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E Raviola

Publications and source records attributed to E Raviola.

At least 37 records · Page 2Linked to original sources
PubMed1988

Increase in retinal vasoactive intestinal polypeptide after eyelid fusion in primates.

Lids were fused in six neonatal and one adult macaque monkey (Macaca mulatta and Macaca arctoides) and were kept fused for 1 to 18.5 months. The juvenile macaques, but not the adult one, developed myopia due to excessive elongation of the eye. In all animals, the immunohistochemical reactivity of the retina for vasoactive intestinal polypeptide (VIP) was much higher in the closed than in the open eyes. The neuropeptide was localized to the perikaryon and dendrites of amacrine cells. No difference was observed in substance P immunoreactivity between open and closed eyes, suggesting that the observed effect is selective. The change in VIP immunoreactivity could be the result of an increase in peptide synthesis, a decrease in peptide release, or a combination of the two. These results indicate that VIP may play a part in the regulation of postnatal ocular growth.

Animals↗
PubMed1988

Rod photoreceptors dissociated from the adult rabbit retina.

Rod photoreceptors have been isolated from the adult rabbit retina using enzymatic and mechanical dissociation procedures; their fine structure, synaptic activity, and long-term viability were examined using conventional electron-microscopic, quick-freezing, and cell culture techniques. Freshly dissociated photoreceptors were well-preserved compared to their counterparts in the intact retina. About half of the cells, however, exhibited broad continuity between inner and outer segments. Quick-frozen, freeze-substituted rods differed from chemically fixed cells in 3 respects: (1) there was an increased amount of granular matrix in the cytoplasm, mitochondria, and rough endoplasmic reticulum; (2) branching and anastomosing profiles of smooth endoplasmic reticulum had disappeared from the inner segment; and (3) the number of synaptic vesicles within the spherule was highly variable, in some cases leaving synaptic ribbons completely denuded of their halo of vesicles. Light-adapted, solitary rod cells continued to be synaptically active: their endings were capable of endocytosis when placed in the dark in the presence of extracellular ferritin and tracer was incorporated into vesicles and vacuoles; this uptake was much reduced when the cells were incubated with the tracer in the light. Thus, synaptic vesicle regeneration was stimulated in the dark, suggesting that vesicles underwent exocytosis in the dark. Isolated rod cells adhered poorly to most standard substrates; without proper adhesion, cells deteriorated in 2-4 hr. However, photoreceptors did adhere to glutaraldehyde-fixed Vitrogen gels and could be maintained for over 48 hr on this substrate if kept in a complete medium at 22 degrees C. In contrast, Müller cells adhered quickly to a laminin substrate with their endfoot processes. The differential adhesion properties of Müller and photoreceptor cells may be useful in obtaining pure populations of glial cells or neurons from the adult mammalian retina.

Animals↗
PubMed1987

Excitatory dyad synapse in rabbit retina.

In the inner plexiform layer of the rabbit retina, the synaptic endings of bipolar cells contact a pair of postsynaptic processes at an unusual type of specialized junction, the dyad synapse. One of the members of the postsynaptic dyad may return conventional feedback synapses onto the bipolar endings. Freeze-fracturing demonstrates that, opposite the presynaptic active zone, both postsynaptic membranes contain an aggregate of intramembrane particles that remain associated with the outer leaflet (E face) of the fractured plasmalemma; this is a feature typical of excitatory synapses in the central nervous system. Intracellular recordings followed by injection of horseradish peroxidase showed that at the dyad synapse the endings of rod bipolar cells are usually presynaptic to the dendrites of two amacrine cells, one narrow-field and bistratified (AII) and the other wide-field (A17). Only the A17 rod amacrine cell returns feedback synapses onto the bipolar endings. Both amacrine cells respond to illumination with transient-sustained depolarizations, dominated by rods; thus, the polarity of their light responses is the same as that of rod bipolar cells. We conclude that the dyad synapses established by rod bipolar cells with the two types of amacrine cells are excitatory.

Action Potentials↗
PubMed1986

The rod pathway in the rabbit retina: a depolarizing bipolar and amacrine cell.

Anatomical and electrophysiological techniques were combined to study the morphology, synaptic connections, and response properties of two neurons in the rod pathway of the rabbit retina: the rod bipolar cell and the narrow-field, bistratified (NFB) amacrine cell. Rod bipolars receive synaptic input from rod cells in the outer plexiform layer (OPL), where their dendrites end as central elements in the invaginating synapse of rod spherules. Their main synaptic output in the inner plexiform layer (IPL) is onto NFB amacrine cells and at least one other type of amacrine, which in turn feeds a reciprocal synapse back onto the bipolar endings. Rod bipolars, or a variety of them, respond to diffuse, white light stimulation with a transient-sustained depolarization dominated by rods; with high-intensity flashes, they generate a secondary depolarization at off, which is homologous to the rod aftereffect of horizontal cells, although opposite in polarity. NFB amacrine cells receive synaptic input from rod bipolars, cone bipolars, and other types of amacrine cells; they are presynaptic to ganglion cell dendrites and communicate via gap junctions with other processes, whose parent neuron has not yet been identified. They respond to light with a triphasic potential, characterized by a depolarizing transient at on, followed by a sustained plateau phase, and finally by a hyperpolarizing transient at off. Threshold of their responses is the same as in the depolarizing rod bipolars and saturation is reached with nearly the same stimulus intensity in both neurons. Furthermore, NFB amacrine cells exhibit a depolarizing rod aftereffect at the termination of high-intensity flashes. Thus, this amacrine cell type is inserted in series along the rod pathway in the rabbit retina and modulates the transfer of scotopic signals from rod bipolars to ganglion cells.

Animals↗
PubMed1985

An animal model of myopia.

Myopia develops in macaque monkeys when their lids are surgically fused at birth and kept closed for one year. This experimental refractive error has many features in common with human myopia: It is caused by progressive axial elongation of the eye, is often accompanied by fundus changes, and can only be induced before eye growth has been completed. Myopia does not develop in animals raised in the dark; thus, it is triggered by an alteration of the visual input and is presumably mediated by the nervous system. In Macaca arctoides, atropine administration prevents abnormal eye elongation, and this suggests that lid-fusion myopia is caused by excessive accommodation. In M. mulatta, atropine is ineffective; furthermore, myopia develops when lids are sutured after interruption of the optic pathways. Thus, in this species accommodation can be ruled out as a determinant of eye elongation, and other neural mechanisms may be responsible for the refractive error. Our experiments suggest that the refractive state is largely programmed on a genetic basis, but that an abnormal visual experience can disrupt the process of postnatal eye growth and induce axial myopia.

Accommodation, Ocular↗
PubMed1985

Structure of the sinus-lining cells in the popliteal lymph node of the rabbit.

The structure of the sinus walls in the popliteal lymph node of the rabbit was studied with the electron microscope. In the marginal sinus, the endothelial cells are connected by gap junctions, puncta adherentia, and surface specializations characterized by focal approximation of the adjoining membranes without fusion. They possess large numbers of simple and compound uncoated invaginations of the plasma membrane that are closed by a diaphragm with a central thickening. The tissue strands that straddle the lumen of the sinus consist of a fibrous core containing both collagen and elastic fibers, surrounded by endothelial cells identical to those composing the outer sinus wall. Cortical sinuses that run independently of the trabeculae were identified by exploiting the fact that their endothelial cells accumulate lymph-borne ferritin, and their lumen is outlined by horseradish peroxidase administered intravenously. They are lined by a flattened, continuous endothelium and lack luminal strands. The walls of the medullary sinuses consist of endothelial cells and macrophages. The endothelial cells are interconnected by specialized junctions and contain fewer plasmalemmal vesicles than in the cortex; furthermore, dense granules are present in their cytoplasm. Macrophages adhere to the surface of the endothelial cells; typically, none of the junctional specializations that characterize the interface between endothelial cells connect endothelial cells to macrophages. However, at points along the contact region with the endothelium, the plasmalemma of the macrophage is decorated by an attachment plaque of fluffy cytoplasmic material. Sinus endothelial cells slowly accumulate lymph-borne ferritin like vascular endothelial cells elsewhere in the body, whereas macrophages contain both ferritin and engulfed erythrocytes.

Animals↗
PubMed1985

Rod cells dissociated from mature salamander retina: ultrastructure and uptake of horseradish peroxidase.

To test the effects of isolation on adult neurons, we investigated the fine structure and synaptic activity of rod cells dissociated from the mature salamander retina and maintained in vitro. First, freshly isolated rod cells appeared remarkably similar to their counterparts in the intact retina: the outer segment retained its stack of membranous disks and the inner segment contained its normal complements of organelles. Some reorganization of the cell surface, however, was observed: (a) radial fins, present at the level of the cell body, were lost; and (b) the apical and distal surfaces of the inner and outer segments, respectively became broadly fused. Second, the synaptic endings or pedicles retained their presynaptic active zones: reconstruction of serially sectioned pedicles by using three-dimensional computer graphics revealed that 73% of the synaptic ribbons remained attached to the plasmalemma either at the cell surface or along its invaginations. Finally, tracer experiments that used horseradish peroxidase demonstrated that dissociated rod cells recycled synaptic vesicle membrane in the dark and thus probably released transmitter by exocytosis. Under optimal conditions, a maximum of 40% of the synaptic vesicles within the pedicle were labeled. As in the intact retina, uptake of horseradish peroxidase was suppressed by light. Thus, freshly dissociated receptor neurons retained many of their adult morphological and physiological characteristics. In long-term culture, the photoreceptors tended to round up; however, active zones were present even 2 wk after removal of the postsynaptic processes.

Ambystoma↗
PubMed1983

Variations in structure and response properties of horizontal cells in the retina of the rabbit.

The response waveform of rabbit horizontal cells to diffuse white light stimulation was correlated with their anatomy by intracellular injection of horseradish peroxidase. In both axonless horizontal cells and the somatic end of axon-bearing cells the light evoked hyperpolarization may exhibit a transient at the onset of high intensity stimuli and is consistently followed by a rod aftereffect at stimulus cessation. In both types of cells the on-transient may be small and the rod aftereffect very prominent; this response pattern, however, is more frequently a property of the somatic end of axon-bearing cells. The morphology of axon-bearing cells is the same regardless of their response properties. On the other hand, axonless horizontal cells exhibit a wide variation in shape and the vast majority of them have asymmetric dendritic fields. No correlation, however, exists between cell shape and response properties. These are also independent of the location of horizontal cells in the retina or the orientation of their long axis with respect to the optic nerve head and medullary rays.

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

Membrane specializations in the outer plexiform layer of the turtle retina.

The internal organization of the plasma membrane at specialized contacts in the outer plexiform layer of the turtle, Pseudemys scripta elegans, was analyzed with the aid of the freeze-fracturing technique. In the invaginating synapse of cone pedicles the plasma membrane of the photoreceptor ending contains an aggregate of P-face particles, images of synaptic vesicle exocytosis, and rows of forming coated vesicles which are arranged in sequence from apex to base of the synaptic ridge. Thus, freeze-fracturing provides positive evidence that the synaptic ridge represents the active zone at the surface of the photoreceptor endings. Horizontal cell processes of dyads and triads have an aggregate of P-face particles opposite the apex of the ridge, but lack images of vesicle exocytosis. Deep-etching and rotary-shadowing demonstrate that an array of minute protrusions decorates the true outer surface of the horizontal cell membrane at the site of the intramembrane particle aggregate. The membrane of the invaginating bipolar dendrite is unspecialized. At basal junctions, the cone pedicle membrane has a sparse complement of P-face particles, but images of vesicle exocytosis are absent. The adjoining bipolar membrane is characterized by a prominent aggregate of E-face particles, often arranged in an orthogonal lattice. The freeze-fracture profile therefore suggests the existence of (1) a sign-conserving cone-to-horizontal cell synapse; (2) a sign-inverting synapse between cones and invaginating bipolar dendrites; and (3) a sign-conserving synapse between cones and bipolar dendrites at basal junctions. No freeze-fracture evidence was found for a horizontal-to-cone or horizontal-to-bipolar cell synapse within the synaptic invaginations.

Animals↗
PubMed1982

Horizontal cells in the retina of the rabbit.

The light responses, morphology, and connections of horizontal cells (HCs) were studied in the retina of the rabbit using intracellular recordings and the injection of visible markers. Two types of HCs were identified, axonless and axon-bearing HCs. Axonless HCs and the somatic end of axon-bearing HCs respond to white light of varying intensity with graded hyperpolarizations; both display a transient superimposed on the sustained hyperpolarization at stimulus initiation and a small rod aftereffect at the cessation of high intensity stimuli. Anatomically, both are connected to cones, but their responses also suggest rod influence. Both summate stimuli from a retinal area which is much larger than their respective fields. However, only axonless HCs transfer a fluorescent, low molecular weight dye to adjoining, homologous cells. The axon terminal of axon-bearing HCs has response properties different from those of the cell body: the transient at stimulus initiation is absent; furthermore, at high levels of illumination, the rod aftereffect becomes equal in amplitude to the primary hyperpolarization. Anatomically, it is connected to rods, but its responses also suggest cone influence. Its receptive field approximates in diameter its anatomical spread and it does not transfer fluorescent dye to its neighbors.

Animals↗