Biomedical subjects

L H Margaritis

Publications and source records attributed to L H Margaritis.

6 recordsLinked to original sources

PubMed1979

Structural and image analysis of a crystalline layer from dipteran eggshell.

A crystalline layer has been identified as a constituent of the eggshell in the dipteran Drosophila melanogaster. This 400A thick intermediate chorionic layer (ICL) is composed of eight 50A thick sublayers and lies between the vitelline membrane and the endochorion. Whole mount views of isolated ICL after negative staining reveal P2 planar periodicity which, when analyzed further by optical diffraction and filtering, showed 1st (100A), 2nd, 3rd and 4th order reflections.

Animals↗

PubMed1979

Response of the cornea to far ultraviolet light: an ultrastructural study.

Quantitative changes were measured and ultrastructural alterations were detected in rabbit corneas after exposure to a far ultraviolet irradiation (UV). Low dose exposure (105 - 8 x 105 erg/cm2) resulted one day later in a thicker epithelium and loss of the intercellular permeability barrier. In corneas exposed to higher doses (5 x 106 erg/cm2), the epithelium was considerably thinner one day later, whereas 4 days later it was of normal thickness and the endothelial cells became degenerated. The highest UV dose exposure used (a total of 20 x 106 erg/cm2 given in 4 equal daily doses) resulted in (1) swelling of the stroma and disorganization of the collagen fibers; (2) disappearance of the basement membrane; (3) degeneration of the endothelial cells; and (4) considerable reduction of epithelium thickness.

Animals↗

PubMed1977

Rotary replication for freeze-etching.

Rotary replication has been adapted to freeze-etching and evaluated using T4 polyheads, erythrocyte ghosts, and chloroplast membranes. Conventional electron microscopy, electron diffraction, and optical diffraction and filtering indicate that platinum-carbon rotary replication renders radially symmetrical contrast and 25 A resolution to freeze-etched specimens so as to clarify subunit structure not normally evident in unidirectional shadow replicas.

Carbon↗

PubMed1976

Three dimensional structure of the endochorion in wild type Drosophila melanogaster.

The endochorion of the Drosophila melanogaster eggshell has been isolated and its structure examined by transmission and scanning electron microscopy. In the main shell the thin inner endochorion (floor) shows small pits or pores and characteristic fenestrae crossed by irregular strands; vertical columns surrounded by air spaces separate this layer from the thick outer endochorion (roof) which is covered by a regular, external reticulum of thin fibers. The endochorion of the respiratory horns has sharply divided dorsal and ventral surfaces, with characteristic structures somewhat reminiscent of the floor and the external reticulum of the roof, respectively.

Animals↗

PubMed1976

Quantitative and comparative ultrastructure of the vertebrate cornea. I. Urodele Amphibia.

The cornea of the urodele amphibian Triturus c. cristatus was studied ultrastructurally in order to provide the basis for a comparison among corneas throughout the vertebrate phylum. The cornea of this salamander consists of relatively thick epithelium and basement membrane and thin Descemet's membrane, unlike the mammalian corneas. The outermost epithelial cells contain Ruthenium Red stainable extracellular filaments and intracellular vesicles which are thought to play a role in the process of lubricating the corneal surface. Occluding junctions have been observed in the apical region of the superficial epithelial cells and are considered as barriers to the intercellular passage of material. A thin substantia propria (stroma) consists of about 40 collagenous highly organized lamellae. The thicknesses of the basement membrane, Descemet's membrane and the epithelium are believed to represent the primitive situation in the process of corneal evolution.

Animals↗

PubMed1976

Quantitative changes and ultrastructural alterations of the cornea in response to ultraviolet light. II. Effects of amphibia; elucidation of desmosomal structure and basement membrane synthesis.

The effects of far ultraviolet light irradiation upon an amphibian cornea were studied to compare the effects observed both quantitatively and ultrastructurally with data obtained after UV irradiation of mammalian corneas. The ultimate goal of this series of investigations is the elucidation of the alterations and the regeneration mechanisms, which might reflect existing morphological diversities among the species, observed in vertebrate corneas following exposure to UV light. It was found that while the epithelial cells undergo oedema after low dose exposures and are gradually damaged after high doses of UV light, 2-4 days leter a new epithelium has been formed. Intercellular permeability is increased by low dose exposure as was detected by the penetration of Ruthenium Red into the intercellular clefts. Under these conditions desmosomal structure revealed a 21-laminar configuration. The basement membrane of the amphibian, unlike that of the mammal, does not dissolve away upon exposure but shows localized disruptions which are thought to accommodate the passage of leucocytes from stroma to epithelium. That a new basement membrane is subsequently formed is evident by the existence of extracellular and intracellular secretion granules. In comparison to irradiated rabbit corneas, this stroma remains remarkably at the same thickness following a high dose exposure although a noticeable disorganization of collagen arrangement is apparent. Finally, as in the case of the rabbit corneas, a secondary degeneration of endothelium was observed 4 days after a moderate dose exposure.

Animals↗