In-vitro characterization of a cochlear implant system for recording of evoked compound action potentials

<p>Abstract</p> <p>Background</p> <p>Modern cochlear implants have integrated recording systems for measuring electrically evoked compound action potentials of the auditory nerve. The characterization of such recording systems is important for establishing a reliable basis for the interpretation of signals acquired in vivo. In this study we investigated the characteristics of the recording system integrated into the MED-EL PULSARCI¹⁰⁰cochlear implant, especially its linearity and resolution, in order to develop a mathematical model describing the recording system.</p> <p>Methods</p> <p>In-vitro setup: The cochlear implant, including all attached electrodes, was fixed in a tank of physiologic saline solution. Sinusoidal signals of the same frequency but with different amplitudes were delivered via a signal generator for measuring and recording on a single electrode.</p> <p>Computer simulations: A basic mathematical model including the main elements of the recording system, i.e. amplification and digitalization stage, was developed. For this, digital output for sinusoidal input signals of different amplitudes were calculated using in-vitro recordings as reference.</p> <p>Results</p> <p>Using an averaging of 100 measurements the recording system behaved linearly down to approximately -60 dB of the input signal range. Using the same method, a system resolution of 10 μV was determined for sinusoidal signals. The simulation results were in very good agreement with the results obtained from in-vitro experiments.</p> <p>Conclusions</p> <p>The recording system implemented in the MED-EL PULSARCI¹⁰⁰cochlear implant for measuring the evoked compound action potential of the auditory nerve operates reliably. The developed mathematical model provides a good approximation of the recording system.</p

Roots under attack : Contrasting plant responses to below- and aboveground insect herbivory

The distinctive ecology of root herbivores, the complexity and diversity of root-microbe interactions, and the physical nature of the soil matrix mean that plant responses to root herbivory extrapolate poorly from our understanding of responses to aboveground herbivores. For example, root attack induces different changes in phytohormones to those in damaged leaves, including a lower but more potent burst of jasmonates in several plant species. Root secondary metabolite responses also differ markedly, although patterns between roots and shoots are harder to discern. Root defences must therefore be investigated in their own ecophysiological and evolutionary context, specifically one which incorporates root microbial symbionts and antagonists, if we are to better understand the battle between plants and their hidden herbivores

Semiautomated Statistical Discontinuity Analyses from Scanline Data of Fractured Rock Masses

Quantitative statistical discontinuity analysis of fractured rock masses is commonly applied in the fields of engineering geology, rock mechanics, slope stability, and hydrogeology. This study presents a workflow for the semiautomatic determination of basic discontinuity parameters, such as spacing, frequency, trace length, and termination, from scanline surveys written for the open-source software Octave. The aim is to provide theoretical background information and scripts for a quick introduction to all interested parties from academia and consulting, in order to promote the use of widely known and accepted statistical evaluation methods. Data from a study site in granodioritic rock are analyzed in the context of the proposed workflow. These test data and all scripts (m-files) used in the study are provided in order to minimize initial training time. The scripts provided herein are kept short and simple, but can be used as a basis for advanced automation of the workflow and presentation of the results

Semiautomated Statistical Discontinuity Analyses from Scanline Data of Fractured Rock Masses

Quantitative statistical discontinuity analysis of fractured rock masses is commonly applied in the fields of engineering geology, rock mechanics, slope stability, and hydrogeology. This study presents a workflow for the semiautomatic determination of basic discontinuity parameters, such as spacing, frequency, trace length, and termination, from scanline surveys written for the open-source software Octave. The aim is to provide theoretical background information and scripts for a quick introduction to all interested parties from academia and consulting, in order to promote the use of widely known and accepted statistical evaluation methods. Data from a study site in granodioritic rock are analyzed in the context of the proposed workflow. These test data and all scripts (m-files) used in the study are provided in order to minimize initial training time. The scripts provided herein are kept short and simple, but can be used as a basis for advanced automation of the workflow and presentation of the results

A Nicotiana attenuata cell wall invertase inhibitor (NaCWII) reduces growth and increases secondary metabolite biosynthesis in herbivore-attacked plants

Plant invertases are sucrolytic enzymes that are essential for the regulation of carbohydrate metabolism and source–sink relationships. While their activity has been well documented during abiotic and biotic stresses, the role of proteinaceous invertase inhibitors in regulating these changes is unknown. Here, we identify a putative Nicotiana attenuata cell wall invertase inhibitor (NaCWII) which is strongly up-regulated in a jasmonate (JA)-dependent manner following simulated attack by the specialist herbivore Manduca sexta. To understand the role of NaCWII in planta, we silenced its expression by RNA interference and measured changes in primary and secondary metabolism and plant growth following simulated herbivory. NaCWII-silenced plants displayed a stronger depletion of carbohydrates and a reduced capacity to increase secondary metabolite pools relative to their empty vector control counterparts. This coincided with the attenuation of herbivore-induced CWI inhibition and growth suppression characteristic of wild-type plants. Together our findings suggest that NaCWII may act as a regulatory switch located downstream of JA accumulation which fine-tunes the plant's balance between growth and defense metabolism under herbivore attack. Although carbohydrates are not typically viewed as key factors in plant growth and defense, our study shows that interfering with their catabolism strongly influences plant responses to herbivory

Leaf-herbivore attack reduces carbon reserves and regrowth from the roots via jasmonate and auxin signaling

Herbivore attack leads to resource conflicts between plant defensive strategies. Photoassimilates are required for defensive compounds and carbon storage below ground and may therefore be depleted or enriched in the roots of herbivore-defoliated plants. The potential role of belowground tissues as mediators of induced tolerance–defense trade-offs is unknown. We evaluated signaling and carbohydrate dynamics in the roots of Nicotiana attenuata following Manduca sexta attack. Experimental and natural genetic variability was exploited to link the observed metabolite patterns to plant tolerance and resistance. Leaf-herbivore attack decreased sugar and starch concentrations in the roots and reduced regrowth from the rootstock and flower production in the glasshouse and the field. Leaf-derived jasmonates were identified as major regulators of this root-mediated resource-based trade-off: lower jasmonate levels were associated with decreased defense, increased carbohydrate levels and improved regrowth from the rootstock. Application and transport inhibition experiments, in combination with silencing of the sucrose non-fermenting (SNF) -related kinase GAL83, indicated that auxins may act as additional signals that regulate regrowth patterns. In conclusion, our study shows that the ability to mobilize defenses has a hidden resource-based cost below ground that constrains defoliation tolerance. Jasmonate- and auxin-dependent mechanisms may lead to divergent defensive plant strategies against herbivores in nature

Herbivory-induced jasmonates constrain plant sugar accumulation and growth by antagonizing gibberellin signaling and not by promoting secondary metabolite production

Plants respond to herbivory by reconfiguring hormonal networks, increasing secondary metabolite production and decreasing growth. Furthermore, some plants display a decrease in leaf energy reserves in the form of soluble sugars and starch, leading to the hypothesis that herbivory-induced secondary metabolite production and growth reduction may be linked through a carbohydrate-based resource trade-off. In order to test the above hypothesis, we measured leaf carbohydrates and plant growth in seven genetically engineered Nicotiana attenuata genotypes that are deficient in one or several major herbivore-induced, jasmonate-dependent defensive secondary metabolites and proteins. Furthermore, we manipulated gibberellin and jasmonate signaling, and quantified the impact of these phytohormones on secondary metabolite production, sugar accumulation and growth. Simulated herbivore attack by Manduca sexta specifically reduced leaf sugar concentrations and growth in a jasmonate-dependent manner. These effects were similar or even stronger in defenseless genotypes with intact jasmonate signaling. Gibberellin complementation rescued carbohydrate accumulation and growth in induced plants without impairing the induction of defensive secondary metabolites. These results are consistent with a hormonal antagonism model rather than a resource–cost model to explain the negative relationship between herbivory-induced defenses, leaf energy reserves and growth