M. Hirsch

Formation of intercellular spaces and junctions in regenerating rabbit corneal endothelium

Abstract Rabbit corneal endothelium was destroyed over a diameter of 10 mm using liquid nitrogen applied for 15 sec to the anterior surface. The corneas were afterwards removed at different periods, from 1 day to 2 months and studied by light microscopy after silver impregnation, by transmission electron microscopy, and by scanning electron microscopy in order to study the formation of new intercellular spaces and junctions in the regenerating endothelium. The intercellular spaces and junctions are all reconstituted at the end of the fifth day, when the whole of Descemets membrane is entirely covered by cells. This period also corresponds to the recovery of the endothelial function. The dynamics of the formation of intercellular spaces are described, and the rapid appearance of two types of junctions as soon as contact between cells is completed. Junctions of the first type, always at the apex of the cells, are single or multiple with adjacent intra-cytoplasmic opacities and correspond to the junctional elements of the “terminal bar”. Junctions of the second type, on the lateral plasma membranes of the cells, are not constantly observed; they are straight, or curved. or circular; their length is variable, and they possess a periodicity in their structure, and correspond to gap junctions.

Morphology of tight junctions in the ciliary epithelium of rabbits during arachidonic acid-induced breakdown of the blood-aqueous barrier

SummaryA reversible breakdown of the blood-aqueous barrier in the iridial processes of rabbits has been induced by arachidonic acid as demonstrated by the passage of horseradish peroxidase at places through the tight junctions. Freeze-fracture images reveal very discontinuous Pface ridges. However, the analysis of complementary replicas demonstrates that discontinuities of P-face ridges are always complemented by particles or short bars found in the E-face furrows. Though the problem exists of correlating freeze-fracture images of the junctional structure to the focal passage of horseradish peroxidase, the data suggest that the discontinuities of P-face ridges cannot be the structural counterpart of the passage of horseradish peroxidase. Alternative pathways of horseradish peroxidase are discussed in context with the offset bifibrillary model of the junction.

Selective and reversible breakdown of the tight junctional barrier in the rabbit ciliary body induced by arachidonic acid: a tracer and freeze-fracture study

Arachidonic acid induced a reversible breakdown of the blood-aqueous barrier in the iridial processes of the rabbit ciliary body, whereas the ciliary processes were not affected under the conditions of this study. The focal passage of horseradish peroxidase through the tight junctions was demonstrated. In freeze-fracture images, this breakdown of the barrier function was associated with focal changes: an alteration in the geometry of the tight junctional network; an increase in the number of discontinuities of the P-face ridges and particles and short bars in the E-face furrows; an increase in the density of intramembranous particles within the junctional area. The significance of the ultrastructural alterations of the tight junctions as a structural counterpart of the physiological changes is discussed.

The Development of the Irido-corneal Angle in the Chick Embryo

The iridocorneal angle of the chick embryo was examined by scanning electron microscopy from the 7th day to the 19th day of development. The mesodermal tissue situated between the corneal endothelium and the iris differentiated into trabecular cells. These cells formed a strip on the 9th day and enlarged on the 13th day to form long cellular fibres. The trabecular mesh work was recognizable on the 15th day and reached full development only on the 19th day. The development of the trabecular meshwork was probably much earlier than is usually described. It began with differentiation of the corneal endothelial cells and these cells acquired a multipolar cell body with long cellular processes. The last stage is probably regulated to avoid an abnormal development of the angle structure. These results can be correlated with those obtained in the morphological examination of the structure of the angle in congenital glaucoma and the “cleavage syndrome” of the anterior chamber.