Adaptive responses of peripheral lateral line nerve fibres to sinusoidal wave stimuli

Sensory adaptation is characterized by a reduction in the firing frequency of neurons to prolonged stimulation, also called spike frequency adaptation. This has been documented for sensory neurons of the visual, olfactory, electrosensory, and auditory system both in response to constant-amplitude and to sinusoidal stimuli, but has thus far not been described systematically for the lateral line system. We recorded neuronal activity from primary afferent nerve fibres in the lateral line in goldfish in response to sinusoidal wave stimuli. Depending on stimulus characteristics, afferent fibre responses exhibited a distinct onset followed by a decline in firing rate to an apparent steady-state level, i.e., they exhibited adaptation. The degree of adaptation, measured as the percent decrease in firing rate between onset and steady-state, increased with stimulus amplitude and frequency and with increasing steepness of the rising flank of the stimulus. This may in part be due to the velocity and/or acceleration sensitivity of the lateral line receptors. The time course of the response decline, i.e., the time course of adaptation was best-fit by a power function. This is consistent with the previous studies on spike frequency adaptation in sensory afferents of weakly electric fish.

In situ denitrification and DNRA rates in groundwater beneath an integrated constructed wetland

Evaluation of the environmental benefits of constructed wetlands (CWs) requires an understanding of their impacts on the groundwater quality under the wetlands. Empirical mass-balance (nitrogen in/nitrogen out) approaches for estimating nitrogen (N) removal in CWs do not characterise the final fate of N; where nitrate (NO₃^--N) could be reduced to either ammonium (NH₄⁺-N) or N₂ with the potential for significant production of N₂O. Herein, in situ denitrification and DNRA (dissimilatory nitrate reduction to ammonium) rates were measured in groundwater beneath cells of an earthen lined integrated constructed wetland (ICW, used to remove the nutrients from municipal wastewater) using the ¹⁵N-enriched NO₃^--N push-pull method. Experiments were conducted utilising replicated (n = 3) shallow (1 m depth) and deep (4 m depth) piezometers installed along two control planes. These control planes allowed for the assessment of groundwater underlying high (Cell 2, septic tank waste) and low (Cell 3) load cells of the ICW. Background piezometers were also installed off-site. Results showed that denitrification (N₂O-N + N₂-N) and DNRA were major NO₃^--N consumption processes accounting together for 54-79% of the total biochemical consumption of the applied NO₃^--N. Of which 14-16% and 40-63% were consumed by denitrification and DNRA, respectively. Both processes differed significantly across ICW cells indicating that N transformation depends on nutrient loading rates and were significantly higher in shallow compared to the deep groundwater. In such a reduced environment (low dissolved oxygen and low redox potential), higher DNRA over the denitrification rate can be attributed to the high C concentration and high TC/NO₃^--N ratio. Low pH (6.5-7.1) in this system might have limited denitrification to some extent to an incomplete state, evidenced by a high N₂O-N/(N₂O-N+N₂-N) ratio (0.35 ± 0.17, SE). A relatively higher N₂O-N/(N₂O-N+N₂-N) ratio and higher DNRA rate over denitrification, suggest that the end products of N transformations are reactive. This N₂O can be consumed to N₂ and/or emitted to the atmosphere. The DNRA rate and accumulation of NH₄⁺-N indicated that the ICW created a suitable groundwater biogeochemical environment that enhanced NO₃^--N reduction to NH₄⁺-N. This study showed that CWs significantly influence NO₃^--N attenuation to reactive forms of N in the groundwater beneath them and that solely focusing on within wetland NO₃^--N attenuation can underestimate the environmental benefits of wetlands.

Liquid-state carbon-13 hyperpolarization generated in an MRI system for fast imaging

Hyperpolarized (HP) tracers dramatically increase the sensitivity of magnetic resonance imaging (MRI) to monitor metabolism non-invasively and in vivo. Their production, however, requires an extra polarizing device (polarizer) whose complexity, operation and cost can exceed that of an MRI system itself. Furthermore, the lifetime of HP tracers is short and some of the enhancement is lost during transfer to the application site. Here, we present the production of HP tracers in water without an external polarizer: by Synthesis Amid the Magnet Bore, A Dramatically Enhanced Nuclear Alignment (SAMBADENA) is achieved within seconds, corresponding to a hyperpolarization of ∼20%. As transfer of the tracer is no longer required, SAMBADENA may permit a higher polarization at the time of detection at a fraction of the cost and complexity of external polarizers. This development is particularly promising in light of the recently extended portfolio of biomedically relevant para-hydrogen-tracers and may lead to new diagnostic applications.

Hyperpolarized MRI uses molecules with a nuclear spin polarization beyond the thermodynamic equilibrium to enhance imaging contrast. Here, Schmidt et al. enable a single MRI system to both generate a hyperpolarized tracer and perform imaging, eliminating the need for an external polarizer.

Delocalization of a Vacancy across Two Neon Atoms Bound by the van der Waals Force

We experimentally study 2p photoionization of neon dimers (Ne_{2}) at a photon energy of hν=36.56  eV. By postselection of ionization events which lead to a dissociation into Ne^{+}+Ne we obtain the photoelectron angular emission distribution in the molecular frame. This distribution is symmetric with respect to the direction of the charged vs neutral fragment. It shows an inverted Cohen-Fano double slit interference pattern of two spherical waves emitted coherently but with opposite phases from the two atoms of the dimer.

Imaging the Temporal Evolution of Molecular Orbitals during Ultrafast Dissociation

We investigate the temporal evolution of molecular frame angular distributions of Auger electrons emitted during ultrafast dissociation of HCl following a resonant single-photon excitation. The electron emission pattern changes its shape from that of a molecular σ orbital to that of an atomic p state as the system evolves from a molecule into two separated atoms.

Climate analogues suggest limited potential for intensification of production on current croplands under climate change

Climate change could pose a major challenge to efforts towards strongly increase food production over the coming decades. However, model simulations of future climate-impacts on crop yields differ substantially in the magnitude and even direction of the projected change. Combining observations of current maximum-attainable yield with climate analogues, we provide a complementary method of assessing the effect of climate change on crop yields. Strong reductions in attainable yields of major cereal crops are found across a large fraction of current cropland by 2050. These areas are vulnerable to climate change and have greatly reduced opportunity for agricultural intensification. However, the total land area, including regions not currently used for crops, climatically suitable for high attainable yields of maize, wheat and rice is similar by 2050 to the present-day. Large shifts in land-use patterns and crop choice will likely be necessary to sustain production growth rates and keep pace with demand.

Simulations of the impact of future climate change on crop yield vary considerably. Here, the authors use a climate analogue approach to estimate the response of maximum attainable yield to climate change and predict that large shifts in land use and crop choice would be required to meet demand.

Key knowledge and data gaps in modelling the influence of CO2 concentration on the terrestrial carbon sink

Primary productivity of terrestrial vegetation is expected to increase under the influence of increasing atmospheric carbon dioxide concentrations ([CO₂]). Depending on the fate of such additionally fixed carbon, this could lead to an increase in terrestrial carbon storage, and thus a net terrestrial sink of atmospheric carbon. Such a mechanism is generally believed to be the primary global driver behind the observed large net uptake of anthropogenic CO₂ emissions by the biosphere. Mechanisms driving CO₂ uptake in the Terrestrial Biosphere Models (TBMs) used to attribute and project terrestrial carbon sinks, including that from increased [CO₂], remain in large parts unchanged since those models were conceived two decades ago. However, there exists a large body of new data and understanding providing an opportunity to update these models, and directing towards important topics for further research. In this review we highlight recent developments in understanding of the effects of elevated [CO₂] on photosynthesis, and in particular on the fate of additionally fixed carbon within the plant with its implications for carbon turnover rates, on the regulation of photosynthesis in response to environmental limitations on in-plant carbon sinks, and on emergent ecosystem responses. We recommend possible avenues for model improvement and identify requirements for better data on core processes relevant to the understanding and modelling of the effect of increasing [CO₂] on the global terrestrial carbon sink.

Early Endothelial Progenitor Cells (eEPCs) in systemic sclerosis (SSc) - dynamics of cellular regeneration and mesenchymal transdifferentiation

BACKGROUND

Patients with systemic sclerosis (SSc) are endagered by tissue fibrosis and by microvasculopathy, with the latter caused by endothelial cell expansion/proliferation. SSc-associated fibrosis potentially results from mesenchymal transdifferentiation of endothelial cells. Early Endothelial Progenitor Cells (eEPCs) act proangiogenic under diverse conditions. Aim of the study was to analyze eEPC regeneration and mesenchymal transdifferentiation in patients with limited and diffuse SSs (lSSc and dSSc).

METHODS

Patients with both, lSSc and dSSc were included into the study. The following parameters were evaluated: eEPC numbers and regeneration, concentrations of vasomodulatory mediators, mesenchymal properties of blood-derived eEPC. Serum samples of healthy subjects and SS patients were used for stimulation of cultured human eEPC, subsequently followed by analysis of mesenchymal cell characteristics and mobility.

RESULTS

Twenty-nine patients were included into the study. Regenerative activity of blood-derived eEPCs did not differ between Controls and patients. Circulating eEPC were significantly lower in all patients with SSc, and in limited and diffuse SSc (lSSc/dSSc). Serum concentrations of promesenchymal TGF-b was elevated in all patients with SSc. Cultured mononuclear cells from SS patients displayed higher abundances of CD31 and of CD31 and aSMA combined. Finally, serum from SSc patients inhibited migration of cultured eEPCs and the cells showed lower sensitivity towards the endothelin antagonist Bosentan.

CONCLUSIONS

The eEPC system, which represents an essential element of the endogenous vascular repair machinery is affected in SSc. The increased appearance of mesenchymal properties in eEPC may indicate that alterations of the cells potentially contribute to the accumulation of connective tissue and to vascular malfunction.