RecruitNet: A global database of plant recruitment networks

Plant recruitment interactions (i.e., what recruits under what) shape the composition, diversity, and structure of plant communities. Despite the huge body of knowledge on the mechanisms underlying recruitment interactions among species, we still know little about the structure of the recruitment networks emerging in ecological communities. Modeling and analyzing the community-level structure of plant recruitment interactions as a complex network can provide relevant information on ecological and evolutionary processes acting both at the species and ecosystem levels. We report a data set containing 143 plant recruitment networks in 23 countries across five continents, including temperate and tropical ecosystems. Each network identifies the species under which another species recruits. All networks report the number of recruits (i.e., individuals) per species. The data set includes >850,000 recruiting individuals involved in 118,411 paired interactions among 3318 vascular plant species across the globe. The cover of canopy species and open ground is also provided. Three sampling protocols were used: (1) The Recruitment Network (RN) protocol (106 networks) focuses on interactions among established plants ("canopy species") and plants in their early stages of recruitment ("recruit species"). A series of plots was delimited within a locality, and all the individuals recruiting and their canopy species were identified; (2) The paired Canopy-Open (pCO) protocol (26 networks) consists in locating a potential canopy plant and identifying recruiting individuals under the canopy and in a nearby open space of the same area; (3) The Georeferenced plot (GP) protocol (11 networks) consists in using information from georeferenced individual plants in large plots to infer canopy-recruit interactions. Some networks incorporate data for both herbs and woody species, whereas others focus exclusively on woody species. The location of each study site, geographical coordinates, country, locality, responsible author, sampling dates, sampling method, and life habits of both canopy and recruit species are provided. This database will allow researchers to test ecological, biogeographical, and evolutionary hypotheses related to plant recruitment interactions. There are no copyright restrictions on the data set; please cite this data paper when using these data in publications.

Extensive pollen-mediated gene flow across intensively managed landscapes in an insect-pollinated shrub native to semiarid habitats

Our knowledge of the impact of landscape fragmentation on gene flow patterns is mainly drawn from tropical and temperate ecosystems, where landscape features, such as the distance of a tree to the forest edge, drive connectivity and mating patterns. Yet, the structure of arid and semiarid plant communities - with open canopies and a scattered distribution of trees - differs greatly from those that are well-characterized in the literature. As a result, we ignore whether the documented consequences of landscape fragmentation on plant mating and gene flow patterns also hold for native plant communities in arid and semiarid regions. We investigated the relative contribution of plant traits, pollinator activity, and individual neighbourhood in explaining variation in mating and gene flow patterns of an insect-pollinated semiarid arborescent shrub, Ziziphus lotus, at three sites embedded in highly altered agriculture landscapes. We used 14 SSRs, seed paternity analyses, and individual mixed effect mating models (MEMMi) to estimate the individual mating variables and the pollen dispersal kernel at each site. Individual spatial location, flower density, and floral visitation rate explained most of the variation of mating variables. Unexpectedly, individual correlated paternity was very low and shrubs surrounded by the most degraded matrix exhibited an increased fraction of pollen immigration and a high effective number of pollen donors per mother shrub. Overall, our results reveal that an active pollinator assemblage ensures highly efficient mating, and maintains pollen-mediated gene flow and notable connectivity levels, even in highly altered landscapes, potentially halting genetic isolation within and between distant sites.

TRY plant trait database - enhanced coverage and open access

Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives.

Regeneration of a keystone semiarid shrub over its range in Spain: habitat degradation overrides the positive effects of plant-animal mutualisms

Global change drivers are currently affecting semiarid ecosystems. Because these ecosystems differ from others in biotic and abiotic filters, cues for plant regeneration and management derived from elsewhere may not be applicable to semiarid ecosystems. We sought to determine the extent to which regional variation in regeneration prospects of a long-lived semiarid keystone shrub depends on anthropogenic habitat degradation, plant-animal interactions and climate determinants. We investigated the regeneration ability (via population size structure, juvenile density and juvenile/adult ratio), fruit set and seed dispersal of Ziziphus lotus in 25 localities spanning the range of its threatened habitats in Spain. We dissected the relative contribution of different regeneration determinants using multiple regression and structural equation modelling. Population regeneration was extremely poor, and size structures were biased towards large classes and low juvenile densities and juvenile/adult ratios. Poor regeneration was often coincident with seed dispersal collapse. However, the positive effect of seed dispersal on population regeneration disappeared after considering its relationship with habitat degradation. Protected areas did have juveniles. Together, these data suggest that habitat degradation directly impacts juvenile establishment. Our results provide insights into habitat and species management at the regional level. Z. lotus populations are currently driven by persistence-based dynamics through the longevity of the species. Nonetheless, collapsed seed dispersal, poor regeneration and the removal of adults from their habitats forecast extinction of Z. lotus in many remnants. The extreme longevity of Z. lotus provides opportunities for recovery of its populations and habitats through effective enforcement of regulations.

Dropping out of a transdiagnostic online intervention: A qualitative analysis of client's experiences

INTRODUCTION

An important concern in Internet-based treatments (IBTs) for emotional disorders is the high dropout rate from these protocols. Although dropout rates are usually reported in research studies, very few studies qualitatively explore the experiences of patients who drop out of IBTs. Examining the experiences of these clients may help to find ways to tackle this problem.

METHOD

A Consensual Qualitative Research study was applied in 10 intentionally-selected patients who dropped out of a transdiagnostic IBT.

RESULTS

22 categories were identified within 6 domains. Among the clients an undeniable pattern arose regarding the insufficient support due to the absence of a therapist and the lack of specificity of the contents to their own problems.

CONCLUSIONS

The analyzed content has direct impact on the clinical application of IBTs. A more tailored manage of expectations as well as strategies to enhance the therapeutic relationship in certain clients are identified as the two key elements in order to improve the dropout in IBTs. Going further, in the mid and long run, ideographic interventions would be vital. The present study permits to better grasp the phenomenon of dropout in IBTs and delineate specific implications both in terms of research, training and practice.

Development and characterization of microsatellite primers in the endangered Mediterranean shrub Ziziphus lotus (Rhamnaceae)

PREMISE OF THE STUDY

Microsatellite primers were developed to characterize and evaluate patterns of genetic diversity and structure in the endangered Mediterranean shrub Ziziphus lotus (Rhamnaceae).

METHODS AND RESULTS

Twenty microsatellite primers were developed for Z. lotus, of which 14 were polymorphic. We evaluated microsatellite polymorphism in 97 specimens from 18 Spanish and seven Moroccan populations. Between two and eight alleles were found per locus, and the average number of alleles was 5.54. Observed heterozygosity and expected heterozygosity ranged from 0.08 to 0.90 and from 0.08 to 0.82, respectively. Nine of these primers also amplified microsatellite loci in Z. jujuba.

CONCLUSIONS

The microsatellite markers described here will be useful in studies on genetic variation, population genetic structure, and gene flow in the fragmented habitat of this species. These markers are a valuable resource for designing appropriate conservation measures for the species in the Mediterranean range.

Cytoskeleton disruption in chondrocytes from a rat osteoarthrosic (OA) -induced model: its potential role in OA pathogenesis

Morphological and functional changes of chondrocytes are typical in OA cartilage. In this work, we have described noteworthy changes in intermediate filaments cytoskeleton evidenced by transmission electron microscopy. Alterations in the distribution as well as in the content of vimentin, actin, and tubulin have been described by specific fluorescence labelling of each cytoskeletal component and confocal analysis. Normal vs OA cartilages showed a reduction in the percentage of labelled chondrocytes of 37.1% for vimentin, 4.7% for actin, and 20.1% for tubulin. Statistical analysis of fluorescence intensities (mean % +/- SEM) between normal and OA rat cartilage revealed a highly significant difference in vimentin, a significant difference in tubulin, and a non-significant difference in actin. Moreover, by western blot, altered electrophoretic patterns were observed mainly for vimentin and tubulin in OA cartilage in comparison with normal cartilage. These results allow us to suggest that substantial changes in vimentin and tubulin cytoskeleton of chondrocytes might be involved in OA pathogenesis.

Surface properties and in vitro cytopathic effect of various strains of Trichomonas vaginalis

The in vitro cytopathic effect of four strains of Trichomonas vaginalis on cultured epithelial monolayers was analyzed through electrophysiology and electron microscopy. Interaction of trichomonads of two virulent strains (GT-10 and GT-13) with cultured MDCK cell monolayers mounted in Ussing chambers produced a rapid decrease in transepithelial resistance to less than 30% of control values after only 15 min. By 30 min the electrical resistance was practically abolished by the virulent parasites. In contrast, of two attenuated strains of trichomonads (GT-3 and GT-7) analyzed under similar conditions, GT-3 trophozoites required 180 min to reduce transepithelial resistance to 9% of control values, while monolayers in contact with GT-7 parasites still showed 28% of control values at this time of incubation. Sequential scanning electron microscopy confirmed the much faster and widespread cytopathic effect of virulent parasites. In contrast, the slow lytic process produced by attenuated trophozoites was reduced to focal areas of direct contact with epithelial cells. Another difference was found by measurement of the surface charge of the four strains of T. vaginalis by means of cell microelectrophoresis. While the two virulent strains showed a negative surface charge, the two attenuated strains had no detectable surface charge at neutral pH. When parasites were incubated with cationized ferritin and studied with transmission electron microscopy the surface of virulent trichomonads appeared heavily labeled, whereas the surface of attenuated parasites had only sparse and irregular ferritin binding.

Ultrastructural study of Entamoeba invadens encystation and excystation

In the life cycle of Entamoeba species, the cyst and all the processes associated to it have been poorly studied. Entamoeba invadens, a serpent's parasite, has been commonly accepted as a model for the study of encystation and excystation. Here we analyzed through scanning and transmission electron microscopy the in vitro morphological differentiation of both processes. During encystation, the formation of an irregular net of fibrillar material on the surface of precysts was observed. In thin sections of cryofixed and cryosubstituted specimens, abundant vacuoles containing a microfibrillar material of similar appearance to the structural components of the cyst wall were found in the cytoplasm. Assays with a calcofluor probe on cryosections of encysting trophozoites and precysts showed the presence of fluorescent circular cytoplasmic structures. In the cyst stage, the fluorescence was located on the surface. During excystation, the detachment of the metacyst from the cyst wall was observed through scanning electron microscopy. Metacysts endocyting amorphous material which may correspond to cyst wall residues were commonly found. By transmission electron microscopy the formation of a crescent-shaped space between the plasma membrane and the cyst wall was observed. Abundant small electrondense bodies were found in the cytoplasm. Many of them were in close apposition to the plasma membrane and frequently some of them were seen projecting towards this newly formed space. Our results suggest that the microfibrillar content of the vacuoles corresponds to the cyst wall material, that the electrondense bodies may be involved in the excystation process, and that part of the cyst wall residues may be endocyted by the parasite.

Ultrastructural cytochemical observations of the cell coat of two Trichomonas vaginalis isolates with different degree of virulence

The cell coat of two Trichomonas vaginalis isolates with different degree of virulence isolated in Mexico from symptomatic women was studied by cytochemical assays. The use of carbohydrate cell surface markers allowed us to visualize greater electron-dense deposits in the highly virulent T. vaginalis isolate than in the less virulent one. On the contrary, parasites treated with concanavalin A showed a heavy uniform electron-dense deposit on the cell surface that was similar in both isolates. When parasites were treated with cationized ferritin the amount of bounded particles on the cell surface was greater in the higher virulent isolate.

Acanthamoeba castellanii: ultrastructure of trophozoites using fast freeze-fixation followed by freeze-substitution

In recent years, the use of fast-freeze fixation followed by freeze-substitution has been shown to be the procedure that best satisfies the ultrastructural preservation of cellular components due to the rapidity of the fixation procedure and the reduction of artifacts compared to chemical fixation. When these techniques were used to study the fine structure of axenically cultured trophozoites of Acantamoeba castellanii, an improved preservation of the whole cell was observed. The ground substance of the cytoplasm is densely packed with fibrogranular material which is frequently removed with the use of conventional techniques. Also, the ultrarapid physical stabilization allows the visualization of fusion and fission processes of cytoplasmic vacuoles and vesicles. The nuclear structure and cytoplasmic microfilaments as well as membranous structures were clearly identified. Low temperature techniques combine the advantage of fast-freeze fixation for the physical stabilization of organic molecules and their stabilization by the substitution medium at low temperature giving rise not only to a better preservation of the cell ultrastructure but providing a favorable basis for immunocytochemistry at the electron microscopy level.

Entamoeba histolytica : a novel cysteine protease and an adhesin form the 112 kDa surface protein

Here, we present evidence that a cysteine protease (EhCP112) and a protein with an adherence domain (EhADH112) form the Entamoeba histolytica 112 kDa adhesin. Immunoelectron microscopy and immunofluorescence assays using monoclonal antibodies (mAbAdh) revealed that, during phagocytosis, the adhesin is translocated from the plasma membrane to phagocytic vacuoles. mAbAdh inhibited 54% adherence, 41% phagocytosis, and 35% and 62% destruction of MDCK cell monolayers by live trophozoites and their extracts respectively. We cloned a 3587 bp DNA fragment (Eh112 ) with two open reading frames (ORFs) separated by a 188 bp non-coding region. The ORF at the 5' end (Ehcp112 ) encodes a protein with a cysteine protease active site, a transmembranal segment and an RGD motif. The second ORF (Ehadh112 ) encodes a protein recognized by mAbAdh with three putative transmembranal segments and four glycosylation sites. Northern blot, primer extension and Southern blot experiments revealed that Ehcp112 and Ehadh112 are two adjacent genes in DNA. Ehcp112 and Ehadh112 genes were expressed in bacteria. The recombinant peptides presented protease activity and inhibited adherence and phagocytosis, respectively, and both were recognized by mAbAdh. The EhCP112 and EhADH112 peptides could be joined by covalent or strong electrostatic forces, which are not broken during phagocytosis.

Congo red effect on cyst viability and cell wall structure of encysting. Entamoeba invadens

BACKGROUND

The cell wall of Entamoeba invadens cysts is composed of chitin microfibrils as the main structural component. It has been demonstrated in yeast that the chitin cell wall assembly is altered by dyes such as Congo red (CR) and Calcofluor.

METHODS

The purpose of this work was to study the cell wall assembly under the effect of CR dye on encysting E. invadens by means of light and electron microscopy, after the amebas were subjected to the effect of 100-2,000 micrograms CR/mL. Experiments were performed either in BI-S-33 or in mLG media.

RESULTS

Trophozoite growth was not inhibited by 100-1,000 micrograms/mL CR after 8 days of incubation in BI-S-33 medium. However, low levels of growth were observed with 2,000 micrograms/mL of dye. No significant differences in morphologically viable (hyaline) cyst production occurred after 24-48 h, when 100 micrograms CR/mL was used, while the highest concentration of CR (2,000 micrograms/mL) resulted in a significant decrease of hyaline cyst yield; dead cysts prevailed in cultures, particularly at 72 h of CR treatment. Differentiation of amebas incubated in the presence of 500-2,000 micrograms/mL CR produced abnormal chitin deposits, rendering irregularly thick or double cell walls, as shown by transmission and scanning electron microscopy. Cyst cultures obtained under 100 micrograms/mL CR produced as many trophozoites as did the control when they were incubated in BI-S-33, but only low numbers of trophozoites were found in culture cysts obtained under higher CR doses.

CONCLUSION

Our results suggest that CR affects E. invadens encystment, alters the cell wall formation, and also affects the cyst viability.

Trichomonas vaginalis: in vitro phagocytosis of lactobacilli, vaginal epithelial cells, leukocytes, and erythrocytes

This paper explores the interaction of two strains of Trichomonas vaginalis, of high and low virulence, with the cell types present in the microenvironment of the parasite during human infections. With the use of transmission and scanning electron microscopy the sequence of internalization by T. vaginalis of Döderlein's lactobacilli, and of vaginal epithelial cells, leukocytes, and erythrocytes was documented. Furthermore, the degradation of ingested material by colocalization of acid phosphatase activity in phagocytic vacuoles was demonstrated. Phagocytosis of all cell types analyzed was found in both strains studied, although the highly virulent strain internalized target cells more rapidly than the less virulent one. Ultrastructural evidence indicated that phagocytosis takes place through two distinct mechanisms, only one involving the formation of a phagocytic stoma, characteristic of professional phagocytes. T. vaginalis phagocytosis may be both an efficient means of obtaining nutrients for the parasite and a significant factor in the pathogenesis of trichomonal infections of the human genitourinary tract.

Trichomonas vaginalis: ultrastructural bases of the cytopathic effect

The in vitro cytopathic effect of Trichomonas vaginalis on epithelial cells was explored through the interaction of trophozoites of the virulent strain GT-10 with MDCK monolayers. The interaction was analyzed through electrophysiology, video microscopy, and transmission and scanning electron microscopy. Electrical measurements revealed that living parasites produced severe damage to the cell monolayers within 30 min, manifested as a rapid decrease in transepithelial resistance. Microscopic observations demonstrated that when placed in contact with epithelial cells, trichomonas formed clumps through interdigitations and transient plasma membrane junctions between adjacent parasites. Also, attached trophozoites adopted an ameboid shape. The in vitro cytopathic action of T. vaginalis on MDCK cells was initially evident by modifications of the plasma membrane, resulting in opening of tight junctions, membrane blebbing, and monolayer disruption. After 15 min of interaction the damage was focal, concentrating at sites where parasite clumps adhered to the monolayer. At 30 min practically all MDCK cells were dead, whether or not trichomonas were attached to them. These events were followed by detachment of lysed cells and complete disruption of the monolayer at 60 min. Electron microscopy demonstrated a peculiar form of adhesion that appears to be specific for trichomonas, in which the basal surface of T. vaginalis formed slender channels through which microvilli and cytoplasmic fragments of epithelial cells were internalized. The same sequence of lytic events was found with the less virulent GT-3 strain. However, the time course of cytolysis with GT-3 parasites was much slower, and lysis was limited to areas of attachment of T. vaginalis.

Signalling of Trichomonas vaginalis for amoeboid transformation and adhesion synthesis follows cytoadherence

The cytoadherence of Trichomonas vaginalis, the sexually transmitted flagellated protozoan, to vaginal epithelial cells (VECs) is the key to infection. Electron microscopy revealed that in vitro-grown parasites having typical globular shape transformed rapidly after contact with VECs into thin, flat, amoeboid cells, maximizing the area of adhesion to the surface of VECs. Amoebic trichomonads formed filopodia and pseudopodia, which interdigitated at distinct sites on the plasma membrane of target cells. In contrast, the amoeboid transformation did not occur for T. vaginalis interacting with HeLa cells, the previously used in vitro host model cell. Initial parasitism of VECs by a single organism was followed by establishment of a monolayer of trichomonads on the host cell. Finally, parasites adhering to either VECs or HeLa cells were induced to synthesize greater amounts of the four previously described adhesins. Therefore, distinct signals after contact with either epithelial cell type leads to the morphological transformation and/or induction of adhesion synthesis by T. vaginalis.

[The electron microscopic findings of helicoid bacteria lining the mucosa of the cecum in guinea pigs]

This study has revealed that helical bacteria inhabiting the mucous membrane of the cecum of guinea pigs are localized in the parietal zone of the epithelium and can be detected as biological film consisting of many microcolonies. Helical bacteria are attached to the epithelium by insertion of one of the ends of an eukaryotic cell into the space between microvilli without damaging epithelial cells and their microvilli. Helical bacteria have been found to use the "anchor" type of attachment to the epithelium, which ensures the stability of their high population level in the biotope. These microorganisms appear on the mucous membrane of the epithelium, starting from day 15 of the life of guinea pigs. At the period of the transition of suckling guinea pigs to independent nourishment the population of helical bacteria is partially suppressed due to the appearance of bacillary and filamentous forms of bacteria, but later, after the adaptation of the animals to their diet, helical bacteria become normal resident microflora which forms biofilm covering large areas of the mucous membrane and the entrances of crypts of Lieberkühn.

Elimination of epimural microflora from guinea pig cecal epithelium by antimicrobial drugs

The effect of antimicrobial drugs on epimural bacteria of guinea pig cecum was assessed by scanning electron microscopy. Metronidazole (500 hg/ml), neomycin (50 hg/ml) or both combined were given orally in drinking water ad libitum for five consecutive days, and representative fragments of cecum were processed for analysis. In untreated animals large areas of mucosa were lined by spiral-shaped bacteria were eliminated by treatment with neomycin, only remaining fusiform bacteria at openings of crypts. metronidazole was effective for eliminating all bacterial populations; the same effect was achieved with a combination of neomycin and metronidazole, rendering the cecum free of epimural bacteria, the health of guinea pig was unaffected by these treatments. The cecal epithelium of antimicrobial-treated animals can be used for experimental studies without interference of epimural bacteria.

[In vitro model for the analysis of the interaction between Shigella flexneri and the intestinal epithelium]

An in vitro study of the adhesion and invasion of Shigella flexneri was implemented, by means of incubation of laminary cuts of cecal mucosa of Dunkin-Hartley guinea pigs in a suspension of Shigella flexneri, which was isolated from a patient with bacillary dysentery. The laminae were placed in plastic chambers for two hours at 37%C. After this the bacterial suspension was discarded so as to eliminate the bacilli which were not adhered. The epithelium was washed with saline and was processed for analysis with scanning electron microscope. The topology of the mucosa incubated with Shigella flexneri was similar to that of the witnesses. The bacteria which adhered to the mucosa were dispersed individually or in clumps of varied numbers. The main alteration observed upon the epithelial surface were depressions due to a lateral separation of the microvilli which may have originated the endocytic stomas containing bacterias. The results of this study allow the proposition of the use of explants, so as to study the interaction between Shigella flexneri and the intestinal epithelium, with the possibility of modifying different experimental variables.

Trichinella spiralis: ultrastructure of the body wall of newborn and muscle larvae

The body wall structure of muscle and newborn larvae of Trichinella spiralis was studied using transmission and scanning electron microscopy. Differences were found in the structure of the cuticle of the two developmental stages. In the case of the cuticle of the muscle larvae only transverse striae were present whereas the newborn larvae cuticle showed both transverse and longitudinal striations. In the two parasite stages the outer surface of the cuticle appears as a three-layered structure. The hypodermis presents well defined cellular components similar in fine structure in both stages. The plasma membrane of the hypodermal cells in the muscle larvae shows abundant short finger-like projections, that are not present in newborn larvae.

Giardia lamblia: surface charge of human isolates in culture

The surface charge of Giardia lamblia trophozoites from axenic cultures of strains recently isolated in Mexico from human cases of symptomatic and asymptomatic giardiasis was studied by means of cellular microelectrophoresis and ultrastructural cytochemistry. It is concluded that ionogenic surface groups confer a negative surface charge on trophozoites of G. lamblia and that no significant differences exist between the surface charge of trophozoites of symptomatic and asymptomatic origin.

Electrical properties and morphology of single vascular smooth muscle cells in culture

Single vascular smooth muscle cells (VSMC) were isolated from the caudal artery and vein and studied after 2 or 3 days in culture. Current clamp with intracellular microelectrodes and "whole-cell" voltage-clamp techniques were used. Also, scanning and transmission electron microscopy studies were performed, revealing morphological characteristics of smooth muscle in culture. Cells could contract in response to electrical and chemical stimuli. The passive membrane properties recorded with intracellular microelectrodes in a mammalian saline were as follows: 1) for artery, resting potential Vm = -56 +/- 5 mV (mean +/- SD), input resistance Rin = 590 +/- 35 M omega, membrane time constant tau m = 19 +/- 2 ms, membrane capacity C/cm2 = 1.3 +/- 0.2 microF/cm2, and length constant lambda = 900 +/- 40 micron; and 2) for vein, Vm = -66 +/- 3 mV, Rin = 450 +/- 25 M omega, tau m = 19 +/- 2 ms, C/cm2 = 1.0 +/- 0.1 microF/cm2, and lambda = 1,300 +/- 200 micron. The values calculated for a short cable and the observed change of the membrane potential as a single exponential, in response to hyperpolarizing pulses of current, both indicate that the cell membrane behaves as an isopotential surface. With hyperpolarizing pulses, both cell types gave linear voltage-current (V-I) relationships with a constant slope, Rin. On the other hand, depolarizing pulses elicited outward rectification. Voltage-clamp experiments show an outward voltage-dependent K+ current (IK) when the cell membrane is depolarized beyond approximately equal to -40 mV from holding levels approximately equal to -60 mV. Maximum slope conductances were of approximately 120 microS/cm2. Blocking of K+ channels with tetraethylammonium ions did not unmask an inward current. These results indicate that VSMC from rat caudal artery and vein in culture have K+ channels responsible for the graded depolarization of the cell membrane in response to an electrical stimulus. Furthermore, this experimental approach seems to be adequate to further study the electrical responses of VSMC from vessels at distinct stages of development, and to follow these responses as the cells change in a defined environment.

Intestinal invasive amebiasis: an experimental model in rodents using axenic or monoxenic strains of Entamoeba histolytica

A new experimental model for the production of early stages of invasive intestinal amebiasis in hamsters or guinea pigs with axenic or monoxenic cultures of Entamoeba histolytica of the HM1:IMSS strain is reported. The model is called the washed-closed cecal loop, because it involves the washing out of the cecum contents of conventionally raised animals and the formation of a closed loop, into which amebas are inoculated. Colonization occurred in all inoculated animals. After 48 hr, macroscopic ulcerations of the cecal mucosa were found in approximately one-half (5/12) of the animals inoculated with axenic amebas and in more than two-thirds (10/12) of those inoculated with monoxenic parasites. The amebic nature of the mucosal ulcerations was confirmed by light and transmission electron microscopy, as well as by scanning electron microscopy (SEM) of fractured samples of cecal mucosa. SEM provided a rapid and reliable technique to assess both the extent and the nature of the lesions. This model is particularly useful for the study of the pathogenesis of early intestinal lesions produced by virulent amebas, and may also be applied to experimental studies on the immunology of invasive intestinal amebiasis.

Structural bases of the cytolytic mechanisms of Entamoeba histolytica

The cellular bases of the powerful cytolytic activity of the human protozoan parasite Entamoeba histolytica were explored by studying the effect of the virulent strain HM1:IMSS on epithelial monolayers of MDCK cells using a combination of time-lapse microcinematography and transmission and scanning electron microscopy. Early alterations of the epithelial cell membranes were detected by measuring changes in the transepithelial electrical resistance of MDCK monolayers mounted in Ussing chambers. The aggressive mechanism of E. histolytica trophozoites was found to be a complex, multifactorial phenomenon that included hit-and-run damage to the plasma membrane of effector cells mediated through contact, phagocytosis of lysed or apparently intact, but detached, MDCK cells, and intracellular degradation of ingested cells. Following contact with amebas, the epithelial monolayers showed a pronounced lowering of transepithelial resistance, opening of tight junctions, distortion of microvilli, surface blebbing, and the presence of minute focal discontinuities in the plasma membrane. There was no evidence of amebic exocytosis, membrane fusion, or junction formation between the parasite and host plasma membranes. Although modifications in the epithelial cell membranes usually preceded lysis, the cytolytic activity of the parasite did not exclusively involve damage to the plasma membrane of the cultured host cells but also was mediated by avid phagocytosis, the displacement and separation of neighboring cells by means of pseudopodial activity, and the "pinching-off" of the peripheral cytoplasm of epithelial cells.

Scanning electron microscopy of attached trophozoites of pathogenic Entamoeba histolytica

The surface morphology of Entamoeba histolytica trophozoites of HM 1:IMSS (axenic and monoxenic) and HK9 (axenic) strains cultured on plastic and MDCK cell substrates was examined using scanning electron microscopy (SEM). The conditions for processing trophozoites were determined by comparing the SEM observations with the morphology of living amebas examined by light microscopy. The most frequent surface differentiations in all the amebas observed with SEM were lobopodia. Round cytoplasmic projections were found in approximately half of the axenic amebas. Endocytic stomas and filopodia were more common in monoxenic cultures while the uroid was found in only 2-8% of all examined amebas. The basal surfaces of the trophozoites, involved in both attachment and cytolysis, showed no unusual features, except for the presence of a small number of short filopodia at the outer edge. No differences were found in the morphology of amebas grown on artificial and natural substrates. These observations demonstrate that there are significant quantitative differences in the surface morphology of cultured trophozoites of different strains of E. histolytica and that association with bacteria produces an increase in the relative number of surface specializations of the parasite.

The filum terminale of the frog spinal cord. Light and electron microscopic observations

The filum terminale, or terminal portion of the spinal cord, was studied in normal adult frogs (Rana pipiens) bu means of light and electron microscopy. Astroglial cells are the predominant elements in this region. The rostral portion of the filum terminale consists mainly of (1) a peripheral dense ring of myelinated and some unmyelinated nerve fibers, and processes of astrobytes terminating at the subpial space; (2) an intermediate zone, in which astrocytes are the main cellular elements in addition to a few degenerated neurons; and (3) a central region where the central canal is lined by dark and light ependymal cells. In the caudal portion of the filum terminale, the amount of neuropil is greatly reduced. This region os formed mainly by astrocytic glial cells and very few neuronal elements. The central canal in the caudal portion is located ventrally and contains a lining consisting almost exclusively of dark ependymal cells.

The cell surface of Trypanosoma cruzi: cytochemistry and freeze-fracture

The ultrastructure of epimastigotes of Trypanosoma cruzi, obtained from acellular cultures, and bloodstream trypomastigotes, isolated from infected mice, were studied by thin-sectioning and freeze-fracturing techniques. Epimastigotes showed a thin (5 nm) surface coat when stained with ruthenium red, while the surface coat of trypomastigotes was more prominent (15 nm thick). Both P and E faces of the plasma membrane of T. cruzi had roughly the same number of intramembranous particles (IMP) as seen by freeze-fracture. The plasma membrane of bloodstream trypomastigotes had less IMP than epimastigotes. Several differentiations of the plasma membrane was observed. In epimastigotes a cytostome appears as a particle-poor region delimited by a pallisade-like row of adjacent IMP. Bloodstream trypomastigotes did not have a cytostome. Instead, abundant pinocytic vesicles were observed. At the base of the flagellum of epimastigotes a ciliary necklace was found. At this region, the surface coat was differentiated as long, hair-like projections after staining with ruthenium red. The flagellar membrane had less IMP than the body membrane. Clusters of IMP were present on both faces of the flagellar membrane at the flagellar-body adhesion zone of epimastigotes. Linear arrays of IMP were also seen. In bloostream trypomastigotes clusters of particles were observed both on the flagellar and cell body membranes. Our observations demonstrate the presence of considerable structural variations of the T. cruzi plasma membrane at the two stages of the life cycle studied.