Bugs with a backpack: the function of nymphal camouflage in the West African assassin bugs Paredocla andAcanthaspis spp.

The nymphs of the West African assassin bugs Paredocla and Acanthaspis spp. disguise themselves with a cover of dust, sand and soil particles (‘dust coat’) and additionally pile a ‘backpack’ of larger objects, such as empty prey corpses and plant parts, on their abdomen. We investigated the effect of this conspicuous camouflage in interactions of the bugs with ants, their main prey, as well as in encounters with their own predators. Experiments with three ant species showed that the dust coat impedes chemical and tactile recognition of the nymphs by ant workers and thus may serve to increase their hunting success. The backpack appeared to play only a minor role in this context. In arena experiments with three potential predators (spiders, geckos and centipedes), camouflaged nymphs were significantly more likely to survive than denuded bugs. Here the observed effect was mainly attributable to the backpack, which enhanced the concealing effect of the dust coat and confused visually orienting predators. In addition, in the case of an attack, it could be shed to distract the enemy while the bug escaped, thus functioning in a similar manner as a lizard’s tail.     

Air-borne dust and its protein in laboratory animal facilities

Atopic individuals who were exposed to dust in animal rooms for a long time were more likely than non-atopics to have animal-related symptoms. Standard skin prick tests were performed using crude antigens from dander and urine, and 75 to 100% of atopic persons had positive skin reactions. It seems that allergens in animal rooms result from air-borne dust and the dust originates in animal urine and dander. The protein content occurs as dust particles both below and above 10 micron in diameter. The dust particles above 10 micron cannot pass through face masks, so half of the dust protein is arrested under the mask, but smaller particles pass through. In order to minimize the symptoms, we need to improve the design of cages, animal rooms, experimental rooms, ventilation systems and other protective equipment.     

Composition and chirality of amino acids in aerosol/dust from laboratory and residential enclosures

Initial results from the analyses of geological and anthropological samples for amino acids were difficult to accept because of the high enantiomeric purities of the analytes (i.e., predominantly L-amino acids). Consequently, sources of contamination had to be considered. All sources were eliminated except for direct atmospheric contamination. Essentially invisible, microscopic, aerosol/dust was found to rapidly contaminate the surface of samples and sample containers even after brief exposure times in clean laboratories. Contamination increased with exposure time. The aerosol/dust amino acids were contained predominantly in a proteinaceous material. Aerosol/dust from different locations can contain different percentages of proteinoid/amino acid material. However, the relative concentrations of the amino acids were similar for both laboratory and residential samples. The enantiomeric purity of the L-amino acids studied in aerosol/dust appears to be 99% or greater for the samples examined. Thus, even slight contamination of any sample with microscopic dust or aerosol particles can skew the results of trace amino acid analyses and amino acid e.e. determinations.     

Sedimentary records of carbonaceous particles from fossil fuel combustion

Carbonaceous particles produced by fossil fuel combustion can be found in considerable amounts in recent lake sediments. As these particles contain elemental carbon they are resistant to chemical decomposition and therefore both well preserved in sediments and possible to quantify. Sediment samples can be oxidized with H₂O₂ and digested with HF without the particles being destroyed. The pioneers in studying carbonaceous particles in lake sediments in relation to fossil fuel combustion were J. J. Griffin and E. D. Goldberg. They measured elemental carbon concentrations in Lake Michigan sediments, mainly by infrared assay. On the basis of these analyses, size distribution measurements and also morphological studies of single particles they concluded that the carbonaceous particle record reflected the onset of industrial activity and the increased intensities of fossil fuel combustion during the twentieth century. Similar results have been obtained from another lake in the USA by B. K. Kothari and M. Wahlen. We have counted spherical carbonaceous particles (larger than 5–10 µm), which are characteristic for oil and coal burning, in several lake sediments. In Swedish lakes, the annual accumulation of coarse carbonaceous spheres in varved sediments and the concentration stratigraphy in non-varved sediments, follow the same main pattern as statistical data for the Swedish coal and oil combustion over the last two centuries. Coarse carbonaceous spheres in two sediment profiles from Scottish lakes have also been counted. As for the USA and Sweden the sedimentary record was found to reflect the history of fossil fuel combustion.     

Animal-vegetal polarity in the plasma membrane of a molluscan egg: a quantitative freeze-fracture study

Using freeze-fracture electron microscopy, the numerical particle distribution in the fertilized Nassarius egg plasma membrane has been analyzed in four areas at different positions along the animal-vegetal axis of the egg. These areas can be distinguished by distinct microvilli patterns and differences in microvilli densities. In all areas, more IMPs (intramembrane particles) are present on the P face than on the corresponding E face. The ratio of the number of IMPs present on E and P face is similar in all areas (0.48-0.55) except for the most animal part of the vegetal hemisphere, where relatively more IMPs remain attached to the exterior half of the fractured membrane (E/P ratio = 0.88). The IMP density at the vegetal pole of the egg is considerably higher than in the animal hemisphere and in the animal part of the vegetal hemisphere. This difference is due to an increased number of IMPs in all size classes (4-18 nm). In the area adjacent to the vegetal pole the density of particles is also higher than in the two more animal areas, but here the difference is exclusively due to the smaller IMP size classes (4-8 nm). Statistical analysis of our data reveals that the area adjacent to the vegetal pole patch is significantly different from the other areas with respect to the distribution of the IMPs over the different IMP size classes. These results demonstrate the polar organization of the Nassarius egg plasma membrane. The possible role of this surface heterogeneity in the spatial organization of the egg cell and the later embryo is discussed.     

A standard procedure for measuring rodent bedding particle size and dust content

Hardwood dust can cause dermatitis, respiratory disease, allergies and nasal cancer in humans. A major concern with animal hardwood bedding is its dust content and its possible effects on animals and animal technicians. Previous reports on the quality control of rodent bedding did not specify sample size or shake time for measuring bedding particle size and dust content. These variables could alter particle size analyses. In an effort to more accurately characterize bedding particle size and dust content, 50g and 100g samples of hardwood bedding were shaken for 0.5, 1, 2, 3, 4, or 5 minutes in a portable sieve shaker containing U.S. standard sieves (Nos. 8, 20, 30 and 50) to determine optimum sample size and shake time. Significant differences (P less than 0.05 or greater) were observed in the percent of bedding retained on a No. 8 sieve when 50g and 100g samples were taken for 30 seconds or for 1 minute. Samples shaken for 2 or more minutes did not show any statistical differences in the percent of bedding which was retained on or passed through the different sieves. Major differences occurred in the percent of bedding which was retained or passed through the different sieves, when the shake time was varied from 0.5 to 5 minutes. These results indicated that 0.5 or 1 minute was definitely not enough time to accurately measure bedding particle size and dust content and that the sample size and shake time must be consistent in order to accurately compare the particle size and dust content of different shipments of bedding or to compare bedding from different vendors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spatial differentiation in photosynthetic and non-photosynthetic membranes of Rhodopseudomonas palustris.

The cytoplasmic membrane and the photosynthetic intracytoplasmic membranes of Rhodopseudomonas palustris are spatially differentiated into regions of extremely high intramembrane-particle density (4,400 to 9,800/micron 2) and areas of lower intramembrane-particle density (2,700 to 5,900/micron 2). The high intramembrane-particle-density areas were always seen in association with photosynthetic membrane stacks. This differentiation was also seen in those areas of the cytoplasmic membrane which adhere to the underlying intracytoplasmic membranes, implying that the cytoplasmic membrane too is differentiated for photosynthesis in these regions. Changes in intramembrane-particle size distribution in response to changes in light intensity during growth were measured. We found that, as light levels were decreased from 8,500 to 100 lx, the average particle diameter in the protoplasmic face of stacked intracytoplasmic and cytoplasmic membranes increased from 8.6 to 10.3 nm. We also observed a distinct periodicity in the sizes of the intramembrane particles found in the stacked regions--7.5, 10.0, 12.5, and 15.0 nm--with the larger-size peaks becoming more pronounced as light intensity decreased. This suggests that, as light levels decrease, subunits of discrete size are being added to a core particle. A comparison of propane jet-frozen cells versus fixed, glycerinated, and then frozen cells indicated that ultrarapid freezing leads to a higher quality of fine-structure preservation than does chemical fixation followed by glycerination and conventional freezing in Freon-12 or propane. The intramembrane particles appeared to be more regular in size, lacking the deformed or jagged appearance displayed in fixed preparations.     

Comparing the chlorine disinfection of detached biofilm clusters with those of sessile biofilms and planktonic cells in single- and dual-species cultures

Although the detachment of cells from biofilms is of fundamental importance to the dissemination of organisms in both public health and clinical settings, the disinfection efficacies of commonly used biocides on detached biofilm particles have not been investigated. Therefore, the question arises whether cells in detached aggregates can be killed with disinfectant concentrations sufficient to inactivate planktonic cells. Burkholderia cepacia and Pseudomonas aeruginosa were grown in standardized laboratory reactors as single species and in coculture. Cluster size distributions in chemostats and biofilm reactor effluent were measured. Chlorine susceptibility was assessed for planktonic cultures, attached biofilm, and particles and cells detached from the biofilm. Disinfection tolerance generally increased with a higher percentage of larger cell clusters in the chemostat and detached biofilm. Samples with a lower percentage of large clusters were more easily disinfected. Thus, disinfection tolerance depended on the cluster size distribution rather than sample type for chemostat and detached biofilm. Intact biofilms were more tolerant to chlorine independent of species. Homogenization of samples led to significantly increased susceptibility in all biofilm samples as well as detached clusters for single-species B. cepacia, B. cepacia in coculture, and P. aeruginosa in coculture. The disinfection efficacy was also dependent on species composition; coculture was advantageous to the survival of both species when grown as a biofilm or as clusters detached from biofilm but, surprisingly, resulted in a lower disinfection tolerance when they were grown as a mixed planktonic culture.     

Partitioning of Lead in Urban Street Dust Based on the Particle Size Distribution and Chemical Environments

The objective of the present study was to investigate the distribution of lead among the physical fractions and between the various chemical forms of urban street dust. In order to achieve this aim, street dust samples were collected from three major roads with high traffic volume and one minor road with a low traffic density in urban areas of Az Zarqa City, Jordan. The dust samples (N = 6 for each site) were split into two portions. One part was employed for physical size fractionation and the other portion for chemical and physical analyses. A sequential extraction procedure was used to determine Pb associated with various chemical and physical fractions. It was found that about half of the lead was associated with the carbonate fraction and Fe-Mn oxides were ranked second, followed by the exchangeable and organic fractions. A general trend of increasing lead levels with decreasing particle size in street dust was observed. The current study showed that leaded gasoline was the major source for the elevated lead levels in street dust. Therefore, for those countries still employing leaded gasoline, such as Jordan, substantial reductions in lead contamination of street dust and roadside soils could be achieved by prohibiting the use of Pb additives. Consequently, many health benefits could be expected for the entire population and especially for children. The accuracy of lead results was checked by periodic analysis of SRM Soil 7. Observed concentrations were within 5% of certified value in analyzed SRM for lead.     

Freeze-fracture study of rat liver peroxisomes: evidence for an induction of intramembrane particles by agents stimulating peroxisomal proliferation

The membrane ultrastructure of isolated rat liver peroxisomes has been observed by rapid freezing and freeze-fracture techniques. Unidirectional and rotary shadowing allows a clear visualization of the intramembrane particles (IMPs) on both the protoplasmic fracture (PF) leaflet and the endoplasmic fracture (EF) leaflet and reveals an asymmetric distribution of IMPs. Both fracture faces were uniformly studded by IMPs, and the frequency was about seven times higher on the P face (2322 per 1.0 micron2) than on the E face (322 per 1.0 micron2). Administration of the peroxisomal proliferator clofibrate (ethyl-p-chlorophenoxyisobutyrate) induced a marked increase in the frequency of IMPs on both the P face (2.2-fold) and the E face (1.7-fold). The average size decreased (P less than 0.001) from 45.7 +/- 16.5 nm2 to 35.2 +/- 10.8 nm2 on the P face. A similar increase in the frequency of IMPs was observed on the P face (1.8-fold) and the E face (1.8-fold) of peroxisomes from rats fed a semisynthetic diet containing 20% (w/w) of partially hydrogenated fish oil. The average size increased (P less than 0.001) from 36.6 +/- 19.7 to 50.0 +/- 23.5 nm2 on the E face. This study demonstrates alterations both in frequency and size distribution of IMPs in liver peroxisomal membranes on exposure of rats to agents known to induce peroxisomal proliferation. The increase in frequency of IMPs was as expected from the observed increase in one of the major integral membrane polypeptides, with apparent molecular mass of 69 (or 70) kDa, in proliferating rat liver peroxisomes.     

Properties of the inner pore region of TRPV1 channels revealed by block with quaternary ammoniums

The transient receptor potential vanilloid 1 (TRPV1) nonselective cationic channel is a polymodal receptor that activates in response to a wide variety of stimuli. To date, little structural information about this channel is available. Here, we used quaternary ammonium ions (QAs) of different sizes in an effort to gain some insight into the nature and dimensions of the pore of TRPV1. We found that all four QAs used, tetraethylammonium (TEA), tetrapropylammonium (TPrA), tetrabutylammonium, and tetrapentylammonium, block the TRPV1 channel from the intracellular face of the channel in a voltage-dependent manner, and that block by these molecules occurs with different kinetics, with the bigger molecules becoming slower blockers. We also found that TPrA and the larger QAs can only block the channel in the open state, and that they interfere with the channel's activation gate upon closing, which is observed as a slowing of tail current kinetics. TEA does not interfere with the activation gate, indicating that this molecule can reside in its blocking site even when the channel is closed. The dependence of the rate constants on the size of the blocker suggests a size of around 10 Å for the inner pore of TRPV1 channels.     

Distribution of intramembranous particles and filipin-sterol complexes in the spermatid and spermatozoon of Culex quinquefasciatus (Culicidae).

A freeze-fracture study was carried out on spermatid and spermatozoon of the mosquito Culex quinquefasciatus. In the spermatid plasma membrane few and randomly distributed intramembranous particles were observed. In the spermatozoon the density of intramembranous particles was higher on the P- than on the E-fracture face of the plasma membrane. Two populations of particles were observed. Large particles (about 15 nm in diameter) are regularly arranged in double rows as a zipper-line, longitudinally oriented in relation to the main cell axis. These strands of particles were observed in the posterior head region, mainly associated with the E-fracture face. Filipin was used to analyse the presence and distribution of cholesterol in thin sections and freeze-fracture replicas. Filipin-sterol complexes were not homogeneously distributed throughout the spermatozoon plasma membrane. They were more abundant on the P-fracture face of the membrane lining the nuclear region. The results obtained show that Culex spermatozoon differs from those of other species in that its plasma membrane exhibits only a membrane domain, the zipper-line, localized in the postacrosomal region.     

Effect of Temperature on the Distribution of Membrane Particles in Streptococcus faecalis as Seen by the Freeze-Fracture Technique

When cells of Streptococcus faecalis ATCC 9790 were incubated at temperatures above 10 C before being frozen for freeze-fracture, a random distribution of particles was observed on the outer fracture face of the freeze-cleaved cell membrane. However, when cells were incubated below 10 C before freezing, particleless patches were seen on this membrane surface. The size of the patches produced on chilling could be increased by centrifugation or by storing the chilled cells overnight at about 3 C. Patch formation appeared readily reversible, since the medium and large patches that formed on chilling could not be observed in cells warmed for 10 s at 25 C. However, during the transition from the patch to patchless state, smaller patches not seen in the chilled cells were observed. This suggested that the smaller patches might have been intermediate forms produced by the fragmentation of larger patches on warming.     

Membrane structure of nonactivated and activated human blood platelets as revealed by freeze-fracture: evidence for particle redistribution during platelet contraction

The distribution of intramembrane particles of nonactivated and activated human blood platelets was studied by freeze-fracture under various experimental conditions to see whether morphological evidence for a structural coupling between the platelet actomyosin system and the fibrin network in a retracting clot could be established. Membrane particles were evenly distributed in nonactivated platelets; the total number (E + P faces) was approximately 1,500/micrometers 2 of membrane, and there were two to three times more particles present on the E face than on the P face. Transformation of discoid platelets to "spiny spheres" by cooling did not change the particle distribution. Platelet activation and aggregation by serum or ADP caused no change in membrane particle density or distribution. Particle distribution was not changed in Ca2+-activated platelets fixed immediately before fibrin formation, but after fibrin formation and during clot retraction, particles were sometimes most frequent on the P face and tended to form distinct clusters, and aggregates of E face pits were observed. Blood platelets contain contractile proteins that are distinct as filaments in platelets in retracting clots. We suggest that the redistribution of particles seen in activated platelets during clot retraction reflects the esablishment of mechanical transmembrane links between the platelet actomyosin system and the fibrin net. The P-face particle clusters may represent sites of force transmission between actin filaments bonded to the inside of the membrane and the fibrin network at the outside. Thus, whereas membrane particles may not be directly involved in the attachment of actin filaments to membranes, the transmission of the force of the contractile system to an exterior substrate apparently involves the intramembrane particles.     

Identification by microscopically controlled comet assay of peritoneal macrophages in a mixture of peritoneal exudate for DNA strand break analysis

A simple modification of the alkaline comet assay allows the study of DNA damage in a specific cell type in a mixture of primary cells. Peritoneal macrophages from mice are selected from other peritoneal exudate cells without complex preparation and separation steps by their size and shape of the nuclei and their comets. The DNA damage can be well characterised by the manually monitored parameter 'tail length'. Complex measurement of the 'tail moment', often used for characterising DNA damage is not required, a fact which further simplifies the protocol. The distribution of tail length within one sample is symmetric and can be described by a Gaussian distribution and the mean tail length. As a first application, UV-A sensitivity of resident and stimulated macrophages was studied. The resident macrophages were more sensitive to UV-A than the stimulated ones. DNA damage repair follows the same simple monoexponential time course for both cell types. The simplicity of results, i.e., applicability of tail lengths and Gaussian statistics as well as monoexponential kinetics, suggest that microscopically controlled comet assay is well suited to study elementary processes of DNA damage induction and repair.     

Ultrastructural study of cholestasis induced by longterm treatment with estradiol valerate. II. Gap junctional analysis

Treatment of male Wistar rats with estradiol valerate induced alterations in hepatic gap junctions as visualized by the freeze-fracture technique. The alterations involved the spacing, and regularity of packing of the membrane particles of the P face (PF) and complementary pits on the E face (EF), as well as internalization and changes in the number, size and shape of the junctional domains. In approximately 20% of the PF's of the lateral membrane of treated animals the nonjunctional IMPs were aggregated, while the bile canalicular membrane was never involved, maintaining its random distribution of particles. It is proposed that the changes in junctional area and the more general arrangement of the junctional particles may indicate a decrease in coupling between hepatocytes. The invaginations of gap junctions may represent a means for removing gap junctional membrane from the surface or may be an expression of a higher turnover of gap junctions. We assume that the alterations observed here are due to the specific effects of estrogen. This study addresses in detail a number of possible sites of activity and modes of action for estrogen.     

Quantitation of particles in the freeze-fractured nuclear membrane after renal ischemia.

Changes in the number and sizes of membrane-associated particles have been quantitated in the protoplasmic (P) and exoplasmic (E) fracture faces of the outer membrane of nuclei isolated from the inner cortex following renal ischemia and reflow in the rat. No changes were observed in the inner nuclear membrane. After 20-min ischemia, the number of particles in both fracture faces decreased. With reflow, the total number of particles decreased after both 20- and 60-min ischemia. The partition coefficient (Kp = CPF/CEF) increased from 10 to 11 and 17 at 20- and 60-min ischemia then fell below control values to a Kp of 7 after 120 min. After reflow, Kp steadily decreased except after 20-min ischemia followed by 240-min reflow when Kp began to rise. The sizes of particles were predominantly 60 A in the P face of control outer membranes but became larger after ischemia. After 20- and 60-min ischemia with reflow, the size distribution became more normal. The shifts in particle numbers and sizes seem to indicate modifications within the membrane resulting from ischemia.     

Is variation in tail vertebral morphology linked to habitat use in chameleons?

Chameleons (Chamaeleonidae) are known for their arboreal lifestyle, in which they make use of their prehensile tail. Yet, some species have a more terrestrial lifestyle, such as Brookesia and Rieppeleon species, as well as some chameleons of the genera Chamaeleo and Bradypodion. The main goal of this study was to identify the key anatomical features of the tail vertebral morphology associated with prehensile capacity. Both interspecific and intra-individual variation in skeletal tail morphology was investigated. For this, a 3D-shape analysis was performed on vertebral morphology using μCT-images of different species of prehensile and nonprehensile tailed chameleons. A difference in overall tail size and caudal vertebral morphology does exist between prehensile and nonprehensile taxa. Nonprehensile tailed species have a shorter tail with fewer vertebrae, a generally shorter neural spine and shorter transverse processes that are positioned more anteriorly (with respect to the vertebral center). The longer tails of prehensile species have more vertebrae as well as an increased length of the processes, likely providing a greater area for muscle attachment. At the intra-individual level, regional variation is observed with more robust proximal tail vertebrae having longer processes. The distal part has relatively longer vertebrae with shorter processes. Although longer, the small size and high number of the distal vertebrae allows the tail to coil around perches.     

The eyespot of the flagellateTetraselmis cordiformis stein (Chlorophyceae): Structural spezialization of the outer chloroplast membrane and its possible significance in phototaxis of green algae

Summary The eyespot region of the flagellateTetraselmis cordiformis Stein (Chlorophyceae) was investigated with the freeze-fracture technique. The only fracture faces observed in this region were the two complementary fracture faces (PF and EF) of the outer chloroplast envelope membrane. Intramembranous particle numbers on both fracture faces of this membrane were significantly higher in the eyespot region as compared to regions outside the eye-spot. Higher numbers of particles on the PF face in the eyespot region were mainly caused by an increase in particle numbers of the size class 6–8 mm, while on the EF face particle size distribution was not significantly different between eyespot and other regions. Functional implications are discussed and evidence is presented that the outer chloroplast envelope membrane may be the site of photoreceptor location in green algal phototaxis.     

Freeze-fracture and electrophysiological studies of newly developed acetylcholine receptors in Xenopus embryonic muscle cells

The development of acetylcholine receptors on Xenopus embryonic muscle cells both in culture and in situ was studied using electrophysiology and freeze-fracture electron microscopy. Acetylcholine sensitivity first appeared at developmental stage 20 and gradually increased up to about stage 31. Freeze-fracture of muscle cells that were nonsensitive to acetylcholine revealed diffusely distributed small P-face intramembraneous particles. When cells acquired sensitivity to acetylcholine, a different group of diffusely distributed large P-face particles began to appear. This group of particles was analyzed by subtracting the size distribution found on nonsensitive cells from that found on sensitive cells. We call this group of particles difference particles. The sizes of difference particles were large (peak diameter 11 nm). The density of difference particles gradually increased with development. The density of small particles (less than 9 nm) did not change with development. At later stages (32-36) aggregates of large particles appeared, which probably represent acetylcholine receptor clusters. The size distribution of difference particles was close to that of the aggregated particles, suggesting that at least part of difference particles represent diffusely distributed acetylcholine receptors. Difference particles exist mostly in solitary form (occasionally double), indicating that an acetylcholine receptor can be functional in solitary form. This result also shows that diffuse acetylcholine receptors that have previously been observed with 125I- alpha-bungarotoxin autoradiography do indeed exist in solitary forms not as microaggregates.