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排序方式: 共有63条查询结果,搜索用时 31 毫秒
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Adcock KH Brown DJ Shearer MC Shewan D Schachner M Smith GM Geller HM Fawcett JW 《The European journal of neuroscience》2004,20(6):1425-1435
Axon regeneration in vivo is blocked at boundaries between Schwann cells and astrocytes, such as occur at the dorsal root entry zone and around peripheral nerve or Schwann cell grafts. We have created a tissue culture model of these boundaries in Schwann cell - astrocyte monolayer co-cultures. Axon behaviour resembles that in vivo, with axons showing a strong preference for Schwann cells over astrocytes. At boundaries between the two cell types, axons growing on astrocytes cross readily onto Schwann cells, but only 15% of axons growing on Schwann cells are able to cross onto astrocytes. Treatment with chondroitinase or chlorate to reduce inhibition by proteoglycans did not change this behaviour. The neural adhesion molecule L1 is present on Schwann cells and not astrocytes, and manipulation of L1 by application of an antibody, L1-Fc in solution, or adenoviral transduction of L1 into astrocytes increased the proportion of axons able to cross onto astrocytes to 40-50%. Elevating cAMP levels increased crossing from Schwann cells onto astrocytes in live and fixed cultures, and had a co-operative effect with NT-3 but not with NGF. Inactivation of Rho with a cell-permeant form of C3 exoenzyme also increased crossing from Schwann cells to astrocytes. Our experiments indicate that the preference of axons for Schwann cells is largely mediated by the presence of L1 on Schwann cells but not astrocytes, and that manipulation of growth cone signalling pathways can allow axons to disregard boundaries between the two cell types. 相似文献
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Melanie Blackless Anthony Charuvastra Amanda Derryck Anne Fausto-Sterling Karl Lauzanne Ellen Lee 《American journal of human biology》2000,12(2):151-166
The belief that Homo sapiens is absolutely dimorphic with the respect to sex chromosome composition, gonadal structure, hormone levels, and the structure of the internal genital duct systems and external genitalia, derives from the platonic ideal that for each sex there is a single, universally correct developmental pathway and outcome. We surveyed the medical literature from 1955 to the present for studies of the frequency of deviation from the ideal male or female. We conclude that this frequency may be as high as 2% of live births. The frequency of individuals receiving “corrective” genital surgery, however, probably runs between 1 and 2 per 1,000 live births (0.1–0.2%). Am. J. Hum. Biol. 12:151–166, 2000. © 2000 Wiley-Liss, Inc. 相似文献
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Purpose. The purpose of this study is to investigate the interaction of cationic polyamino acids, polylysine and polyarginine, with rat pulmonary surfactant at the air/water interface.
Methods. Surface pressure measurements of rat pulmonary surfactant in the presence and absence of polyamino acids were carried out in both dynamic and static modes.
Results. In dynamic cycle studies, compression and expansion of adsorbed surfactant films in the presence of the cationic polyamino acids resulted in a delayed attainment of the plateau surface pressure. In area studies of spread surfactant films at constant surface pressure, cationic polyamino acids in the subphase resulted in an increase in film area. Increased film area was also observed when a polyamino acid was injected beneath films of dipalmitoyl-phosphatidylcholine/phosphatidylglycerol. In the presence of the cationic polyamino acids, the equilibrium surface pressure (at constant film area) of pulmonary surfactant was elevated in a concentration- and molecular weight-dependent manner.
Conclusions. These data indicate that the model cationic peptides interact with surfactant lipid, possibly electrostatically with phosphatidylglycerol. It is concluded that the surface activity of pulmonary surfactant is significantly inhibited by the presence of the polycations, possibly by the formation of a mixed lipid/polyamino acid film. 相似文献
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Sharma N Ramachandran S Bowers M Yegappan M Brown R Aziz S Chapman R Yu BW 《Cancer chemotherapy and pharmacology》2000,46(4):329-337
Purpose: To determine factors which influence the sensitivity of human colorectal carcinoma cell lines to paclitaxel. Methods: The paclitaxel sensitivity of ten human colorectal carcinoma cell lines, and a panel of RKO colon carcinoma cell lines,
isogenic except for p53 status, were studied. The inhibitory concentrations causing a 50% decrease in growth (IC50) were assayed after 3, 24, and 96 h after paclitaxel exposure. The doubling time (DT) and cell cycle parameters of cells
were also measured. The expression of the multidrug resistance glycoprotein-1 (MDR-1), bcl-2 and bax was quantitatively assessed
by immunoblotting. Results: Mean IC50 values at 24 and 96 h drug exposure were about 1.5 logs lower than the IC50 values at 3 h, regardless of the p53 status. No difference was found between the IC50 values of wild-type and mutant p53 cells, or among the RKO panel of cells. Correlation analysis showed that: (1) resistance
was associated with longer DTs, but this was generally abated by a 96-h exposure; (2) with a 3-h exposure, the combination
of MDR, bcl-2 and bax parameters with DT (DT + MDR + bcl-2–bax) best correlated with IC50 values (r=0.77); (3) with a 96-h exposure, in spite of the generally decreased IC50 values, a combination of MDR-1, bcl-2 and bax parameters (MDR + bcl-2–bax) best correlated with the IC50 values (r=0.71). Conclusions: These results suggest that the exposure duration, DT, and expression of MDR-1, bcl-2 and bax each contribute to paclitaxel
sensitivity of human colorectal carcinoma cells. In assessing paclitaxel drug resistance, multiple factors should always be
considered. There may be a therapeutic window for taxanes in colon cancer by optimizing pharmacokinetics and modulating MDR-1
and bcl-2 resistance factors.
Received: 13 September 1999 / Accepted: 26 April 2000 相似文献