Inhibition modifies the effects of slow calcium-activated potassium channels on epileptiform activity in a neuronal network model

Generation of epileptiform activity typically results from a change in the balance between network excitation and inhibition. Experimental evidence indicates that alterations of either synaptic activity or intrinsic membrane properties can produce increased network excitation. The slow Ca²⁺-activated K⁺ currents (sI_AHP) are important modulators of neuronal firing rate and excitability and have important established and potential roles in epileptogenesis. While the effects of changes in sI_AHP on individual neuronal excitability are readily studied and well established, the effects of such changes on network behavior are less well known. The experiments here utilize a defined small network model of multicompartment pyramidal cells and an inhibitory interneuron to study the effects of changes in sI_AHP on network behavior. The benefits of this model system include the ability to observe activity in all cells in a network and the effects of interactions of multiple simultaneous influences. In the model with no inhibitory interneuron, increasing sI_AHP results in progressively decreasing burst activity. Adding an inhibitory interneuron changes the observed effects; at modest inhibitory strengths, increasing sI_AHP in all network neurons actually results in increased network bursting (except at very high values). The duration of the burst activity is influenced by the length of delay in a feedback loop, with longer loops resulting in more prolonged bursting. These observations illustrate that the study of potential antiepileptogenic membrane effects must be extended to realistic networks. Network inhibition can dramatically alter the observations seen in pure excitatory networks.     

Measuring the Surface Roughness of Stream Stones

Measuring the fine-scale heterogeneity of stones and other substrates is a challenge for benthic ecologists. I describe a method for measuring the roughness of stones that is based on the ratio of two surface area measurements: one that follows substrate contours and one based on a similar-sized modified spheroid. This roughness index is easily measured, assesses the entire surface of stones, and enables the measurement of replicate stones. Roughness measurements of 14 rock types demonstrated that values obtained were consistent with perceived roughness and porosity. Application of the roughness index to a published data set produced a curvilinear relationship between stone roughness and the biomass of algae in roughness-associated crevices.     

A spatial analytical approach for selecting reintroduction sites for burbot in English rivers

1. Availability of suitable habitat is a prerequisite for species reintroduction success, and to ensure population persistence, investigations of a species’ habitat utilisation throughout its life history should be conducted as part of a feasibility study. 2. Habitat utilisation models for burbot, Lota lota, developed using data from field studies conducted in France and Germany and information from the literature were used to assess the feasibility of reintroducing burbot into rivers of its former native range in eastern England. 3. Per cent tree roots, aquatic vegetation and flow types were important predictors of adult burbot abundance. Furthermore, the habitat utilisation models were supplemented with information from the literature, which suggested that off‐channel habitat such as wetlands and backwaters is important for spawning and nursery stages. 4. An assessment of the habitat availability in the rivers of the burbot’s former native range using variables related to spawning and nursery and adult life stages showed that although adult habitat was widely distributed, the availability of spawning and nursery habitat was less abundant, potentially limiting successful reestablishment. 5. Potential suitable habitat was concentrated in the central and southern areas of the species’ former English distribution. Overall, rivers of the burbot’s former range potentially afford suitable habitat to sustain a reintroduced population. However, sites should be preferentially selected on the basis of having appropriate spawning and nursery areas.     

Organically modified silica nanoparticles are biocompatible and can be targeted to neurons in vivo

The application of nanotechnology in biological research is beginning to have a major impact leading to the development of new types of tools for human health. One focus of nanobiotechnology is the development of nanoparticle-based formulations for use in drug or gene delivery systems. However most of the nano probes currently in use have varying levels of toxicity in cells or whole organisms and therefore are not suitable for in vivo application or long-term use. Here we test the potential of a novel silica based nanoparticle (organically modified silica, ORMOSIL) in living neurons within a whole organism. We show that feeding ORMOSIL nanoparticles to Drosophila has no effect on viability. ORMOSIL nanoparticles penetrate into living brains, neuronal cell bodies and axonal projections. In the neuronal cell body, nanoparticles are present in the cytoplasm, but not in the nucleus. Strikingly, incorporation of ORMOSIL nanoparticles into the brain did not induce aberrant neuronal death or interfered with normal neuronal processes. Our results in Drosophila indicate that these novel silica based nanoparticles are biocompatible and not toxic to whole organisms, and has potential for the development of long-term applications.     

Does rock chemistry affect periphyton accrual in streams?

Stones of different rock types often accrue different amounts of periphytic algae. Although algal biomass may be positively related to stone roughness, the confounding role of rock chemistry is unclear. This independent effect of rock chemistry on benthic algae was tested using the nutrient-diffusing technique, by incorporating powdered stone, rather than nutrients, into the agar matrix. Rocks tested were sandstone, obsidian, schist, greywacke, pumice, gypsum, limestone, serpentine, and phosphorite. Petri-dishes containing powdered rock and agar, and covered with a permeable cellulose filter, were incubated in eight pools in a granitic stream. Algal biomass did not differ among any of the nine rock types and plain agar control, whereas biomass differed among the concurrently placed nutrient diffusing substrates (the stream was phosphorus-limited). Algal composition was more related to an upstream-downstream gradient (for filamentous algae) and pool-specific effects (deposition of fine sediment for diatoms) than rock chemistry. This minimal effect of rock chemistry may be caused by the low dissolution rate of stones. Handling editor: J. Padisak     

Characterization of the diatom flora in the Lower Mountain Fork (Oklahoma,USA), a novel regulated river with a disjunct population of the diatom Didymosphenia geminata (Bacillariophyta)

Regulated rivers are novel ecosystems with altered temperature and flow regimes that can be used to test distribution patterns of microscopic organisms, such as diatoms. Our objective was to describe the spatial and seasonal patterns of diatoms in a cold-water, oligotrophic river within a region of warm-water, mesotrophic rivers. The Lower Mountain Fork, in south-east Oklahoma (USA), is maintained as a year-around, stocked fishery by the release of cold, hypolimnetic water from Broken Bow Lake and is the southern-most known site of Didymosphenia geminata in North America. Epilithic diatoms were sampled six times at nine sites over a distance of 15.5 km and, within this area, 27 times at the site of the main Didymosphenia bloom. Percentage composition data were analysed for assemblage composition using multivariate analysis, nutrient specificity using a diatom-based metric, and species associations using similarity profiles. Eighty-eight taxa were found, of which 10 were unidentifiable and included local undescribed species and species clusters. Three species [Gomphonema (parvulum morph), Achnanthidium rivulare and Achnanthidium minutissimum] comprised over 60% of the diatom abundance at all sites, and downstream and seasonal patterns were evident for both these and less abundant taxa. Notably, diatom assemblages in the three sites below the dam were similar to that at the lowermost site, below a much smaller dam. The oligotraphentic diatom assemblage reflected the water chemistry of the river. The Didymosphenia bloom had been scoured by a large spate prior to the study and the species was present at two of the nine sites in low numbers but failed to bloom during the study, possibly because of a trend towards increasing phosphorus concentrations in the reservoir (Didymosphenia blooms under low P concentrations). No other species shared Didymosphenia’s distribution pattern over the study reach, highlighting the novelty of Didymosphenia’s presence in the river.     

Long-term platinum retention after treatment with cisplatin and oxaliplatin

Background  

The aim of this study was to evaluate long-term platinum retention in patients treated with cisplatin and oxaliplatin.