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PubMedDate not supplied

Regional topography of rod and immunocytochemically characterized "blue" and "green" cone photoreceptors in rabbit retina.

Evidence from several sources indicates that the photoreceptors of rabbit retina include rods, green cones and blue cones, and that blue-green color opponency occurs in select retinal ganglion cells. One of us (Famiglietti) has identified wide-field cone bipolar cells as probable blue-cone-selective bipolars, and type C horizontal cells as possibly connected to blue cones. We wished to extend the analysis of blue cone pathways in rabbit retina and to characterize the topographic distribution of blue and green cones. Two monoclonal antibodies raised against chicken visual pigments are reported to label medium- and long-wavelength cones (COS-1) and short-wavelength cones (OS-2) in all mammalian retinas studied thus far (Szél and colleagues). Using selective labeling with these two antibodies and a nonselective method in nasal and temporal halves of the same retinas, we have found that densities of photoreceptors vary systematically, depending upon the size of the eye and age of the animal. In 'standard' New Zealand rabbits of 2-3 kg (2-3 months old), rods reached a peak density of about 300,000/mm2 just dorsal to the visual streak, while cones exhibit peak density at mid-visual streak of about 18,000/mm2. Published measurements of visual acuity in rabbit are less than predicted by this calculation. The ratio of cones to rods is significantly higher in ventral retina, where the density of cones declines to a plateau of 10,000-12,000/mm2, when compared to dorsal retina, where cones are uniformly distributed at a density of about 7000/mm2. The density of OS-2 labeled (presumably "blue") cones is uniformly low, 1000-1500/mm2, in a wide expanse that includes dorsal retina, the visual streak, and much of ventral retina, except for a region of higher density along the vertical midline. We confirm that there is a far ventral horizontal region near the perimeter that is populated exclusively by a high density (about 13,000/mm2) of OS-2-positive cones (Juliusson and colleagues). This region does not extend to the ventral retinal margin, however, where cone density drops precipitously. Transitional zones between COS-1 and OS-2 labeling, in a region of relatively high and uniform cone density, where sums of COS-1 and OS-2 labeling are higher than expected and in which weakly and strongly labeled cones are intermixed, raise questions about the identities of the visual pigment epitopes, the possibility of double labeling, and therefore the possibility of dual expression of pigments in single cones. The "inverted-T-shaped" topography of higher density OS-2 labeling raises doubts about the significance of a ventral concentration of blue cones for visual function in rabbit retina.

Aging↗
PubMed2001

A prospective evaluation of the Heidelberg retina flowmeter in diagnosing ischaemia following branch retinal vein occlusion: a masked, controlled comparison with fluorescein angiography.

PURPOSE: To evaluate the use of the Heidelberg retina flowmeter (HRF) in diagnosing retinal ischaemia following macular branch retinal vein occlusion. METHODS: Ten patients with ischaemic macular branch retinal vein occlusion, as determined by strict fluorescein angiographic criteria, were examined with the HRF. Blood flow, blood volume and blood velocity characteristics from areas of ischaemic and non-ischaemic retina were recorded and the results between the normal and ischaemic areas of retina compared with paired t-test analysis. Ten healthy volunteers were similarly examined and acted as a control group. RESULTS: Compared with normal retina the HRF recorded a statistically significant reduction in blood flow within the ischaemic retina in 7 of the 10 study patients. In 2 patients the HRF actually recorded a statistically significant increase in blood flow in the area of ischaemic retina; there was no significant difference in the blood flow recorded in the normal and ischaemic retina in the remaining patient. HRF examination of the control group revealed a significant difference in the blood flow between two areas of apparently normal retina in 3 of the 10 volunteers. CONCLUSION: The HRF is not a reliable tool for diagnosing retinal ischaemia following branch retinal vein occlusion. Our results may suggest that the HRF blood flow recordings are not derived from the retinal circulation alone, but represent the cumulative blood flow through the combined circulations of the retina and choriocapillaris.

Aged↗
PubMed2003

Retina-specific expression of 5A11/Basigin-2, a member of the immunoglobulin gene superfamily.

PURPOSE: 5A11/Basigin has recently been identified as a critical glycoprotein for full maturity and function of the mouse retina. However, the biological function of 5A11/Basigin has yet to be determined. Previous reports indicate the presence of multiple 5A11/Basigin polypeptides within the retina. Therefore, in an effort to determine the function of 5A11/Basigin, the molecular diversity of its expression was evaluated. METHODS: Northern blot and immunoblot techniques were used to evaluate the number of forms of 5A11/Basigin in the mouse retina. cDNA cloning, using a mouse retina library or RT-PCR from rat, chicken, zebrafish, and human retina, was performed to determine the sequence of 5A11/Basigin transcripts. A peptide was generated, based on the deduced amino acid sequence, for subsequent antibody production. Localization of 5A11/Basigin expression was evaluated by immunoblot, immunohistochemistry, and real-time RT-PCR. RESULTS: Two 5A11/Basigin transcripts of approximately 1.5 kb and approximately 1.8 kb, which correspond to glycosylated proteins of approximately 45 and approximately 55 kDa, respectively, were identified in mouse retina. The shorter form was previously cloned. However, the longer form, a splice variant of mouse 5A11/Basigin, is a member of the immunoglobulin gene superfamily and has been named 5A11/Basigin-2. Homologous transcripts were also cloned from rat, chicken, zebrafish, and human retina. 5A11/Basigin-2 expression was limited to the retina, specifically to photoreceptor cells, where it appeared to be most concentrated in the inner segments. CONCLUSIONS: The specific and limited expression of 5A11/Basigin-2 explicitly within photoreceptor cells implies that this glycoprotein plays a fundamental role within the retina. However, its role remains to be determined.

Amino Acid Sequence↗
PubMed2006

Why do mutations in the ubiquitously expressed housekeeping gene IMPDH1 cause retina-specific photoreceptor degeneration?

PURPOSE: The purpose of this study was to investigate retinal inosine monophosphate dehydrogenase 1 (IMPDH1) transcripts and proteins to gain an understanding of how mutations in IMPDH1 lead to retinal disease. Mutations in IMPDH1 cause the RP10 form of autosomal dominant retinitis pigmentosa (adRP) and are a rare cause of dominant Leber congenital amaurosis (LCA). IMPDH1 is a highly conserved, widely expressed housekeeping gene, the product of which catalyzes the rate-limiting step of de novo guanine synthesis. Despite its conservation and ubiquity, the clinical consequences of missense mutations in IMPDH1 are limited to the retina, and the disease mechanism is currently unknown. METHODS: A variety of methods were used to address the unique features of IMPDH1 in the retina, including Northern blot analysis, serial analysis of gene expression (SAGE), immunohistochemistry, transcript sequencing, and Western blot analysis. RESULTS: Results of the experiments showed that IMPDH1 levels are higher in the retina than in any other tissue tested. Specifically, IMPDH1 is found predominately in the inner segment and synaptic terminals of retinal photoreceptors. The predominant transcripts of IMPDH1 in human retina are the result of alternate splicing and alternate start sites of translation. They are significantly different from those in other tissues, and these variant transcripts encode distinct proteins. Further, the proportions of IMPDH1 transcripts and proteins in human retina are different from those in mouse retina. CONCLUSIONS: Identification of unique retinal isoforms supports the existence of a novel IMPDH1 function in the retina, one that is probably altered by disease-causing mutations. This alone, or coupled with the high levels of IMPDH1 in the retina, may explain the retina-specific phenotype associated with IMPDH1 mutations. Elucidating the functional properties of these unique, human retinal isoforms is crucial to understanding the pathophysiology of IMPDH1 mutations.

Amino Acid Sequence↗
PubMed2006

Effects of mercury intoxication on the response of horizontal cells of the retina of thraira fish (Hoplias malabaricus).

Methyl mercury (MeHg) is highly neurotoxic, affecting visual function in addition to other central nervous system functions. The effect of mercury intoxication on the amplitude of horizontal cell responses to light was studied in the retina of the fish Hoplias malabaricus. Intracellular responses were recorded from horizontal cells of fish previously intoxicated with MeHg by intraperitoneal injection (IP group) or by trophic exposure (T group). Only one retina per fish was used. The doses of MeHg chloride administered to the IP group were 0.01, 0.05, 0.1, 1.0, 2.0, and 6.0 mg/kg. The amplitudes of the horizontal cell responses were lower than control in individuals exposed to 0.01 (N = 4 retinas), 0.05 (N = 2 retinas) and 0.1 mg/kg (N = 1 retina), whereas no responses were recorded in the 1.0, 2.0, and 6.0 mg/kg groups. T group individuals were fed young specimens of Astyanax sp previously injected with MeHg corresponding to 0.75 (N = 1 retina), 0.075 (N = 8 retinas) or 0.0075 (N = 4 retinas) mg/kg fish body weight. After 14 doses, one every 5 days, the amplitude of the horizontal cell response was higher than control in individuals exposed to 0.075 and 0.0075 mg/kg, and lower in individuals exposed to 0.75 mg/kg. We conclude that intoxication with MeHg affects the electrophysiological response of the horizontal cells in the retina, either reducing or increasing its amplitude compared to control, and that these effects are related to the dose and/or to the mode of administration.

Animals↗
PubMed1999

Light treatment enhances photoreceptor survival in dystrophic retinas of Royal College of Surgeons rats.

PURPOSE: To determine whether treatment with bright light elicits a protective response that enhances photoreceptor survival in Royal College of Surgeons (RCS) rats with inherited retinal degeneration. METHODS: RCS rats were illuminated for 10 to 12 hours with 130 foot-candles (fc) of white or green light. Untreated littermates that were kept under low cyclic light levels were used as control subjects. Photoreceptor survival was determined by quantitative analysis of photoreceptor nuclei and ultrastructural assessment of cellular organization. Basic fibroblast growth factor (bFGF) and ciliary neurotrophic factor (CNTF) gene expression were determined at the mRNA and protein levels. RESULTS: Treatments of RCS rats with a single dose of bright light on postnatal day 23 (P23) greatly enhanced photoreceptor survival. Ultrasturctural analysis revealed intact inner segments in light-treated retinas, whereas in untreated retinas only remnants of inner segments were observed. By P42, numerous viable nuclei were counted in the posterior retina of light-treated rats, whereas most of the remaining nuclei in untreated RCS rat retinas were highly pyknotic. At 2.5 days after treatment with a single dose of bright light, bFGF gene expression was significantly higher than in untreated RCS rat retinas. By P42, bFGF protein levels were still significantly higher in the treated retinas. CONCLUSIONS: Exogenous bFGF has been shown to promote photoreceptor survival in the RCS rat retina. Thus, the increased bFGF expression that was measured in the light-treated RCS rat retinas may be a protective response to light stress, which supports the observed rescue of photoreceptors in light-treated RCS rat retinas.

Animals↗
PubMed2004

Connexin 36 in photoreceptor cells: studies on transgenic rod-less and cone-less mouse retinas.

PURPOSE: Rod-cone gap junctions permit transmittal of rod visual information to the cone pathway. A recent report has shown that this transfer does not occur in mice in which the gap junction protein connexin 36 is knocked out indicating that rod-cone gap junctions are assembled from this protein. It remains unresolved, however, whether rods, cones or both express connexin 36. We have tried to address this question with the use of transgenic rod-less and cone-less mice. METHODS: Deletion of Nrl, a transcription factor, results in a complete loss of rods with a concomitant increase in S-cones. We used this as the rod-less (cone-only) model. Cone-less (rod-only) retinas were from mice expressing an attenuated diphtheria toxin gene under the control of a promoter selective for cones. Nearly all long wavelength cones and 95% of short wavelength cones are missing in this model. Fixed retinal sections from these two models and age matched controls were used to detect connexin 36 gap junctions by immunofluorescence. RESULTS: Punctate immunofluorescence, indicating the presence of gap junctions, was observed in the inner and outer plexiform layers of both wild type and cone-less and rod-less retinas. Our assumption was that immunofluorescence due to photoreceptor gap junctions would be observed in the outer plexiform layer. In all the animals, most of the immunofluorescence was in the inner plexiform layer, with only a marginal reaction in the outer plexiform layer. In cone-only (rod-less) retina, immunofluorescence in the outer plexiform layer increased by more than 20 fold compared to wild type. In rod-only (cone-less) retina, the outer plexiform layer showed about a 30% decrease in immunofluorescence. In both rod-less and cone-less retinas, immunofluorescence in the inner plexiform layer was higher than in the wild type by 25-50%. CONCLUSIONS: Cones constitute only about 3% of photoreceptors in the wild type retina while they make up 100% of the photoreceptors in cone-only retina. This increase in their numbers coincided with a 20 fold increase in immunofluorescence in the outer plexiform layer, strongly suggesting that cones express connexin 36. Conversely, when the cone numbers went down from 3% to near zero in cone-less retina, immunofluorescence decreased by about 30% in the outer plexiform layer, suggesting again that cones express the connexin and that they contribute to its presence disproportionately more than their numbers indicate. The results from both rod-less and cone-less animals are strongly indicative of cones expressing connexin 36, but are not sufficient to conclude whether rods express the protein. An unexpected observation from our experiments is that immunofluorescence increases slightly in the inner plexiform layer in both rod-less and cone-less retina for reasons that need further investigation.

Animals↗
PubMed1980

The localization of lectin binding sites on photoreceptor outer segments and pigment epithelium of dystrophic retinas.

Carbohydrate-containing macromolecules on pigment epithelium (PE) and photoreceptor outer segment (OS) membranes of 14 to 16-day-old Royal College of Surgeons (RCS) rats and their genetic control (RCS-rdy+) have been localized with peroxidase-conjugated lectins from wheat germ agglutinin (WGA), Ricinus communis (RCA), Lens culinaris (LCA), and concanavalin A (Con A). All lectins stain the plasma membranes of photoreceptor inner segments and intact OSs of normal (RCS-rdy+) and dystrophic (RCS) retinas. In the normal retinas, all lectins stain also the plasma membranes of shed OSs, and WGA stains some intradisc membranes. In contrast, WGA, RCA, and Con A do not label the OS debris membranes in dystrophic retinas, but LCA labels some of them. In both normal and dystophic retinas, WGA uniformly labels both proximal and distal membrane surfaces of PE mcirovilli, whereas RCA labels primarily the distal regions. Con A labels both normal and dystrophic PE microvilli sparsely, and LCA stains the PE microvilli in RCS-rdy+ retinas more intensely than those in the RCS retinas. The major differences between the lectin labeling in normal and dystrophic retinas are the presence of LCA staining on OS debris and the absence of any other lectin staining on these membranes. Other differences are the sparse LCA staining on dystrophic PE microvillous membranes vs. the normal and the presence of WGA staining on OS intradisc membranes of normal retinas. These differences may reflect changes in the accessibility or composition of certain cell surface sugars on OS membranes and PE microvilli which may be related to the diminished rate of phagocytosis in RCS retinas.

Agglutinins↗
PubMed1996

Expression of neurotrophins and trk receptors in the avian retina.

Using the RNase protection assay, we have found that nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) are expressed in the avian retina during development. The expression peaks around embryonic days 12-15, with decreasing levels at later stages of development. Abundant levels of NGF and BDNF but low levels of NT-3 mRNA were found in the adult retina. We also found that light/darkness regulated the levels of NGF and BDNF mRNAs but not the levels of NT-3 mRNA in the 5-day-old chicken retina. It was demonstrated that NGF and BDNF mRNA levels were up-regulated by light exposure. The cellular localization of mRNA expression for the neurotrophins and neurotrophin receptors TrkA, TrkB, and TrkC in the retina was studied using in situ hybridization. The patterns of NGF and trkA mRNA expression were very similar and were localized to the external part of the inner nuclear layer on the border with the outer plexiform layer and corresponded to the localization of horizontal cells. NT-3 labeling was also found over the external part of the inner nuclear layer, whereas trkC mRNA was found over all layers in the retina. BDNF labeling was found over all layers in the retina, whereas TrkB labeling was intense over cells in the ganglion cell layer, which is in agreement with the response of ganglion cells to BDNF stimulation. Functional neurotrophin receptors were suggested by the response of retinal explants to neurotrophin stimulation. These data indicate that the neurotrophins play local roles in the retina that involve interactions between specific neuronal populations, which were identified by the localization of the Trk receptor expression. The data also suggest that NGF and BDNF expression is regulated by normal neuron usage in the retina.

Animals↗
PubMed2002

Cellular localization of cyclooxygenase-1 and cyclooxygenase-2 in the normal mouse, rat, and human retina.

Prostaglandins, synthesized by cyclooxygenase (COX), regulate diverse neurophysiological actions such as regulation of autonomic responses, transmission of pain, generation of fever, control of sleep-wake cycle, synaptic signaling, and cross-talk between neurons and glia in the central nervous system. Although prostaglandins have been widely studied in the anterior segment tissues of the eye, relatively little is known about prostaglandins in the neural retina. By using immunohistochemistry, we have compared the cellular expression and localization of COX-1 and COX-2 in the normal mouse, rat, and human retina. In the normal mouse retina, COX-1 immunoreactivity is present in the outer segments of photoreceptor cells, horizontal cells, microglia, retinal ganglion cells, and displaced amacrine cells. In the normal rat retina, COX-1 immunoreactivity is present in microglia, retinal ganglion cells, and displaced amacrine cells. In the normal human retina, COX-1 immunoreactivity is present in microglia, astrocytes, retinal ganglion cells, and displaced amacrine cells. In the normal mouse and rat retina, COX-2 immunoreactivity is present in processes of the outer plexiform layer and in certain amacrine cells and retinal ganglion cells. In the normal human retina, COX-2 immunoreactivity is only present in processes of the outer plexiform layer. These results suggest that prostaglandins, synthesized by COX-1 or COX-2, may contribute to normal physiological and homeostatic functions in the retina.

Amacrine Cells↗
PubMed2003

Morphological analysis of disabled-1-immunoreactive amacrine cells in the guinea pig retina.

Disabled-1 (Dab1) is an adapter molecule in a signaling pathway, stimulated by reelin, that controls cell positioning in the developing brain. It localizes to selected neurons in the nervous system, including the retina, and Dab1-like immunoreactivity is present in AII amacrine cells in the mouse retina. This study was conducted to characterize Dab1-labeled cells in the guinea pig retina in detail using immunocytochemistry, quantitative analysis, and electron microscopy. Dab1 immunoreactivity is present in a class of amacrine cell bodies located in the inner nuclear layer adjacent to the inner plexiform layer (IPL). These cells give rise to processes that ramify the entire depth of the IPL. Double-labeling experiments demonstrated that these amacrine cells make contacts with the axon terminals of rod bipolar cells and that their processes make contacts with each other via connexin 36 in sublamina b of the IPL. In addition, all Dab1-labeled amacrine cells showed glycine transporter 1 immunoreactivity, indicating that they are glycinergic. The density of Dab1-labeled AII amacrine cells decreased from about 3,750 cells/mm(2) in the central retina to 1,725 cells/mm(2) in the peripheral retina. Dab1-labeled amacrine cells receive synaptic inputs from the axon terminals of rod bipolar cells in stratum 5 of the IPL. From these morphological features, Dab1-labeled cells of the guinea pig retina resemble the AII amacrine cells described in other mammalian species. Thus, the rod pathway of the guinea pig retina follows the general mammalian scheme and Dab1 antisera can be used to identify AII amacrine cells in the mammalian retina.

Amacrine Cells↗
PubMed1978

The number and distribution of ganglion cells in the cat's retina.

The number of ganglion cells in the cat's retina, and the pattern of their distribution over the retina, have been reinvestigated. Criteria are presented for the identification of ganglion cells in Nissl-stained whole mounts, most particularly for the distinction between small ganglion cells and neuroglial cells, by reference to retinas with no ganglion cells (obtained by nerve section) and to areas to retina containing a population of only small ganglion cells (obtained by optic tract section). Using these criteria, the number of ganglion cells was counted in four retinas (mean total 116,250). The number of large or "giant" cells (presumably the somas of Y-cells and of alpha-cells) varied from 4,200 to 7,100. Overall these cells comprised 4.0-6.3% of the total ganglion cell population. Their distribution over the retina showed a concentration around the area centralis, with a localized minimum density at the area centralis, and a concentration in the visual streak. These concentrations of large cells were quantitatively less than the concentrations of smaller cells in the area centralis and visual streak, so that the relative frequency of large cells was minimal (mean 1.6%) at the area centralis and increased steadily up to 5.5-6.9% in peripheral retina. Their relative frequency was distinctly lower along the visual streak than in peripheral retina above or below the streak.

Animals↗
PubMed1980

Postnatal development of GABA-ergic neurons in the rabbit retina.

Uptake, synthesis, storage, and release of gamma-aminobutyric acid (GABA) are some of the characteristic properties of GABA-ergic neurons. In the present study, we have used these properties as physiological probes to follow the emergence and maturation of GABA-ergic neurons during postnatal development of the rabbit retina. There is autoradiographic, immunocytochemical, and pharmacological evidence that some amacrine cells and certain neurons in the ganglion cell layer probably use GABA as the neurotransmitter. These neurons take up GABA, contain the GABA-synthesizing enzyme L-glutamic acid decarboxylase (GAD, EC 4.1.1.15), and release the accumulated GABA by a CA++-dependent mechanism when depolorized with high extracellular K+ concentration. In this study, we show that certain neurons in the newborn retina already possess a specific mechanism for GABA uptake. The positions and numbers of these cells in the developing retina suggest that they will become GABA-ergic neurons in the adult retina. These putative GABA-ergic neurons are, however, probably immature at birth because newborn retinas contain only low levels of GABA and GAD. Additionally, there is relatively little K+-stimulated, Ca++-dependent release of (3H)-GABA from the newborn retinas. GABA concentrations and GAD activities in developing retinas increase steadily postnatally, reaching about 80% of the adult levels by day 9. The activities of the GABA-degrading enzyme, GABA-glutamate transaminase (GABA-T, EC 2.6.1.19), follow a similar pattern of maturation during retinal development. K+ stimulated GABA release, however, remains low until about day 6, and then increases dramatically from 20% to 85% of the adult level over the next 3 days. Taken together, our results indicate that in the rabbit retina, the commitment by certain neurons to use GABA as the transmitter is made prenatally. These neurons are immature at birth but are biochemically, physiologically, and probably functionally mature by about 9 days after birth.

4-Aminobutyrate Transaminase↗
PubMed1980

Postnatal development of glycinergic neurons in the rabbit retina.

Certain neurons in the adult rabbit retina possess a high-affinity uptake mechanism for glycine and release it in response to elevated K+ concentrations in the medium. Although the evidence is not yet complete, these properties, together with pharmacological studies, suggest that the glycine-accumulating neurons may be a subpopulation of amacrine cells and may use glycine as a neurotransmitter. In the present study, we have used the uptake and K+-stimulated release of glycine as physiological probes to follow the emergence and maturation of putative glycinergic neurons during postnatal development of the rabbit retina. We show that certain neurons in the newborn retina already possess a specific high-affinity mechanism for glycine uptake. The positions and density of these cells in the developing retina suggest that they will become glycine-accumulating neurons of the adult retina. Thus, similar to our earlier study on the development of GABA-ergic neurons in this retina, the commitment by certain retinal neurons to be glycinergic, if indeed these cells use glycine as the transmitter, is made prenatally. These putative glycinergic neurons are, however, probably immature at birth, because they do not release the accumulated glycine in response to high K+ concentrations in the medium. In fact, there is practically no K+-stimulated release of preloaded glycine from the retina until about 7 days after birth, after which the release increases drastically to about 65% of the adult level on day 10 and 80% on day 12. Assuming that this release originates synaptically, our finding suggests that the putative glycinergic neurons may be functionally mature by 10-12 days after birth. Additionally, our results show that during development of the rabbit retina, the mechanism for high-affinity glycine uptake emerges and matures much earlier than the mechanism for K+-stimulated glycine release.

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↗
PubMed1985

Development of the human retina: patterns of cell distribution and redistribution in the ganglion cell layer.

Neurogenesis in the ventricular layer and the development of cell topography in the ganglion cell layer have been studied in whole-mounts of human fetal retinae. At the end of the embryonic period mitotic figures were seen over the entire outer surface of the retina. By about 14 weeks gestation mitosis had ceased in central retina and differentiation of photoreceptor nuclei was evident within a well-defined area which constituted about 2% of total retina area. This area was approximately centered on the site of the putative fovea, identified by the exclusive development of cone nuclei at that location. The area of retina in which mitosis had ceased increased as gestation progressed. By mid-gestation mitosis in the ventricular layer occupied about 77% of the outer surface of the retina and by about 30 weeks gestation mitosis in the ventricular layer had ceased. Cell density distributions in the ganglion cell layer were nonuniform at all stages studied (14-40 weeks). Densities were highest at about 17 weeks gestation, and by mid-gestation the adult pattern of cell topography was present with maps showing elevated cell densities in posterior retina and along the horizontal meridian. Cell densities generally declined throughout the remainder of the gestation period, except in the posterior retina, where densities in the perifoveal ganglion cell layer remained high during the second half of gestation. There is a rapid decline in cell density in the foveal ganglion cell layer toward the end of gestation, and it is suggested that the persistence of high densities in the perifoveal region may be related to migration of cells away from the developing fovea. The total population of cells in the ganglion cell layer was highest (2.2-2.5 million cells) between about weeks 18 and 30 of gestation. After this the cell population declined rapidly to 1.5-1.7 million cells. It is suggested that naturally occurring neuronal death is largely responsible for this decline.

Cell Count↗
PubMed1987

Serotonin and dopamine in the retina of a lizard.

The objective of this paper is to report the presence and localization of serotonin and dopamine in the retina of the lizard Uta stansburiana. High performance liquid chromatography and electrochemical detection were used to identify and quantitate the two amines. Both compounds are present as endogenous molecules in this retina and are found in concentrations similar to those reported in other non-mammalian retinas. The same methods were employed to confirm, in the isolated retina, the synthesis of serotonin from precursor, tryptophan. Immunocytochemical methods were used to localize, in the neural retina, serotonin and the rate-limiting enzyme of dopamine synthesis, tyrosine hydroxylase. Serotonin immunoreactivity was observed in bistratified amacrine cells (ca. 7 micron dia.) with processes ramifying in sublayers 1, 4, and 5 of the inner plexiform layer. Immunoreactivity to tyrosine hydroxylase was observed in a different population of bistratified amacrine cells (ca. 11 micron dia.) that had processes ramifying in sublayers 1 and 5 (and perhaps 3) of the inner plexiform layer. The enzymes for further metabolism of dopamine were not found in the retina of this lizard by immunocytochemical methods. The results of this research suggest that only single classes of serotoninergic and dopaminergic neurons are present in the retina of U. stansburiana. This retina might, therefore be an appropriate place in which to investigate the functioning of these amines in visual information processing.

Animals↗
PubMed1991

Vasoactive intestinal polypeptide-containing cells in the rabbit retina: immunohistochemical localization and quantitative analysis.

Vasoactive intestinal polypeptide (VIP) possesses neuroactive properties in the nervous system. In this study we characterized VIP immunoreactive neurons in the rabbit retina to provide a basis for a better understanding of the role of this peptide in retinal functions and to further define the morphology of wide-field amacrine cells. VIP immunoreactivity was demonstrated in colchicine-treated retinas. Immunolabeling was observed in amacrine cells located in the proximal inner nuclear layer and, occasionally, in the ganglion cell layer and inner plexiform layer (IPL). Varicose fibers were distributed in laminae 1, 3, and 5 of the IPL. The distribution of VIP immunoreactive cells showed a peak of approximately 50 cells/mm2 in the visual streak and minimum values of approximately 12 cells/mm2 in the peripheral retina. The total number of VIP immunopositive neurons was estimated to be about 11,000. Cell body diameters in the visual streak (8-9 microns) were slightly smaller than those measured in the dorsal or in the ventral retina (9-10 microns). The distribution of nearest neighbor distances (approximately 109 microns in the visual streak and approximately 99 microns in the peripheral retina) showed that VIP immunoreactive neurons were nonrandomly spaced. Labeled neurons emitted one to three thick primary processes, arborizing in secondary processes and collaterals rich in varicosities; these processes often crossed among different IPL laminae. Arborization fields of individual cells overlapped extensively. In the dorsal retina, estimated areas of single arborization fields were larger and processes had lower branching frequency than in the visual streak and in the ventral retina. On the whole, VIP immunoreactive amacrine cells gave rise to a loose meshwork of fibers in the IPL. These characteristics indicate VIP is contained in a class of wide-field amacrine cells and is likely to be involved in widespread regulatory or modulatory functions rather than in the direct transmission of visual information through the retina.

Animals↗