Elevation of superior vena caval pressure increases extravascular lung water after endotoxemia

In many sheep Escherichia coli endotoxin results in pulmonary hypertension, increased microvascular permeability, pulmonary edema, and increased central venous pressure. Since lung lymph drains into the systemic veins, increases in venous pressure may impair lymph flow sufficiently to enhance the accumulation of extravascular fluid. We tested the hypothesis that, following endotoxin, elevating the venous pressure would increase extravascular fluid. Thirteen sheep were chronically instrumented with catheters to monitor left atrial pressure (LAP), pulmonary arterial pressure (PAP), and superior vena caval pressure (SVCP) as well as balloons to elevate LAP and SVCP. These sheep received 4 micrograms/kg endotoxin, and following the pulmonary hypertensive spike the left atrial balloon was inflated so that (PAP + LAP)/2 = colloid osmotic pressure. It was necessary to control PAP + LAP in this way to minimize the sheep-to-sheep differences in the pulmonary hypertension. We elevated the SVCP to 10 or 17 mmHg or allowed it to stay low (3.2 mmHg). After a 3-h period, we killed the sheep and removed the right lungs for determination of the extravascular fluid-to-blood-free dry weight ratio (EVF). Sheep with SVCP elevated to 10 or 17 mmHg had significant increases in EVF (5.2 +/- 0.1 and 5.6 +/- 1.2) compared with the sheep in which we did not elevate SVCP (EVF = 4.5 +/- 0.4). These results indicate that sustained elevation in central venous pressure in patients contributes to the amount of pulmonary edema associated with endotoxemia.     

Brain-derived neurotrophic factor in the hypothalamic paraventricular nucleus reduces energy intake

Recent studies show that brain-derived neurotrophic factor (BDNF) decreases feeding and body weight after peripheral and ventricular administration. BDNF mRNA and protein, and its receptor tyrosine kinase B (TrkB) are widely distributed in the hypothalamus and other brain regions. However, there are few reports on specific brain sites of actions for BDNF. We evaluated the effect of BDNF in the hypothalamic paraventricular nucleus (PVN) on feeding. BDNF injected unilaterally or bilaterally into the PVN of food-deprived and nondeprived rats significantly decreased feeding and body weight gain within the 0- to 24-h and 24- to 48-h postinjection intervals. Effective doses producing inhibition of feeding behavior did not establish a conditioned taste aversion. PVN BDNF significantly decreased PVN neuropeptide Y (NPY)-induced feeding at 1, 2, and 4 h following injection. BDNF administration in the PVN abolished food-restriction-induced NPY gene expression in the hypothalamic arcuate nucleus. In conclusion, BDNF in the PVN significantly decreases food intake and body weight gain, suggesting that the PVN is an important site of action for BDNF in its effects on energy metabolism. Furthermore, BDNF appears to interact with NPY in its anorectic actions, although a direct effect on NPY remains to be established.     

Variable clinical responses of a scrub typhus outbred mouse model to feeding by Orientia tsutsugamushi infected mites

Rodents are the natural hosts for Leptotrombidium mites that transmit Orientia tsutsugamushi, the causative agent of scrub typhus, a potentially fatal febrile human disease. Utilizing mite lines that included O. tsutsugamushi infected and non-infected Leptotrombidium species we investigated the varied infection response of outbred mice (ICR) exposed to L. chiangraiensis (Lc), L. imphalum (Li) and L. deliense (Ld). Each of six mite lines (Lc1, Lc5, Li3, Li4, Li7 and Ld) was separately placed in the inner ears of ICR mice either as a single individual (individual feeding, IF) or as a group of 2-4 individuals (pool feeding, PF). The species of infected chigger feeding on mice significantly affected mortality rates of the mice, with mite lines of Lc causing higher mean (±SE) mortality (90.7 ± 3.6 %) than mite lines of Li (62.9 ± 5.6 %) or Ld (53.6 ± 5.8 %). Mouse responses which included time to death, food consumption and total mice weight change depended on mite species and their O. tsutsugamushi genotype, more than on feeding procedure (IF vs. PF) except for mite lines within the Lc. Infected mite lines of Lc were the most virulent infected mites assessed whereas the infected Ld species was the least virulent for the ICR. Mice killed by various mite lines showed enlarged spleens and produced ascites. The results of this investigation of the clinical responses of ICR mice to feeding by various infected mite lines indicated that the different species of infected mites and their O. tsutsugamushi genotype produced different clinical presentations in ICR mice, a scrub typhus mouse model which mimics the natural transmission of O. tsutsugamushi that is critical for understanding scrub typhus disease in terms of natural transmission, host-pathogen-vector interaction and vaccine development.     

Nitrogen enrichment contributes to positive responses to soil microbial communities in three invasive plant species

Increased resource availability and feedbacks with soil biota have both been invoked as potential mechanisms of plant invasion. Nitrogen (N) deposition can enhance invasion in some ecosystems, and this could be the result of increased soil N availability as well as shifts in soil biota. In a two-phase, full-factorial greenhouse experiment, we tested effects of N availability and N-impacted soil communities on growth responses of three Mediterranean plant species invasive in California: Bromus diandrus, Centaurea melitensis, and Hirschfeldia incana. In the first phase, plants were grown individually in pots and inoculated with sterile soil, soil from control field plots or soil from high N addition plots, and with or without supplemental N. In the second phase, we grew the same species in soils conditioned in the first phase. We hypothesized growth responses would differ across species due to species-specific relationships with soil biota, but overall increased N availability and N-impacted soil communities would enhance plant growth. In the first phase, Centaurea had the greatest growth response when inoculated with N-impacted soil, while Bromus and Hirschfeldia performed best in low N soil communities. However, in phase two all species exhibited positive growth responses in N-impacted soil communities under high N availability. While species may differ in responses to soil biota and N, growth responses to soils conditioned by conspecifics appear to be most positive in all species under high N availability and/or in soil communities previously impacted by simulated N deposition. Our results suggest N deposition could facilitate invasion due to direct impacts of soil N enrichment on plant growth, as well as through feedbacks with the soil microbial community.     

Sexually selected skin colour is heritable and related to fecundity in a non-human primate

Sexual selection promotes the prevalence of heritable traits that increase an individual''s reproductive rate. Despite theoretically strong directional selection, sexually selected traits can show inter-individual variation. Here, we investigate whether red skin ornamentation, a rare example of a male mammalian trait involved in mate attraction, influences fecundity and is heritable in rhesus macaques (Macaca mulatta), and explore the mechanisms that are involved in maintaining trait variation. Interestingly, the trait is expressed by and is attractive to both sexes. We collected facial images of 266 free-ranging individuals and modelled skin redness and darkness to rhesus macaque vision. We used 20 years of genetic parentage data to calculate selection gradients on the trait and perform heritability analyses. Results show that males who were both darkly coloured and high-ranking enjoyed higher fecundity. Female skin redness was positively linked to fecundity, although it remains unclear whether this influences male selectiveness. Heritability explained 10–15% of the variation in redness and darkness, and up to 30% for skin darkness when sexes are considered separately, suggesting sex-influenced inheritance. Our results suggest that inter-individual variation is maintained through condition-dependence, with an added effect of balancing selection on male skin darkness, providing rare evidence for a mammalian trait selected through inter-sexual selection.     

Diminished AMPK signaling response to fasting in thioredoxin-interacting protein knockout mice

Thioredoxin-interacting protein (Txnip) knockout (TKO) mice exhibit impaired response to fasting. Herein, we showed that activation of adenine monophosphate-activated protein kinase and cellular AMP levels were diminished in the heart and soleus muscle but not in gastrocnemius muscle of fasting TKO mice. Similarly, glycogen content in fasted TKO mice was increased in oxidative muscles but was not different in glycolytic muscles. These data suggest Txnip deficiency has a higher impact on oxidative muscle than glycolytic muscles and provide new insights into the metabolic role of Txnip.