Short-Term Dorsal Genital Nerve Stimulation Increases Subjective Arousal in Women With and Without Spinal Cord Injury: A Preliminary Investigation.

OBJECTIVES: Female sexual dysfunction (FSD) affects an estimated 40% of women. Unfortunately, FSD is understudied, leading to limited treatment options for FSD. Neuromodulation has shown some success in alleviating FSD symptoms. We developed a pilot study to investigate the short-term effect of electrical stimulation of the dorsal genital nerve and tibial nerve on sexual arousal in healthy women, women with FSD, and women with spinal cord injury (SCI) and FSD. MATERIALS AND METHODS: This study comprises a randomized crossover design in three groups: women with SCI, women with non-neurogenic FSD, and women without FSD or SCI. The primary outcome measure was change in vaginal pulse amplitude (VPA) from baseline. Secondary outcome measures were changes in subjective arousal, heart rate, and mean arterial pressure from baseline. Participants attended one or two study sessions where they received either transcutaneous dorsal genital nerve stimulation (DGNS) or tibial nerve stimulation (TNS). At each session, a vaginal photoplethysmography sensor was used to measure VPA. Participants also rated their level of subjective arousal and were asked to report any pelvic sensations. RESULTS: We found that subjective arousal increased significantly from before to after stimulation in DGNS study sessions across all women. TNS had no effect on subjective arousal. There were significant differences in VPA between baseline and stimulation, baseline and recovery, and stimulation and recovery periods among participants, but there were no trends across groups or stimulation type. Two participants with complete SCIs experienced genital sensations. CONCLUSIONS: To our knowledge, this is the first study to measure sexual arousal in response to short-term neuromodulation in women. This study indicates that short-term DGNS but not TNS can increase subjective arousal, but the effect of stimulation on genital arousal is inconclusive. This study provides further support for DGNS as a treatment for FSD.

Pudendal, but not tibial, nerve stimulation modulates vulvar blood perfusion in anesthetized rodents.

INTRODUCTION AND HYPOTHESIS: Preclinical studies have shown that neuromodulation can increase vaginal blood perfusion, but the effect on vulvar blood perfusion is unknown. We hypothesized that pudendal and tibial nerve stimulation could evoke an increase in vulvar blood perfusion. METHODS: We used female Sprague-Dawley rats for non-survival procedures under urethane anesthesia. We measured perineal blood perfusion in response to 20-minute periods of pudendal and tibial nerve stimulation using laser speckle contrast imaging (LSCI). After a thoracic-level spinalization and a rest period, we repeated each stimulation trial. We calculated average blood perfusion before, during, and after stimulation for three perineal regions (vulva, anus, and inner thigh), for each nerve target and spinal cord condition. RESULTS: We observed a significant increase in vulvar, anal, and inner thigh blood perfusion during pudendal nerve stimulation in spinally intact and spinalized rats. Tibial nerve stimulation had no effect on perineal blood perfusion for both spinally intact and spinalized rats. CONCLUSIONS: This is the first study to examine vulvar hemodynamics with LSCI in response to nerve stimulation. This study demonstrates that pudendal nerve stimulation modulates vulvar blood perfusion, indicating the potential of pudendal neuromodulation to improve genital blood flow as a treatment for women with sexual dysfunction. This study provides further support for neuromodulation as a treatment for women with sexual arousal disorders. Studies in unanesthetized animal models of genital arousal disorders are needed to obtain further insights into the mechanisms of neural control over genital hemodynamics.

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. Chen J, Zhong Y, Wang J, et al. Vaginal Lubrication and Pressure Increase Induced by Pudendal Nerve Stimulation in Cats. J Sex Med 2022;19:1517-1523.

Sacral neuromodulation of bladder underactivity induced by prolonged pudendal afferent firing in cats.

This study examined the effect of sacral neuromodulation on persistent bladder underactivity induced by prolonged pudendal nerve stimulation (PudNS). In 10 α-chloralose-anesthetized cats, repetitive application of 30-min PudNS induced bladder underactivity evident as an increase in bladder capacity during a cystometrogram (CMG). S1 or S2 dorsal root stimulation (15 or 30 Hz) at 1 or 1.5 times threshold intensity (T) for inducing reflex hindlimb movement (S1) or anal sphincter twitch (S2) was applied during a CMG to determine if the stimulation can reverse the bladder underactivity. Persistent (>3 h) bladder underactivity consisting of a significant increase in bladder capacity to 163.1 ± 11.3% of control was induced after repetitive (1-10 times) application of 30-min PudNS. S2 but not S1 dorsal root stimulation at 15 Hz and 1 T intensity reversed the PudNS-induced bladder underactivity by significantly reducing the large bladder capacity to 124.3 ± 12.9% of control. Other stimulation parameters were not effective. After the induction of persistent underactivity, recordings of reflex bladder activity under isovolumetric conditions revealed that S2 dorsal root stimulation consistently induced the largest bladder contraction at 15 Hz and 1 T when compared with other frequencies (5-40 Hz) or intensities (0.25-1.5 T). This study provides basic science evidence consistent with the hypothesis that abnormal pudendal afferent activity contributes to the bladder underactivity in Fowler's syndrome and that sacral neuromodulation treats this disorder by reversing the bladder inhibition induced by pudendal nerve afferent activity.

Mapping a Danger Zone of the Dorsal Nerve of the Clitoris: Implications in Female Cosmetic Genital Surgery.

BACKGROUND: The literature regarding the route of the dorsal nerve of the clitoris is sparse and lacks surgical focus. With an increasing number of procedures being performed on the labia, it is important to elucidate the route and note any variation from normal of the nerve. METHODS: Fifty-one cadavers were dissected to yield 97 dorsal nerve of the clitoris samples. Measurements were taken from (1) the dorsal nerve of the clitoris penetration point of the perineal membrane to the urethra, (2) the nerve's penetration point of the perineal membrane to the pubic bone, (3) the angle of the clitoris to the branch point of the dorsal nerve of the clitoris, and (4) the branch point of the nerve to the distalmost point of the glans clitoris. Any anomalous branching patterns of the dorsal nerve of the clitoris were recorded and classified. RESULTS: The means and standard deviations of each measurement were used to create a surgical danger zone. The mean of each measurement was (1) 34.63 mm, (2) 5.74 mm, (3) -3.07 mm, and (4) 30.40 mm, respectively. In addition, six distinct branching patterns were observed, organized, and classified based on the location and number of branches observed. CONCLUSIONS: The dorsal nerve of the clitoris has multiple branching patterns and typically travels along the same course in most women. Further investigation of the course and three-dimensional position of the dorsal nerve of the clitoris is warranted to preserve sexual sensation as the frequency of procedures involving the female pudendum increases.

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.

Assessment of sacral spinal excitability using stimulus-response curves of the bulbocavernosus reflex.

OBJECTIVE: To analyze and quantify sacral spinal excitability through bulbocavernosus reflex (BCR) stimulus-response curves. METHODS: Thirty subjects with upper motor neuron lesions (UMN) and nine controls were included in this prospective, monocentric study. Sacral spinal excitability was assessed using stimulus-response curves of the BCR, modeled at different bladder filling volumes relative to the desire to void (as defined by the International Continence Society) during a cystometry. Variations in α (i.e. the slope of the stimulus-response curve) were considered as an indicator of the modulation of sacral spinal excitability. RESULTS: In all subjects, α increased during bladder filling suggesting the modulation of spinal sacral excitability during the filling phase. This increase was over 30% in 96.7% of neurological subjects and 88.9% of controls. The increase was higher before the first sensation to void in the neurological population (163.15%), compared to controls, (29.91%), p < 0.001. CONCLUSIONS: We showed the possibility of using BCR stimulus-response curves to characterize sacral spinal response with an amplification of this response during bladder filling as well as a difference in this response amplification in patients with UMN in comparison with a control group. SIGNIFICANCE: BCR, through stimulus-response curves, might be an indicator of pelvic-perineal exaggerated reflex response and possibly a tool for evaluating treatment effectiveness.

Tetanic stimulation of the pudendal nerve prior to transcranial electrical stimulation augments the amplitude of motor evoked potentials during pediatric neurosurgery.

OBJECTIVE: Reportedly, tetanic stimulation prior to transcranial electrical stimulation (TES) facilitates elicitation of motor evoked potentials (MEPs) by a mechanism involving increased corticomotoneuronal excitability in response to somatosensory input. However, the posttetanic MEP following stimulation of a pure sensory nerve has never been reported. Furthermore, no previous reports have described posttetanic MEPs in pediatric patients. The aim of this study was to investigate the efficacy of posttetanic MEPs in pediatric neurosurgery patients and to compare the effects on posttetanic MEP after tetanic stimulation of the sensory branch of the pudendal nerve versus the standard median and tibial nerves, which contain a mixture of sensory and motor fibers. METHODS: In 31 consecutive pediatric patients with a mean age of 6.0 ± 5.1 years who underwent lumbosacral surgery, MEPs were elicited by TES without tetanic stimulation (conventional MEPs [c-MEPs]) and following tetanic stimulation of the unilateral median and tibial nerves (mt-MEPs) and the sensory branch of the pudendal nerve (p-MEP). Compound muscle action potentials were elicited from abductor pollicis brevis (APB), gastrocnemius (Gc), tibialis anterior (TA), and adductor hallucis (AH) muscles. The success rate of monitoring each MEP and the increases in the ratios of mt-MEP and p-MEP to c-MEP were investigated. RESULTS: The success rate of monitoring p-MEPs was higher than those of mt-MEPs and c-MEPs (87.5%, 72.6%, and 63.3%, respectively; p < 0.01, adjusted by Bonferroni correction). The mean increase in the ratio of p-MEP to c-MEP for all muscles was significantly higher than that of mt-MEP to c-MEP (3.64 ± 4.03 vs 1.98 ± 2.23, p < 0.01). Subanalysis of individual muscles demonstrated significant differences in the increases in the ratios between p-MEP and mt-MEP in the APB bilaterally, as well as ipsilateral Gc, contralateral TA, and bilateral AH muscles. CONCLUSIONS: Tetanic stimulation prior to TES can augment the amplitude of MEPs during pediatric neurosurgery, the effect being larger with pudendal nerve stimulation than tetanic stimulation of the unilateral median and tibial nerves. TES elicitation of p-MEPs might be useful in pediatric patients in whom it is difficult to elicit c-MEPs.

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

Neurogenic bladder management after spinal cord injury (SCI) is very challenging. Daily urethral catheterization is most commonly used to empty the bladder, which causes frequent infections of the lower urinary tract. This study reports a novel idea to restore both continence and micturition after SCI by an implantable pudendal nerve stimulator (PNS). The PNS was surgically implanted in four cats with complete SCI at T9-T10 spinal level and tested weekly for 13-14 weeks under awake conditions. These chronic SCI cats consistently exhibited large residual bladder volumes (average 40-50 ml) due to their inability to void efficiently, while urine leakage also occurred frequently. The PNS which consisted of stimulating the pudendal nerve at 20-30 Hz to trigger a spinal reflex bladder contraction and at the same time blocking the pudendal nerves bilaterally with 10 kHz stimulation to relax the external urethral sphincter and reduce the urethral outlet resistance successfully induced highly efficient (average 80-100%), low pressure (<50 cmH2O) voiding. The PNS at 5 Hz also promoted urine storage by inhibiting reflex bladder activity and increasing bladder capacity. At the end of 14-week chronic testing, low pressure efficient voiding induced by PNS was further confirmed under anesthesia by directly measuring voiding pressure using a bladder catheter inserted through the bladder dome. This study demonstrated the efficacy and safety of the PNS in awake chronic SCI cats, suggesting that a novel neuroprosthesis can be developed for humans to restore bladder function after SCI by stimulating and/or blocking the pudendal nerves.

The pudendal nerve motor branch regenerates via a brain derived neurotrophic factor mediated mechanism.

Peripheral nerve injuries can significantly reduce quality of life. While some recover, most do not recover fully, resulting in neuropathic pain and loss of sensation and motor function. Research on the mechanisms of peripheral nerve regeneration could elucidate poor patient outcomes and potential treatments. This study was designed to determine if brain derived neurotrophic factor (BDNF) is necessary for pudendal nerve regeneration and functional recovery. Peripheral administration of tyrosine kinase B functional chimera (TrkB) was used to inhibit the BDNF regenerative pathway. Female Sprague-Dawley rats received tyrosine kinase B functional chimera (TrkB) or saline after a pudendal nerve crush (PNC) or Sham PNC and were divided into three groups: Sham PNC, PNC + Saline, and PNC + TrkB. Seven days after injury, relative ßII tubulin expression (1.0 ± 0.2) was significantly decreased after PNC + TrkB compared to PNC + saline (2.9 ± 1.0). Three weeks after injury, BDNF plasma concentration (1320.8 ± 278.1 pg/ml) was significantly reduced in PNC + TrkB compared to PNC + saline rats (2053.4 ± 211.0 pg/ml). Pudendal nerve motor branch firing rate (54.0 ± 9.5 Hz) was significantly decreased in the PNC + TrkB group compared to the PNC + saline group (120.4 ± 17.1 Hz); while nerve firing rate of the PNC + saline group was not significantly different from sham PNC rats (121.8 ± 26.6 Hz). This study demonstrated that peripheral administration of TrkB bound free BDNF and inhibited the regenerative response after PNC. BDNF is necessary for normal PN motor branch recovery after PNC.

Properties of Renshaw-like cells excited by recurrent collaterals of pudendal motoneurons in the cat.

Although anatomical studies have indicated pudendal motoneurons to give off recurrent collaterals, they are not considered to make synapses onto interneurons, such as Renshaw cells, and rather terminate their own signals. No study till date has examined interneurons being driven by recurrent collaterals of pudendal motoneurons. Here, we aimed to investigate the existence of Renshaw cells driven by pudendal motoneurons along with the recurrent inhibition of the latter. Extracellular recordings were obtained from the ventral horn of the sacral spinal cord of anesthetized cats. Dorsal roots were sectioned, and motor axons were electrically stimulated. Renshaw-like cells driven by recurrent collaterals, with high-frequency firings at short latency discharge, were observed around Onuf's nucleus. However, the recurrent inhibitory post-synaptic potentials were not recorded by intracellular recordings from the pudendal motoneurons. In summary, we found Renshaw-like cells driven by pudendal motoneurons, but we could not identify the synaptic connection of these neurons.

The rodent vaginal microbiome across the estrous cycle and the effect of genital nerve electrical stimulation.

Treatment options are limited for the approximately 40% of postmenopausal women worldwide who suffer from female sexual dysfunction (FSD). Neural stimulation has shown potential as a treatment for genital arousal FSD, however the mechanisms for its improvement are unknown. One potential cause of some cases of genital arousal FSD are changes to the composition of the vaginal microbiota, which is associated with vulvovaginal atrophy. The primary hypothesis of this study was that neural stimulation may induce healthy changes in the vaginal microbiome, thereby improving genital arousal FSD symptoms. In this study we used healthy rats, which are a common animal model for sexual function, however the rat vaginal microbiome is understudied. Thus this study also sought to examine the composition of the rat vaginal microbiota. Treatment rats (n = 5) received 30 minutes of cutaneous electrical stimulation targeting the genital branch of the pudendal nerve, and Control animals (n = 4) had 30-minute sessions without stimulation. Vaginal lavage samples were taken during a 14-day baseline period including multiple estrous periods and after twice-weekly 30-minute sessions across a six-week trial period. Analysis of 16S rRNA gene sequences was used to characterize the rat vaginal microbiota in baseline samples and determine the effect of stimulation. We found that the rat vaginal microbiota is dominated by Proteobacteria, Firmicutes, and Actinobacteria, which changed in relative abundance during the estrous cycle and in relationship to each other. While the overall stimulation effects were unclear in these healthy rats, some Treatment animals had less alteration in microbiota composition between sequential samples than Control animals, suggesting that stimulation may help stabilize the vaginal microbiome. Future studies may consider additional physiological parameters, in addition to the microbiome composition, to further examine vaginal health and the effects of stimulation.

Activity-Based Training Alters Penile Reflex Responses in a Rat Model of Spinal Cord Injury.

INTRODUCTION: Multisystem functional gains have been reported in males with spinal cord injury (SCI) after undergoing activity-based training (ABT), including increases in scoring of sexual function and reports of improved erectile function. AIM: This study aims to examine the effect of daily 60-minute locomotor training and exercise in general on sexual function in a rat SCI contusion model. METHODS: Male Wistar rats received a T9 contusion SCI. Animals were randomized into 4 groups: a quadrupedal stepping group (SCI + QT), a forelimb-only exercise group (SCI + FT), a non-trained harnessed group (SCI + NT), and a home cage non-trained group (SCI + HC). The 2 non-trained groups were combined (SCI) post hoc. Daily training sessions were 60 minutes in duration for 8 weeks. Urine samples were collected during bi-weekly 24-hour metabolic cage behavioral testing. Latency, numbers of penile dorsiflexion, and glans cupping were recorded during bi-weekly penile dorsiflexion reflex (PDFR) testing. Terminal electromyography (EMG) recordings of the bulbospongiosus muscle (BSM) were recorded in response to stimulation of the dorsal nerve of the penis (DNP). OUTCOMES: ABT after SCI had a significant effect on PDFR, as well as BSM EMG latency and burst duration. RESULTS: SCI causes a significant decrease in the latency to onset of PDFR. After 8 weeks of ABT, SCI + QT animals had a significantly increased latency relative to the post-SCI baseline. BSM EMG response to DNP stimulation had a significantly decreased latency and increase in average and maximum amplitude in SCI + QT animals. SCI animals had a significantly longer burst duration than trained animals. Time between PDFR events, penile dorsiflexion, glans cupping, and urine testosterone were not affected by ABT. CLINICAL IMPLICATIONS: ABT has a positive influence on sexual function and provides a potential therapy to enhance the efficacy of current sexual dysfunction therapies in the male SCI population. STRENGTHS AND LIMITATIONS: Several significant small improvements in sexual function were found in a clinically relevant rat model of SCI using a readily available rehabilitative therapy. The limited findings could reflect insensitivity of the PDFR as a measure of erectile function. CONCLUSIONS: These results indicate that task-specific stepping and/or loading provide sensory input to the spinal cord impacting the neural circuitry responsible for sexual function. Steadman CJ, Hoey RF, Montgomery LR, et al. Activity-Based Training Alters Penile Reflex Responses in a Rat Model of Spinal Cord Injury. J Sex Med 2019; 16:1143-1154.

Urethral regions with differential tissular composition may underlie urinary continence and voiding function in female rats.

AIMS: To analyze, in female rats, the anatomical and histological features of the urethra and its relationship with the vagina and clitoris, and its innervation. METHODS: Seventeen adult female Wistar rats were used. Gross anatomy and acetylcholinesterase (AchE) histochemistry were performed to describe the urethral features, adjacent structures, and innervation. The histomorphometric characteristics of the urethra were determined in transversal, longitudinal, or coronal sections stained with Masson's Trichrome. RESULTS: The female rat urethra is not a homogeneous tubular organ. The pre-pelvic and pelvic regions are firmly attached to the vagina with belt-like striated fibers forming a urethra-vaginal complex. The bulbar regions have curved segments and a narrow lumen. The clitoral region is characterized by a urethra-clitoral complex surrounded by a vascular plexus. The lumen area and thickness of the urethral layers significantly varied between regions (P < 0.05). Innervation of the urethra arrives from the major pelvic ganglion, the dorsal nerve of the clitoris (DNC), and the motor branch of the sacral plexus (MBSP). CONCLUSIONS: Differential tissular composition of the urethra may underlie urinary continence and voiding dysfunction through different physiological mechanisms. The urethra-vagina complex seems to be the main site controlling urinary continence through active muscular mechanisms, while the bulbar urethra provides passive mechanisms and the urethra-clitoris complex seems to be crucial for distal urethral closure by means of a periurethral vascular network.

Sensory pudendal nerve stimulation increases bladder capacity through sympathetic mechanisms in cyclophosphamide-induced cystitis rats.

AIMS: Interstitial cystitis and bladder pain syndrome is a prevalent health concern with inadequate treatments. Neuromodulation has emerged as a therapeutic option to treat patients refractory to standard care. The objective of this study was to determine the efficacy and mechanism(s) of sensory pudendal nerve stimulation on bladder function in cystitis rats. METHODS: Female rats were administered saline (n = 8) or cyclophosphamide (CYP, 150 mg/kg IP, n = 16) and single-trial cystometry experiments were conducted under urethane anesthesia 48 h after injection. Electrical stimulation (0.02-0.22 mA, 10-20 Hz) was delivered to the sensory branch of the pudendal nerve and its effect on the bladder and external urethral sphincter were measured. Stimulation trials were also conducted following bilateral hypogastric nerve transection (HGNT) or pharmacological inhibition of beta-adrenergic receptors (propranolol, 1 mg/kg IV) to determine the mechanisms of bladder inhibition. RESULTS: CYP-induced cystitis decreased bladder capacity (P = 0.0352) and bladder compliance (P = 0.024) by up to 38% of control. Electrical stimulation of the sensory pudendal nerve increased bladder capacity (P < 0.0001) in control and CYP rats by up to 51-52% of their respective baselines. HGNT did not influence bladder inhibition generated by sensory pudendal nerve stimulation in control rats, whereas HGNT and propranolol decreased the efficacy of electrical stimulation in CYP rats. CONCLUSIONS: Sympathetic reflex activity mediates sensory pudendal nerve stimulation in CYP treated but not control rats. These studies demonstrate an alternative approach to neuromodulation in cystitis and establish mechanistic changes during stimulation that may enable the development of novel therapeutics.

The frequency spectrum of bladder non-voiding activity as a trigger-event for conditional stimulation: Closed-loop inhibition of bladder contractions in rats.

AIMS: To test the hypothesis that the frequency of bladder non-voiding contractions (NVCs) can be used as a trigger event for closed-loop conditional inhibition of detrusor contractions via tibial nerve (TN) or dorsal penile nerve (DPN) stimulation. METHODS: In urethane anaesthetized male Wistar rats, the bladder was filled continuously with saline to evoke contractions. To test the plausibility of conditional inhibition via the TN, electrical stimulation was switched on manually when the pressure increased above a threshold of 10 cmH2 0 above the baseline. For testing conditional stimulation via the DPN, the pressure signal was continuously stored and a baseline threshold, the area under the curve (AUC) of the amplitude spectrum in the 0.2-20 Hz range of a 5 s window at the beginning of filling was calculated. When the AUC of subsequent pressure windows superseded the baseline threshold, the DPN was automatically stimulated. RESULTS: TN stimulation failed to inhibit evoked voiding contractions. The NVC frequency spectrum based DPN stimulation successfully inhibited 70% of the evoked contractions and resulted in a 45% increase in bladder capacity (BC). CONCLUSIONS: While, conditional TN stimulation failed to suppress bladder contractions, DPN stimulation, automatically triggered by an increased frequency of bladder non-voiding activity, resulted in bladder inhibition, and a consequential increase in BC. This study demonstrates the plausibility of using the frequency of NVCs as a trigger event for conditional inhibition of detrusor contractions.

Non-invasive electromyographic estimation of motor unit number in the external anal sphincter of the rat.

AIMS: The external anal sphincter (EAS) is essential for maintaining fecal continence. Neurological disorders or traumatic injuries to muscle and nervous systems could lead to EAS denervation. Currently, there are no techniques available to document global innervation changes in the EAS in vivo. The aim of this study was to develop a novel approach to non-invasively estimate the number of functioning motor units (MUs) in the EAS and validate with immunofluorescent techniques in rats. METHODS: Intra-rectal surface electromyography (EMG) signals of the EAS, induced by a series of intra-vaginally delivered pudendal nerve stimulations with different intensities, were recorded. Variation in EMG responses at different intensities was used to estimate the value of a single motor unit potential (SMUP) in order to perform the proposed EAS motor unit number estimation (MUNE) approach. The EAS MUNE was tested in 12 female Sprague-Dawley rats, and validated by comparing against the EAS myofiber counting results achieved by performing immunostaining of acetylcholine receptors in 7 of the 12 rats. RESULTS: The mean MU number was 35 ± 9, with an averaged SMUP size of 52.49 ± 20.39 µV. The mean number of successfully identified myofibers was 652.7 ± 130.6 myofiber/EAS. Significance of linear regression between the immunofluorescent results and the MUNE was confirmed (P < 0.01). CONCLUSIONS: Our study represents the first effort to non-invasively assess the innervation of the EAS in vivo using the rat as a pre-clinical model. This approach can potentially enable future clinical applications for advanced diagnosis and treatment of neurogenic EAS disorders.

Time-Frequency Analysis of Increases in Vaginal Blood Perfusion Elicited by Long-Duration Pudendal Neuromodulation in Anesthetized Rats.

OBJECTIVES: Female sexual dysfunction (FSD) affects a significant portion of the population. Although treatment options for FSD are limited, neuromodulation for bladder dysfunction has improved sexual function in some women. A few studies have investigated peripheral neuromodulation for eliciting changes in vaginal blood flow, as a proxy for modulating genital sexual arousal, however results are generally transient. Our central hypothesis is that repeated or extended-duration pudendal nerve stimulation can elicit maintained vaginal blood flow increases. MATERIALS AND METHODS: Under ketamine anesthesia, the pudendal nerve of 14 female rats was stimulated at varying frequencies (1-100 Hz) and durations (0.15-60 min). Vaginal blood perfusion was measured with a laser Doppler flowmetry probe. Changes in blood perfusion were determined through raw signal analysis and increases in the energy of neurogenic (0.076-0.200 Hz) and myogenic (0.200-0.740 Hz) frequency bands through wavelet analysis. Additionally, a convolution model was developed for a carry-over stimulation effect. RESULTS: Each experiment had significant increases in vaginal blood perfusion due to pudendal nerve stimulation. In addition, there were large concurrent increases in neurogenic and myogenic frequency-band energy in 11/14 experiments, with an average maximal response at 31.3 min after stimulation initiation. An effective stimulation model with a 30-min carry-over effect had a stronger correlation to blood perfusion than the stimulation period itself. CONCLUSIONS: Repeated or extended-duration pudendal nerve stimulation can elicit maintained increases in vaginal blood perfusion. This work indicates the potential for pudendal neuromodulation as a method for increasing genital arousal as a potential treatment for FSD.

An excitatory reflex from the superficial peroneal nerve to the bladder in cats.

This study in α-chloralose-anesthetized cats discovered an excitatory peroneal nerve-to-bladder reflex. A urethral catheter was used to infuse the bladder with saline and record bladder pressure changes. Electrical stimulation was applied to the superficial peroneal nerve to trigger reflex bladder activity. With the bladder distended at a volume ~90% of bladder capacity, superficial peroneal nerve stimulation (PNS) at 1-3 Hz and threshold (T) intensity for inducing muscle twitching on the posterior thigh induced large-amplitude (40-150 cmH2O) bladder contractions. PNS (1-3 Hz, 1-2T) applied during cystometrograms (CMGs) when the bladder was slowly (1-3 ml/min) infused with saline significantly (P < 0.01) reduced bladder capacity to ~80% of the control capacity and significantly (P < 0.05) enhanced reflex bladder contractions. To determine the impact of PNS on tibial nerve stimulation (TNS)-induced changes in bladder function, PNS was delivered following TNS. TNS of 30-min duration produced long-lasting poststimulation inhibition and significantly (P < 0.01) increased bladder capacity to 140.5 ± 7.6% of the control capacity. During the post-TNS inhibition period, PNS (1-3 Hz, 1-4T) applied during CMGs completely restored bladder capacity to the control level and significantly (P < 0.05) increased the duration of reflex bladder contractions to ~200% of control. The excitatory peroneal nerve-to-bladder reflex could also be activated by transcutaneous PNS using skin surface electrodes attached to the dorsal surface of the foot. These results raise the possibility of developing novel neuromodulation therapies to treat underactive bladder and nonobstructive urinary retention.

Hypothesized summative anal physiology score correlates but poorly predicts incontinence severity.

AIM: To explore the relationship between such a construct and an existing continence score. METHODS: A retrospective study of incontinent patients who underwent anal physiology (AP) was performed. AP results and Cleveland Clinic Continence Scores (CCCS) were extracted. An anal physiology score (APS) was developed using maximum resting pressures (MRP), anal canal length (ACL), internal and external sphincter defects and pudendal terminal motor latency. Univariate associations between each variable, APS and CCCS were assessed. Multiple regression analyses were performed. RESULTS: Of 508 (419 women) patients, 311 had both APS and CCCS measured. Average MRP was 51 mmHg (SD 23.2 mmHg) for men and 39 mmHg (19.2 mmHg) for women. Functional ACL was 1.7 cm for men and 0.7 cm for women. Univariate analyses demonstrated significant associations between CCCS and MRP (P = 0.0002), ACL (P = 0.0006) and pudendal neuropathy (P < 0.0001). The association between APS and CCCS was significant (P < 0.0001) but accounted for only 9.2% of the variability in CCCS. Multiple regression showed that the variables most useful in predicting CCCS were external sphincter defect, pudendal neuropathy and previous pelvic surgery, but only improving the scores predictive ability to 12.5%. CONCLUSION: This study shows that the ability of AP tests to predict continence scores improves when considered collectively, but that a constructed summation model before and after multiple regression is poor at predicting the variability in continence scores.