摘要:

AbstractEggs of the marine clamSpisula solidissimawere examined by the technique of freeze‐substitution. Morphology of the cytoplasm was investigated as a function of cellular water content using osmotic means to control water concentration. In eggs frozen in less than double strength sea water, ice crystallization usually occurred throughout the cell. In eggs frozen in double to triple strength sea water, 10–75% of the eggs were devoid of ice crystals in the cytoplasm and in triple strength sea water, also in the nucleus. From these results and from a detailed analysis of cells in which both ice crystals and ice crystal‐free regions occurred it is concluded that cells or parts of cells may be frozen free of ice crystals if their free water content is reduced. Reduction in free water content may occur in several ways: deliberate dehydration by osmotic means; accidental dehydration by evaporation of water from cells prior to freezing; osmotic dehydration of one region by an adjacent one in which ice crystallization is in progress. In ice crystal‐free cells, all common cell inclusions could be rec

ISSN:0002-9106    

DOI:10.1002/aja.1001300102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractStudies of ice crystal‐free eggs of the clamSpisula solidissimausing freeze‐substitution techniques are described. Formation of ice in cells may be avoided by removing sufficient intracellular water prior to freezing. After such treatment, most subcellular inclusions can be recognized and have dimensions similar to those seen after chemical fixation. Golgi regions, ribosomes, endoplasmic reticulum, nuclear envelope, annulate lamellae, yolk and the vitelline membrane resemble their counterparts in chemically fixed eggs. Mitochondria, however, lack the space normally found between cristae walls, and the resulting structure resembles two unit membranes “back to back.” Several inclusions and structures not seen in chemically fixed eggs are described: light bodies are found in groups of two to eight near the Golgi regions; cores occur in the microvilli of the vitelline membrane, microtubules are found in the cytoplasm of the unfertilized egg and 220 to 250 Å particles, which are not ribosomes, occur regularly arranged along micr

ISSN:0002-9106    

DOI:10.1002/aja.1001300103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractEggs of the clamSpisula solidissimawere studied by freeze‐substitution techniques at the time of the first meiotic division. The mitotic apparatus is organized into regions containing microtubules, endoplasmic reticulum, ribosomes and mitochondria which surround densely stained amorphous regions. The amorphous regions, which appear to be channels running through the mitotic apparatus, are radially arranged in the asters and are parallel to the spindle axis. Microtubule‐associated particles, each about 250 Å in diameter, are arranged in crystalline arrays around the microtubules of the mitotic apparatus. After a period of time in hypertonic sea water the mitotic apparatus disappears and the microtubule‐associated particles remain aggregated in hexagonally packed crystals. Histochemical tests suggest that the particles are composed of polysaccharide material. Other particles and inclusions show orientation relative to the mitotic apparatus axis or show non‐uniform localization in the egg. The possible meaning of such localization and orientation in the physiology of the egg is d

ISSN:0002-9106    

DOI:10.1002/aja.1001300104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractThe presence of microvilli and well‐developed organelles in the cells of the non‐ciliated intermediate segment of the ammocoete nephron suggests that this is not simply a conducting tubule but may be involved in the formation of urine. This region more closely resembles the thin limb of the loop of Henle of mammals than the intermediate segment of lower vertebrates.The distal segment consists ofdarkandlightcells possessing varying amounts of glycogen, mitochondria, and smooth endoplasmic reticulum. Basal infoldings of the plasma membrane are lacking in the distal cells but wide intercellular spaces are present. Angular prismatic mitochondrial cristae are found within the glycogen‐rich cells of the intermediate and distal segments.The collecting segment also possesses narrow intercellular spaces as well as an abundance of organelles, particularly smooth endoplasmic reticulum and mitochondria, suggesting that this region may also be involved in urine form

ISSN:0002-9106    

DOI:10.1002/aja.1001300105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractThe rat acoustic nerve is separated into central and peripheral portions by an astrocytic glial dome which is convex peripheralward. The long central portion is of typical central nervous system structure with narrow extracellular space (100–200 Å in width), oligodendrocytes and astrocytes. The glial dome is penetrated by acoustic nerve fibers at a node of Ranvier; the basal lamina of the astrocytes is reflected back over the peripheral Schwann cells at this site. Centrally, the myelin is thinner than peripherally.Acoustic nerve neurons, ranging in size from 25–60 μ, occur in the central portion of the nerve and may be divided into two groups based upon size and density of organelles: large and medium‐sized. All the neurons possess an eccentric nucleus and a peripheral clear zone in the perikaryon beneath which Nissl substance is aggregated, but the medium‐sized neurons have fewer organelles than the large cells. Dendrites and axons are similar in ultrastructure.While collagenous fibrils, fibroblasts, Schwann cells and extensive extracellular space occur in the peripheral portion of the nerve, no structure corresponding to perineurium or epineurium exists. Instead, dura mater surrounds the acoustic nerve within the modiolus and the pia mater encloses bundles of nerve fibers up to the modiolar foramina where it is reflected back as arachnoid mater. Nerve fibers traversing the modiolar foramina are devoid of a meningeal or perineurial covering; this condition also prevails in the osseous spiral lamina, although wisps of pia‐like cells enclose groups of ganglion cells and nerve fibers in the spiral tract. These findings may help to explain acoustic nerve involvement in pathological processes such as meningitis and e

ISSN:0002-9106    

DOI:10.1002/aja.1001300106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

摘要:

AbstractMembrane‐coating granules are found in close association with the Golgi apparatus, and their apparent size, shape and internal substructure varies with the plane of section.After a membrane‐coating granule is discharged into the intercellular space, it dissociates into distinct units, the pentalamellar discs, which are stacked like coins in the intact granule. Subsequently, discs become applied to and appear to fuse with the outer leaflets of the horny cell membranes, resulting in the formation of a nine‐layered membrane‐disc complex. When this complex cleaves at the junction of the thick dense lamella and distal lighter lamella of the disc, a pentalaminar horny‐cell surface membrane results. The more common surface membrane, however, is trilaminar consisting of thickened inner leaflet, lighter middle leaflet, and thickened outer leaflet. The thickened outer leaflet may result from the addition of amorphous intercellular material derived from membrane‐coating granules or from the fusion of two outer leaflets, as in the formation of a tight junction.The thickened inner leaflet results from the deposition of dense material onto the cytoplasmic face of the inner leaflet; there exists a regional variation in its dimensions. The side of the cell facing the surface of the epithelium has a thickened inner leaflet varying in width between 140 and 180 Å, whereas the side facing the underlying cell is only about 100 Å thick.Discs and amorphous material derived from membrane‐coating granules coat and thicken the plasma membrane by modifying the outer leaflet, and thus may play a role in the barrier function of the

ISSN:0002-9106    

DOI:10.1002/aja.1001300107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001300101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1971

数据来源: WILEY