American Journal of Anatomy最新文献

The three-dimensional structure of alveolar epithelial type II cells was imaged using a computer-based system designed for reconstruction and quantitative analysis of serially sectioned specimens. Six type II cells were reconstructed from serial ultrathin sections of lungs from two Sprague Dawley male rats and the results were compared to standard morphometric estimates of type II cell composition from five other Sprague Dawley male rats. A minor portion of the type II cell surface was in contact with the alveolar airspace while most of the cell surface was embedded in the alveolar septal interstitium. The type II cells contained multiple Golgi regions located close to the nucleus. Mitochondria formed a few branching filamentous networks extending throughout the cell. The reconstructed cells appeared to represent a homogeneous population having fractional volumes of intracellular organelles very similar to those found by morphometric techniques. The spatial distribution of secretory organelle volume suggests that the organization of this cell type reflects an ordered progression of secretory particle maturation which is consistent with earlier hypotheses of lamellar body assembly.

The histochemical localization of dipeptidyl peptidase II (Dpp II; E.C. 3.4.14.2) activity was demonstrated at the light microscope level in the rat spinal cord. Prominent staining was observed in motoneurons of the ventral horn and in medium to large neurons in the deep laminae of the dorsal horn, the intermediate gray, and in lamina X surrounding the spinal canal. Within neurons, Dpp II was localized largely in cell perikarya and large primary dendrites with no staining observed in cell nuclei. Neurons in the superficial dorsal horn lack Dpp II enzyme activity. Nonneuronal elements which also stained prominently were pericytes associated with blood vessels and ependymal cells lining the lumen of the spinal canal. A few oligodendrocytes and astrocytes were also stained, but they represented a minor component of the total amount of Dpp II activity. Following ventral root injury, Dpp-II-containing motoneurons degenerate; some glial cells in the region of degenerating neurons become Dpp II positive. The localized distribution of Dpp II in spinal cord neurons suggests that this proteolytic enzyme may play a role in the metabolism of an unidentified neuropeptide.

Distributions of 53 motor axons to different types of intrafusal fibers were reconstructed from serial 1-micron-thick transverse sections of 13 poles of spindles in the rat soleus muscle. The mean number of motor axons that innervated a spindle pole was 4.1. Approximately 60% of motor axons lost their myelination prior to or shortly after entry into the periaxial fluid space of spindles. Motor innervation to the juxtaequatorial portion of nuclear bag fibers (particularly the bag1) consisted of groups of short, synaptic contacts that were terminations of thin, unmyelinated axons. In contrast, motor endings on both the bag1 and bag2 fibers were platelike in the polar intracapsular region. Chain fibers had a single midpolar platelike ending. The ratio of motor axons that innervated the bag1 fiber exclusively to axons that innervated bag2 and/or chain fibers was 1:1. However, one-fourth of motor axons coinnervated the dynamic bag1 fiber in conjunction with static bag2 and/or chain fibers. Thus the complete separation of motor control of the dynamic bag1 and static bag2 intrafusal systems observed in cat tenuissimus spindles is neither representative of the pattern of motor innervation in all other species of mammals nor essential to normal spindle function.

Intact, 14- to 21-day fetal rat lung pairs, neonatal lungs, and cultured 15- and 16-day lung explants were examined in 2-micron-thick glycol methacrylate sections stained by PAS-lead hematoxylin. Selected stages were also studied in histochemical preparations for aliesterase and formaldehyde-induced monoamine fluorescence, as well as by scanning and transmission electron microscopy. Neuroepithelial bodies (NEBs) first appear in pseudoglandular lungs at 15 days in vivo as pyramidal groups of basal, diffusely lead-hematoxylin-positive cells in glycogen-depleted epithelium of main and lobar bronchi. By day 16, primitive NEBs occur within three to four generations of the terminal buds, and older, proximal bodies are larger and more distinctive than at 15 days. Aliesterase activity is first detected in basally located, developing NEBs on day 16. During the canalicular and alveolar sac periods, NEBs appear and mature on a proximal-to-distal gradient along the airway, as they do in developing rabbit and human lungs. As earlier-formed airways elongate, additional NEBs appear and supplement the population already present. By days 20-21, NEBs occur at all airway levels down to the bronchiolo-alveolar junctions, and many of the cells have discrete PAS- and lead-hematoxylin-positive, infranuclear granules. Near term some NEBs exhibit serotonin fluorescence after incubation in 5-hydroxytryptophan and have abundant, ca. 100-nm, electron-dense granules. These are concentrated toward the cell base like the stained granules visualized by light microscopy. Similar results were obtained from lungs placed in organ culture. From 2 days in culture to a time equivalent to term, NEB formation parallels that in vivo, indicating that developmental requirements are met in in vitro. Taken altogether, morphologic and cytochemical evidence suggests that NEBs of rats are functional in late fetal life and that their development is relatively independent of extrapulmonary influences and of the intraepithelial ingrowth of sensory nerve endings.

Previous studies have shown that the functionally enigmatic pineal "synaptic" ribbons are structurally a heterogeneous group of organelles consisting of rodlike ribbons sensu stricto, spherules, and intermediate forms. As ribbons and spherules react differently under various experimental conditions, these organelles were studied qualitatively and quantitatively during the postnatal period in guinea pigs. It was found that the pinealocytes were highly differentiated at birth and contained all three forms of "synaptic" structures. Ribbons and intermediate forms were more abundant than spherules and exhibited a striking increase in number on postnatal days 1 and 2; this increase was followed by a distinct trough and by a second peak at days 12 and 13, after which their numbers declined to reach adult levels by day 20. The spherules were small in number at birth and did not show the large immediate postnatal increase observed for the ribbons and intermediate forms. Instead there was a steady numerical increase up to day 12 (absolute number) or day 15 (relative numbers), followed by a decrease to adult level by day 20. Whereas during the early postnatal period (days 1 to 3) the majority of pinealocytes were characterized by ribbons and intermediate forms, with increasing age spherule-bearing pinealocytes increased in number. As ribbons and spherules were usually not found in the same pinealocyte, the present findings are interpreted to mean that ribbons and spherules characterize different types of pinealocytes showing an inverse numerical development postnatally. Developmentally intermediate forms behave like ribbons.

Early-, mid- and late-passage cultures (population doubling levels 12, 35, and 51, respectively) of IMR-90 fibroblasts were exposed to 3H-thymidine for 48 h prior to fixation in situ for morphometric analysis in order to determine quantitatively what ultrastructural changes accompany the loss of proliferative capacity during aging in vitro. Analysis of autoradiographs, both at the light and electron microscopic levels, with an image analyzer followed by ANOVA statistical scrutiny demonstrated that a significant increase in relative cell area, an indicator of cell size, was characteristic of cells unable to incorporate 3H-TdR at both mid- and late-passage, but not at early-passage levels. Nuclear size also increased significantly with progressive passage level but was not related to proliferative capacity. No significant difference in the area fraction of nucleoli per unit area of nucleus or of mitochondria, Golgi, or lysosomes was seen in either subpopulation at any passage level. Dilated cisternae of rough endoplasmic reticulum in early-passage cells were seen if cells were harvested with trypsin and fixed either before or after centrifugation, but were not seen in labeled or unlabeled cells from any passage level when cultures were fixed in situ. We conclude that a significant increase in cell size is the only significant morphological change associated with the loss of proliferative capacity of IRM-90 fibroblasts. Furthermore, our data indicate that there is no accumulation of secondary lysosomes in human diploid fibroblasts during aging in vitro; we therefore cannot support any hypothesis of aging or proliferative decline that is based mechanistically upon this phenomenon.

The stomachs of adult CD1 mice were investigated by anatomical examination and light microscopy. Serial sections were prepared of entire stomachs; the various types of gastric glands were characterized; and, using every 30th or 60th serial section, maps of gland distribution were obtained through point-plotting serial reconstruction. Gross examination shows that the cephalic third of the stomach consists of a thin-walled, domelike structure, the forestomach. The rest of the organ, or stomach proper, is subdivided into two parts, the thick-walled corpus, which approximately occupies the middle third, and the less vascular pyloric antrum which forms the remaining caudal third of the organ. Histologically, glands are absent from the forestomach mucosa but are numerous throughout the stomach proper. They are of two main types, namely, zymogenic glands, which contain, among others, zymogenic cells, and mucous glands, which lack these cells but contain mucous cells. Both gland types show a few enteroendocrine cells. Moreover, some of the mucous glands include parietal cells (mucoparietal glands), while others do not (pure mucous glands). Mucosal maps reveal that the glands of each type are located in distinct areas of the mucosa. Thus a compact zymogenic region may be defined, occupying 56% of the glandular mucosa and containing only zymogenic glands. The mucous region, on the other hand, composed only of mucous glands, is extensive and divided into a narrow cephalic band (5.2% of the glandular mucosa) and a large caudal part (38.8%). Along the lesser curvature these parts are continuous, and together they encapsulate the zymogenic region. In proximity to the border of this region, and only there, do the mucous glands include parietal cells. A comparison of mucosal maps and gross features indicates that the corpus includes both the zymogenic region and the cephalic band of mucous glands, whereas the antrum is composed entirely of the mucous glands of the caudal part.

In order to demonstrate the possible role of prostaglandins in preovulatory follicular development, immature mice superovulated with pregnant mare serum followed 40 hours later by luteinizing hormone (LH) were treated with the prostaglandin-synthetase inhibitor, indomethacin. Indomethacin (10 mg/kg) injected at varying intervals prior to or following LH inhibited ovulation most effectively when administered within 2 hours of the ovulatory gonadotropin. This inhibition was accompanied by (1) suppression of the morphological changes normally occurring within the follicular wall during preovulatory development and (2) failure of germinal vesicle breakdown (GVBD) in two-thirds of the follicles examined. When GVBD occurred, indomethacin treatment appeared to delay meiotic maturation. Cumulus tissue was more compact than in control follicles and maintained a close association with the oocyte. These results suggest that alterations in the morphology of the follicle prior to ovulation--specifically, thinning of the apical follicular wall and meiotic maturation--are regulated by prostaglandins.

Mesoderm formation in the mouse embryo begins at 6.5-6.75 days p.c. (postcoitum) when a primitive streak is formed along the posterior side of the egg cylinder. Epiblast cells in a localized region separate from one another and spread laterally between the primitive endoderm and the rest of the epiblast. The newly formed mesoderm contributes to both embryonic and extraembryonic regions. When the endoderm is removed, a definitive somitomeric pattern is first observed in the lateral sings of mesoderm of the mid-primitive-streak-stage embryo. The sequential appearance and the placement of somitomeres in the gastrulating mouse embryo are closely related to the general changes in physical dimensions and to the pattern of tissue growth which occur during the maturation of the egg cylinder. By the late-primitive-streak stage, about four somitomeres are present in the paraxial mesoderm on either side of the embryonic axis. These somitomeres will undergo morphogenesis and give rise to the cranial segments and head mesenchyme of neurulating embryos (Meier and Tam, 1982). The midline or axial mesoderm, consisting of prechordal plate and notochord, is derived from the head process mesoderm originating from the anterior end of the primitive streak. Cells of the head process are compact and adherent to the endoderm. The early presence of a somitomeric pattern which persists and is added to throughout subsequent phases of mesoderm formation suggests that spreading mesodermal cells have relatively stable neighbor relationships. This morphological evidence supports the idea that the expansion of the mesoderm during gastrulation results from tissue growth and progressive deposition of cells from the primitive streak. Cell migration may be limited principally to nonsomitomeric mesodermal cells found in the leading edge of the spreading lateral wings.

As a necessary preliminary step to the study of pulmonary hypertension and edema, the structure of the pulmonary vasculature of seven normal dogs was examined in detail to distinguish arteries and veins. For light microscopy and morphometry, the left lung was injected from the arterial and venous sides with pigmented gelatin masses of different colors. The right lung was fixed for electron microscopy. The percentage of medial muscle thickness of arteries was greater (P less than 0.05) than that of veins, for vessels over 200 micrometer diameter. Smooth muscle cells extended more peripherally into arteries (including in vessels less than 50 micrometer) than into veins. The larger arteries were elastic or transitional in type, whereas larger veins were muscular. The arteries branched with the airways. Fifty percent of arteries under 50 micrometer and more than 50% of veins under 200 micrometer were surrounded by alveoli. Muscular arteries had a thick media between distinct internal and external elastic laminae, whereas veins had no internal lamina but had a thin media separated from a thick adventitia by an external elastic lamina. By electron microscopy, the muscular arteries had tightly packed smooth muscle cells with few myoendothelial junctions; the venous smooth muscle cells were arranged loosely, and more numerous myoendothelial junctions were seen. no definite differences were noted between nonmuscular arteries and veins. The functional implications of these morphological findings (differential reactions to pharmacological agents, distensibility of pulmonary arteries and veins, and responses of small vessels to alveolar pressure) are discussed.