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Net ecosystem exchange (NEE) of C varies greatly among Arctic ecosystems. Here, we show that approximately 75 per cent of this variation can be accounted for in a single regression model that predicts NEE as a function of leaf area index (LAI), air temperature and photosynthetically active radiation (PAR). The model was developed in concert with a survey of the light response of NEE in Arctic and subarctic tundras in Alaska, Greenland, Svalbard and Sweden. Model parametrizations based on data collected in one part of the Arctic can be used to predict NEE in other parts of the Arctic with accuracy similar to that of predictions based on data collected in the same site where NEE is predicted. The principal requirement for the dataset is that it should contain a sufficiently wide range of measurements of NEE at both high and low values of LAI, air temperature and PAR, to properly constrain the estimates of model parameters. Canopy N content can also be substituted for leaf area in predicting NEE, with equal or greater accuracy, but substitution of soil temperature for air temperature does not improve predictions. Overall, the results suggest a remarkable convergence in regulation of NEE in diverse ecosystem types throughout the Arctic. [ABSTRACT FROM AUTHOR]

Extreme weather events can have strong negative impacts on species survival and community structure when surpassing lethal thresholds. Extreme, short-lived, winter warming events in the Arctic rapidly melt snow and expose ecosystems to unseasonably warm air (for instance, 2-10 °C for 2-14 days) but upon return to normal winter climate exposes the ecosystem to much colder temperatures due to the loss of insulating snow. Single events have been shown to reduce plant reproduction and increase shoot mortality, but impacts of multiple events are little understood as are the broader impacts on community structure, growth, carbon balance, and nutrient cycling. To address these issues, we simulated week-long extreme winter warming events - using infrared heating lamps and soil warming cables - for 3 consecutive years in a sub-Arctic heathland dominated by the dwarf shrubs Empetrum hermaphroditum, Vaccinium vitis-idaea (both evergreen) and Vaccinium myrtillus (deciduous). During the growing seasons after the second and third winter event, spring bud burst was delayed by up to a week for E. hermaphroditum and V. myrtillus, and berry production reduced by 11-75% and 52-95% for E. hermaphroditum and V. myrtillus, respectively. Greater shoot mortality occurred in E. hermaphroditum (up to 52%), V. vitis-idaea (51%), and V. myrtillus (80%). Root growth was reduced by more than 25% but soil nutrient availability remained unaffected. Gross primary productivity was reduced by more than 50% in the summer following the third simulation. Overall, the extent of damage was considerable, and critically plant responses were opposite in direction to the increased growth seen in long-term summer warming simulations and the 'greening' seen for some arctic regions. Given the Arctic is warming more in winter than summer, and extreme events are predicted to become more frequent, this generates large uncertainty in our current understanding of arctic ecosystem responses to climate change. [ABSTRACT FROM AUTHOR]

In the accompanying paper we describe how MRK-409 unexpectedly produced sedation in man at relatively low levels of GABAA receptor occupancy (∼10%). Since it was not clear whether this sedation was mediated via the α2/α3 or α1 GABAA subtype(s), we characterized the properties of TPA023B, a high-affinity imidazotriazine which, like MRK-409, has partial agonist efficacy at the α2 and α3 subtype but is an antagonist at the α1 subtype, at which MRK-409 has weak partial agonism. TPA023B gave dose- and time-dependent occupancy of rat brain GABAA receptors as measured using an in vivo [3H]flumazenil binding assay, with 50% occupancy corresponding to a respective dose and plasma drug concentration of 0.09 mg/kg and 19 ng/mL, the latter of which was similar to that observed in mice (25 ng/mL) and comparable to values obtained in baboon and man using [11C]flumazenil PET (10 and 5.8 ng/mL, respectively). TPA023B was anxiolytic in rodent and primate (squirrel monkey) models of anxiety (elevated plus maze, fear-potentiated startle, conditioned suppression of drinking, conditioned emotional response) yet had no significant effects in rodent or primate assays of ataxia and/or myorelaxation (rotarod, chain-pulling, lever pressing), up to doses (10 mg/kg) corresponding to occupancy of greater than 99%. In man, TPA023B was well tolerated at a dose (1.5 mg) that produced occupancy of >50%, suggesting that the sedation previously seen with MRK-409 is due to the partial agonist efficacy of that compound at the α1 subtype, and highlighting the importance of antagonist efficacy at this particular GABAA receptor population for avoiding sedation in man. [ABSTRACT FROM PUBLISHER]

MRK-409 binds to α1-, α2-, α3- and α5-containing human recombinant GABAA receptors with comparable high affinity (0.21—0.40 nM). However, MRK-409 has greater agonist efficacy at the α3 compared with α1 subtypes (respective efficacies relative to the full agonist chlordiazepoxide of 0.45 and 0.18). This compound readily penetrates the brain in rats and occupies the benzodiazepine site of GABAA receptors, measured using an in vivo [3H]flumazenil binding assay, with an Occ50 of 2.2 mg/kg p.o. and a corresponding plasma EC50 of 115 ng/mL. Behaviourally, the α3-preferring agonist efficacy profile of MRK-409 produced anxiolytic-like activity in rodent and primate unconditioned and conditioned models of anxiety with minimum effective doses corresponding to occupancies, depending on the particular model, ranging from ∼35% to 65% yet there were minimal overt signs of sedation at occupancies greater than 90%. In humans, however, safety and tolerability studies showed that there was pronounced sedation at a dose of 2 mg, resulting in a maximal tolerated dose of 1 mg. This 2 mg dose corresponded to a Cmax plasma concentration of 28 ng/mL, which, based on the rodent plasma EC50 for occupancy of 115 ng/mL, suggested that sedation in humans occurs at low levels of occupancy. This was confirmed in human positron emission tomography studies, in which [11C]flumazenil uptake following a single dose of 1 mg MRK-409 was comparable to that of placebo, indicating that occupancy of GABAA receptor benzodiazepine binding sites by MRK-409 was below the limits of detection (i.e. <10%). Taken together, these data show that MRK-409 causes sedation in humans at a dose (2 mg) corresponding to levels of occupancy considerably less than those predicted from rodent models to be required for anxiolytic efficacy (∼35—65%). Thus, the preclinical non-sedating anxiolytic profile of MRK-409 did not translate into humans and further development of this compound was halted. [ABSTRACT FROM PUBLISHER]

The article presents information on a study about the changes in the numbers of breeding wader birds on wetlands and farmland in Badenoch and Strathspey, Scotland from 2000 to 2005. The bird species that were studied include lapwings, curlews, snipes, redshanks, and oystercatchers. The study shows that the total number of pairs of these birds declined from 3,381 in 2000 to 2,429 in 2005. The number of oystercatchers increased by 9 percent while redshanks decreased by 25 percent.

1 Arctic landscapes are characterized by extreme vegetation patchiness, often with sharply defined borders between very different vegetation types. This patchiness makes it difficult to predict landscape-level C balance and its change in response to environment. 2 Here we develop a model of net CO2 flux by arctic landscapes that is independent of vegetation composition, using instead a measure of leaf area derived from NDVI (normalized-difference vegetation index). 3 Using the light response of CO2 flux (net ecosystem exchange, NEE) measured in a wide range of vegetation in arctic Alaska and Sweden, we exercise the model using various data subsets for parameter estimation and tests of predictions. 4 Overall, the model consistently explains ~80% of the variance in NEE knowing only the estimated leaf area index (LAI), photosynthetically active photon flux density (PPFD) and air temperature. 5 Model parameters derived from measurements made in one site or vegetation type can be used to predict NEE in other sites or vegetation types with acceptable accuracy and precision. Further improvements in model prediction may come from incorporating an estimate of moss area in addition to LAI, and from using vegetation-specific estimates of LAI. 6 The success of this model at predicting NEE independent of any information on species composition indicates a high level of convergence in canopy structure and function in the arctic landscape. [ABSTRACT FROM AUTHOR]

1 The arctic environment is highly heterogeneous in terms of plant distribution and productivity. If we are to make regional scale predictions of carbon exchange it is necessary to find robust relationships that can simplify this variability. One such potential relationship is that of leaf area to photosynthetic CO2 flux at the canopy scale. 2 In this paper we assess the effectiveness of canopy leaf area in explaining variation in gross primary productivity (GPP): (i) across different vegetation types; (ii) at various stages of leaf development; and (iii) under enhanced nutrient availability. To do this we measure net CO2 flux light response curves with a 1 × 1 m chamber, and calculate GPP at a photosynthetic photon flux density (PPFD) of 600 µmol m−2 s−1. 3 At a subarctic site in Sweden, we report 10-fold variation in GPP among natural vegetation types with leaf area index (LAI) values of 0.05–2.31 m2 m−2. At a site of similar latitude in Alaska we document substantially elevated rates of GPP in fertilized vegetation. 4 We can explain 80% of the observed variation in GPP in natural vegetation (including vegetation measured before deciduous leaf bud burst) by leaf area alone, when leaf area is predicted from measurements of normalized difference vegetation index (NDVI). 5 In fertilized vegetation the relative increase in leaf area between control and fertilized treatments exceeds the relative increase in GPP. This suggests that higher leaf area causes increased self-shading, or that lower leaf nitrogen per unit leaf area causes a reduction in the rate of photosynthesis. 6 The results of this study indicate that canopy leaf area is an excellent predictor of GPP in diverse low arctic tundra, across a wide range of plant functional types. [ABSTRACT FROM AUTHOR]

Inhibitory neurotransmission in the brain is largely mediated by GABAA receptors. Potentiation of GABA receptor activation through an allosteric benzodiazepine (BZ) site produces the sedative, anxiolytic, muscle relaxant, anticonvulsant and cognition-impairing effects of clinically used BZs such as diazepam. We created genetically modified mice (α1 H101R) with a diazepam-insensitive α1 subtype and a selective BZ site ligand, L-838,417, to explore GABAA receptor subtypes mediating specific physiological effects. These two complimentary approaches revealed that the α1 subtype mediated the sedative, but not the anxiolytic effects of benzodiazepines. This finding suggests ways to improve anxiolytics and to develop drugs for other neurological disorders based on their specificity for GABAA receptor subtypes in distinct neuronal circuits. [ABSTRACT FROM AUTHOR]

The current study assesses the relationship between presenting symptomatology of the self-labeled Hispanic popular diagnosis of ataques de nervios and the specific co-morbid psychiatric diagnoses. Hispanic subjects seeking treatment at an anxiety disorders clinic (n = 156) were assessed with a specially designed self-report instrument for both traditional ataque de nervios and panic symptoms, and with structured or semistructured psychiatric interviews for Axis-I disorders. This report focuses on 102 subjects with ataque de nervios who also met criteria for panic disorder, other anxiety disorders, or an affective disorder. Distinct ataque symptom patterns correlated with co-existing panic disorder, affective disorders, or other anxiety disorders. Individuals with both ataque and panic disorder reported the most asphyxia, fear of dying, and increased fear during their ataques. People with ataques who also met criteria for affective disorder reported the most anger, screaming, becoming aggressive, and breaking things during ataques. Ataque positive subjects with other anxiety disorders were less salient for both panic-like and emotional-anger symptoms. The findings suggest that (a) ataque de nervios is a popular label referring to several distinct patterns of loss of emotional control, (b) the type of loss of emotional control is influenced by the associated psychiatric disorder, and (c) ataque symptom patterns may be a useful clinical marker for detecting psychiatric disorders. Further study is needed to examine the relationship between ataque de nervios and psychiatric disorders, as well as the relationship to cultural, demographic, environmental, and personality factors. [ABSTRACT FROM AUTHOR]

One hundred and two Hispanic persons who presented for treatment at a specialized anxiety disorders clinic were evaluated at intake using the Anxiety Disorders Interview Schedule-Revised (ADIS-R; DiNardo and Barlow [1988] Albany: Center for Stress and Anxiety Disorders, State University of New York at Albany). Results indicated that 14% of these patients suffered from anxiety and/or affective disorders that were not adequately captured by our current diagnostic system. Given that the majority of these cases were characterized by predominantly anxious features, further investigation was undertaken to determine the degree of overlap between these patients (anxiety disorder, not otherwise specified; NOS) and those with generalized anxiety disorder (GAD). The two groups differed only with regard to the number of excessive worries they reported and not in terms of somatic symptomatology, psychosocial stressors, or demographic variables. These data suggest that excessive worry may be a discriminating factor between the GAD and NOS groups, providing support for the notion of GAD as a disorder of chromic worry. Future research is needed to tease apart the relative influences of culture and socioeconomic status on our findings. [ABSTRACT FROM AUTHOR]