Growing through predation windows: effects on body size development in young fish

The degree to which growth in early life stages of animals is regulated via density‐dependent feedbacks through prey resources is much debated. Here we have studied the influence of size‐ and density‐dependent mechanisms as well as size‐selective predation pressure by cannibalistic perch Perca fluviatilis on growth patterns of young‐of‐the‐year (YOY) perch covering several lakes and years. We found no influence of initial size or temperature on early body size development of perch. In contrast, there was a negative relationship between reproductive output and the length of YOY perch at five weeks of age. However, rather than an effect of density‐dependent growth mediated via depressed resources the relationship was driven by positive size‐selective cannibalism removing large individuals. Hence, given a positive correlation between the density of victims and predation pressure by cannibals, size‐dependent interactions between cannibals and their victims may wrongly be interpreted as patterns of density‐dependent growth in the victim cohort. Overall, our results support the view that density‐dependent resource‐limitation in early life stages is rare. Still, patterns of density‐dependent growth may emerge, but from variation in size‐selective predation pressure rather than density as such. This illustrates the importance of taking overall population demography and predatory interactions into account when studying growth patterns among recruiting individuals.     

Synaesthetic Colour in the Brain: Beyond Colour Areas. A Functional Magnetic Resonance Imaging Study of Synaesthetes and Matched Controls

Background

In synaesthesia, sensations in a particular modality cause additional experiences in a second, unstimulated modality (e.g., letters elicit colour). Understanding how synaesthesia is mediated in the brain can help to understand normal processes of perceptual awareness and multisensory integration. In several neuroimaging studies, enhanced brain activity for grapheme-colour synaesthesia has been found in ventral-occipital areas that are also involved in real colour processing. Our question was whether the neural correlates of synaesthetically induced colour and real colour experience are truly shared.

Methodology/Principal Findings

First, in a free viewing functional magnetic resonance imaging (fMRI) experiment, we located main effects of synaesthesia in left superior parietal lobule and in colour related areas. In the left superior parietal lobe, individual differences between synaesthetes (projector-associator distinction) also influenced brain activity, confirming the importance of the left superior parietal lobe for synaesthesia. Next, we applied a repetition suppression paradigm in fMRI, in which a decrease in the BOLD (blood-oxygenated-level-dependent) response is generally observed for repeated stimuli. We hypothesized that synaesthetically induced colours would lead to a reduction in BOLD response for subsequently presented real colours, if the neural correlates were overlapping. We did find BOLD suppression effects induced by synaesthesia, but not within the colour areas.

Conclusions/Significance

Because synaesthetically induced colours were not able to suppress BOLD effects for real colour, we conclude that the neural correlates of synaesthetic colour experience and real colour experience are not fully shared. We propose that synaesthetic colour experiences are mediated by higher-order visual pathways that lie beyond the scope of classical, ventral-occipital visual areas. Feedback from these areas, in which the left parietal cortex is likely to play an important role, may induce V4 activation and the percept of synaesthetic colour.     

Flow cytometric analysis of mitochondria from CA1 and CA3 regions of rat hippocampus reveals differences in permeability transition pore activation

Mitochondria are important in the pathophysiology of several neurodegenerative diseases, and mitochondrial production of reactive oxygen species (ROS), membrane depolarization, permeability changes and release of apoptogenic proteins are involved in these processes. Following brain insults, cell death often occurs in discrete regions of the brain, such as the subregions of the hippocampus. To analyse mitochondrial structure and function in such subregions, only small amounts of mitochondria are available. We developed a protocol for flow cytometric analysis of very small samples of isolated brain mitochondria, and analysed mitochondrial swelling and formation of ROS in mitochondria from the CA1 and CA3 regions of the hippocampus. Calcium-induced mitochondrial swelling was measured, and fluorescent probes were used to selectively stain mitochondria (nonyl acridine orange), to measure membrane potential (tetramethylrhodamine-methyl-ester, 1,1',3,3,3',3'-hexamethylindodicarbocyanine-iodide) and to measure production of ROS (2',7'-dichlorodihydrofluorescein-diacetate). We found that formation of ROS and mitochondrial permeability transition pore activation were higher in mitochondria from the CA1 than from the CA3 region, and propose that differences in mitochondrial properties partly underlie the selective vulnerability of the CA1 region to brain insults. We also conclude that flow cytometry is a useful tool to analyse the role of mitochondria in cell death processes.     

Helicobacter pylori infection and gastroesophageal reflux in a population-based study (The HUNT Study)

BACKGROUND AND AIM: It has been suggested that Helicobacter pylori infection may prevent gastroesophageal reflux, possibly through gastric atrophy. Since, however, previous results are contradictory and no population-based studies are available, the relationship between H. pylori and reflux remains uncertain. The aim of this study was to investigate this relationship in a population-based, nested, case-control study. METHODS: From a cohort of 65,363 individuals, representing 71.2% of the adult population in the Norwegian county of Nord-Trondelag, we randomly selected 472 persons with recurrent reflux symptoms (cases) and 472 without such symptoms (controls). Occurrence of H. pylori and its virulence factor cagA was determined serologically, using an immunoblot assay. Gastric atrophy was assessed through serum levels of pepsinogen I. Odds ratios (OR) with 95% confidence intervals (CI), adjusted for potential confounding factors, represented relative risks. RESULTS: H. pylori infection was not associated with a decreased risk of reflux symptoms (OR 1.1, 95% CI 0.8-1.6), irrespective of positive cagA status (OR 1.1, 95% CI 0.8-1.5). Gastric atrophy reduced the risk of reflux symptoms (OR 0.2, 95% CI 0.0-0.6). Infection with H. pylori entailed a ninefold increase in the risk of gastric atrophy compared to non-infection (OR 8.9, 95% CI 2.0-39.9). CONCLUSIONS: H. pylori infection, irrespective of cagA status, did not affect the occurrence of reflux symptoms in this population-based setting. Infected individuals are at increased risk of gastric atrophy, which in turn reduces reflux symptoms, but due to the low frequency of gastric atrophy among infected individuals overall, there was no association with reflux symptoms on a population level.     

Endothelium-dependent vascular responses induced by leukotriene B4

Leukotriene B(4) (LTB(4)) is an inflammatory mediator derived from the 5-lipoxygenase pathway of arachidonic acid metabolism and has recently implicated in the pathogenesis of atherosclerosis. There are two membrane bound receptors for LTB(4): BLT(1) and BLT(2), which represent the high and low affinity receptors, respectively. BLT receptors are expressed on leukocytes, and LTB(4) is a potent chemoattractant for neutrophils, eosinophils, and T lymphocytes. Recent studies have in addition shown that LTB(4) is an indirectly acting vasoconstrictor of isolated vascular preparations. In the guinea pig aorta, the LTB(4)-induced contractions were inhibited by endothelium-denudation. In addition, pre-treatment with the NO synthase inhibitor, L-NOARG, significantly enhanced the contractions induced by LTB(4). The contractile response induced by LTB(4) in the guinea pig aorta was abolished by the selective BLT(1) receptor antagonist U75302 and the expression of BLT(1) receptor mRNA in the guinea pig aorta was established by RT-PCR. Taken together, these results suggest that LTB(4) activates BLT(1) receptors on the endothelium of the guinea pig aorta, associated with the release of both contractile factors and NO.     

Thousands of RAD-seq Loci Fully Resolve the Phylogeny of the Highly Disjunct Arctic-Alpine Genus Diapensia (Diapensiaceae)

Restriction-site associated DNA sequencing (RAD-seq) has recently become an important method to generate genome-wide molecular data for species delimitation, phylogeography, and population genetic studies. However, very few empirical studies have so far tested its applicability in phylogenetic reconstruction. The alpine-arctic genus Diapensia was selected to study the origin of the disjunction between the Arctic and the Himalayan-Hengduan Mountains (HHM). However, a previous phylogenetic analysis based on one nuclear and four plastid DNA regions failed to resolve the oldest divergences in Diapensia as well as the relationship between the two HHM species. Here we reconstruct a fully resolved phylogeny of Diapensia and address the conflict between the currently accepted taxonomy and the gene trees in the HHM species using RAD-seq. Based on a data set containing 2,650 loci selected to maximize the number of parsimony informative sites and allowing for a high level of missing data (51%), the phylogeny of Diapensia was fully resolved and each of the four species was reciprocally monophyletic. Whereas the arctic D. lapponica was inferred as sister to the HHM clade in the previous study, the RAD-seq data resolved the two arctic species as sisters to the HHM clade. Similar relationships were inferred from a differently filtered data set with far fewer loci (114) and less missing data (21%), but with lower support and with one of the two HHM species as non-monophyletic. Bayesian concordance analysis and Patterson’s D-statistic tests suggested that admixture has occurred between the two HHM species.