nNOS(+) striatal neurons, a subpopulation spared in Huntington's Disease, possess functional NMDA receptors but fail to generate mitochondrial ROS in response to an excitotoxic challenge.

Huntington's disease (HD) is a neurodegenerative condition characterized by severe neuronal loss in the cortex and striatum that leads to motor and behavioral deficits. Excitotoxicity is thought to be involved in HD and several studies have indicated that NMDA receptor (NMDAR) overactivation can play a role in the selective neuronal loss found in HD. Interestingly, a small subset of striatal neurons (less than 1% of the overall population) is found to be spared in post-mortem HD brains. These neurons are medium-sized aspiny interneurons that highly express the neuronal isoform of nitric oxide synthase (nNOS). Intriguingly, neurons expressing large amounts of nNOS [hereafter indicated as nNOS(+) neurons] show reduced vulnerability to NMDAR-mediated excitotoxicity. Mechanisms underlying this reduced vulnerability are still largely unknown and may shed some light on pathogenic mechanisms involved in HD. One untested possibility is that nNOS(+) neurons possess fewer or less functioning NMDARs. Employing single cell calcium imaging we challenged this hypothesis and found that cultured striatal nNOS(+) neurons show NMDAR-evoked responses that are identical to the ones observed in the overall population of neurons that express lower levels of nNOS [nNOS(-) neurons]. NMDAR-dependent deregulation of intraneuronal Ca(2+) is known to generate high levels of reactive oxygen species of mitochondrial origin (mt-ROS), a crucial step in the excitotoxic cascade. With confocal imaging and dihydrorhodamine (DHR; a ROS-sensitive probe) we compared mt-ROS levels generated by NMDAR activation in nNOS(+) and (-) cultured striatal neurons. DHR experiments revealed that nNOS(+) neurons failed to produce significant amounts of mt-ROS in response to NMDA exposure, thereby providing a potential mechanism for their reduced vulnerability to excitotoxicity and decreased vulnerability in HD

Evidence for elevated emissions from high-latitude wetlands contributing to high atmospheric CH4 concentration in the early Holocene

The major increase in atmospheric methane (CH4) concentration during the last glacial-interglacial transition provides a useful example for understanding the interactions and feedbacks among Earth\u27s climate, biosphere carbon cycling, and atmospheric chemistry. However, the causes of CH4 doubling during the last deglaciation are still uncertain and debated. Although the ice-core data consistently suggest a dominant contribution from northern high-latitude wetlands in the early Holocene, identifying the actual sources from the ground-based data has been elusive. Here we present data syntheses and a case study from Alaska to demonstrate the importance of northern wetlands in contributing to high atmospheric CH4concentration in the early Holocene. Our data indicate that new peatland formation as well as peat accumulation in northern high-latitude regions increased more than threefold in the early Holocene in response to climate warming and the availability of new habitat as a result of deglaciation. Furthermore, we show that marshes and wet fens that represent early stages of wetland succession were likely more widespread in the early Holocene. These wetlands are associated with high CH4 emissions due to high primary productivity and the presence of emergent plant species that facilitate CH4 transport to the atmosphere. We argue that early wetland succession and rapid peat accumulation and expansion (not simply initiation) contributed to high CH4 emissions from northern regions, potentially contributing to the sharp rise in atmospheric CH4 at the onset of the Holocene

Effects of soil rewetting and thawing on soil gas fluxes: a review of current literature and suggestions for future research

The rewetting of dry soils and the thawing of frozen soils are short-term, transitional phenomena in terms of hydrology and the thermodynamics of soil systems. The impact of these short-term phenomena on larger scale ecosystem fluxes is increasingly recognized, and a growing number of studies show that these events affect fluxes of soil gases such as carbon dioxide (CO<sub>2</sub>), methane (CH<sub>4</sub>), nitrous oxide (N<sub>2</sub>O), ammonia (NH<sub>3</sub>) and nitric oxide (NO). Global climate models predict that future climatic change is likely to alter the frequency and intensity of drying-rewetting events and thawing of frozen soils. These future scenarios highlight the importance of understanding how rewetting and thawing will influence dynamics of these soil gases. This study summarizes findings using a new database containing 338 studies conducted from 1956 to 2011, and highlights open research questions. The database revealed conflicting results following rewetting and thawing in various terrestrial ecosystems and among soil gases, ranging from large increases in fluxes to non-significant changes. Studies reporting lower gas fluxes before rewetting tended to find higher post-rewetting fluxes for CO<sub>2</sub>, N<sub>2</sub>O and NO; in addition, increases in N<sub>2</sub>O flux following thawing were greater in warmer climate regions. We discuss possible mechanisms and controls that regulate flux responses, and recommend that a high temporal resolution of flux measurements is critical to capture rapid changes in gas fluxes after these soil perturbations. Finally, we propose that future studies should investigate the interactions between biological (i.e., microbial community and gas production) and physical (i.e., porosity, diffusivity, dissolution) changes in soil gas fluxes, apply techniques to capture rapid changes (i.e., automated measurements), and explore synergistic experimental and modelling approaches

Dimension Spectra of Lines

This paper investigates the algorithmic dimension spectra of lines in the Euclidean plane. Given any line L with slope a and vertical intercept b, the dimension spectrum sp(L) is the set of all effective Hausdorff dimensions of individual points on L. We draw on Kolmogorov complexity and geometrical arguments to show that if the effective Hausdorff dimension dim(a, b) is equal to the effective packing dimension Dim(a, b), then sp(L) contains a unit interval. We also show that, if the dimension dim(a, b) is at least one, then sp(L) is infinite. Together with previous work, this implies that the dimension spectrum of any line is infinite

Vertical zonation of testate amoebae in the Elatia Mires, northern Greece : palaeoecological evidence for a wetland response to recent climate change or autogenic processes?

The Elatia Mires of northern Greece are unique ecosystems of high conservation value. The mires are climatically marginal and may be sensitive to changing hydroclimate, while northern Greece has experienced a significant increase in aridity since the late twentieth century. To investigate the impact of recent climatic change on the hydrology of the mires, the palaeoecological record was investigated from three near-surface monoliths extracted from two sites. Testate amoebae were analysed as sensitive indicators of hydrology. Results were interpreted using transfer function models to provide quantitative reconstructions of changing water table depth and pH. AMS radiocarbon dates and 210Pb suggest the peats were deposited within the last c. 50 years, but do not allow a secure chronology to be established. Results from all three profiles show a distinct shift towards a more xerophilic community particularly noted by increases in Euglypha species. Transfer function results infer a distinct lowering of water tables in this period. A hydrological response to recent climate change is a tenable hypothesis to explain this change; however other possible explanations include selective test decay, vertical zonation of living amoebae, ombrotrophication and local hydrological change. It is suggested that a peatland response to climatic change is the most probable hypothesis, showing the sensitivity of marginal peatlands to recent climatic change

Social (network) psychology: How networks shape performance, persistence, and access to information

Social psychologists have long been interested in understanding behavior as a function of both individuals and the social structures in which they are embedded. However, since the cognitive revolution of the 1960s, processes internal to individuals have received greater attention than structural influences. This dissertation examines how networks may shape important real-world outcomes beyond intrapsychic phenomena across three studies in varied contexts. In doing so, this work suggests that the networks to which people belong—whether networks of social ties or networks of information—provide both affordances and constraints that affect behavior and outcomes. Chapter I provides a brief introduction to social network analysis as a set of theoretical, methodological, and analytical tools. Chapter II examines the gender gap in negotiation performance. Findings suggest that disparities between male and female MBA students in class social network positions predict this gap more strongly than intrapsychic mechanisms more commonly studied, such as apprehension about negotiating and stereotype threat. Chapter III examines how students’ social networks promote persistence over time in a high-stress science, technology, engineering, and math (STEM) setting. This chapter pulls social network analysis into an experimental context by examining the effects of a randomly assigned social psychological intervention on students’ social networks and subsequent persistence in the biosciences. Chapter IV approaches networks from a different angle, examining how online news media are organized into network structures that may contribute to selective exposure to homogenous information. Finally, Chapter V discusses implications of these three studies. Specifically, I discuss implications for education research, intervention science, and the growing area of social network psychology

Peatland Initiation, Carbon Accumulation, and 2 ka Depth in the James Bay Lowland and Adjacent Regions

Copyright © 2014 University of Colorado at Boulder, Institute of Arctic and Alpine ResearchPeatlands surrounding Hudson and James Bays form the second largest peatland complex in the world and contain major stores of soil carbon (C). This study utilized a transect of eight ombrotrophic peat cores from remote regions of central and northern Ontario to quantify the magnitude and rate of C accumulation since peatland initiation and for the past 2000 calendar years before present (2 ka). These new data were supplemented by 17 millennially resolved chronologies from a literature review covering the Boreal Shield, Hudson Plains, and Taiga Shield bordering Hudson and James Bays. Peatlands initiated in central and northern Ontario by 7.8 ka following deglaciation and isostatic emergence of northern areas to above sea level. Total C accumulated since inception averaged 109.7 ± (std. dev.) 36.2 kg C m–2. Approximately 40% of total soil C has accumulated since 2 ka at an average apparent rate of 20.2 ± 6.9 g C m–2 yr–1. The 2 ka depths correlate significantly and positively with modern gridded climate estimates for mean annual precipitation, mean annual air temperature, growing degree-days > 0 °C, and photosynthetically active radiation integrated over days > 0 °C. There are significantly shallower depths in permafrost peatlands. Vertical peat accumulation was likely constrained by temperature, growing season length, and photosynthetically active radiation over the last 2 ka in the Hudson Bay Lowlands and surrounding regions.US National Science Foundatio

Open-mindedness predicts racial, political, and socioeconomic diversity of real-world friendship networks

This is the accepted version of the article that was published in the journal Group Processes & Intergroup Relations. The full published version may be found at https://doi.org/10.1177/13684302251324887. This version may be used for non-commercial purposes only and may not be altered or transformed.Even in environments offering ample opportunities to interact with people from diverse backgrounds, people differ in their tendency to form intergroup friendships. Whereas some develop intergroup friendships, others prefer befriending ingroup members, contributing to prejudice and polarization. We identify open-mindedness—an inclination to engage with and understand different perspectives—as an individual difference predicting the racial, political, and socioeconomic diversity of real-world friendship networks. In a longitudinal study of 1,423 eighth–ninth graders, more open-minded adolescents developed more racially diverse friendship networks over 2 years. Two additional studies (total N = 1,585 adults) replicated and extended this finding: Open-mindedness predicted greater racial, political, and socioeconomic diversity of friends, and was more consistently associated with friendship diversity than Big Five openness to experience. The associations between open-mindedness and friendship diversity were partly explained by open-minded individuals’ lower avoidance of interaction with outgroup members. Building open-mindedness may be one individual-level approach to promote friendships across divides

TARP γ-7 selectively enhances synaptic expression of calcium-permeable AMPARs

Regulation of calcium-permeable AMPA receptors (CP-AMPARs) is crucial in normal synaptic function and neurological disease states. Although transmembrane AMPAR regulatory proteins (TARPs) such as stargazin (γ-2) modulate the properties of calcium-impermeable AMPARs (CI-AMPARs) and promote their synaptic targeting, the TARP-specific rules governing CP-AMPAR synaptic trafficking remain unclear. We used RNA interference to manipulate AMPAR-subunit and TARP expression in γ-2–lacking stargazer cerebellar granule cells—the classic model of TARP deficiency. We found that TARP γ-7 selectively enhanced the synaptic expression of CP-AMPARs and suppressed CI-AMPARs, identifying a pivotal role of γ-7 in regulating the prevalence of CP-AMPARs. In the absence of associated TARPs, both CP-AMPARs and CI-AMPARs were able to localize to synapses and mediate transmission, although their properties were altered. Our results also establish that TARPed synaptic receptors in granule cells require both γ-2 and γ-7 and reveal an unexpected basis for the loss of AMPAR-mediated transmission in stargazer mice

Carbon budget for 1.5 and 2oC targets lowered by natural wetland and permafrost feedbacks

Methane emissions from natural wetlands and carbon release from permafrost thaw have a positive feedback on climate, yet are not represented in most state-of-the-art climate models. Furthermore, a fraction of the thawed permafrost carbon is released as methane, enhancing the combined feedback strength. We present simulations with an intermediate complexity climate model which follow prescribed global warming pathways to stabilisation at 1.5°C or 2.0°C above pre-industrial levels by the year 2100, and that incorporates a state-of-the-art global land surface model with updated descriptions of wetland and permafrost carbon release. We demonstrate that the climate feedbacks from those two processes are substantial. Specifically, permissible anthropogenic fossil fuel CO2 emission budgets are reduced by 17-23% (47-56 GtC) for stabilisation at 1.5°C, and 9-13% (52-57 GtC) for 2.0°C stabilisation. In our simulations these feedback processes respond faster at temperatures below 1.5°C, and the differences between the 1.5°C and 2°C targets are disproportionately small. This key finding is due to our interest in transient emission pathways to the year 2100 and does not consider the longer term implications of these feedback processes. We conclude that natural feedback processes from wetlands and permafrost must be considered in assessments of transient emission pathways to limit global warming