge to urinate, which can lead to a poor quality of life. We aim to improve open-loop sacral neuromodulation therapy by developing a conditional stimulation paradigm using neural recordings from dorsal root ganglia (DRG) as sensory feedback. Experiments were performed in 5 anesthetized felines. We implemented a Kalman filter-based algorithm to estimate the bladder pressure in real-time using sacral-level DRG neural recordings and initiated sacral root electrical stimulation when the algorithm detected an increase in bladder pressure. Closed-loop neuromodulation was performed during continuous cystometry and compared to bladder fills with continuous and no stimulation. Overall, closed-loop stimulation increased bladder capacity by 13.8% over no stimulation (p < 0.001) and reduced stimulation time versus continuous stimulation by 57.7%. High-confidence bladder single units had a reduced sensitivity during stimulation, with lower linear trendline fits and higher pressure thresholds for firing observed during stimulation trials. This study demonstrates the utility of decoding bladder pressure from neural activity for closed-loop control of sacral neuromodulation. An underlying mechanism for sacral neuromodulation may be a reduction in bladder sensory neuron activity during stimulation. Real-time validation during behavioral studies is necessary prior to clinical translation of closed-loop sacral neuromodulation.

Screening and Optimization of Nerve Targets and Parameters Reveals Inhibitory Effect of Pudendal Stimulation on Rat Bladder Hypersensitivity

BACKGROUND AND OBJECTIVES

Neuromodulation has been reported to reliably improve symptoms of bladder overactivity and sometimes pain. The effect of electrical stimulation of several nerve pathways demonstrated to alter cystometric responses to bladder distension was examined on nociceptive responses in models of bladder hypersensitivity.

METHODS

Bladder hypersensitivity was produced by several published methods including neonatal inflammation, acute inflammation, and chronic stress. Effects of different sites of stimulation (L6 and T13 nerve roots, proximal and distal pudendal nerves [PNs]) on nociceptive reflex responses to urinary bladder distension in urethane-anesthetized female rats were assessed and a parametric analysis of parameters of stimulation was performed.

RESULTS

Bilateral biphasic stimulation of the proximal PNs resulted in statistically significant inhibition of visceromotor and cardiovascular responses to bladder distension in rats made hypersensitive by neonatal bladder inflammation. We found a range of optimal stimulation frequencies (5-10 Hz) which produced robust inhibitory effects when using short pulse widths (100-240 μs). Onset of inhibition was within minutes and persisted for several minutes after the stimulus was discontinued. Use of bilateral PN stimulation in acute inflammation and stress-induced hypersensitivity models as well as unilateral stimulation, very distal PN cutaneous branch stimulation, and stimulation of the T13 and L6 nerve roots all proved ineffective with the parameters used.

CONCLUSIONS

This study suggests that inhibitory effects of bilateral PN stimulation can be evoked in a rodent hypersensitivity model at relatively low frequencies with short pulse widths. The onset of effect is rapid, which suggests the potential for treating episodic pain in painful bladder disorders.

Sacral neuromodulation of nociceptive bladder overactivity in cats

AIMS

To investigate the effects of electrical stimulation of sacral dorsal/ventral roots on irritation-induced bladder overactivity, reveal possible different mechanisms under nociceptive bladder conditions, and establish a large animal model of sacral neuromodulation.

METHODS

Intravesical infusion of 0.5% acetic acid (AA) was used to irritate the bladder and induce bladder overactivity in cats under α-chloralose anesthesia. Electrical stimulation (5, 15, or 30 Hz) was applied to individual S1-S3 dorsal or ventral roots at or below motor threshold intensity. Repeated cystometrograms (CMGs) were performed with/without the stimulation to determine the inhibition of bladder overactivity.

RESULTS

AA irritation induced bladder overactivity and significantly (P < 0.05) reduced the bladder capacity to 62.6 ± 11.7% of control capacity measured during saline CMGs. At threshold intensity for inducing reflex twitching of the anal sphincter or toe, S1/S2 dorsal root stimulation at 5 Hz but not at 15 or 30 Hz inhibited bladder overactivity and significantly (P < 0.05) increased bladder capacity to 187.3 ± 41.6% and 155.5 ± 9.7% respectively, of AA control capacity. Stimulation of S3 dorsal root or S1-S3 ventral roots was not effective. Repeated stimulation of S1-S3 dorsal root did not induced a post-stimulation inhibition.

CONCLUSIONS

This study established a cat model of sacral neuromodualation of nociceptive bladder overactivity. The results revealed that the mechanisms underlying sacral neuromodulation are different for nociceptive and non-nociceptive bladder activity.

Effects of sacral neuromodulation on isolated urinary bladder function in a rat model of spinal cord injury

INTRODUCTION

Sacral neuromodulation has been considered as an effective treatment option for various types of chronic voiding dysfunction, but the mechanism of action has not been well understood. The aim of this study was to evaluate the effect of chronic sacral neuromodulation on isolated bladder functions in a rat model of spinal cord injury.

MATERIALS AND METHODS

Female Sprague-Dawley rats (250-300 g; N = 20) were assigned to four groups as follows: 1) control group (N = 6); 2) spinal cord transection group (SCT; N = 5); 3) spinal cord transection + sacral neuromodulation group (SCT + SNM; N = 5); 4) sham (spinal cord transection + electrode wire implantation without sacral neuromodulation; N = 4). The rats in the SCT, SCT + SNM, and sham groups were anesthetized with ketamine (60 mg/kg, i.p.) and xylazine (7 mg/kg, i.p.). The spinal cord was completely transected at T8-T9 level in SCT and SCT + SNM groups. Electrode wires were implanted into S3 dorsal foramina in both sham and SNM groups, but only the SNM group was subjected to electrical stimulation for four hours a day for three weeks. Twenty-one days later, the rats were sacrificed via anesthetic overdose, and isolated longitudinal bladder strip preparations were placed in organ baths for the investigation of their isometric responses to pharmacological agents.

RESULTS

In isometric contraction experiments, SCT was found to increase the contraction responses of the bladder strips to muscarinic stimulation, and SNM could not prevent this increase. In isometric relaxation experiments, SCT caused a decrease in β-adrenergic relaxation responses, and SNM augmented the bladder's β-adrenergic relaxation responses. Nitric oxide did not affect the relaxation responses.

CONCLUSION

In our rat model of SCT, SNM seemed to alter adrenergic receptor function in the urinary bladder. Further studies are required to clarify the mechanism of these alterations at the level of bladder receptors following sacral neuromodulation.

Neural pathways involved in sacral neuromodulation of reflex bladder activity in cats

This study examined the mechanisms underlying the effects of sacral neuromodulation on reflex bladder activity in chloralose-anesthetized cats. Bladder activity was recorded during cystometrograms (CMGs) or under isovolumetric conditions. An S1-S3 dorsal (DRT) or ventral root (VRT) was electrically stimulated at a range of frequencies (1-30 Hz) and at intensities relative to threshold (0.25-2T) for evoking anal/toe twitches. Stimulation of DRTs but not VRTs at 1T intensity and frequencies of 1-30 Hz inhibited isovolumetric rhythmic bladder contractions. A 5-Hz DRT stimulation during CMGs was optimal for increasing (P < 0.05) bladder capacity (BC), but stimulation at 15 and 30 Hz was ineffective. Stimulation of the S1 DRT was more effective (increases BC to 144% and 164% of control at 1T and 2T, respectively) than S2 DRT stimulation (increases BC to 132% and 150% of control). Bilateral transection of the hypogastric or pudendal nerves did not change the inhibitory effect induced by S1 DRT stimulation. Repeated stimulation of S1 and S2 DRTs during multiple CMGs elicited a significant (P < 0.05) increase in BC (to 155 ± 11% of control) that persisted after termination of the stimulation. These results in cats suggest that the inhibition of reflex bladder activity by sacral neuromodulation occurs primarily in the central nervous system by inhibiting the ascending or descending pathways of the spinobulbospinal micturition reflex.

How sacral nerve stimulation works in patients with faecal incontinence

AIM

Sacral nerve stimulation (SNS) reduces incontinence episodes and improves the quality of life of patients treated for faecal incontinence. However, the exact mechanism of action of this technique remains unclear. The present article reviews the pertinent neuroanatomy and neurophysiology related to SNS and provides explanations for potential mechanisms of action.

METHOD

A systematic review of the literature was performed for studies of the potential mechanisms of action of SNS, using MEDLINE, PubMed, Embase and the Cochrane Library. Articles dealing with the technique, adverse events and economic evaluations of SNS, as well as literature reviews, were excluded, except for reviews dealing with the mechanisms of action of SNS. The following inclusion criteria were used to select articles: (i) articles in English, (ii) randomized, double-blinded, sham-controlled studies, and (iii) cohort studies. Case-control studies or retrospective studies were cited only when randomized or cohort studies could not be found.

RESULTS

We propose three hypotheses to explain the mechanism of action of SNS: (i) a somato-visceral reflex, (ii) a modulation of the perception of afferent information, and (iii) an increase in external anal sphincter activity.

CONCLUSION

The mechanism of action of SNS in patients with faecal incontinence almost certainly depends on the modulation of spinal and/or supraspinal afferent inputs. Further research on humans and animals will be required to gain a better understanding of the mechanisms of action of SNS.

Activity and Expression of Nitric Oxide Synthase in Rat Bladder after Sacral Neuromodulation

The aim of our study is to investigate the effects of chronic sacral neuromodulation on Nitric Oxide (NO) metabolism in the rat bladder. 26 female Sprangue-Dawley rats were considered: group I, normal control rats; group II, a sham treatment, in whom catheters for electrical stimulation were placed in the S1 foramen bilaterally and left in place for 21 days, without performing neuromodulation; group III in whom electrical sacral neuromodulation was performed for 21 days. Finally a cystectomy was performed and the bladder biopsy specimens were sent for immunostaining with n-NOS and i-NOS. Morphological and immunohistochemical analysis was carried out, and evaluated in urothelial cells, endothelial cells and muscle fibers of the muscularis propria. Differences between the 3 groups were analyzed by Student Newman-Keuls test. We could observe that urothelial and endothelial i-NOS (37.00±4.69 and 59.00±7.42 respectively) and urothelial n-NOS (36.80±7.85) expression are significantly increased in neuromodulated rats, compared to groups 1 and 2 (p < 0.005). In conclusion, the increase of i-NOS expression on endothelial cells after sacral neuromodulation could be in some way related to angiogenetic responses in the microvascular structures; the increase of n-NOS and i-NOS expression on urothelial cells can suggest that NO is able to influence the plasticity of bladder response, inducing the release of messengers within the urothelium. This study can therefore improve our understanding of the mechanisms of sacral neuromodulation on chronic bladder dysfunction; further studies will need to better demonstrate the role of angiogenesis in the bladder after sacral neuromodulation and to investigate the effects of neuromodulation in rats with chronically induced bladder dysfunction.

Sacral nerve stimulation: neuromodulation for voiding dysfunction and pain

Voiding dysfunction, which includes incontinence, retention, and chronic pelvic pain, is a relatively frequent problem that can be difficult to manage. Neuromodulation via stimulation of the sacral nerves has been shown to improve these symptoms, although the exact mechanisms remain elusive. Techniques for nerve stimulation may vary, depending on the disease, location of pain, and the patient's anatomy. In addition to placement of electrodes on the sacral nerve roots, modulation has also been reported by peripheral branches of the sacral nerves including the pudendal and posterior tibial nerves. Newer surgical techniques have significantly decreased the morbidity of the procedures and increased the probability of a successful outcome.

Biomechanical and histologic comparison of single-layer continuous Cushing and simple continuous appositional cystotomy closure by use of poliglecaprone 25 in rats with experimentally induced inflammation of the urinary bladder

OBJECTIVE

To biomechanically and histologically compare single-layer continuous Cushing and simple continuous appositional cystotomy closure in rats with xylene-induced cystitis.

ANIMALS

40 female Sprague-Dawley rats.

PROCEDURE

Rats were anesthetized, their urinary bladders catheterized and evacuated, and xylene instilled in each bladder for 5 minutes and then aspirated. Forty-eight hours later, ventral midline celiotomy and cystotomy (8 mm) were performed. Cystotomies were closed with 6-0 poliglecaprone 25 by use of a single-layer continuous Cushing or simple continuous appositional pattern (20 rats/group), and cystotomy times were recorded. Rats were allocated to healing durations (5 rats/group) of 0, 3, 7, and 14 days. Celiotomies were closed in a routine manner. After the allotted healing interval, another celiotomy was performed, the urethra cannulated, and ureters ligated. The cannula was secured to the urethra, and the bladder infused at 0.1 mL/min. Leak pressure volume, leak pressure, peak pressure volume, and peak pressure were recorded via a pressure transducer. Bladders were harvested and histologically assessed.

RESULTS

Cystotomy time, biomechanical testing values, and overall inflammation scores did not differ between closure methods for any healing duration. Both methods had significantly greater leak pressures, with the appositional method also having significantly greater peak pressures on day 7, compared to day 0. Biomechanical testing values decreased from day 7 to 14 as a result of juxtaincisional weakening of the bladder and xylene-induced changes in collagen.

CONCLUSIONS AND CLINICAL RELEVANCE

Simple continuous appositional was equal biomechanically and histologically to continuous Cushing for all comparison variables. Poliglecaprone 25 was acceptable for cystotomy closure.

Interaction between neurotransmitter antagonists and effects of sacral neuromodulation in rats with chronically hyperactive bladder

OBJECTIVE

To investigate to what extent antagonists of spinal neurotransmitters interact with the effects of sacral neuromodulation in a rat model of a chronically hyperactive urinary bladder.

MATERIALS AND METHODS

In female rats the urinary bladder was instilled with turpentine oil 2.5% to induce cystitis. After surviving for 10 days the rats were anaesthetized with urethane, the bladder catheterized and connected to a pressure transducer. Stimulating electrodes were placed in the sacral foramina bilaterally. The spinal cord was exposed by a laminectomy, and a small pool was placed on the cord for intrathecal administration of neurotransmitter antagonists. Sacral neuromodulation was applied before and after administering the antagonists. The antagonists used were: memantine, an antagonist for N-methyl-D-aspartate (NMDA) receptors; CNQX, an antagonist for non-NMDA receptors, and L-NAPNA, a blocker of nitric oxide synthase.

RESULTS

With no electrical neuromodulation, memantine and L-NAPNA abolished the cystitis-induced bladder contractions for approximately 4 and approximately 37 min, respectively. The effect of CNQX was similar to that of artificial cerebrospinal fluid. Electrical sacral modulation with no antagonists also transiently abolished the bladder contractions; at the highest intensity used, the pause was 2-3 min. Superfusion of the spinal cord with CNQX reduced this effect of neuromodulation significantly, whereas memantine had no influence, and L-NAPNA increased the neuromodulation-induced pause.

CONCLUSIONS

The results suggest that non-NMDA receptors are involved in the effects of sacral neuromodulation, whereas NMDA receptors appear to have no role. Nitric oxide is essential for maintaining the chronic hyperactive state of the urinary bladder.