Electrophysiological identification of the sugar cell in antennal taste sensilla of the predatory ground beetle Pterostichus aethiops

By single sensillum tip recording technique, in addition to the salt and pH cells found in antennal taste sensilla of some ground beetles earlier, the third chemosensory cell of four innervating these large sensilla was electrophysiologically identified as a sugar cell in the ground beetle Pterostichus aethiops. This cell generated action potentials of considerably smaller amplitude than those of the salt and pH cells, and phasic-tonically responded to sucrose and glucose over the range of 1-1000 mM tested. Responses were concentration dependent, with sucrose generating more spikes than glucose. During the first second of the response, maximum rates of firing of the sugar cell reached up to 19 and 37 imp/s when stimulated with 1000 mM glucose and sucrose, respectively. Three to four seconds later, the responses decreased close to zero. Both sugars are important in plant carbohydrate metabolism. These ground dwelling insects may come into contact with live and decayed plant material everywhere in their habitat including their preferred overwintering sites in brown-rot decayed wood. In conclusion, we hypothesize that high content of soluble sugars in their overwintering sites and refugia is unfavourable for these ground beetles, most probably to avoid contact with dangerous fungi.     

p75 neurotrophin receptor regulates tissue fibrosis through inhibition of plasminogen activation via a PDE4/cAMP/PKA pathway

Clearance of fibrin through proteolytic degradation is a critical step of matrix remodeling that contributes to tissue repair in a variety of pathological conditions, such as stroke, atherosclerosis, and pulmonary disease. However, the molecular mechanisms that regulate fibrin deposition are not known. Here, we report that the p75 neurotrophin receptor (p75^NTR), a TNF receptor superfamily member up-regulated after tissue injury, blocks fibrinolysis by down-regulating the serine protease, tissue plasminogen activator (tPA), and up-regulating plasminogen activator inhibitor-1 (PAI-1). We have discovered a new mechanism in which phosphodiesterase PDE4A4/5 interacts with p75^NTR to enhance cAMP degradation. The p75^NTR-dependent down-regulation of cAMP results in a decrease in extracellular proteolytic activity. This mechanism is supported in vivo in p75^NTR-deficient mice, which show increased proteolysis after sciatic nerve injury and lung fibrosis. Our results reveal a novel pathogenic mechanism by which p75^NTR regulates degradation of cAMP and perpetuates scar formation after injury.     

Half a century of Scots pine forest ecosystem monitoring reveals long‐term effects of atmospheric deposition and climate change

At two forest sites in Germany (Pfaffenwinkel, Pustert) stocked with mature Scots pine (Pinus sylvestris L.), we investigated changes of topsoil chemistry during the recent 40 years by soil inventories conducted on replicated control plots of fertilization experiments, allowing a statistical analysis. Additionally, we monitored the nutritional status of both stands from 1964 until 2019 and quantified stand growth during the monitoring period by repeated stand inventories. Moreover, we monitored climate variables (air temperature and precipitation) and calculated annual climatic water balances from 1991 to 2019. Atmospheric nitrogen (N) and sulfur (S) deposition between 1964 and 2019 was estimated for the period 1969–2019 by combining annual deposition measurements conducted in 1985–1987 and 2004 with long‐term deposition records from long‐term forest monitoring stations. We investigated interrelations between topsoil chemistry, stand nutrition, stand growth, deposition, and climate trends. At both sites, the onset of the new millennium was a turning point of important biogeochemical processes. Topsoil acidification turned into re‐alkalinization, soil organic matter (SOM) accumulation stopped, and likely turned into SOM depletion. In the new millennium, topsoil stocks of S and plant‐available phosphorus (P) as well as S and P concentrations in Scots pine foliage decreased substantially; yet, age‐referenced stand growth remained at levels far above those expected from yield table data. Tree P and S nutrition as well as climate change (increased temperature and drought stress) have replaced soil acidification as major future challenges for both forests. Understanding of P and S cycling and water fluxes in forest ecosystems, and consideration of these issues in forest management is important for successfully tackling the new challenges. Our study illustrates the importance of long‐term forest monitoring to identify slow, but substantial changes of forest biogeochemistry driven by natural and anthropogenic global change.     

Electrophysiological identification of cold receptors on the antennae of the ground beetle Pterostichus aethiops

Abstract.  In single-sensillum extracellular electrophysiological recordings, terminal campaniform sensilla at the tip of antennae of the ground beetle Pterostichus aethiops (Pz., 1797) show action potentials of three sensory cells, A-, B- and C-cells, distinguished by differences in their spike amplitudes. Only the A-cell, with the largest spike amplitude, is highly sensitive to temperature fluctuations, showing remarkable changes in its firing rate induced by changes in temperature of 0.1 °C. The firing rate of A-cells at 23 °C varies from 15–52 Hz among different beetles. Mean impulse frequency of A-cells is found to be a function of steady temperature, the firing rate decreasing with temperature increase. A-cells respond to a rapid temperature drop with a strong phasic-tonic reaction; larger decreases in temperature evoke higher peak frequency values. Maximum peak frequencies, varying from 380–630 Hz in different beetles, are induced by temperature decreases of 3–10 °C, whereas temperature rise strongly inhibits impulse activity of the A-cell. The first manifestation of rapid warming in the nerve impulse sequence is a very long interspike period, followed by diminished activity. Both the length of the long interspike period and the rate of following impulse activity are functions of temperature change; hence, A-cells respond to temperature changes as typical cold receptors, similar to coeloconic and short hair-like sensilla in other insects.     

Effect of amino acid substitutions on the candidacidal activity of LFampin 265-284

LFampin 265-284, derived from bovine lactoferrin, has broad-spectrum antimicrobial activity against the yeast Candida albicans and several Gram-positive and Gram-negative bacteria. A glycine substitution scan was used to identify residues that are important for its candidacidal activity. Each single substitution of a positively charged residue led to considerable reduction in candidacidal activity, for each residue to a different extent. Substitution within the helix-facilitating N-terminal sequence DLIW had less severe effect; substitution of Ile and Trp led to a somewhat reduced potency. No substantial effects were found on the propensity to adopt a helical structure or to bind to C. albicans cells.     

General Description of Partly Meromictic Hypertrophic Lake Verevi,its Ecological Status,Changes during the Past Eight Decades,and Restoration Problems

The present study describes generally the ecosystem of Lake Verevi while more detailed approaches are presented in the same issue. The main task of the article is to estimate long-term changes and find the best method for the restoration of good ecological status. Lake Verevi (surface 12.6 ha, mean depth 3.6 m, maximum depth 11 m, drainage area 1.1 km², water exchange 0.63-times per year) is a hypertrophic hard-water lake located in town Elva (6400 inhabitants). Long-term complex limnological investigations have taken place since 1929. The lake has been contaminated by irregular discharge of urban wastewaters from oxidation ponds since 1978, flood from streets, and infiltrated waters from the surrounding farms. The so-called spring meromixis occurred due to extremely warm springs in recent years. The index value of buffer capacity of Lake Verevi calculated from natural conditions is on the medium level. Water properties were analysed according to the requirements of the EU Water Framework Directive. According to the classification, water quality as a long-term average of surface layers is moderate-good, but the water quality of bottom layers is bad. Values in deeper layers usually exceed 20–30 times the calculated reference values by Vighi and Chiaudani’s model. Naturally, at the beginning of the 20th century the limnological type of the lake was moderately eutrophic. During the 1980s and 1990s the ecosystem was out of balance by abiotic characteristics as well as by plankton indicators. Rapid fluctuations of species composition and abundance can be found in recent years. Seasonal variations are considerable and species composition differs remarkably also in the water column. The dominating macrophyte species vary from year to year. Since the annual amount of precipitation from the atmosphere onto the lake surface is several times higher, the impact of swimmers could be considered irrelevant. Some restoration methods were discussed. The first step, stopping external pollution, was completed by damming the inlet. Drainage (siphoning) of the hypolimnetic water is discussed. Secondary pollution occurs because Fe:P values are below the threshold. The authors propose to use phosphorus precipitation and hypolimnetic aeration instead of siphoning.     

Lactoferrampin, an antimicrobial peptide of bovine lactoferrin, exerts its candidacidal activity by a cluster of positively charged residues at the C-terminus in combination with a helix-facilitating N-terminal part

The antimicrobial activity of bovine lactoferrin (bLF) is attributed to lactoferricin, which is situated in the N1-domain of bLF. Recently, another antimicrobial domain consisting of residues 268-284, designated lactoferrampin (LFampin), has been identified in the N1-domain of bLF, which exhibited antimicrobial activity against Candida albicans and several bacteria. In the present study, the candidacidal activity of a series of peptides spanning this antimicrobial domain was investigated in relation to the charge and the capacity to form a helical conformation in hydrophobic environments. C-Terminal truncation of LFampin resulted in a drastic decrease in candidacidal activity. Positively charged residues clustered at the C-terminal side of the LFampin domain appeared to be crucial for the candidacidal activity. The ability to adopt helical conformations did not change when LFampin was truncated at the C-terminal side. N-Terminally truncated LFampin peptides, truncated up to the sequence 270-284, were more reluctant to adopt a helical conformation. Therefore, we conclude that the C-terminal part of LFampin 265-284, which is the most active peptide, is crucial for its candidacidal activity, due to the presence of clustered positive charges, and that the N-terminal part is essential for activity as it facilitates helix formation.     

Engineering disulfide bonds of the novel human beta-defensins hBD-27 and hBD-28: differences in disulfide formation and biological activity among human beta-defensins

Human beta-defensins comprise a large number of peptides that play a functional role in the innate and adaptive immune system. Recently, clusters of new beta-defensin genes with predominant expression in testicular tissue have been discovered on different chromosomes by bioinformatics. beta-Defensins share a common pattern of three disulfides that are essential for their biological effects. Here we report for the first time the chemical synthesis of the new fully disulfide-bonded beta-defensins hBD-27 and hBD-28, and compare the results with synthetic procedures to obtain the known hBD-2 and hBD-3. While hBD-27 was readily converted into a product with the desired disulfide pattern by oxidative folding, hBD-28 required a selective protective group strategy to introduce the three disulfide bonds. The established synthetic processes were applied to the synthesis of hBD-2, which, like hBD-27, was accessible by oxidative folding, whereas hBD-3 required a selective strategy comparable to hBD-28. Experimental work demonstrated that trityl, acetamidomethyl, and t-butyl are superior to other protection strategies. However, the suitable pairwise arrangement of the protective groups can be different, as shown here for hBD-3 and hBD-28. Determination of the minimum inhibitory concentration against different bacteria revealed that hBD-27, in contrast to other beta-defensins tested, has virtually no antimicrobial activity. Compared to the other peptides tested, hBD-27 showed almost no cytotoxic activity, measured by hemoglobin release of erythrocytes. This might be due to the low positive net charge, which is significantly higher for hBD-2, hBD-3, and hBD-28.     

Electrophysiological identification of hygroreceptor neurons from the antennal dome-shaped sensilla in the ground beetle Pterostichus oblongopunctatus

This study gives the first electrophysiological evidence of hygroreceptors in carabids. Extracellular recordings from the antennal dome-shaped sensilla of the carabid beetle Pterostichus oblolongopunctatus (Coleoptera, Carabidae) clearly show the presence of moist and dry neuron antagonistically responding to humidity changes. The cold neuron of the same sensillum did not respond to changes in humidity. For the first time, we demonstrate that the binary system of two antagonistic hygroreceptor neurons discriminates differences between steady-state humidity levels more sensitively than either neuron separately. Another advantage of the binary system is that it guarantees immediate and strong phasic-tonic response to rapid humidity changes in either direction. In the hygrosensing system of carabids, this would allow detection of subtle step-changes in humidity with greater sensitivity than differences in steady-state values of humidity. Thus, construction of the hygrosensing system with opposing receptor neurons may allow insects to detect environmental humidity differences critical for their habitat and microhabitat selection, and survival with great precision.     

Responses of antennal campaniform sensilla to rapid temperature changes in ground beetles of the tribe platynini with different habitat preferences and daily activity rhythms

Responses of temperature sensitive (cold) cells from the antenna of ground beetles (tribe Platynini) were compared in species with different ecological preferences and daily activity rhythms. Action potential rates were characterized at various temperatures (ranges 23-39 degrees C) and during rapid changes in it (Deltat=0.5-15 degrees C). The stationary firing frequencies were nearly twice as high in eurythermic open field ground beetles Agonum muelleri and Anchomenus dorsalis (firing rates ranging from 22 to 47imp/s) than in a stenothermic forest species Platynus assimilis. In the eurythermic species, the firing rate did not significantly depend on temperature (Anchomenus dorsalis range of 23-27 degrees C and Agonum muelleri range of 23-33 degrees C) but plots of firing rate versus temperature showed rapid declines when lethally high temperatures were approached. In contrast, a nearly linear decline of the firing rate/temperature curve was observed in Platynus assimilis. Responses to rapid temperature decreases were also considerably higher in eurythermic species. Both the peak frequency of the initial burst (maximum 420-650Hz) as well as the sustained discharge in the first 4s of the response were higher than in Platynus assimilis. Long silent periods, lasting up to several seconds, that occurred at the beginning of the response to rapid warming were significantly shorter in Agonum muelleri and Anchomenus dorsalis compared to Platynus assimilis. These findings suggest that the responses of thermoreceptors to temperature changes may be correlated with specific ecological preferences.