Hypoxic pulmonary vasoconstriction as a regulator of alveolar-capillary oxygen flux: A computational model of ventilation-perfusion matching

The relationship between regional variabilities in airflow (ventilation) and blood flow (perfusion) is a critical determinant of gas exchange efficiency in the lungs. Hypoxic pulmonary vasoconstriction is understood to be the primary active regulator of ventilation-perfusion matching, where upstream arterioles constrict to direct blood flow away from areas that have low oxygen supply. However, it is not understood how the integrated action of hypoxic pulmonary vasoconstriction affects oxygen transport at the system level. In this study we develop, and make functional predictions with a multi-scale multi-physics model of ventilation-perfusion matching governed by the mechanism of hypoxic pulmonary vasoconstriction. Our model consists of (a) morphometrically realistic 2D pulmonary vascular networks to the level of large arterioles and venules; (b) a tileable lumped-parameter model of vascular fluid and wall mechanics that accounts for the influence of alveolar pressure; (c) oxygen transport accounting for oxygen bound to hemoglobin and dissolved in plasma; and (d) a novel empirical model of hypoxic pulmonary vasoconstriction. Our model simulations predict that under the artificial test condition of a uniform ventilation distribution (1) hypoxic pulmonary vasoconstriction matches perfusion to ventilation; (2) hypoxic pulmonary vasoconstriction homogenizes regional alveolar-capillary oxygen flux; and (3) hypoxic pulmonary vasoconstriction increases whole-lobe oxygen uptake by improving ventilation-perfusion matching.     

Multi-particle sampling in Monte Carlo simulations on fluids: efficiency and extended implementations

Various technical aspects affecting the efficiency of a recently proposed novel Monte Carlo (MC) simulation scheme based on biased simultaneous displacements/rotations of all particles of the system are investigated using two polarisable models of water, the Chialvo–Cummings and Brodholt–Sampoli–Vallauri models, as a test case. Necessary expressions for polarisable site–site interaction models are derived along with a novel smoothing of the potential at the cut-off distance. In addition to the common thermodynamic and structural properties, the mean-squared displacements, rotation relaxation, speed of equilibration (translational order parameter, TOP) and autocorrelation coefficients have been computed as well, in order to assess the efficiency of the method. Gain in speed by parallelisation has also been examined. Performance of the method is coumpared with both the standard one-particle move method and the available approximate methods. It is shown that the multi-particle move (MPM) method performs about by a factor of 10 faster for the systems considered when compared with the common MC scheme, and several times faster when compared with the approximate methods. Parallelised codes of the MPM method may then perform about 70 times faster than the conventional MC. These conclusions hold true for the system size simulated (N = 256) because the efficiency of the multi-particle method depends on the size of the system: its efficiency even increases with increasing number of particles.     

Floral Phytochemistry: Impact of Volatile Organic Compounds and Nectar Secondary Metabolites on Pollinator Behavior and Health

Plants produce a plethora of phytochemicals including sugars, amino acids (AAs), volatile organic compounds (VOCs) and secondary metabolites (SMs) with different ecological functions. To attract pollinators and defenders and ensure reproductive success, plants mainly rely on VOCs, while to reward insects, plants synthesize nectar rich in sugars and AAs. Furthermore, plant SMs can play various roles. Some components are able to interact with the nervous system of insects by binding to neuron receptor proteins and thus manipulate pollinator behavior. Others, like alkaloids and phenolics, protect from nectar robbers and enhance memory and foraging efficiency, or, as in the case of flavonoids, exhibit high antioxidant activities supporting pollinator well-being. This review discusses the impact of VOCs and nectar SMs on insect behavior and pollinator health.     

An experimental study on post-mortem dissolution and overgrowth processes affecting coccolith assemblages: A rapid and complex process

Coccolith dissolution together with post-mortem morphological features are immensely important phenomena that can affect assemblage compositions, complicate taxonomic identification as well as provide valuable palaeoenvironmental insights. This study summarizes the effects of pH oscillations on post-mortem coccolith morphologies and the abundances and compositions of calcareous nannoplankton assemblages in three distinct types of material—(i) Cretaceous chalk, (ii) Miocene marls, and (iii) late Holocene calcareous ooze. Two independent experimental runs within a semi-enclosed system setting were realized to observe assemblage alterations. One experiment was realized with the presence of bacteria and, in contrast, the second one inhibited their potential effect on the studied system. The pH was gradually decreased within the range of 8.3–6.4 using a reaction of CO₂ with H₂O forming weak carbonic acid (H₂CO₃), thereby affecting [${\mathrm{CO}}_3^{2-}$]. Further, a subsequent overgrowth study was carried out during spontaneous degassing accompanied by a gradual pH rise. The experiment revealed that the process and intensity of coccolith corrosion and subsequent overgrowth build-ups are influenced by a plethora of different factors such as (i) pH and associated seawater chemistry, (ii) mineral composition of the sediment, (iii) the presence of coccoliths within a protective substrate (faecal pellets, pores, pits), and (iv) the presence/absence of bacteria. Nannoplankton assemblages with corroded coccoliths or with coccoliths with overgrowth build-ups showed that the observed relative abundances of taxa experienced alteration from the original compositions. Additionally, extreme pH oscillations may result in enhanced morphological changes that make coccoliths unidentifiable structures, and might even evoke the absence of coccoliths in the fossil record.     

Computational identification of miRNAs,their targets and functions in three‐spined stickleback (Gasterosteus aculeatus)

An intriguing question in biology is how the evolution of gene regulation is shaped by natural selection in natural populations. Among the many known regulatory mechanisms, regulation of gene expression by microRNAs (miRNAs) is of critical importance. However, our understanding of their evolution in natural populations is limited. Studying the role of miRNAs in three‐spined stickleback, an important natural model for speciation research, may provide new insights into adaptive polymorphisms. However, lack of annotation of miRNA genes in its genome is a bottleneck. To fill this research gap, we used the genome of three‐spined stickleback to predict miRNAs and their targets. We predicted 1486 mature miRNAs using the homology‐based miRNA prediction approach. We then performed functional annotation and enrichment analysis of these targets, which identified over‐represented motifs. Further, a database resource (GAmiRdb) has been developed for dynamically searching miRNAs and their targets exclusively in three‐spined stickleback. Finally, the database was used in two case studies focusing on freshwater adaptation in natural populations. In the first study, we found 44 genomic regions overlapping with predicted miRNA targets. In the second study, we identified two SNPs altering the MRE seed site of sperm‐specific glyceraldehyde‐3‐phosphate gene. These findings highlight the importance of the GAmiRdb knowledge base in understanding adaptive evolution.     

Effect of adrenalectomy and corticosterone on cocaine-induced sensitization in rats.

Effects of adrenalectomy (ADX) and corticosterone (CORT) on the development and expression of sensitization to the locomotor effect of cocaine (COC) were studied in rats. Sensitization was evoked by 5 daily injections of COC (10 mg/kg) and measured after a challenge dose of the drug (10 mg/kg) after a 5-day withdrawal (on day 10 of the experiment). ADX, performed before the start of COC administration, completely blocked the manifestation of COC-induced sensitization. In contrast, ADX performed on animals already sensitized to COC did not affect the sensitized locomotor activity response to a challenge dose of COC (on day 18). Pretreatment with CORT, 10 mg/kg, but not 5 mg/kg, before each of the 5 daily COC injections facilitated the development of COC sensitization, tested after a 5-day withdrawal. When pretreated with CORT alone (10 mg/kg), the challenge dose of COC administered on day 10 induced cross-sensitization to CORT. CORT (10 mg/kg) injected acutely before COC on day 10, potentiated the expression of COC sensitization. When given alone, on day 10 CORT (5-10 mg/kg) induced an increase in the locomotor activity of rats pretreated daily (5 injections) with COC. No drug treatment induced conditioned locomotion, as measured after saline challenge on day 8. Our results indicate that CORT facilitates the development and expression of COC sensitization, while ADX blocks the initiation of the behavioral phenomenon only. Moreover, there takes place cross-sensitization between CORT and COC, which indicates a close relationship between the drug-related mechanism and behavioral sensitization.