The effects of warming by active and passive means on the subsequent responses to cold water immersion

Two experiments were undertaken to investigate the effects of warming the body upon the responses during a subsequent cold water immersion (CWI). In both experiments the subjects, wearing swimming costumes, undertook two 45-min CWIs in water at 15° C. In experiment 1, 12 subjects exercised on a cycle ergometer until their rectal temperatures (T _re) rose by an average of 0.73°C. They were then immediately immersed in the cold water. Before their other CWI they rested seated on a cycle ergometer (control condition). In experiment 2, 16 different subjects were immersed in a hot bath (40° C) until their T _re rose by an average of 0.9° C; they were then immediately immersed in the cold water. Before their other CWI they were immersed in thermoneutral water (35° C; control condition). Heart rate in both experiments and respiratory frequency in experiment 1 were significantly (P < 0.05) higher during the first 30 s of CWI following active warming. In experiment 1, the rate of fall of T _re during the final 15 min of CWI was significantly (P < 0.01) faster when CWI followed active warming (2.46° C · h^–1) compared with the control condition (1.68°C · h^–1). However, this rate was observed when absolute T _re was still above that seen in the control CWIs. It is possible, therefore, that if longer CWIs had been undertaken, the two temperature curves may have converged and thereafter fallen at similar rates; this was the case with the aural temperature (T _au) seen in experiment 1 and the T _au and T _re in experiment 2. It is concluded that pre-warming is neither beneficial nor detrimental to survival prospects during a subsequent CWI.     

Fruiting of ectomycorrhizal basidiomycetes on unburned and prescribed burned hard-pine/hardwood plots after drought-breaking rainfalls on the Allegheny Mountains of southwestern Virginia

A headfire upward along the crest to the peak of a foothill during February 1988 had been prescribed to lower the possibility of a wildfire during the dry season on the Jefferson National Forest. Some surface litter plus annual and perennial stems on one-half of a stand of Pinus pungens/P. rigida had been destroyed. Subsequent development of ectomycorrhizal sporophores of basidiomycetes was recorded regularly within equal areas of burned and unburned portions and within a nearby unburned stand of P. virginiana. Each plot had a few ectomycorrhizal hardwoods, mainly Quercus spp. First fruiting was noted under burned P. pungens 3 weeks after a general rain in mid-July and after 4 weeks under both. By the end of November, when fruiting ceased, 138 separable taxa had been collected of which 95 had been identified. A list of the fungi and data on current and previously reported host associations, occurrence on each of the substrates, times and frequencies of fruiting, periodicity of genera, and variations in weather conditions are presented.     

Hydraulic properties of sphagnum peat moss and tuff (scoria) and their potential effects on water availability

The importance of macrostructure to root growth of ryegrass (L. perenne) seedlings sown on the soil surface was studied in two soils in which the macrostructure had resulted mainly from root growth and macro-faunal activity. Sets of paired soil cores were used, one of each pair undisturbed and the other ground and repacked to the field bulk density. Undisturbed and repacked soils were first compared at equal water potentials in the range −1.9 to −300 kPa. At equal water potential, the undisturbed soil always had the greater strength (penetration resistance), and root growth was always greater in the repacked soil with no macrostructure than it was in the soil with macrostructure intact. At equal high strength (low water potentials) it appeared that root growth was better when soils were structured. When strength was low (high water potentials), root growth was better in the unstructured soil. Soils were then compared during drying cycles over 21 days. The average rate at which roots grew to a depth of 60 mm, and also the final percentage of plants with a root reaching 60 mm depth, was greatest in repacked soils without macrostructure. The species of vegetation growing in the soil before the experiment affected root growth in undisturbed soil; growth was slower where annual grasses and white clover had grown compared with soil which had supported a perennial grass. It appears that relatively few roots locate and grow in the macrostructure. Other roots grow in the matrix, if it is soft enough to be deformed by roots. Roots in the matrix of a structured soil grow more slowly than roots in structureless soil of equal bulk density and water potential. The development of macrostructure in an otherwise structureless soil, of the type studied, is of no advantage to most roots. However, once a macrostructure has developed, the few roots locating suitable macropores are able to grow at low water potential when soil strength is high. The importance of macrostructure to establishing seedlings in the field lies in rapid penetration of at least a few roots to a depth that escapes surface drying during seasonal drought. ei]{gnB E}{fnClothier}     

Annual survival rate and age structure of habu,Trimeresurus flavoviridis (Viperidae), on Minna island,Japan: Estimation from removal trapping

A population of a viperid snake,Trimeresurus flavoviridis, was studied over 10 years by removal trapping on a small subtropical island in Japan. The sex ratio of trapped individuals changed seasonally, but was not biased to either sex in the whole sample of 258 individuals. The age of each individual was estimated through the size structure and the age-size relationship. The minimum number of individuals at the beginning of the study was estimated through accumulating older individuals trapped in the subsequent years. By assuming an annual natural survival rate in the course of this accumulation, an age structure was simulated which led to calculate a resulted natural survival rate. The assumed rate of 0.62 fitted best to the resulted one. The annual trapped proportion estimated on the simulated absolute number of individuals was higher in older individuals than in younger ones with the overall mean of 16%.     

Survival of serotinous seedbanks during bushfires: Comparative studies of Hakea species from southeastern Australia

Abstract The study assessed the survival, during bushfires, of seedbanks of six serotinous Hakea species found in the Sydney region of southeastern Australia. The survival of seeds was examined when fruits were heated in a muffle furnace at ambient temperatures ranging from 200–800°C for 1 min. For each species, fruit weight and dimensions of fruit walls were measured to characterize insulation. A field experiment was performed to examine the survival of the serotinous seedbank of Hakea dactyloides in a bushfire. Ambient and internal fruit temperatures were recorded during the fire. The viability of seeds from fruits exposed to the fire was tested and compared with an unburnt sample. Viability of seeds within fruits exposed in the furnace varied according to species. Seeds of large fruited species such as Hakea constablei and Hakea propinqua survived, whereas those of the small fruited species Hakea teretifolia and H. dactyloides suffered significant mortality. The threshold temperature for death in four species was linearly related to the thickness of lower and lateral fruit walls, and to dry weight of fruits. Internal and external temperatures of fruits decreased with increasing height on experimental H. dactyloides plants in the field. High levels of mortality (relative to the unburnt control) corresponded with fire temperature maxima greater than 400°C (external) and greater than 60°C (internal). In general, these temperatures occur when shrub crowns burn. A high risk of death for H. dactyloides, H. teretifolia and H. sericea seeds will result because fruits of these species have thin walls.     

Evolution of aging: Testing the theory usingDrosophila

Evolutionary explanations of aging (or senescence) fall into two classes. First, organisms might have evolved the optimal life history, in which survival and fertility late in life are sacrificed for the sake of early reproduction or high pre-adult survival. Second, the life history might be depressed below this optimal compromise by the influx of deleterious mutations; since selection against late-acting mutations is weaker, deleterious mutations will impose a greater load on late life. We discuss ways in which these theories might be investigated and distinguished, with reference to experimental work withDrosophila. While genetic correlations between life history traits determine the immediate response to selection, they are hard to measure, and may not reflect the fundamental constraints on life history. Long term selection experiments are more likely to be informative. The third approach of using experimental manipulations suffers from some of the same problems as measures of genetic correlations; however, these two approaches may be fruitful when used together. The experimental results so far suggest that aging inDrosophila has evolved in part as a consequence of selection for an optimal life history, and in part as a result of accumulation of predominantly late-acting deleterious mutations. Quantification of these effects presents a major challenge for the future.     

Sensitivity of Escherichia coli acrA mutants to psoralen plus near-ultraviolet radiation

The sensitivity to psoralen plus near-ultraviolet radiation (PUVA) was compared in a pair of E. coli strains differing at the acrA locus. Survival was determined for both bacteria and phage lambda. AcrA mutant cells were 40 times more sensitive than wild type to the lethal effect of PUVA. Free lambda phage exposed to PUVA survived as well when plated on acrA mutants as on wild type. In contrast, prophage lambda CI857 ind carried in lysogenic acrA strains was hypersensitive to PUVA. The enhanced sensitivity of bacterial and lambda DNA, when inside acrA cells, was paralleled by an increased photobinding of radiolabelled psoralens in the mutant. Binding was increased specifically to DNA rather than to nucleic acids in general. The difference in psoralen-binding ability determined by the acrA gene persisted after permeabilizing treatment of the cells. The results suggest that the acrA mutation causes an alteration specifically in the environment of the cellular DNA so as to allow increased intercalation and photobinding of psoralens.     

Studies on the damage to Escherichia coli cell membrane caused by different rates of freeze-thawing

Freeze-thawing of Escherichia coli cells caused a release of cell membrane components such as protein, phospholipids and lipopolysaccharides. A greater amount of release and a lesser extent of cell survival were seen in slow freeze-thawing than in rapid freeze-thawing. Several dehydrogenases in the cells were also freed. The mode of release was also dependent on the rate of freeze-thawing.The materials released by slow freeze-thawing were found to be mostly composed of outer membrane components, whereas the materials released by rapid freeze-thawing contained cytoplasmic as well as outer membrane components. The chemical composition of these fragments differed significantly from that of the original membranes. The relative content of cytoplasmic membrane-bound enzymes in these fragments also differed from that of the cytoplasmic membrane.The fragmentation was assumed to have resulted mainly from the crystallization of external water. In slow freeze-thawing, it was considered that the phase separation of the membrane phospholipid bilayer increased the possibility of outer membrane fragmentation. Rapid freeze-thawing caused cytoplasmic membrane damage to the cells as well as to the outer membrane. In rapid freeze-thawing, the effect of phase separation appeared to be small because of rapid passage through the transition temperatures.The presence of 10% glycerol completely inhibited the release of cellular materials and enzymes. Cell survival was maintained at a high level in the glycerol-treated samples whether freeze-thawed slowly or rapidly.     

Primary cultures and the levels of cytochromeP450 in hepatocytes from mouse,rat, hamster,and rabbit liver

Summary Hepatocyte primary cultures (HPC) derived from rat, mouse, hamster, and rabbit liver were characterized for a variety of parameters. The conditions that maximized recovery, attachment, and survival varied between species. Hepatocytes from all four species were capable of attaching in serum-free Williams’ medium E (WME), but optimal attachment as monolayer cultures was achieved for mouse and hamster HPC in medium receiving 1% calf serum supplementation. Hamster hepatocytes required additional cations, whereas rabbit and rat hepatocytes displayed maximal attachment in medium supplemented with 10% calf serum. Survival of mouse and rabbit hepatocytes after 24 h in serum supplemented media was in the order of 90%. Rat and hamster hepatocyte 24 h survival was approximately 70 and 60%, respectively, and was not significantly affected by serum supplementation. Hepatocytes from each species varied in their content of cytochromeP450 at the time of isolation and in the rate of reduction during culture. Mouse and rat hepatocytes demonstrated the most rapid decline in content during the initial 24 h in culture, whereas concentrations in rabbit hepatocytes were virtually unchanged. The rate of decline inP450 concentrations in hamster hepatocytes was intermediate between those displayed by rat and rabbit hepatocytes. These studies have delineated conditions useful for the culture of hepatocytes from four species and have documented the status of an important parameter of their functional capability. This study was supported by EPA contract 68-01-6179. C. J. Maslansky was a recipient of a Monsanto Fund Fellowship in Toxicology.     

Nerve Growth Factor: Biological Significance, Measurement and Distribution

NGF proteins probably act as informational molecules transferred from end organs to the neurons of the sympathetic nervous system. The direct demonstration of the NGF content of most end organs requires assays more sensitive than those currently available. The high levels of NGF produced by some organs are probably of some other physiological significance.