Study of the mechanisms of BUdR-induced cleft palate in the mouse

This study was designed to examine the pathogenesis of bromodeoxyuridine (BUdR)-induced clefts of the secondary palate in the LACA mouse. Intraperitoneal injections of BUdR (500 mg/kg body weight) were given at various days and combinations of days between E11 and E15 (plug day = E1). Treatment on E11 alone resulted in approximately 22% of fetuses with cleft palate when the latter were examined either on E16 or E19. Treatment on E11 and E12 approximately doubled the above incidence, and treatment on E11, 12 and 13 raised it to 100%. However, no treatment, either single or multiple, caused cleft palate when given later than E11. This suggests that the cellular changes caused by BUdR that lead to cleft palate must be inflicted during E11 and that such damage can be repaired in about 80% of embryos. All fetuses with cleft palate had severe micrognathia on E16 and E19, which skeletal staining showed to be the result of a bilateral sigmoid buckling of Meckel's cartilage. Studies with the scanning electron microscope (SEM) on E15, 16, and 19 suggested strongly that the micrognathia caused a relative macroglossia and hence mechanical interference with palatal shelf reorientation. Histological studies with the light microscope showed that BUdR caused cellular necrosis in many embryonic tissues during the 24 hours after its administration. This necrosis was strikingly more severe in the mandibular rudiment of the first branchial arch than in the maxillary. The latter observation accords well with findings by other workers that cell proliferation is more rapid in the mandibular blastema than in the maxillary. Transmission electron microscope (TEM) studies of the buckled region of Meckel's cartilage failed to reveal any ultrastructural differences from control Meckel's cartilage. Hence BUdR had only interfered with the shape of the cartilage but not with its histiogenesis. We conclude that BUdR, by its cytotoxicity or antidifferentiative effects, interfered with the formation of the anterior end of Meckel's cartilage, initiating a chain of events leading through micrognathia and relative macroglossia to failure of palatal shelf reorientation and cleft palate.     

Development of the lung in mice with bromodeoxyuridine-induced cleft palate

Clinical and laboratory observations show that denial of free communication between the amniotic fluid and lung fluid results in pulmonary hypoplasia. Thus, cleft palate resulting from tongue obstruction to palatal shelf elevation might be associated with disturbed lung development. This association exists in the Pena-Shokeir phenotype. The goal of these experiments was to see what effect bromodeoxyuridine (BUdR)-induced cleft palate had on lung development. LACA mice were injected with 500 mg/kg BUdR on E11 or E11 and E12 of gestation, a treatment known to produce a 25% and 50% incidence of cleft palate, respectively. BUdR had a direct retarding effect on lung growth but, when cleft palate occurred as well, the lungs were more severely affected. Morphometry showed that lungs from fetuses with cleft palate had only one-half the saccular volume of controls or of treated fetuses with normal palates. Although hypoplastic, lungs associated with cleft palate had type I and type II pneumocytes, and the latter were shown by electron microscopy to be capable of producing surfactant. Hence, cellular differentiation had not been affected by the treatment. Fetuses with cleft palate had less amniotic fluid than controls but significantly more than those with normal palates after treatment. Thus, the pattern of abnormalities in this animal model bears some resemblance to that of the human Pena-Shokeir phenotype.     

The effects of cadmium exposure on the cytology and function of primary cultures from rainbow trout

Cultured epidermal cells from explants of skin of rainbow trout were used to study the cytological and functional changes following sublethal exposure to cadmium stress. The aim was to develop diagnostic markers for ecotoxicology. Cultures were exposed to the pollutant for 48 h. Cell structural and cytological changes were established by light and electron microscopy. Metabolic alterations were detected by immunohistochemistry. The relation between the initiation of cellular alterations and cadmium concentrations was compared in cultures exposed in commercially-available serum-free and serum-containing medium. The expression of stress proteins (metallothionein and heat shock protein) was also studied. Rainbow trout epithelial cells exposed to cadmium showed typical morphological changes indicative of cell death by apoptosis. Sublethal exposure also resulted in cellular metabolic disturbances with increased deposits of glycogen. Increased melanization was also observed. These changes appeared at lower concentrations of cadmium when cells were exposed in serum-free media than in serum-containing media. Cadmium induced the expression of heat shock proteins but not of metallothioneins. The results broadly confirm in vivo findings for cadmium toxicity and suggest that this in vitro technique may have applications in aquatic toxicology. © 1998 John Wiley & Sons, Ltd.     

Effects of Ceftiofur and Chlortetracycline Treatment Strategies on Antimicrobial Susceptibility and on tet(A), tet(B), and bla CMY-2 Resistance Genes among E. coli Isolated from the Feces of Feedlot Cattle

A randomized controlled field trial was conducted to evaluate the effects of two sets of treatment strategies on ceftiofur and tetracycline resistance in feedlot cattle. The strategies consisted of ceftiofur crystalline-free acid (CCFA) administered to either one or all of the steers within a pen, followed by feeding or not feeding a therapeutic dose of chlortetracycline (CTC). Eighty-eight steers were randomly allocated to eight pens of 11 steers each. Both treatment regimens were randomly assigned to the pens in a two-way full factorial design. Non-type-specific (NTS) E. coli (n = 1,050) were isolated from fecal samples gathered on Days 0, 4, 12, and 26. Antimicrobial susceptibility profiles were determined using a microbroth dilution technique. PCR was used to detect tet(A), tet(B), and bla _CMY-2 genes within each isolate. Chlortetracycline administration greatly exacerbated the already increased levels of both phenotypic and genotypic ceftiofur resistance conferred by prior CCFA treatment (P<0.05). The four treatment regimens also influenced the phenotypic multidrug resistance count of NTS E. coli populations. Chlortetracycline treatment alone was associated with an increased probability of selecting isolates that harbored tet(B) versus tet(A) (P<0.05); meanwhile, there was an inverse association between finding tet(A) versus tet(B) genes for any given regimen (P<0.05). The presence of a tet(A) gene was associated with an isolate exhibiting reduced phenotypic susceptibility to a higher median number of antimicrobials (n = 289, median = 6; 95% CI = 4–8) compared with the tet(B) gene (n = 208, median = 3; 95% CI = 3–4). Results indicate that CTC can exacerbate ceftiofur resistance following CCFA therapy and therefore should be avoided, especially when considering their use in sequence. Further studies are required to establish the animal-level effects of co-housing antimicrobial-treated and non-treated animals together.     

Human endothelial cells cultured on microporous filters used for leukocyte transmigration studies form monolayers on both sides of the filter

Summary A growing number of studies on the mechanism of leukocyte transendothelial migration use endothelial cells grown on microporous filters as an in vitro model of endothelium. Ultrastructural examination of such a model system previously demonstrated that human pulmonary artery endothelial cells (HPAEC) formed confluent monolayers on both sides of the 3-μm-pore filter (Mackarel et al., 1999). To determine whether this was a characteristic specific to pulmonary artery endothelial cells, the growth characteristics of a human pulmonary microvascular endothelial cell type (HMVEC-L) and the widely used human umbilical vein endothelial cells (HUVEC) on 3-μm microporous filters were examined by transmission electron microscopy (TEM). Similar to HPAEC, HMVEC-L and HUVEC were also found to grow on both sides of the filter. All three endothelial cell types were capable of migrating through the 3 μm pores of the filter to form a monolayer on the filter underside. The endothelial cells on the underside were orientated in an inverted position with the luminal surface facing away from the filter. Such ‘bilayer’ formation was observed at a range of seeding densities and in different culture media. Despite the presence of a bilayer of endothelial cells, TEM demonstrated that neutrophils migrated successfully across the cell-filter-cell system. Previous transmigration reports in which an in vitro model similar to ours was used have often assumed only one layer of endothelial cells. The observations reported here indicate that while endothelial cells on microporous filters are useful models for examining leukocyte-endothelial interactions, they are not appropriate for studies examining endothelial cell ‘sidedness.’     

Exogenous seeding of cerebral β-amyloid deposition in βAPP-transgenic rats

Deposition of the amyloid-β (Aβ) peptide in senile plaques and cerebral Aβ angiopathy (CAA) can be stimulated in Aβ-precursor protein (APP)-transgenic mice by the intracerebral injection of dilute brain extracts containing aggregated Aβ seeds. Growing evidence implicates a prion-like mechanism of corruptive protein templating in this phenomenon, in which aggregated Aβ itself is the seed. Unlike prion disease, which can be induced de novo in animals that are unlikely to spontaneously develop the disease, previous experiments with Aβ seeding have employed animal models that, as they age, eventually will generate Aβ lesions in the absence of seeding. In the present study, we first established that a transgenic rat model expressing human APP (APP21 line) does not manifest endogenous deposits of Aβ within the course of its median lifespan (30?months). Next, we injected 3-month-old APP21 rats intrahippocampally with dilute Alzheimer brain extracts containing aggregated Aβ. After a 9-month incubation period, these rats had developed senile plaques and CAA in the injected hippocampus, whereas control rats remained free of such lesions. These findings underscore the co-dependence of agent and host in governing seeded protein aggregation, and show that cerebral Aβ-amyloidosis can be induced even in animals that are relatively refractory to the spontaneous origination of parenchymal and vascular deposits of Aβ.     

Primary culture and histological characterization of phagocytic cells from rainbow trout Oncorhynchus mykiss

In this study the pronephros of rainbow trout Oncorhynchus mykiss was explanted and cultured. The morphology of cultured cells suggested they were leukocyte derived. To confirm this, cells were incubated with non-opsonized fluorescent beads and human apoptotic polymorphonuclear leukocytes (PMN) to establish that they were capable of phagocytosis and that they became activated following exposure to apoptotic bodies. The cells were studied using light microscopy, transmission electron microscopy and a live cell observer system. Cells in culture were also stained with phalloidin to identify actin reorganization following activation. Cultured cells ingested the inert beads and apoptotic PMNs and c . 80% of cells became activated following exposure to the apoptotic PMN, evidenced by enhanced filopodial extensions. This methodology may play a role in future studies, in particular, the competence of macrophages following exposure to radiation can now be tested.     

High‐Performance Tandem Organic Solar Cells Using HSolar as the Interconnecting Layer

Tandem structure provides a practical way to realize high efficiency organic photovoltaic cells, it can be used to extend the wavelength coverage for light harvesting. The interconnecting layer (ICL) between subcells plays a critical role in the reproducibility and performance of tandem solar cells, yet the processability of the ICL has been a challenge. In this work the fabrication of highly reproducible and efficient tandem solar cells by employing a commercially available material, PEDOT:PSS HTL Solar (HSolar), as the hole transporting material used for the ICL is reported. Comparing with the conventional PEDOT:PSS Al 4083 (c‐PEDOT), HSolar offers a better wettability on the underlying nonfullerene photoactive layers, resulting in better charge extraction properties of the ICL. When FTAZ:IT‐M and PTB7‐Th:IEICO‐4F are used as the subcells, a power conversion efficiency (PCE) of 14.7% is achieved in the tandem solar cell. To validate the processability of these tandem solar cells, three other research groups have successfully fabricated tandem devices using the same recipe and the highest PCE obtained is 16.1%. With further development of donor polymers and device optimization, the device simulation results show that a PCE > 22% can be realized in tandem cells in the near future.