ISSN:1059-910X    

DOI:10.1002/jemt.1070220302

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

年代:1992

数据来源: WILEY

摘要:

AbstractThere is a great variety in the morphological appearance of olfactory structures across the metazoan animal kingdom. Despite this variety the receptive structures themselves have a strikingly similar architecture, namely some type of elongated cellular extension that is spanned by a membrane and surrounded by mucus. These cellular extensions can either be modified primary or secondary cilia, or microvilli. There are more similarities between membranes of these extensions than between the cytoskeletal elements immediately underneath the membranes. One might infer that the cytoskeletal elements of the cellular extensions merely serve as a scaffold for the membranes, whereas the similarity in membrane ultrastructure provides morphological evidence supporting the concept that these membranes are responsible for the initial olfactory transduction process. The transduced message is transported to the brain, where it is decoded to initiate the cascade of events resulting in the organisms' appropriate behavioral response to the initial odorous stimulus. The varying appearance of olfactory structures across the animal kingdom is probably produced by evolutionary pressure to adapt the olfactory system to the animal's environment. This review deals with the ultrastructural aspects of these facets of olfaction. © 1992 Wiley‐Liss, I

ISSN:1059-910X    

DOI:10.1002/jemt.1070220303

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe ciliated protists (ciliates) offer a unique opportunity to explore the relationship between chemoreception and cell structure. Ciliates resemble chemosensory neurons in their responses to stimuli and presence of cilia. Ciliates have highly patterned surfaces that should permit precise localization of chemoreceptors in relation to effector organelles. Furthermore, ciliates are easy to grow and to manipulate genetically; they can also be readily studied biochemically and by electrophysiological techniques. This review contains a comparative description of the ultrastructural features of the ciliate cell surface relevant to chemoreception, examines the structural features of putative chemoreceptive cilia, and provides a summary of the electron microscopic information available so far bearing on chemoreceptive aspects of swimming, feeding, excretion, endocytosis, and sexual responses of ciliates. The electron microscopic identification and localization of specific chemoreceptive macromolecules and organelles at the molecular level have not yet been achieved in ciliates. These await the development of specific probes for chemoreceptor and transduction macromolecules. Nevertheless, the electron microscope has provided a wealth of information about the surface features of clliates where chemoreception is believed to take place. Such morphological information will prove essential to a complete understanding of reception and transduction at the molecular level. In the ciliates, major questions to be answered relate to the apportionment of chemoreceptive functions between the cilia and cell soma, the global distribution of receptors in relation to the anterior‐posterior, dorsal‐ventral, and left‐right axes of the cell, and the relationship of receptors to ultrastructural components of the cell coat, cell membrane, and cytoskeleton. © 1992 Wiley‐L

ISSN:1059-910X    

DOI:10.1002/jemt.1070220304

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

年代:1992

数据来源: WILEY

摘要:

AbstractChemoreceptors in coelenterates and ctenophores have not been identified with certainty. Among prospective chemoreceptive cells are the sensory nerve cells, the cnidocyst bearing cnidocytes, and the epitheliomuscular cells that are likely to be involved in feeding or aggression. Both behaviors are mediated by coordinated chemical and mechanical reception. This is reflected in the close apposition of putative chemo‐ and mechanoreceptors. Among the structures that have been designated as likely chemo‐ and/or mechanoreceptors are stereocilia, kinocilia, and/or microvilli which are universally present on all the putative chemoreceptor complexes, while gland cells and mucous secretions are prevalent. Evidence that the actin‐containing stereocilia are chemically modulated mechanoreceptors is presented for several forms. © 1992 Wiley‐L

ISSN:1059-910X    

DOI:10.1002/jemt.1070220305

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe flatworms (Platyhelminthes) and the round worms (Nematoda) are phylexhibiting strikingly different levels of cellular organization. In both, sensilla are composed of the endings of sensory dendrites intercalated into their epidermis.In flatworms, sensilla that penetrate the syncytial epidermis bear sensory processes derived from cilia. In free‐living species, the sensory processes more closely resemble motile cilia, while in parasites, greater deviations occur from the classical cilium pattern. Estimates of the function of the various sensilla have been largely arbitrary, and remain based on ultrastructural features.Sensilla in round worms lie below or within a heavy secreted cuticle. Two glia‐like cell types occur. The socket cell mediates contact with cuticle and is responsible for cuticular modifications essential for operation of the sensillum. The sheath cell forms a receptor cavity around the sensory processes and regulates its environment. Sensory processes vary greatly from the classical cilium pattern. Absence of a basal body, but preservation of a ciliary necklace, suggests that the latter has a primary importance in sensory transduction. Estimates of function are based largely on ultrastructural features and analogies to arthropod sensilla. Genetic studies with the free‐living nematodeCaenorhabditisare beginning to demonstrate details of function and development.Speculations on the roles of basal bodies, rootlets, and vesicles and on the significance of recessed sensilla are given. © 1992 Wiley‐L

ISSN:1059-910X    

DOI:10.1002/jemt.1070220306

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

年代:1992

数据来源: WILEY

摘要:

AbstractDuctile phase toughened composites contain phases with significantly different physical properties. Consequently, these phases thin at different rates depending on the sample preparation procedure. A new TEM foil preparation method for the ductile phase toughened Nb‐10 a/o Si material has been developed. The method involves chemical thinning in a 70% nitric acid/ 30% hydrofluoric acid solution followed by electropolishing in a 12.5% sulfuric acid/87.5% methanol electrolyte at −40°C. This procedure for making TEM foils results in large thin areas with the minimum of artifacts. Mechanical grinding of a sample followed by either ion milling, dimpling, or electropolishing produced foils with large electron transparent areas, but with uncharacteristic features of the original Nb‐10 a/o Si alloy microstructure. These artifacts were identified as dislocations, surface mottling, and antiphase domains. © 1992 Wiley‐

ISSN:1059-910X    

DOI:10.1002/jemt.1070220307

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe growth of cultured epithelial cells on permeable supports allows increased cell differentiation and the assessment of a variety of transcellular and paracellular transport processes. The need to assess the corresponding ultrastructural characteristics of these cells underidentical conditions prompted this laboratory to develop a reliable method for producing freezefracture replicas of these cultures. Sections of filter inserts with the cell‐side facing up are placed between layers of polyvinyl alcohol with a strip of mylar positioned on the upper layer of polyvinyl alcohol. Following freezing, the monolayer is fractured by lifting the mylar strip from the assembly. The result is a consistent fracture of the apical membrane sufficient for analysis of tight junction sealing strands, microvilli distribution, and intramembranous particle (IMP) distribution between apical and lateral membrane domains. This method utilizes standard equipment and readily available materials and, most importantly, allows the freeze‐fracture and replication of an undisturbed cell monolayer. © 1992 Wiley‐Lis

ISSN:1059-910X    

DOI:10.1002/jemt.1070220308

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

年代:1992

数据来源: WILEY

ISSN:1059-910X    

DOI:10.1002/jemt.1070220309

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

年代:1992

数据来源: WILEY

ISSN:1059-910X    

DOI:10.1002/jemt.1070220301

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

年代:1992

数据来源: WILEY