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Biomedical subjects

G Raviola

Publications and source records attributed to G Raviola.

At least 19 recordsLinked to original sources
PubMed1989

Fine structural defects in a case of congenital microcoria.

A case of congenital miosis associated with myopia and cataract is described. Tissue obtained at iridectomy was examined with the electron microscope and compared with a specimen of normal iris. The miotic iris was found to be hypoplastic and to display differences in the cellular density of the stroma. The contractile processes of the dilator myoepithelium were conspicuously absent from the underlying stroma, and the existing myofibrils were much disarranged.

Adult↗
PubMed1989

Immunogold staining of elastin in the wall of the retinal arteries in Macaca mulatta.

Elastin has been demonstrated in the wall of the retinal arteries in or immediately adjacent to the optic disc of adult Macaca mulatta using the immunogold labelling technique with delta-elastin antibody. Since elastin is thought to provide elasticity to the walls of these vessels, perhaps its presence in the retinal arteries plays a role in contractility and regulation of blood flow throughout the retinal vascular system.

Animals↗
PubMed1987

Intercellular junctions between fibroblasts in connective tissues of the eye of macaque monkeys. A thin section and freeze fracture analysis.

Thin-section electron microscopy and freeze fracture were used in the analysis of the intercellular junctions between fibroblasts in connective tissues of the eye of Macaca mulatta, M. fascicularis, and M. arctoides. Fibroblasts located in the subconjunctival loose connective tissue, anterior sclera, scleral spur, iris stroma, ciliary body stroma, and posterior choroid were jointed by three kinds of junctions. Gap junctions were of different sizes and frequently composed of a small number of connexons organized in polygonal aggregates or linear arrays. Tight junctions were represented by isolated strands and never composed a continuous belt around the cells. Intermediate junctions were seen in thin sections but did not have any representation in the interior of the plasma membrane. It remains to be established whether, as is the case in other tissues, pathologic conditions of the eye are accompanied by some changes in the morphology and distribution of intercellular junctions between fibroblasts.

Animals↗
PubMed1987

The structural basis of the inner blood-retina barrier in the eye of Macaca mulatta.

This is a morphological analysis of the inner blood-retina barrier in various segments of the retinal vasculature in the eye of Macaque monkeys. The primary aims of this study are to identify the components of the walls of the arteries, central capillaries, peripheral capillaries and veins of the retina using light and electron microscopy, and to compare and contrast junctional morphology as revealed by thin section electron microscopy and freeze-fracture. The walls of these vascular segments are composed of continuous endothelium, muscle cells or pericytes, and connective tissue. Endothelial cells are joined by tight and gap junctions. In freeze-fracture replicas, tight junctions consist of a continuous, complex network of branching and anastomosing strands which do not possess free endings. The intramembrane strands of tight junction remain preferentially associated with the outer membrane leaflet or E-face of the endothelial plasma membrane and sit at the bottom of linear strands or grooves. However, particles and fragments of the intramembrane strands may be avulsed from the E-face during the fracture process and are associated with ridges on the inner membrane leaflet or P-face. The total number of plasmalemmal vesicles per unit area of endothelial cell for each vascular segment in thin sections is less than non-barrier endothelium, but greater than barrier endothelium. The paucity of plasmalemmal vesicles and the complexity of the tight junctional network contribute to the barrier function of the retinal vascular endothelium.

Animals↗
PubMed1986

Evidence for a secretory process, distinct from that of the aqueous humour, in the ciliary epithelium of Macaca mulatta.

In the ciliary epithelium of normal Rhesus monkeys, groups or islands of cells are present in which an intense secretory activity takes place. This is distinct from activity in aqueous humour production. In these regions of the epithelium the cytoplasm of the nonpigmented cells contains a well developed rough endoplasmic reticulum, numerous Golgi complexes and secretory granules containing an amorphous material of variable density. This material is discharged by a process of exocytosis into the intercellular spaces between the facing apices of the nonpigmented and pigmented cells and from here it percolates into the intercellular spaces between pigmented cells. The endothelial cells of the fenestrated capillaries located underneath these regions of actively secreting nonpigmented cells frequently contain, in their cytoplasm, granules of moderately dense material, suggesting a transport from the ciliary body stroma into the blood stream. Upon stimulation with pilocarpine the secretory activity of the nonpigmented cells is greatly increased and the intercellular spaces of the epithelium, including the ciliary channels, are frequently dilated and contain abundant osmiophilic material. These morphological observations suggest that, in addition to actively transporting aqueous humour, the ciliary epithelium produces a secretory material that diffuses into the ciliary body stroma and possibly enters into the blood stream across the walls of the fenestrated vessels.

Animals↗
PubMed1985

Morphology and permeability properties of blood capillaries in extraocular muscles of macaque monkeys.

Extrinsic eye muscles are very different from other skeletal muscles with regard to the morphology of their fibers and response to drugs. In addition, they are provided with an unusually rich blood supply. Since it had been previously reported that the capillaries of extraocular muscles are, at least in part, of the fenestrated type, a feature unusual for skeletal muscles, we have analyzed the morphology of these vessels in macaque monkeys and tested their permeability properties with horseradish peroxidase (HRP). Our study of the blood capillaries in the superior rectus muscle and levator palpebrae superioris in Macaca mulatta and M. fascicularis has demonstrated that these vessels are morphologically similar to the capillaries of other skeletal muscles. Furthermore, when HRP is introduced intravenam, it is transported out of the vessels by a vesicular transcellular mechanism. When HRP is injected in the interstitial spaces of the muscles, it is returned to the lumen by an identical vesicular transcellular transport. Thus, a bidirectional movement of macromolecules can take place across the walls of these vessels, and such a movement is not different from that previously reported for other skeletal muscles.

Animals↗
PubMed1985

Morphological evidence for the transfer of anionic macromolecules from the interior of the eye to the blood stream.

We have either introduced into the vitreous space or perfused through the anterior chamber of macaque monkey eyes two anionic tracers, anionic ferritin (AF) and horseradish peroxidase (HRP) and a cationic probe, cationic ferritin (CF). We have observed that the anionic molecules, but not the cationic one, are transported to the blood stream by plasmalemmal vesicles of the endothelial cells in both the retinal and the iridial vasculature. We suggest that a variety of organic anions of different MW which are commonly present in the eye tissues may be returned to the blood by the same morphological mechanism.

Animals↗
PubMed1985

Asymmetric distribution of charged domains on the two fronts of the endothelium of iris blood vessels.

The authors have studied the distribution of anionic and cationic sites on both luminal and abluminal endothelial aspects of iridial vessels in Macaca mulatta and Macaca fascicularis. With the animals in general anesthesia, anionic ferritin (AF) and cationic ferritin (CF) were either injected intravenam or perfused at known intraocular pressure (15-20 mmHg) through the anterior chamber. AF introduced intravenam was retained in the vessels' lumen. The tight junctions between the endothelial cells were impermeable and the plasmalemmal vesicles did not transport tracer to the iridial stroma. In contrast, when perfused through the anterior chamber, AF was present in the vessels' lumen. Here again the tight junctions between the endothelial cells were impermeable, but AF was contained within a great number of plasmalemmal vesicles. Iridial vessels were impermeable to CF perfused into the lumen, but a continuous layer of CF particles was found to adhere to the luminal plasma membrane. When perfused through the anterior chamber, CF was bound to the proteoglycans associated with collagen fibrils of the iridial stroma and basal laminae of stromal, pericytic, and endothelial cells but was never found in the vessels' lumen. These results indicate that different electrical charges are associated with the plasmalemmal vesicles on the luminal and abluminal fronts of iridial vessels. The authors suggest that in these vessels a unidirectional vesicular transport is responsible for the selective movement of anionic organic substances from the tissues of the eye to the bloodstream.

Animals↗
PubMed1985

Interreceptor junction in the double cone of the chicken retina.

The two elements of the double cones in the chicken retina (Gallus gallus domesticus) are joined by a specialized junction located at the level of the myoid of the principal cone and the perikaryon of the accessory cone, in close proximity to the outer limiting membrane. In thin sections, the plasma membranes of the two elements of the cones are seen to approach each other closely being separated by a cleft of 3 to 11 nm; short gap junctions are interposed. A layer of fine filamentous material is constantly present on the cytoplasmic side of the plasma membranes. In replicas of freeze-fractured retinas the junction appears as a fascia composed of small polygonal gap junctions connected to one another by linear gap junctions. Solitary arrays of gap junctional particles are also present. In close proximity to the gap junctions the membrane matrix appears devoid of intramembrane particles. We conclude that the elements of the double cones are connected to one another by gap junctions with associated intermediate junction. The presence of gap junctions suggests that the two elements of the double cones are electrically coupled.

Animals↗
PubMed1984

Computed tomography of aqueous humour outflow pathways.

The anterior chamber of adult Rhesus monkeys (Macaca mulatta) was perfused with a radio-opaque contrast medium (Amipaque; mol. wt 789 daltons) at controlled intraocular pressure (IOP), and its subsequent distribution examined by computed tomography. In the living monkey no contrast medium was detectable outside the anterior chamber, even after prolonged (8 hr) perfusion. However, if the animal was then killed, and the IOP maintained artificially at its previous level, opacity appeared immediately throughout the anterior segment. Subsequent scans showed the contrast medium to diffuse into the anterior orbital tissues, and to move posteriorward through the globe wall and extraocular muscles. None entered the vitreous body and very little progressed behind the point at which the extraocular muscles exited from Tenon's capsule. Elevation of IOP did not appear to accelerate this posterior diffusion. It is inferred that in vivo contrast medium passing into the posterior, non-conventional aqueous drainage pathway is cleared immediately by the circulating blood in the uvea and possibly also the extraocular muscle. Tenon's capsule may provide a barrier to further intra-orbital diffusion.

Animals↗
PubMed1984

Unidirectional transport mechanism of horseradish peroxidase in the vessels of the iris.

When horseradish peroxidase (HRP) is introduced into the blood stream it is retained in the lumen of the iridial vessels. In this paper, we report that when the same tracer is perfused into the anterior chamber of macaque monkeys, it permeates the stroma of the iris and penetrates the lumen of iridial vessels by transcellular vesicular transport. This unidirectional movement of HRP out of the eye is not inhibited by ouabain or fluoroacetate.

Animals↗
PubMed1983

Unidirectional vesicular transport mechanism in retinal vessels.

When horseradish peroxidase (HRP) is introduced into the bloodstream, it is retained in the lumen of the retinal vessels (blood-retina barrier). In this paper, we report that when the same tracer is injected into the vitreous body, it penetrates the lumen of retinal vessels by transcellular vesicular transport. This unidirectional movement of macromolecules out of the eye is not inhibited by ouabain, fluoroacetate, or low temperatures.

Animals↗
PubMed1983

The structural basis of the blood-aqueous barrier in the chicken eye.

In order to identify the structural basis of the blood aqueous barrier in the chicken eye, the morphology of the blood vessels and epithelium of the ciliary body were examined with light microscopy, conventional electron microscopy, and the freeze-fracturing technique; the permeability properties of the vessels and epithelium were tested with intravascular injection of horseradish peroxidase (HRP). The ciliary body and iris of the adult chicken are supplied principally by a single temporal long posterior ciliary artery that, by dividing into two branches, gives rise to the great circle of the iris. From this circle multiple branches reach the iris, while a few run posteriorly to the ciliary body stroma. Most of the blood supply to the ciliary body stroma is derived from vessels that return from the iris, run in the valleys between ciliary processes, and are continuous, at the ora serrata, with the veins of the vortex system. Electron microscopy shows that the vessels of the ciliary body stroma differ from their counterpart in mammals in two respects: (1) the endothelial cells are joined by simple but continuous zonulae occludentes; (2) the openings in the endothelial lining (plasmalemmal vesicles, fenestrae, and transendothelial channels) are less numerous. The walls of these vessels retard, but do not prevent the diffusion of intravenously injected HRP into the surrounding connective tissue spaces. From the ciliary body stroma, HRP diffuses into the intercellular clefts of the ciliary epithelium, but its progression toward the posterior chamber is blocked by very complex zonulae occludentes between the nonpigmented cells. Thus, in chickens as in mammals tight junctions between the nonpigmented cells of the ciliary epithelium represent the structural equivalent of the blood-aqueous barrier.

Animals↗
PubMed1983

Conjunctival and episcleral blood vessels are permeable to blood-borne horseradish peroxidase.

The vessels of the conjunctival and episcleral plexuses of Macaca mulatta eye are of the continuous type. Most of the vessels in the conjunctival plexus have the diameter of capillaries, while the vast majority of the vessels in the episcleral plexus are venules. Both types of vessels have a simple wall, which consists of an endothelium and a discontinuous layer of pericytes. The aim of this study was to establish their permeability properties to blood-borne horseradish peroxidase (HRP). After intravenous injection of HRP, in 200 microns chopper sections of the anterior segment of the eye examined with the light microscope, the subconjunctival and episcleral tissues appear intensely and diffusely stained by the reaction product. The electron microscope shows that HRP escapes from the vessels lumen by crossing the interendothelial clefts and, in addition, a great number of pinocytotic vesicles loaded with HRP are present on the luminal, tissue front and in the cytoplasm of the endothelial cells. HRP, which rapidly penetrates the loose connective tissue of the region, reaches the spaces between the cells of the conjunctival epithelium where it is finally blocked by the zonulae occludentes that connect the most superficial epithelial cells. A slow diffusion into the compact tissue of the cornea and of the sclera was also observed. Thus, under normal conditions, blood-borne macromolecules can freely diffuse into the subconjunctival and episcleral loose connective tissues. On the other hand, one can equally expect that the aqueous humor that reaches the episcleral and conjunctival blood plexuses through the canal of Schlemm and collector channels can freely diffuse into the subconjunctival spaces across the walls of these permeable vessels.

Animals↗
PubMed1982

Structure of the synaptic membranes in the inner plexiform layer of the retina: a freeze-fracture study in monkeys and rabbits.

The internal structure of the synaptic membranes in the inner plexiform layer (IPL) of the retina of monkeys and rabbits was studied with the freeze-fracturing technique. In ribbon synapses, the presynaptic active zone is characterized by an aggregate of P-face particles, images of synaptic vesicle exocytosis, and forming coated vesicles which occupy distinct, contiguous membrane domains from apex to base of the synaptic ridge. The postsynaptic membrane contains a prominent aggregate of homogeneous particles which remain associated with the E-face. In the presynaptic membrane of conventional synapses, images of synaptic vesicle exocytosis are intermingled with large P-face particles, whereas forming coated vesicles surround the active zone. Three types of internal organization characterize the postsynaptic membrane of conventional synapses. Usually, the postsynaptic membrane exhibits the same internal structure as the surrounding nonjunctional plasmalemma. A second, less common type of conventional synapse contains a loose aggregate of heterogeneous particles which remain associated with the P-face. Finally, synapses were exceptionally found which are macular in shape and contain an aggregate of E-free particles within the postsynaptic membrane. The freeze-fracture evidence suggests that the axonal endings of bipolar cells--or at least some of them--make excitatory synapses, whereas the vast majority of amacrine cell dendrites make inhibitory synapses. Additional specializations of the cell surface in the IPL include gap junctions, puncta adhaerentia, subsurface cisterns, and cell corner aggregates.

Animals↗
PubMed1982

Schwalbe line's cells: a new cell type in the trabecular meshwork of Macaca mulatta.

In the eye of Macaca mulatta, at the anterior end of the trabecular meshwork, just beneath the ridge known as Schwalbe line in gonioscopy, cells are present that contain secretory inclusions. These cells have been termed Schwalbe line's cells. They form a discontinuous cord, oriented circumferentially at the corneal periphery, deep to the endothelial lining of the anterior chamber. They are characterized by a prominent Golgi apparatus and by two types of secretory granules: round bodies, up to 0.6 micron in diameter and containing moderately dense material, and larger inclusions, up to 1 micron in diameter and consisting of stacks of osmiophilic lamellae. Membrane whorls and fragments are also commonly found in the spaces between the cells and possibly arise from exocytosis of the lamellar bodies. Schwalbe line's cells have been observed in young as well as in old animals. They are joined to one another by gap junctions and puncta adhaerentia. Because their cytoplasmic inclusions bear a striking morphological resemblance to the multilamellar bodies or cytosomes of the type II alveolar epithelial cells of the lung, the hypothesis is advanced that Schwalbe line's cells produce a phospholipid material that is released in the aqueous humor and thus facilitates its movement through the tissues of the sclerocorneal angle.

Animals↗
PubMed1982

The homogeneous structure of blood vessels in the vascular tree of Macaca mulatta iris.

This study reports the results of a systematic analysis of the iris vasculature in Macaca mulatta. Through the application of a variety of morphologic procedures it has been demonstrated that in rhesus monkeys, all iridial vessels, regardless of their diameter, have a similar structure. Their walls consist of (1) endothelial cells in a continuous layer resting on a basal lamina, which are provided with a small number of blunt luminal protrusions and slender basal lamellae; (2) pericytes sandwiched between two layers of the basal lamina, which are characterized by a smooth basal surface and adluminal processes that interdigitate with the basal leaflets of the endothelial cells; and (3) an adventitia of fibroblasts, melanocytes, and occasional macrophages arranged in one or more layers. Typical smooth muscle cells are not found in any vessels of M. mulatta iris. Thus the vessels of the rhesus monkey iris have a remarkably homogeneous morphologic appearance and cannot be classified according to the traditional criteria for arterioles, capillaries, and venules.

Animals↗