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PubMed2003

Evidence that ganglion cells react to retinal detachment.

Growth associated protein 43 (GAP 43) is involved in synapse formation and it is expressed in the retina in a very specific pattern. Although GAP 43 is downregulated at the time of synapse formation, it can be re-expressed following injury such as axotomy or ischemia. Because of this we sought to characterize the expression of GAP 43 after retinal detachment (RD). Immunoblot, immunocytochemical and quantitative polymerase chain reaction (QPCR) techniques were used to assess the level of GAP 43 expression after experimental RD. GAP 43 was localized to three sublaminae of the inner plexiform layer of the normal retina. GAP 43 became upregulated in a subset of retinal ganglion cells following at least 7 days of RD. By immunoblot GAP 43 could be detected by 3 days. QPCR shows the upregulation of GAP 43 message by 6hr of detachment. To further characterize changes in ganglion cells, we used an antibody to neurofilament 70 and 200kDa (NF) proteins. Anti-NF labels horizontal cells, ganglion cell dendrites in the inner plexiform layer, and ganglion cell axons (fasicles) in the normal retina. Following detachment it is upregulated in horizontal cells and ganglion cells. When detached retina was double labelled with anti-GAP 43 and anti-NF, some cells were labelled with both markers, while others labelled with only one. We have previously shown that second order neurons respond to detachment; here we show that third order neurons are responding as well. Cellular remodelling of this type in response to detachment may explain the slow recovery of vision that often occurs after reattachment, or those changes that are often assumed to be permanent.

Animals↗

PubMed1993

Number, distribution, and morphology of retinal ganglion cells with axons regenerated into peripheral nerve graft in adult cats.

The optic nerve of adult cats was transected and an autologous peripheral nerve was transplanted to the stump. Two months later retinal ganglion cells (RGCs) that had regenerated their axons were retrogradely labeled with fluorescent dye injected into the graft. The more than 4000 labeled cells, which were 3.0-4.3% of total ganglion cell number in the intact retina, were distributed in a high-density area elongating horizontally, in a pattern similar to that observed in the intact retina. The dendritic morphology of RGCs with regenerated axons was examined after intracellular injections of HRP or Lucifer yellow in vitro. The morphology of alpha- and gamma-cells appeared comparable to normal, whereas the dendrites of some beta-cells seemed to degenerate. Some "unclassified" cells could not be identified as alpha-, beta-, or gamma-cells. The main dendrites of most unclassified cells were thin and less ramified than alpha- and beta-cells. Some unclassified cells had a vacant area in their dendritic fields, suggesting degenerative change in dendrites. The distal dendrites of some unclassified and gamma-cells had many fine processes that probably regrew during axonal regeneration. The proportion of alpha-, beta-, and other cells including gamma- and unclassified cells in the regenerating cell population was evaluated by examining all of the Lucifer yellow-injected cells in local patches. The average proportion of alpha-cells was 23.9%, about six times higher than in intact retinas. The average proportion of beta-cells was 50.3%, slightly higher than in intact retinas. The remaining cells (25.7%) could not be categorized as alpha or beta; this proportion is about half that found in intact retinas. These findings suggest that alpha-cells have the highest capacity to regenerate their axons into nerve grafts, rather than all types equally regenerating their axons.

Animals↗

PubMed2006

Calcium-induced calcium release in rod photoreceptor terminals boosts synaptic transmission during maintained depolarization.

We examined the contribution of calcium-induced calcium release (CICR) to synaptic transmission from rod photoreceptor terminals. Whole-cell recording and confocal calcium imaging experiments were conducted on rods with intact synaptic terminals in a retinal slice preparation from salamander. Low concentrations of ryanodine stimulated calcium increases in rod terminals, consistent with the presence of ryanodine receptors. Application of strong depolarizing steps (-70 to -10 mV) exceeding 200 ms or longer in duration evoked a wave of calcium that spread across the synaptic terminals of voltage-clamped rods. This secondary calcium increase was blocked by high concentrations of ryanodine, indicating it was due to CICR. Ryanodine (50 microm) had no significant effect on rod calcium current (I(ca)) although it slightly diminished rod light-evoked voltage responses. Bath application of 50 microm ryanodine strongly inhibited light-evoked currents in horizontal cells. Whether applied extracellularly or delivered into the rod cell through the patch pipette, ryanodine (50 microm) also inhibited excitatory post-synaptic currents (EPSCs) evoked in horizontal cells by depolarizing steps applied to rods. Ryanodine caused a preferential reduction in the later portions of EPSCs evoked by depolarizing steps of 200 ms or longer. These results indicate that CICR enhances calcium increases in rod terminals evoked by sustained depolarization, which in turn acts to boost synaptic exocytosis from rods.

Animals↗

PubMed1981

The topography of primate retina: a study of the human, bushbaby, and new- and old-world monkeys.

The distribution of ganglion cells has been studied in the retinas of four primates: the prosimian bushbaby, the New-World squirrel monkey, the Old-World crab-eating cynamolgous monkey, and the human. The sizes of ganglion cell somas were also measured at a number of retinal locations and compared with similar measurements in the cat retina to test for the presence in primates of retinal specializations such as the visual streak, and for gradients in retinal structure, such as that between temporal and nasal retina. In all four primates, ganglion cell somas in peripheral retina ranged considerably in diameter (6-16 micrometer in the bushbaby, 8-22 micrometer in the squirrel monkey, 8-23 micrometer in the cynamolgous monkey, 8-26 micrometer in the human). It seems likely that the strong physiological correlates of soma size which have been described among cat retinal ganglion cells and among the relay cells of the macaque lateral geniculate nucleus are generally present in primates. In all four primates, evidence was also obtained of a visual streak specialization; the isodensity lines in ganglion cell density maps were horizontally elongated, and small-bodied ganglion cells were relatively more common in the region of the proposed streak than in other areas of peripheral retina. However, the visual streak seems less well developed than in the cat; among the four primate species examined it was best developed in the bushbaby, at least as assessed by the shape of the isodensity lines. All four primates showed a clear foveal specialization, but this feature seemed least developed in the bushbaby. At the fovea, ganglion cells are smaller in soma size than in peripheral retina; they also seemed more uniform in size, although some distinctly larger cells persist in the human and bushbaby. Soma size measurements also provided evidence of a difference between nasal and temporal areas of peripheral retina comparable to that reported for the cat and other species. Thus the primate retinas examined show features, such as the foveal specialization, which seem unique to them among mammals. They also show features, such as nasal-temporal differences in ganglion cell size, and (though weakly developed) a visual streak, which they have in common with other mammals with widely different phylogenetic histories.

Animals↗

PubMed1998

Immunohistochemical localization of taurine in the retina of developing and adult human and adult monkey.

The localization of taurine in the retina of fetal (12-25 weeks of gestation), postnatal (five-month-old infant) and adult human (35- and 65-year-old) was examined by immunohistochemistry. Additionally, retinas of fresh adult monkey, which served as positive controls, were employed. No immunoreactivity was found in the fetal retinas from 12-15 weeks of gestation. At 1617 weeks of gestation, the ganglion cells and some of their axons were conspicuously labelled for taurine. At 18-19 weeks, Muller glial endfeet, the inner plexiform layer, some amacrine and putative horizontal cells and photoreceptors showed moderate immunoreactivity. With further development at 20-21 and 24-25 weeks of gestation, the immunoreactivity was prominent in Muller cell endfeet, some bipolar cells and in horizontal cells that were aligned in a row in the inner nuclear layer, close to the fovea. At both fetal stages, the photoreceptors and horizontal cells showed strong immunoreactivity. In the postnatal infant retina, taurine immunoreactivity was present in some amacrine cells and photoreceptor inner segments and nuclei, but not in ganglion and horizontal cells, which was also the pattern noted in the adult monkey and human retinas. With development, a shift in the intensity of taurine immunoreactivity was noted towards the outer retina. The expression of taurine immunoreactivity in most fetal retinal neurons implies a role for this amino acid in the normal development as well as maturation of human retina.

Adult↗

PubMed2003

Analysis of EphB receptors and their ligands in the developing retinocollicular system of the wallaby reveals dynamic patterns of expression in the retina.

The expression of EphB1 and B2 receptors and ephrins-B1, -B2 and -B3 in the retina and superior colliculus of the wallaby (Macropus eugenii) was examined during the development of the retinocollicular projection, using reverse transcription-polymerase chain reaction and immunohistochemistry. There was an early transient differential expression of EphB2 that was higher in ventral retina and restricted to the outer neuroblast layer, whereas a high ventral to low dorsal gradient of ephrin-B2 expression occurred there throughout the study period. However, there was no dorsoventral gradient of receptors or ligands in retinal ganglion cells or a mediolateral gradient of ephrins in the colliculus. These findings suggest a limited role for these molecules in topographic mapping across the mediolateral colliculus in the wallaby. Early in retinal development there is a complementary pattern of expression of ephrin-B1 and -B2 in the outer neuroblast layer that overlaps with expression of EphB2. Ganglion and amacrine cells also express EphB2. As development proceeds subpopulations of putative horizontal and bipolar cells, also expressing EphB2, come to reside in the inner nuclear layer and ephrin-B1 is expressed throughout the outer nuclear layer. At the same time cells expressing ephrin-B2, and subpopulations of horizontal and bipolar cells come to reside in the inner nuclear layer and there is a corresponding decrease in ephrin-B2 expression in the outer nuclear layer. This pattern of coexpression of receptors and ligands suggests a role for them in cell migration and maintenance of laminar boundaries.

Aging↗

PubMed2000

Novel myosin VI isoform is abundantly expressed in retina.

Several forms of sensory deficit have been associated with unconventional myosin defects in humans and other animals. Normal hearing in mammals has been shown to require functional myosin VI (Avraham et al., 1995) and myosin VIIA (Gibson et al., 1995; Liu et al., 1997), and the combined blindness and deafness of Usher syndrome type IB has been shown to be produced by specific defects in myosin VIIA (Weil et al., 1997). Here we report the cloning and characterization of two distinct myosin VI isoforms (FMVIA and FMVIB) initially identified in a degenerate PCR screen of retinal cDNA from the striped bass, Morone saxatilis. Open reading frames for FMVIA and FMVIB encode predicted proteins of 1304 and 1270 amino acids respectively, which are 83% identical at the amino acid level. Both fish isoforms are likewise approximately 83-86% identical to mammalian class VI myosins (Hasson and Mooseker, 1994). Northern blot analysis revealed that FMVIA mRNA is broadly expressed and most abundant in kidney, a pattern similar to that previously reported for mammalian myosin VI. FMVIB expression is dramatically more abundant in retina than in any other tissue examined. Antibodies directed against pig myosin VI (Hasson and Mooseker, 1994) detect a doublet at approximately 150 kDa in bass retina and RPE. Since both fish VIA and VIB isoforms share high sequence identity with pig myosin VI within the domain used for antibody production, it seems likely that this antibody crossreacts with both FMVIA and FMVIB. Immunocytochemistry with this same affinity-purified rabbit anti-myosin VI antibody shows that myosin VI isoforms are primarily localized in photoreceptors, horizontal cells and Müller cells in both fish and primate retinas. This report is the first demonstration that two myosin VI genes are expressed in the same organism and the same cell type (RPE). The relatively high abundance of FMVIB expression in retina suggests that it may play an important role in retinal motility events.

Amino Acid Sequence↗

PubMed1997

Synaptic growth in the rod terminals of mice after partial photoreceptor cell loss: a three-dimensional ultrastructural study.

Following partial loss of photoreceptor cells in the retina of mice afflicted by mutant genes, damaging light exposure, or old age, some of the remaining rod cells exhibited a process of growth in their synapses with the second order retinal neurons. This growth was recognized by the presence of multiple synaptic sites in some of the rod terminals in the outer plexiform layer. In this study, a comparative analysis of the microanatomical changes in the synaptic structures of the rod terminals in the retina of normal, rds homozygous and heterozygous mutant and light exposed albino mice was undertaken by using a computer-aided three-dimensional reconstruction. A rod terminal normally showed the presence of 1 synaptic complex consisting of a single synaptic ribbon located between 2 processes of horizontal cells and 2 bipolar cell dendrites. In a rod terminal showing an enlarged synaptic complex, 2 or 3 separate synaptic ribbons formed the centres of separate synaptic sites; each of the sites was characterized by the presence of 2 laterally placed horizontal cell processes and 2 bipolar cell dendrites. However, these processes from the multiple synaptic sites were observed to arise from the 2 horizontal and the 2 bipolar cell elements that were normally present in the rod terminal. Thus proliferation of synaptic sites in the rod terminals occurred through growth and sprouting from the processes of the second order neuronal components present within the terminals. The altered synaptic complexes in the variously affected groups were structurally comparable and appeared to have resulted from similar microanatomical changes. The increase in the frequency of rod terminals with multiple synaptic sites occurred as a sequel to increasing photoreceptor cell loss that was recorded at different age points in the different experimental groups. It is concluded that rod synapses in the adult mammalian retina possess structural plasticity that permits compensatory growth.

Aging↗

PubMed2004

Vanilloid receptor like 1 (VRL1) immunoreactivity in mammalian retina: colocalization with somatostatin and purinergic P2X1 receptors.

The distribution of vanilloid receptor like1 immunoreactivity (VRL1-IR) in the retinas of rat, cat, and monkey was studied by single- and double-labeling immunocytochemistry. The patterns were similar for all three species in that VRL1-IR was most prominent in the inner plexiform layer, with scattered compact projections to the outer plexiform layer (OPL). VRL1-immunoreactive cell bodies were present throughout the rat retina, represented by amacrine cells in the inner nuclear layer and ganglion cell layer (GCL). In cat and monkey retinas, VRL1-immunoreactive cell bodies were restricted to the GCL in the inferior retina. Occasional cell bodies were associated with retinal blood vessels, but their identity as pericytes, glia, or neurons is uncertain. All VRL1-immunoreactive cells and processes colocalized with somatostatin and purinergic P2X1 receptor-IR but not with tyrosine hydroxylase-IR. VRL1-immunoreactive processes in the OPL did not label with antisera against synaptic vesicle 2 (SV2), suggesting that they were dendritic and did not derive from interplexiform cells. However, VRL1-immunoreactive processes in the far periphery toward the pars plana labeled for SV2, suggesting that these processes were presynaptic. The VRL1-immunoreactive cell bodies in the monkey GCL were not calbindin-immunoreactive, demonstrating that they were not displaced H2 horizontal cells. The VRL1-immunoreactive cells in cat and monkey could represent biplexiform and/or associational ganglion cells that receive input in the OPL throughout the retina and direct output to the far periphery. The presence of P2X1 receptors and vanilloid receptor like 1 protein on somatostatin-containing neurons in mammalian retina adds to the growing complexity regarding the chemical control of retinal function that is likely to include the microcirculation.

Animals↗

PubMed2005

Decreased glutathione transferase levels in rd1/rd1 mouse retina: replenishment protects photoreceptors in retinal explants.

Currently much attention is focused on glutathione S transferase (GST)-induced suppression of apoptosis. The objective of our studies was therefore to see if GST isoenzymes rescue photoreceptors in retinal explants from rd1/rd1 mice, in which photoreceptors degenerate rapidly. Eyes from C3H rd1/rd1 and +/+ mice were collected at various time points between postnatal day (PN) 2 and PN28. Localization and content of alpha-GST and mu-GST was investigated by immunofluorescence and semi-quantitative Western blot analysis, respectively. In addition, PN2 and PN7 retinal explants were cultured till PN28, during which they were treated with 10 ng/ml alpha-GST or mu-GST. The spatiotemporal expression of both GST isoforms was closely similar: early presence in ganglion cell layer after which staining became restricted to Muller cells (particularly in the endfeet) and horizontal cell fibers in both rd1/rd1 and +/+. Doublets of alpha-GST and mu-GST were detected by Western blot analysis. Densitometry of these bands indicated steady reduction of alpha-GST content in rd1/rd1 retina starting from the second postnatal week. When alpha-GST and mu-GST were added exogenously to rd1/rd1 explants, photoreceptor rescue was produced that was more prominent in PN2 than in PN7 explants and more effective by alpha-GST than mu-GST. We propose that alpha-GST neuroprotection is mediated by reduction of tissue oxidative stress.

Animals↗

PubMedDate not supplied

Expression of glycine and the glycine transporter Glyt-1 in the developing rat retina.

Previous studies show that glycine transporter-1 (glyt-1) is a consistent membrane marker of adult retinal neurons that are likely to release glycine at their synaptic terminals (Pow, 1998; Vaney et al., 1998; Pow & Hendrickson, 1999). The current study investigated when glyt-1 immunoreactivity appeared in the postnatal rat retina, and whether all glycine-containing neurons also labelled for glyt-1. Ganglion cells, horizontal cells, and photoreceptors showed transient labelling. Many cells in the ganglion cell layer are immunoreactive for both glycine and glyt-1 at postnatal day (Pd) 1 but both are minimal by Pd5. Transient immunoreactivity for both glyt-1 and glycine was observed in presumptive horizontal cells between Pd5 and Pd10. At Pd1 many cells in the outer part of the retina which resembled immature photoreceptors were heavily labelled for glycine, but did not express glyt-1 these disappeared at older ages. These findings suggest diverse mechanisms and transient roles for glycine in the developing rat retina. In the adult rat retina, a subpopulation of amacrine cells are prominently immunoreactive for both glycine and glyt-1. These cells labelled for glycine at Pd1, but did not express significant levels of glyt-1 until Pd5. Processes from these amacrine cells did not reach the inner half of the inner plexiform layer until Pd10-14. Bipolar cells became glycine-IR between Pd10 and Pd14, but consistently lacked any glyt-1 immunoreactivity. This temporal pattern of labelling strongly indicates that bipolar cells label for glycine when gap junctions become functional between glycine/glyt-1 immunoreactive amacrine cells and cone bipolar cells.

Amino Acid Transport Systems, Neutral↗

PubMed1992

Responses of Visual-Tracking Neurons from Cortical Area MST-I to Visual, Eye and Head Motion.

Thirty-one neurons which exhibited ocular pursuit-related activity [visual-tracking (VT) neurons] were found clustered within area MST-I (the lateral part of area MST) of two rhesus monkeys. Their responses were studied to determine whether this activity was correlated only with pursuit eye movement or with head movement as well. The latter hypothesis appeared to be preferable since visual, eye movement and head movement inputs were found to be mapped in register onto most of these cells. First, in each cell tested (n=19) the pursuit response persisted even in the absence of retinal image motion, offering clear evidence for non-visual input. Second, 22 of the 31 cells were directionally responsive to moving visual stimuli and in 20 of these the preferred directions for the visual motion and pursuit responses agreed closely. Responses were also obtained from many of the same cells during suppression of both the horizontal and the vertical vestibulo-ocular reflex (VOR). In each case, where directional visual, pursuit and VOR suppression responses were each obtained, vector addition of responses during suppression of the horizontal and vertical VOR resulted in an estimated preferred direction for head rotation which was closely aligned with the preferred direction previously obtained for eye motion or visual motion. In addition, the preferred direction of head movement was conserved even when the VOR was elicited by passive head rotation in complete darkness, although the responses in this instance were, on average, only 62% of those obtained during VOR suppression. Our interpretation is that, at present, MST-I VT neurons are best described as encoding the direction of target motion in space-centred coordinates by integrating inputs reflecting retinal image motion plus eye and head movement.

Journal Article↗

PubMed1994

The structure and development of dopaminergic interplexiform cells in the retina of the brown trout, Salmo trutta fario: a tyrosine hydroxylase immunocytochemical study.

The organisation and development of the dopaminergic (DA) system in the retina of the adult brown trout were studied with tyrosine hydroxylase immunocytochemical techniques. Adult DA cells are rather homogeneous in appearance and possess thick dendritic processes running to the ganglion cell layer and thinner axonal processes which run to the horizontal cell layer, where they form a rich plexus of varicose fibres closely associated with the surface of these cells. Contact of DA fibres with photoreceptor processes was not observed. We therefore consider this DA population to consist mainly of interplexiform cells. These cells appear late in development, being first observed in prehatching (16 mm) embryos (after photoreceptors have begun to differentiate). DA cells increased in number throughout the fry and juvenile stages, but even in the largest juveniles studied (30-35 mm) the size of the DA cell population was only about 20% of that in adults. DA cells appear to arise in the marginal retina. In developing stages (embryos and fry) only inner nuclear layer processes were observed, the horizontal cell layer DA plexus appearing late in development (28 mm juveniles).

Animals↗

PubMed1987

Horizontal cells contribute to the receptive field surround of ganglion cells in the rabbit retina.

The influence of horizontal cells on ganglion cells in the rabbit retina was examined by injecting current intracellularly into horizontal cells while simultaneously monitoring the extracellular spike activity of nearby single-unit ganglion cells. Hyperpolarizing current injected into horizontal cells decreased the firing rate of on-center brisk ganglion cells and increased the firing rate of off-center brisk ganglion cells. Depolarizing current produced opposite effects on on-center and off-center brisk ganglion cells. These findings are consistent with the view that horizontal cells in the rabbit contribute to the antagonistic surround excitation of brisk ganglion cells.

Action Potentials↗

PubMed1992

Biphasic retinal neurogenesis in the brush-tailed possum, Trichosurus vulpecula: further evidence for the mechanisms involved in formation of ganglion cell density gradients.

We investigated cell generation in the retina of the brush-tailed possum (Trichosurus vulpecula) by using tritiated (3H)-thymidine labelling of newly generated cells. Animals aged between postnatal day (P) 5 and 85 each received a single injection of 3H-thymidine. Following autoradiographic processing, maps of labelled cells were constructed from retinal sections. Retinal cell generation takes place in two phases, the first is concluding in the retinal periphery at P53 as the second is seen to commence in midtemporal retina. In the first phase, cells in central retina are generated earlier than those in peripheral regions. In the second phase, cells complete their final division in midtemporal retina first and in the periphery last. Cells generated in the first phase comprise virtually all cells in the ganglion cell layer, amacrine cells, horizontal cells, and cones. Ganglion cells are produced at a slightly earlier stage than displaced amacrine cells, horizontal cells, or cones. Amacrine cells in the inner nuclear layer are the final cells produced in the first phase. When ganglion cells and amacrine cells are pooled, their combined rate of production matches that of the other cell types. These data indicate that the ratio of displaced amacrine cells: horizontal cells: cones: combined ganglion cells and amacrine cells does not change throughout development. However, the ratio of ganglion cells:macrines changes steadily as development proceeds to favour amacrine cells. In the second phase, sparse numbers of nonganglion cells in the ganglion cell layer and large numbers of bipolar and Müller cells are produced along with all rods. The two phases in the possum are similar to those seen in the wallaby, the quokka. However, fewer cells are added in central retina in the possum than in the quokka and cell addition continues for a more extended period in the periphery in the possum. We suggest that this difference in cell addition could account for the development of a more pronounced visual streak of retinal ganglion cells in the possum than in the quokka. A comparison of possum retinal cell generation with that of other marsupials adds support for the "homochrony theory."

Aging↗

PubMedDate not supplied

Identification of retinal neurons in a regressive rodent eye (the naked mole-rat).

The retina consists of many parallel circuits designed to maximize the gathering of important information from the environment. Each of these circuits is comprised of a number of different cell types combined in modules that tile the retina. To a subterranean animal, vision is of relatively less importance. Knowledge of how circuits and their elements are altered in response to the subterranean environment is useful both in understanding processes of regressive evolution and in retinal processing itself. We examined common cell types in the retina of the naked mole-rat, Heterocephalus glaber with immunocytochemical markers and retrograde staining of ganglion cells from optic nerve injections. The stains used show that the naked mole-rat eye has retained multiple ganglion cell types, 1-2 types of horizontal cell, rod bipolar and multiple types of cone bipolar cells, and several types of common amacrine cells. However, no labeling was found with antibodies to the dopamine-synthesizing enzyme, tyrosine hydroxylase. Although most of the well-characterized mammalian cell types are present in the regressive mole-rat eye, their structural organization is considerably less regular than in more sighted mammals. We found less precision of depth of stratification in the inner plexiform layer and also less precision in their lateral coverage of the retina. The results suggest that image formation is not very important in these animals, but that circuits beyond those required for circadian entrainment remain in place.

Amacrine Cells↗

PubMedDate not supplied

Expression of glycine and the glycine transporter glyt-1 in the developing rat retina.

Previous studies show that glycine transporter-1 (glyt-1) is a consistent membrane marker of adult retinal neurons that are likely to release glycine at their synaptic terminals (Pow, 1998; Vaney et al., 1998; Pow & Hendrickson, 1999). The current study investigated when glyt-1 immunoreactivity appeared in the postnatal rat retina, and whether all glycine-containing neurons also labelled for glyt-1. Ganglion cells, horizontal cells, and photoreceptors showed transient labelling. Many cells in the ganglion cell layer are immunoreactive for both glycine and glyt-1 at postnatal day (Pd) 1 but both are minimal by Pd5. Transient immunoreactivity for both glyt-1 and glycine was observed in presumptive horizontal cells between Pd5 and Pd10. At Pd1 many cells in the outer part of the retina which resembled immature photoreceptors were heavily labelled for glycine, but did not express glyt-1; these disappeared at older ages. These findings suggest diverse mechanisms and transient roles for glycine in the developing rat retina. In the adult rat retina, a subpopulation of amacrine cells are prominently immunoreactive for both glycine and glyt-1. These cells labelled for glycine at Pd1, but did not express significant levels of glyt-1 until Pd5. Processes from these amacrine cells did not reach the inner half of the inner plexiform layer until Pd10-14. Bipolar cells became glycine-IR between Pd10 and Pd14, but consistently lacked any glyt-1 immunoreactivity. This temporal pattern of labelling strongly indicates that bipolar cells label for glycine when gap junctions become functional between glycine/glyt-1 immunoreactive amacrine cells and cone bipolar cells.

Amino Acid Transport Systems, Neutral↗

PubMed1989

Neural differentiation in the retina of the larval sea lamprey (Petromyzon marinus).

The peripheral retina of the sea lamprey develops in a 5-year-long process in which only certain neurons differentiate each year. The growth of cell layers, the differentiation of the neurons, and the morphology of their dendrites and axons were studied with normal, HRP, and Golgi preparations. Ganglion cells are differentiated in 3-year-old larvae, amacrine and horizontal cells in 4-year-old larvae, photoreceptor cells in stage I transformers, and bipolar cells in stage III transformers. Each new development is expressed as a radial gradient of differentiation. As a result of this protracted and stepped process, lamprey retinal neurons, particularly ganglion cells, differentiate in the absence of other cells to which they will ultimately be connected and may express their individual genetic programs more fully than in other vertebrate retinas. This could account for the unusual relationship of the ganglion cell, inner plexiform, and optic nerve layers and for the very high ratio of displaced to orthotopic ganglion cells.

Animals↗