The Influence of Synaptic Weight Distribution on Neuronal Population Dynamics

The manner in which different distributions of synaptic weights onto cortical neurons shape their spiking activity remains open. To characterize a homogeneous neuronal population, we use the master equation for generalized leaky integrate-and-fire neurons with shot-noise synapses. We develop fast semi-analytic numerical methods to solve this equation for either current or conductance synapses, with and without synaptic depression. We show that its solutions match simulations of equivalent neuronal networks better than those of the Fokker-Planck equation and we compute bounds on the network response to non-instantaneous synapses. We apply these methods to study different synaptic weight distributions in feed-forward networks. We characterize the synaptic amplitude distributions using a set of measures, called tail weight numbers, designed to quantify the preponderance of very strong synapses. Even if synaptic amplitude distributions are equated for both the total current and average synaptic weight, distributions with sparse but strong synapses produce higher responses for small inputs, leading to a larger operating range. Furthermore, despite their small number, such synapses enable the network to respond faster and with more stability in the face of external fluctuations.     

Gamma–Radiation-Assisted Synthesis of Luminescent ZnO/Ag Heterostructure Core–Shell Nanocomposites

There is increasing interest in tuning the physical properties of semiconductor nanostructures using metal nanoparticles. In this work, ZnO nanosphere covered with Ag nanoparticles were synthesized using gamma–radiation-assisted method. The amount of deposited Ag nanoparticles is controlled by changing irradiation dose in the range of 30–100 kGy in order to tune the semiconductor–metal interaction. The successful deposition of Ag on the ZnO nanoparticles is examined by analyzing the morphology, microstructure, optical, and magnetic properties of ZnO/Ag nanoparticles through field emission scanning electron (FESEM), microscopy X-ray diffraction spectra, UV-visible absorption, photoluminescence measurement, and vibrating sample magnetometer. FESEM and elemental mapping results confirmed that Ag nanoparticles have been concentrated at the surface of spherical ZnO particles. Moreover, formation of pure metallic Ag nanoparticles has been confirmed by XRD analysis. UV-visible absorption spectra of obtained ZnO/Ag showed two combined peaks, a weak peak at the shoulder around 360 nm corresponds to ZnO and a sharp absorption at 420 nm refers to spherical Ag nanoparticles. Obtained results from photoluminescence revealed that the near-band-edge emission and defect-related visible emission bands of ZnO could be enhanced dramatically at the same time by deposition of Ag nanoparticles, which was ascribed to localized surface plasmon–exciton coupling and surface plasmon scattering. Controlling the semiconductor and metal coupling effect is interesting because of its application in highly efficient optoelectronic devices and biosensor.     

Phyto-assisted synthesis of zinc oxide nanoparticles using Cassia alata and its antibacterial activity against Escherichia coli

Zinc oxide, an established inorganic metal oxide in nanoparticles form exhibits tremendous anti-bacterial activity. The present study focuses on determining the anti-bacterial activity of green synthesized zinc oxide nanoparticles (ZnO NPs). Results clearly validate the effective synthesis of spherical shaped nanoparticles with average size range of 60–80 nm. SEM and EDAX data buttresses the results obtained by XRD pattern in terms of size and purity. ZnO NPs exhibited dose-dependent anti-bacterial activity against Escherichia coli (E. coli) and the IC₅₀ value was calculated to be around 20 μg/mL. Growth kinetics study was conducted in the presence of nanoparticles which demonstrated the bacteriostatic effect of ZnO NPs. The study recommends the potential use of ZnO NPs in industries like food, pharmaceutical, agriculture, cosmetic industries for its anti-bacterial activity.     

DNA methylation provides insight into intergenerational risk for preterm birth in African Americans

African Americans are at increased risk for spontaneous preterm birth (PTB). Though PTB is heritable, genetic studies have not identified variants that account for its intergenerational risk, prompting the hypothesis that epigenetic factors may also contribute. The objective of this study was to evaluate DNA methylation from maternal leukocytes to identify patterns specific to PTB and its intergenerational risk. DNA from peripheral leukocytes from African American women that delivered preterm (24–34 weeks; N = 16) or at term (39–41 weeks; N = 24) was assessed for DNA methylation using the HumanMethylation450 BeadChip. In maternal samples, 17,829 CpG sites associated with PTB, but no CpG site remained associated after correction for multiple comparisons. Examination of paired maternal-fetal samples identified 5,171 CpG sites in which methylation of maternal samples correlated with methylation of her respective fetus (FDR < 0.05). These correlated sites were enriched for association with PTB in maternal leukocytes. The majority of correlated CpG sites could be attributed to one or more genetic variants. They were also significantly more likely to be in genes involved in metabolic, cardiovascular, and immune pathways, suggesting a role for genetic and environmental contributions to PTB risk and chronic disease. The results of this study may provide insight into the factors underlying intergenerational risk for PTB and its consequences.     

Reactive oxygen species and anti-oxidant defenses in tail of tadpoles, Xenopus laevis

Tail regression in tadpoles is one of the most spectacular events in anuran metamorphosis. Reactive oxygen species and oxidative stress play an important role during this process. Presently, the cell- and tissue-specific localization of antioxidant enzymes such as superoxide dismutase (SOD) and catalase as well as neuronal and inducible nitric oxide synthase isoforms (nNOS and iNOS) responsible for production of nitric oxide (NO) were carried out during different stages of metamorphosis in tail of tadpole Xenopus laevis. NO also has profound effect on the mitochondrial function having its own nitric oxide NOS enzyme. Hence, in situ staining for NO and mitochondria also was investigated. The distribution of nNOS and iNOS was found to be stage specific, and the gene expression of nNOS was up-regulated by thyroxin treatment. In situ staining for NO and mitochondria shows co-localization, suggesting mitochondria being one of the sources of NO. SOD and catalase showed significant co-localization during earlier stages of metamorphosis, but before the tail regression begins, there was a significant decrease in activity as well as co-localization suggesting increased ROS accumulation. These findings are discussed in terms of putative functional importance of ROS and cytoplasmic as well as mitochondrial derived NO in programmed cell death in tail tissue.