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Notes: Increasing evidence suggests that neuronal apoptosis is triggered by the inappropriate activation of cyclin-dependent kinases leading to an abortive re-entry of neurons into the cell cycle. Pharmacological inhibitors of cell-cycle progression may therefore have value in the treatment of neurodegenerative diseases in humans. GW8510 is a 3′ substituted indolone that was developed recently as an inhibitor of cyclin-dependent kinase 2 (CDK2). We found that GW8510 inhibits the death of cerebellar granule neurons caused by switching them from high potassium (HK) medium to low potassium (LK) medium. Although GW8510 inhibits CDK2 and other CDKs when tested in in vitro biochemical assays, when used on cultured neurons it only inhibits CDK5, a cytoplasmic CDK that is not associated with cell-cycle progression. Treatment of cultured HEK293T cells with GW8510 does not inhibit cell-cycle progression, consistent with its inability to inhibit mitotic CDKs in intact cells. Neuroprotection by GW8510 is independent of Akt and MEK-ERK signaling. Furthermore, GW8510 does not block the LK-induced activation of Gsk3βand, while inhibiting c-jun phosphorylation, does not inhibit the increase in c-jun expression observed in apoptotic neurons. We also examined the effectiveness of other 3′ substituted indolone compounds to protect against neuronal apoptosis. We found that like GW8510, the VEGF Receptor 2 Kinase Inhibitors [3-(1H-pyrrol-2-ylmethylene)-1,3-dihydroindol-2-one], {(Z)-3-[2,4-Dimethyl-3-(ethoxycarbonyl)pyrrol-5-yl)methylidenyl]indol-2-one} and [(Z)-5-Bromo-3-(4,5,6,6-tetrahydro-1H-indol-2-ylmethylene)-1,3-dihydroindol-2-one], the Src family kinase inhibitor SU6656 and a commercially available inactive structural analog of an RNA-dependent protein kinase inhibitor 5-Chloro-3-(3,5-dichloro-4-hydroxybenzylidene)-1,3-dihydro-indol-2-one, are all neuroprotective when tested on LK-treated neurons. Along with our recent identification of the c-Raf inhibitor GW5074 (also a 3′ substituted indolone) as a neuroprotective compound, our findings identify the 3′ substituted indolone as a core structure for the designing of neuroprotective drugs that may be used to treat neurodegenerative diseases in humans.

Notes: We review major experimental and theoretical studies on microcirculation and hemorheology, focusing on mechanics of blood flow and the vascular wall. We discuss flow of the blood formed elements [red blood cells (RBCs), white blood cells or leukocytes (WBCs) and platelets] in individual arterioles, capillaries, and venules, and in microvascular networks. We also review mechanical and rheological properties of the formed elements and their interactions with the vascular wall. We discuss short-term and long-term regulation of the microvasculature; the modes of regulation include metabolic, myogenic, and shear-stress-dependent mechanisms as well as vascular adaptation such as angiogenesis and vascular remodeling.

Notes: At sites where soil or ground water contains chemicals of concern, there is the potential for chemical vapors to migrate through the subsurface to nearby basements, buildings, and other enclosed spaces. The 1991 Johnson and Ettinger algorithm and subsequent refinements are often used to assess the significance of this pathway and to establish target cleanup levels. To facilitate its use, the U.S. EPA distributes spreadsheets programmed with the 1991 Johnson and Ettinger algorithm. These user-friendly spreadsheets make the equations more accessible; however, the U.S. EPA spreadsheets require a large number of inputs (〉20), and as a result, relationships between model inputs and outputs are not well understood and users are not able to identify and focus on the critical inputs. The U.S. EPA spreadsheets also allow users to inadvertently enter inconsistent and unreasonable sets of input values, and these often lead to unreasonable outputs. The objective of this work, therefore, is to help users develop a better understanding of the relationships between inputs and outputs so that they can identify critical inputs and also to ensure reasonableness of inputs and outputs. The 1991 Johnson and Ettinger algorithm is introduced, and differences between it and its U.S. EPA spreadsheet implementation are identified. Next, results from a parametric analysis of the algorithm are used to create a flowchart-based approach for identifying the application-specific critical inputs. Use of the flowchart-based approach is then illustrated and validated through comparison with the results of a more traditional sensitivity analysis for four scenarios. Recommendations are also given for the reformulation of inputs to minimize misapplication of the algorithm and the spreadsheets, and reasonable ranges for reformulated input values are discussed.

Notes: 1. We examined the contribution of algal cells to periphytic organic carbon and assessed the effects of variable biomass composition on the carbon : phosphorus (C : P) ratio of periphyton. We compiled more than 5000 published and unpublished observations of periphytic carbon : chlorophyll a (C : Chl) ratios, an index of algal prevalence, from a variety of substrata collected from lake and low-salinity coastal habitats. In addition, we converted estimates of algal biovolume into algal C to obtain an independent measure of cellular algal carbon in periphyton. This information was used in a model relating periphyton C : P ratio to algal cellular carbon, the algal C : P ratio, and the C : P ratio of non-algal organic matter in periphyton.2. The mean C : Chl ratio of periphyton (405) was relatively high with values in 〉25% of the samples exceeding 500. On average, 8.4% of total periphyton C was accounted for by C in algal cells. Only 15% of samples were found to have more than 15% periphyton C in cellular algal carbon. Our model showed a nonlinear relationship between periphytic C : P ratios and the C : P ratio of algal cells in the periphyton when non-algal organic matter was present. However, even at relatively low cellular algal C (〈10% of total C), algal C : P ratios can strongly affect the C : P ratio of periphyton as a whole (i.e. algal cells plus other organic matter).3. The high C : Chl ratios and the low biovolume-derived algal C of periphyton samples in our data set indicate that algal cells are typically a minor component of organic carbon in periphyton, However, this minor contribution would not preclude algal cellular stoichiometry from notably influencing periphyton C : P ratios.

Notes: 1. Ecological stoichiometry is a conceptual framework that considers how the balance of energy and elements affects and is affected by organisms in the environment. This perspective has seen recent development primarily in marine and freshwater pelagic ecosystems but its widescale application to freshwater benthic ecosystems remains limited.2. This paper briefly introduces the concept of ecological stoichiometry, its potential application to freshwater benthic ecosystems, and it provides an overview of a series of papers that use a stoichiometric approach to illustrate the utility of this concept for studying a range of central questions about benthic ecosystems.3. Papers in this issue include a detailed description of the elemental composition of stream benthic invertebrates, an analysis of the algal content of and its effects on C : P stoichiometry of periphyton, two reports exploring the stoichiometry of stromatolites and their snail consumers in a stream fed by thermal springs, an examination of the stoichiometric effects on stream periphyton and macroinvertebrates of slight nutrient enrichment resulting from treated sewage effluents, a study of nutrient release ratios and their control from crayfish and snails, a paper addressing the stoichiometric effects on fish and plankton that result from benthic food subsidies to fish, a study of the stoichiometry of tree leaves and litter and floodplain arthropods in the riparian zone of the Rio Grande, and a synthesis examining the current state and future potential of benthic stoichiometry.4. The insights from these and other studies suggest that ecological stoichiometry has great potential to guide scientific thought and resolve long-standing problems in ecology. Increasing use of this stoichiometric perspective should thus lead to a deeper understanding of important ecological processes in freshwater benthic ecosystems.

Notes: 1. Ecological stoichiometry deals with the mass balance of multiple key elements [e.g. carbon (C), nitrogen (N), phosphorus (P)] in ecological systems. This conceptual framework, largely developed in the pelagic zone of lakes, has been successfully applied to topics ranging from population dynamics to biogeochemical cycling. More recently, an explicit stoichiometric approach has also been used in many other environments, including freshwater benthic ecosystems.2. Description of elemental patterns among benthic resources and consumers provides a useful starting point for understanding causes of variation and stoichiometric imbalance in feeding interactions. Although there is considerable overlap among categories, terrestrially-derived resources, such as wood, leaf litter and green leaves have substantially higher C : nutrient ratios than other resources of both terrestrial and aquatic origin, such as periphyton and fine particulate organic matter. The elemental composition of these resources for benthic consumers is modulated by a range of factors and processes, including nutrient availability and ratios, particle size and microbial colonisation.3. Among consumers in benthic systems, bacteria are the most nutrient-rich, followed (in descending order) by fishes, invertebrate predators, invertebrate primary consumers, and fungi. Differences in consumer C : nutrient ratios appear to be related to broad-scale phylogenetic differences which determine body size, growth rate and resource allocation to structural body constituents (e.g. P-rich bone).4. Benthic consumers can influence the stoichiometry of dissolved nutrients and basal resources in multiple ways. Direct consumption alters the stoichiometry of food resources by increasing nutrient availability (e.g. reduced boundary layer thickness on substrata) or through removal of nutrient-rich patches (e.g. selective feeding on fungal patches within leaf litter). In addition, consumers alter the stoichiometry of resources and dissolved nutrient pools through the return of egested or excreted nutrients. In some cases, consumer excretion supplies a large proportion of the nutrients required by algae and heterotrophic microbes and alters elemental ratios of dissolved nutrient pools.5. Organic matter decomposition in benthic systems is accompanied by significant changes in the elemental composition of organic matter. Microbial colonisation of leaf litter influences C : nutrient ratios, and patterns of microbial succession (e.g. fungi followed by bacteria) may be under some degree of stoichiometric control. Large elemental imbalances exist between particulate organic matter and detritivores, which is likely to constrain growth rates and invertebrate secondary production. Such imbalances may therefore select for behavioural and other strategies for dealing with them. Comminution of large particles by benthic consumers alters detrital C : nutrient ratios and can influence the stoichiometry of elemental export from whole catchments.6. A stoichiometric framework is likely to advance understanding of biogeochemical cycling in benthic ecosystems. A set of scenarios is developed that explores the influence of microbial elemental composition on nutrient spiralling parameters in streams, such as uptake length and uptake rate ratios. The presented hypothetical examples identify when the elemental composition of benthic stream organisms is likely to predict nutrient uptake ratios and conditions that would cause benthic stoichiometry and nutrient uptake from the water column to become uncoupled.