Immunohistochemical evidence of synaptic retraction, cytoarchitectural remodeling, and cell death in the inner retina of the rat model of Oygen-Induced Retinopathy (OIR)

Purpose. Postnatal exposure to hyperoxia destroys the plexiform layers of the neonatal rat retina, resulting in significant electroretinographic anomalies. The purpose of this study was to identify the mechanisms at the origin of this loss. Methods. Sprague-Dawley (SD) and Long Evans (LE) rats were exposed to hyperoxia from birth to postnatal day (P) 6 or P14 and from P6 to P14, after which rats were euthanatized at P6, P14, or P60. Results. At P60, synaptophysin staining confirmed the lack of functional synaptic terminals in SD (outer plexiform layer [OPL]) and LE (OPL and inner plexiform layer [IPL]) rats. Uneven staining of ON-bipolar cell terminals with mGluR6 suggests that their loss could play a role in OPL thinning. Protein kinase C(PKC)-α and recoverin (rod and cone ON-bipolar cells, respectively) showed a lack of dendritic terminals in the OPL with disorganized axonal projections in the IPL. Although photoreceptor nuclei appeared intact, a decrease in bassoon staining (synaptic ribbon terminals) suggests limited communication to the inner retina. Findings were significantly more pronounced in LE rats. An increase in TUNEL-positive cells was observed in LE (inner nuclear layer [INL] and outer nuclear layer [ONL]) and SD (INL) rats after P0 to P14 exposure (425.3%, 102.2%, and 146.3% greater than control, respectively [P < 0.05]). Conclusions. Results suggest that cell death and synaptic retraction are at the root of OPL thinning. Increased TUNEL-positive cells in the INL confirm that cells die, at least in part, because of apoptosis. These findings propose a previously undescribed mechanism of cell death and synaptic retraction that are likely at the origin of the functional consequences of hyperoxia.

Rotenone induces degeneration of photoreceptors and impairs the dopaminergic system in the rat retina

Rotenone is a widely used pesticide and a potent inhibitor of mitochondrial complex I (NADH-quinone reductase) that elicits the degeneration of dopaminergic neurons and thereby the appearance of a parkinsonian syndrome. Here we have addressed the alterations induced by rotenone at the functional, morphological and molecular levels in the retina, including those involving both dopaminergic and non-dopaminergic retinal neurons. Rotenone-treated rats showed abnormalities in equilibrium, postural instability and involuntary movements. In their outer retina we observed a loss of photoreceptors, and a reduced synaptic connectivity between those remaining and their postsynaptic neurons. A dramatic loss of mitochondria was observed in the inner segments, as well as in the axon terminals of photoreceptors. In the inner retina we observed a decrease in the expression of dopaminergic cell molecular markers, including loss of tyrosine hydroxylase immunoreactivity, associated with a reduction of the dopaminergic plexus and cell bodies. An increase in immunoreactivity of AII amacrine cells for parvalbumin, a Ca2+-scavenging protein, was also detected. These abnormalities were accompanied by a decrease in the amplitude of scotopic and photopic a- and b-waves and an increase in the b-wave implicit time, as well as by a lower amplitude and greater latency in oscillatory potentials. These results indicate that rotenone induces loss of vision by promoting photoreceptor cell death and impairment of the dopaminergic retinal system.

RNA-Seq expression profile of genes related to neurodegenerative disorders affecting the human retina

Human neurodegenerative diseases, such as Parkinson’s disease (PD) and the neuromuscular disorders called dystroglycanopathies (DGPs), cause retinal impairments. We have used RNA-Seq technology to catalog all known genes linked to PD and DGPs expressed in the human retina and quantitate their mRNA levels in terms of FPKM. We have also characterized their expression profiles in the retina by determining their exonic, intronic and exon-intron junction expression levels, as well as the alternative splicing pattern of particular genes. We believe these data could pave the way toward understanding the molecular bases of sight deficiencies associated with neurodegenerative disorders.

Alterations in energy metabolism, neuroprotection and visual signal transduction in the retina of parkinsonian, MPTP-treated monkeys

Parkinson disease is mainly characterized by the degeneration of dopaminergic neurons in the central nervous system, including the retina. Different interrelated molecular mechanisms underlying Parkinson disease-associated neuronal death have been put forward in the brain, including oxidative stress and mitochondrial dysfunction. Systemic injection of the proneurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to monkeys elicits the appearance of a parkinsonian syndrome, including morphological and functional impairments in the retina. However, the intracellular events leading to derangement of dopaminergic and other retinal neurons in MPTP-treated animal models have not been so far investigated. Here we have used a comparative proteomics approach to identify proteins differentially expressed in the retina of MPTP-treated monkeys. Proteins were solubilized from the neural retinas of control and MPTP-treated animals, labelled separately with two different cyanine fluorophores and run pairwise on 2D DIGE gels. Out of >700 protein spots resolved and quantified, 36 were found to exhibit statistically significant differences in their expression levels, of at least ±1.4-fold, in the parkinsonian monkey retina compared with controls. Most of these spots were excised from preparative 2D gels, trypsinized and subjected to MALDI-TOF MS and LC-MS/MS analyses. Data obtained were used for protein sequence database interrogation, and 15 different proteins were successfully identified, of which 13 were underexpressed and 2 overexpressed. These proteins were involved in key cellular functional pathways such as glycolysis and mitochondrial electron transport, neuronal protection against stress and survival, and phototransduction processes. These functional categories underscore that alterations in energy metabolism, neuroprotective mechanisms and signal transduction are involved in MPTPinduced neuronal degeneration in the retina, in similarity to mechanisms thought to underlie neuronal death in the Parkinson’s diseased brain and neurodegenerative diseases of the retina proper.

Does Müller cell differentiation occur prior to the emergence of synapses in embryonic turtle retina?

Müller cells are the main glial cells in the retina, and are related to plexiform layer activity. Recent studies have demonstrated that Müller cells are involved in the synaptic conservation, plasticity, development and metabolism of glutamate. During turtle retinal development, layers, cells and synapses appear at different times. The aim of this research is to study the emergence of Müller cells during embryonic development and their relationship with the synaptogenesis. The authors used retinas from Trachemys scripta elegans embryos at stages S14, 18, 20, 23, and 26. Some retinas were processed with immunocytochemistry in order to detect the presence of glutamine synthetase in Müller cells, which was used as a marker of these cells. Other retinas from the same stages were processed for ultrastructural studies. Samples were observed in confocal and transmission electron microscopes, respectively. The present results show that glutamine synthetase expression in Müller cells occurs at S18, before the emergence of the retinal layers and the early synapses.

Electroretinographical and histological study of mouse retina after optic nerve section: a comparison between wild-type and retinal degeneration 1 mice

Background: Retinal ganglion cell death underlies the pathophysiology of neurodegenerative disorders such as glaucoma or optic nerve trauma. To assess the potential influence of photoreceptor degeneration on retinal ganglion cell survival, and to evaluate functionality, we took advantage of the optic nerve section mouse model. Methods: Surviving retinal ganglion cells were double-stained by exposing both superior colliculi to fluorogold, and by applying dextran-tetramethylrhodamine to the injured optic nerve stump. To assess retinal function in wild-type animals, electroretinograms were recorded on the injured eyes and compared with the contralateral. Similar labelling experiments were carried out on retinal degeneration 1 mice. Surviving retinal ganglion cells were counted 21 days after axotomy and compared with wild-type mice. No functional experiments were performed on retinal degeneration 1 animals because they do not develop normal electroretinographical responses. Results: A significant decrease in retinal ganglion cell density was observed 6 days after axotomy in the wild type. Functional studies revealed that, in scotopic conditions, axotomy induced a significant amplitude decrease in the positive scotopic threshold response component of the electroretinogram. Such decrease paralleled cell loss, suggesting it may be an appropriate technique to evaluate functionality. When comparing retinal ganglion cell densities in wild-type and retinal degeneration 1 mice, a significant greater survival was observed on the latter. Conclusions: After optic nerve section, electroretinographical recordings exhibited a progressive decrease in the amplitude of the positive scotopic threshold response wave, reflecting ganglion cell loss. Interestingly, rod degeneration seemed, at least initially, to protect from axotomy-driven damage.

Physiological and Morphological Similarities between the Octodon Degus Retina and the Human Retina

Octodon degus is a rodent with diurnal crepuscular activity. Here we compare the function and morphology of the retina of this diurnal rodent with the retinas of nocturnal rodents and humans.

La complejidad de las distrofias hereditarias de la retina: un obstáculo y un reto

ACTO conjunto de FARPE-FUNDALUCE con la SEBBM en el marco de su XXXVII Congreso. Conferencia: La complejidad de las distrofias hereditarias de la retina: Un obstáculo y un reto (José Martín Nieto).

Expression and cellular localization of the voltage-gated calcium channel α2δ3 in the rodent retina

High-voltage-activated calcium channels are hetero-oligomeric protein complexes that mediate multiple cellular processes, including the influx of extracellular Ca2+, neurotransmitter release, gene transcription, and synaptic plasticity. These channels consist of a primary α1 pore-forming subunit, which is associated with an extracellular α2δ subunit and an intracellular β auxiliary subunit, which alter the gating properties and trafficking of the calcium channel. The cellular localization of the α2δ3 subunit in the mouse and rat retina is unknown. In this study using RT-PCR, a single band at ∼305 bp corresponding to the predicted size of the α2δ3 subunit fragment was found in mouse and rat retina and brain homogenates. Western blotting of rodent retina and brain homogenates showed a single 123-kDa band. Immunohistochemistry with an affinity-purified antibody to the α2δ3 subunit revealed immunoreactive cell bodies in the ganglion cell layer and inner nuclear layer and immunoreactive processes in the inner plexiform layer and the outer plexiform layer. α2δ3 immunoreactivity was localized to multiple cell types, including ganglion, amacrine, and bipolar cells and photoreceptors, but not horizontal cells. The expression of the α2δ3 calcium channel subunit to multiple cell types suggests that this subunit participates widely in Ca-channel-mediated signaling in the retina.

Propagation, structural similarity and image quality

Póster presentado en SPIE Photonics Europe, Brussels, 16-19 April 2012.

Tauroursodeoxycholic acid prevents retinal degeneration in transgenic P23H rats

Purpose. To evaluate the preventive effect of tauroursodeoxycholic acid (TUDCA) on photoreceptor degeneration, synaptic connectivity and functional activity of the retina in the transgenic P23H rat, an animal model of autosomal dominant retinitis pigmentosa (RP). Methods. P23H line-3 rats were injected with TUDCA once a week from postnatal day (P)21 to P120, in parallel with vehicle-administered controls. At P120, functional activity of the retina was evaluated by electroretinographic (ERG) recording. The effects of TUDCA on the number, morphology, integrity, and synaptic connectivity of retinal cells were characterized by immunofluorescence confocal microscopy. Results. The amplitude of ERG a- and b-waves was significantly higher in TUDCA-treated animals under both scotopic and photopic conditions than in control animals. In the central area of the retina, TUDCA-treated P23H rats showed threefold more photoreceptors than control animals. The number of TUNEL-positive cells was significantly smaller in TUDCA-treated rats, in which photoreceptor morphology was preserved. Presynaptic and postsynaptic elements, as well as the synaptic contacts between photoreceptors and bipolar or horizontal cells, were preserved in TUDCA-treated P23H rats. Furthermore, in TUDCA-treated rat retinas, the number of both rod bipolar and horizontal cell bodies, as well as the density of their synaptic terminals in the outer plexiform layer, was greater than in control rats. Conclusions. TUDCA treatment was capable of preserving cone and rod structure and function, together with their contacts with their postsynaptic neurons. The neuroprotective effects of TUDCA make this compound potentially useful for delaying retinal degeneration in RP.

Time course modifications in organotypic culture of human neuroretina

The purpose of this study was to characterize organ culture of human neuroretina and to establish survival and early degeneration patterns of neural and glial cells. Sixteen neuroretina explants were prepared from 2 postmortem eyes of 2 individuals. Four explants were used as fresh retina controls, and 12 were evaluated at 3, 6, and 9 days of culture. Neuroretina explants (5 × 5 mm) were cultured in Transwell® dishes with the photoreceptor layer facing the supporting membrane. Culture medium (Neurobasal A-based) was maintained in contact with the membrane beneath the explant. Cryostat and ultrathin sections were prepared for immunohistochemistry and electron microscopy. Neuroretinal modifications were evaluated after toluidine blue staining and after immunostaining for neuronal and glial cell markers. Ultrastructural changes were analyzed by electron microscopy. From 0 to 9 days in culture, there was progressive retinal degeneration, including early pyknosis of photoreceptor nuclei, cellular vacuolization in the ganglion cell layer, decrease of both plexiform layer thicknesses, disruption and truncation of photoreceptor outer segments (OS), and marked reduction in the number of nuclei at both nuclear layers where the cells were less densely packed. At 3 days there was swelling of cone OS with impairment of pedicles, loss of axons and dendrites of horizontal and rod bipolar cells that stained for calbindin (CB) and protein kinase C (PKC-α), respectively. After 9 days, horizontal cells were pyknotic and without terminal tips. There were similar degenerative processes in the outer plexiform layer for rod bipolar cells and loss of axon terminal lateral varicosities in the inner plexiform layer. Glial fibrillary acidic protein (GFAP) staining did not reveal a dramatic increase of gliosis in Müller cells. However, some Müller cells were CB immunoreactive at 6 days of culture. Over 9 days of culture, human neuroretina explants underwent morphological changes in photoreceptors, particularly the OS and axon terminals, and in postsynaptic horizontal and bipolar cells. These early changes, not previously described in cultured human samples, reproduce some celullar modifications after retinal damage. Thus, this model may be suitable to evaluate therapeutic agents during retinal degeneration processes.

Age-related functional and structural retinal modifications in the Igf1−/− null mouse

Background. Mutations in the gene encoding human insulin-like growth factor-I (IGF-I) cause syndromic neurosensorial deafness. To understand the precise role of IGF-I in retinal physiology, we have studied the morphology and electrophysiology of the retina of the Igf1−/− mice in comparison with that of the Igf1+/− and Igf1+/+ animals during aging. Methods. Serological concentrations of IGF-I, glycemia and body weight were determined in Igf1+/+, Igf1+/− and Igf1−/− mice at different times up to 360 days of age. We have analyzed hearing by recording the auditory brainstem responses (ABR), the retinal function by electroretinographic (ERG) responses and the retinal morphology by immunohistochemical labeling on retinal preparations at different ages. Results. IGF-I levels are gradually reduced with aging in the mouse. Deaf Igf1−/− mice had an almost flat scotopic ERG response and a photopic ERG response of very small amplitude at postnatal age 360 days (P360). At the same age, Igf1+/− mice still showed both scotopic and photopic ERG responses, but a significant decrease in the ERG wave amplitudes was observed when compared with those of Igf1+/+ mice. Immunohistochemical analysis showed that P360 Igf1−/− mice suffered important structural modifications in the first synapse of the retinal pathway, that affected mainly the postsynaptic processes from horizontal and bipolar cells. A decrease in bassoon and synaptophysin staining in both rod and cone synaptic terminals suggested a reduced photoreceptor output to the inner retina. Retinal morphology of the P360 Igf1+/− mice showed only small alterations in the horizontal and bipolar cell processes, when compared with Igf1+/+ mice of matched age. Conclusions. In the mouse, IGF-I deficit causes an age-related visual loss, besides a congenital deafness. The present results support the use of the Igf1−/− mouse as a new model for the study of human syndromic deaf-blindness.