Anti-Inflammatory Effects of Two-Week Sacral Nerve Stimulation Therapy in Patients With Ulcerative Colitis

BACKGROUND AND AIMS

Sacral nerve stimulation (SNS) showed anti-inflammatory properties in animal models of inflammatory bowel disease. We aimed to evaluate the effectiveness and safety of SNS in patients with ulcerative colitis (UC).

MATERIALS AND METHODS

Twenty-six patients with mild and moderate disease were randomized into two groups: SNS (delivered at S3 and S4 sacral foramina) and sham-SNS (delivered 8-10 mm away from sacral foramina), with the therapy applied once daily for one hour, for two weeks. We evaluated the Mayo score and several exploratory biomarkers, including C-reactive protein in the plasma, pro-inflammatory cytokines and norepinephrine in the serum, assessment of autonomic activity, and diversity and abundance of fecal microbiota species.

RESULTS

After two weeks, 73% of the subjects in the SNS group achieved clinical response, compared with 27% in the sham-SNS group. Levels of C-reactive protein, pro-inflammatory cytokines in the serum, and autonomic activity were significantly improved toward a healthy profile in the SNS group but not in the sham-SNS group. Absolute abundance of fecal microbiota species and one of the metabolic pathways were changed in the SNS group but not in the sham-SNS group. Significant correlations were observed between pro-inflammatory cytokines and norepinephrine in the serum on the one side and fecal microbiota phyla on the other side.

CONCLUSIONS

Patients with mild and moderate UC were responsive to a two-week SNS therapy. After performing further studies to evaluate its efficacy and safety, temporary SNS delivered through acupuncture needles may become a useful screening tool for identifying SNS therapy responders before considering long-term implantation of the implantable pulse generator and SNS leads for performing long-term SNS therapy.

Vagus Nerve Stimulation and Sacral Nerve Stimulation for Inflammatory Bowel Disease: A Systematic Review

Background and objectives

In this systematic review, we assessed the efficacy, potential mechanisms, and safety of two neuromodulation therapies in patients with inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis. The first therapy is vagus nerve stimulation (VNS) utilizing implantable or transcutaneous electrodes, and the second is sacral nerve stimulation (SNS) using implantable or percutaneous electrodes.

Methods

We conducted a systematic literature review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The PubMed database was comprehensively searched, and studies were rigorously assessed for inclusion and exclusion criteria.

Results

Our analysis encompassed five clinical studies, three on VNS and two on SNS. Most investigated studies demonstrated significant beneficial effects on IBD symptoms, including disease activity, severity of intestinal lesions, and intestinal pain. When evaluating the impact on key IBD pathophysiologies, both VNS and SNS exhibited trends toward reducing biomarkers of intestinal mucosal inflammation and mitigating sympathetic dominance. Importantly, none of the evaluated neuromodulation methods resulted in long-term adverse effects.

Conclusions

Cumulative evidence from the evaluated studies indicates that VNS and SNS therapies effectively alleviate IBD symptoms and may hold promise in addressing the underlying pathophysiologies of IBD, including intestinal mucosal inflammation and sympathetic dominance. Consequently, they represent valuable options for individualized IBD treatment.

Neuromodulation for Gastroesophageal Reflux Disease: A Systematic Review

Background and objectives

In this systematic review, we evaluated the efficacy, mechanisms and safety of three neuromodulation therapies in patients with gastroesophageal reflux disease (GERD), including the effect of neuromodulation therapies on symptoms and key GERD pathophysiologies, lower esophageal sphincter (LES) pressure, esophageal motility, gastric motility, and parasympathetic activity. The first therapy is LES electrical stimulation using an implantable electrical stimulator, the second is transcutaneous electrical acustimulation, and the third is manual acupuncture.

Methods

A systematic review of literature according to the PRISMA guidelines was performed. Online databases searched include Medline (Ovid), Embase, and PubMed. Studies were assessed for inclusion and exclusion criteria with Covidence, a systematic review software.

Results

The analysis included thirteen clinical studies. Four papers included were registered under two open-label trials on ClinicalTrials.gov for LES electrical stimulation; Five randomized trials with sham-treated controls were analyzed for transcutaneous electrical acustimulation; Four studies, including three involving standard therapy controls and one involving shamtreated controls were included for manual acupuncture. All evaluated studies demonstrated significant beneficial effects on GERD symptoms, using patient-completed questionnaires, objective 24-h measurement of esophageal pH, and patient-reported use of proton pump inhibitors. In evaluating the effect on key GERD pathophysiologies, electrical stimulation significantly increased LES pressure, and transcutaneous electrical acustimulation significantly improved esophageal motility, gastric motility, and parasympathetic activity. None of the evaluated neuromodulation methods produced severe adverse effects.

Conclusions

Cumulative evidence from the evaluated studies indicates that neuromodulation therapies were effective in treating the GERD symptoms and key underlying GERD pathophysiologies. They are thus valuable options for individualized GERD treatment.

Bioelectronic medicine for restoring autonomic balance in autoimmune diseases

The aim of this mini-review is to introduce most prevalent autoimmune diseases, emphasize the importance of sympatho-parasympathetic imbalance in these autoimmune diseases, demonstrate how such imbalance can be effectively treated using the bioelectronic medicine, and describe potential mechanisms of bioelectronic medicine effects on the autoimmune activity at the cellular and molecular levels.

Blocking Ocular Sympathetic Activity Inhibits Choroidal Neovascularization

Purpose: To investigate how modulating ocular sympathetic activity affects progression of choroidal neovascularization (CNV), a hallmark feature of wet age-related macular degeneration (AMD).

Methods: In the first of two studies, Brown Norway rats underwent laser-induced CNV and were assigned to one of the following groups: daily eye drops of artificial tears (n = 10; control group); daily eye drops of the β-adrenoreceptor agonist isoproterenol (n = 10); daily eye drops of the β-adrenoreceptor antagonist propranolol (n = 10); sympathetic internal carotid nerve (ICN) transection 6 weeks prior to laser-induced CNV (n = 10). In the second study, rats underwent laser-induced CNV followed by ICN transection at different time points: immediately after the laser injury (n = 6), 7 days after the laser injury (n = 6), and sham surgery 7 days after the laser injury (n = 6; control group). All animals were euthanized 14 days after laser application. CNV development was quantified with fluorescein angiography and optical coherence tomography (in vivo), as well as lesion volume analysis using 3D confocal reconstruction (postmortem). Angiogenic growth factor protein levels in the choroid were measured with ELISA.

Results: In the first study, blocking ocular sympathetic activity through pharmacological or surgical manipulation led to a 75% or 70% reduction in CNV lesion volume versus the control group, respectively (P < 0.001). Stimulating ocular sympathetic activity with isoproterenol also led to a reduction in lesion volume, but only by 27% versus controls (P < 0.05). VEGF protein levels in the choroid were elevated in the three treatment groups (P < 0.01). In the second study, fluorescein angiography and CNV lesion volume analysis indicated that surgically removing the ocular sympathetic supply inhibited progression of laser-induced CNV, regardless of whether ICN transection was performed on the same day or 7 days after the laser injury.

Conclusion: Surgical and pharmacological block of ocular sympathetic activity can inhibit progression of CNV in a rat model. Therefore, electrical block of ICN activity could be a potential bioelectronic medicine strategy for treating wet AMD.

Configuring intracortical microelectrode arrays and stimulus parameters to minimize neuron loss during prolonged intracortical electrical stimulation

BACKGROUND

Previous studies have shown that neurons of the cerebral cortex can be injured by implantation of, and stimulation with, implanted microelectrodes.

OBJECTIVES

Objective 1 was to determine parameters of microstimulation delivered through multisite intracortical microelectrode arrays that will activate neurons of the feline cerebral cortex without causing loss of neurons.

OBJECTIVE

2 was to determine if the stimulus parameters that induced loss of cortical neurons differed for all cortical neurons vs. the subset of inhibitory neurons expressing parvalbumin.

METHODS

The intracortical microstimulation was applied for 7 h/day for 20 days (140 h). Microelectrode site areas were 2000 and 4000 μm², Q was 2-8 nanocoulombs (nC) at 50 Hz, and QD was 50-400 μcoulombs/cm².

RESULTS

Neuron loss due to stimulation was minimal at Q = 2 Ncp, but at 8 Ncp, 20%-50% of neurons within 250 μm of the stimulated microelectrodes were lost, compared to unstimulated microelectrodes. Loss was greatest in tissue facing electrode sites. Stimulation-induced loss was similar for neurons labeled for NeuN and for inhibitory neurons expressing parvalbumin. Correlation between neuron loss and QD was not significant. Electrodes in the medullary pyramidal tract recorded neuronal activity evoked by stimulation in the cerebral cortex. The pyramidal neurons were activated by intracortical stimulation of 2 nC/phase. 140 h of microstimulation at 2 nC/phase and 50 Hz induced minimal neuron loss.

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.

Sympathetic Effects of Internal Carotid Nerve Manipulation on Choroidal Vascularity and Related Measures

Purpose

To investigate specific effects of denervation and stimulation of the internal carotid nerve (ICN) on the choroid and retina.

Methods

Female Sprague Dawley rats underwent unilateral ICN transection (n = 20) or acute ICN electrical stimulation (n = 7). Rats in the denervation group were euthanized 6 weeks after nerve transection, and eyes were analyzed for changes in choroidal vascularity (via histomorphometry) or angiogenic growth factors and inflammatory markers (via ELISA). Rats in the stimulation group received acute ICN electrical stimulation with a bipolar cuff electrode over a range of stimulus amplitudes, frequencies, and pulse widths. Choroidal blood flow and pupil diameter were monitored before, during, and after stimulation.

Results

Six weeks after unilateral ICN transection, sympathectomized choroids exhibited increased vascularity, defined as the percentage of choroidal surface area occupied by blood vessel lumina. Vascular endothelial growth factor (VEGF) and VEGF receptor-2 (VEGFR-2) protein levels in denervated choroids were 61% and 124% higher than in contralateral choroids, respectively. TNF-α levels in denervated retinas increased by 3.3-fold relative to levels in contralateral retinas. In animals undergoing acute ICN electrical stimulation, mydriasis and reduced choroidal blood flow were observed in the ipsilateral eye. The magnitude of the reduction in blood flow correlated positively with stimulus frequency.

Conclusions

Modulation of ICN activity reveals a potential role of the ocular sympathetic system in regulating endpoints related to neovascular diseases of the eye.

EMG characteristics of the external anal sphincter guarding reflex and effects of a unilateral ventral root avulsion injury in rhesus macaques ( Macaca mulatta)

The external anal sphincter (EAS) is important for the maintenance of bowel continence and may be compromised by a variety of neuropathic conditions. However, large animal models for the study of EAS functions have been sparse. The EAS guarding reflex was examined by electromyography (EMG) in neurologically intact rhesus macaques ( n = 6) and at 4-6 wk after a unilateral EAS denervation from an L6-S3 ventral root avulsion (VRA) injury ( n = 6). Baseline EAS EMG recordings were quiescent in all subjects, and evoked responses showed an initial large-amplitude EMG activity, which gradually returned to baseline within 1-2 min. At 4-6 wk postoperatively, the EAS guarding reflex showed a significantly reduced EMG response duration of 47 ± 15 s and area under the curve (AUC) of 0.198 ± 0.097 mV·s compared with the corresponding evoked EAS EMG duration of 102 ± 19 s and AUC of 0.803 ± 0.225 mV·s ( P < 0.05) in the control group. Detailed time- and frequency-domain analysis of the evoked EAS EMG responses for the first 40 s showed no difference between groups for the maximum amplitude but a significant decrease for the mean amplitude across the study period and an early AUC reduction for the first 10 s in the VRA injury group. Time-frequency analysis and power spectrum plots indicated decreased intensity and a narrower midrange of frequencies in the VRA injury group. We conclude that the EAS guarding reflex in rhesus macaques shows characteristic EMG features in control subjects and signs of partial target denervation after a unilateral L6-S3 VRA injury. NEW & NOTEWORTHY The external anal sphincter guarding reflex showed initial large-amplitude peaks and a gradual return to a quiescent baseline after a rectal probe stimulus in rhesus macaques. At 4-6 wk after a unilateral ventral root avulsion (VRA) injury, the electromyography duration, mean amplitude, and area under the curve measurements were decreased. Time-frequency analysis and power spectrum plots indicated decreased intensity and a narrowed midrange of frequencies in the VRA injury cohort.

High-Frequency Electrical Modulation of the Superior Ovarian Nerve as a Treatment of Polycystic Ovary Syndrome in the Rat

The polycystic ovary syndrome (PCOS) is the most prevalent ovarian pathology in women, with excessive sympathetic activity in the superior ovarian nerve (SON) playing an important role in inducing the PCOS symptoms in the rats and humans. Our previous studies have shown that surgical transection of the SON can reverse the disease progression, prompting us to explore the effect of the kilohertz frequency alternating current (KHFAC) modulation as a method of reversible non-surgical suppression of the nerve activity in the rodent model of PCOS. 56 animals were randomly allocated to three groups: the Control group (n = 18), the PCOS group (n = 15), and the PCOS + KHFAC group (n = 23). The physiological, anatomical, and biochemical parameters of ovarian function were evaluated during the progression of the experimentally-induced PCOS and during long-term KHFAC modulation applied for 2-3 weeks. The KHFAC modulation has been able to reverse the pathological changes in assessed PCOS parameters, namely the irregular or absent estrous cycling, formation of ovarian cysts, reduction in the number of corpora lutea, and ovarian norepinephrine concentration. The fertility capacity was similar in the PCOS and the PCOS + KHFAC groups, indicating the safety of KHFAC modulation approach. In summary, these results suggest that the KHFAC modulation approach of suppressing the SON activity could become a useful treatment modality for PCOS and potentially other pathological ovarian conditions.

Bioelectronic modulation of carotid sinus nerve activity in the rat: a potential therapeutic approach for type 2 diabetes

AIMS/HYPOTHESIS

A new class of treatments termed bioelectronic medicines are now emerging that aim to target individual nerve fibres or specific brain circuits in pathological conditions to repair lost function and reinstate a healthy balance. Carotid sinus nerve (CSN) denervation has been shown to improve glucose homeostasis in insulin-resistant and glucose-intolerant rats; however, these positive effects from surgery appear to diminish over time and are heavily caveated by the severe adverse effects associated with permanent loss of chemosensory function. Herein we characterise the ability of a novel bioelectronic application, classified as kilohertz frequency alternating current (KHFAC) modulation, to suppress neural signals within the CSN of rodents.

METHODS

Rats were fed either a chow or high-fat/high-sucrose (HFHSu) diet (60% lipid-rich diet plus 35% sucrose drinking water) over 14 weeks. Neural interfaces were bilaterally implanted in the CSNs and attached to an external pulse generator. The rats were then randomised to KHFAC or sham modulation groups. KHFAC modulation variables were defined acutely by respiratory and cardiac responses to hypoxia (10% O₂ + 90% N₂). Insulin sensitivity was evaluated periodically through an ITT and glucose tolerance by an OGTT.

RESULTS

KHFAC modulation of the CSN, applied over 9 weeks, restored insulin sensitivity (constant of the insulin tolerance test [K_ITT] HFHSu sham, 2.56 ± 0.41% glucose/min; K_ITT HFHSu KHFAC, 5.01 ± 0.52% glucose/min) and glucose tolerance (AUC HFHSu sham, 1278 ± 20.36 mmol/l × min; AUC HFHSu KHFAC, 1054.15 ± 62.64 mmol/l × min) in rat models of type 2 diabetes. Upon cessation of KHFAC, insulin resistance and glucose intolerance returned to normal values within 5 weeks.

CONCLUSIONS/INTERPRETATION

KHFAC modulation of the CSN improves metabolic control in rat models of type 2 diabetes. These positive outcomes have significant translational potential as a novel therapeutic modality for the purpose of treating metabolic diseases in humans.

Correlations between histology and neuronal activity recorded by microelectrodes implanted chronically in the cerebral cortex

OBJECTIVE

To quantify relations between the neuronal activity recorded with chronically-implanted intracortical microelectrodes and the histology of the surrounding tissue, using radial distance from the tip sites and time after array implantation as parameters.

APPROACH

'Utah'-type intracortical microelectrode arrays were implanted into cats' sensorimotor cortex for 275-364 days. The brain tissue around the implants was immuno-stained for the neuronal marker NeuN and for the astrocyte marker GFAP. Pearson's product-moment correlations were used to quantify the relations between these markers and the amplitudes of the recorded neuronal action potentials (APs) and their signal-to-noise ratios (S/N).

MAIN RESULTS

S/N was more stable over post-implant time than was AP amplitude, but its increased correlation with neuronal density after many months indicates ongoing loss of neurons around the microelectrodes. S/N was correlated with neuron density out to at least 140 μm from the microelectrodes, while AP amplitude was correlated with neuron density and GFAP density within ∼80 μm. Correlations between AP amplitude and histology markers (GFAP and NeuN density) were strongest immediately after implantation, while correlation between the neuron density and S/N was strongest near the time the animals were sacrificed. Unlike AP amplitude, there was no significant correlation between S/N and density of GFAP around the tip sites.

SIGNIFICANCE

Our findings indicate an evolving interaction between changes in the tissue surrounding the microelectrodes and the microelectrode's electrical properties. Ongoing loss of neurons around recording microelectrodes, and the interactions between their delayed electrical deterioration and early tissue scarring around the tips appear to pose the greatest threats to the microelectrodes' long-term functionality.

Cuff electrodes for very small diameter nerves -- prototyping and first recordings in vivo

A fabrication method for cuff electrodes to interface small nerves was developed. Medical grade silicone rubber conforms the body of the cuff and insulation of the wires, platinum was used as metal for the embedded wiring and contacts. Planar electrode arrays where fabricated using a picosecond laser and then positioned into a carrying tube to provide the third dimension with the desired inner diameter (Ø 0.3-0.5 mm). The post preparation of the cuffs after structuring allows the fabrication of a stable self-closing flap that insulates the opening slit of the cuff without the need of extra sutures. Basic for the success of the cuff is the laser-based local thinning of both the silicone rubber and the metal at defined sections. This is critical to permit the PDMS' body to dominate the mechanical properties. Finite element modeling was applied to optimize the displacement ability of the cuff, leading to design capable of withstanding multiple implantation procedures without wire damage. Furthermore, the contact's surface was roughened by laser patterning to increase the charge injection capacity of Pt to 285 μC/cm(2) measured by voltage transient detection during pulse testing. The cuff electrodes were placed on a small sympathetic nerve of an adult female Sprague-Dawley rat for recording of spontaneous and evoked neural activity in vivo.

Matrigel coatings for Parylene sheath neural probes

The biologically derived hydrogel Matrigel (MG) was used to coat a Parylene-based sheath intracortical electrode to act as a mechanical and biological buffer as well as a matrix for delivering bioactive molecules to modulate the cellular response and improve recording quality. MG was loaded with dexamethasone to reduce the immune response together with nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) to maintain neuronal density and encourage neuronal ingrowth toward electrodes within the sheath. Coating the Parylene sheath electrode with the loaded MG significantly improved the signal-to-noise ratio for neural events recorded from the motor cortex in rat for more than 3 months. Electron microscopy showed even coverage of both the Parylene substrate and the platinum recording electrodes. Electrochemical impedance spectroscopy (EIS) of coated electrodes in 1× phosphate-buffered saline demonstrated low impedance required for recording neural signals. This result was confirmed by in vivo EIS data, showing significantly decreased impedance during the first week of recording. Dexamethasone, NGF, and BDNF loaded into MG were released within 1 day in 1× phosphate-buffered saline. Although previous studies showed that MG loaded with either the immunosuppressant or the neurotrophic factor cocktail provided modest improvement in recording quality in a 1-month in vivo study, the combination of these bioactive molecules did not improve the signal quality over coating probes with only MG in a 3-month in vivo study. The MG coating may further improve recording quality by optimizing the in vivo release profile for the bioactive molecules.

Effects of millimeter wave irradiation and equivalent thermal heating on the activity of individual neurons in the leech ganglion

Many of today's radiofrequency-emitting devices in telecommunication, telemedicine, transportation safety, and security/military applications use the millimeter wave (MMW) band (30–300 GHz). To evaluate the biological safety and possible applications of this radiofrequency band for neuroscience and neurology, we have investigated the physiological effects of low-intensity 60-GHz electromagnetic irradiation on individual neurons in the leech midbody ganglia. We applied incident power densities of 1, 2, and 4 mW/cm² to the whole ganglion for a period of 1 min while recording the action potential with a standard sharp electrode electrophysiology setup. For comparison, the recognized U.S. safe exposure limit is 1 mW/cm² for 6 min. During the exposure to MMWs and gradual bath heating at a rate of 0.04°C/s (2.4°C/min), the ganglionic neurons exhibited similar dose-dependent hyperpolarization of the plasma membrane and decrease in the action potential amplitude. However, narrowing of the action potential half-width during MMW irradiation at 4 mW/cm² was 5 times more pronounced compared with that during equivalent bath heating of 0.6°C. Even more dramatic difference in the effects of MMW irradiation and bath heating was noted in the firing rate, which was suppressed at all applied MMW power densities and increased in a dose-dependent manner during gradual bath heating. The mechanism of enhanced narrowing of action potentials and suppressed firing by MMW irradiation, compared with that by gradual bath heating, is hypothesized to involve specific coupling of MMW energy with the neuronal plasma membrane.

Altered brainstem auditory evoked potentials in a rat central sensitization model are similar to those in migraine

Migraine symptoms often include auditory discomfort. Nitroglycerin (NTG)-triggered central sensitization (CS) provides a rodent model of migraine, but auditory brainstem pathways have not yet been studied in this example. Our objective was to examine brainstem auditory evoked potentials (BAEPs) in rat CS as a measure of possible auditory abnormalities. We used four subdermal electrodes to record horizontal (h) and vertical (v) dipole channel BAEPs before and after injection of NTG or saline. We measured the peak latencies (PLs), interpeak latencies (IPLs), and amplitudes for detectable waveforms evoked by 8, 16, or 32 kHz auditory stimulation. At 8 kHz stimulation, vertical channel positive PLs of waves 4, 5, and 6 (vP4, vP5, and vP6), and related IPLs from earlier negative or positive peaks (vN1-vP4, vN1-vP5, vN1-vP6; vP3-vP4, vP3-vP6) increased significantly 2h after NTG injection compared to the saline group. However, BAEP peak amplitudes at all frequencies, PLs and IPLs from the horizontal channel at all frequencies, and the vertical channel stimulated at 16 and 32 kHz showed no significant/consistent change. For the first time in the rat CS model, we show that BAEP PLs and IPLs ranging from putative bilateral medial superior olivary nuclei (P4) to the more rostral structures such as the medial geniculate body (P6) were prolonged 2h after NTG administration. These BAEP alterations could reflect changes in neurotransmitters and/or hypoperfusion in the midbrain. The similarity of our results with previous human studies further validates the rodent CS model for future migraine research.

Encoding of the amplitude modulation of pulsatile electrical stimulation in the feline cochlear nucleus by neurons in the inferior colliculus; effects of stimulus pulse rate

OBJECTIVES

Persons without a functional auditory nerve cannot benefit from cochlear implants, but some hearing can be restored by an auditory brainstem implant (ABI) with stimulating electrodes implanted on the surface of the cochlear nucleus (CN). Most users benefit from their ABI, but speech recognition tends to be poorer than for users of cochlear implants. Psychophysical studies suggest that poor modulation detection may contribute to the limited performance of ABI users. In a cat model, we determined how the pulse rate of the electrical stimulus applied within or on the CN affects temporal and rate encoding of amplitude modulation (AM) by neurons in the central nucleus of the inferior colliculus (ICC).

APPROACH

Stimulating microelectrodes were implanted chronically in and on the cats' CN, and multi-site recording microelectrodes were implanted chronically into the ICC. Encoding of AM pulse trains by neurons in the ICC was characterized as vector strength (VS), the synchrony of neural activity with the AM, and as the mean rate of neuronal action potentials (neuronal spike rate (NSR)).

MAIN RESULTS

For intranuclear microstimulation, encoding of AM as VS was up to 3 dB greater when stimulus pulse rate was increased from 250 to 500 pps, but only for neuronal units with low best acoustic frequencies, and when the electrical stimulation was modulated at low frequencies (10-20 Hz). For stimulation on the surface of the CN, VS was similar at 250 and 500 pps, and the dynamic range of the VS was reduced for pulse rates greater than 250 pps. Modulation depth was encoded strongly as VS when the maximum stimulus amplitude was held constant across a range of modulation depth. This 'constant maximum' protocol allows enhancement of modulation depth while preserving overall dynamic range. However, modulation depth was not encoded as strongly as NSR.

SIGNIFICANCE

The findings have implications for improved sound processors for present and future ABIs. The performance of ABIs may benefit from using pulse rates greater than those presently used in most ABIs, and by sound processing strategies that enhance the modulation depth of the electrical stimulus while preserving dynamic range.

Light-triggered modulation of cellular electrical activity by ruthenium diimine nanoswitches

Ruthenium diimine complexes have previously been used to facilitate light-activated electron transfer in the study of redox metalloproteins. Excitation at 488 nm leads to a photoexcited state, in which the complex can either accept or donate an electron, respectively, in the presence of a soluble sacrificial reductant or oxidant. Here, we describe a novel application of these complexes in mediating light-induced changes in cellular electrical activity. We demonstrate that RubpyC17 ([Ru(bpy)(2)(bpy-C17)](2+), where bpy is 2,2'-bipyridine and bpy-C17 is 2,2'-4-heptadecyl-4'-methyl-bipyridine), readily incorporates into the plasma membrane of cells, as evidenced by membrane-confined luminescence. Excitable cells incubated in RubpyC17 and then illuminated at 488 nm in the presence of the reductant ascorbate undergo membrane depolarization leading to firing of action potentials. In contrast, the same experiment performed with the oxidant ferricyanide, instead of ascorbate, leads to hyperpolarization. These experiments suggest that illumination of membrane-associated RubpyC17 in the presence of ascorbate alters the cell membrane potential by increasing the negative charge on the outer face of the cell membrane capacitor, effectively depolarizing the cell membrane. We rule out two alternative explanations for light-induced membrane potential changes, using patch clamp experiments: (1) light-induced direct interaction of RubpyC17 with ion channels and (2) light-induced membrane perforation. We show that incorporation of RubpyC17 into the plasma membrane of neuroendocrine cells enables light-induced secretion as monitored by amperometry. While the present work is focused on ruthenium diimine complexes, the findings point more generally to broader application of other transition metal complexes to mediate light-induced biological changes.

Wireless microstimulators for neural prosthetics

One of the roadblocks in the field of neural prosthetics is the lack of microelectronic devices for neural stimulation that can last a lifetime in the central nervous system. Wireless multi-electrode arrays are being developed to improve the longevity of implants by eliminating the wire interconnects as well as the chronic tissue reactions due to the tethering forces generated by these wires. An area of research that has not been sufficiently investigated is a simple single-channel passive microstimulator that can collect the stimulus energy that is transmitted wirelessly through the tissue and immediately convert it into the stimulus pulse. For example, many neural prosthetic approaches to intraspinal microstimulation require only a few channels of stimulation. Wired spinal cord implants are not practical for human subjects because of the extensive flexions and rotations that the spinal cord experiences. Thus, intraspinal microstimulation may be a pioneering application that can benefit from submillimeter-size floating stimulators. Possible means of energizing such a floating microstimulator, such as optical, acoustic, and electromagnetic waves, are discussed.

Wireless microstimulators for neural prosthetics

One of the roadblocks in the field of neural prosthetics is the lack of microelectronic devices for neural stimulation that can last a lifetime in the central nervous system. Wireless multi-electrode arrays are being developed to improve the longevity of implants by eliminating the wire interconnects as well as the chronic tissue reactions due to the tethering forces generated by these wires. An area of research that has not been sufficiently investigated is a simple single-channel passive microstimulator that can collect the stimulus energy that is transmitted wirelessly through the tissue and immediately convert it into the stimulus pulse. For example, many neural prosthetic approaches to intraspinal microstimulation require only a few channels of stimulation. Wired spinal cord implants are not practical for human subjects because of the extensive flexions and rotations that the spinal cord experiences. Thus, intraspinal microstimulation may be a pioneering application that can benefit from submillimeter-size floating stimulators. Possible means of energizing such a floating microstimulator, such as optical, acoustic, and electromagnetic waves, are discussed.

Modulation of neuronal activity and plasma membrane properties with low-power millimeter waves in organotypic cortical slices

As millimeter waves (MMWs) are being increasingly used in communications and military applications, their potential effects on biological tissue has become an important issue for scientific inquiry. Specifically, several MMW effects on the whole-nerve activity were reported, but the underlying neuronal changes remain unexplored. This study used slices of cortical tissue to evaluate the MMW effects on individual pyramidal neurons under conditions mimicking their in vivo environment. The applied levels of MMW power are three orders of magnitude below the existing safe limit for human exposure of 1 mW cm(-2). Surprisingly, even at these low power levels, MMWs were able to produce considerable changes in neuronal firing rate and plasma membrane properties. At the power density approaching 1 microW cm(-2), 1 min of MMW exposure reduced the firing rate to one third of the pre-exposure level in four out of eight examined neurons. The width of the action potentials was narrowed by MMW exposure to 17% of the baseline value and the membrane input resistance decreased to 54% of the baseline value across all neurons. These effects were short lasting (2 min or less) and were accompanied by MMW-induced heating of the bath solution at 3 degrees C. Comparison of these results with previously published data on the effects of general bath heating of 10 degrees C indicated that MMW-induced effects cannot be fully attributed to heating and may involve specific MMW absorption by the tissue. Blocking of the intracellular Ca(2+)-mediated signaling did not significantly alter the MMW-induced neuronal responses suggesting that MMWs interacted directly with the neuronal plasma membrane. The presented results constitute the first demonstration of direct real-time monitoring of the impact of MMWs on nervous tissue at a microscopic scale. Implication of these findings for the therapeutic modulation of neuronal excitability is discussed.

Neuronal loss due to prolonged controlled-current stimulation with chronically implanted microelectrodes in the cat cerebral cortex

Activated iridium microelectrodes were implanted for 450-1282 days in the sensorimotor cortex of seven adult domestic cats and then pulsed for 240 h (8 h per day for 30 days) at 50 Hz. Continuous stimulation at 2 nC/phase and with a geometric charge density of 100 microC cm(-2) produced no detectable change in neuronal density in the tissue surrounding the microelectrode tips. However, pulsing with a continuous 100% duty cycle at 4 nC/phase and with a geometric charge density of 200 microC cm(-2) induced loss of cortical neurons over a radius of at least 150 microm from the electrode tips. The same stimulus regimen but with a duty cycle of 50% (1 s of stimulation, and then 1 s without stimulation repeated for 8 h) produced neuronal loss within a smaller radius, approximately 60 microm from the center of the electrode tips. However, there also was significant loss of neurons surrounding the unpulsed electrodes, presumably as a result of mechanical injury due to their insertion into and long-term residence in the tissue, and this was responsible for most of the neuronal loss within 150 microm of the electrodes pulsed with the 50% duty cycle.

Neuronal activity evoked in the inferior colliculus of the cat by surface macroelectrodes and penetrating microelectrodes implanted in the cochlear nucleus

Persons lacking functional auditory nerves cannot benefit from cochlear implants, but an auditory brainstem implant (ABI) utilizing stimulating electrodes adjacent to or on their cochlear nucleus (CN) can restore some hearing. We are investigating the feasibility of supplementing these surface electrodes with penetrating microstimulating electrodes within the ventral CN (VCN), and how the two types of electrodes can be used synergistically. Multiunit neuronal responses evoked by VCN electrical stimulation with surface electrodes and microelectrodes were recorded in the inferior colliculus (ICC) of five cats. The findings are consistent with those from patients with type II neurofibromatosis who received ABIs with both surface and microelectrodes. The patients described percepts from their microelectrodes as more similar to pure tones than those from their surface electrodes, consistent with the greater tonotopic selectivity of microelectrodes in the cats' VCN. Also, the patients describe percepts from their surface electrodes as louder than those from the microelectrodes, while in the cat, the neuronal activity evoked in the ICC by the surface electrodes tended to be greater. This concordance helps to validate our cat model as a means of investigating the synergistic use of surface and penetrating electrodes in a clinical ABI.

Bidirectional telemetry controller for neuroprosthetic devices

We present versatile multifunctional programmable controller with bidirectional data telemetry, implemented using existing commercial microchips and standard Bluetooth protocol, which adds convenience, reliability, and ease-of-use to neuroprosthetic devices. Controller, weighing 190 g, is placed on animal's back and provides bidirectional sustained telemetry rate of 500 kb/s , allowing real-time control of stimulation parameters and viewing of acquired data. In continuously-active state, controller consumes approximately 420 mW and operates without recharge for 8 h . It features independent 16-channel current-controlled stimulation, allowing current steering; customizable stimulus current waveforms; recording of stimulus voltage waveforms and evoked neuronal responses with stimulus artifact blanking circuitry. Flexibility, scalability, cost-efficiency, and a user-friendly computer interface of this device allow use in animal testing for variety of neuroprosthetic applications. Initial testing of the controller has been done in a feline model of brainstem auditory prosthesis. In this model, the electrical stimulation is applied to the array of microelectrodes implanted in the ventral cochlear nucleus, while the evoked neuronal activity was recorded with the electrode implanted in the contralateral inferior colliculus. Stimulus voltage waveforms to monitor the access impedance of the electrodes were acquired at the rate of 312 kilosamples/s. Evoked neuronal activity in the inferior colliculus was recorded after the blanking (transient silencing) of the recording amplifier during the stimulus pulse, allowing the detection of neuronal responses within 100 mus after the end of the stimulus pulse applied in the cochlear nucleus.

Spinal hyperexcitability and bladder hyperreflexia during reversible frontal cortical inactivation induced by low-frequency electrical stimulation in the cat

Spinal hyperexcitability and hyperreflexia gradually develop in the majority of stroke patients. These pathologies develop as a result of reduced cortical modulation of spinal reflexes, mediated largely indirectly via relays in the brainstem and other subcortical structures. Cortical control of spinal reflexes is markedly different in small animals, such as rodents, while in some larger species, such as cats, it is more comparable to that in humans. In this study, we developed a novel model of stroke in the cat, with controllable and reversible inhibition of cortical neuronal activity appearing approximately 1h after initiation of low-frequency electrical stimulation in the frontal cerebral cortex, evidenced by a large increase in the alpha frequency band (7-14 Hz) of the frontal electrocorticographic signal. Hyperreflexia of the urinary bladder developed 3h or more after induction of reversible cortical inactivation with optimized stimulation parameters (frequency of 1-2 Hz, amplitude of 10 mA, applied for 30 min). The bladder hyperreflexia persisted for at least 8h, and disappeared within 24h. At the S2 level of the spinal cord, where neural circuits mediating micturition and other pelvic reflexes reside, we have recorded an increase in neuronal activity correlated with the development of hyperreflexia. The low-frequency stimulation-induced reversible cortical inactivation model of stroke is highly reproducible and allows evaluation of spinal hyperexcitability and hyperreflexia using within-animal comparisons across experimental conditions, which can be of great value in examination of mechanisms of spinal hyperreflexia following stroke or brain trauma, and for developing more effective treatments for these conditions.

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.

Performance of multisite silicon microprobes implanted chronically in the ventral cochlear nucleus of the cat

A central auditory prosthesis based on microstimulation within the ventral cochlear nucleus (VCN) offers a means of restoring hearing to persons whose auditory nerve has been destroyed bilaterally and cannot benefit from cochlear implants. Arrays of silicon probes with 16 stimulating sites were implanted into the VCN of adult cats, for up to 314 days. Compound neuronal responses evoked from the sites in the VCN were recorded periodically in the central nucleus of the contralateral inferior colliculus (ICC). The threshold and growth of most of the responses were stable for at least 250 days after implantation of the arrays. The responses evoked from the deepest and shallowest electrode sites did exhibit some changes over time but none of the thresholds exceeded 10 microA. The thresholds and growth of the compound responses from most of the stimulating sites were very stable over time, and comparable to those of chronically implanted single-site iridium microelectrodes. Multiunit neuronal activity evoked from the stimulating sites in the VCN was recorded along the dorsolateral-ventromedial (DLVM) axis of the ICC. The distribution, span and degree of overlap of the multiunit activity demonstrated the utility of the multisite, multishank array configuration as a means of accessing the neuronal populations in the VCN that encode various acoustic frequencies. These findings are encouraging for the prospects of developing an auditory prosthesis employing multi-site silicon microprobes.

Functional reinnervation of the rat lower urinary tract after cauda equina injury and repair

Conus medullaris and/or cauda equina forms of spinal cord injury commonly result in a permanent loss of bladder function. Here, we developed a cauda equina injury and repair rodent model to investigate whether surgical implantation of avulsed lumbosacral ventral roots into the spinal cord can promote functional recovery of the lower urinary tract. Adult female rats underwent sham surgery (n = 6), bilateral L5-S2 ventral root avulsion (VRA) injury (n = 5), or bilateral L5-S2 VRA followed by an acute implantation of the avulsed L6 and S1 ventral roots into the conus medullaris (n = 6). At 12 weeks after operation, the avulsed group demonstrated urinary retention, absence of bladder contractions and external urethral sphincter (EUS) electromyographic (EMG) activation during urodynamic recordings, increased bladder size, and retrograde death of autonomic and motoneurons in the spinal cord. In contrast, the implanted group showed reduced urinary retention, return of reflexive bladder voiding contractions coincident with EUS EMG activation, anatomical reinnervation of the EUS demonstrated by retrograde neuronal labeling, normalization of bladder size, and a significant neuroprotection of both autonomic and motoneurons. In addition, a positive correlation between motoneuronal survival and voiding efficiency was observed in the implanted group. Our results show that implantation of avulsed lumbosacral ventral roots into the spinal cord promotes reinnervation of the urinary tract and return of functional micturition reflexes, suggesting that this surgical repair strategy may also be of clinical interest after conus medullaris and cauda equina injuries.

Microelectrode array for chronic deep-brain microstimulation and recording

We have developed an array of microelectrodes that is suitable for long-term implantation into the subthalamic nucleus (STN) or the globus pallidus and is able to record from single neurons, as well as deliver localized microstimulation. This device can be used to investigate the mechanisms by which deep brain stimulation can ameliorate the symptoms of Parkinson's disease and other movement disorders, and also may be the basis for a new clinical tool for the treatment of Parkinson's disease, by capitalizing on the high spatial specificity of intranuclear microstimulation. The array includes 16 activated iridium microelectrodes, 5-6 mm in length, within a cluster approximately 1.8 mm in diameter. We have fabricated the array using materials carrying the USP Category VI classification, and we have developed an apparatus and a procedure for implanting the microelectrode arrays into the deep brain. Ten arrays have been implanted into the STN of domestic cats, and one into the internal segment of the globus pallidus, for 140-415 days. During that time, we were able to record action potentials from individual neurons, on 4 to 8 of the 16 channels. The microelectrode' active surface areas ranged from 500 to 2000 microm2. Controlled-current pulses, 26.5 microA in amplitude and 150 micros/phase in duration (4 nC/phase) were used to excite neurons in the cat's STN. In addition to direct activation, the stimulus modulated the neuronal activity over a distance of at least 1.2 mm from the site of stimulation. These parameters did not induce histologically detectable changes around the tip sites after 35 hours of stimulation at 100 Hz (7 hours of stimulation per day, on 5 successive days), if the electrode' active surface area was 1000 microm2 or greater.

Arrays for chronic functional microstimulation of the lumbosacral spinal cord

Our objective is to develop neural prostheses based on an array of microelectrodes implanted into the sacral spinal cord, that will allow persons with spinal cord injuries to regain control of their bladder and bowels. For our chronic cat model, we have developed two microelectrode arrays, one type containing nine discrete activated iridium microelectrodes and the second utilizing silicon substrate probes with multiple electrode sites on each probe. Both types can elicit an increase in the pressure within the urinary bladder of more than 40-mm Hg and/or relaxation of the urethral sphincter. A stimulus of 100 microA and 400 micros/ph at 20 Hz (charge-balanced pulses) was required to induce a large increase in bladder pressure or relaxation of the urethral sphincter. We found that 24 h of continuous stimulation with these parameters induced tissue injury (disrupted neuropil, infiltration of inflammatory cells, and loss of neurons close to the tip sites). However, a neural prosthesis that is intended to restore bladder control after spinal cord injury would not operate continuously. Thus, when this stimulus was applied for 24 h, at a 10% duty cycle (1 min of stimulation, then 9 min without stimulation) only minimal histologic changes were observed.

Mapping of spinal cord circuits controlling the bladder and external urethral sphincter functions in the rabbit

AIMS

A primary purpose of this study was to evaluate the rabbit as a model for studying the spinal circuitry controlling the bladder emptying. We aimed to map the locations of the neuronal circuitry controlling the external urethral sphincter (EUS) and the detrusor by stimulating at different spinal cord locations with a microelectrode, while recording the responses from these muscles.

METHODS

Spinal cord microstimulation was performed in the intermediate zone of the gray matter at the L7-S4 spinal cord levels in eight rabbits with empty and full bladders. Bladder activity was measured as intravesical pressure (IVP) changes and EUS activity was measured via electromyographic (EMG) electrodes positioned within the urethra.

RESULTS

Under both bladder conditions, EUS activation was produced from similar locations in the spinal cord comprising a continuous area in the intermediate zone of the S2-S3 spinal cord. This region extended 25 mm in the rostrocaudal dimension, at least 1 mm lateral to the midline, and 0.5-1 mm in the dorsoventral dimension at a depth of 2-3 mm beneath the dorsal surface. No locations in the intermediate zone produced EUS inhibition. The S2-S3 spinal region, stimulation of which produced the strongest EUS activation, also produced modest bladder contractions.

CONCLUSIONS

Overall, the results indicate that spinal cord networks controlling bladder and EUS activation in the rabbit are overlapping and clustered into columns extending rostrocaudally. The lack of spinal locations producing EUS inhibition and large bladder contractions make the rabbit an unattractive model for studies of neuroprosthetic spinal control of micturition.

Altered glutamate receptor function during recovery of bladder detrusor-external urethral sphincter coordination in a rat model of spinal cord injury

Coordination of the bladder detrusor and the external urethral sphincter is a supraspinally controlled reflex that is essential for efficient micturition. This coordination is permanently lost after spinal cord transection but can recover chronically after incomplete spinal cord injury (SCI). As glutamatergic transmission plays a key role in all levels of detrusor-external urethral sphincter coordination, we examined the role of potential alterations in glutamatergic control in its recovery after SCI. Rats were subjected to standardized incomplete contusion injury. Detrusor-external urethral sphincter coordination was evaluated urodynamically at 5 days (subacute) and 8 weeks (chronic) after SCI. Sensitivity of coordinated activation of the external urethral sphincter in response to bladder distension to the alpha -amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid/kainate antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo(f)quinoxaline-7-sulfonamide disodium (NBQX) and to the N-methyl-D-aspartate (NMDA) antagonist R(--3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP) was determined by intrathecal application at the L6 spinal cord level during urodynamic recordings. We found that while detrusor contractions recovered at 5 days after SCI, coordinated activation of the external urethral sphincter was significantly impaired at 5 days and recovered only by 8 weeks. There was no difference in sensitivity of detrusor-external urethral sphincter coordination to NBQX at the subacute or chronic time points. However, external urethral sphincter response to bladder distension was sensitive to a 50% lower dose of CPP at 5 days compared with uninjured rats or chronic recovered SCI rats. Thus, alterations in NMDA receptor function appeared to be involved in recovery of detrusor-external urethral sphincter coordination after incomplete SCI.

Coordination of the bladder detrusor and the external urethral sphincter in a rat model of spinal cord injury: effect of injury severity

Recovery of urinary tract function after spinal cord injury (SCI) is important in its own right and may also serve as a model for studying mechanisms of functional recovery after injury in the CNS. Normal micturition requires coordinated activation of smooth muscle of the bladder (detrusor) and striated muscle of the external urethral sphincter (EUS) that is controlled by spinal and supraspinal circuitry. We used a clinically relevant rat model of thoracic spinal cord contusion injury to examine the effect of varying the degree of residual supraspinal connections on chronic detrusor-EUS coordination. Urodynamic evaluation at 8 weeks after SCI showed that detrusor contractions of the bladder recovered similarly in groups of rats injured with a 10 gm weight dropped 12.5, 25, or 50 mm onto the spinal cord. In contrast, the degree of coordinated activation of the EUS varied with the severity of initial injury and the degree of preservation of white matter at the injury site. The 12.5 mm SCI resulted in the sparing of 20% of the white matter at the injury site and complete recovery of detrusor-EUS coordination. In more severely injured rats, the chronic recovery of detrusor-EUS coordination was very incomplete and correlated to decreased innervation of lower motoneurons by descending control pathways and their increased levels of mRNA for glutamate receptor subunits NR2A and GluR2. These results show that the extent of recovery of detrusor-EUS coordination depends on injury severity and the degree of residual connections with brainstem control centers.

Assessment of lower urinary tract functional deficit in rats with contusive spinal cord injury

Traumatic spinal cord injury (SCI) produces lower urinary tract (LUT) dysfunction that has been studied in surgical transection models. Our aim was to assess LUT functional deficit in a clinically relevant model of incomplete SCI to investigate how partial preservation of supraspinal connections might affect LUT dysfunction. Standardized weight-drop contusion (10 g x 2.5 cm) or complete transection, was produced at T8 in female Sprague-Dawley rats. Behavioral tests were used to assess hind limb sensorimotor function at Day 1 after surgery and weekly thereafter. The urometric experiments were conducted on groups (n = 7) of uninjured rats and on injured rats during Weeks 1 and 2 after SCI (before and after spontaneous voiding was established) as well as Week 2 after a complete transection (n = 3). Under anesthesia, the bladder was continuously perfused with saline. Changes in bladder pressure and external urethral sphincter (EUS) electrical activity were monitored. The bladder was then dissected and weighed and both the bladder and spinal cord were fixed for pathoanatomical analyses. Our results indicate that several aspects of LUT dysfunction after contusive SCI were similar to transection, e.g., reduction of voiding efficiency (approximately 5% of normal value), decrease in inter-contraction interval (47%), increase in bladder capacity (8-fold), and weight (4.6-fold). One aspect appeared different from transection--partial recovery from acute bladder/sphincter dyssynergia. Because the coordination of bladder and EUS function is mediated by brainstem pathways, partial recovery of synergy after SCI was likely due to sparing of some relevant bulbospinal projections as was confirmed by retrograde transneuronal viral tracing.