Electrical stimulation of renal nerves for modulating urine glucose excretion in rats.
ABSTRACT: Background:The role of the kidney in glucose homeostasis has gained global interest. Kidneys are innervated by renal nerves, and renal denervation animal models have shown improved glucose regulation. We hypothesized that stimulation of renal nerves at kilohertz frequencies, which can block propagation of action potentials, would increase urine glucose excretion. Conversely, we hypothesized that low frequency stimulation, which has been shown to increase renal nerve activity, would decrease urine glucose excretion. Methods:We performed non-survival experiments on male rats under thiobutabarbital anesthesia. A cuff electrode was placed around the left renal artery, encircling the renal nerves. Ureters were cannulated bilaterally to obtain urine samples from each kidney independently for comparison. Renal nerves were stimulated at kilohertz frequencies (1-50 kHz) or low frequencies (2-5 Hz), with intravenous administration of a glucose bolus shortly into the 25-40-min stimulation period. Urine samples were collected at 5-10-min intervals, and colorimetric assays were used to quantify glucose excretion and concentration between stimulated and non-stimulated kidneys. A Kruskal-Wallis test was performed across all stimulation frequencies (??=?0.05), followed by a post-hoc Wilcoxon rank sum test with Bonferroni correction (??=?0.005). Results:For kilohertz frequency trials, the stimulated kidney yielded a higher average total urine glucose excretion at 33 kHz (+?24.5%; n?=?9) than 1 kHz (-?5.9%; n?=?6) and 50 kHz (+?2.3%; n?=?14). In low frequency stimulation trials, 5 Hz stimulation led to a lower average total urine glucose excretion (-?40.4%; n?=?6) than 2 Hz (-?27.2%; n?=?5). The average total urine glucose excretion between 33 kHz and 5 Hz was statistically significant (p?
Project description:OBJECTIVE:There is growing interest in electrical neuromodulation of peripheral nerves, particularly autonomic nerves, to treat various diseases. Electrical signals in the kilohertz frequency (KHF) range can produce different responses, including conduction block. For example, EnteroMedics' vBloc® therapy for obesity delivers 5?kHz stimulation to block the abdominal vagus nerves, but the mechanisms of action are unclear. APPROACH:We developed a two-part computational model, coupling a 3D finite element model of a cuff electrode around the human abdominal vagus nerve with biophysically-realistic electrical circuit equivalent (cable) model axons (1, 2, and 5.7 µm in diameter). We developed an automated algorithm to classify conduction responses as subthreshold (transmission), KHF-evoked activity (excitation), or block. We quantified neural responses across kilohertz frequencies (5-20?kHz), amplitudes (1-8 mA), and electrode designs. MAIN RESULTS:We found heterogeneous conduction responses across the modeled nerve trunk, both for a given parameter set and across parameter sets, although most suprathreshold responses were excitation, rather than block. The firing patterns were irregular near transmission and block boundaries, but otherwise regular, and mean firing rates varied with electrode-fibre distance. Further, we identified excitation responses at amplitudes above block threshold, termed 're-excitation', arising from action potentials initiated at virtual cathodes. Excitation and block thresholds decreased with smaller electrode-fibre distances, larger fibre diameters, and lower kilohertz frequencies. A point source model predicted a larger fraction of blocked fibres and greater change of threshold with distance as compared to the realistic cuff and nerve model. SIGNIFICANCE:Our findings of widespread asynchronous KHF-evoked activity suggest that conduction block in the abdominal vagus nerves is unlikely with current clinical parameters. Our results indicate that compound neural or downstream muscle force recordings may be unreliable as quantitative measures of neural activity for in vivo studies or as biomarkers in closed-loop clinical devices.
Project description:INTRODUCTION:Kilohertz frequency spinal cord stimulation (kHz-SCS) deposits significantly more power in tissue compared to SCS at conventional frequencies, reflecting increased duty cycle (pulse compression). We hypothesize kHz-SCS increases local tissue temperature by joule heat, which may influence the clinical outcomes. METHODS:To establish the role of tissue heating in KHZ-SCS, a decisive first step is to characterize the range of temperature changes expected during conventional and KHZ-SCS protocols. Fiber optic probes quantified temperature increases around an experimental SCS lead in a bath phantom. These data were used to verify a SCS lead heat-transfer model based on joule heat. Temperature increases were then predicted in a seven-compartment (soft tissue, vertebral bone, fat, intervertebral disc, meninges, spinal cord with nerve roots) geometric human spinal cord model under varied parameterization. RESULTS:The experimentally constrained bio-heat model shows SCS waveform power (waveform RMS) determines tissue heating at the spinal cord and surrounding tissues. For example, we predict temperature increased at dorsal spinal cord of 0.18-1.72?°C during 3.5?mA peak 10?KHz stimulation with a 40-10-40 ?s biphasic pulse pattern, 0.09-0.22?°C during 3.5?mA 1?KHz 100-100-100 ?s stimulation, and less than 0.05?°C during 3.5?mA 50?Hz 200-100-200 ?s stimulation. Notably, peak heating of the spinal cord and other tissues increases superlinearly with stimulation power and so are especially sensitive to incremental changes in SCS pulse amplitude or frequency (with associated pulse compression). Further supporting distinct SCS intervention strategies based on heating; the spatial profile of temperature changes is more uniform compared to electric fields, which suggests less sensitivity to lead position. CONCLUSIONS:Tissue heating may impact short and long-term outcomes of KHZ-SCS, and even as an adjunct mechanism, suggests distinct strategies for lead position and programming optimization.
Project description:The PROCO RCT is a multicenter, double-blind, crossover, randomized controlled trial (RCT) that investigated the effects of rate on analgesia in kilohertz frequency (1-10 kHz) spinal cord stimulation (SCS).Patients were implanted with SCS systems and underwent an eight-week search to identify the best location ("sweet spot") of stimulation at 10 kHz within the searched region (T8-T11). An electronic diary (e-diary) prompted patients for pain scores three times per day. Patients who responded to 10 kHz per e-diary numeric rating scale (ED-NRS) pain scores proceeded to double-blind rate randomization. Patients received 1, 4, 7, and 10 kHz SCS at the same sweet spot found for 10 kHz in randomized order (four weeks at each frequency). For each frequency, pulse width and amplitude were titrated to optimize therapy.All frequencies provided equivalent pain relief as measured by ED-NRS (p???0.002). However, mean charge per second differed across frequencies, with 1 kHz SCS requiring 60-70% less charge than higher frequencies (p???0.0002).The PROCO RCT provides Level I evidence for equivalent pain relief from 1 to 10 kHz with appropriate titration of pulse width and amplitude. 1 kHz required significantly less charge than higher frequencies.
Project description:Spinal cord stimulation (SCS) is a useful neuromodulatory technique for treatment of certain neuropathic pain conditions. However, the optimal stimulation parameters remain unclear.In rats after L5 spinal nerve ligation, the authors compared the inhibitory effects on mechanical hypersensitivity from bipolar SCS of different intensities (20, 40, and 80% motor threshold) and frequencies (50, 1 kHz, and 10?kHz). The authors then compared the effects of 1 and 50 Hz dorsal column stimulation at high- and low-stimulus intensities on conduction properties of afferent A?/?-fibers and spinal wide-dynamic-range neuronal excitability.Three consecutive daily SCS at different frequencies progressively inhibited mechanical hypersensitivity in an intensity-dependent manner. At 80% motor threshold, the ipsilateral paw withdrawal threshold (% preinjury) increased significantly from pre-SCS measures, beginning with the first day of SCS at the frequencies of 1?kHz (50.2?±?5.7% from 23.9?±?2.6%, n = 19, mean ± SEM) and 10?kHz (50.8?±?4.4% from 27.9?±?2.3%, n = 17), whereas it was significantly increased beginning on the second day in the 50 Hz group (38.9?±?4.6% from 23.8?±?2.1%, n = 17). At high intensity, both 1 and 50 Hz dorsal column stimulation reduced A?/?-compound action potential size recorded at the sciatic nerve, but only 1?kHz stimulation was partially effective at the lower intensity. The number of actions potentials in C-fiber component of wide-dynamic-range neuronal response to windup-inducing stimulation was significantly decreased after 50 Hz (147.4?±?23.6 from 228.1?±?39.0, n = 13), but not 1?kHz (n = 15), dorsal column stimulation.Kilohertz SCS attenuated mechanical hypersensitivity in a time course and amplitude that differed from conventional 50 Hz SCS, and may involve different peripheral and spinal segmental mechanisms.
Project description:BACKGROUND AND PURPOSE: In the present study, a rodent model was used to investigate whether the alpha(2A)-adrenoceptor (alpha(2A)) represents the presynaptic autoinhibitory receptor regulating sympathetic transmitter release in the kidney. Moreover, the potential role of alpha(2A) as a heteroceptor regulating adenosine triphosphate (ATP) release was tested. EXPERIMENTAL APPROACH: Kidneys from wild-type (WT) and alpha(2A)-knockout (KO) mice were isolated and perfused. Renal nerves were stimulated with platinum-electrodes. Endogenously released noradrenaline (NA) was measured by HPLC. The perfusion pressure was monitored continuously. KEY RESULTS: Renal nerve stimulation (RNS) induced a frequency (1,2,5,7.5,10,15 Hz)-dependent release of NA in WT mice (994+/-373, 2355+/-541, 6375+/-950, 11626+/-1818, 19138+/-2001 pg NA g(-1) kidney (means+/-s.e.m.)). There was a 2.7-fold (5 Hz) increase of NA release in alpha(2A)-KO mice. In WT animals alpha-adrenoceptor blockade by phentolamine increased RNS-induced NA release in a concentration-dependent manner up to 350% of control. No facilitation by phentolamine was observed in alpha(2A)-KO mice. Pressor responses to 1 Hz and 2 Hz were resistant to alpha(1)-adrenoceptor blockade (0.03 microM prazosin) but abolished by P(2) receptor blockade (5 microM PPADS). Blockade of alpha(2)-adrenoceptors (1 microM rauwolscine) increased these purinergic pressor responses to 296+/-112% (1 Hz) in WT but not in alpha(2A)-KO mice. Exogenous ATP (100 microM) increased basal but not RNS-induced NA release. CONCLUSIONS AND IMPLICATIONS: alpha(2A)-Adrenoceptor-activation inhibits NA and ATP release from renal sympathetic nerves. Pressor responses to RNS at higher stimulation frequencies (>2 Hz) are mediated by NA. At lower frequencies neuronally released ATP seems to be the predominant transmitter mediating renovascular resistance.
Project description:BACKGROUND:High-frequency alternating currents of greater than 1 kHz applied on peripheral nerves has been used in animal studies to produce a motor nerve block. It has been evidenced that frequencies higher than 5 kHz are necessary to produce a complete peripheral nerve block in primates, whose nerve thickness is more similar to humans. The aim of the study was to determine the effect on muscle strength after the application of a high-frequency stimulation at 5 and 10 kHz compared to sham stimulation in healthy volunteers. FINDINGS:Transcutaneous stimulation at 5 kHz, 10 kHz and sham stimulation were applied to eleven healthy volunteers over the ulnar and median nerves for 20 min. Maximal handgrip strength was measured before, during, immediately after the intervention, and 10 min after the end of intervention. The 10 kHz stimulation showed a lower handgrip strength during the intervention (28.1 N, SEM 3.9) when compared to 5 kHz (31.1 N, SEM 3.6; p?<?0.001) and to sham stimulation (33.7 N, SEM 3.9; p?<?0.001). Furthermore, only stimulation at 10 kHz decreased handgrip strength when compared to baseline. CONCLUSIONS:These findings suggest high-frequency stimulation has an inhibitory effect over muscle strength. Future studies are required in patients that are characterized by motor hyperactive such as spasticity or tremors. CLINICAL TRIAL REGISTRATION:NCT, NCT03169049 . Registered on 30 May 2017.
Project description:Different guidelines are adopted in clinics and countries to assess pure tone hearing sensitivity in children with otitis media with effusion (OME). Some guidelines specify a broad range of audiometric frequencies that must be tested and from which average thresholds determined, while others leave test frequencies unspecified. For guidelines that suggest specific frequencies there are various pure tone frequencies and frequency ranges given. The present study investigated whether (1) a full range of audiometric frequencies is required to evaluate hearing loss caused by OME in children, or if neighboring frequencies provide essentially the same threshold information, and (2) if different combinations of test frequency pure tone averaging calculations may affect decision criteria for surgical treatment. In a retrospective cohort study, right and left ear air conduction pure tone threshold data were obtained, from 125 Hz to 8 kHz, for 96 children with OME aged 4 to 12 years. Paired t-tests, correlation tests (Pearson's r, Cronbach's alpha, intraclass correlation) and absolute differences were used to examine the relationships among pure tone audiometric (PTA) frequencies for all ears with hearing loss. 168 ears were found to have OME-related hearing loss. Only the 125 Hz-250 Hz comparison showed no statistically significant difference between neighboring thresholds. However, only the 4 kHz and 8 kHz comparison showed a clinically significant mean difference of ≥ 10 dB. When viewing individual differences, comparison between 250 Hz and 500 Hz, 125 Hz and 500 Hz, and 4 kHz and 8 kHz, showed a large number of ears with clinically significant differences between test frequencies. Comparisons among low frequency 3 PTA average (500 Hz, 1 kHz, 2 kHz), high frequency 3 PTA average (1 kHz, 2 kHz, 4 kHz), and 4 frequency PTA average (500 Hz, 1 kHz, 2 kHz, 4 kHz) showed no statistically significant differences, with very strong correlations for all comparisons. In addition, for all the combinations of PTA averages, no clinically significant differences were found for the various comparisons or among individual results. Clinically, testing hearing sensitivity in the 125 Hz to 8 kHz range is worthwhile in evaluating hearing sensitivity in children with OME due to large individual variability across audiometric frequencies. However, frequencies tested for criterion averages for surgical treatments of children with OME may be restricted to 3 frequency PTA averages, either an average of 500 Hz, 1 kHz, 2 kHz or an average of 1 kHz, 2 kHz, 4 kHz, as no clinically significant differences were found using these or a 4 frequency averaging technique. For research purposes, 250 Hz can proxy for hearing thresholds at 125 Hz; and the low frequency 3 PTA average, high frequency 3 PTA average and 4 frequency PTA average may be used interchangeably, as no statistically significant differences were found among these measures.
Project description:Deep brain stimulation (DBS) is an established therapy for movement disorders, including tremor, dystonia, and Parkinson's disease, but the mechanisms of action are not well understood. Symptom suppression by DBS typically requires stimulation frequencies ?100 Hz, but when the frequency is increased above ~2 kHz, the effectiveness in tremor suppression declines (Benabid et al., 1991). We sought to test the hypothesis that the decline in efficacy at high frequencies is associated with desynchronization of the activity generated within a population of stimulated neurons. Regularization of neuronal firing is strongly correlated with tremor suppression by DBS, and desynchronization would disrupt the regularization of neuronal activity. We implemented computational models of CNS axons with either deterministic or stochastic membrane dynamics, and quantified the response of populations of model nerve fibers to extracellular stimulation at different frequencies and amplitudes. As stimulation frequency was increased from 2 to 80 Hz the regularity of neuronal firing increased (as assessed with direct estimates of entropy), in accord with the clinical effects on tremor of increasing stimulation frequency (Kuncel et al., 2006). Further, at frequencies between 80 and 500 Hz, increasing the stimulation amplitude (i.e., the proportion of neurons activated by the stimulus) increased the regularity of neuronal activity across the population, in accord with the clinical effects on tremor of stimulation amplitude (Kuncel et al., 2007). However, at stimulation frequencies above 1 kHz the regularity of neuronal firing declined due to irregular patterns of action potential generation and conduction block. The reductions in neuronal regularity that occurred at high frequencies paralleled the previously reported decline in tremor reduction and may be responsible for the loss of efficacy of DBS at very high frequencies. This analysis provides further support for the hypothesis that effective DBS masks the intrinsic patterns of activity in the stimulated neurons and replaces it with regularized firing.
Project description:The goal of the present study was to evaluate and characterize the motile responses of guinea pig OHCs, stimulated at frequencies varying from 50 Hz to 4 kHz, using high-definition, high-speed video recording and fully automatic image analysis software. Cells stimulated in continuous, burst and sweeping modes with an external alternating electrical field showed robust fast and slow motility, which were dependent on frequency, mode and intensity of stimulation. In response to continuous stimulation, electromotile amplitude ranged from 0.3% to 3.2% of total cell length, whereas cell length usually decreased in amounts varying from 0.1% to 4.3%. Electromotile amplitude in OHCs stimulated with square wave's sweeps was near constant up to 200 Hz, progressively decreased between 200 Hz and 2 kHz, and then remained constant up to 4 kHz. In continuous and burst modes electromotility followed cycle-by-cycle the electrical stimulus, but it required 1-2 s to fully develop and reach maximal amplitude. Instead, slow cell length changes started about 0.6 s after the beginning and continuously developed up to 3 s after the end of electrical stimulation. Incubation of OHCs with 10 mM salicylate affected electromotility but not slow motility, whereas incubation with 3 mM gadolinium affected both. Thus, combination of external electrical stimulation, high-speed video recording and advanced image analysis software provides information about OHC motile responses at acoustic frequencies with an unprecedented detail, opening new areas of research in the field of OHC mechanics.
Project description:Pelvic floor muscle stretch injury during pregnancy and birth is associated with the incidence of stress urinary incontinence (SUI), a condition that affects 30-60% of the female population and is characterized by involuntary urine leakage during physical activity, further exacerbated by aging. Aging and multiparous rabbits suffer pelvic nerve and muscle damage, resulting in alterations in pelvic floor muscular contraction and low urethral pressure, resembling SUI. However, the extent of nerve injury is not fully understood. Here, we used electron microscopy analysis of pelvic and perineal nerves in multiparous rabbits to describe the extent of stretch nerve injury based on axon count, axon size, myelin-to-axon ratio, and elliptical ratio. Compared to young nulliparous controls, mid-age multiparous animals showed an increase in the density of unmyelinated axons and in myelin thickness in both nerves, albeit more significant in the bulbospongiosus nerve. This revealed a partial but sustained damage to these nerves, and the presence of some regenerated axons. Additionally, we tested whether electrical stimulation of the bulbospongiosus nerve would induce muscle contraction and urethral closure. Using a miniature wireless stimulator implanted on this perineal nerve in young nulliparous and middle age multiparous female rabbits, we confirmed that these partially damaged nerves can be acutely depolarized, either at low (2-5 Hz) or medium (10-20 Hz) frequencies, to induce a proportional increase in urethral pressure. Evaluation of micturition volume in the mid-age multiparous animals after perineal nerve stimulation, effectively reversed a baseline deficit, increasing it 2-fold (p = 0.02). These results support the notion that selective neuromodulation of pelvic floor muscles might serve as a potential treatment for SUI.