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Results for “Retinal Horizontal Cells”

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PubMed1999

The dopamine D2 receptor subfamily in rat retina: ultrastructural immunogold and in situ hybridization studies.

Dopamine, a major neurotransmitter in the vertebrate retina, is released from interplexiform cells and a restricted subset of amacrine cells. Dopamine effects vary between different retinal cell types, most likely due to differences in cell-specific receptor subtype expression. Identification of cells expressing receptors of the D2-subfamily (D2R, D3R, D4R) on a light microscopical level has rendered equivocal results, and no information is as yet available concerning the subcellular distribution of receptor protein. In the present study, D2R and D2/3R subtype-specific antisera, and D2R-, D3R- and D4R-specific oligonucleotide probes were used for ultrastructural and in situ hybridization analyses of the receptor subtype distribution in the rat retina. Light and electron microscopy showed that in addition to the known localization of intense D2R-immunoreactivity in all dopaminergic cells immunoreactive for tyrosine hydroxylase (TH), homogeneous, less intense D2R-immunoreactivity was also seen throughout the inner plexiform layer (IPL). Ultrastructurally, many additional amacrine cell processes devoid of TH-immunoreactivity at all levels of the inner plexiform layer were immunoreactive. D2R-immunoreactivity was found mainly on intracellular vesicles, and immunoreactivity associated with the plasma membrane was always extrasynaptic. No D2R-immunoreactivity was found in amacrine cell somata postsynaptic to the so-called dopaminergic 'ring endings'. Many D2R-mRNA reactive cells were observed throughout the inner nuclear layer. Morphologically, labelled cells resemble amacrines and bipolars but not horizontal cells. Reactivity with splice variant-specific oligonucleotide probes suggested that the D2LR variant is the predominant if not the only D2R isoform in the rat retina. D2R-mRNA reactivity was not observed in other retinal layers, in particular not in photoreceptor inner segments, which displayed D4R-mRNA reactivity. D3R-mRNA reactivity was not detected. The results indicate that D2-like responses are mediated through the D2R subtype, by an autoreceptor mechanism in dopaminergic cells, and by volume transmission in non-dopaminergic cells of the inner retina. D2-like responses in photoreceptors probably represent D4R activation.

Animals↗

PubMedDate not supplied

Alterations in NMDA receptor expression during retinal degeneration in the RCS rat.

To determine how a progressive loss of photoreceptor cells and the concomitant loss of glutamatergic input to second-order neurons can affect inner-retinal signaling, glutamate receptor expression was analyzed in the Royal College of Surgeons (RCS) rat, an animal model of retinitis pigmentosa. Immunohistochemistry was performed on retinal sections of RCS rats and congenic controls between postnatal (P) day 3 and the aged adult (up to P350) using specific antibodies against N-methyl-D-aspartate (NMDA) subunits. All NMDA subunits (NR1, NR2A-2D) were expressed in control and dystrophic retinas at all ages, and distinct patterns of labeling were found in horizontal cells, subpopulations of amacrine cells and ganglion cells, as well as in the outer and inner plexiform layer (IPL). NRI immunoreactivity in the inner plexiform layer of adult control retinas was concentrated in two distinct bands, indicating a synaptic localization of NMDA receptors in the OFF and ON signal pathways. In the RCS retina, these bands of NRI immunoreactivity in the IPL were much weaker in animals older than P40. In parallel, NR2B immunoreactivity in the outer plexiform layer (OPL) of RCS rats was always reduced compared to controls and vanished between P40 and P120. The most striking alteration observed in the degenerating retina, however, was a strong expression of NRI immunoreactivity in Müller cell processes in the inner retina which was not observed in control animals and which was present prior to any visible sign of photoreceptor degeneration. The results suggest functional changes in glutamatergic receptor signaling in the dystrophic retina and a possible involvement of Müller cells in early processes of this disease.

Aging↗

PubMed2002

Retinal topography of ganglion cells and putative UV-sensitive cones in two Antarctic fishes: Pagothenia borchgrevinki and Trematomus bernacchii (Nototheniidae).

Accessory corner cones (ACC) have recently been suggested to be UV-sensitive photoreceptor cells. With a view toward explaining prey detection, we examined the topography of retinal ganglion cells and ACCs in two Antarctic nototheniids occupying different ecological niches: the cryopelagic Pagothenia borchgrevinki and the benthic Trematomus bernacchii. Isodensity maps of retinal ganglion cells showed that the main visual axis, coincident with the feeding vector, was in a forward direction in both species. Visual acuity was determined as 3.64 and 4.77 cycles/degree for the respective species. In P. borchgrevinki the highest density of ACCs was associated with the eye's main visual axis. This suggested that this species uses UV-vision during forward-swims and probably in encounters with prey. On the other hand, T. bernacchii possessed two horizontal band-shaped high-density areas of ACCs, which stretched from temporal to nasal and ventral to peripheral retinal regions. Therefore, this species appears to use UV-vision to watch prey across the entire circumference of the lateral area and in the water column above its head.

Animals↗

PubMed1985

[Local nonuniformities in the syncytium of the horizontal cells of the retina in the turtle].

Electrical coupling between horizontal cells of the turtle retina was investigated by means of two microelectrodes (current and recording ones) penetrating neighbouring cells at a fixed distance from each other. The morphological coupling was revealed by means of fluorescent dye Lucifer Yellow. The electrical coupling was confirmed between elements of similar type (L1--axonal terminals, or L2--cell bodies, or R/G type cells) and no coupling was found between elements of different types, though L1 and L2 are directly connected through thin axons. In the L1 syncytium the electrical coupling at small (less than or equal to 50 microns) but fixed distances between microelectrodes could differ several times depending on the minimal displacement of microelectrodes. This local nonuniformity of coupling can be explained on the basis of structural nonuniformities in the L1 (axon terminal) network. It is unlikely however that the structural nonuniformities can influence the functional properties of horizontal cell network when the retina is stimulated adequately (by light).

Animals↗

PubMed2002

Cell-specific expression of plasma membrane calcium ATPase isoforms in retinal neurons.

Ca(2+) extrusion by high-affinity plasma membrane calcium ATPases (PMCAs) is a principal mechanism for the clearance of Ca(2+) from the cytosol. The PMCA family consists of four isoforms (PMCA1-4). Little is known about the selective expression of these isoforms in brain tissues or about the physiological function conferred upon neurons by any given isoform. We investigated the cellular and subcellular distribution of PMCA isoforms in a mammalian retina. Mouse photoreceptors, cone bipolar cells and horizontal cells, which respond to light with a graded polarization, express isoform 1 (PMCA1) of the PMCA family. PMCA2 is localized to rod bipolar cells, horizontal cells, amacrine cells, and ganglion cells, and PMCA3 is predominantly expressed in spiking neurons, including both amacrine and ganglion cells but is also found in horizontal cells. PMCA4 was found to be selectively expressed in both synaptic layers. Optical measurements of Ca(2+) clearance showed that PMCAs mediate Ca(2+) extrusion in both rod and cone bipolar cells. In addition, we found that rod bipolar cells, but not cone bipolar cells possess a prominent Na(+)/Ca(2+) exchange mechanism. We conclude that PMCA isoforms are selectively expressed in retinal neurons and that processes of Ca(2+) clearance are different in rod and cone bipolar cells.

Amacrine Cells↗

PubMed1985

Distribution of ganglion cells in the retina of adult pigmented ferret.

The retinal ganglion cell distribution in adult pigmented ferret was mapped in Nissl-stained retinas and in retinas back-filled with HRP after large bilateral injections of the enzyme into the brain. In common with other carnivores the ferret has an area of peak cell density equivalent to the area centralis and a prominent visual streak of high cell density extending horizontally across the retina. The maximum ganglion cell densities for the retinas were estimated to be 3500-5200 cells/mm2 in Nissl-stained, dehydrated retinas and 3300-4300 cells/mm2 in HRP-labelled, undehydrated retinas. Three cell types were distinguished in the HRP-labelled retinas and they appear to correspond to alpha-, beta- and gamma-cell types of cat retina. However, unlike in cat, the retinal ganglion cells of the ferret do not consistently fall into 3 distinct groups with respect to cell size, nor is there a tendency for the cells in the area centralis to be smaller than those in the peripheral retina. Estimates for the total number of ganglion cells of 82,000 and 88,000 were obtained from Nissl-stained retinas, and of 74,000, 75,000 and 78,000 from HRP-labelled retinas.

Animals↗

PubMed1966

Mechanism of polarized light perception.

As background for a report on our current selective adaptation experiments in decapod crustaceans, the various facts and hypotheses generally relevant to intraretinal sensitivity to polarized light in arthropods as well as cephalopods have been marshaled. On the basis of this review, the following working hypotheses have been made. 1) One ommatidium in the compound eye is the functional unit in image perception but contains in its component retinular cells subunits which can work independently in detecting other visual parameters, such as polarization. 2) Single retinular cells do respond differentially to light polarized in various planes. 3) Light sensitivity, including e-vector detection, is localized in the rhab domeres, which comprise closely packed arrays of microvilli protruding axially from retinular cells; the dichroism of the photopigment molecules, which are contained within the microvilli, provides the molecular basis of e-vector detection. 4) The visual pigment molecules have their major dichroic axis aligned predominantly parallel to the long axis of the microvillus containing them; typically all microvilli in a single rhab domere are closely parallel to one another, thus comprising at the cellular level a unit dichroic analyzer with maximum optical density to photons vibrating in the direction parallel to these microvillous protrusions. 5) In most decapod crustaceans, in cephalopods, and in some insects the microvilli in all rhabdomeres of a retinula are oriented in only two directions, perpendicular. to each other. Therefore, e-vector perception must depend at the retinular level on a two channel system consisting of a pair of dichroic analyzers with their major transmitting axes fixed at a 90 degrees angle determined by the two directions of microvillus orientation. Our new results on selective adaptation in the eye of Cardisoma provide direct experimental evidence for such a two-channel analyzer in which the pair of functional units have their maximum sensitivity to polarization in the same retinal directions as the rhab dom microvilli observed in electron micrographs. In turn, these directions correspond with the vertical and horizontal axes of the animal's normal spatial orientation. In e-vector detection the seven retinular cells of a single decapod ommatidium thus form two operational subgroups of four and three cells, respectively (39). The correspondence of the electrophysiological evidence for a dual polarization analyzer with the perpendicular directions shown by the microvilli in a single rhabdom strengthens the idea that one ommatidium is enough for detecting e-vector orientation. On this evidence we may conclude that the model developed above for a two-channel polarization analyzer effectively accounts for the relevant spectrophotometric, fine-structural, electrophysiological, and behavioral data currently available for a considerable number of arthropods and cephalopods.

Adaptation, Ocular↗

PubMed1984

Effects of dopamine on photopic L-type S-potentials in the catfish retina.

Photopic L-type responses were recorded from the soma and the axon terminal of horizontal cells of the catfish (Ictalurus punctatus) retina in eye-cup preparations. The responses were produced by a spot of light with 100-micron diameter (intensity, 10 microW/cm2), which was flashed or steadily illuminated and swept along a 6-mm length over the retinal surface at a speed of 0.95 mm/sec. In some experiments, a traveling random bar stimulus was used instead of the sweeping spot. While recording the responses, dopamine (DA) was applied in a jet form via a nebulizer over the retinal preparation or as superfusate to the eye-cup preparation. DA increased the response amplitude by about 50% and markedly narrowed the spatial profile of the responses from the soma but not from the axon terminal. These DA effects were observed in both normal retinas and those from which DA cells had been deprived by prior intraocular injection of 6-hydroxydopamine. Deprival of DA cells from the retina resulted in a slightly wider spatial profile of the soma and axon terminal responses than that in normal retinas. The results indicate that the spatial properties of photopic L-type responses are modulated by DA at the soma level of horizontal cells.

Animals↗

PubMedDate not supplied

Gycine and GABA interact to regulate the nitric oxide/cGMP signaling pathway in the turtle retina.

Nitric oxide (NO) is a free radical that is important in retinal signal transduction and cyclic guanosine monophosphate (cGMP) is a critical downstream messenger of NO. The NO/cGMP signaling pathway has been shown to modulate neurotransmitter release and gap junction coupling in horizontal cells and amacrine cells, and increase the gain of the light response in photoreceptors. However, many of the mechanisms controlling the production of NO and cGMP remain unclear. Previous studies have shown activation of NO/cGMP production in response to stimulation with N-methyl-d-aspartate (NMDA) or nicotine, and the differential modulation of cGMP production by GABA(A) and GABA(C) receptors (GABA(A)Rs and GABA(C)Rs). This study used cGMP immunocytochemistry and NO imaging to investigate how the inhibitory GABAergic and glycinergic systems modulate the production of NO and cGMP. Our data show that blocking glycine receptors (GLYR) with strychnine (STRY) produced moderate increases in cGMP-like immunoreactivity (cGMP-LI) in select types of amacrine and bipolar cells, and strong increases in NO-induced fluorescence (NO-IF). TPMPA, a selective GABACR antagonist, greatly reduced the increases in cGMP-LI stimulated by STRY, but did not influence the increase in NO-IF stimulated by STRY. Bicuculline (BIC), a GABA(A)R antagonist, however, enhanced the increases in both the cGMP-LI and NO-IF stimulated by STRY. CNQX, a selective antagonist for alpha-Amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid hydrobromide/kainic acid (AMPA/KA) receptors, eliminated both the increases in cGMP-LI and NO-IF stimulated by STRY, while MK801, a selective antagonist for NMDA receptors, slightly increased the cGMP-LI and slightly decreased the NO-IF stimulated by STRY. Finally, double labeling of NO-stimulated cGMP and either GLY or GABA indicated that cGMP predominantly colocalized with GLY. Taken together, these findings support the hypothesis that GLY and GABA interact in the regulation of the NO/cGMP signaling pathway, where GLY primarily inhibits NO production and GABA has a greater effect on cGMP production. Such interacting inhibitory pathways could shape the course of signal transduction of the NO/cGMP pathway under different physiological situations.

Animals↗

PubMed1986

Analysis of a glycinergic inhibitory pathway in the cat retina.

Incubation of cat retinas with 3H-glycine in vitro, followed by horizontal sectioning and autoradiography, showed labeling of 10-12% of bipolar cells and 45% of amacrine cells. To ascertain the effects of glycine-accumulating bipolar and amacrine cells on the response properties of retinal ganglion cells, in vivo iontophoretic studies were performed in the cat eye. Glycine inhibited all ganglion cells, and this action was blocked by strychnine. Aminophosphonobutyric acid (APB) suppressed ON-ganglion cells, but activated OFF-ganglion cells. The influence of APB upon OFF-ganglion cells could be completely blocked by strychnine. In the mudpuppy, APB suppressed ON-bipolar cells without affecting OFF-bipolar cells and without direct effects on other retinal neurons (Slaughter and Miller, 1981, 1985). If APB has the same mode of action in the cat retina, the present results suggest a glycinergic inhibitory input of the ON-channel upon OFF-ganglion cells.

Aminobutyrates↗

PubMedDate not supplied

[Effect of the level of lighting on 14C-GABA efflux from the isolated retina of the frog Rana ridibunda].

Studies have been made of the effect of changes in illumination levels on 14C + GABA efflux in the isolated retina of the frog R. ridibunda. When the retina loaded with 14C-GABA is stimulated by darkness, the efflux of radioactivity immediately increases. After reaching a peak, the efflux of 14C-GABA slightly decreases attaining steady level which is higher than the level of spontaneous efflux observed during weak (approximately 0.05 lux) illumination. This high level is preserved as long as the retina remains in darkness. During illumination of the retina (transition from darkness to 60 lux), two types of response are observed. In some cases, insignificant increase of GABA efflux from the retina is followed by its rapid decrease up to the level which is observed during weak illumination. In other cases, immediately after illumination the decrease in GABA efflux takes place (in 6 experiments out of 10). In accordance with the data of Voaden [6], it is suggested that 14C + GABA is liberated from horizontal and amacrine cells. The data obtained in the present investigation are discussed in terms of Trifonov [14] and Byzov [15] hypothesis. These data confirm the idea that GABA acts as a retinal neurotransmitter in the frog.

Animals↗

PubMed1992

The retinal distribution of ganglion cells with crossed and uncrossed projections and the visual field representation in the opossum.

The retinal distribution of ganglion cells with crossed and uncrossed projections in the South American opossum, Didelphis marsupialis, was revealed by delivering HRP to one optic tract or to retinal targets of one hemisphere. The cells with uncrossed projections are restricted to the temporal retina, comprising 1/3 of the total retinal area, with a sharp transition at the naso-temporal boundary. Besides being distributed over the nasal 2/3 of the retina, cells with crossed projections are intermingled with those with uncrossed projections over the entire temporal retina. Quantitative analysis about the representation of the horizontal meridian on four specimens revealed that the maximum density of cells with uncrossed projections is on the average located at 3.2 mm (SD = 0.21), i.e. 34.8 deg, temporal to the optic disk, falling to 10% at 2.1 mm (SD = 0.14) or 22.8 deg. On the other hand, the peak for cells with crossed projections is more nasally placed at 1.8 mm (SD = 0.18), i.e. 19.6 deg. Between these two maxima, the site wherein the densities of cells with crossed and uncrossed projections are about equal is on the average about 2.7 mm (SD = 0.25) form the optic disk, i.e. 29.3 deg. This estimate supports the hypothesis that the retinal intersection of the vertical meridian lies within the region of split representation of crossed and uncrossed ganglion cells. In addition, it was observed that the opossum's retina has a large contingent of cells with uncrossed projections temporal to an eccentricity of 2.7 mm from the optic disk, where it represents roughly 2/3 of the ganglion cells. These data corroborate the relevance of the opossum as a non-primate model for visual work.

Animals↗

PubMed2005

Calcium-binding protein distribution in the retina of strepsirhine and haplorhine primates.

Calcium-binding proteins are involved in numerous functional roles in the retina and are widely distributed in almost all retinal neurons. The present study aimed to characterize the distribution of the calcium-binding proteins calbindin, calretinin, parvalbumin and recoverin in relation to retinal cell types in a strepsirhine primate (mouse lemur, Microcebus) in comparison with primate species of the three main haplorhine lineages (marmoset, macaque and human), as well as a rodent (gerbil, Taterillus). The main findings show that whereas the recoverin antibody labels both rod and cone photoreceptors in all species, calbindin consistently labels cones, but not rods, in the haplorhine primates marmoset, macaque and human, but none of the photoreceptors in the mouse lemur. Marmoset and macaque also show a distinct label of cone outer segments with calretinin. Depending on the species, bipolar cells express calbindin and/or recoverin, while amacrine, horizontal and ganglion cells are labeled to varying degrees with calbindin, calretinin and parvalbumin. Haplorhine and strepsirhine primates clearly differ in the expression of calcium-binding protein expression in horizontal cells. In all haplorhine species, horizontal cells are densely labeled with parvalbumin whereas in mouse lemur horizontal cells express calbindin but not parvalbumin. Several characteristics of the calcium-binding immunostaining in the retina of the mouse lemur are similar to those observed in the rodent, and distinguish this species from the diurnal haphorhine primates. These differences may be related to adaptations of retinal structure and function to the nocturnal niche, since nocturnal strepsirhine and haphorhine (Tarsius and Aotus) primates share some features of calcium-binding expression.

Aged↗

PubMed1992

Morphogenesis of retinal ganglion cells during formation of the fovea in the Rhesus macaque.

The morphology of retinal ganglion cells within the central retina during formation of the fovea was examined in retinal explants with horseradish-peroxidase histochemistry. A foveal depression was first apparent in retinal wholemounts at embryonic day 112 (E112; gestational term is approximately 165 days). At earlier fetal ages, the site of the future fovea was identified by several criteria that included peak density of ganglion cells, lack of blood vessels in the inner retinal layers, arcuate fiber bundles, and the absence of rod outer segments in the photoreceptor layer. Prior to E112, the terminal dendritic arbor of retinal ganglion cells within the central retina extended into the inner plexiform layer and were located directly beneath their somas of origin or at most were slightly displaced from it. For example, at E90 the mean horizontal displacement of the geometric center of the dendritic arbor from the somas of cells within 600 microns of the estimated center of the future fovea was 4.1 microns (S.D. 2.7, range 1.0-10.0, n = 97). Following formation of the foveal depression the dendritic arbors of cells were significantly displaced from their somas. For example, at E138 the mean displacement was 41.2 microns (S.D. 12.2, range 12.0-56.0, n = 97). The displacement of the dendritic arbor which occurred during this period was not accounted for by areal growth of the dendritic arbor, the somas, or the retina, but was produced by the lengthening of the primary dendritic trunk. Moreover, no significant displacement was observed within the remaining 1.5-6.5 mm of the central retina. These observations provide evidence supporting early speculations that the formation of the foveal pit occurs, in part, by the radial migration of ganglion cells from the center of the fovea during its formation. Our analyses suggest that this migration occurs by the lengthening of the primary dendrite presumably by the addition of membrane. This migration is in a direction opposite to the inward movement of photoreceptors that occurs during late fetal and early postnatal periods (Packer et al., 1990, Journal of Comparative Neurology 298, 472-493).

Animals↗

PubMed1993

[Peripheral retinal correspondence after retinal detachment].

BACKGROUND: Occasionally, patients who underwent surgery for complicated retinal detachment report spatial distortions. This may be due to a translocation of photoreceptors when they become reattached to the pigment epithelium. We wanted to find out if, and to what extent, similar translocations occur after a simple buckling operation. METHODS: Binocular retinal correspondence was used as an indicator of photoreceptor translocation. Correspondence was measured in the peripheral visual field at eccentricities of 5, 10 and 20 degrees, using a mirror haploscope. We examined two normal observers, one patient having had surgery for complicated retinal detachment including retinotomy, and 23 patients who had simple radial buckling operations. RESULTS: The patient who had received complicated detachment surgery including retinotomy revealed a tremendous shift in correspondence. Of the 23 patients who had simple radial buckle operations, only 10 were able to sustain central fixation while being tested in the periphery. Of these 10 patients, 2 showed distortions of peripheral retinal correspondence in the area of previous retinal detachment. However, only one of them remembered some spatial distortion after surgery. CONCLUSION: As a rule, photoreceptors become correctly reattached after radial buckle operations for retinal detachment. Rarely, vertical or horizontal translocations of about 1 to 2 degrees occur, but this does not usually lead to metamorphopsia.

Adult↗

PubMed2000

Effects of long-term spectral deprivation on the morphological organization of the outer retina of the blue acara (Aequidens pulcher).

To investigate the developmental plasticity of colour vision, we reared fish with a trichromatic cone system (Aequidens pulcher) under three near-monochromatic lights, differentially stimulating each spectral cone type from the larval stage to the age of at least one year. Control conditions comprised white lights of two intensities. The treatments did not affect the visual pigments, hut led to significant changes in cone outer segment lengths. Furthermore, in the blue-reared group the density of single cones within the retina was reduced by two-thirds after 18 months of exposure, while no changes were observed in the other groups. The connectivity of cone horizontal cells with the single cones was influenced by the intensity and spectral composition of the rearing lights: H1 cells were more sensitive to the spectral component, whereas H2 cells responded to intensity cues. In the blue-light group the dynamics of horizontal cell synaptic spinule formation and degradation were severely compromised. These observations show that long-term spectral deprivation leads to significant morphological changes at the level of photoreceptors and horizontal cells. While the reactions of photoreceptors may be interpreted mostly in terms of compensation, the functional consequences of the changes observed on the horizontal cell level remain to be determined electrophysiologically.

Animals↗

PubMed2000

To what extent are the retinal capillaries ensheathed by Müller cells? A stereological study in the tree shrew Tupaia belangeri.

The cellular ensheathment of capillaries in the 3 outer capillary layers of the central retina of the adult tree shrew Tupaia belangeri was studied quantitatively by transmission electron microscopy. Using a stereological approach, the relative surface of capillary basal lamina ensheathed by Müller cells and by nonmacroglial cells (collectively termed non-Müller cells) was estimated in 5 animals. The participation of Müller cells was distinctly different in the 3 capillary layers studied. In the outermost capillary layer 1, the mean (standard deviation) percentage surface coverage by non-Müller cell processes was 46.8 (15.3)%. Much less of the capillary basal lamina was ensheathed by non-Müller cells in capillary layers 2 and 3 (3.0 (2.1)% and 0.3 (0.3)% respectively). The observed total variation of the stereological estimates for the surface fraction of Müller cells (expressed as the between-subject coefficient of variation) was significantly higher in capillary layer 1 (28.8%) compared with capillary layers 2 (2.2%) and 3 (0.3%). In capillary layer 1, the high observed total variation was due to a high biological variation among animals for the fractions of both Müller cell and non-Müller cell ensheathment. The rare occurrence of direct contacts between the capillary basal lamina and the perikarya of either microglial cells (capillary layer 3) or amacrine cells (capillary layer 2) corresponded well to the low stereological values obtained for the relative capillary surface ensheathed by non-Müller cells in these capillary layers. Previously, extensive and frequent contacts between the basal lamina of capillaries belonging to capillary layer 1 and horizontal cells had been observed in single sections. The present study quantitatively demonstrates a marked paucity of macroglial investment of capillaries located in capillary layer 1 of Tupaia. It can be concluded that horizontal cells ensheath most of the capillary surface not invested by Müller cells.

Animals↗

PubMed1989

Quantitative analysis of the retinal ganglion cell layer and optic nerve of the barn owl Tyto alba.

The visual capacity of the common barn owl (Tyto alba) was studied by quantitative analysis of the retina and optic nerve. Cell counts in the ganglion cell layer of the whole-mounted retina revealed a temporal area centralis with peak cell density of 12,500 cells/mm2 and a horizontal streak of high cell density extending from the area centralis into the nasal retina. Integration of the ganglion cell density map gave an estimated total of 1.4 million cells for the ganglion cell layer. Electron microscopy of a single, complete section of the optic nerve revealed a bimodal fiber diameter spectrum (modes at 0.3 and 0.9 microns; bin width = 0.2 microns), with diameters ranging from 0.15 microns (unmyelinated) to 6.05 microns (myelinated, sheath included). The total axon count for the optic nerve was estimated from sample counts to be about 680,000 axons (25% unmyelinated). Therefore, roughly half of the cells in the retinal ganglion cell layer do not send axons into the optic nerve. With certain assumptions, the data predict a visual spatial acuity for barn owls on the order of 8 cycles/degree, a value similar to the known behaviorally measured acuities of masked owls (10 cycles/degree) and domestic cats (6 cycles/degree).

Animals↗