ISSN:1059-910X    

DOI:10.1002/jemt.1070260202

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

年代:1993

数据来源: WILEY

摘要:

AbstractWe have examined developing taste buds in fungiform papillae of rats from the 18th day of gestation (E18) to the 15th postnatal day (P15). Nerve processes were seen in the epithelium of E18 rats before taste buds were obvious. At E20, early taste buds were visible, but were embedded within the epithelium, i.e., their cells were shielded from the oral cavity by overlying squamous epithelium. At this stage, the epithelium on the lateral aspects of the fungiform papillae was keratinized, but that overlying the taste bud was not. Some taste bud cells at E20 contained synapse‐like structures near their contacts with nerve processes. In postnatal animals, keratinized epithelial cells were seen overlying taste buds, but taste pores were not observed until P10. How, then, do stimuli reach the taste cells and elicit physiological and behavioral responses as reported by others? The keratinized epithelium overlying the buds was unlike that on the lateral aspect of the papilla in at least one significant way. Few lamellated bodies were present in intercellular spaces beneath the stratum corneum, whereas these were abundant in the corresponding location within epithelium on the slope of the papilla. Although some were present within the squamous epithelium overlying the bud, they apparently were not released into the intercellular space. These lipid‐rich lamellated bodies are thought to represent the water barrier of the epithelium, i.e., the barrier which prevents aqueous solutions from passing through the epithelium. We determined that the keratinized epithelium overlying the taste bud was permeable to a tracer, lanthanum nitrate, whereas that on the lateral surface was not. Lanthanum was visualized around taste cells and around nerve profiles within and near the taste bud. We propose that the absence of an aqueous permeability barrier in the epithelium overlying taste buds likely explains the ability of tastants to reach the taste bud cells and nerves in the developmental period before pore formation. © 1993 Wiley‐Lis

ISSN:1059-910X    

DOI:10.1002/jemt.1070260203

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe taste bud is a receptor form observed across vertebrates. The present report compares chick taste buds to those of other vertebrates using light and electron microscopy.Unlike mammals, but common to many modern avians, the dorsal surface of chick anterior tongue lacks taste papillae and taste buds. Ultrastructurally, chick buds located in the anterior floor of the mouth (as in some reptiles and amphibians) and palate contain dark, intermediate, light, and basal cell types. Dark, intermediate, and light cells extend microvilli into intragemmal lumina and pores communicating with the oral cavity. As specialized features, dark cell apices lack dense granules and exhibit short microvilli relative to light and intermediate cells. Dark cell cytoplasmic fingers envelop intragemmal nerve fibers and cells as in other species, and sometimes contain abundant clear vesicles. Nerve profile expansions often are located adjacent to dark, intermediate, and light cell nuclei. Classical afferent synaptic contacts are rarely observed.Taste cell turnover is suggested by mitotic and degenerating figures in chick buds. In addition, tritiated thymidine injected into hatchlings, whose anterior mandibular oral taste bud population approximates that in adults, reveals a turnover rate of about 4.5 days. This is about half that observed in altricial mammals, reflecting a species difference or developmental factor in precocial avians.It is concluded that chick taste buds exhibit morphologic features common to other vertebrate buds with specializations reflecting the influences of niche, glandular relations, and/or age. © 1993 Wiley‐Liss, I

ISSN:1059-910X    

DOI:10.1002/jemt.1070260204

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe epithelial downgrowth arises in the presumptive foliate papilla region of the tongue approximately at prenatal day 22, and the distal portion of the primary epithelial cell cords transforms to the bifurcated serous gland and excretory duct between prenatal day 30 and postnatal day 2. The excretory ducts extend upward through the primary epithelial cell cords at rather random intervals and are open to the tongue surface between postnatal days 1 and 2. In this process, successive connections between the adjacent ascending excretory ducts occur mainly due to desquamation of the keratinized lining cells of the ducts, resulting in the formation of the foliate gutter.Taste bud primordia appear in the primary epithelial cell cords by nerve penetration through the basal lamina from prenatal day 30 and nearly fully formed taste buds facing the ascending excretory ducts have been already observed before the foliate gutter formation is completed.In the differentiation process of chemoreceptor (type III) cells from less‐differentiated basal (type IV) cells, subsurface cisterns of endoplasmic reticulum are occasionally present where nerve endings make contact. Since subsurface cisterns have been considered to be involved in reciprocal or efferent synaptic transmission, it is reasonable to consider that these morphological specializations may take a role in neurotrophic signals for differentiation of the chemoreceptor cells. © 1993 Wiley‐Liss,

ISSN:1059-910X    

DOI:10.1002/jemt.1070260205

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

年代:1993

数据来源: WILEY

摘要:

AbstractThaumatin is a protein that tastes intensely sweet only to Old World monkeys and to higher primates, including man. Here we used pre‐embedding ultrastructural methods to study the distribution of thaumatin in apical regions of Rhesus monkey foliate papillae, using thaumatin conjugated to 5 nm gold particles. With freeze‐substitution we saw that gold‐labeled thaumatin bound to an electron‐opaque, sponge‐like secretory substance inside the taste bud pores. Labeled thaumatin was found at the surface of the secretory substance even deep inside the pore, where other, unlabeled cellular structures surrounded the substance. With freeze‐fracture deep‐etching the secretory substance that bound the thaumatin‐gold particles appeared coarsely granular. There was no labeling of any other taste bud pore structure, including microvilli and small membranelined vesicles. Pre‐incubation with an excess of unlabeled thaumatin inhibited binding with goldlabeled thaumatin. The results suggest that the secretory substance had the greatest affinity of all taste pore structures to the sweet‐tasting compound under our experimental conditions. Therefore, gustatory reception probably involves various taste compound binding structures, microvilli, and also secretory substances like the one described here which bound thaumatin. We speculate that the secretory substance may bind taste stimuli and serve as an intermediate between stimuli and receptors. It could be involved in stimulus removal or delivery or both. ©

ISSN:1059-910X    

DOI:10.1002/jemt.1070260206

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

年代:1993

数据来源: WILEY

摘要:

AbstractWe have used high voltage electron microscopy and computer‐generated three‐dimensional reconstructions from serial sections to elucidate the structure of taste bud cells and their associated synapses in fungiform taste buds of the mouse. Five fungiform taste buds (two of which were serially sectioned) were examined with the high‐voltage electron microscope (HVEM). We identified the synaptic connections from taste cells onto sensory nerve fibers and classified the presynaptic taste cells based on previously established ultrastructural criteria. From those data we have distinguished dark, intermediate, and light cells in murine fungiform taste buds. Synapses in murine fungiform taste buds are fewer in number, but contain many more vesicles than synapses in either foliate or circumvallate taste buds. Synapses in mouse circumvallate and foliate taste buds typically contain a few to several synaptic vesicles per section, whereas fungiform synapses may have in excess of 100 vesicles per profile. The significance of these differences in the numbers of synapses and synaptic structure between fungiform and circumvallate/foliate synapses is not known. Based on the small number of synapses observed in fungiform taste buds, we speculate that fungiform taste buds have only a few cells transducing sensory stimuli at any given time. Alternatively, communication of sensory information from the taste receptor cells to the afferent nerve fibers may be mediated by some other mechanism(s) in addition to classical chemical synapses. © Wiley‐L

ISSN:1059-910X    

DOI:10.1002/jemt.1070260207

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

年代:1993

数据来源: WILEY

摘要:

AbstractA novel cross‐sectional sample preparation technique for quantum wire (QWR) structures is described. By coating a thin layer of Au with a designed pattern on the sample as a marker to indicate the position of the wire pattern, the location of the thinned area can be controlled precisely. An example of applying this technique to an InGaAs/GaAs QWR structure is demonstrated. This technique can also be applied to any other small dimensional structures or devices with specific regions of interest. © Wiley‐Liss,

ISSN:1059-910X    

DOI:10.1002/jemt.1070260208

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

年代:1993

数据来源: WILEY

摘要:

AbstractA selected area mechanical polishing technique has been developed to improve the precision of cross‐sectional TEM sample preparation, based upon the early work of Benedict and colleagues [Benedict et al. (1990) MRS Symp. Proc. Vol. 199, p. 189]. TEM samples were made from a pre‐selected section through the middle of a 1 μm wide band of transistors extending laterally for more than 1 mm by precise control over the plane of polish with a corresponding reduction in sample preparation time. To illustrate the application of this technique, a uniformly thin, electron transparent TEM sample of a single, specific, failed transistor is obtained from a 4 mm by 10 mm device array. © Wiley‐Li

ISSN:1059-910X    

DOI:10.1002/jemt.1070260209

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

年代:1993

数据来源: WILEY

ISSN:1059-910X    

DOI:10.1002/jemt.1070260210

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

年代:1993

数据来源: WILEY

ISSN:1059-910X    

DOI:10.1002/jemt.1070260211

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

年代:1993

数据来源: WILEY