Development of chick and rat endocardial cushions (cardiac mesenchyme) was studied histologically (using Nomarski differential interference optics on living and unfixed tissue), ultrastructurally (scanning and transmission electron microscopy), cytochemically (using acidified dialyzed iron as a visual probe for polyanionic material) and autoradiographically (using 35S) to elucidate the origin of the mesenchyme, the morphologic sequences leading to cushion formation and secretion of sulfated glycosaminoglycans, if any, by migrating mesenchymal cells. Cushion formation was similar for both species. Mesenchymal cells appeared initially, in 16- to 18-somite embryos, beneath the endothelium (which lacked a basal lamina) of the future atrioventricular canal and outflow tract. The cytoplasm of cushion mesenchymal cells was structurally similar to the ensothelium; probably these cells arose by proliferation of the endothelium. Mitotic figures among the "seeded" cells were also numerous. Cushion cells were initially attached to the endothelium by desmosomes but acquired motile apparatus (pseudopodia and filopodia containing microtubules and microfilamentous bundles). Serial sectioning of successively-aged embryos (20-44 somites) indicated a centrifugal migratory direction. Interaction of the cell processes with extracellular matrix suggested that the latter was used as a migratory substrate. Contact of the advancing wedge of cushion cells with the myocardium produced no alteration in cell structure or mitotic activity. Localization of hyaluronidase-sensitive, dialyzed iron (DI) precipitates in 250-nm Golgi vacuoles and hyaluronidase-sensitive 35S-endangendered silver grains over cushion cells indicated that this tissue contributed sulfated macromolecules to the matrix. Localization of hyaluronidase-labile, DI material in coated, endocytic-like vesicles and caveolae also suggested potential modification or conditioning of the matrix by migrating mesenchymal cells. Altogether, the study established loci in developing cushions where disruption where disruption of the developmental sequence could engender valvular or septal defects.

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Recently, the Medical University of South Carolina adopted a lecture recording system (LRS). A retrospective study of LRS was implemented to document the students' perceptions, pattern of usage, and impact on the students' grades in three basic sciences courses (Cell Biology/Histology, Physiology, and Neurosciences). The number of accesses and length of viewings of the recordings were recorded per week for each student and correlated with the grades in each of the three courses. Attendance records were not available. The results showed considerable variability in the use of the LRS by both faculty and students during the entire semester and across all three courses, including week to week variations. Data indicated that 30% of the students did not use the LRS at all with 41% of the students using it very little (less than 10 times for a total of 131 recordings). Specific patterns of usage were identified for each of the three courses throughout the semester, with an increase in access prior or during examination weeks. However, the statistical analysis showed that there was no correlation between the final grades and the usage of LRS. Finally, a survey of the students' perception showed that 74% agreed/strongly agreed that the recordings were useful with 6% disagreeing/strongly disagreeing and 11% undecided. This study showed that the use of LRS might be a viable alternative for students unable to attend lecture due to circumstances such as illness but that more research is needed to truly understand the best pedagogical use of LRS.

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