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Results for “retinal organoid”

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At least 19 recordsLinked to original sources
PubMed2026

Long-term functional synaptic integration of genome-edited retinal organoids in a primate model of macular degeneration.

Retinal organoids represent a promising regenerative strategy for restoring vision in retinal degenerative diseases, but the capacity of host cone bipolar cells in the primate macula to rewire with transplanted photoreceptors has not been established. In this study, we transplanted genome-edited ISL1-/- human retinal organoids lacking ON-bipolar cells into an acute laser-induced macular photoreceptor ablation non-human primate model. Using immunohistochemistry, ultrastructural imaging, and focal macular electroretinography, we demonstrate that host rod and cone bipolar cells actively extend dendrites toward grafted photoreceptors and form synaptic contacts, with evidence of functional signal transmission in a subset of transplanted eyes. Longitudinal, per-eye analyses revealed that host ON-bipolar responses improved in two of four eyes with ISL1-/- graft by up to 21.6% and remained stable for up to 2 years post transplantation. Moreover, OFF-pathway connectivity showed potential progressive maturation, with delayed increase in d-wave after 13 months in one of those eyes. These findings provide the first demonstration of long-term anatomical host-graft synaptic integration in the primate macula, establishing that central cone bipolar circuits retain the capacity for durable rewiring with human stem-cell-derived grafts. Our results highlight ISL1-/- retinal organoids as a promising approach for central vision restoration in macular degeneration.

Animals↗
PubMed1976

Ophthalmoscopic signs of obstructed axoplasmic transport after ocular vascular occlusions.

When axoplasmic transport in ganglion-cell axons is interrupted by ischaemia organelles accumulate in distended axon terminals at the edges of the infarct. This report illustrates the localized opaque swelling of nerve fibres shich develops at or near the optic disc after occlusion of the central retinal or posterior ciliary arteries. No such swelling occurs in patients who have a combined occlusion of these vessels.

Arterial Occlusive Diseases↗
PubMed1985

Rapid mobility of motile varicosities and inclusions containing alpha-spectrin, actin, and calmodulin in regenerating axons in vitro.

Time-lapse video recording was used to investigate the bidirectional movements of motile varicosities and intervening phase-dense (IPD) inclusions associated with axons of goldfish retinal ganglion cells regenerating in vitro. In addition, analyses of fine structure and immunocytochemical distributions of alpha-spectrin (fodrin), actin, and calmodulin in axonal fields were undertaken. Varicosities and IPD inclusions undergo saltations in a random manner at mean rates of 0.218 and 3.33 micron/sec, respectively. Experiments involving calcium antagonists or depletion of internal calcium stores resulted in an arrest of all intra-axonal movement, indicating that saltations of the two mobile structures are dependent on intra-axonal calcium. The predominant structure in varicosities is a large aggregation of an anastomosing, tubular, smooth endoplasmic reticulum embedded in an amorphous matrix, suggesting a form of "packaged" cytomembranes undergoing bulk transport. IPD inclusions, presumably carrying membranes, appear to shuttle between varicosities and growth cones during axon elongation, and between growth cones and varicosities during axon retraction. alpha-Spectrin, actin, and calmodulin were shown by immunocytochemistry to be preferentially distributed to varicosities and IPD inclusions. The co-transport of spectrin, actin, and calmodulin with cytomembranes undergoing rapid saltations departs from reported results of radioactive labeling experiments insofar as spectrin, actin, and calmodulin are not normally associated with rapidly transported membrane components in the latter studies. Possible reasons for the discrepancy are discussed. Our results suggest that spectrin and actin may play a role in the packaging and axoplasmic transport of cytomembranes concerned with plasmalemma recycling.

Actins↗
PubMed1985

Evidence for self-absorption of terminals by developing axons of retinal ganglion cells in the chick.

The appearance of membrane-bound degenerative organelles in chick optic nerve axons was studied at the electron microscopic level. A semiquantitative analysis revealed a sharp increase in the number of axons containing accumulations of such organelles during the second day after hatching. In dark-reared chicks this increase was retarded, suggesting the presence of a light-influenced event in the early post-hatch period.

Animals↗
PubMed1984

Intracellular control of axial shape in non-uniform neurites: a serial electron microscopic analysis of organelles and microtubules in AI and AII retinal amacrine neurites.

AI and AII cat retinal amacrine cells have highly varicose non-uniform, neuritic processes. Processes of both types were reconstructed via a computer system using serial electron micrographs. These reconstructions were analyzed for (a) varicosity volume, surface area, and length, (b) "neck" volume, surface area, and length, (c) number of microtubules within the varicosity, (d) number of microtubules within the "neck," and (e) volume and surface area of mitochondria and smooth endoplasmic reticulum and large smooth vesicular bodies within the processes. Correlation of these parameters revealed a linear relationship between the number of microtubules in the necks and mean neck cross-sectional area (rs = 0.780, P less than 0.001), while microtubule number within the varicosities showed no correlation with varicosity volume (rs = 0.239, P greater than 0.2). Varicosity volume did, however, correlate strongly with the summed volume of mitochondria and smooth vesicular bodies contained within the varicosity for both cell types examined. The ratio between membranous organelle volume and varicosity volume for AI amacrine processes of 1:6.97 (rs = 0.927), differed from the ratio of 1:1.80 for the AII amacrine processes (rs = 0.987). Similar relationships were observed in other nonvaricose neurites such as optic tract axons. Membranous organelles appear to contribute an additional obligatory volume to the cytosol that can be as much as seven times the organelles' direct volume. These observations suggest that both the cytoskeletal components, and the membrane organelles play a direct role in determining neurite shape.

Animals↗
PubMed1980

The lateral eyes of the scorpion, Androctonus australis.

The dioptric apparatus of the lateral eyes of the scorpion, Androctonus australis, consists of a cuticular lens, but lacks a vitreous body. The retina is formed by (1) retinula cells displaying a contiguous network of rhabdoms; (2) arhabdomeric cells bearing a distal dendrite that contacts retinula cells via numerous projections and ends before the rhabdomere of the retinula cells; (3) pigment cells that ensheath retinula and arhabdomeric cells with the exception of the contact regions; and (4) neurosecretory fibres possibly originating in the supraesophageal ganglion. The ratio of the number of retinula to arhabdomeric cells is determined to be close to 2:1 in the three larger anterolateral eyes, in contrast to the median eyes where the ratio is 5:1. The construction of the dioptric apparatus as well as the anatomy of the retina imply that in the lateral eyes of Androctonus australis visual acuity is reduced. A certain degree of spatial discrimination, however, may be retained by the presence of a relatively high number of arhabdomeric cells. It is suggested that the lateral eyes of A. australis mainly function as light detectors, e.g., for Zeitgeber stimuli.

Animals↗
PubMed1980

Fine structure of the compound eyes and interfacetal mechanoreceptors of Cicindela tranquebarica Herbst (Coleoptera: Cicindelidae).

The structure of the compound eyes of adult Cicindela tranquebarica Herbst was examined by use of light, scanning, and transmission electron microscopy. Each ommatidium of these photopic eyes is eucone and has a "subcorneal layer" situated between the corneal lens and crystalline cone. A distal rhabdomere consisting only of microvilli from retinula cell seven, a more proximal, rectangular, fused rhabdom formed from six retinula cells, and a basal, eighth retinula cell with a spherical rhabdomere comprise the light sensitive portions of the ommatidium. The "subcorneal layer" consists of lamellae of endocuticular microfibrils and, in surface view, shows 11 concave polygons. Proximal extensions of the crystalline thread form inter-retinular fibres containing microtubules between retinula cells 1/2, 3/4, 5/6, and 7/1. The primary pigment cells are devoid of pigment granules, but are rich in rough endoplasmic reticulum. Proximal to each retinula cell nucleus are two basal bodies, one perpendicular to the other. The more proximal basal body extends two fibrillar feet proximally which fuse to form a horizontally-banded ciliary rootlet extending the length of the retinula peripheral to the rhabdom. Each ommatidium is surrounded by 16 secondary pigment cells. Interfacetal mechanoreceptors between some adjacent lenses each have a single bipolar neuron, with a dendritic sheath, tubular body, cilium, outer and inner sheath cells, and an axon surrounded by a neurilemma sheath cell.

Animals↗
PubMed1972

The cellular pathology of experimental hypertension. VI. Alterations in retinal vasculature.

The ultrastructure of retinal arterial vessels from rats with severe renal hypertension has been studied. The permeability of retinal vessels has also been examined by means of vascular labeling technics utilizing horseradish peroxidase and microperoxidase as tracer substances. Small retinal arteries and arterioles exhibit foci of smooth muscle necrosis characterized initially by fragmentation of medial smooth muscle cells, and subsequently by loss of myofilaments and release of free vesicles, vacuoles and other cytoplasmic organelles extracellularly. Evidence for increased permeability is observed occasionally in retinal capillaries and less frequently in arteries and arterioles. The enzymatic tracers penetrate the tight junctions of the endothelial cells and are found in the basement membranes adjacent to endothelial and smooth muscle cells, as well as in expanded extracellular spaces around the capillaries. The alterations in the ultrastructure and permeability of retinal vessels in experimental hypertension have been compared with that of visceral and cerebral cortical vessels.

Animals↗
PubMed1987

Daily changes of structure, function and rhodopsin content in the compound eye of the crab Hemigrapsus sanguineus.

The compound eye of the crab hemigrapsus sanguineus undergoes daily changes in morphology as determined by light and electron microscopy, both in the quantity of chromophore substances studied by HPLC and in visual sensitivity as shown by electrophysiological techniques. 1. At a temperature of 20 degrees C, the rhabdom occupation ratio (ROR) of an ommatidial retinula was 11.6% (maximum) at midnight, 8.0 times larger than the minimum value at midday (1.4%). 2. Observations by freeze-fracture revealed that the densities of intra-membranous particles (9-11 nm in diameter) of rhabdomeric membrane were ca. 2000/microns 2 and ca. 3000/microns 2 for night and daytime compound eyes, respectively. 3. Screening pigment granules migrated longitudinally and aggregated at night, but dispersed during the day. Reflecting pigment granules migrate transversally in the proximal half of the reticula layer i.e. cytoplasmic extensions containing reflecting pigment granules squeeze between neighbouring retinula cells causing optical isolation (Fig. 4). Thus the screening pigment granules within the retinula cells show longitudinal migration and radial movement so that the daytime rhabdoms are closely surrounded by the pigment granules. 4. At 20 degrees C, the total amount of chromophore of the visual pigment (11-cis and all-trans-retinal) was 1.4 times larger at night than during the day i.e. 46.6 pmol/eye at midnight and 33.2 pmol/eye at midday. Calculations of the total surface area of rhabdomeric membrane, total number of intra-membranous particles in rhabdomeric membrane and the total number of chromophore molecules in a compound eye, indicate that a considerable amount of chromophore-protein complex exists outside the rhabdom during the day. 5. The change in rhabdom size and quantity of chromophore were highly dependent on temperature. At 10 degrees C both rhabdom size and amount of chromophore stayed close to daytime levels throughout the 24 hours. 6. The intracellularly determined relative sensitivity of the dark adapted night eye to a point source of light was about twice as high as the dark-adapted day eye. Most of the increase in the sensitivity is attributed primarily to the effect of reflecting pigment migration around the basement membrane and, secondarily, to the changes in the amount and properties of the photoreceptive membrane. The results form the basis of a detailed discussion as to how an apposition eye can function possibly as a night-eye.

Animals↗
PubMed1984

Localization of axonally transported label in chick retinal ganglion cell axons after intravitreal injections of wheat germ agglutinin conjugated to horseradish peroxidase.

We have studied the subcellular localization of peroxidase-labeled organelles after anterograde axonal transport by chick retinal ganglion cells that had been exposed 23-25 h earlier to wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). After intravitreal injection of WGA-HRP, we found in the optic tectum that 82% of labeled organelles were located within axons and axon terminals. The organelles included: tubules and cisternae of the smooth endoplasmic reticulum, hypolemmal cisternae, vesicles, dense bodies and multivesticular bodies. We also measured the distances between the centers of the labeled organelles and the plasma membrane of these profiles. The density of organelles (number of organelles/micron 2) was plotted as a function of distance from the plasma membrane. Irrespective of the dose of lectin-peroxidase injected, labeled organelles were most densely concentrated in a 30 nm wide annular zone centered 75 nm in from the plasma membrane. In axon terminals the labeled organelles were most concentrated 75-90 nm in from the plasma membrane. Assuming that the peroxidase label indicates the presence of WGA-HRP, we conclude that after anterograde axonal transport the lectin accumulates in lysosomal organelles and elements of the smooth endoplasmic reticulum. Therefore, in contrast to the more restricted localization of [125I]WGA as inferred from electron microscopic autoradiography after uptake and transport by the same cell type, WGA-HRP-labeled organelles are found more diffusely within the axoplasm, particularly in axon terminals. Furthermore, peroxidase-labeled organelles in dendritic, glial or neuronal cell bodies in the tectum were seen less frequently than expected based on evidence of frequent transfer to second cells after intravitreal injections of [125I]WGA. Thus, we infer that at these concentrations WGA labeled with HRP may not be transferred intercellularly as efficiently as even lower concentrations of iodinated WGA are apparently transferred.

Animals↗