摘要:

AbstractUnderstanding the mechanisms of muscle pattern formation requires that the complete sequence of ontogenetic events be defined, particularly in the emergence of architectural complexity and in the spatial relations between muscles and skeletal elements. This analysis of visceral arch myogenesis in quail (Coturnix coturnix japonica) embryos identifies the location of premuscle condensations and subsequent segregation of individual muscles, documents the initial orientation of myofibers and changes in alignment associated with maturation, and describes the spatial and temporal relations between muscle development and the formation of connective tissues.Premuscle condensations form within the visceral arches on embryonic days 2–4, before skeletal elements make their appearance. Discrete muscles may form from the subdivision of a muscle mass after fiber orientations have been established (e.g., jaw adductor and hyobranchial muscles) or by the segregation of a mesenchymal cluster from the condensation prior to the appearance of oriented fibers (e.g., protractor, muscle of the columella).The rate and pattern of subsequent muscle maturation are closely associated with the development of the hard tissues. Myogenesis in 4–9‐day embryos centers around the quadrate cartilage, the retroarticular process of the mandibular (Meckel's) cartilage, and the epibranchial cartilage. Muscles form attachments on these elements and remain without additional attachments until the appropriate elements (e.g., otic capsule, pterygoid bone) develop. No single description of myogenic events applies to all visceral arch muscles, nor is there an arch‐specific pattern of ontogeny. Rather, each muscle has distinctive characteristics based on its spatial relations within the developi

ISSN:0002-9106    

DOI:10.1002/aja.1001830402

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

年代:1988

数据来源: WILEY

摘要:

AbstractIndia‐ink‐imaged blood‐vessel networks in cleared tympanic membranes and adnexa from ten neonatal dogs were examined microscopically and photographed. The major significance of the study lies in documentation of a dual source of arterial supply, a bilaminar relationship of arterial and venous plexuses intrinsic to the tympanic membrane, and a consistent major venous pathway relative to a definite locus (pars flaccida of the membrane). Illustration of all three types of blood pathways (arteries, veins, and capillaries) provides new vasculoanatomic data that are essential to ear surgery, specifically—to myringotomies and myringoplasties. A comparison was made between dog and human tympanic membrane structures and their arterial supplies. Close similarities suggested that dog tympanic membrane might serve as a suitable model for development of innovative surgical procedures and as a model for rehearsal of difficult techniques. The results of this investigation provide a valuable caveat to oto

ISSN:0002-9106    

DOI:10.1002/aja.1001830403

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

年代:1988

数据来源: WILEY

摘要:

AbstractExtracted human deciduous teeth undergoing physiological root resorption were fixed with a mixture of formaldehyde and glutaraldehyde and processed for scanning (SEM) and analytical transmission electron microscopy, as well as acid trimeta‐phosphatase cytochemistry. The granulated tissues, which are rich in multinucleated odontoclasts and capillary vessels, formed various resorption lacunae on the resorbing dentin surfaces. SEM observations of dentin surfaces treated with sodium hypochlorite revealed two types of resorption lacunae: deep, round lacunae in which the peritubular matrix of dentinal tubules was strongly dissolved; and shallow, irregular lacunae with intact peritubular matrix. In trypsin‐treated materials, the resorption surfaces were characterized by the presence of numerous collagen fibers in both the peritubular and intertubular matrices, suggesting demineralization of the surface dentin. Odontoclasts were characterized by the presence of abundant mitochondria, perinuclear stacks of Golgi membranes, various lysosomes, numerous endocytotic vacuoles, and a well‐developed ruffled border against the resorption lacunae. Most endocytotic vacuoles were distributed in the cytoplasm between the ruffled border and the nuclei. In undemineralized ultrathin sections, the surface dentin of resorption lacunae consisted of collagen fibers and apatite crystals and had a lower packing density than those in unresorbed, deeper dentin. Many apatite crystals were demonstrated to be present in the extracellular channels of the ruffled border and in adjacent endocytotic vacuoles derived from it. Lysosomes located in the perinuclear cytoplasm of odontoclasts contained amorphous dense material and/or a small amount of crystals. An energy‐dispersive x‐ray micro‐analysis of apatite crystals in undemineralized sections indicated that the energy spectrum peaks of Ca and P detected from crystals in resorbing dentin were much lower than those in unresorbed dentin. Similarly, lower spectrum peaks of Ca and P were obtained from crystals found in the ruffled border and endocytotic vacuoles of odontoclasts. A slight trace Ca peak also was detected in the amorphous dense material in lysosomes of odontoclasts. The enzyme cytochemistry of lysosomal acid trimetaphosphatase indicated that odontoclasts had intense enzymatic activity in the Golgi membranes, endoplasmic reticulum cisternae, lysosomes, and endocytotic vacuoles. Dense reaction precipitates of enzymatic activity also were found along the dentin surfaces of resorption lacunae occupied by odontoclast ruffled borders. These results suggest that, during physiological root resorption of human deciduous teeth, odontoclasts perform, at least in part, extracellular demineralization of the surface dentin and subsequently resorb and dissolve some liberated apati

ISSN:0002-9106    

DOI:10.1002/aja.1001830404

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

年代:1988

数据来源: WILEY

摘要:

AbstractImmunohistochemical staining for glial fibrillary acidic protein (GFAP) was employed as a tool for quantification of astrocytes in the rat brain. One‐micron‐methacrylate sections were prepared from 70‐μm slices stained for GFAP by using a preembedding staining procedure. Numbers/unit area of astrocytes and nonastrocytes were determined for cortex, corpus callosum, and hippocampal neuropil. In each, counts from GFAP‐stained, toluidine‐blue‐counterstained sections were compared with counts obtained from sections stained with toluidine blue alone. Numbers of nonastrocytes and total glia in all three regions were comparable in both groups of sections. Astrocyte counts in the cortex and hippocampus also showed no significant differences between the two groups. In contrast, the number of astrocytes in the corpus callosum was significantly lower in GFAP‐stained, toluidine‐blue‐counterstained sections than in sections stained with toluidine blue alone. GFAP immunohistochemistry is a useful tool for the quantification of astrocytes in semithin plastic sec

ISSN:0002-9106    

DOI:10.1002/aja.1001830405

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

年代:1988

数据来源: WILEY

摘要:

AbstractDevelopment of the dermal ridges in volar skin was investigated in 28 pigtailed macaque (Macaca nemestrina) fetuses of known gestational age, ranging from 51 days postconception to newborn. Histology, scanning electron microscopy, and staining of the abraded dermal surface were used in the study. Morphological features of the dermal‐epidermal system and their changes with advancing age are described. Chronology was established for stages in the development of the volar skin, i.e., the differentiation of the primary and secondary epidermal ridges (PER and SER) at the undersurface of the epidermis corresponding to the formation of primary and secondary dermal ridges (PDR and SDR) and the development of the dermal papillae. PDRs were first seen at 55 gestational days and SDRs at 93 days. Differentiation of sweat ducts occurred over the period between 60 and 119 gestational days. A regional sequence of differentiation starting with the digital apices of the hand and ending in the calcar area and the phalanges of the foot was documented. Generally, morphogenesis in the macaque was accelerated relative to that in the human fetus by approximately 3 week

ISSN:0002-9106    

DOI:10.1002/aja.1001830406

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

年代:1988

数据来源: WILEY

摘要:

AbstractMembrane specializations of the contact region between afferent nerve endings and supporting cells of the sensory epithelia of guinea‐pig vestibular endorgans were examined by thin‐section and freeze‐fracture electron microscopy. The calyx‐type nerve endings (C‐endings) are separated from supporting cells (SC) by a 25–30 nm space. At irregular intervals along the upper lateral surface of supporting cells, the intercellular space narrows markedly to form special close contacts between the C‐ending and SC plasma membranes. Freeze‐fracture replicas reveal membrane specializations—orthogonal arrays of particulate units—in the region where the close intercellular contacts were found in sections. Orthogonal arrays consisting of from 5 to 20 units were observed on the cytoplasmic (P) fracture face of the lateral SC plasma membrane. These particulate units form a 12 × 12‐nm square, and each unit is composed of four 6‐nm subunits. Possible roles of the orthogo

ISSN:0002-9106    

DOI:10.1002/aja.1001830407

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe chronology of development of spindle neural elements was examined by electron microscopy in fetal and neonatal rats. The three types of intrafusal muscle fiber of spindles from the soleus muscle acquired sensory and motor innervation in the same sequence as they formed—bag2, bag1, and chain. Both the primary and secondary afferents contacted developing spindles before day 20 of gestation. Sensory endings were present on myoblasts, myotubes, and myofibers in all intrafusal bundles regardless of age. The basic features of the sensory innervation—first‐order branching of the parent axon, separation of the primary and secondary sensory regions, and location of both primary and secondary endings beneath the basal lamina of the intrafusal fibers—were all established by the fourth postnatal day. Cross‐terminals, sensory terminals shared by more than one intrafusal fiber, were more numerous at all developmental stages than in mature spindles. No afferents to immature spindles were supernumerary, and no sensory axons appeared to retract from terminations on intrafusal fibers. The earliest motor axons contacted spindles on the 20th day of gestation or shortly afterward. More motor axons supplied the immature spindles, and a greater number of axon terminals were visible at immature intrafusal motor endings than in adult spindles; hence, retraction of supernumerary motor axons accompanies maturation of the fusimotor system analogous to that observed during the maturation of the skeletomotor system. Motor endings were observed only on the relatively mature myofibers; intrafusal myoblasts and myotubes lacked motor innervation in all age groups. This independence of the early stages of intrafusal fiber assembly from motor innervation may reflect a special inherent myogenic potential of intrafusal myotubes or may stem from the innervation of spindles by sens

ISSN:0002-9106    

DOI:10.1002/aja.1001830408

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

年代:1988

数据来源: WILEY

摘要:

AbstractStages in the development of sensory ganglia in the regenerating newt tail after amputation are described by taking advantage of the rostrocaudal developmental gradient of the regenerating tail. A series of ganglia, beginning at the tip of the regenerate and progressing rostrally, were examined. Eight‐week regenerates were used because they showed the most complete array of stages. The first recognizable ganglia appear as small clusters of cells sitting dorsally on the already established ventral roots. The cluster of ganglionic cells steadily expands with the addition of many new cells. Signs of cell differentiation within the ganglion precede the formation of the dorsal root rudiment, which assumes several different configurations but most commonly enters the cord close to the ventral root. Our material suggests that ganglion precursor cells originate in the ventral region of the developing spinal cord and migrate out of the cord by travelling along the ventral root until, at a suitable distance from the cord, they halt, proliferate, and eventually differentiate. In the regenerate, we saw no evidence of neural crest cells—such as those that give rise to ganglia in the trunk region during development—forming at the dorsal region of the regenerated neural tube. Nor was there any morphological evidence of mesenchymal contribution to the ganglion cell clu

ISSN:0002-9106    

DOI:10.1002/aja.1001830409

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

年代:1988

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001830401

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

年代:1988

数据来源: WILEY