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D C PEASE

Publications and source records attributed to D C PEASE.

At least 19 recordsLinked to original sources
PubMed1963

THE ULTRASTRUCTURE OF FLAGELLAR FIBRILS.

The tips of rat sperm tails were slightly frayed by mechanical agitation, thus exposing the fibrils, which were then studied by electron microscopy after negative staining. Only the fibrils survived this treatment. Each fibril proved to be a cylinder with a hollow core. The walls of the cylinders were made up of 10 longitudinally oriented filaments. The filaments had a markedly beaded appearance, with a repeating period of 88 A. The filament thickness (bead width) was approximately 35 to 40 A. Beads of neighboring filaments were in register with each other so that cross-linking bound the filaments together to complete the wall structure of each fibril. The center-to-center spacing from one filament to the next was 55 to 60 A. The periodicity and the diameters of the filaments make it unlikely that the filaments are related to either actin or myosin. From the way the fibrils kinked, it can be inferred that they possessed considerable mechanical strength. It is consistent with present knowledge that fibrils of the mitotic apparatus may have the same basic structure as the flagellar fibrils. Under some circumstances, pairs of fibrils separated from one another along their length, except at their extreme tips. It was apparent that there was special bridging material to be found there. In other preparations, however, the paired fibrils remained together, indicating a powerful coupling mechanism.

Actin Cytoskeleton↗
PubMed1959

Electron microscopy of the tapetum lucidum of the cat.

The fine structure of the tapetum of the cat eye has been investigated by electron microscopy. The tapetum is made up of modified choroidal cells, seen as polygonal plates grouped around penetrating blood vessels which terminate in the anastomosing capillary network of the choriocapillaris. The tapetal cells are rectangular in cross-section, set in regular brick-like rows, and attain a depth of some thirty-five cell layers in the central region. This number is gradually reduced peripherally, and is replaced at the margin of the tapetum by normal choroidal tissue. The individual cells are packed with long slender rods 0.1 micro by 4 to 5 micro. The rods are packed in groups and with their long axes oriented roughly parallel to the plane of the retinal surface. Each cell contains several such groups. Cells at the periphery or in the outer layers of the tapetum are frequently seen to contain both tapetal rods and melanin granules, the latter typical of the choroidal melanocytes. Also melanocyte granules may have intermediate shapes. These observations plus the similar density of the two inclusions lead to the belief that the tapetal rods may be melanin derivatives. A fibrous connective tissue layer lies between the tapetum and the retina. The subretinal capillary network, the choriocapillaris, rests on this layer and is covered by the basement membrane of the retinal epithelium. The cytoplasm of the retinal epithelium exhibits marked absorptive modifications where it comes in contact with the vessels of the choriocapillaris. This fibrous layer and the basement membrane of the retinal epithelium apparently comprise the structural elements of Bruch's membrane.

Animals↗
PubMed1957

Electron microscopy of the pacinian corpuscle.

The Pacinian corpuscle has a framework of cytoplasmic lamellae arranged concentrically in the outer zone, and bilaterally in the core. Between these is an intermediate growth zone. The inner core shows an unexpected complexity in that its component lamellae are arranged in two symmetrical groups of nested cytoplasmic sheets. Longitudinal tissue spaces form clefts separating the two groups. The perikarya of the core lamellae lie in or near the intermediate growth zone, and send arms into the clefts. The arms then branch and terminate as lamellae which interdigitate with those of neighboring cells. The single nerve fiber loses its myelin sheath just before it reaches the inner core but retains its Schwann cell cytoplasmic covering for a short additional distance. The Schwann sheath is not continuous with the lamellae of the inner core. Inside the core the fiber contains a striking circumferential palisade of radially disposed mitochondria. The fiber does not arborize. Vascular capillaries penetrate the hilar region of the corpuscle only as far as the myelinated sheath of the nerve, and they have not been seen elsewhere in the corpuscle. There is direct continuity between the clefts of the core and tissue spaces in the vicinity of the capillaries. It is likely that this provides a route whereby metabolites reach the active nerve ending, as well as the cells of the growth zone. The outer zone consists of at least 30 flattened concentric cytoplasmic lamellae separated from one another by relatively wide fluid-filled spaces. Collagenous fibrils are present, particularly on the outer surface of lamellae, and tend to be oriented circularly. The girdle of proliferating cells constituting the growth zone, which is prominent in corpuscles from young animals, is the layer from which the outer lamellae are derived. Osmotic forces probably elevate the lamellae, and maintain turgor pressure.

Animals↗