Midget and parasol ganglion cells of the primate retina express the alpha1 subunit of the glycine receptor

Glycine is a major inhibitory neurotransmitter in the mammalian retina and has been shown to influence the responses of ganglion cells. Midget and parasol ganglion cells serve distinct physiological roles in the primate retina and show differences in their response characteristics to light stimuli. In the present study, we addressed the question of whether the expression of glycine receptors differs in midget and parasol ganglion cells. Ganglion cells in the retinae of marmoset and macaque monkeys were injected with Neurobiotin in a live in vitro retinal whole-mount preparation. Retinal pieces were then processed with an antibody against the alpha1 subunit of the glycine receptor. Strong punctate immunoreactivity indicative of synaptic localization is present in the ON and OFF sublamina of the inner plexiform layer. Many of the immunoreactive puncta coincide with the dendrites of both midget and parasol ganglion cells. Immunoreactive puncta are present on distal and proximal dendrites of ON and OFF cells. These results suggest that ON and OFF midget and parasol cells do not differ with respect to the distribution of the alpha1 subunit of the glycine receptor.     

A coupled network for parasol but not midget ganglion cells in the primate retina.

Intracellular injections of Neurobiotin were used to determine whether the major ganglion cell classes of the macaque monkey retina, the magnocellular-projecting parasol, and the parvocellular-projecting midget cells showed evidence of cellular coupling similar to that recently described for cat retinal ganglion cells. Ganglion cells were labeled with the fluorescent dye acridine orange in an in vitro, isolated retina preparation and were selectively targeted for intracellular injection under direct microscopic control. The macaque midget cells, like the beta cells of the cat's retina, showed no evidence of tracer coupling when injected with Neurobiotin. By contrast, Neurobiotin-filled parasol cells, like cat alpha cells, showed a distinct pattern of tracer coupling to each other (homotypic coupling) and to amacrine cells (heterotypic coupling). In instances of homotypic coupling, the injected parasol cell was surrounded by a regular array of 3-6 neighboring parasol cells. The somata and proximal dendrites of these tracer-coupled cells were lightly labeled and appeared to costratify with the injected cell. Analysis of the nearest-neighbor distances for the parasol cell clusters showed that dendritic-field overlap remained constant as dendritic-field size increased from 100-400 microns in diameter. At least two amacrine cell types showed tracer coupling to parasol cells. One amacrine type had a small soma and thin, sparsely branching dendrites that extended for 1-2 mm in the inner plexiform layer. A second amacrine type had a relatively large soma, thick main dendrites, and distinct, axon-like processes that extended for at least 2-3 mm in the inner plexiform layer. The main dendrites of the large amacrine cells were closely apposed to the dendrites of parasol cells and may be the site of Neurobiotin transfer between the two cell types. We suggest that the tracer coupling between neighboring parasol cells takes place indirectly via the dendrites of the large amacrine cells and provides a mechanism, absent in midget cells, for increasing parasol cell receptive-field size and luminance contrast sensitivity.     

Structure-function relations of parasol cells in the normal and glaucomatous primate retina

PURPOSE: The purpose of this study was to examine the effect that chronic elevation of intraocular pressure has on the intrinsic and visual response properties of parasol cells in the primate retina. METHODS: A primate model of experimental glaucoma was combined with intracellular recording and staining techniques using an isolated retina preparation. Intrinsic electrical properties were examined by injection of depolarizing and hyperpolarizing currents. Visual responses were studied using drifting and counterphased gratings. Morphologic comparisons were made by injecting recorded cells with Neurobiotin and analyzing them quantitatively with a computer-based neuron reconstruction system. RESULTS: Structurally, parasol cells from glaucomatous eyes had smaller somata and smaller, less complex dendritic arbors, resulting in a significant reduction in total dendrite length and surface area. Functionally, these neurons did not differ from normal in their mean resting membrane potentials, input resistances, or thresholds to electrical activation, but did differ in membrane time constants and spike duration. Parasol cells from both normal and glaucomatous eyes preferred low-spatial-frequency stimuli, but significantly fewer glaucoma-related cells were driven visually-in particular, by patterned stimuli. Glaucomatous cells also did not respond as well to visual stimuli presented at increased temporal frequencies. CONCLUSIONS: Ganglion cells in the glaucomatous eye retain most of their normal intrinsic electrical properties, but are less responsive, both spatially and temporally, to visual stimuli. The reduction in visual responsiveness most likely results from significant changes in dendritic architecture, which affects their level of innervation by more distal retinal neurons.     

Development of glutamatergic synapses in the rat retina: the postnatal expression of ionotropic glutamate receptor subunits

We examined the distribution of the AMPA glutamate receptor subunits GluR1 to GluR4, of the kainate receptor subunits GluR6/7 and KA2, and of the glutamate receptor subunits delta1/2, during postnatal development of the rat retina by immunocytochemistry and light microscopy using receptor subunit specific antisera. The various ionotropic glutamate receptor subunits were expressed early in postnatal rat retina, and most of the subunits, with the exception of delta1/2. were found in both synaptic layers of rat retina. The glutamate receptor subunits studied showed differences in their time of appearance, their spatial distribution patterns, and in their expression levels in the developing rat retina. Interestingly, most of the AMPA receptor subunits were expressed earlier than the kainate receptor subunits in the two synaptic layers of the retina, indicating that AMPA glutamate receptors play an important role in early postnatal glutamatergic synaptic transmission. We also studied the ultrastructural localization of the AMPA glutamate receptor subunits GluR1 to GluR4 by immunocytochemistry and electron microscopy in the inner plexiform layer of the mature rat retina. Most of the subunits were found postsynaptic to the ribbon synapses of OFF-cone, ON-cone, and rod bipolar cells. The results of this study suggest an involvement of ionotropic glutamate receptors in processes of synaptic maturation and the formation of synaptic circuitries in the developing plexiform layers of the retina. Furthermore, AMPA and kainate receptors play a role in synaptic processing and in the development of both the scotopic and photopic pathways in the rat retina.     

Mosaic properties of midget and parasol ganglion cells in the marmoset retina

We measured mosaic properties of midget and parasol ganglion cells in the retina of a New World monkey, the common marmoset Callithrix jacchus . We addressed the functional specialization of these populations for color and spatial vision, by comparing the mosaic of ganglion cells in dichromatic ("red-green color blind") and trichromatic marmosets. Ganglion cells were labelled by photolytic amplification of retrograde marker ("photofilling") following injections into the lateral geniculate nucleus, or by intracellular injection in an in vitro retinal preparation. The dendritic-field size, shape, and overlap of neighboring cells were measured. We show that in marmosets, both midget and parasol cells exhibit a radial bias, so that the long axis of the dendritic field points towards the fovea. The radial bias is similar for parasol cells and midget cells, despite the fact that midget cell dendritic fields are more elongated than are those of parasol cells. The dendritic fields of midget ganglion cells from the same (ON or OFF) response-type array show very little overlap, consistent with the low coverage of the midget mosaic in humans. No large differences in radial bias, or overlap, were seen on comparing retinae from dichromatic and trichromatic animals. These data suggest that radial bias in ganglion cell populations is a consistent feature of the primate retina. Furthermore, they suggest that the mosaic properties of the midget cell population are associated with high spatial resolution rather than being specifically associated with trichromatic color vision.     

Distribution of bipolar input to midget and parasol ganglion cells in marmoset retina

Different types of retinal ganglion cell show differences in their response properties. Here we investigated the question of whether these differences are related to the distribution of the synaptic input to the dendritic tree. We measured the distribution and density of synaptic input to the dendrites of midget and parasol ganglion cells in the retina of a New World monkey, the marmoset, Callithrix jacchus. Ganglion cells were retrogradely labeled by dye injection into parvocellular or magnocellular regions of the lateral geniculate nucleus and subsequently photo-filled. Presumed bipolar cell synapses were identified immunocytochemically using antibodies against the ribbon protein CtBP2 or the GluR4 subunit of the AMPA receptor. For all cells, colocalized immunoreactive puncta were distributed across the entire dendritic tree. The density of the presumed bipolar input to midget ganglion cells was comparable for both synaptic markers, suggesting that the AMPA receptor GluR4 subunit is expressed at all synapses between midget bipolar and midget ganglion cells. Midget ganglion cells had an average of nine colocalized immunoreactive puncta per 100 microm2 dendritic surface, and parasol cells had an average of seven colocalized immunoreactive puncta per 100 microm2 dendritic surface. The densities were comparable in different regions of the dendritic tree and were not influenced by the location of the cells with respect to the fovea. Our findings suggest that the differences in the response characteristics of midget and parasol cells are not due to differences in the density of synaptic input to their dendritic tree.     

Orientation sensitivity of ganglion cells in primate retina

The two-dimensional shape of the receptive field center of macaque retinal ganglion cells was determined by measuring responses to drifting sinusoidal gratings of different spatial frequency and orientation. The responses of most cells to high spatial frequencies depended on grating orientation, indicating that their centers were not circularly symmetric. In general, center shape was well described by an ellipse. The major axis of the ellipse tended to point towards the fovea or perpendicular to this. Parvocellular pathway cells had greater center ellipticity than magnocellular pathway cells; the median ratio of the major-to-minor axis was 1.72 and 1.38, respectively. Parvocellular pathway cells also had centers that were often bimodal in shape, suggesting that they received patchy cone/bipolar cell input. We conclude that most ganglion cells in primate retina have elongated receptive field centers and thus show orientation sensitivity.     

Localization of ionotropic glutamate receptors to invaginating dendrites at the cone synapse in primate retina

The separation of OFF pathways that signal light decrements from ON pathways that signal light increments occurs at the first retinal synapse. The dendrites of OFF bipolar cells abut the cone pedicle at basal positions distal to the site of glutamate release and express ligand-gated or ionotropic glutamate receptors (GluR). The dendrites of ON bipolar cells penetrate narrow invaginations of the cone pedicle proximal to the site of release and express the G-protein-coupled, metabotropic glutamate receptor, mGluR6. However, recent studies demonstrating the expression of GluR subunits in the rodent rod bipolar cell, known to yield an ON response to light, call this basic segregation of receptors into question. The light-microscopic distribution of many glutamate receptors in the primate retina is now well established. We reexamined their ultrastructural localization in the outer retina of Macaca fascicularis to test systematically whether invaginating dendrites at the cone synapse, presumably from ON bipolar cells, also express one or more ionotropic subunits. Using preembedding immunocytochemistry for electron microscopy, we quantified the distribution of the AMPA-sensitive subunits GluR2/3 and GluR4 and of the kainate-sensitive subunits GluR6/7 across 207 labeled dendrites occupying specific morphological loci at the cone pedicle. We report, in agreement with published investigations, that the majority of labeled processes for GluR2/3 (70%) and GluR4 (67%) either occupy basal positions or arise from horizontal cells. For GluR6/7, we find a significantly lower fraction of labeled processes at these positions (47%). We also find a considerable number of labeled dendrites for GluR2/3 (10%), GluR4 (21%), and GluR6/7 (18%) at invaginating positions. Surprisingly, for each subunit, the remainder of labeled processes corresponds to "fingers" of presynaptic cytoplasm within the cone invagination.     

Amacrine and bipolar inputs to midget and parasol ganglion cells in marmoset retina

Retinal ganglion cells receive excitatory synapses from bipolar cells and inhibitory synapses from amacrine cells. Previous studies in primate suggest that the strength of inhibitory amacrine input is greater to cells in peripheral retina than to foveal (central) cells. A comprehensive study of a large number of ganglion cells at different eccentricities, however, is still lacking. Here, we compared the amacrine and bipolar input to midget and parasol ganglion cells in central and peripheral retina of marmosets (Callithrix jacchus). Ganglion cells were labeled by retrograde filling from the lateral geniculate nucleus or by intracellular injection. Presumed amacrine input was identified with antibodies against gephyrin; presumed bipolar input was identified with antibodies against the GluR4 subunit of the AMPA receptor. In vertical sections, about 40% of gephyrin immunoreactive (IR) puncta were colocalized with GABAA receptor subunits, whereas immunoreactivity for gephyrin and GluR4 was found at distinct sets of puncta. The density of gephyrin IR puncta associated with ganglion cell dendrites was comparable for midget and parasol cells at all eccentricities studied (up to 2 mm or about 16 degrees of visual angle for midget cells and up to 10 mm or >80 degrees of visual angle for parasol cells). In central retina, the densities of gephyrin IR and GluR4 IR puncta associated with the dendrites of midget and parasol cells are comparable, but the average density of GluR4 IR puncta decreased slightly in peripheral parasol cells. These anatomical results indicate that the ratio of amacrine to bipolar input does not account for the distinct functional properties of parasol and midget cells or for functional differences between cells of the same type in central and peripheral retina.     

Elevated glucose changes the expression of ionotropic glutamate receptor subunits and impairs calcium homeostasis in retinal neural cells

PURPOSE: Altered glutamatergic neurotransmission and calcium homeostasis may contribute to retinal neural cell dysfunction and apoptosis in diabetic retinopathy (DR). The purpose of this study was to determine the effect of high glucose on the protein content of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and kainate glutamate receptor subunits, particularly the GluR2 subunit, because it controls Ca2+ permeability of AMPA receptor-associated channels. The effect of high glucose on the concentration of cytosolic free calcium ([Ca2+]i) was also investigated. METHODS: The protein content of GluR1, GluR2, GluR6/7, and KA2 subunits was assessed by Western blot. Cobalt staining was used to identify cells containing calcium/cobalt-permeable AMPA receptors. The [Ca2+]i changes evoked by KCl or kainate were recorded by live-cell confocal microscopy in R28 cells and in primary cultures of rat retina, loaded with fluo-4. RESULTS: In primary cultures, high glucose significantly decreased the protein content of GluR1 and GluR6/7 subunits and increased the protein content of GluR2 and KA2 subunits. High glucose decreased the number of cobalt-positive cells, suggesting a decrease in calcium permeability through AMPA receptor-associated channels. In high-glucose-treated cells, changes in [Ca2+]i were greater than in control cells, and the recovery to basal levels was delayed. However, in the absence of Na+, to prevent the activation of voltage-sensitive calcium channels, the [Ca2+]i changes evoked by kainate in the presence of cyclothiazide, which inhibits AMPA receptor desensitization, were significantly lower in high-glucose-treated cells than in control cultures, further indicating that AMPA receptors were less permeable to calcium. Mannitol, used as an osmotic control, did not cause significant changes compared with the control. CONCLUSIONS: The results suggest that elevated glucose may alter glutamate neurotransmission and calcium homeostasis in the retina, which may have implications for the mechanisms of vision loss in DR.     

Bipolar input to melanopsin containing ganglion cells in primate retina

Two morphological types of melanopsin-expressing ganglion cells have been described in primate retina. Both types show intrinsic light responses as well as rod- and cone-driven ON-type responses. Outer stratifying cells have their dendrites close to the inner nuclear layer (OFF sublamina); inner stratifying cells have their dendrites close to the ganglion cell layer (ON sublamina). Both inner and outer stratifying cells receive synaptic input via ribbon synapses, but the bipolar cell types providing this input have not been identified. Here, we addressed the question whether the diffuse (ON) cone bipolar type DB6 and/or rod bipolar cells contact melanopsin-expressing ganglion cells. Melanopsin containing ganglion cells in marmoset (Callithrix jacchus) and macaque (Macaca fascicularis) retinas were identified immunohistochemically; DB6 cells were labeled with antibodies against the carbohydrate epitope CD15, rod bipolar cells were labeled with antibodies against protein kinase C, and putative synapses between the two cells types were identified with antibodies against piccolo. For one inner cell, nearly all of the DB6 axon terminals that overlap with its dendrites in the two-dimensional space show areas of close contact. In vertical sections, the large majority of the areas of close contact also contain a synaptic punctum, suggesting that DB6 cells contact inner melanopsin cells. The output from DB6 cells accounts for about 30% of synapses onto inner melanopsin cells. Synaptic contacts between rod bipolar axons and inner dendrites were not observed. In the OFF sublamina, about 10% of the DB6 axons are closely associated with dendrites of outer cells, and in about a third of these areas, axonal en passant synapses are detected. This result suggests that DB6 cells may also provide input to outer melanopsin cells.     

Size and distribution of ganglion cells in the bovine retina

In whole mounts of the bovine retina stained with cresylviolet, size and topographical distribution of ganglion cells were studied with the aid of a semiautomatic measuring device. At different locations within the streak and in the retinal periphery, ganglion cell sizes were measured. Each sample area was 0.05 mm² and contained 50–300 cells. In three retinae a total of 5813 ganglion cells were measured. Three size classes could be distinguished: small cells (<70μm²) medium sized cells (70–250 μm²), and large cells (>250 μm²). The medium sized cells were numerically predominant in the streak. The highest density of this cell class was found at the temporal end of the streak. The small cells, on the other hand, occurred predominantly in the periphery of the retina.     

Distribution of the alpha1 subunit of the GABA(A) receptor on midget and parasol ganglion cells in the retina of the common marmoset Callithrix jacchus

The inhibitory neurotransmitter gamma aminobutyric acid (GABA) has been shown to influence the responses of ganglion cells in the mammalian retina. Consistently, GABA(A) receptor subunits have been localized to different ganglion cell types. In this study, the distribution of the alpha1 subunit of the GABA(A) receptor on the dendrites of midget and parasol ganglion cells was investigated quantitatively in the retina of a New World monkey, the marmoset. Ganglion cells were injected with Neurobiotin in a live in vitro retinal whole-mount preparation. Retinal pieces were then processed with an antibody against the alpha1 subunit of the GABA(A) receptor. Strong punctate immunoreactivity indicative of synaptic localization is present in the ON and OFF sublamina of the inner plexiform layer. Many of the immunoreactive puncta coincide with the dendrites of both midget and parasol ganglion cells. Immunoreactive puncta are present on distal and proximal dendrites of ON and OFF cells of both ganglion cell types. On average, parasol cells show a slight increase in the spatial density of immunoreactive puncta with distance from the soma, whereas the density of immunoreactive puncta on midget cells stays even. Parasol ganglion cells show a slightly higher average density of immunoreactive puncta (0.083 puncta/microm dendrite) than midget cells (0.054 puncta/microm dendrite).     

Localization of AMPA-selective glutamate receptor subunits in the cat retina: a light- and electron-microscopic study

The distribution of AMPA-selective glutamate receptor subunits was studied in the cat retina using antisera against GluR1 and GluR2/3. Both antisera were localized in postsynaptic sites in the outer plexiform layer (OPL) as well as the inner plexiform layer (IPL). Immunoreactivity for GluR1 was seen in a subpopulation of OFF cone bipolar cells and a number of amacrine and ganglion cells. Within the IPL, processes staining for GluR1 received input from OFF and ON cone bipolar cells but not from rod bipolars. Labeling for GluR2/3 was seen in horizontal cells, an occasional cone bipolar cell, and numerous amacrine and ganglion cells. In the IPL, GluR2/3 staining was postsynaptic to cone bipolar cells in both sublaminae. AII amacrine cells which receive rod bipolar input were also labeled for GluR2/3. With both antisera, staining was limited to a single member of the bipolar dyad complex, providing morphological evidence for functional diversity in glutamatergic pathways.     

Combination of rod and cone inputs in parasol ganglion cells of the magnocellular pathway

This study investigates how rod and cone inputs are combined in the magnocellular (MC) pathway in the mesopic luminance range, when both rods and cones are active. Responses of parafoveal MC ganglion cells from macaque retina were measured as a function of temporal frequency (0.62-20 Hz) or contrast (0.05-0.55) at mesopic light levels (0.2, 2, 20, and 200 td). Stimuli were of three modulation types: (1) isolated rod stimuli (only rod signals were modulated), (2) isolated cone stimuli (only cone luminance signals from long- and middle-wavelength sensitive cones were modulated), and (3) combined rod and cone stimuli (both rod and cone luminance signals were modulated in phase, as with conventional stimuli). The results showed that under mesopic conditions, the relative rod and cone inputs to the MC cells varied with light level and they are combined linearly prior to saturation. Further, rod contrast gain is relatively stable over the mesopic range while cone contrast gain increased with light level. Finally, the measured rod and cone inputs are consistent with the measured human temporal contrast sensitivity functions under comparable stimulation conditions.     

The morphological characterization and distribution of displaced ganglion cells in the anuran retina

The number, dendritic morphology, and retinal distribution of displaced ganglion cells were studied in two anuran species, Xenopus laevis and Bufo marinus. Horseradish peroxidase or cobaltic lysine complex was applied to the cut end of the optic nerve, and the size, shape, and retinal position of retrogradely filled ganglion cells displaced into the inner nuclear layer were determined in retinal wholemount and sectioned material. Approximately 1% of ganglion cells in Xenopus and 0.1% in Bufo were found to be displaced. In both species, many of the previously described orthotopic ganglion cell types (Straznicky & Straznicky, 1988; Straznicky et al., 1990) were present among displaced ganglion cells. In Xenopus more displaced ganglion cells were found in the retinal periphery than in the retinal center, and they formed 3 or 4 distinct bands around the optic nerve head. In Bufo the incidence of displaced ganglion cells was higher along the visual streak than in the dorsal and ventral peripheral retina. These results indicate that the distribution of displaced ganglion cells approximates the retinal distribution of orthotopic ganglion cells. One of the likely mechanisms to account for this developmental paradox may be that the formation of the inner plexiform layer, adjacent to the ciliary margin, acts as a mechanical barrier by preventing the entry of some of the late developing ganglion cells into the ganglion cell layer.     

负透镜诱导型近视豚鼠视网膜中谷氨酸及其受体的表达

目的　观察谷氨酸及其离子型受体Ｎ-甲基-Ｄ-天冬氨酸受体（Ｎ-ｍｅｔｈｙｌ-Ｄ-ａｓｐａｒｔａｔｅｒｅｃｅｐｔｏｒ,ＮＭＤＡＲ）功能亚单位ＮＲ２Ａ在近视豚鼠视网膜上的动态表达,探讨其在近视发病过程中的作用。方法　选取３周龄健康三色短毛豚鼠１２０只,采用随机数字表法分为０周正常组、２周正常组、２周近视组、４周正常组、４周近视组,每组２４只;正常组不作任何干预,近视组右眼均戴－１０Ｄ透镜,左眼不戴镜作为对照。入组前与处死前均进行屈光度及眼轴长度检测,腹腔注射过量水合氯醛处死,并分离视网膜,采用高效液相色谱分析检测视网膜中谷氨酸的含量变化,实时荧光定量ＰＣＲ以及ＥＬＩＳＡ分别检测豚鼠视网膜中ＮＲ２ＡｍＲＮＡ及其蛋白水平的表达变化。结果　造模前各组屈光度及眼轴长度差异均无统计学意义（均为Ｐ＞０．０５）。造模后各组与造模前比较,眼轴长度及屈光度差异均有统计学意义（２周正常组Ｐ＜０．０５,２周近视组Ｐ＜０．００５,４周正常组Ｐ＜０．０１,４周近视组Ｐ＜０．００１）。造模后,正常组间眼轴长度和屈光度比较差异均有统计学意义（Ｆ＝２０．３２,Ｐ＜０．０１;Ｆ＝１９９．６５,Ｐ＜０．０１）;２周近视组与４周近视组比较,右眼眼轴长度和屈光度差异均有统计学意义（Ｆ＝７８．９６,Ｐ＜０．００１;Ｆ＝２５２．１０,Ｐ＜０．００１）,左眼眼轴长度和屈光度差异均无统计学意义（Ｆ＝１３．６６,Ｐ＞０．０５;Ｆ＝２１．２０,Ｐ＞０．０５）;２周近视组与４周近视组右眼分别与相应的左眼比较,眼轴长度差异均有统计学意义（２周近视组:ｔ＝９．５１５,Ｐ＜０．００５;４周近视组:ｔ＝９．４４９,Ｐ＜０．００１）,屈光度差异同样均有统计学意义（２周近视组:ｔ＝８．８９７,Ｐ＜０．００１;４周近视组:ｔ＝１７．２３５,Ｐ＜０．００１）。视网膜中谷氨酸含量正常组之间差异均无统计学意义（均为Ｐ＞０．０５）;造模后２周近视组与４周近视组比较,右眼视网膜中谷氨酸含量逐渐增加,差异有统计学意义（ｔ＝３６．２３０,Ｐ＜０．０１）。造模后２周近视组较２周正常组右眼谷氨酸含量增加,差异有统计学意义（ｔ＝－２３．２４０,Ｐ＜０．０５）;同样４周近视组较４周正常组右眼谷氨酸含量亦增加,差异亦有统计学意义（ｔ＝－５３．６９０,Ｐ＜０．０１）。视网膜中ＮＲ２ＡｍＲＮＡ的表达量,正常组之间差异均无统计学意义（均为Ｐ＞０．０５）。造模后４周近视组与２周近视组比较,右眼视网膜ＮＲ２ＡｍＲＮＡ表达量明显上调,差异有统计学意义（ｔ＝５５．６６０,Ｐ＜０．００１）;２周近视组与２周正常组右眼比较表达量增加,差异有统计学意义（ｔ＝－１５．０８６,Ｐ＜０．００５）,同样４周近视组与４周正常组右眼比较差异亦有统计学意义（ｔ＝－４３．２７６,Ｐ＜０．００１）。正常组之间视网膜中ＮＲ２Ａ蛋白表达量,差异无统计学意义（均为Ｐ＞０．０５）。４周近视组与２周近视组比较,右眼视网膜ＮＲ２Ａ蛋白表达量明显上调,差异有统计学意义（ｔ＝４３．２１０,Ｐ＜０．００５）;２周近视组与２周正常组右眼比较ＮＲ２Ａ蛋白表达量增加,差异有统计学意义（ｔ＝－２．３６５,Ｐ＜０．０５）,同样４周近视组与４周正常组右眼比较差异亦有统计学意义（ｔ＝－５．５１８,Ｐ＜０．０１）。结论负透镜诱导型近视豚鼠视网膜中谷氨酸及其ＮＭＤＡＲ受体亚单位ＮＲ２Ａ在透镜诱导眼中表达上调,并随透镜诱导时间的延长和近视程度的加深而增加。     

AMPA-selective glutamate receptor subunits GluR2 and GluR4 in the cat retina: an immunocytochemical study

AMPA-selective glutamate receptors play a major role in glutamatergic neurotransmission in the retina and are expressed in a variety of neuronal subpopulations. In the present study, immunocytochemical techniques were used to visualize the distribution of GluR2 and GluR4 subunits in the cat retina. Results were compared with previous localizations of GluR1 and GluR2/3. Staining for GluR2 was limited to a small number of amacrine and ganglion cells whereas GluR4 staining was present in A-type horizontal cells, many amacrine cells including type AII amacrine cells, and the majority of the cells in the ganglion cell layer. Analysis of synaptic relationships in the outer plexiform layer showed the GluR4 subunit to be concentrated at the contacts of cone photoreceptors with A-horizontal cells. In the inner plexiform layer, both GluR2 and GluR4 were postsynaptic to cone bipolar cells at dyad contacts although GluR2 staining was limited to one of the postsynaptic elements whereas GluR4 immunoreactivity was often seen in both postsynaptic elements. Unlike GluR2, GluR4 was also postsynaptic to rod bipolar cells where it could be visualized in processes of AII amacrine cells. The data indicate that GluR3 and GluR4 subunits are colocalized in a number of cell types including A-type horizontal cells, AII amacrine cells, and alpha ganglion cells, but whether they are combined in the same multimeric receptors remains to be determined.     

Synaptic input to an ON parasol ganglion cell in the macaque retina: a serial section analysis

A labeled ON parasol ganglion cell from a macaque retina was analyzed in serial, ultrathin sections. It received 13% of its input from diffuse bipolar cells. These directed a large proportion of their output to amacrine cells but received a relatively small proportion of their amacrine cell input via feedback synapses. In these respects, they were similar to the DB3 bipolar cells that make synapses onto OFF parasol cells. Bipolar cell axons that contacted the ON parasol cell in stratum 4 of the inner plexiform layer always made synapses onto the dendrite, and therefore, the number of bipolar cell synapses onto these ganglion cells could be estimated reliably by light microscopy in the future. Amacrine cells provided the majority of inputs to the ON parasol cell. Only a few of the presynaptic amacrine cell processes received inputs from the same bipolar cells as the parasol cells, and most of the presynaptic amacrine cell processes did not receive any inputs at all within the series. These findings suggest that most of the inhibitory input to the ON parasol cell originates from other areas of the retina. Amacrine cells presynaptic to the parasol ganglion cell interacted very infrequently with other neurons in the circuit, and therefore, they would be expected to act independently, for the most part.