Experimental evidence for extreme dispersal limitation in tropical forest birds.

Movements of organisms between habitat remnants can affect metapopulation structure, community assembly dynamics, gene flow and conservation strategy. In the tropical landscapes that support the majority of global biodiversity and where forest fragmentation is accelerating, there is particular urgency to understand how dispersal across habitats mediates the demography, distribution and differentiation of organisms. By employing unique dispersal challenge experiments coupled with exhaustive inventories of birds in a Panamanian lacustrine archipelago, we show that the ability to fly even short distances (< 100 m) between habitat fragments varies dramatically and consistently among species of forest birds, and that this variation correlates strongly with species' extinction histories and current distributions across the archipelago. This extreme variation in flight capability indicates that species' persistence in isolated forest remnants will be differentially mediated by their respective dispersal abilities, and that corridors connecting such fragments will be essential for the maintenance of avian diversity in fragmented tropical landscapes.

Structural and functional roles of cytoskeletal proteins during repair of native guinea pig intestinal epithelium.

The cytoskeletal events that assist restitution of the native intestinal epithelium are poorly understood. To enhance our understanding of repair mechanisms in the native intestinal epithelium we assessed the functional role of actin and the temporal and spatial alterations in actin and villin that occur in native enterocytes migrating in response to injury. Using a well-characterized in vitro Ussing chamber model of native intestine epithelial restitution, the actin inhibitor cytochalasin D (CD) was applied to determine the functional importance of actin to restitution as assessed by sensitive electrophysiological means and structural techniques. Additionally we used phalloidin and indirect immunohistochemistry to localize and semiquantitate F-actin and villin in migrating cells during restitution. We report new data that shows that when cytoskeletal changes were impaired with CD, the epithelial monolayer was re-established in fewer than 20% of CD-treated villi, cells bordering the epithelial defect did not assume the characteristic phenotype associated with migrating cells, and transepithelial resistance did not return to pre-injury levels. F-actin and villin were present at the leading edge of the migrating cells, basolateral F-actin was decreased, and cytoplasmic villin was increased as determined by phalloidin and immunohistochemical methods. We conclude that in vitro repair of the native intestinal epithelium is functionally and structurally dependent on major changes in the cytoskeleton of cells involved in re-establishing the epithelial monolayer over a complex extracellular matrix.

The effect of Lactobacillus GG on the initiation and promotion of DMH-induced intestinal tumors in the rat.

Male Fischer 344 rats were fed a 20% or a 5% corn oil diet and were injected subcutaneously with dimethylhydrazine (DMH) weekly for 16 weeks. In addition, an approximately equal number of animals challenged with DMH were fed daily, until the end of the study, 2 x 10(10) Lactobacillus casei subsp. rhamnosus strain GG starting three weeks before DMH administration or after the ninth weekly injection. The feeding of the Lactobacillus GG before and during carcinogen treatment resulted in a significant decrease in the incidence of colon tumors and the number of small intestinal and colon tumors per tumor-bearing animal for rats fed a 20% corn oil diet. This decrease in tumor incidence or number of tumors was not seen when animals were fed the Lactobacillus after the ninth week of carcinogen treatment. Animals fed a 5% corn oil diet had a lower tumor incidence and number of tumors resulting from the decrease in dietary fat; in addition the feeding of Lactobacillus GG before the carcinogen challenge resulted in a lower incidence of colon tumors. These studies show that a specific strain of L. casei subsp. rhamnosus designated GG can interfere with the initiation or early promotional stages of DMH-induced intestinal tumorigenesis, and this effect is most pronounced for animals fed a high-fat diet.

Use of a lectin as an enterocyte-specific cell surface marker for flow cytometric analysis of isolated native small intestinal epithelial cells.

Little use has been made of flow cytometry in evaluating small intestinal epithelial cells. Obtaining pure epithelial cell populations devoid of peripheral blood contaminants and intraepithelial lymphocytes contributes to the difficulties encountered in flow cytometry studies. We have investigated the use of lectins as enterocyte specific cell markers using lectin histochemistry, and have identified one lectin, UEA-1, which binds exclusively and specifically to intestinal epithelial cell brush border. Additionally, we have exploited that specificity using flow cytometry and FITC-UEA-1 to identify and separate native intestinal epithelial cells from a mixed cell population isolated by mechanical vibration. This fluorescent-lectin technique is a unique and simple method to identify native small intestinal epithelial cells in a mixed cell population; it may be exploited by flow cytometric sorting of a pure population for biochemical study or as an enterocyte specific label for surface receptor flow cytometric studies in the research or clinical setting.

Fate of polarized membrane components and evidence for microvillus disassembly on migrating enterocytes during repair of native intestinal epithelium.

BACKGROUND: Maintenance of enterocyte polarity is crucial to normal intestinal function. Tight junctions and cell-matrix interactions play a role in maintaining polarized cell membrane domains. In many intestinal epithelial wounds, normal cell-cell associations mediated by tight junctions are lost. The goal of this study was to examine the fate of an apically restricted fucosylated glycoconjugate (FGC) and basolaterally restricted Na/K-ATPase in a model of intestinal epithelial repair. Comparisons are made to isolated enterocytes in which cell-matrix interactions are disrupted as well. EXPERIMENTAL DESIGN: We present a novel physiologically relevant model of intestinal epithelial injury and restitution that was used to examine the fate of two polarized membrane components by fluorescent and ultrastructural techniques. In addition, we used mechanical vibration to isolate enterocytes as individual and short sheets of cells from the intestinal basement membrane and evaluated the fate of these restricted membrane components using immuno- and lectin histochemistry. RESULTS: Na/K-ATPase maintained its basolateral membrane location in restituting epithelial but relocated to a nonbasolateral position in the majority of isolated enterocytes. The FGC maintained its apical restriction in isolated enterocytes and in epithelial cells migrating across denuded basement membrane. An additional and important observation noted in this study was a drastic alteration in shape of migrating epithelial cells characterized by diminution and loss of microvilli as the cells migrated across the injury. CONCLUSIONS: We conclude from our results that maintenance of Na/K-ATPase to a basolateral membrane position is influenced by cell-matrix interactions. In contrast, restriction of FGC to the apical membrane of enterocytes is dependent on the presence of microvilli and is not related to either cell-cell or cell-matrix interactions. Additionally, we suggest a new model of intestinal repair in which microvilli are disassembled. We speculate that membrane from disassembled microvilli, as well as lateral cell membrane, are used at the leading edge of the migrating cell.

Lectin histochemistry of mammalian Brunner's glands.

Lectin histochemical study was performed on twenty-eight specimens of formalin-fixed paraffin embedded tissues of proximal duodenum from human, cat, dog and Rhesus (macaque) monkey to demonstrate the pattern of carbohydrate residues in submucosal glands of Brunner as compared to that of the duodenal absorptive and goblet cells. Ten different biotinylated lectins were used as probes, and avidin-biotin-peroxidase (ABC) or avidin-gold-silver (AGS) complexes were used as "visualants". Brunner's gland cells of the four species studied exhibited a similar lectin-binding pattern which differ from other duodenal cells. The epithelium of Brunner's gland stained intensely with Ricinus communis agglutinin-I (RCA-I), succinylated-WGA (S-WGA) and wheat-germ agglutinin (WGA), moderately with Bandeirea simplicifolia agglutinin-I (BS-I), Concanavalia ensiformis agglutinin (Con A) peanut agglutinin (PNA) and Ulex europaeus agglutinin-I (UEA-I) and occasionally with Dolichos biflorus agglutinin (DBA), Lens culinaris agglutinin (LCA) and soybean agglutinin (SBA). Desialylation with neuraminidase resulted in only a slight elevation in binding intensities of PNA, DBA and SBA, indicating that glycoconjugates of the Brunner's gland cells are rich in asialo-oligosaccharides, which differs from duodenal epithelial cells. In addition, these histochemical reagents were useful in localizing Brunner's gland elements in the duodenal mucosa.

New radioimmunoadsorbent method for detection of hepatitis B surface antigen.

A radioimmunoadsorbent assay for the detection of hepatitis B surface antigen (HBsAG) is described. The method uses small DEAE-cellulose columns to adsorb HBsAg from serum or plasma samples, and it uses 125 I-labeled antibody to HBsAg to detect the adsorbed antigen. A single 2-h incubation at 45 degrees C is used in the procedure. The sensitivity of the method was determined with the Bureau of Biologics HBsAg reference panels and was shown to be equivalent to other third-generation test methods. The specificity of the method was evaluated by testing specimens from blood donors, dialysis patients, and hospital staff in parallel with commercial radioimmunoassay kits for HBsAg. In the tests performed on 2,868 blood donor specimens, 6 positive specimens were identified by both the radioimmunoadsorbent method and the commercial radioimmunoassay kits. These positive specimens were confirmed by a counterimmunoelectrophoresis procedure. One nonconfirmable, repeatably positive specimen was observed with the radioimmunoadsorbent method. In testing 1,250 specimens from dialysis patients and hospital staff, 120 confirmable positive specimens were identified by both the radioimmunoadsorbent method and a commercial test. Overall, the false positive rate for the radioimmunoadsorbent method was found to be less than 1%.

Immunochemiluminometric assay for hepatitis B surface antigen.

A novel "sandwich" immunoassay for hepatitis B surface antigen monitored by chemiluminescence is described. The method involves use of an antibody-coated microtitration plate and requires 100 micro L of test specimen. The antigen binds to the antibody during the first 2-h incubation and, after an intermediate wash step, the sandwich is completed by 2-h incubation with antibody to antigen that has been labeled with an isoluminol derivative. A final wash step follows. A luminometer, built in-house, adds "microperoxidase" and peroxide, to initiate chemiluminescence, and provides automated readout at 10-s intervals. Results compare well in specificity and sensitivity with those of a comparison radioimmunoassay procedure. Within- and between-assay variability (CV) is 7 to 13% (n = 6). All reagents are stable at 4 degrees C for at least several months. Use of a non-radioisotopic label in this assay avoids the stability problems and inconvenience associated with radioactivity.