Receptor-mediated regulation of calcium mobilization and cyclic GMP synthesis in neuroblastoma cells

In neuroblastoma N1E 115 cells, carbachol, histamine and PGE1 elevated cyclic GMP content and, induced the efflux of preloaded 45Ca2+, the release of membrane-bound Ca2+ measured by fluorescent CTC, and the increase in [Ca2+]i as measured by Quin 2 fluorescence. The time course of the responses, the absolute requirement of extracellular Ca2+, the inhibition by receptor blockers, and the concentration dependency on histamine were all similar between these responses. The observation indicates that the mobilization of Ca2+, especially the increase of [Ca2+]i, may be intimately linked to the synthesis of cyclic GMP in the cells.     

Forward mutation assay of V79 cells to 6-thioguanine resistance in a soft agar technique that eliminates effects of metabolic co-operation

A technique involving culture in soft agar was used for the assay of forward mutation of V79 cells to 6-thioguanine (6TG) resistance. The main reason for the use of soft agar was to prevent reduction in recovery of mutants depending on the cell density plated for mutation selection, which is the chief problem in the liquid method, and which results mainly from metabolic co-operation due to cell-to-cell contact.V79 cells grew well in fortified soft agar medium (DMEM + 20% FBS) showing cloning efficiencies (>80%) as high as in liquid culture. Therefore, V79/HGPRT mutagenesis could be assayed quantitatively in soft agar culture.The frequency of 6TG-resistant colonies in agar selective medium increased linearly with increase in concentration of EMS. Toxicity and mutagenic responses were greater in soft agar than in liquid culture.In cultures of untreated and EMS-treated cells, more than 95% of the 6TG-resistant colonies isolated were aminopterin-sensitive.Use of soft agar for selection prevented the reduction in the number of mutants with increase in the size of incula on plating up to 1?2 × 10⁶ cells per 9-cm dish: in liquid culture, even with a lower plating number (2 × 10⁵ cells per 9-cm dish), a notable reduction in numbers of mutants was observed. This character was re-examined in a reconstruction experiment. The results show that, when up to 2 × 10⁶ cells were plated per 9-cm dish, 6TG-resistant cells were almost completely recovered from the soft agar medium, whereas only 10% were recovered from liquid culture.     

Modelling Mediterranean pasture dynamies

Pasture vegetation in an open woodland of Quercus rotundifolia subjected to periodic ploughing was sampled in spring during 8 consecutive years. The frequency of herbaceous species was recorded in a total of 69 permanent plots located on 5 adjacent sites with similar lithology, slope and orientation but differing in age since previous ploughing.Vegetation dynamics expressed as trajectories of permanent plots in a non-metric multidimensional scaling space has been modelled in terms of evironmental variables. By fitting a generalized linear model, the dynamics are shown to be related to years since last ploughing, geographical location of plots, total annual rainfall and November rainfall. Meteorological patterns of the sampling period are also described.Abbreviations GLM = Generalized Linear Model - NMDS = Non-metric Multi-Dimensional Scaling - UPGMA = Unweighted Pair-Group Method using Arithmetic Averages     

Effects of fronto-occipital artificial cranial vault modification on the cranial base and face.

Artificial reshaping of the cranial vault has been practiced by many human groups and provides a natural experiment in which the relationships of neurocranial, cranial base, and facial growth can be investigated. We test the hypothesis that fronto-occipital artificial reshaping of the neurocranial vault results in specific changes in the cranial base and face. Fronto-occipital reshaping results from the application of pads or a cradle board which constrains cranial vault growth, limiting growth between the frontal and occipital and allowing compensatory growth of the parietals in a mediolateral direction. Two skeletal series including both normal and artificially modified crania are analyzed, a prehistoric Peruvian Ancon sample (47 normal, 64 modified crania) and a Songish Indian sample from British Columbia (6 normal, 4 modified). Three-dimensional coordinates of 53 landmarks were measured with a diagraph and used to form 9 finite elements as a prelude to finite element scaling analysis. Finite element scaling was used to compare average normal and modified crania and the results were evaluated for statistical significance using a bootstrap test. Fronto-occipitally reshaped Ancon crania are significantly different from normal in the vault, cranial base, and face. The vault is compressed along an anterior-superior to posterior-inferior axis and expanded along a mediolateral axis in modified individuals. The cranial base is wider and shallower in the modified crania and the face is foreshortened and wider with the anterior orbital rim moving inferior and posterior towards the cranial base. The Songish crania display a different modification of the vault and face, indicating that important differences may exist in the morphological effects of fronto-occipital reshaping from one group to another.     

Two-phase species–time relationships in North American land birds

The species–time relationship (STR) is a macroecological pattern describing the increase in the observed species richness with the length of time censused. Understanding STRs is important for understanding the ecological processes underlying temporal turnover and species richness. However, accurate characterization of the STR has been hampered by the influence of sampling. I analysed STRs for 521 breeding bird survey communities. I used a model of sampling effects to demonstrate that the increase in richness was not due exclusively to sampling. I estimated the time scale at which ecological processes became dominant over sampling effects using a two‐phase model combining a sampling phase and either a power function or logarithmic ecological phase. These two‐phase models performed significantly better than sampling alone and better than simple power and logarithmic functions. Most community dynamics were dominated by ecological processes over scales <5 years. This technique provides an example of a rigorous, quantitative approach to separating sampling from ecological processes.     

Marginality: scale determined processes and the conservation of the British butterfly fauna

Marginality describes the impact that environmental and landscape factors have in decreasing the probability of population survival and persistence. It may be imposed by extreme conditions or resource scarcity. Typically, it affects populations at the range edge but can also affect populations within the core of ranges, and produces a number of symptoms: characteristically demographic, but also morphological, physiological, biochemical and genetic. In this paper, the causes and effects of marginality on British butterflies are compared in edge and centre of range populations. Issues of temporal and spatial scales are examined, as is the relevance of marginality to the conservation of single and multiple species populations. The recognition of marginality questions the appropriateness of many so-called spatially realistic models of populations and highlights areas of research which have hitherto been ignored. Projected changes in land use and climate have implications for marginality in core and peripheral populations; in view of this, current scales of mapping are found to be unsuitable for monitoring fragmentation and the increasing marginalization of butterfly species in the British landscape.     

Stomatal responses to increased CO2: implications from the plant to the global scale

Increased atmospheric CO₂ often but not always leads to large decreases in leaf conductance. Decreased leaf conductance has important implications for a number of components of CO₂ responses, from the plant to the global scale. All of the factors that are sensitive to a change in soil moisture, either amount or timing, may be affected by increased CO₂. The list of potentially sensitive processes includes soil evaporation, run-off, decomposition, and physiological adjustments of plants, as well as factors such as canopy development and the composition of the plant and microbial communities. Experimental evidence concerning ecosystem-scale consequences of the effects of CO₂ on water use is only beginning to accumulate, but the initial indication is that, in water-limited areas, the effects of CO₂-induced changes in leaf conductance are comparable in importance to those of CO,₂-induced changes in photosynthesis. Above the leaf scale, a number of processes interact to modulate the response of canopy or regional evapotran-spiration to increased CO₂. While some components of these processes tend to amplify the sensitivity of evapo-transpiration to altered leaf conductance, the most likely overall pattern is one in which the responses of canopy and regional evapotranspiration are substantially smaller than the responses of canopy conductance. The effects of increased CO₂ on canopy evapotranspiration are likely to be smallest in aerodynamically smooth canopies with high leaf conductances. Under these circumstances, which are largely restricted to agriculture, decreases in evapotranspiration may be only one-fourth as large as decreases in canopy conductance. Decreased canopy conductances over large regions may lead to altered climate, including increased temperature and decreased precipitation. The simulation experiments to date predict small effects globally, but these could be important regionally, especially in combination with radiative (greenhouse) effects of increased CO₂.