Astrocytes Optimize the Synaptic Transmission of Information

Chemical synapses transmit information via the release of neurotransmitter-filled vesicles from the presynaptic terminal. Using computational modeling, we predict that the limited availability of neurotransmitter resources in combination with the spontaneous release of vesicles limits the maximum degree of enhancement of synaptic transmission. This gives rise to an optimal tuning that depends on the number of active zones. There is strong experimental evidence that astrocytes that enwrap synapses can modulate the probabilities of vesicle release through bidirectional signaling and hence regulate synaptic transmission. For low-fidelity hippocampal synapses, which typically have only one or two active zones, the predicted optimal values lie close to those determined by experimentally measured astrocytic feedback, suggesting that astrocytes optimize synaptic transmission of information

Provenance of Chinese Loess: Evidence from Stable Lead Isotope

Twenty-seven samples of typical loess and paleosol strata collected in nine different regions of the Chinese Loess Plateau (CLP) were fractionated into PM(1.0), PM(2.5), PM(10) and Total Suspended Particulates (TSP) (particulate matter with aerodynamic diameters less than 1.0, 2.5, 10 and 30 mu m, respectively) by a resuspension chamber at the Desert Research Institute (DRI; Reno, NV, United States). The amounts and isotope ratios of lead (Pb) were quantified in the loess samples. Our size-segregated analysis demonstrated that the Pb isotopic composition in the loess-paleosol deposits was preserved after grain-size sorting and that therefore the isotope ratio can serve as a proxy for source tracing. A similar pattern of Pb isotope ratios was observed for sediment collected from potential source regions and the loess samples suggested that the Gobi and deserts in southern Mongolia and northern China are major sources for the deposits in the CLP. No significant deviation of Pb isotope amount was found between the nine samples of loess and paleosol strata, implying the stability of loess sources during the glacial and interglacial regime.</p

Characterization of particulate-bound polycyclic aromatic compounds (PACs) and their oxidations in heavy polluted atmosphere: A case study in urban Beijing, China during haze events

Characterizations on polycyclic aromatic compounds (PACs) during frequent haze periods have been conducted in an urban site of Beijing, China. Particulate polycyclic aromatic hydrocarbons (PAHs) and oxygenated-PAHs (OPAHs) and other carbonaceous matters were quantified. The average PM2.5 during haze events (256.3 +/- 103.7 mu g/m(3)) were one magnitude over than that of clear periods (CRs, 24.7 +/- 27.7 mu g/m(3)). The average total quantified PAHs (Sigma PAHs) and OPAHs (Sigma OPAHs) during haze events were 423.9 +/- 178.4 ng/m(3) and 581.4 +/- 299.8 ng/m(3), respectively, which were approximately 10 times higher than those of 40.3 +/- 68.2 ng/m(3) and 54.4 +/- 82.4 ng/m(3) in clear days. Four-rings PAHs had the highest compositions. 1,8-Naphthalic anhydride (1,8-NA) is the most abundant OPAHs, accounted for 49.8% of Sigma OPAHs, followed by 9,10-anthraquinone (9,10-AQ) (13.8%) and benzo(a)anthracene-7,12-dione (BaAQ) (8.31%). In haze events, the contents of 5- to 7-rings PAHs decreased by 2.32% compared with those of clear days, while lower molecular weight fractions of 3- and 4-rings PAHs increased. The relationships between PAHs, OPAHs and relative humidity (RH) were found to be exponential. High oxygenation rate (R-0) ratios of OPAH/PAH represents higher rates in secondary formation or degradation and gas-particle conversion for each PAH or OPAH during the wintertime. Significant positive correlation between BeP and OPAHs (r = 0.97), combined with the results of photochemical aging and negatively correlationwith O-3, suggest that secondary atmospheric reactions of PAHs played an important role in the burden of OPAHs

Real-Time Characterization of Particle-Bound Polycyclic Aromatic Hydrocarbons at a Heavily Trafficked Roadside Site

A continuous photo-electric aerosol sensor (PAS) was used to characterize the particle-bound polycyclic aromatic hydrocarbons (p-PAHs) content at a heavily trafficked roadside site in Hong Kong. The measurements at the roadside station were performed for nine months from January to September 2005. For the total quantified p-PAHs, the PAS output shows good correlations to the data obtained with the offline quartz-fiber aerosol filter collection method. The average concentration of corrected p-PAHs was 5.3 +/- 3.7 ng/m(3), ranging from 0.2 to 22.0 ng/m(3). The p-PAHs concentrations increased in the daytime in accordance with the heavy amount of road traffic, and decreased in the nighttime due to less traffic. Hourly p-PAHs concentrations had high correlation coefficients with all goods vehicles (&gt;0.9) and large buses (similar to 0.8), showing that diesel vehicle emissions are the primary source of p-PAHs. The day-to-day variation of p-PAHs is significant, because it was influenced by various factors (e. g., traffic levels, mixing height, and potential pollution sources).</p