Restoring both continence and micturition after chronic spinal cord injury by pudendal neuromodulation

A New Rat Model of Sacral Cord Injury Producing a Neurogenic Bladder and Its Functional and Mechanistic Studies

Sacral spinal cord injury (SSCI) can disrupt bladder neuromodulation and impair detrusor function. Current studies provide limited information on the histologic and genetic changes associated with SSCI-related neurogenic lower urinary tract dysfunction (NLUTD), resulting in few treatment options. This study aimed to establish a simple animal model of SSCI to better understand the disease progression. Ninety 8-week-old Sprague-Dawley (SD) rats were randomly separated into sham operation and SSCI groups. The SSCI group underwent sacral spinal cord injury, while the sham group did not. Urodynamic and histological assessments were conducted at various intervals (1, 2, 3, 4, and 6 weeks) post-injury to elucidate the disease process. Urodynamic examinations revealed significant bladder dysfunction in the SSCI group compared to the sham group, stabilizing around 3-4 weeks post-injury. Histological examination, including hematoxylin-eosin and Masson's trichrome staining, correlated these functional changes with bladder microstructural alterations. RNA-seq was performed on bladder tissues from the sham group and SSCI group at 6 weeks to identify differentially expressed genes and pathways. Selected genes were further analyzed using polymerase chain reaction (PCR). The findings indicated a pronounced inflammatory response in the first 2 weeks post-SSCI, progressing to bladder fibrosis at 3-4 weeks. In conclusion, this study presents a reliable, reproducible, and straightforward SSCI model, providing insights into bladder functional and morphological alterations post-SSCI and laying the groundwork for future therapeutic research.

Nerve transfer for restoration of lower motor neuron-lesioned bladder, urethral and anal sphincter function. Part 4: Effectiveness of the motor reinnervation

In pilot work, we showed that somatic nerve transfers can restore motor function in long-term decentralized dogs. We continue to explore the effectiveness of motor reinnervation in 30 female dogs. After anesthesia, 12 underwent bilateral transection of coccygeal and sacral (S) spinal roots, dorsal roots of lumbar (L)7, and hypogastric nerves. Twelve months postdecentralization, eight underwent transfer of obturator nerve branches to pelvic nerve vesical branches, and sciatic nerve branches to pudendal nerves, followed by 10 mo recovery (ObNT-ScNT Reinn). The remaining four were euthanized 18 mo postdecentralization (Decentralized). Results were compared with 18 Controls. Squat-and-void postures were tracked during awake cystometry. None showed squat-and-void postures during the decentralization phase. Seven of eight ObNT-ScNT Reinn began showing such postures by 6 mo postreinnervation; one showed a return of defecation postures. Retrograde dyes were injected into the bladder and urethra 3 wk before euthanasia, at which point, roots and transferred nerves were electrically stimulated to evaluate motor function. Upon L2-L6 root stimulation, five of eight ObNT-ScNT Reinn showed elevated detrusor pressure and four showed elevated urethral pressure, compared with L7-S3 root stimulation. After stimulation of sciatic-to-pudendal transferred nerves, three of eight ObNT-ScNT Reinn showed elevated urethral pressure; all showed elevated anal sphincter pressure. Retrogradely labeled neurons were observed in L2-L6 ventral horns (in laminae VI, VIII, and IX) of ObNT-ScNT Reinn versus Controls in which labeled neurons were observed in L7-S3 ventral horns (in lamina VII). This data supports the use of nerve transfer techniques for the restoration of bladder function.NEW & NOTEWORTHY This data supports the use of nerve transfer techniques for the restoration of bladder function.

Functional mapping of the lower urinary tract by epidural electrical stimulation of the spinal cord in decerebrated cat model

Several neurologic diseases including spinal cord injury, Parkinson's disease or multiple sclerosis are accompanied by disturbances of the lower urinary tract functions. Clinical data indicates that chronic spinal cord stimulation can improve not only motor function but also ability to store urine and control micturition. Decoding the spinal mechanisms that regulate the functioning of detrusor (Detr) and external urethral sphincter (EUS) muscles is essential for effective neuromodulation therapy in patients with disturbances of micturition. In the present work we performed a mapping of Detr and EUS activity by applying epidural electrical stimulation (EES) at different levels of the spinal cord in decerebrated cat model. The study was performed in 5 adult male cats, evoked potentials were generated by EES aiming to recruit various spinal pathways responsible for LUT and hindlimbs control. Recruitment of Detr occurred mainly with stimulation of the lower thoracic and upper lumbar spinal cord (T13-L1 spinal segments). Responses in the EUS, in general, occurred with stimulation of all the studied sites of the spinal cord, however, a pronounced specificity was noted for the lower lumbar/upper sacral sections (L7-S1 spinal segments). These features were confirmed by comparing the normalized values of the slope angles used to approximate the recruitment curve data by the linear regression method. Thus, these findings are in accordance with our previous data obtained in rats and could be used for development of novel site-specific neuromodulation therapeutic approaches.

Real-time prediction of bladder urine leakage using fuzzy inference system and dual Kalman filtering in cats

The use of electrical stimulation devices to manage bladder incontinence relies on the application of continuous inhibitory stimulation. However, continuous stimulation can result in tissue fatigue and increased delivered charge. Here, we employ a real-time algorithm to provide a short-time prediction of urine leakage using the high-resolution power spectrum of the bladder pressure during the presence of non-voiding contractions (NVC) in normal and overactive bladder (OAB) cats. The proposed method is threshold-free and does not require pre-training. The analysis revealed that there is a significant difference between voiding contraction (VC) and NVC pressures as well as band powers (0.5-5 Hz) during both normal and OAB conditions. Also, most of the first leakage points occurred after the maximum VC pressure, while all of them were observed subsequent to the maximum VC spectral power. Kalman-Fuzzy method predicted urine leakage on average 2.2 s and 1.6 s before its occurrence and an average of 2.0 s and 1.1 s after the contraction started with success rates of 94.2% and 100% in normal and OAB cats, respectively. This work presents a promising approach for developing a neuroprosthesis device, with on-demand stimulation to control bladder incontinence.

A Multielectrode Nerve Cuff for Chronic Velocity Selective Recording in a sheep model

Supra-sacral spinal cord injury (SCI) causes loss of bladder fullness sensation and bladder over-activity, leading to retention and incontinence respectively. Velocity selective recording (VSR) of nerve roots innervating the bladder might enable identification of bladder activity. A 10-electrode nerve cuff for sacral nerve root VSR was developed and tested in a sheep model during acute surgeries and chronic implantation for 6 months. The cuff performed well, with 5.90±1.90 kΩ electrode, and <~800 Ω tissue impedance after 189 days implantation with a stable device and tissues. This is important information for assessing the feasibility of chronic VSR.Clinical Relevance-This demonstrates the manufacturing and performance of a neural interface for chronic monitoring of bladder nerve afferents with applications in urinary incontinence and retention management following SCI.

Assessing Neurogenic Lower Urinary Tract Dysfunction after Spinal Cord Injury: Animal Models in Preclinical Neuro-Urology Research

Neurogenic bladder dysfunction is a condition that affects both bladder storage and voiding function and remains one of the leading causes of morbidity after spinal cord injury (SCI). The vast majority of individuals with severe SCI develop neurogenic lower urinary tract dysfunction (NLUTD), with symptoms ranging from neurogenic detrusor overactivity, detrusor sphincter dyssynergia, or sphincter underactivity depending on the location and extent of the spinal lesion. Animal models are critical to our fundamental understanding of lower urinary tract function and its dysfunction after SCI, in addition to providing a platform for the assessment of potential therapies. Given the need to develop and evaluate novel assessment tools, as well as therapeutic approaches in animal models of SCI prior to human translation, urodynamics assessment techniques have been implemented to measure NLUTD function in a variety of animals, including rats, mice, cats, dogs and pigs. In this narrative review, we summarize the literature on the use of animal models for cystometry testing in the assessment of SCI-related NLUTD. We also discuss the advantages and disadvantages of various animal models, and opportunities for future research.

Pudendal Nerve Block by Adaptively Stepwise Increasing the Intensity of High-Frequency (10 kHz) Biphasic Stimulation

OBJECTIVE

The purpose of this study is to determine whether adaptively stepwise increasing the intensity of a high-frequency (10 kHz) biphasic stimulation (HFBS) can produce nerve conduction block without generating a large initial response.

MATERIALS AND METHODS

In anesthetized cats, three cuff electrodes were implanted on the left pudendal nerve for stimulation or block. The urethral pressure increase induced by pudendal nerve stimulation was used to measure the pudendal nerve block induced by HFBS.

RESULTS

HFBS applied suddenly with a large step increase in intensity induced a large (86 ± 16 cmH2O) urethral pressure increase before it blocked pudendal nerve conduction. However, HFBS applied by adaptively stepwise increasing the intensity every 10 to 60 seconds over a long period (33-301 minutes; average 108 ± 35 minutes) with many small intensity increases (0.005-0.1 mA) induced no response or low-amplitude high-frequency urethral pressure changes before it blocked pudendal nerve conduction. The minimal HFBS intensities required by the two different methods to block pudendal nerve conduction are similar.

CONCLUSION

This study is important for better understanding the possible mechanisms underlying the HFBS-induced nerve block and provides the possibility of developing a new nerve block method for clinical applications in which an initial large response is a concern.

Temperature Effect on Nerve Conduction Block Induced by High-Frequency (kHz) Biphasic Stimulation

OBJECTIVES

This study aims to determine temperature effect on nerve conduction block induced by high-frequency (kHz) biphasic stimulation (HFBS).

MATERIALS AND METHODS

Frog sciatic nerve-muscle preparation was immersed in Ringer's solution at a temperature of 15 or 20 °C. To induce muscle contractions, a bipolar cuff electrode delivered low-frequency (0.25 Hz) stimulation to the nerve. To induce nerve block, a tripolar cuff electrode was placed distal to the bipolar cuff electrode to deliver HFBS (2 or 10 kHz). A bipolar hook electrode distal to the blocking electrode was used to confirm that the nerve block occurred locally at the site of HFBS. A thread tied onto the foot was attached to a force transducer to measure the muscle contraction force.

RESULTS

At 15 °C, both 2- and 10-kHz HFBSs elicited an initial transient muscle contraction and then produced nerve block during the stimulation (ie, acute block), with the 10 kHz having a significantly (p < 0.001) higher acute block threshold (5.9 ± 0.8 mA peak amplitude) than the 2 kHz (1.9 ± 0.3 mA). When the temperature was increased to 20 °C, the acute block threshold for the 10-kHz HFBS was significantly (p < 0.0001) decreased from 5.2 ± 0.3 to 4.4 ± 0.2 mA, whereas the 2-kHz HFBS induced a tonic muscle contraction during the stimulation but elicited nerve block after terminating the 2-kHz HFBS (ie, poststimulation block) with an increased block duration at a higher stimulation intensity.

CONCLUSION

Temperature has an important influence on HFBS-induced nerve block. The blocking mechanisms underlying acute and poststimulation nerve blocks are likely to be very different.

Vaginal Lubrication and Pressure Increase Induced by Pudendal Nerve Stimulation in Cats

BACKGROUND

Vaginal lubrication and contractions are among the top difficulties affecting sexual intercourse in women after spinal cord injury.

AIM

This study aimed at determining if pudendal nerve stimulation (PNS) can improve vaginal lubrication and induce increases in vaginal pressure.

METHODS

In anesthetized cats, a small piece of cotton was inserted into the vagina for 10 minutes with or without PNS to measure vaginal wetness by the weight increase of the vaginal cotton. Then, a small balloon catheter was inserted into the vagina to measure the pressure increase induced by PNS. Intensity response of the vagina to PNS (30 Hz, 0.2 ms, 5 seconds) was determined at 1-4 times of intensity threshold (T) for PNS to induce an observable vaginal pressure increase. Frequency response was determined at 2T intensity in a range of PNS frequencies (5-50 Hz). Finally, fatigue in vaginal pressure was determined by applying PNS (30 Hz, 2T) either continuously or intermittently (5 seconds on and 5 seconds off) for 4 minutes.

OUTCOMES

The effectiveness of PNS in increasing vaginal wetness and pressure is evaluated.

RESULTS

PNS significantly (P = .0327) increased the measurement of vaginal wetness from 15.8 ± 3.8 mg during control without stimulation to 32.4 ± 4.7 mg after stimulation. Vaginal pressure increased as PNS intensity or frequency increased. PNS (30 Hz, 2T) induced vaginal pressure increase ≥80% of the maximal response. Intermittent PNS induced significantly (P = .0354) smaller fatigue (45.6 ± 3.7%) in vaginal pressure than continuous PNS (69.1 ± 3.0%) during the 4-minute stimulation.

CLINICAL TRANSLATION

This study raises the possibility of developing a novel pudendal neuromodulation device to improve female sexual function after spinal cord injury.

STRENGTHS & LIMITATIONS

This study provides preclinical data supporting the development of a novel pudendal neuromodulation device. The limitation includes the lack of chemical analysis of the vaginal secretion.

CONCLUSION

PNS can improve vaginal lubrication and induce increases in vaginal pressure.

Neurogenic Bladder Physiology, Pathogenesis, and Management after Spinal Cord Injury

Urinary incontinence is common after spinal cord injury (SCI) due to loss of supraspinal coordination and unabated reflexes in both autonomic and somatic nervous systems; if unchecked, these disturbances can become life-threatening. This manuscript will review normal anatomy and physiology of the urinary system and discuss pathophysiology secondary to SCI. This includes a discussion of autonomic dysreflexia, as well as its diagnosis and management. The kidneys and the ureters, representing the upper urinary tract system, can be at risk related to dyssynergy between the urethral sphincters and high pressures that lead to potential vesicoureteral reflux, urinary tract infections, and calculi associated with neurogenic lower urinary tract dysfunction (NLUTD). Recent guidelines for diagnosis, evaluation, treatment and follow up of the neurogenic bladder will be reviewed and options provided for risk stratification and management. Mechanical, pharmacological, neurolysis and surgical management will be discussed.

Defecation induced by stimulation of sacral S2 spinal root in cats

The aim of this study was to determine whether stimulation of sacral spinal nerve roots can induce defecation in cats. In anesthetized cats, bipolar hook electrodes were placed on the S1-S3 dorsal and/or ventral roots. Stimulus pulses (1-50 Hz, 0.2 ms) were applied to an individual S1-S3 root to induce proximal/distal colon contractions and defecation. Balloon catheters were inserted into the proximal and distal colon to measure contraction pressure. Glass marbles were inserted into the rectum to demonstrate defecation by videotaping the elimination of marbles. Stimulation of the S2 ventral root at 7 Hz induced significantly (P < 0.05) larger contractions (32 ± 9 cmH₂O) in both proximal and distal colon than stimulation of the S1 or S3 ventral root. Intermittent (5 times) stimulation (1 min on and 1 min off) of both dorsal and ventral S2 roots at 7 Hz produced reproducible colon contractions without fatigue, whereas continuous stimulation of 5-min duration caused significant fatigue in colon contractions. Stimulation (7 Hz) of both dorsal and ventral S2 roots together successfully induced defecation that eliminated 1 or 2 marbles from the rectum. This study indicates the possibility to develop a novel neuromodulation device to restore defecation function after spinal cord injury using a minimally invasive surgical approach to insert a lead electrode via the sacral foramen to stimulate a sacral spinal root.NEW & NOTEWORTHY This study in cats determined the optimal stimulation parameters and the spinal segment for sacral spinal root stimulation to induce colon contraction. The results have significant implications for design of a novel neuromodulation device to restore defecation function after spinal cord injury (SCI) and for optimizing sacral neuromodulation parameters to treat non-SCI people with chronic constipation.

Adapting the Finetech-Brindley Sacral Anterior Root Stimulator for Bioelectronic Medicine. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2021;2021:6406-6411. [PMID: 34892578 DOI: 10.1109/embc46164.2021.9630995] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The Finetech-Brindley Sacral Anterior Root Stimulator (SARS) is a low cost and reliable system. The architecture has been used for various bioelectric treatments, including several thousand implanted systems for restoring bladder function following spinal cord injury (SCI). Extending the operational frequency range would expand the capability of the system; enabling, for example, the exploration of eliminating the rhizotomy through an electrical nerve block. The distributed architecture of the SARS system enables stimulation parameters to be adjusted without modifying the implant design or manufacturing. To explore the design degrees-of-freedom, a circuit simulation was created and validated using a modified SARS system that supported stimulation frequencies up to 600 Hz. The simulation was also used to explore high frequency (up to 30kHz) behaviour, and to determine the constraints on charge delivered at the higher rates. A key constraint found was the DC blocking capacitors, designed originally for low frequency operation, not fully discharging within a shortened stimulation period. Within these current implant constraints, we demonstrate the potential capability for higher frequency operation that is consistent with presynaptic stimulation block, and also define targeted circuit improvements for future extension of stimulation capability.

Low pressure voiding induced by stimulation and 1 kHz post-stimulation block of the pudendal nerves in cats

The goal of this study is to induce low-pressure voiding by stimulation and bilateral 1 kHz post-stimulation block of the pudendal nerves. In anesthetized cats, wire hook electrodes were placed on the left and/or right pudendal nerves. Stimulus pulses (30 Hz, 0.2 ms) were applied to one pudendal nerve to induce a reflex bladder contraction and to produce contractions of the external urethral sphincter (EUS). High frequency (1 kHz) biphasic stimulation was applied to block axonal conduction in both pudendal nerves and block EUS activity. In 4 cats, a catheter was inserted into the distal urethra to perfuse and measure the back pressure caused by the EUS contraction. In another 5 cats, a catheter was inserted into the bladder dome and the urethra was left open to allow voiding. The 1 kHz stimulation (30-60 s, 0.5-5 mA) delivered via a wire hook electrode completely blocked pudendal nerve conduction for ≥2 min after terminating the stimulation, i.e., a post-stimulation block. The block gradually disappeared in 6-18 min. The block duration increased with increasing amplitude or duration of the 1 kHz stimulation. Without the 1 kHz block, 30 Hz stimulation alone induced high-pressure (90 cmH₂O) voiding. When combined with the 1 kHz block, the 30 Hz stimulation induced low-pressure (≤50 cmH₂O) voiding with a high voiding efficiency (80%). In summary, a minimally invasive surgical approach might be developed to restore voiding function after spinal cord injury by stimulation and block of the pudendal nerves using lead electrodes.