Transient and cumulative memory impairments induced by GSM 1.8 GHz cell phone signal in a mouse model

This study was designed to investigate the transient and cumulative impairments in spatial and non-spatial memory of C57Bl/6J mice exposed to GSM 1.8 GHz signal for 90 min daily by a typical cellular (mobile) phone at a specific absorption rate value of 0.11 W/kg. Free-moving male mice 2 months old were irradiated in two experimental protocols, lasting for 66 and for 148 days respectively. Each protocol used three groups of animals (n = 8 each for exposed, sham exposed and controls) in combination with two behavioural paradigms, the object recognition task and the object location task sequentially applied at different time points. One-way analysis of variance revealed statistically significant impairments of both types of memory gradually accumulating, with more pronounced effects on the spatial memory. The impairments persisted even 2 weeks after interruption of the 8 weeks daily exposure, whereas the memory of mice as detected by both tasks showed a full recovery approximately 1 month later. Intermittent every other day exposure for 1 month had no effect on both types of memory. The data suggest that visual information processing mechanisms in hippocampus, perirhinal and entorhinal cortex are gradually malfunctioning upon long-term daily exposure, a phenotype that persists for at least 2 weeks after interruption of radiation, returning to normal memory performance levels 4 weeks later. It is postulated that cellular repair mechanisms are operating to eliminate the memory affecting molecules. The overall contribution of several possible mechanisms to the observed cumulative and transient impairments in spatial and non-spatial memory is discussed.     

Metacommunities of spiders in grassland habitat fragments of an agricultural landscape

Arthropod communities in fragmented agricultural landscapes depend on local processes and the interactions between communities in the habitat islands. We aimed to study metacommunity structure of spiders, a group that is known for high dispersal power, local niche partitioning and for engaging in species interactions. While living in fragmented habitats could lead to nestedness, other ecological traits of spiders might equally lead to patterns dominated either by species interactions or habitat filtering. We asked, which community pattern will prevail in a typical agricultural landscape with isolated patches of semi-natural habitats. Such a situation was studied by sampling spiders in 28 grassland locations in a Hungarian agricultural landscape. We used the elements of metacommunity structure (EMS) framework to distinguish between alternative patterns that reveal community organization. The EMS analysis indicated coherent species ranges, high turnover and boundary clumping, suggesting Clementsian community organization. The greatest variation in species composition was explained by local habitat characteristics, indicating habitat filtering. The influence of dispersal could be detected by the significant effect of landscape composition, which was strongest at 500 m. We conclude that dispersal allows spiders to respond coherently to the environment, creating similar communities in similar habitats. Consistent habitat differences, such as species rich versus species poor vegetation, lead to recognisably different, recurrent communities. These characteristics make spiders a predictable and diverse source of natural enemies in agricultural landscapes. Sensitivity to habitat composition at medium distances warns us that landscape homogenization may alter these metacommunity processes.     

A new algorithm quantifies the roles of wind and midge flight activity in the bluetongue epizootic in northwest Europe

The 2006 bluetongue (BT) outbreak in northwestern Europe had devastating effects on cattle and sheep in that intensively farmed area. The role of wind in disease spread, through its effect on Culicoides dispersal, is still uncertain, and remains unquantified. We examine here the relationship between farm-level infection dates and wind speed and direction within the framework of a novel model involving both mechanistic and stochastic steps. We consider wind as both a carrier of host semio-chemicals, to which midges might respond by upwind flight, and as a transporter of the midges themselves, in a more or less downwind direction. For completeness, we also consider midge movement independent of wind and various combinations of upwind, downwind and random movements. Using stochastic simulation, we are able to explain infection onset at 94 per cent of the 2025 affected farms. We conclude that 54 per cent of outbreaks occurred through (presumably midge) movement of infections over distances of no more than 5 km, 92 per cent over distances of no more than 31 km and only 2 per cent over any greater distances. The modal value for all infections combined is less than 1 km. Our analysis suggests that previous claims for a higher frequency of long-distance infections are unfounded. We suggest that many apparent long-distance infections resulted from sequences of shorter-range infections; a 'stepping stone' effect. Our analysis also found that downwind movement (the only sort so far considered in explanations of BT epidemics) is responsible for only 39 per cent of all infections, and highlights the effective contribution to disease spread of upwind midge movement, which accounted for 38 per cent of all infections. The importance of midge flight speed is also investigated. Within the same model framework, lower midge active flight speed (of 0.13 rather than 0.5 m s(-1)) reduced virtually to zero the role of upwind movement, mainly because modelled wind speeds in the area concerned were usually greater than such flight speed. Our analysis, therefore, highlights the need to improve our knowledge of midge flight speed in field situations, which is still very poorly understood. Finally, the model returned an intrinsic incubation period of 8 days, in accordance with the values reported in the literature. We argue that better understanding of the movement of infected insect vectors is an important ingredient in the management of future outbreaks of BT in Europe, and other devastating vector-borne diseases elsewhere.     

字母位置对左右视野的识别影响

目的:考查左右视野中不同位置字母的辨别力。方法:采用探测刺激的方法对左右视野中字母位置的识别差异进行了研究。结果:通过SPSS15.0进行重复测量方差分析得出:①不同视野的错误率主效应显著(F=5.98,P<0.05);②探测位置的主效应非常显著(F=15.39,P<0.01);③不同视野与探测字母位置的交互作用非常显著(F=11.60,P<0.001)。结论:①位置错误多于字母错误,并且位置错误中所报告的字母更靠近中央凹。②左视野中的首字母有较差的辨别力,而右视野中的尾字母有较差的辨别力。③左视野中存在知觉系统的限制,而不是词汇识别策略中大脑左右半球的差异。④对词汇识别中大脑左半球平行加工、右半球系列加工的说法提出了质疑。     

The response of herbaceous-layer vegetation to anthropogenic disturbance in intermittent stream bottomland forests of southern Indiana,USA

Between 1993 and 1995 we sampled herbaceous layer vegetation on 84 plots in Platanus/Asarum Wet-Mesic Bottomland forests to determine how these forests have responded to human disturbance. Four different disturbance types were sampled (abandoned agricultural are as, clearcuts, group-selection openings, and single-tree selection openings), and uncut 80–100 year-old reference stands were sampled for comparison. Detrended Correspondence Analysis (DCA), distance analyses (chord distance and normalized Euclidean distance) and similarity analysis (Bray-Curtis similarity coefficient) suggest that agricultural use has shifted herbaceous-layer vegetation composition away from that typical of the reference forests, but that clearcutting, group-selection harvest, and single-tree selection harvest have not greatly shifted herbaceous composition. This shift in vegetation on abandoned agricultural land resulted from a loss of indicator species, such as Cardamine concatenata (Michx.) Sw., Stellaria pubera Michx., and Laportea canadensis (L.) Weddell and an influx of disturbance, exotic, and nonforest species (e.g., Lycopodium complanatum L., Lonicera japonica Thunb. and Senecio aureus L.). However, only two species found in reference stands, Erigenia bulbosa (Michx.) Nutt. and Sphenopholis obtusata (Michx.) Scribn., were missing from clearcuts, group-selection openings, and single-tree selection openings. The species richness values of abandoned agriculture, clearcut, and group-selection plots were generally greater than those of single-tree selection and reference plots. Abandoned agricultural areas had much greater total species richness because of the influx of dry-site, exotic, disturbance, and non-forest species.     

Ontogenetic shifts in competitive interactions and intra-guild predation between two wolf spider species

Abstract. 1. The wolf spiders (Araneae: Lycosidae) Hogna helluo (Walckenaer) and Pardosa milvina Hentz co-occur in soybean fields of south-west Ohio, U.S.A. As adults, Hogna is the larger species and has the competitive advantage in most interactions; due to differing phenologies, however, their size-classes frequently overlap and as such there is potential for shifts in competitive ability and intra-guild predation. The hypothesis that competitive interactions and intra-guild predation will favour Pardosa when Pardosa is similar-sized, or has a size advantage over Hogna , was tested in laboratory and field experiments.
2. Studies in laboratory arenas, pairing similar-sized individuals of these species and Hogna spiderlings with larger spiders of both species, revealed that intra-guild predation seldom occurs with similar-sized Hogna and Pardosa , however Pardosa will consume small Hogna individuals in laboratory arenas.
3. Field experiments involved stocking high densities (50 m^{– 2} ) of Pardosa and Hogna in enclosures placed in soybean fields. In experiments with spiders of similar size, no interspecific effects were uncovered, but an intraspecific effect was found for Pardosa as its survival and weight gain were lower in the presence of more conspecifics. Large Hogna or Pardosa had no effect on the survival or weight gain of Hogna spiderlings.
4. Although Hogna is a better competitor as an adult, it has no advantage over Pardosa when their size-classes overlap, and Pardosa effects on Hogna may be inconsequential under field conditions. Therefore, the co-existence of these species is fostered by the fact that there are few negative interspecific interactions during their ontogeny.     

Determination of asparagine and glutamine in polypeptides using bis(I,I-trifluoroacetoxy)iodobenzene

A simple yet accurate method is described by which the numbers of asparagine and glutamine residues in polypeptides can be determined. The method involves difference analysis of the aspartic acid and glutamic acid contents of the polypeptide after acid hydrolysis (in 6 n HCl), without and with prior treatment of the sample with bis(I,I-trifluoroacetoxy)iodobenzene. Under the conditions described, this reagent quantitatively converts the carboxamide residues to the corresponding amines, which are eluted near (and interfere with the estimation of) the lysine peak on conventional ion-exchange amino acid analysis. During the carboxamide conversion, certain amino acid residues sensitive to oxidation are partially or completely destroyed and cannot be accurately determined.     

Variability between species in K/Ca ratios of successional plants

Summary The K/Ca ratios of six dominant perennial herbs on two abandoned agricultural fields in souther Ontario, Canada, were determined for June and September. Differential uptake of potassium and calcium conformed to root cation exchange theory, suggesting at least one possible mechanism influencing interspecific variability in mineral element composition of successional plants. K/Ca ratios were generally lowest for the legume, highest for the three gramineous species, and intermediate for the two dicotyledonous forbs.     

Formulas for preparing phantom muscle tissue at various radiofrequencies

The dielectric properties of various test samples of phantom tissue were measured using an automated and temperature-controlled slotted line. The ingredients for phantom materials were determined for simulating high-water content tissue at 13.56, 27.12, 40.68, 70, 100, 200, 300, 433, 750, 915, and 2,450 MHz. The ingredients consisted of water, TX-150 (a gelling agent), sodium chloride, and polyethylene powder (200-2,450 MHz) or aluminum powder (13.56-100 MHz). The dielectric constant and conductivity of these materials at different temperatures (15, 22, 30 degrees C) were characterized.     

Behavioral monitoring of rats during exposure to air ions and DC electric fields

Air ions and direct current (DC) electric fields have been reported to exert subtle behavioral and biological effects on rodents and humans. These effects often appear inconsistent, yet there have been few attempts to resolve these inconsistencies by experimental replication. Rats exposed to negatively or positively charged air ions over a wide range of concentrations and exposure periods have been reported to show alterations in their level of locomotor activity. In this study, locomotor activity of Sprague-Dawley rats was quantified during exposure to either unipolar air ions and DC fields of the same polarity or DC fields alone. Both polarities were studied. Air ion concentrations were 5.0 X 10(3), DC fields were 3 kV/m, and exposures lasted 2, 18, or 66 h. In one experiment rats were exposed to DC fields of 12 kV/m. No exposure condition exerted any effect on locomotor activity or rearing behavior. In addition, no behavioral perturbations were observed after the onset of any of the exposure conditions, suggesting that the rats may have failed to detect the altered environment.