Accurate simulation of cuff electrode stimulation predicting in-vivo strength-duration thresholds.

BACKGROUND: In-silico experiments used to optimize and inform how peripheral nerve based electrode designs perform hold the promise of greatly reducing the guesswork with new designs as well as the number of animals used to identify and prove promising designs. Given adequate realism, in-silico experiments offer the promise of identifying putative mechanisms that further inform exploration of novel stimulation and recording techniques and their interactions with bioelectric phenomena. However, despite using validated nerve fiber models, when applied to the more complex case of an implanted extracellular electrode, the in-silico experiments often do not compare quantitatively with the results of experiments conducted in in-vivo experiments. This suggests that the accuracy/realism of the environment and the lamination of the nerve bundle plays an important role in this discrepancy. This paper describes the sensitivity of in-silico models to the electrical parameter estimates and volume conductor type used. METHODS: In-vivo work was performed on rat vagus nerves (N = 2) to characterize the strength-duration curve for various peaks identified in a compound nerve action potential (CAP) measured via a needle electrode. The vagus nerve has several distinct populations of nerve fiber calibers and types. Recruitment of a fiber caliber/type generates distinct peaks that can be identified, and whose conduction delay correlates to a conduction velocity. Peaks were identified by their recruitment thresholds and associated to their conduction velocities by the conduction delays of their peaks. An in-silico analog of the in-vivo experiment was constructed and experiments were run at the two extreme volume conductor cases: (1) The nerve in-saline, and (2) the nerve in-air. The specifically targeted electrical parameters were extraneural environment (in-air versus saline submersion), the resistivity (ρ) of the epineurium and perineurium, and the relative permittivity (εr ) of those same tissues. A time varying finite element method (FEM) model of the potential distribution vs time was quantified and projected onto a modified McIntyre, Richardson, and Grill (MRG), myelinated spinal nerve, active fiber model in NEURON to identify the threshold of activation as a function of stimulus pulse amplitude versus pulse width versus fiber diameter. The in-silico results were then compared to the in-vivo results. RESULTS: The finite element method simulations spanned two macro environments: in-saline and in-air. For these environments, the resistivities for low and high frequencies as well as two different permittivity cases were used. Between these 8 cases unique cases it was found that the most accurate combination of those variables was the in-air environment for low-frequency resistivity (ρ0 ) and ex-vivo a measured permittivity (εr,measured ) from unpublished ex-vivo experiments in canine vagal nerve, achieving a high degree of convergence (r2  = 0.96). As the in-vivo work was conducted in in-air, the in-air boundary condition test case was convergent with the in-silico results. CONCLUSIONS: The results of this investigation suggest that increasing realism in simulations begets more accurate predictions. Of particular importance are (ρ) and extraneural environment, with reactive electrical parameters becoming important for input waveforms with energy in higher frequencies.

In vivo peripheral nerve activation using sinusoidal low-frequency alternating currents.

BACKGROUND: The sinusoidal low-frequency alternating current (LFAC) waveform was explored recently as a novel means to evoke nerve conduction block. In the present work, we explored whether increasing the amplitude of the LFAC waveform results in nerve fiber activation in autonomic nerves. In-silico methods and preliminary work in somatic nerves indicated a potential frequency dependency on the threshold of activation. The Hering-Breuer (HB) reflex was used as a biomarker to detect cervical vagus nerve activation. METHODS: Experiments were conducted in isoflurane-anesthetized swine (n = 5). Two stimulating bipolar cuff electrodes and a tripolar recording cuff electrode were implanted on the left vagus nerve. To ensure the electrical stimulation affects only the afferent pathways, the nerve was crushed caudal to the electrodes to eliminate cardiac effects. (1) Standard pulse stimulation (Vstim) using a monophasic train of pulses was applied through the caudal electrode to elicit HB reflex and to identify the activated nerve fiber type. (2) Continuous sinusoidal LFAC waveform with a frequency ranging from 5 through 20 Hz was applied to the rostral electrode without Vstim to explore the activation thresholds at each LFAC frequency. In both cases, the activation of nerve fibers was detected by a HB reflex-induced reduction in the breathing rate. RESULTS: LFAC was found to be capable of eliciting an HB response. The LFAC activation thresholds were found to be frequency-dependent. The HB threshold was 1.02 ± 0.3 mAp at 5 Hz, 0.66 ± 0.3 mAp at 10 Hz, and 0.44 ± 0.2 mAp at 20 Hz. In comparison, it was 0.7 ± 0.47 mA for a 100 µs pulse. The LFAC amplitude was within the linear limits of the electrode interface. Damage to the cuff electrodes or the nerve tissues was not observed. Analysis of Vstim-based compound nerve action potentials (CNAP) indicated that the decrease in breathing rate was found to be correlated with the activation of slower components of the CNAP suggesting that LFAC reached and elicited responses from these slower fibers associated with afferents projecting to the HB response. CONCLUSIONS: These results suggest the feasibility of the LFAC waveform at 5, 10, and 20 Hz to activate autonomic nerve fibers and potentially provide a new modality to the neurorehabilitation field.

A Reversible Low Frequency Alternating Current Nerve Conduction Block Applied to Mammalian Autonomic Nerves.

Electrical stimulation can be used to modulate activity within the nervous system in one of two modes: (1) Activation, where activity is added to the neural signalling pathways, or (2) Block, where activity in the nerve is reduced or eliminated. In principle, electrical nerve conduction block has many attractive properties compared to pharmaceutical or surgical interventions. These include reversibility, localization, and tunability for nerve caliber and type. However, methods to effect electrical nerve block are relatively new. Some methods can have associated drawbacks, such as the need for large currents, the production of irreversible chemical byproducts, and onset responses. These can lead to irreversible nerve damage or undesirable neural responses. In the present study we describe a novel low frequency alternating current blocking waveform (LFACb) and measure its efficacy to reversibly block the bradycardic effect elicited by vagal stimulation in anaesthetised rat model. The waveform is a sinusoidal, zero mean(charge balanced), current waveform presented at 1 Hz to bipolar electrodes. Standard pulse stimulation was delivered through Pt-Black coated PtIr bipolar hook electrodes to evoke bradycardia. The conditioning LFAC waveform was presented either through a set of CorTec® bipolar cuff electrodes with Amplicoat® coated Pt contacts, or a second set of Pt Black coated PtIr hook electrodes. The conditioning electrodes were placed caudal to the pulse stimulation hook electrodes. Block of bradycardic effect was assessed by quantifying changes in heart rate during the stimulation stages of LFAC alone, LFAC-and-vagal, and vagal alone. The LFAC achieved 86.2±11.1% and 84.3±4.6% block using hook (N = 7) and cuff (N = 5) electrodes, respectively, at current levels less than 110 µAp (current to peak). The potential across the LFAC delivering electrodes were continuously monitored to verify that the blocking effect was immediately reversed upon discontinuing the LFAC. Thus, LFACb produced a high degree of nerve block at current levels comparable to pulse stimulation amplitudes to activate nerves, resulting in a measurable functional change of a biomarker in the mammalian nervous system.

Novel fiber-rich lentil flours as snack-type functional foods: an extrusion cooking effect on bioactive compounds.

Novel snack-type functional foods based on extruded lentil flours could convey the related health benefit of their bioactive compounds, provide a gluten-free alternative to consumers, and potentially increase the consumption of pulses. Extrusion treatment promoted an increase in galactopinitol, ciceritol, raffinose, stachyose and total α-galactoside content, in most lentil flours. As α-galactosides may act as prebiotics, they could convey beneficial effects to human and monogastric animals. Conversely, extrusion significantly (p < 0.05) reduced the inositol hexaphosphate content to less phosphorylated phytates (inositol pentaphosphate and inositol tetraphosphate), which provide health effects. The gluten-free formulation (control formulation #3) presented the highest significant (p < 0.05) drop in the inositol hexaphosphate of 14.7-fold decrease, but had a large increase in inositol pentaphosphate, due to extrusion processing. These two results are desirable in the finished product. Extrusion also caused a significant (p < 0.05) reduction in the trypsin content and completely inactivated lectin, in all processed samples.

Occupational IgE-mediated allergy after exposure to lupine seed flour.

The ingestion of lupine seed flour (LSF) has been reported as a cause of allergic reactions, particularly in patients sensitized to peanut, but there is little evidence of its allergenic potential after inhalation. We sought to evaluate the clinical and immunologic reactivity to lupine in employees working with this seed flour. An occupational history was obtained in 7 subjects (median age, 35 years) working with LSF at an agricultural research center. Three subjects (1, 6, and 7) reported work-related allergy symptoms immediately after being exposed to lupine. Skin prick test results with LSF extract were positive in these 3 patients with work-related symptoms. Moreover, lupine-specific IgE antibodies were detected in subjects 6 and 7. In subject 6, the controlled exposure to LSF elicited immediate naso-ocular symptoms without changes in FEV(1). In subject 7, a bronchial provocation with LSF extract elicited an immediate fall (25%) in FEV(1). Double-blinded, placebo-controlled LSF oral challenge results were positive in subjects 6 and 7. Immunologic reactivity to other legumes was detected in subjects 6 and 7, but specific inhalation testing and oral challenge results were negative. Thus, the inhalation of lupine flour could be an important cause of allergic sensitization in exposed workers and might give rise to occupational asthma and food allergy.

Purification and characterization of a phytate-degrading enzyme from germinated faba beans (Vicia faba Var. Alameda).

A phytate-degrading enzyme was purified approximately 2190-fold from germinated 4-day-old faba bean seedlings to apparent homogeneity with a recovery of 6% referred to the phytase activity in the crude extract. It behaves as a monomeric protein of a molecular mass of approximately 65 kDa. The phytate-degrading enzyme belongs to the acidic phytases. It exhibits a single pH optimum at 5.0. Optimal temperature for the degradation of sodium phytate is 50 degrees C. Kinetic parameters for the hydrolysis of sodium phytate are K(M) = 148 micromol L(-1) and k(cat) = 704 s(-1) at 35 degrees C and pH 5.0. The faba bean phytase exhibits a broad affinity for various phosphorylated compounds and hydrolyzes phytate in a stepwise manner. The first hydrolysis product was identified as D/L-myo-inositol(1,2,3,4,5)pentakisphosphate.

Lens culinaris, Phaseolus vulgaris and vicia faba lectins specifically trigger IL-8 production by the human colon carcinoma cell line CACO-2.

Cultured Caco-2 cells were stimulated with Lens culinaris, Phaseolus vulgarisandVicia fabalectins. The production of IL-1, IL-6, IL-8 and MCP-1 was measured by ELISA and RT-PCR. IL-8 production appeared to be specifically triggered upon stimulation with all three lectins used, since none of the other cytokines tested were produced. The IL-8 secreted may induce the extravasation of activated neutrophils and generate tissue damage. A similar mechanism may be implicated in the lesions observed after infection by some enteric pathogens, with lectin-like domains on their membrane. Finally, this model may be suitable one to study the regulation of IL-8 production.

Effect of soaking, cooking and germination on the oligosaccharide content of selected Nigerian legume seeds.

The identity and quantity of and effect of processing on raffinose oligosaccharides in raw, mature seeds of lima beans (Phaseolus lunatus), pigeon peas (Cajanus cajan), African yam beans (Sphenostylis sternocarpa) and jackbeans (Canavalia ensiformis) were investigated. Sucrose, raffinose, stachyose and verbascose were identified by HPLC in all the legume seeds. The total alpha-galactoside contents of the seeds in decreasing order were African yam beans 3.84 mg/100 mg; white lima beans 3.62 mg/100 mg; cream pigeon peas 3.51 mg/100 mg; red lima beans 3.37 mg/100 mg; jackbeans 2.83 mg/100 mg and brown pigeon peas 2.34 mg/100 mg. The predominant oligosaccharide was verbascose in pigeon peas and stachyose in the other three legumes. Cooking unsoaked seeds brought about a greater reduction in the total alpha-galactoside content than soaking for nine hours. The removal of oligosaccharides was higher in legumes cooked in alkaline solution than in water. Germination quantitatively reduced raffinose, stachyose and verbascose while sucrose was increased in all seeds except red lima beans and jackbeans.

Anti-nutritional constituents of six underutilized legumes grown in Nigeria.

Six underutilized legume seeds grown in Nigeria namely, red and white lima beans, brown and cream pigeon pea, African yam bean and jackbean were analysed for different anti-nutritional factors Sojasapogenol B was identified as the predominant sapogenol in lima beans and jackbeans by capillary gas chromatography. The content of total inositol phosphates and individual inositol phosphates (IP6, IP5, IP4 and IP3) were analysed by ion-pair HPLC, being in the range of other legumes. Trace quantities of lupanine were identified as the alkaloid in jackbean. alpha-Galactosides were present in all the legume seeds, stachyose being the predominant galactoside in lima beans, African yam bean and jackbean, and verbascose in pigeon pea. The haemagglutinating activity was estimated as a measure of the lectin content of the samples. African yam bean was found to have the highest heamagglutinating activity. Tannins were found to be in low quantities. The presence of these anti-nutrients in relation to the nutritional value of the legume is discussed.

Effect of natural fermentation on the content of inositol phosphates in lentils.

The effects of natural fermentation upon phytic acid and less phosphorylated inositol phosphates of Lens culinaris var vulgaris cultivar Magda-20 were investigated. Seven fermentation runs were made following a 2(2) complete factorial design with three replicated centre points to study the effect of different conditions of temperature (28, 35 and 42 degrees C) and broth concentration (79, 150 and 221 g/l). Samples were taken for each of them at daily intervals (0, 24, 48, 72 and 96 h). The pH value declined sharply in the first 24 h of fermentation, becoming stabilized from this time. The relation between lactic acid and titratable acidity presented important differences between the different fermentations, ranging from 30-80%. Phytic acid (IP6), inositol pentakis (IP5), tetrakis (IP4) and tris-(IP3) phosphates were quantitatively determined. The content of total inositol phosphates showed a maximum reduction of 63% at 72 h under the fermentation conditions of 42 degrees C and 79 g/l.

Variation of favism-inducing factors (vicine, convicine and L-DOPA) during pod development in Vicia faba L.

Changes in the concentrations of vicine, convicine and L-DOPA in two cultivars of Vicia faba L. seeds in different stages of pod development were determined by high performance liquid chromatography (HPLC). The vicine and convicine content was highest in fresh green cotyledons (moisture content about 80%) and gradually declined until a constant level was reached when seed dry matter percentage was around 40%. A similar pattern of variation in glucoside concentration was observed for the seed coat. The pods contained neither vicine nor convicine but they were particularly rich in L-DOPA. These compounds were not homogeneously distributed in the seeds.