Ultrastructural observations on beaded alpha-motoneuron dendrites

Beaded dendrites of alpha-motoneurons intracellularly labelled with horseradish peroxidase (HRP) were studied ultrastructurally in eight adult cats. For comparison, adjacent unlabelled beaded dendrites of unknown origin were also included in the study. Electron microscopy revealed no signs of degeneration or poor fixation according to common criteria. With the exception of the HRP-reaction product no difference in structure was observed between labelled and unlabelled beaded dendrites. Both the beads and their interconnecting segments were postsynaptic to boutons of normal appearance containing spherical (S-type boutons) or flattened vesicles (F-type boutons). The values for synaptic covering and synaptic packing density of the beaded dendritic regions, which usually were located in the periphery of the dendritic trees, were clearly lower than values obtained previously for cell bodies and proximal dendrites of alpha-motoneurons.     

Ultrastructural observations on beaded α-motoneuron dendrites

Beaded dendrites of 1α-motoneurons intracellularly labelled with horseradish peroxidase (HRP) were studied ultrastructurally in eight adult cats. For comparison, adjacent unlabelled beaded dendrites of unknown origin were also included in the study. Electron microscopy revealed no signs of degeneration or poor fixation according to common criteria. With the exception of the HRP-reaction product no difference in structure was observed between labelled and unlabelled beaded dendrites. Both the beads and their interconnecting segments were postsynaptic to boutons of normal appearance containing spherical (S-type boutons) or flattened vesicles (F-type boutons). The values for synaptic covering and synaptic packing density of the beaded dendritic regions, which usually were located in the periphery of the dendritic trees, were clearly lower than values obtained previously for cell bodies and proximal dendrites of a-motoneurons.     

Ultrastructural observations on gynecomastia

Ten cases of gynecomastia were studied by electron microscopy. The ducts showed proliferation of both epithelial and myoepithelial cells. Intracytoplasmic lumina, previously thought to be a feature of malignant breast lesions, were seen. Squamous metaplasia was observed in some cases. The stroma showed fibroblasts, myofibroblasts, and, occasionally, pericytes. The general morphology of gynecomastia is similar to that of benign lesions of the female breast at the ultrastructural level. The features of the stromal cells reflect the effects of estrogenic stimulation.     

Ultrastructural observations on the capillaries of human thyroid tumours.

Ultrastructure of the capillaries of malignant and benign thyroid tumours has been examined. The material consisted of biopsies from six cases of thyroid papillary carcinoma, one case of follicular (foetal type) adenoma and six cases of nodular adenomatous goitre. In the group of nodular adenomatous goitre and in the follicular adenoma, the capillary wall was made up of fenestrated endothelium similar to that of capillaries of normal human thyroid. The fenestrae occupied a large area of the endothelial wall. Micro- and macropinocytotic vesicles were frequent in the endothelial cytoplasm. In the thyroid carcinomas the papillary structures always contained numerous capillaries with fenestrated endothelium. The microfollicular area and the solid tumoral areas of the papillary carcinoma showed occasional capillaries with fenestrated endothelium, but many capillaries were lined with continuous endothelium. The capillaries in all the specimens were surrounded externally by a continuous basement membrane which was frequently bilaminate or multilaminate. This study indicates that capillaries with fenestrated endothelium are characteristic of thyroid tumours which arise from follicular cells.     

Ultrastructural observations on the pathogenesis of aspirin-induced gastric erosions.

It is shown by transmission electron-microscopy that the first structural change in rats, following a dose of aspirin, is to the basement membrane of the endothelial cell of the capillary and post-capillary venule. This leads to the breakdown of small blood vessels before any other cytolytic effect. This is a focal effect and it is proposed that the erosion develops as an ischaemic infarct.     

Ultrastructural characterization of effector-target interactions for human neonatal and adult NK cells reveals reduced intercellular surface contacts of neonatal cells

Limitations in neonatal natural killer (NK) cell responses may be associated with the less efficient newborn capacity to solve viral infections. Although these limitations have been extensively reported they are poorly characterized. Making use of the major histocompatibility complex (MHC) class I negative cell line K562, the parameters required for the initial events involved in neonatal NK/target cell interactions were determined and compared with adult blood NK cell/target cell interactions. Ultrastructural characterization of effector-target cell interactions revealed that neonatal NK cells are more strongly activated upon contact with K562 cells than adult blood NK cells. Furthermore, the neonatal capacity to establish contacts, in particular extensive contacts, is significantly reduced when compared with adult blood NK cells. However, no significant differences were found either in the cell surface expression levels or activation state of LFA-1, which could account for the reduced intercellular contacts. Because extensive contacts are crucial for effective immunologic synapse formation, these data suggest that a limited or nonsustained positive signaling may occur on neonatal NK cells, restricting their NK cell-mediated lysis capacity.     

Ultrastructural observations on smooth muscle tumors

The ultrastructure of a series of primary and metastatic smooth muscle tumors is reviewed. Myofilaments and other smooth muscle features were present in all primary leiomyosarcomas of the soft tissues and uterus. They were also present but were less plentiful in most of the metastatic leiomyosarcomas. Electron microscopy is therefore a useful method to establish the diagnosis of a suspected leiomyosarcoma. Stromal tumors of the gastro-intestinal tract may require correlated immunocytochemical and ultrastructural studies for their identification: 9 of the 50 cases examined were positive with immunostaining for S-100 protein, and 16 tumors with epithelioid transformation did not show evidence of smooth muscle differentiation by electron microscopy.     

Ultrastructural and immunocytochemical observations on angiosarcomas

Forty-seven angiosarcomas have been studied by light and electron microscopy. Neoplastic endothelial cells do not consistently display specific ultrastructural features, but certain aspects of the fine structure of the cells and their arrangement can be useful to establish or confirm the diagnosis. Experience with the common endothelial cell markers as diagnostic aids is briefly reviewed.     

Ultrastructural observations on Ehrlichia equi organisms in equine granulocytes.

The ultrastructure of the etiological agent of equine ehrlichiosis, Ehrlichia equi, was studied in equine peripheral leukocytes. The organisms occurred within membrane-lined cytoplasmic vacuoles of neutrophils and eosinophils. Ovoid, round, and rod-shaped profiles were observed. From 1 to 33 organisms were present in a thin-section profile of a cytoplasmic vacuole. Many cells contained multiple organism-containing vacuoles. The organisms had a cell wall and plasma membrane, and internally they consisted of electron-dense and lucid areas. A great variation in size was observed. The morphological features were most consistent with agents of the genus Ehrlichia.     

Ultrastructural observations on morphogenesis of atypical cilia

Though ultrastructural studies of bronchial epithelium both in man and in experimental animals revealed in a variety of conditions the presence of pathologically altered cilia, little is known about their genesis and significance. In this work we have described the alterations noticed in ciliary morphology during the formation of atypical cilia. A probable mechanism for their production is also proposed on the basis of our results.     

Ultrastructural observations on a follicular carcinoma of the thyroid gland.

Electron microscopic studies were performed on a follicular carcinoma removed from a 31-year-old woman. The tumor was poorly differentiated and inoperable but distinctly follicular in pattern. Ultrastructurally, the neoplasm had many of the features of papillary carcinoma, follicular adenoma, and anaplastic carcinoma. Due to the presence of secretory granules it even somewhat resembled medullary carcinoma, but the granules were distinctly larger, and the production of amyloid was definitely excluded.     

Ultrastructural observations of cytoplasmic inclusions in Tay-Sachs lymphocytes.

Our preliminary study on the circulating leukocytes from two children with Tay-Sachs disease and six heterozygotes from four different families is reported at the levels of both light and transmission electron microscopy. Ultrastructural investigation revealed two types of cytoplasmic inclusions in the lymphocytes of the Tay-Sachs homozygotes. The heterozygotes demonstrated only one of the inclusion forms within the cytoplasm of their circulating lymphocytes. These fine structural observations have not been described previously in Tay-Sachs disease and they may suggest new functional implications for the involvement of the lymphocyte in this storage disorder.     

Target-cell membrane alterations induced by lymphotoxin. Ultrastructural observations.

Upon in vitro stimulation by antigens or mitogens, lymphocytes release a series of lymphokines. One such lymphocyte mediator is lymphotoxin, which appears to be responsible for in vitro lymphocyte-mediated cytolysis. Employing immuno-electron microscopy with ferritin- or peroxidase-labeled antibody, we observed patchy localization of the mediator on the plasma membranes of target L cells exposed to lymphotoxin, often in areas overlying a microfilament web. When studying lymphotoxin-affected cells by electron microscopy of freeze-fracture replicas, we observed aggrlasma membrane, with intervening areas which were frequently particle free. Sometimes the affected cells revealed plasma-membrane lesions suggesting intramembranous "blisters."     

Experimental pyelonephritis in the cat. 2. Ultrastructural observations

An ultrastructural study was made of the renal cortical lesions in cats with pyelonephritis produced by experimental Escherichia coli infection and temporary renal obstruction. The most striking changes were interstitial fibrosis, thickening and folding of the tubular basement membrane, and atrophy of renal tubular epithelium. Interstitial inflammatory cells were mainly lymphocytes and plasma cells. Release of renal tubular lipid into the interstitium occurred commonly but did not appear to provoke additional cellular response. Glomerular changes included segmental sclerosis, wrinkling and collapse of basement membrane, thickening and fragmentation of Bowman's capsule, and periglomerular fibrosis. The changes described are similar to those which occur in a variety of human and animal nephropathies and represent non-specific responses to injury.     

Ultrastructural observations on experimentally produced melanin pigmentation of the corneal epithelium.

Melanin pigmentation of the corneal epithelium was induced in pigmented guinea pigs by the topical application of colchicine to their eyes or by corneal cauterization with silver nitrate. With colchicine the pigmentation was preceded by the development of an abnormal corneal epithelium in which numerous cells became arrested in cell division. The corneal melanosis resulted largely from the migration of melanocytes into the corneal epithelium from the normally pigmented contiguous conjunctiva and to a lesser extent from the presence of melanin granules within corneal epithelial cells. In both models a leukocytic and vascular invasion of the cornea proceded and accompanied the migration of melanocytes into the corneal epithelium. Electron microscopy disclosed cells with the same morphology as conjunctival melanocytes between the epithelial cells of the cornea. Mature melanin granules were also present within some squamous epithelial cells as individual granules or as clusters. The ultrastructural findings are viewed in relation to how melanin granules are transferred from melanocytes to epithelial cells. Evidence is presented which suggests that malanin granule transfer may follow the fusion of the membranes of the melanocytes and epithelial cells.