Bladder and urethral sphincter responses evoked by microstimulation of S2 sacral spinal cord in spinal cord intact and chronic spinal cord injured cats

The inhibitory effect of intraspinal microstimulation of the sacral spinal cord on nonlinear bladder reflex dynamics in cats

Objective

Electrical stimulation of the pudendal nerve, pelvic nerve, sacral dorsal root ganglion (DRG), and spinal cord has been explored to treat urinary incontinence and overactive bladder (OAB). This study introduces sacral intraspinal microstimulation (ISMS) as a novel method to inhibit spontaneous bladder reflexes in anesthetized cats. In addition, we investigated the effects of intermittent and switching stimulation patterns on bladder inhibition.

Methods

The electrode was implanted in the dorsal horn of the S2 spinal cord. Bladder pressure was recorded under isovolumetric conditions, and the stimulation parameters were adjusted to inhibit spontaneous bladder contractions. Nonlinear dynamic methods, including chaos theory, were employed to analyze the complexity of bladder reflexes.

Results

Results demonstrated that ISMS targeting the dorsal horn of the S2 spinal segment effectively suppressed high-amplitude spontaneous contractions. Furthermore, bladder reflexes exhibited complex dynamics, ranging from regular to chaotic patterns, with transitions between these states. Importantly, ISMS was able to stabilize these chaotic dynamics, leading to more controlled bladder behavior.

Conclusion

These findings suggest that sacral ISMS offers a promising, targeted alternative to traditional stimulation therapies, potentially providing a new therapeutic approach for managing OAB and urinary incontinence by regulating chaotic bladder activity.

An innovative electrical neurostimulation approach to mimic reflexive urination control in spinal cord injury models

Neurogenic lower urinary tract dysfunction (NLUTD) is a frequent consequence of spinal cord injury (SCI), leading to symptoms that significantly impact quality of life. Although many life-saving techniques are available, current treatment strategies for managing NLUTD still exhibit limitations and drawbacks. Here, we introduce a new electrical neuromodulation strategy involving electrical stimulation of the major pelvic ganglion (MPG) to initiate bladder contraction, in conjunction with innovative programmable (IPG) electrical stimulation on the pudendal nerve (PN) to induce external urethral sphincter (EUS) relaxation in freely moving or anesthetized SCI mice. Furthermore, we conducted the void spot assay, and cystometry coupled with EUS electromyography (EMG) recordings to evaluate voiding function, and monitor bladder pressure and EUS activity. Our findings demonstrate that our novel electrical neuromodulation approach effectively triggers coordinated bladder muscle contraction and EUS relaxation, effectively counteracting SCI-induced NLUTD. Additionally, this electrical neuromodulation method enhances voiding efficiency, closely resembling natural reflexive urination in SCI mice. Thus, our study offers a promising electrical neurostimulation approach aimed at restoring physiological coordination and potentially offering personalized treatment for improving voiding efficiency in individuals with SCI-associated NLUTD.

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.

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.

A general framework for automatic closed-loop control of bladder voiding induced by intraspinal microstimulation in rats

Individuals with spinal cord injury or neurological disorders have problems in voiding function due to the dyssynergic contraction of the urethral sphincter. Here, we introduce a closed-loop control of intraspinal microstimulation (ISMS) for efficient bladder voiding. The strategy is based on asynchronous two-electrode ISMS with combined pulse-amplitude and pulse-frequency modulation without requiring rhizotomy, neurotomy, or high-frequency blocking. Intermittent stimulation is alternately applied to the two electrodes that are implanted in the S2 lateral ventral horn and S1 dorsal gray commissure, to excite the bladder motoneurons and to inhibit the urethral sphincter motoneurons. Asynchronous stimulation would lead to reduce the net electric field and to maximize the selective stimulation. The proposed closed-loop system attains a highly voiding efficiency of 77.2-100%, with an average of 91.28 ± 8.4%. This work represents a promising approach to the development of a natural and robust motor neuroprosthesis device for restoring bladder functions.

Intraspinal stimulation with a silicon-based 3D chronic microelectrode array for bladder voiding in cats

Objective.

Bladder dysfunction is a significant and largely unaddressed problem for people living with spinal cord injury (SCI). Intermittent catheterization does not provide volitional control of micturition and has numerous side effects. Targeted electrical microstimulation of the spinal cord has been previously explored for restoring such volitional control in the animal model of experimental SCI. Here, we continue the development of the intraspinal microstimulation array technology to evaluate its ability to provide more focused and reliable bladder control in the feline animal model.

Approach.

For the first time, a mechanically robust intraspinal multisite silicon array was built using novel microfabrication processes to provide custom-designed tip geometry and 3D electrode distribution. Long-term implantation was performed in eight spinally intact animals for a period up to 6 months, targeting the dorsal gray commissure area in the S2 sacral cord that is known to be involved in the coordination between the bladder detrusor and the external urethral sphincter.

Main results.

About one third of the electrode sites in the that area produced micturition-related responses. The effectiveness of stimulation was further evaluated in one of eight animals after spinal cord transection (SCT). We observed increased bladder responsiveness to stimulation starting at 1 month post-transection, possibly due to supraspinal disinhibition of the spinal circuitry and/or hypertrophy and hyperexcitability of the spinal bladder afferents.

Significance.

3D intraspinal microstimulation arrays can be chronically implanted and provide a beneficial effect on the bladder voiding in the intact spinal cord and after SCT. However, further studies are required to assess longer-term reliability and safety of the developed intraspinal microstimulation array prior to eventual human translation.

Spinal cord stimulation for the restoration of bladder function after spinal cord injury

Spinal cord injury (SCI) results in the inability to empty the bladder voluntarily, and neurogenic detrusor overactivity (NDO) and detrusor sphincter dyssynergia (DSD) negatively impact both the health and quality of life of persons with SCI. Current approaches to treat bladder dysfunction in persons with SCI, including self-catheterisation and anticholinergic medications, are inadequate, and novel approaches are required to restore continence with increased bladder capacity, as well as to provide predictable and efficient on-demand voiding. Improvements in bladder function following SCI have been documented using a number of different modalities of spinal cord stimulation (SCS) in both persons with SCI and animal models, including SCS alone or SCS with concomitant activity-based training. Improvements include increased volitional voiding, voided volumes, bladder capacity, and quality of life, as well as decreases in NDO and DSD. Further, SCS is a well-developed therapy for chronic pain, and existing Food And Drug Administration (FDA)-approved devices provide a clear pathway to sustainable commercial availability and impact. However, the effective stimulation parameters and the appropriate timing and location of stimulation for SCS-mediated restoration of bladder function require further study, and studies are needed to determine underlying mechanisms of action.

Management of neurogenic bladder in patients with Parkinson's disease: A systematic review

AIMS

To assess the different treatment methods in management of neurogenic bladder (NGB) in patients with Parkinson's disease (PD).

METHODS

A systematic search was performed in Cochrane library, EMBASE, Proquest, Clinicaltrial.gov, WHO, Google Scholar, MEDLINE via PubMed, Ovid, ongoing trials registers, and conference proceedings in November 11, 2017. All randomized controlled trials (RCTs) or quasi-RCTs comparing any treatment method for management of NGB in patients with PD were included. The titles and abstracts of all identified studies were evaluated independently by two investigators. Once all of the potential related articles were retrieved, each author separately evaluated the full text of each article and the quality of the methodology of the selected studies using the Cochrane appraisal risk of bias checklist and then the data about the patient's outcomes was extracted. We registered the title in Joanna Briggs Institute (JBI) that is available in http://joannabriggs.org/research/registered_titles.aspx.

RESULTS

We included 41 RCTs or quasi-RCTs or three observational study with a total of 1063 patients that evaluated pharmacological, neurosurgical, botulinum toxin, electrical neuromodulation, and behavioral therapy effects on NGB. Among the included studies only solifenacin succinate double-blind, randomized, placebo-controlled study was assessed as low risk of bias, and treatment led to an improvement in urinary incontinence.

CONCLUSIONS

Although several interventions are available for treatment NGB in patients with PD, at present there is little or no evidence that treatment improves patient outcomes in this population. Additional large, well designed, randomized studies with improved methodology and reporting focused on patient-centered outcomes are needed.

ESTUDO RETROSPECTIVO DE 98 FELINOS SUBMETIDOS À ACUPUNTURA ATENDIDOS EM SERVIÇO DE REABILITAÇÃO E DOR CRÔNICA

Resumo Este estudo retrospectivo avaliou os casos clínicos de felinos atendidos em Serviço de Reabilitação e Dor Crônica, durante 13 anos, totalizando 98 prontuários. Os objetivos deste estudo foram caracterizar o perfil do paciente atendido e avaliar a eficácia da acupuntura (AP) e dos métodos associados a esta técnica no tratamento de doenças em felinos e respectiva evolução clínica. Constatou-se que 69,7% dos pacientes melhoraram após tratamento com AP, 16,7% não apresentaram resposta significativa e 13,6% vieram a óbito. Não foram registrados casos de piora relacionados ao tratamento com AP, embora, dos nove animais que vieram a óbito, três foram devido à progressão da doença primária tratada exclusivamente com AP. As principais afecções tratadas foram relacionadas ao sistema nervoso - sobretudo trauma medular e encefálico - em que se registrou uma melhora em 53,7% dos animais. O tratamento foi considerado eficaz quando os pacientes recuperaram a capacidade normal de deambulação e em casos de doenças medulares quando o escore neurológico mudou de IV (grave) ou V (muito grave) para I (normal) ou II (leve alteração). A técnica de agulha seca foi a mais utilizada para os tratamentos, com 94,7% de prevalência, seguida da eletroacupuntura (30,6%) e da laserpuntura (21,4%). O número de sessões totais de AP foi em média de 6,97±14,97, sendo as mesmas semanais. Conclui-se que o estímulo de acupontos utilizando diferentes métodos foi eficiente para tratar a maioria dos gatos com diversas condições clínicas, evidenciando que esta espécie provavelmente responde tão bem como os cães após o tratamento de AP.

Neurophysiology and neural engineering: a review

Neurophysiology is the branch of physiology concerned with understanding the function of neural systems. Neural engineering (also known as neuroengineering) is a discipline within biomedical engineering that uses engineering techniques to understand, repair, replace, enhance, or otherwise exploit the properties and functions of neural systems. In most cases neural engineering involves the development of an interface between electronic devices and living neural tissue. This review describes the origins of neural engineering, the explosive development of methods and devices commencing in the late 1950s, and the present-day devices that have resulted. The barriers to interfacing electronic devices with living neural tissues are many and varied, and consequently there have been numerous stops and starts along the way. Representative examples are discussed. None of this could have happened without a basic understanding of the relevant neurophysiology. I also consider examples of how neural engineering is repaying the debt to basic neurophysiology with new knowledge and insight.

MRI-Guided Stereotactic System for Delivery of Intraspinal Microstimulation

STUDY DESIGN

Laboratory/animal-based proof of principle study.

OBJECTIVE

To validate the accuracy of a magnetic resonance imaging (MRI)-guided stereotactic system for intraspinal electrode targeting and demonstrate the feasibility of such a system for controlling implantation of intraspinal electrodes.

SUMMARY OF BACKGROUND DATA

Intraspinal microstimulation (ISMS) is an emerging preclinical therapy, which has shown promise for the restoration of motor function following spinal cord injury. However, targeting inaccuracy associated with existing electrode implantation techniques remains a major barrier preventing clinical translation of ISMS.

METHODS

System accuracy was evaluated using a test phantom comprised of nine target locations. Targeting accuracy was determined by calculating the root mean square error between MRI-generated coordinates and actual frame coordinates required to reach the target positions. System performance was further validated in an anesthetized pig model by performing MRI-guided intraspinal electrode implantation and stimulation followed by computed tomography of electrode location. Finally, system compatibility with a commercially available microelectrode array was demonstrated by implanting the array and applying a selection of stimulation amplitudes that evoked hind limb responses.

RESULTS

The root mean square error between actual frame coordinates and software coordinates, both acquired using the test phantom, was 1.09 ± 0.20 mm. Postoperative computed tomography in the anesthetized pig confirmed spatially accurate electrode placement relative to preoperative MRI. Additionally, MRI-guided delivery of a microwire electrode followed by ISMS evoked repeatable electromyography responses in the biceps femoris muscle. Finally, delivery of a microelectrode array produced repeatable and graded hind limb evoked movements.

CONCLUSION

We present a novel frame-based stereotactic system for targeting and delivery of intraspinal instrumentation. This system utilizes MRI guidance to account for variations in anatomy between subjects, thereby improving upon existing ISMS electrode implantation techniques.

LEVEL OF EVIDENCE

N/A.

Inhibitory effects of endomorphin-2 on excitatory synaptic transmission and the neuronal excitability of sacral parasympathetic preganglionic neurons in young rats

The function of the urinary bladder is partly controlled by parasympathetic preganglionic neurons (PPNs) of the sacral parasympathetic nucleus (SPN). Our recent work demonstrated that endomorphin-2 (EM-2)-immunoreactive (IR) terminals form synapses with μ-opioid receptor (MOR)-expressing PPNs in the rat SPN. Here, we examined the effects of EM-2 on excitatory synaptic transmission and the neuronal excitability of the PPNs in young rats (24–30 days old) using a whole-cell patch-clamp approach. PPNs were identified by retrograde labeling with the fluorescent tracer tetramethylrhodamine-dextran (TMR). EM-2 (3 μM) markedly decreased both the amplitude and the frequency of the spontaneous and miniature excitatory postsynaptic currents (sEPSCs and mEPSCs) of PPNs. EM-2 not only decreased the resting membrane potentials (RMPs) in 61.1% of the examined PPNs with half-maximal response at the concentration of 0.282 μM, but also increased the rheobase current and reduced the repetitive action potential firing of PPNs. Analysis of the current–voltage relationship revealed that the EM-2-induced current was reversed at −95 ± 2.5 mV and was suppressed by perfusion of the potassium channel blockers 4-aminopyridine (4-AP) or BaCl₂ or by the addition of guanosine 5′-[β-thio]diphosphate trilithium salt (GDP-β-S) to the pipette solution, suggesting the involvement of the G-protein-coupled inwardly rectifying potassium (GIRK) channel. The above EM-2-invoked inhibitory effects were abolished by the MOR selective antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), indicating that the effects of EM-2 on PPNs were mediated by MOR via pre- and/or post-synaptic mechanisms. EM-2 activated pre- and post-synaptic MORs, inhibiting excitatory neurotransmitter release from the presynaptic terminals and decreasing the excitability of PPNs due to hyperpolarization of their membrane potentials, respectively. These inhibitory effects of EM-2 on PPNs at the spinal cord level may explain the mechanism of action of morphine treatment and morphine-induced bladder dysfunction in the clinic.

Spinal primitives and intra-spinal micro-stimulation (ISMS) based prostheses: a neurobiological perspective on the "known unknowns" in ISMS and future prospects

The current literature on Intra-Spinal Micro-Stimulation (ISMS) for motor prostheses is reviewed in light of neurobiological data on spinal organization, and a neurobiological perspective on output motor modularity, ISMS maps, stimulation combination effects, and stability. By comparing published data in these areas, the review identifies several gaps in current knowledge that are crucial to the development of effective intraspinal neuroprostheses. Gaps can be categorized into a lack of systematic and reproducible details of: (a) Topography and threshold for ISMS across the segmental motor system, the topography of autonomic recruitment by ISMS, and the coupling relations between these two types of outputs in practice. (b) Compositional rules for ISMS motor responses tested across the full range of the target spinal topographies. (c) Rules for ISMS effects' dependence on spinal cord state and neural dynamics during naturally elicited or ISMS triggered behaviors. (d) Plasticity of the compositional rules for ISMS motor responses, and understanding plasticity of ISMS topography in different spinal cord lesion states, disease states, and following rehabilitation. All these knowledge gaps to a greater or lesser extent require novel electrode technology in order to allow high density chronic recording and stimulation. The current lack of this technology may explain why these prominent gaps in the ISMS literature currently exist. It is also argued that given the "known unknowns" in the current ISMS literature, it may be prudent to adopt and develop control schemes that can manage the current results with simple superposition and winner-take-all interactions, but can also incorporate the possible plastic and stochastic dynamic interactions that may emerge in fuller analyses over longer terms, and which have already been noted in some simpler model systems.

Electrical stimulation for the treatment of lower urinary tract dysfunction after spinal cord injury

Electrical stimulation for bladder control is an alternative to traditional methods of treating neurogenic lower urinary tract dysfunction (NLUTD) resulting from spinal cord injury (SCI). In this review, we systematically discuss the neurophysiology of bladder dysfunction following SCI and the applications of electrical stimulation for bladder control following SCI, spanning from historic clinical approaches to recent pre-clinical studies that offer promising new strategies that may improve the feasibility and success of electrical stimulation therapy in patients with SCI. Electrical stimulation provides a unique opportunity to control bladder function by exploiting neural control mechanisms. Our understanding of the applications and limitations of electrical stimulation for bladder control has improved due to many pre-clinical studies performed in animals and translational clinical studies. Techniques that have emerged as possible opportunities to control bladder function include pudendal nerve stimulation and novel methods of stimulation, such as high frequency nerve block. Further development of novel applications of electrical stimulation will drive progress towards effective therapy for SCI. The optimal solution for restoration of bladder control may encompass a combination of efficient, targeted electrical stimulation, possibly at multiple locations, and pharmacological treatment to enhance symptom control.

Spinal stimulation of the upper lumbar spinal cord modulates urethral sphincter activity in rats after spinal cord injury

After spinal cord injury (SCI), the neurogenic bladder is observed to develop asynchronous bladder and external urethral sphincter (EUS) contractions in a condition known as detrusor-sphincter dyssnergia (DSD). Activation of the EUS spinal controlling center located at the upper lumbar spinal cord may contribute to reduce EUS dyssynergic contractions and decrease urethral resistance during voiding. However, this mechanism has not been well studied. This study aimed at evaluating the effects of epidural stimulation (EpS) over the spinal EUS controlling center (L3) in combination with a serotonergic receptor agonist on EUS relaxation in naive rats and chronic (6-8 wk) T8 SCI rats. Cystometrogram and EUS electromyography (EMG) were obtained before and after the intravenous administration of 5HT-1A receptor agonist and antagonist. The latency, duration, frequency, amplitude, and area under curve of EpS-evoked EUS EMG responses were analyzed. EpS on L3 evoked an inhibition of EUS tonic contraction and an excitation of EUS intermittent bursting/relaxation correlating with urine expulsion in intact rats. Combined with a 5HT-1A receptor agonist, EpS on L3 evoked a similar effect in chronic T8 SCI rats to reduce urethral contraction (resistance). This study examined the effect of facilitating the EUS spinal controlling center to switch between urine storage and voiding phases by using EpS and a serotonergic receptor agonist. This novel approach of applying EpS on the EUS controlling center modulates EUS contraction and relaxation as well as reduces urethral resistance during voiding in chronic SCI rats with DSD.

Effects of lateral funiculus sparing, spinal lesion level, and gender on recovery of bladder voiding reflexes and hematuria in rats

Deficits in bladder function are complications following spinal cord injury (SCI), severely affecting quality of life. Normal voiding function requires coordinated contraction of bladder and urethral sphincter muscles dependent upon intact lumbosacral reflex arcs and integration of descending and ascending spinal pathways. We previously reported, in electrophysiological recordings, that segmental reflex circuit neurons in anesthetized male rats were modulated by a bilateral spino-bulbo-spinal pathway in the mid-thoracic lateral funiculus. In the present study, behavioral measures of bladder voiding reflexes and hematuria (hemorrhagic cystitis) were obtained to assess the correlation of plasticity-dependent recovery to the degree of lateral funiculus sparing and mid-thoracic lesion level. Adult rats received mid-thoracic-level lesions at one of the following severities: complete spinal transection; bilateral dorsal column lesion; unilateral hemisection; bilateral dorsal hemisection; a bilateral lesion of the lateral funiculi and dorsal columns; or a severe contusion. Voiding function and hematuria were evaluated by determining whether the bladder was areflexic (requiring manual expression, i.e., "crede maneuver"), reflexive (voiding initiated by perineal stroking), or "automatic" (spontaneous voiding without caretaker assistance). Rats with one or both lateral funiculi spared (i.e., bilateral dorsal column lesion or unilateral hemisection) recovered significantly faster than animals with bilateral lateral funiculus lesions, severe contusion, or complete transection. Bladder reflex recovery time was significantly slower the closer a transection lesion was to T10, suggesting that proximity to the segmental sensory and sympathetic innervation of the upper urinary tract (kidney, ureter) should be avoided in the choice of lesion level for SCI studies of micturition pathways. In addition, hematuria duration was significantly longer in males, compared to females, despite similar bladder reflex onset times. We conclude that the sparing of the mid-thoracic lateral funiculus on one side is required for early recovery of bladder reflex voiding function and resolution of hematuria.

Neuroprosthetic technology for individuals with spinal cord injury

CONTEXT

Spinal cord injury (SCI) results in a loss of function and sensation below the level of the lesion. Neuroprosthetic technology has been developed to help restore motor and autonomic functions as well as to provide sensory feedback.

FINDINGS

This paper provides an overview of neuroprosthetic technology that aims to address the priorities for functional restoration as defined by individuals with SCI. We describe neuroprostheses that are in various stages of preclinical development, clinical testing, and commercialization including functional electrical stimulators, epidural and intraspinal microstimulation, bladder neuroprosthesis, and cortical stimulation for restoring sensation. We also discuss neural recording technologies that may provide command or feedback signals for neuroprosthetic devices.

CONCLUSION/CLINICAL RELEVANCE

Neuroprostheses have begun to address the priorities of individuals with SCI, although there remains room for improvement. In addition to continued technological improvements, closing the loop between the technology and the user may help provide intuitive device control with high levels of performance.

Synaptic connections between endomorphin 2-immunoreactive terminals and μ-opioid receptor-expressing neurons in the sacral parasympathetic nucleus of the rat

The urinary bladder is innervated by parasympathetic preganglionic neurons (PPNs) that express μ-opioid receptors (MOR) in the sacral parasympathetic nucleus (SPN) at lumbosacral segments L6-S1. The SPN also contains endomorphin 2 (EM2)-immunoreactive (IR) fibers and terminals. EM2 is the endogenous ligand of MOR. In the present study, retrograde tract-tracing with cholera toxin subunit b (CTb) or wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) via the pelvic nerve combined with immunohistochemical staining for EM2 and MOR to identify PPNs within the SPN as well as synaptic connections between the EM2-IR terminals and MOR-expressing PPNs in the SPN of the rat. After CTb was injected into the pelvic nerve, CTb retrogradely labeled neurons were almost exclusively located in the lateral part of the intermediolateral gray matter at L6-S1 of the lumbosacral spinal cord. All of the them also expressed MOR. EM2-IR terminals formed symmetric synapses with MOR-IR, WGA-HRP-labeled and WGA-HRP/MOR double-labeled neuronal cell bodies and dendrites within the SPN. These results provided morphological evidence that EM2-containing axon terminals formed symmetric synapses with MOR-expressing PPNs in the SPN. The present results also show that EM2 and MOR might be involved in both the homeostatic control and information transmission of micturition.

Effect of high-frequency alternating current on spinal afferent nociceptive transmission

OBJECTIVE

The study was performed to test the hypothesis that high-frequency alternating current (HFAC) ranging from 2 to 100 kHz delivered to the spinal dorsal roots reduces activity of spinal wide dynamic range (WDR) dorsal horn neurons (DHNs) during noxious peripheral stimulation.

MATERIALS AND METHODS

This hypothesis was tested in both small and large animal in vivo preparations. Single-unit extracellular spinal DHN recordings were performed in seven adult rats and four adult goats while testing various parameters of HFAC delivered to the nerve roots or dorsal root entry zone using various electrode types. Frequencies tested ranged from 2 to 100 kHz but focused on the 3 to 50 kHz range. This study investigated the ability of HFAC to inhibit WDR neuronal activity evoked by noxious mechanical (pinch), and electrical stimuli was tested but was primarily focused on electrical stimulation.

RESULTS

Rat Study: Effects of HFAC were successfully tested on 11 WDR neurons. Suppression or complete blockade of evoked activity was observed in all 11 of these neurons. Complete data sets for neurons systematically tested with 15 baseline and post-HFAC stimulus sweeps were obtained in five neurons, the nociceptive activity of which was suppressed by an average of 69 ± 9.7% (p < 0.0001). Goat Study: HFAC was successfully tested on 15 WDR neurons. Conclusive suppression or complete nociceptive blockade was observed for 12/15 and complete data sets with at least 20 baseline and post-HFAC stimulus sweeps were obtained from eight DHNs. For these neurons the mean activity suppression was 70 ± 10% (p < 0.005).

CONCLUSIONS

Delivery of HFAC to the region of epidural nerve root or nerve root entry inhibited afferent nociceptive input and therefore may have potential to serve as an alternative to traditional spinal cord stimulation without sensory paresthesia as neuronal activation cannot occur at frequencies in this range.

Sacral neuromodulation and refractory overactive bladder: an emerging tool for an old problem

Overactive bladder (OAB) syndrome negatively affects the daily life of many people. Conservative treatments, such as antimuscarinics, do not always lead to sufficient improvement of the complaints and are often associated with considerable side effects resulting in treatment failure. In the case of failure or intolerable side effects, sacral neuromodulation (SNM) and botulinum toxin intravesical injections are minimally invasive and reversible alternatives. Currently, both SNM and botulinum toxin injection have FDA approval for use in OAB patients. This mini-review attempts to provide an update on SNM as a second-line management of adults with refractory OAB, based on the available clinical evidence concerning the efficacy and safety.

Spinal cord stimulation: therapeutic benefits and movement generation after spinal cord injury

Spinal cord injury (SCI) is a devastating neurological condition that leads to loss of motor and sensory function. It commonly causes impairments in limb movements, respiration, bowel and bladder function, as well as secondary complications including pain, spasticity, and pressure ulcers. Numerous interventions such as neuroprotection, regeneration, pharmacology, rehabilitation training, and functional electrical stimulation are under investigation for improving function after SCI. This chapter discusses the use of spinal cord stimulation (epidural and intraspinal electrical stimulation) for alleviating pain and spasticity, and restoring standing and walking. Epidural stimulation is effective in reducing the intensity of intractable pain, but its effectiveness in the treatment of spasticity remains unclear. It can induce rhythmic, locomotor-like movements in the legs, presumably due to the activation of afferent pathways. Intraspinal microstimulation is a new electrical stimulation approach that activates locomotor-related networks within the ventral regions of the lumbosacral spinal cord. In animals, this approach is capable of producing prolonged, fatigue-resistant standing and stepping of the hindlegs. While the results in animals have been very encouraging, technical advancements are necessary prior to its implementation in humans with SCI. Taken collectively, spinal cord stimulation holds substantial promise in restoring function after neural injury or disease.

Pelvic electrical neuromodulation for the treatment of overactive bladder symptoms

Overactive bladder syndrome negatively affects the daily life of many people. First-line conservative treatments, such as antimuscarinics, do not always lead to sufficient improvement of the complaints and/or are often associated with disabling adverse effects leading to treatment failure. Electrical stimulation of the sacral nerves has emerged as an alternative and attractive treatment for refractory cases of bladder overactivity. Few theories attempted to explain its mechanism of action which remains elusive. It involves percutaneous posterior tibial nerve stimulation and more commonly sacral neuromodulation. For the latter, temporary sacral nerve stimulation is the first step. If the test stimulation is successful, a permanent device is implanted. The procedure is safe and reversible. It carries a durable success rate. The technique should be combined with careful followup and attentive adjustments of the stimulation parameters in order to optimize the clinical outcomes. This paper provides a review on the indications, possible mechanisms of action, surgical aspects and possible complications, and safety issues of this technique. The efficacy of the technique is also addressed.

Strategies for spinal cord repair after injury: a review of the literature and information

INTRODUCTION

Thanks to the Internet, we can now have access to more information about spinal cord repair. Spinal cord injured (SCI) patients request more information and hospitals offer specific spinal cord repair medical consultations.

OBJECTIVE

Provide practical and relevant elements to physicians and other healthcare professionals involved in the care of SCI patients in order to provide adequate answers to their questions.

METHOD

Our literature review was based on English and French publications indexed in PubMed and the main Internet websites dedicated to spinal cord repair.

RESULTS

A wide array of research possibilities including notions of anatomy, physiology, biology, anatomopathology and spinal cord imaging is available for the global care of the SCI patient. Prevention and repair strategies (regeneration, transplant, stem cells, gene therapy, biomaterials, using sublesional uninjured spinal tissue, electrical stimulation, brain/computer interface, etc.) for the injured spinal cord are under development. It is necessary to detail the studies conducted and define the limits of these new strategies and benchmark them to the realistic medical and rehabilitation care available to these patients.

CONCLUSION

Research is quickly progressing and clinical trials will be developed in the near future. They will have to answer to strict methodological and ethical guidelines. They will first be designed for a small number of patients. The results will probably be fragmented and progress will be made through different successive steps.

Intraspinal microstimulation for the recovery of function following spinal cord injury

Spinal cord injury is a devastating neurological trauma, often resulting in the impairment of bladder, bowel, and sexual function as well as the loss of voluntary control of muscles innervated by spinal cord segments below the lesion site. Research is ongoing into several classes of therapies to restore lost function. These include the encouragement of neural sparing and regeneration of the affected tissue, and the intervention with pharmacological and rehabilitative means to improve function. This review will focus on the application of electrical current in the spinal cord in order to reactivate extant circuitry which coordinates and controls smooth and skeletal muscle below the injury. We first present a brief historical review of intraspinal microstimulation (ISMS) focusing on its use for restoring bladder function after spinal cord injury as well as its utilization as a research tool for mapping spinal cord circuits that coordinate movements. We then present a review of our own results related to the use of ISMS for restoring standing and walking movements after spinal cord injury. We discuss the mechanisms of action of ISMS and how they relate to observed functional outcomes in animal models. These include the activation of fibers-in-passage which lead to the transsynaptic spread of activation through the spinal cord and the ability of ISMS to produce fatigue-resistant, weight-bearing movements. We present our thoughts on the clinical potential for ISMS with regard to implantation techniques, stability, and damage induced by mechanical and electrical factors. We conclude by suggesting improvements in materials and techniques that are needed in preparation for a clinical proof-of-principle and review our current attempts to achieve these.

Intraspinal stimulation for bladder voiding in cats before and after chronic spinal cord injury

The long-term objective of this study is to develop neural prostheses for people with spinal cord injuries who are unable to voluntarily control their bladder. This feasibility study was performed in 22 adult cats. We implanted an array of microelectrodes into locations in the sacral spinal cord that are involved in the control of micturition reflexes. The effect of microelectrode stimulation was studied under light Propofol anesthesia at monthly intervals for up to 14 months. We found that electrical stimulation in the sacral parasympathetic nucleus at S(2) level or in adjacent ventrolateral white matter produced bladder contractions insufficient for inducing voiding, while stimulation at or immediately dorsal to the dorsal gray commissure at S(1) level produced strong (at least 20 mmHg) bladder contractions as well as strong (at least 40 mm Hg) external urethral sphincter relaxation, resulting in bladder voiding in 14 animals. In a subset of three animals, spinal cord transection was performed. For several months after the transection, intraspinal stimulation continued to be similarly or even more effective in inducing the bladder voiding as before the transection. We speculate that in the absence of the supraspinal connections, the plasticity in the local spinal circuitry played a role in the improved responsiveness to intraspinal stimulation.

Intraspinal stimulation for bladder voiding in cats before and after chronic spinal cord injury

The long-term objective of this study is to develop neural prostheses for people with spinal cord injuries who are unable to voluntarily control their bladder. This feasibility study was performed in 22 adult cats. We implanted an array of microelectrodes into locations in the sacral spinal cord that are involved in the control of micturition reflexes. The effect of microelectrode stimulation was studied under light Propofol anesthesia at monthly intervals for up to 14 months. We found that electrical stimulation in the sacral parasympathetic nucleus at S(2) level or in adjacent ventrolateral white matter produced bladder contractions insufficient for inducing voiding, while stimulation at or immediately dorsal to the dorsal gray commissure at S(1) level produced strong (at least 20 mmHg) bladder contractions as well as strong (at least 40 mm Hg) external urethral sphincter relaxation, resulting in bladder voiding in 14 animals. In a subset of three animals, spinal cord transection was performed. For several months after the transection, intraspinal stimulation continued to be similarly or even more effective in inducing the bladder voiding as before the transection. We speculate that in the absence of the supraspinal connections, the plasticity in the local spinal circuitry played a role in the improved responsiveness to intraspinal stimulation.

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.