Insights into the diet and feeding behavior of immature polar cod (Boreogadus saida) from the under-ice habitat of the central Arctic Ocean.

Polar cod (Boreogadus saida) is an endemic key species of the Arctic Ocean ecosystem. The ecology of this forage fish is well studied in Arctic shelf habitats where a large part of its population lives. However, knowledge about its ecology in the central Arctic Ocean (CAO), including its use of the sea-ice habitat, is hitherto very limited. To increase this knowledge, samples were collected at the under-ice surface during several expeditions to the CAO between 2012 and 2020, including the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The diet of immature B. saida and the taxonomic composition of their potential prey were analysed, showing that both sympagic and pelagic species were important prey items. Stomach contents included expected prey such as copepods and amphipods. Surprisingly, more rarely observed prey such as appendicularians, chaetognaths, and euphausiids were also found to be important. Comparisons of the fish stomach contents with prey distribution data suggests opportunistic feeding. However, relative prey density and catchability are important factors that determine which type of prey is ingested. Prey that ensures limited energy expenditure on hunting and feeding is often found in the stomach contents even though it is not the dominant species present in the environment. To investigate the importance of prey quality and quantity for the growth of B. saida in this area, we measured energy content of dominant prey species and used a bioenergetic model to quantify the effect of variations in diet on growth rate potential. The modeling results suggest that diet variability was largely explained by stomach fullness and, to a lesser degree, the energetic content of the prey. Our results suggest that under climate change, immature B. saida may be at least equally sensitive to a loss in the number of efficiently hunted prey than to a reduction in the prey's energy content. Consequences for the growth and survival of B. saida will not depend on prey presence alone, but also on prey catchability, digestibility, and energy content.

Allometric relationships of ecologically important Antarctic and Arctic zooplankton and fish species.

Allometric relationships between body properties of animals are useful for a wide variety of purposes, such as estimation of biomass, growth, population structure, bioenergetic modelling and carbon flux studies. This study summarizes allometric relationships of zooplankton and nekton species that play major roles in polar marine food webs. Measurements were performed on 639 individuals of 15 species sampled during three expeditions in the Southern Ocean (winter and summer) and 2374 individuals of 14 species sampled during three expeditions in the Arctic Ocean (spring and summer). The information provided by this study fills current knowledge gaps on relationships between length and wet/dry mass of understudied animals, such as various gelatinous zooplankton, and of animals from understudied seasons and maturity stages, for example, for the krill Thysanoessa macrura and larval Euphausia superba caught in winter. Comparisons show that there is intra-specific variation in length-mass relationships of several species depending on season, e.g. for the amphipod Themisto libellula. To investigate the potential use of generalized regression models, comparisons between sexes, maturity stages or age classes were performed and are discussed, such as for the several krill species and T. libellula. Regression model comparisons on age classes of the fish E. antarctica were inconclusive about their general use. Other allometric measurements performed on carapaces, eyes, heads, telsons, tails and otoliths provided models that proved to be useful for estimating length or mass in, e.g. diet studies. In some cases, the suitability of these models may depend on species or developmental stages. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00300-021-02984-4.

A DARPin targeting activated Mac-1 is a novel diagnostic tool and potential anti-inflammatory agent in myocarditis, sepsis and myocardial infarction.

The monocyte ß2-integrin Mac-1 is crucial for leukocyte-endothelium interaction, rendering it an attractive therapeutic target for acute and chronic inflammation. Using phage display, a Designed-Ankyrin-Repeat-Protein (DARPin) was selected as a novel binding protein targeting and blocking the αM I-domain, an activation-specific epitope of Mac-1. This DARPin, named F7, specifically binds to activated Mac-1 on mouse and human monocytes as determined by flow cytometry. Homology modelling and docking studies defined distinct interaction sites which were verified by mutagenesis. Intravital microscopy showed reduced leukocyte-endothelium adhesion in mice treated with this DARPin. Using mouse models of sepsis, myocarditis and ischaemia/reperfusion injury, we demonstrate therapeutic anti-inflammatory effects. Finally, the activated Mac-1-specific DARPin is established as a tool to detect monocyte activation in patients receiving extra-corporeal membrane oxygenation, as well as suffering from sepsis and ST-elevation myocardial infarction. The activated Mac-1-specific DARPin F7 binds preferentially to activated monocytes, detects inflammation in critically ill patients, and inhibits monocyte and neutrophil function as an efficient new anti-inflammatory agent.

The effect of electrode geometry on electrochemical properties measured in saline.

The impedance, cyclic voltammetry, and charge-injection properties of rectangular, sputtered iridium oxide (SIROF) electrodes have been measured in buffered physiological saline over a range of geometric surface areas (GSA) and perimeter-to-area ratios (P/A). Electrodes with a higher P/A are expected to have a lower impedance and higher charge injection capacity (Q(inj)), and both these effects were evident for SIROF electrodes with a GSA in the range 0.0023-0.0031 mm(2). However, the magnitude of the effect was modest. The increase in Q(inj) for rectangular electrodes with a P/A ranging from 94 to 255 mm(-1) was 21-26% depending on pulse width. There was a corresponding decrease in impedance (0.1 to 10(5) Hz) with increasing P/A and an increase in the SIROF charge storage capacity calculated from cyclic voltammetry. To assess the full usefulness of high P/A electrodes for increasing the reversible Q(inj) of an electrode, measurements should now be extended to chronic in vivo preparations.

Electrical performance of penetrating microelectrodes chronically implanted in cat cortex.

Penetrating microelectrode arrays with 2000 µm (2) sputtered iridium oxide (SIROF) electrode sites were implanted in cat cerebral cortex, and their long-term electrochemical performance evaluated in vivo by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and current pulsing. Measurements were made from days 33 to 328 postimplantation. The CV-defined charge storage capacity, measured at 50 mV/s, increased linearly with time over the course of implantation for two arrays and was unchanged for one array. A modest decrease in 1 kHz impedance was also observed. These results suggest an ongoing increase in the apparent electrochemical surface area of the electrodes, which is attributed to electrical leakage pathways arising from cracking of Parylene insulation observed by SEM of explanted arrays. During current pulsing with a 0.0 V interpulse bias, the electrodes readily delivered 8 nC/phase in vitro, but some channels approached or exceeded the water reduction potential during in vivo pulsing. The charge injection capacity in vivo increased linearly with the interpulse bias (0-0.6 V Ag\vert AgCl) from 11.5 to 21.8 nC/ph and with pulse width (150-500 µs) from 8.8 to 14 nC/ph (at 0.0 V bias). These values are lower than those determined from measurements in buffered physiological saline, emphasizing the importance of in vivo measurements in assessing chronic electrode performance. The consequence of current leakage pathways on the charge-injection measurements is also discussed.

Electrical performance of penetrating microelectrodes chronically implanted in cat cortex.

Penetrating multielectrode arrays with electrode coatings of sputtered iridium oxide (SIROF) have been implanted chronically in cat cortex for periods over 300 days. The ability of these electrodes to inject charge at levels above expected thresholds for neural excitation has been examined in vivo by measurements of voltage transients in response to current-controlled, cathodal stimulation pulsing. The effect of current pulse width from 150 µs to 500 µs and voltage biasing of the electrodes in the interpulse period at two levels, 0.0 V and 0.6 V vs. Ag|AgCl, were also investigated. The results of in vivo characterization of the electrodes by open-circuit potential measurements, cyclic voltammetry and impedance spectroscopy are also reported.

Contribution of oxygen reduction to charge injection on platinum and sputtered iridium oxide neural stimulation electrodes.

The extent to which oxygen reduction occurs on sputtered iridium oxide (SIROF) and platinum neural stimulation electrodes was quantified by cyclic voltammetry and voltage-transient measurements in oxygen-saturated physiological saline. Oxygen reduction was the dominant charge-admittance reaction on platinum electrodes during slow-sweep-rate cyclic voltammetry, contributing approximately 12 mC/cm(2) (88% of total charge) to overall cathodal charge capacity. For a 300-nm-thick SIROF electrode, oxygen reduction was a minor reaction contributing 1.3 mC/cm(2), approximately 3% of total charge. During current pulsing with platinum electrodes, oxygen reduction was observed at a level of 7% of the total injected charge. There was no indication of oxygen reduction on pulsed SIROF electrodes. A sweep-rate-dependent contribution of oxygen reduction was observed on penetrating SIROF microelectrodes (nominal surface area 2000 microm(2)) and is interpreted in terms of rate-limited diffusion of oxygen in electrolyte that penetrates the junction between the insulation and electrode shaft. For typical neural stimulation pulses, no oxygen reduction could be observed on penetrating SIROF microelectrodes. Based on the in vivo concentration of dissolved oxygen, it is estimated that oxygen reduction on platinum microelectrodes will contribute less than 0.5% of the total injected charge and considerably less on SIROF electrodes.

Penetrating microelectrode arrays with low-impedance sputtered iridium oxide electrode coatings.

Sputtered iridium oxide (SIROF) is a candidate low-impedance coating for neural stimulation and recording electrodes. SIROF on planar substrates has exhibited a high charge-injection capacity and impedance suitable for indwelling cortical microelectrode applications. In the present work, the properties of SIROF electrode coatings deposited onto multi-shank penetrating arrays intended for intracortical and intraneural applications were examined. The charge-injection properties under constant current pulsing were evaluated for a range of pulsewidths and current densities using voltage transients to determine maximum potential excursions in an inorganic model of interstitial fluid at 37 degrees C. The charge-injection capacity of the SIROFs was significantly improved by the use of positive potential biasing in the interpulse period, but even without bias, the SIROFs reversibly inject higher charge than other iridium oxides or platinum. Typical deliverable charge levels of 25 to 160 nC/phase were obtained with 2000 mum(2) electrodes depending on pulsewidth and interpulse bias. Similar sized platinum electrodes could inject 3 to 8 nC/phase.

Sputtered iridium oxide films for neural stimulation electrodes.

Sputtered iridium oxide films (SIROFs) deposited by DC reactive sputtering from an iridium metal target have been characterized in vitro for their potential as neural recording and stimulation electrodes. SIROFs were deposited over gold metallization on flexible multielectrode arrays fabricated on thin (15 microm) polyimide substrates. SIROF thickness and electrode areas of 200-1300 nm and 1960-125,600 microm(2), respectively, were investigated. The charge-injection capacities of the SIROFs were evaluated in an inorganic interstitial fluid model in response to charge-balanced, cathodal-first current pulses. Charge injection capacities were measured as a function of cathodal pulse width (0.2-1 ms) and potential bias in the interpulse period (0.0 to 0.7 V vs. Ag|AgCl). Depending on the pulse parameters and electrode area, charge-injection capacities ranged from 1-9 mC/cm(2), comparable with activated iridium oxide films (AIROFs) pulsed under similar conditions. Other parameters relevant to the use of SIROF on nerve electrodes, including the thickness dependence of impedance (0.05-10(5) Hz) and the current necessary to maintain a bias in the interpulse region were also determined.

The influence of electrolyte composition on the in vitro charge-injection limits of activated iridium oxide (AIROF) stimulation electrodes.

The effects of ionic conductivity and buffer concentration of electrolytes used for in vitro measurement of the charge-injection limits of activated iridium oxide (AIROF) neural stimulation electrodes have been investigated. Charge-injection limits of AIROF microelectrodes were measured in saline with a range of phosphate buffer concentrations from [PO(4)(3-)] = 0 to [PO(4)(3-)] = 103 mM and ionic conductivities from 2-28 mS cm(-1). The charge-injection limits were insensitive to the buffer concentration, but varied significantly with ionic conductivity. Using 0.4 ms cathodal current pulses at 50 Hz, the charge-injection limit increased from 0.5 mC cm(-2) to 2.1 mC cm(-2) as the conductivity was increased from 2 mS cm(-1) to 28 mS cm(-1). An explanation is proposed in which the observed dependence on ionic conductivity arises from non-uniform reduction and oxidation within the porous AIROF and from uncorrected iR-drops that result in an overestimation of the redox potential during pulsing. Conversely, slow-sweep-rate cyclic voltammograms (CVs) were sensitive to buffer concentration with the potentials of the primary Ir(3+)/Ir(4+) reduction and oxidation reactions shifting approximately 300 mV as the buffer concentration decreased from [PO(4)(3-)] = 103 mM to [PO(4)(3-)] = 0 mM. The CV response was insensitive to ionic conductivity. A comparison of in vitro AIROF charge-injection limits in commonly employed electrolyte models of extracellular fluid revealed a significant dependence on the electrolyte, with more than a factor of 4 difference under some pulsing conditions, emphasizing the need to select an electrolyte model that closely matches the conductivity and ionic composition of the in vivo environment.

Potential-biased, asymmetric waveforms for charge-injection with activated iridium oxide (AIROF) neural stimulation electrodes.

The use of potential biasing and biphasic, asymmetric current pulse waveforms to maximize the charge-injection capacity of activated iridium oxide (AIROF) microelectrodes used for neural stimulation is described. The waveforms retain overall zero net charge for the biphasic pulse, but employ an asymmetry in the current and pulse widths of each phase, with the second phase delivered at a lower current density for a longer period of time than the leading phase. This strategy minimizes polarization of the AIROF by the charge-balancing second phase and permits the use of a more positive anodic bias for cathodal-first pulsing or a more negative cathodic bias for anodal-first pulsing to maximize charge injection. Using 0.4-ms cathodal-first pulses, a maximum charge-injection capacity of 3.3 mC/cm2 was obtained with an 0.6-V bias (versus Ag/AgCl) and a pulse asymmetry of 1:8 in the cathodal and anodal pulse widths. For anodal-first pulsing, a maximum charge capacity of 9.6 mC/cm2 was obtained with an asymmetry of 1:3 at an 0.1-V bias. These measurements were made in vitro in carbonate-buffered saline using microelectrodes with a 2000 microm2 surface area.

In vitro comparison of the charge-injection limits of activated iridium oxide (AIROF) and platinum-iridium microelectrodes.

The charge-injection limits of activated iridium oxide electrodes (AIROF) and PtIr microelectrodes with similar geometric area and shape have been compared in vitro using a stimulation waveform that delivers cathodal current pulses with current-limited control of the electrode bias potential in the interpulse period. Charge-injection limits were compared over a bias range of 0.1-0.7 V (versus Ag/AgCl) and pulse frequencies of 20, 50, and 100 Hz. The AIROF was capable of injecting between 4 and 10 times the charge of the PtIr electrode, with a maximum value of 3.9 mC/cm2 obtained at a 0.7 V bias and 20 Hz frequency.