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Results for “retinal plasticity”

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At least 19 recordsLinked to original sources
PubMed1988

Development and plasticity of retinal X and Y axon terminations in the cat's lateral geniculate nucleus.

The technique of injecting single retinogeniculate fibers with horseradish peroxidase enables the terminal arbors of physiologically identified axons to be fully characterized morphologically. We have used this technique to study the postnatal development of retinal X and Y cell arbors within the cat's lateral geniculate nucleus, and the plasticity of these arbors following a variety of manipulations that perturb normal development. These experiments suggest quite specific sequences and mechanisms for the development of individual X and Y retinogeniculate axons. Retinal X axons appear to innervate the lateral geniculate nucleus before Y axons do, and are probably specified innately to their appropriate target lamina A or A1. By 3-4 weeks postnatally, X axons from each eye develop exuberant terminal arbors within the A laminae that by 12 weeks get pruned to the narrow adult form by later developing Y axon arbors from the same eye. The Y arbors progressively expand to form their characteristic broad terminal zones during this period. The laminar location of Y arbors depends on interactions between axons from the two eyes, and their transverse extent on the presence of normal afferent activity in retinogeniculate fibers.

Animals↗
PubMed1990

The expression of phosphorylated and non-phosphorylated forms of MAP5 in the amphibian CNS.

MAP5 is a microtubule-associated protein that in rat and quail is more abundant in the developing than in the adult brain. Previous studies in our laboratory have shown that MAP5 can be resolved into two forms by SDS-PAGE, MAP5a and MAP5b (Mr 300,000-320,000 Da) with MAP5a representing a highly phosphorylated form of this protein. In the present study, the relationship between MAP5 expression and neuronal growth and plasticity was investigated by assessing the amount and distribution of MAP5a and MAP5b in both the developing Xenopus brain and in different regions of the adult brain where neurons of varying growth potential and plasticity are present. In the larval and metamorphic Xenopus brain, like the neonatal rat brain, MAP5 is present in the highly phosphorylated form, MAP5a, and in concentrated in neuronal processes. In the adult Xenopus brain, MAP5a remains high in the optic tectum but, like the situation in the adult rat brain, is undetectable in the telencephalon. Immunohistochemistry showed that MAP5 was concentrated in the outer layer of the tectum, where ingrowing and plastic retinal ganglion cell axons are found. The correlation between MAP5 expression and phosphorylation and growth potential suggests that this molecule plays an important role in the regulation and organization of the neuronal cytoskeleton during neurite outgrowth and plasticity.

Animals↗
PubMed1987

Retinal transplants into the anterior chamber of the rat eye.

Developing retinas from 13-18-day fetuses and 2-day neonatal Long-Evans rats transplanted into the anterior chamber of adult eyes of the same or different strain (Lewis) survive and differentiate. Light and electron microscopic studies show that the transplants undergo histogenetic differentiation, resulting in the development of neurons and Müller glial cells and formation of nuclear and plexiform layers. Vascular connections develop between the host iris and the retinal transplant. Vessels and nerves, presumably of iridal origin, were seen on the surface of some transplants. Possible manifestations of graft rejection were monitored; signs of tissue rejection in transplants performed in the Long-Evans rats, an outbred strain, were rare and if present they were mild, at least during the survival periods of up to 91 days allowed in these experiments. Transplants into the eyes of Lewis rats were also well tolerated during the survival period. These observations indicate that retinal transplantation to the adult eye of a genetically different host can be successfully achieved and that both embryonic and perinatal retinas are suitable as donor tissue for ocular transplants. The procedure offers ample opportunities for the study of problems related to retinal plasticity.

Animals↗
PubMed1985

Intraocular retinal transplants.

Embryonic rat retinae transplanted into the anterior chamber of adult rat eyes of the same or different strain survive and grow. Light and electron microscopic studies show that the transplants undergo histogenetic differentiation, resulting in the development of mature inner and outer layer neurons and Müller glial cells. Vascular connections develop between the host iris and the retinal transplant. These initial observations indicate that retinal transplantation to a recipient eye is a procedure which offers ample opportunities for the study of problems related to neural development, retinal plasticity and repair.

Animals↗
PubMed1990

Substance P and enkephalins in the superficial layers of the rat superior colliculus: differential plastic effects of retinal deafferentation.

In this work we studied the effects of unilateral eye enucleation on the contents and distribution of leu-enkephalin-, met-enkephalin-arg6-gly7-leu8-, and substance-P-like immunoreactivities (L-ENK-I, ENK-8-I, and SP-I, respectively) in the superficial layers of the rat superior colliculus (SC) by means of the unlabelled antibody peroxidase-antiperoxidase method. In the normal rat only a few L-ENK-I neurons appear dispersed in the stratum griseum superficiale. No immunostained somata appear in the stratum opticum. The most striking effect of unilateral enucleation was the dramatic appearance of a laminarly distributed population of L-ENK-I and/or ENK-8-I neurons in the dorsal stratum opticum of the SC contralateral to the enucleated side. This population of immunoreactive cells was observed with all the survival times examined in the present study (3, 7, 15, and 30 days) and was always accompanied by an increase in the immunostaining of L-ENK-I and/or ENK-8-I fibers in the contralateral stratum griseum superficiale. Enucleation also produced a decrease in the immunostaining of SP-I dendrites that only became obvious 15 days after enucleation. However, the number of SP-I somata or terminal-like immunoreactive structures showed no detectable changes. These results show that retinal deafferentation of the superficial layers of the rat SC has different effects on some immunohistochemically distinguishable neuronal subgroups in the SC, suggesting different functional or trophic relationships of the retinal input to these groups of neurons.

Afferent Pathways↗
PubMed1992

Protective effects of flunarizine on ischemic injury in the rat retina.

Intracellular calcium overload has been implicated to be a major factor in triggering cell death after ischemic neuronal injury. We investigated the effects of flunarizine hydrochloride, a calcium-overload blocker, on pressure-induced retinal ischemia in a rat model. Retinal ischemia was induced in intraocular pressure to 110 mm Hg for 45 minutes. Two regimens of treatment with flunarizine were examined: (1) prophylactic treatment, in which flunarizine was administered before ischemia and in the early phase of reperfusion; and (2) postischemic treatment, in which flunarizine was administered only in the early phase of reperfusion. Injury was evaluated morphologically and morphometrically by measuring the thickness of the inner retinal layers on plastic-embedded retinal sections and by counting the retinal ganglion cells on retinal flat preparations. By morphologic and morphometric criteria, a significant but partial protection of the inner retinal layers was noted in the groups given either regimen. This protective effect of flunarizine suggests that elevated intracellular calcium concentration may play an important role in ischemic retinal injury.

Animals↗
PubMed1990

Development of abnormal lamination and binocular segregation of retinal afferents onto the rat superior colliculus.

Unilateral optic tract lesions made in newborn rats produce abnormal retinotectal pathways on the opposite side. The present investigation was designed to study the development of the abnormal retinal projections in the superior colliculus using anatomical tracing methods. The aberrant uncrossed retinotectal pathway develops within the first postnatal week. In spite of this, the retraction of the crossed projection, which indicates binocular segregation, is of late onset. This indicates that the induced segregation of retinal inputs is not dependent on regressive events such as ganglion cell death and terminal field retraction. These data and the results of lid-suture experiments are consistent with a role for spontaneous retinal activity in the regulation of the plasticity of retinal projections to the rat superior colliculus.

Animals↗
PubMed1977

Dissociation of the vitreo-retinal junction following experimental embolization of retinal circulation.

Spheric plastic beads (7-25 mu in diameter) were injected into the central retinal artery of the owl monkey (Aotus trivirgatus) using a micro-surgical technique. The occlusion of retinal arteriolar branches resulted in posterior vitreous detachment and microcystoid degeneration in inner retinal layers. The dissociation of the vitreoretinal junction showed three different entities: detachment of the vitreous from the basal lamina (inner limiting lamina of the retina), separation of the basal lamina from the retina, and detachment of shreds of glial cells and other degenerated retinal tissue (intraretinal schisis).

Animals↗
PubMed1989

Plasticity and differentiation of embryonic retinal cells after terminal mitosis.

The relation between terminal mitosis and the events that determine the developmental fate of embryonic precursor cells is not well understood. This relation has now been investigated with [3H]thymidine autoradiography to determine the time of cell birth and with a culture system that allows the testing of the developmental potential of cells isolated from the chick embryo retina. Contrary to the situation in vivo, where neuronal differentiation always precedes photoreceptor differentiation, photoreceptor differentiation occurs prematurely and precedes neuronal differentiation when precursor cells are isolated from the retina at early embryonic stages. Thus, cells born by embryonic day 5 (ED-5) give rise predominantly to photoreceptors when isolated for culture on ED-6 but develop mainly as neurons when isolated on ED-8. This suggests that retinal precursor cells retain after terminal mitosis the capacity to develop either as neurons or as photoreceptors. Moreover, photoreceptor differentiation appears to represent a constitutive or "default" pathway that precursor cells follow in the absence of neuron-inducing signals.

Animals↗
PubMed1989

Ribbon synapses of the mammalian retina contain two types of synaptic bodies--ribbons and spheres.

The present paper reports that the synaptic bodies of the retinal ribbon synapses in rat, guinea pig, golden hamster and mouse are a heterogeneous population of organelles. In addition to the well-known synaptic ribbons sensu stricto which consist of a platelike electron-dense central structure surrounded by electron-lucent synaptic vesicles, there are what is termed synaptic spheres, in which the core is not platelike, but round to oval. In rat retinae procured at day, ribbons outnumbered spheres by a factor of 4. At night spheres were not seen in photoreceptor cells. Spheres, like ribbons, may lie some distance from the synaptic site, perhaps indicating transit from their site of origin to the synapse. At night ribbons are longer than at daytime. In addition to the previously described connecting stalks between synaptic vesicles and the electron-dense ribbons, the presence of filamentous stalks between adjacent synaptic vesicles is described. The latter stalks, depending on their presence or absence, may influence the position of the synaptic vesicles in relation to the synaptic body and/or the presynaptic membrane. It is concluded that the plasticity of retinal synapses cannot be fully appreciated unless the temporal changes of ribbons, spheres and the connecting stalks are taken into consideration.

Animals↗
PubMed1985

Vascular casting and scanning electron microscopy of human ocular vascular abnormalities.

Plastic casts of ocular vessels were made from postmortem specimens obtained from patients who had had hypertension and arteriosclerosis, diabetes mellitus, and retinopathy of childhood. In conjunction with scanning electron microscopy, the casts serve as models of pathologic vascular changes, including arteriovenous crossing defects, microaneurysm, localized capillary nonperfusion, and rapidly growing peripheral choroidal vessels. These preliminary findings should serve to encourage further study of ocular vascular abnormalities with the use of plastic casting techniques.

Adult↗
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

Cortical blindness after overlapping retinal-striate lesions: a limit to plasticity in the central visual system.

Lesions in cats, rats, and monkeys that spare more than 2% of the optic tract or visual cortex cause trivial deficits on most measures of vision. Overlap in the topography of the visual system may allow the spared remnant to 'see' a wider field of vision than the physiological map predicts. We tested whether monkeys left with only the lower retinal-field portion of their striate map could see with information coming from the upper half of the retina. In 6 rhesus monkeys the ganglion fibers exiting from the lower half of both retinae were cut with a photocoagulator. Later, the portion of area 17 which, according to the electrophysiological map, controls upper retinal vision, was ablated bilaterally. The combined retinal and striate lesions overlapped to include the entire visual field. Together they produced cortical blindness. The monkeys' performance of two pattern and object tasks remained at chance throughout the survival period. A previous study has described considerable sparing of vision after combined optic tract and visual cortex lesions in cats. Differences in the lesion methods and in the anatomy of the cat and monkey visual system may explain the disagreement.

Animals↗
PubMed1990

Induction of a heat shock gene (hsp70) in rabbit retinal ganglion cells detected by in situ hybridization with plastic-embedded tissue.

Elevation of body temperature by 2-3 degrees C induces a 2.7 kilobase hsp70 mRNA species in the rabbit retina within 1 hr. In situ hybridization with thin sections derived from plastic-embedded tissue permitted a higher level of resolution of retinal cell types compared to procedures which involved the use of frozen tissue sections. A prominent induction of hsp70 mRNA in retinal ganglion cells was observed when an hsp70 riboprobe was utilized for in situ hybridization. These results indicate that this neuronal cell type responds rapidly to fever-like body temperatures by inducing one of the major heat shock genes.

Animals↗
PubMed1988

Glutamate and dopamine modulate synaptic plasticity in horizontal cell dendrites of fish retina.

Horizontal cell dendrites protruding into the cone pedicles in fish retina exhibit a light-dependent plasticity. In a light-adapted retina they form numerous spinules having membrane densities at their tips. These spinules disappear during dark adaptation. Experiments with light- or dark-adapted retinas which were incubated in glutamate or its agonists and antagonists, respectively, revealed that this putative cone transmitter is able to reduce the expression of spinules in a light-adapted retina. Dopamine, on the other hand, induces the formation of spinules in a dark-adapted retina and haloperidol reduces the expression in a light-adapted retina. These data suggest a control of spinules plasticity through two retinal neurotransmitter systems.

Animals↗
PubMed1991

Selective alterations in glutamate receptor subtypes after unilateral orbital enucleation.

Glutamate is the major excitatory neurotransmitter in the rat visual system. Using quantitative autoradiography the effect of unilateral orbital enucleation on [3H]kainate, [3H]alpha-amino-3-hydroxy-5-methyl- isoxazole-4-propionic acid [( 3H]AMPA) and [3H]glutamate binding to kainate, quisqualate and NMDA receptors respectively has been examined within anatomical components of the visual pathway at 4 time points up to 20 days post-lesion. The time course for the degeneration of retinal projection fibres was assessed in a separate group of animals by quantifying [3H]cyclohexyladenosine [( 3H]CHA) binding to presynaptic adenosine A1 receptors. Over the first 5 days after orbital enucleation, there were no significant alterations in glutamate or adenosine A1 receptor binding in visual structures of the visually deprived hemisphere. However, at 10 days post-lesion [3H]AMPA binding was significantly reduced (30%) in the visually deprived superior colliculus but unaltered in other visual structures. At this time point there was also a significant reduction (50%) in [3H]CHA binding in the visually deprived superior colliculus but not in other retino-recipient nuclei. There were similar changes in [3H]AMPA and [3H]CHA binding at 20 days post-enucleation. [3H]Kainate binding was significantly increased in the visually deprived superior colliculus only at 20 days post-enucleation. Saturation analysis of [3H]kainate and [3H]AMPA binding at this time point indicated a selective increase in the Bmax value for the high affinity [3H]kainate binding site and a concomitant decrease in the Bmax value for the high affinity [3H]AMPA binding site in the visually deprived superior colliculus. There were, however, no significant alterations in [3H]AMPA or [3H]kainate binding in other primary projection areas or in secondary visual areas (e.g. visual cortex) at any time point. NMDA sensitive [3H]glutamate binding was unaltered in the visually deprived hemisphere up to 20 days post-enucleation. These results suggest an upregulation of kainate receptors in the visually deprived superior colliculus after orbital enucleation and a loss of presynaptic quisqualate receptors on degenerating retinal fibres. The plastic alterations in kainate receptors in the superior colliculus are supportive of electrophysiological data suggesting a physiological role for these sites in mediating excitatory postsynaptic potentials in tectal neurons.

Animals↗