ISSN:0003-276X    

DOI:10.1002/ar.1092300102

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe structure of the meninges, with particular attention to the architecture of the inner portions of the dura mater and the arachnoid mater, has been reviewed in reference to the probable existence of a “subdural” space. The dura is composed of fibroblasts and large amounts of extracellular collagen. The innermost part of the dura is formed by the dural border cell layer. This layer is characterized by flattened cells with sinuous processes, extracellular spaces containing an amorphous material, and the presence of junctions between its cells. The dural border cell layer is continuous with the inner (meningeal) portions of the dura and may be attached to the underlying arachnoid by an occasional cell junction. The arachnoid consists of an outer part, the arachnoid barrier cell layer, and an inner portion, the arachnoid trabeculae which bridge the subarachnoid space. Arachnoid barrier cells are electron‐lucent, closely apposed to each other, and joined by many cell junctions; in this layer there is little extracellular space and essentially no intercellular material. Arachnoid trabecular cells cross the sub‐arachnoid space in a random manner, have extracellular collagen associated with their flattened processes, and form structures of variable shapes and sizes. There is no evidence of an intervening space between the arachnoid barrier cell layer and the dural border cell layer that would correlate with what has been called the subdural space. When a tissue space is created in this general area of the meninges it is the result of tissue damage and represents, in most instances, a cleaving open of the dural border cell layer. In this situation, extracellular spaces in the dural border cell layer are enlarged, cell junctions are separated, and it is probable that cell membranes are damaged. A survey of reports describing the morphology of the inner and outer capsule of so‐called subdural hematomas in humans reveals that dural border cells are found in both parts of the capsule. Also, experimental infusion of blood into this portion of the meninges in animals frequently dissects open the dural border cell layer. These data support the view that what has been called a subdural hematoma is most frequently a lesion foundwithinthe layer formed by dural border cells.It is suggested that the so‐called subdural space is not a “potential” space since the creation of a cleft in this area of the meninges is the result of tissue damage. In this respect it shares no similarities with legitimate potential spaces (i.e., serous cavities) found at other locations in the body. It is concluded that there is no evidence of a subdural space (actual or potential) in the region of the dura‐arachnoid junction and it is suggested that the termspatium subduralebe removed from

ISSN:0003-276X    

DOI:10.1002/ar.1092300103

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe dura‐arachnoid junction is examined in normal animals and in animals subjected to subdural infusion of blood immediately prior to death, simulating acute subdural hemorrhages. The Norwegian landrace pig is used as the experimental animal. Horseradish peroxidase (HRP) has been added to the injected blood to serve as a macromolecular tracer. The material is studied by light and electron microscopy. Special attention is given to the level of the induced subdural cleavage plane, the total distribution of the infused blood, and the natural sites of drainage.The dura‐arachnoid junction, identified here as the subdural compartment (the dural border layer of others), consists of an avascular tissue with flake‐like, relatively electron‐lucent cells stacked upon each other in several layers with narrow intercellular clefts. Under normal conditions there is no evidence of a so‐called “subdural space.” When under the present experimental conditions bleeding takes place into this cellular tissue, it splits without any particular, predestined cleavage plane, although most often close to the fibrous matter of the dura. The bleeding extends throughout the cerebral and spinal parts of the compartment and also along the spinal nerve roots. Contamination of the subarachnoid space occurs only in some cases subjected to large infusions and apparently only at spinal levels. The HRP diffuses into the dura, but does not traverse the arachnoid

ISSN:0003-276X    

DOI:10.1002/ar.1092300104

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe subdural region within the cranial meninges is examined in guinea pigs by electron microscopy. The fine structures of the arachnoid membrane and dura are described separately in specimens that have been isolated from each other during removal from the cranial cavity. In addition, the fine structure of the intact dura‐arachnoid is described, where the subdural space would be present in an undisrupted state. Lastly, the inner surface of the dura and the outer surface of the arachnoid membrane are examined at the point of separation between the two specimens where the dura is reflected from the arachnoid by experimental dissection. From these observations morphologic criteria are established for identifying the constituents and boundaries of the subdural space and for explaining mechanisms in the histogenetic process of “opening” or enlarging this space.The morphologic identity of the classic subdural space is reinterpreted in light of the findings. The subdural space, traditionally described as a fluid‐filled potential cavity existing in an extracellular compartment, is not apparent in the guinea pig. Instead, fragile cells designated aslight cellsoccupy the compartment between the dura and arachnoid, with very little extracellular space available. Experimental opening of the subdural space occurs, significantly, along pathways extending by fracture through the cytoplasm and intercellular separation of these light cells rather than by enlargement of a preexisting mesothelial‐lined intercellular space between these cells and the true arachnoid cells. Cytoplasmic fine structure of light cells suggests a close kinship with cells in the meningeal layer of the dura. The functional significance of the light cells and their possible role in subdural hematomas is

ISSN:0003-276X    

DOI:10.1002/ar.1092300105

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn situ hybridization (ISH) of myosin heavy chain (MHC) mRNA, immunofluorescent detection of MHC protein, and oxidative enzyme histochemistry were performed on the same fibers in serially sectioned rabbit skeletal muscle. By combining these three techniques quantitatively, on a fiber‐by‐fiber basis, fibers that expressed mRNA complementary to a fast MHC cDNA pMHC24–79 of unknown subtype (Maeda et al., 1987) were classified into fiber types with respect to slow myosin expression and oxidative capacity. As expected, slow fibers had low hybridization to pMHC24–79. Fast fibers were divided into three subtypes. mRNA from the low oxidative fibers (fast‐glycolytic, IIB) did not hybridize with pMHC24–79. Fast fibers whose mRNA hybridized best to pMHC24–79 were mainly in the intermediate range of oxidative capacity (probably IIX). The fast fibers with the highest oxidative capacity had low hybridization to this MHC mRNA (probably IIA). Thus, pMHC24–79 was identified as a clone of a fast isomyosin, tentatively designated as the fast IIX with intermediate oxidative capacity. The expression of more than a single species of fast and slow isomyosin mRNAs in classically defined fiber type was considered in interpretin

ISSN:0003-276X    

DOI:10.1002/ar.1092300106

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe distribution and morphological characteristics of myelinated and non‐myelinated axons innervating the lower canine periodontal ligament (PDL) in adult cats have been analysed. After perfusion fixation and decalcification, the teeth were slit transversely, divided into segments, and embedded in plastic. Ultrathin sections of each segment were examined in the electron microscope and used to reconstruct the whole PDL at 1, 4, 7, and 9 mm from the tooth apex. One millimeter from the tooth apex there were a mean of 920 myelinated axons and 1,415 non‐myelinated axons. The numbers of axons declined toward the tooth crown. Bundles of myelinated and small non‐myelinated axons lay adjacent to the blood vessels midway between the bone and cementum. Isolated myelinated axons appeared to have split away from these main nerve bundles and entered the avascular zone of the ligament, where they lost their myelin sheaths to become large non‐myelinated axons rich in mitochondria. These non‐myelinated axons sometimes appeared to be linked to collagen fibres and were thought to be the mechanoreceptor terminals.Twelve weeks after sectioning and inferior alveolar nerve, the total number of axons innervating the periodontal ligament was 50% of that found in the contralateral controls. The large non‐myelinated axons had smaller mean diameters and contained fewer mitochondria, a change which may be consistent with a reduction in mechanoreceptor e

ISSN:0003-276X    

DOI:10.1002/ar.1092300107

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe have observed an extra atrioventricular node in the normal heart of a human fetus. It is located in the septal wall of the right atrium, subendocardially, and just where Todaro's tendon leaves this wall to go toward the inferior vena cava valve. In its trajectory, this tendon gives way to a remarkable prominence in the cavity of the right atrium: the sinus band. In order to explain the embryogenesis of this extra atrioventricular node, we have studied the normal development of the atrioventricular specific system and have concluded that the atrioventricular node is formed from a growth and displacement toward the atrium of the primitive atrioventricular specific material, which originates from the myocardium of the posterior wall of the atrioventricular canal. Likewise, during its development, the atrioventricular node keeps in close proximity with the Todaro's tendon. In our view, this accounts for the embryogenesis of the extra atrioventricular node, since a fragment of the atrioventricular node can remain cranial to Todaro's tendon and be displaced by it in a craniodorsal direction. This fragment would then lead to the formation of an extra atrioventricular node like the one present in the heart of the fetus we have examined.

ISSN:0003-276X    

DOI:10.1002/ar.1092300108

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

年代:1991

数据来源: WILEY

摘要:

AbstractAlthough the artery wall consists of three distinct layers, only the structures of the intima and media have been well characterized. The adventitia has generally been overlooked. Our examination focused on the organization of elastin and collagen which are the major components of this tunic. Canine infrarenal aortas were excised, stretched to their in vivo length, then pressure fixed in formalin. Transverse, longitudinal, and frontal sections were prepared with specific elastin and collagen stains. Areas of adventitia in these sections were examined with LM, and interconnections between collagen and elastin were photographed at various magnifications. Subsequently, the slides were fractured for attachment to SEM stubs, and the coverslips were demounted. The identical areas were then examined with SEM using the LM micrographs as a guide to identify elastin and collagen. Whole mount aortic ring preparations were digested in formic acid for 72 and 96 h at 45°C to confirm adventitial elastin architecture. The adventitia was organized in alternating lamellae of collagen and elastin. The elastin lamellae consisted of continuous sheets of elastin with a longitudinal fibrillar substructure. Finer circumferential elastin fibers were also identified. These attached to both longitudinal elastin and adjacent collagen lamellae. Collagen lamellae were arranged in broad corrugated bands of fibrils. The unique architecture of the adventitia may explain some of the visco‐elastic properties of the aorta in both normal and pathologic stat

ISSN:0003-276X    

DOI:10.1002/ar.1092300109

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn recent years, the dentition of the pig has been increasingly used as a model for the study of amelogenesis. Indeed, much of our current knowledge on enamel formation derives from biochemical and physicochemical analyses of the organic and inorganic components, respectively, of porcine enamel. As an extension of this previous work, and as the first step in our attempt to correlate known enamel matrix and mineral changes with adjacent enamel organ morphology, the present study was undertaken to provide a description of the morphological events occurring in the enamel organ during porcine amelogenesis. Two‐week‐old miniature swine (minipigs) were fixed by vascular perfusion with glutaraldehyde, the deciduous teeth present at this age were embedded in Epon resin and sectioned, and the cells of the enamel organ at each of the various developmental stages of amelogenesis were examined by light and transmission electron microscopy. In many respects, the morphology of the porcine enamel organ was similar to that previously described in other mammalian species. On the other hand, several particularities were noted and these are discussed in the context of available data correlating cell ultrastructure with putative function during enamel format

ISSN:0003-276X    

DOI:10.1002/ar.1092300110

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe origin of growth cartilages in the neural arch of human fetal vertebrae was investigated in an attempt to resolve the conflicting opinion on ossification in this region. Serial sections of developing vertebrae were examined, and three growth cartilages for each half of the neural arch were found. They have their origin from a single center of ossification. Endochondral bone formation similar to ossification in the diaphysis of a long bone occurs in the neural arch. This information may help in the understanding of how vertebral malformations such as scoliosis and spondylolysis occur during postnatal life.

ISSN:0003-276X    

DOI:10.1002/ar.1092300111

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

年代:1991

数据来源: WILEY