Biomedical subjects

N L L'Hernault

Publications and source records attributed to N L L'Hernault.

7 recordsLinked to original sources

PubMed1996

Ultrastructural features of tissue removed during idiopathic macular hole surgery.

PURPOSE: To compare the ultrastructural features of excised tissue removed during surgery for idiopathic macular holes with the preoperative stage of the macular hole. METHODS: Twelve consecutive patients with a unilateral idiopathic macular hole underwent vitrectomy with surgical removal of the internal limiting membrane of the retina and epiretinal tissue overlying and surrounding the hole. The excised specimens were evaluated with transmission electron microscopy, and findings were compared with the preoperative stage of the macular hole according to the classification of Gass. RESULTS: Surgery was performed on 12 eyes of 12 patients with stage 2, 3, or 4 macular holes. Internal limiting membrane was present in 11 of 12 specimens. Tissue from one of two eyes with stage 2 holes showed cellular elements enmeshed in cortical vitreous. Tissue from four of seven eyes with stage 3 holes and three of three eyes with stage 4 holes had cellular proliferation on the internal limiting membrane. Cells with myofibroblastic differentiation were present in five of the eight cellular proliferations. CONCLUSION: Our results support the clinical stages of idiopathic macular holes described by Gass. Idiopathic macular holes appear to form from contraction of the prefoveal vitreous, and the hole enlarges because of contraction of myofibroblasts on the inner surface of the internal limiting membrane. On the basis of the mechanical mechanisms of idiopathic macular hole formation, removal of the internal limiting membrane and adherent epiretinal tissue surrounding and overlying the macular hole is a reasonable surgical approach to close idiopathic macular holes.

Aged↗

PubMed1995

Ultrastructure in anterior and posterior stroma of perfused human and rabbit corneas. Relation to transparency.

PURPOSE: The authors sought to discover whether there are differences in the degree of spatial order in the fibrillar ultrastructure between anterior and posterior stroma. METHODS: Human corneas were obtained from eye bank eyes. Although they had been classified as normal, some swelling remained after 3 hours of deturgescence. Freshly excised, unswollen rabbit corneas also were used. Image analysis methods were applied to transmission electron micrographs of the anterior, middle, and posterior stroma of these corneas to determine the positions and radii of fibrils, the fraction of total area occupied by fibrils, and the fibril number density. Results were used to calculate the interference factor that appears in the direct summation of the fields for light scattering theory and to estimate the total scattering cross-section per fibril. The interference factor is a measure of the spatial order in the positions and sizes of the fibrils. RESULTS: Electron micrographs showed anterior-posterior variations in size and number density of fibrils. The interference factor at wavelengths of visible light was lower in posterior stroma than in anterior stroma for humans and rabbits. In some instances in humans, the anterior interference factor was characteristic of mildly swollen cornea. When averaged for the electron micrographs analyzed, the anterior stroma was predicted to scatter approximately twice as much light per unit depth as the posterior stroma in humans (at any given wavelength) and approximately three times as much in rabbits. CONCLUSIONS: Calculations of the interference factor showed that there were differences in the anterior-posterior spatial ordering of fibrils. In human corneas, the differences could have been caused by intrinsic in vivo differences between anterior and posterior stroma; however, possible anterior-posterior variations in swelling between the two regions in vitro also could have affected the results.

Aged↗

PubMed1990

Correlative light, transmission, and high resolution (SE-I) scanning electron microscopy studies of rhesus adrenocortical vascular morphology.

A detailed correlative morphologic description using light microscopy (LM), transmission electron microscopy (TEM) and high resolution SE-I scanning electron microscopy (SEM) was conducted on the capillary endothelium of the zona-fasciculata (Z-F) in juvenile male rhesus monkeys. The glucocorticoid synthesis and release phenomena, associated with stress stimulated release of adrenocorticotropic hormone (ACTH) via the hypothalamic-pituitary axis, intimately involves capillaries of the Z-F. A comprehensive study of all the ultrastructural features implicated in the transendothelial uptake of steroidogenic precursors and release of glucocorticoids in perfused rhesus adrenals has not previously been made. This report presents correlative images of transendothelial openings that include previously described single diaphragmed fenestrae and plasmalemma vesicles, and double diaphragmed transendothelial channels. New observations of endothelial cell pockets, tight junctional complexes and membrane filled ghost sacs were recorded from perfused rhesus adrenal. Membranous ghosts associated with adrenocortical endothelium were reported in a previous TEM study of perfused rat, however the potential argument existed that ghosts were artifactual. Their role as steroid hormone releasing structures remains an open question, yet their structural characteristics appear justified based on imaging of identical profiles observed in perfused rhesus adrenocortical specimens. These structural features are considered for the potential of gating and sorting of metabolites, and release of glucocorticoids in response to ACTH stimulated stress events.

Adrenal Cortex↗

PubMed1989

Ultrastructural location of extracellular matrix components in the optic nerve head.

The distributions of laminin and collagen types I through V were determined in optic nerve heads of cynomolgus monkeys using colloidal gold immunoelectron microscopy. Collagen types I and III localized to striated collagen fibrils in arterial walls throughout the optic nerve head and to fibrils comprising the core of the lamina cribrosa beams and optic nerve septa. Collagen type IV and laminin localized to basement membranes of all blood vessels and to basement membranes of astrocytes that lie between the laminar beams and line the optic nerve septa and pia mater. Collagen type V was detected both in striated collagen fibrils and in vascular and astrocyte basement membranes. These results provide a detailed understanding of the optic nerve head extracellular matrix distribution and illustrate a sensitive method for future study of its role in glaucomatous optic nerve damage.

Animals↗

PubMed1988

Cellular proliferation after experimental glaucoma filtration surgery.

We used light microscopic autoradiography to determine the time course of cellular incorporation of tritiated thymidine (a correlate of cell division) following glaucoma filtration surgery in seven eyes of four cynomolgus monkeys with experimental glaucoma. Incorporation of tritiated thymidine was detected as early as 24 hours postoperatively. Peak incorporation occurred five days postoperatively and had returned to baseline levels by day 11. Cells incorporating tritiated thymidine included keratocytes, episcleral cells, corneal and capillary endothelial cells, and conjunctival and corneal epithelial cells. Transmission electron microscopy was correlated with the autoradiographic results to demonstrate that fibroblasts were dividing on the corneoscleral margin. These findings have potential clinical implications for the use of antiproliferative agents after filtration surgery.

Animals↗

PubMed1988

The extracellular matrix composition of the monkey optic nerve head.

The presence and distribution of laminin, heparan sulfate proteoglycan and collagen types I, III and IV were immunohistologically determined in cynomolgus monkey optic nerve heads using the avidin-biotin-peroxidase complex technique. Collagen types I and III were detected within the collagenous plates of the scleral lamina cribrosa, in the septa and pia mater of the postlaminar optic nerve and in blood vessel walls in all regions of the optic nerve head. Collagen type IV, laminin and heparan sulfate proteoglycans were all localized to the margins of the collagenous laminar plates of the scleral lamina cribrosa and along the margins of the optic nerve septa and the pia mater. All three components also appeared beneath the blood vessel endothelium throughout the optic nerve head. Within the lamina cribrosa, collagen types I and III occupy the core of the scleral laminar plates and may provide structural support for optic nerve bundles exiting the eye. The distribution of collagen type IV, laminin and heparan sulfate proteoglycan corresponds to basement membranes from two sources: vascular endothelial cells and glial cells lining the axonal bundles. Abnormalities of these substances may influence optic nerve function and susceptibility to elevated intraocular pressure by altering their mechanical support functions within the nerve head, by interfering with axonal nutrition, or both.

Animals↗

PubMed1987

Chronic glaucoma selectively damages large optic nerve fibers.

To determine whether glaucoma selectively injures a particular size of optic nerve fiber (and its cell body), we induced chronic experimental glaucoma in one eye each of ten monkeys. With automated image analysis, the number and diameter of optic nerve fibers were compared between each glaucomatous eye and its normal fellow eye. Fibers larger than the normal mean diameter atrophied more rapidly in glaucomatous eyes, though no fiber size was spared from damage. The mean fiber diameter for glaucomatous eyes was 0.74 micron, significantly lower than the mean for ten fellow eyes, 0.85 micron (P less than 0.005). There was preferentially greater atrophy of fibers of all sizes in the superior and inferior peripheral nerve sectors, as seen in human eyes with glaucoma. The more rapid atrophy of larger fibers appeared to result from two causes. The areas that suffer most rapid loss of fibers in experimental glaucoma normally contain a high proportion of larger diameter fibers. Furthermore, larger fibers were lost preferentially even in areas of the optic nerve with mild damage, indicating their inherent susceptibility to injury by glaucoma. The tendency for large fibers to be lost in glaucoma has implications for future improvements in testing for early glaucoma damage.

Animals↗