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PubMed2004

Absence of phosphoglucose isomerase-1 in retinal photoreceptor, pigment epithelium and Muller cells.

Macroarray analysis was used to compare equal amounts of cDNA from wild-type and rd/rd (retinal degeneration) mice, collected at P90 when photoreceptor degeneration is virtually complete. A stronger signal for the glycolytic enzyme phosphoglucose isomerase (Gpi1) was observed in the rd/rd sample. Extracellularly, Gpi1 may act as a cytokine, independently described as neuroleukin and autocrine motility factor. Retinal Gpi1 expression was investigated by Northern and Western blot analysis and immunohistochemistry. Double-labelling was performed with antibodies against Gpi1 and calbindin-D, glutamine synthetase, RPE65, calretinin and ultraviolet opsin in order to provide positive cell type identification. Northern and Western blots showed double expression levels per microgram of RNA and protein, respectively, in the rd/rd retina compared with wild-type. However, the total amount of Gpi1 protein per retina was indistinguishable. Gpi1 immunoreactivity was found in ganglion, amacrine, horizontal and bipolar cells, but not in rods, cones, pigment epithelium and Muller cells. This distribution explains why the absolute amounts of Gpi1 protein were not appreciably different between wild-type and the rd/rd phenotype, where rods and cones are absent, whilst the relative contribution of Gpi1 to the total protein and RNA pools differed. Some extracellular immunoreactivity was observed in the photoreceptor matrix around cones in freshly fixed tissue only, which could possibly reflect a role as a cytokine. We propose that glycolysis in Gpi1-negative cells proceeds entirely through the pentose phosphate pathway, creating NADPH at the cost of organic carbon. We hypothesize that the unique metabolic needs of photoreceptors justify this trade-off.

Animals↗

PubMed1991

Glycinergic interplexiform cells make synaptic contact with amacrine cell bodies in goldfish retina.

Recent works utilizing glycine-immunoreactivity (IR) and combined Golgi impregnation and 3H-glycine uptake autoradiography indicate that glycinergic interplexiform cells (IPC) may synapse upon cell bodies in the inner nuclear and ganglion cell layers in fish retina. This possibility was investigated with immunocytochemical techniques using presynaptic and postsynaptic markers for glycinergic neurons: a monoclonal antibody (mAb 7A) against the 93 kDa subunit of the strychnine-sensitive glycine receptor and a polyclonal antiserum against a glycine/BSA conjugate. Synaptic contacts onto the lateral and proximal surfaces of amacrine cell bodies and onto the distal surface of cells in the ganglion cell layer were identified with both probes. The contacts were rare with one contacted amacrine cell/section of 500 linear micron. Serial 1-micron sections were processed alternately for glycine and GABA antisera using postembedding techniques at the light microscopic level. Glycine-IR processes + boutons were apposed to GABA-IR cell bodies in 16 of 17 examples, indicating that the dendro-somatic contacts were onto GABA-immunoreactive amacrine cell bodies. In context of other published morphological data, we suggest that the dendro-somatic synapses were derived from glycinergic IPCs. Glycinergic IPCs receive input from GABAergic horizontal cells and, via a shunt conductance produced by the dendro-somatic contacts, may be involved in controlling the sensitivity, temporal, or spatial properties of amacrine cell responses to large field illumination.

Animals↗

PubMedDate not supplied

Do magnocellular and parvocellular ganglion cells avoid short-wavelength cone input?

We recently developed a new technique to measure cone inputs to visual neurons and used this technique to seek short-wavelength-sensitive (S) cone inputs to parasol, magnocellular (MC) and midget, parvocellular (PC) ganglion cells. Here, we compare our physiological measurements of S-cone weights to those predicted by a random wiring model that assumes cells' receptive fields receive input from mixed cone types. The random wiring model predicts the average weights of S-cone input to be similar to the total percentage of S-cones but with considerable scatter, and the S-cone input polarity to be consistent with that of PC cells' surround and of MC cells' center. This is not consistent with our physiological measurements. We suggest that the ganglion cells' receptive fields may have a mechanism to avoid S-cone inputs, as is the case in the H1 horizontal cells. Previous reports of S-cone inputs, in particular substantial input to MC cells, are likely to reflect variation in prereceptoral filtering and/or the failure to correct for variation in macular pigment.

Animals↗

PubMed2004

Postsynaptic localization of gamma-aminobutyric acid transporters and receptors in the outer plexiform layer of the goldfish retina: An ultrastructural study.

The gamma-aminobutyric acid (GABA)-ergic system in the outer plexiform layer (OPL) of the goldfish retina was studied via light and electron immunohistochemistry. The subcellular distributions of immunoreactivity (-IR) of plasma membrane GABA transporters GAT2 and GAT3, the alpha1 and alpha3 subunits of the ionotropic GABA(A) receptor, and the rho1 subunit of the ionotropic GABA(C) receptor were determined. The localization of the GAT2-IR and GAT3-IR to horizontal cell dendrites at the base of the cone synaptic complex was the main characteristic at the ultrastructural level. Very rarely, GAT2-IR and GAT3-IR were found in horizontal cell dendrites innervating rod spherules. alpha1-IR and alpha3-IR were seen in wide bands in the OPL, whereas rho1-IR appeared as a narrow band in the OPL. Most alpha1-IR was intracellular in rod and cone terminals. Membrane-associated alpha1-IR was observed in cone pedicles but not in rod spherules; postsynaptic elements were also labeled. alpha3-IR was concentrated in the lateral elements of horizontal cell dendrites in cone pedicles. In contrast, rho1-IR was found mainly on the spinules of the horizontal cell dendrites in cone pedicles. In addition, in another type of cone pedicle, rho1-IR was found at the position of OFF-bipolar cell dendrites. alpha3-IR and rho1-IR were rarely found in horizontal cell dendrites innervating rods. We suggest that two GABAergic pathways exist in the outer retina- first, a GABAergic positive loop with GABA receptors mainly on the horizontal cell dendrites and spinules and, second, a GABAergic feedback pathway involving GABA receptors on cone pedicles and GABA transporters on horizontal cells and that this pathway presumably modulates feedback strength from horizontal cells to cones.

Animals↗

PubMed1996

Cobalt ions enhance light responsiveness of carp cone horizontal cells in low calcium.

Effects of cobalt ions (Co2+) on horizontal cells in low extracellular calcium were examined in isolated, superfused carp retinas. While 0.1 mmol/L Co2+ completely suppressed both rod- and cone-driven horizontal cells in normal Ringer's solution, it enhanced light responses of cone horizontal cells in low (0.1 mmol/L) calcium. The enhancement of the cone horizontal cell response by Co2+ was not caused by changes in light responsiveness of cone photoreceptors. Moreover, application of 50 mumol/L IBMX, an inhibitor of phosphodiester enzyme, reduced the suppressive effect of 0.1 mmol/L Co2+ in normal Ringer's solution. In consequence, the above-described enhancement of the cone horizontal cell light responsiveness may be due to a depolarization of cones caused by low calcium, which increases the activity of voltage-dependent calcium channels at cone terminals.

1-Methyl-3-isobutylxanthine↗

PubMed1990

Retinal ganglion cell density and cortical magnification factor in the primate.

The question of whether the large area occupied by the primate fovea in the visual cortex (V1) is the result of a selective amplification of the central visual field, or whether it merely reflects the ganglion cell density of the retina, has been a subject of debate for many years. Measurements of the ganglion cell densities are made difficult by lateral displacements of cells around the fovea and the occurrence of amacrine cells in the ganglion cell layer. We have now identified and counted these amacrine cells by GABA immunocytochemistry and by retrograde degeneration of ganglion cells. By reconstructing the fovea from vertical and horizontal serial sections, we were able to measure the densities of cones, cone pedicles and ganglion cells within the same retina. We found 3-4 ganglion cells for every foveal cone. This ratio decreased to one ganglion cell per cone at an eccentricity of 15-20 deg (3-4 mm) and in peripheral retina there are more cones than ganglion cells. The ganglion cell density changes by a factor of 1000-4000 between peripheral and central retina. A comparable gradient has been reported for the representation of the peripheral and central visual field in V1. We suggest that ganglion cell density can fully account for the cortical magnification factor and there is no need to postulate a selective amplification of the foveal representation.

Animals↗

PubMed1983

The distributions of photoreceptors and ganglion cells in the California ground squirrel, Spermophilus beecheyi.

The topographical distributions of photoreceptors and ganglion cells of the California ground squirrel (Spermophilus beecheyi) were quantified in a light microscopic study. The central retina contains broad, horizontal streaks of high photoreceptor density (40-44,000/mm2) and high ganglion cell density (20-24,000/mm2). The isodensity contours of both cell types are elliptical and oriented along the nasal-temporal axis. There are roughly five-fold decreases in both photoreceptor and ganglion cell densities with increasing eccentricity, the lowest densities being found in the superior retina. Large transitions in cell density and retinal thickness occur across the linear optic nerve head. Rod frequency increases with increasing eccentricity, from 5 to 7% in the central retina to 15 to 20% in the periphery. Roughly 10% of the cones possess wide, dark-staining ellipsoids. These cones are uniformly distributed across the retina which suggests that they may belong to a separate cone class, possibly blue-sensitive cones. The ganglion cell soma size distribution is unimodal, with the majority of somata being 25-50 micron2. Large ganglion cells (somata greater than 100 micron2) are rare in the central retina, but their frequency increases with increasing eccentricity. No evidence for separate size classes of ganglion cells was found. The gradual decrement of photoreceptor density across the ground squirrel retina suggests that there are only relatively small changes in acuity across much of the animal's visual space compared with species possessing either a narrow visual streak or fovea or area centralis.

Animals↗

PubMed1992

Intergeniculate leaflet and suprachiasmatic nucleus organization and connections in the golden hamster.

The intergeniculate leaflet (IGL) is a distinct subdivision of the lateral geniculate complex which receives retinal input and projects upon a circadian pacemaker, the suprachiasmatic nucleus (SCN). In the present study, we have analyzed the organization of the IGL and its connections in the hamster, a species commonly used in circadian rhythm studies. The location of the IGL is defined by the presence of retinal afferents demonstrated by anterograde transport of cholera toxin-HRP, neuropeptide Y-containing neurons and axons, cells retrogradely labeled from the regions of the SCN and contralateral IGL, and substance P-containing axons. It is a long nucleus extending the entire rostrocaudal axis of the geniculate. The most rostral IGL lies between the lateral dorsal thalamus, ventrolateral part, and the horizontal cerebral fissure. It then enlarges ventral to the rostral dorsal lateral geniculate, medial to the optic tract. The mid-portion of the leaflet is a thin lamina intercalated between the dorsal and ventral geniculate nuclei. The extended caudal portion of the nucleus lies lateral and ventral to the medial geniculate and is contiguous with the zona incerta and the lateral terminal nucleus. The IGL contains populations of neuropeptide Y (NPY+) and enkephalin (ENK+) neurons which project to the retinorecipient portion of the SCN. In addition to the immunoreactive perikarya, the IGL contains plexuses of NPY+, ENK+, substance P-, serotonin-, and glutamic acid decarboxylase-immunoreactive axons. Retrograde transport studies demonstrate that, in addition to the NPY+ neurons, there is a population of non-NPY+ neurons projecting upon the SCN.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed2002

Interocular effect of intravitreal injection of 6-hydroxydopamine and dopamine on spinule formation in teleost retina.

Terminal dendrites of cone horizontal cells (HCs) in teleost retinas show numerous spine-like protrusions named spinules, which are invaginated into the cone pedicles during light-adaptation, but retracted during dark-adaptation. Somata of HC show nematosomes whose size decreases as the number of spinules increases. Mechanisms regulating these changes in nematosomes and spinules are only partially understood, being an area of controversy in retinal cell biology. It has been suggested that efferent fibres from the brain to the retina might be involved in the control of spinule formation. Moreover, we have reported that actin depolymerization has an interocular effect on spinule formation, which could be mediated by these fibres. In the present report, we show an interocular effect on spinule dynamics: the monocular intravitreal injection of dopamine (DA) and 6-hydroxydopamine (6-OHDA), two drugs that affect the spinule formation, produces the same effects in the contralateral, untreated eye as in the injected eye. Our results reinforce the idea of an interocular central control of this phenomenon of synaptic plasticity. Dopamine-dependent events in the retina appear to be necessary to forge the afferent signals eliciting this interocular effect.

Adrenergic Agents↗

PubMed1976

[Inhibitory mechanisms within the receptive fields of X-and Y-type retinal ganglion cells of the cat (author's transl)].

Two-stages of the inhibitory mechanisms were assumed within the on-center receptive field (RF) of the cat's retinal ganglion cell on the basis of the following two experiments: 1) Effect of background intensity upon the magnitude of the response to the RF-centered spot of stimulus, and 2) the time course of the inhibitory effect when the additional spot of light is presented in the same RF center region. The first stage is an inhibitory feed-back from horizontal cell to the photoreceptor. Both X-and Y-fields have this feed-back route. By this gain control machanisms, the ganglion cell will respond to the intensity ratio of the spot to the background. [corrected] The second stage of inhibitory mechanism in X-field is the feed-back from sustained amacrine cell to the bipolar cell. Above two stages of feed-back mechanism in X-field explain the strong maintained suppressive effect produced by the additional spot of light. On the other hand, the Y-type ganglion cell will recive the inhibitory input via feed-forward path from trannsient amacrine cell. This explains the transient on- and of f-suppressive effects

Animals↗

PubMed1993

Distribution of actin in cone photoreceptor synapses.

The invaginated photoreceptor terminal harbours a great number of postsynaptic dendrites that contact the photoreceptor terminal at morphologically distinct synapses. In this paper we studied the subcellular distribution of actin in cone photoreceptor synapses of light-adapted goldfish and guppy retinas and its relation to ribbon and spinule synapses. In the outer plexiform layer, fluorescent staining for actin by antibodies and also by fluorescently labelled phalloidin was discontinuous and showed large dot-like immunoreactive structures (3-5 microns in diameter). Immunogold electron microscopy of light-adapted retinas isolated 3 h after the onset of light demonstrated that these dot-like structures corresponded to dendritic profiles of bipolar and horizontal cells within the synaptic cavity of cones. A much less intense staining was observed within the presynaptic cone photoreceptor terminal itself. Immunogold particles were also found overlying the tips of horizontal and bipolar dendrites that form the triadic postsynaptic complex of the ribbon synapse. In contrast to the triads light-induced terminal outgrowings of horizontal cells, also known as spinules, remained largely unlabelled. These observations suggest that actin plays a role in maintenance and/or certain steps of the formation of the postsynaptic dendritic complex.

Actins↗

PubMed1992

The effects of serotonin drugs on horizontal and ganglion cells in the rabbit retina.

We have investigated the effects of a serotonin 5-HT2 antagonist and a 5-HT1A agonist on horizontal and ganglion cells in the rabbit retina. Simultaneous intracellular horizontal cell and extracellular ganglion cell recordings were obtained from a superfused in vitro rabbit eyecup preparation and the effects of bath applied drugs on these cells' light responses observed. Sinusoidally modulated current was also injected into horizontal cells while the extracellular spike activity of nearby, single-unit ganglion cells was monitored. Although the ON components of the light-evoked responses of ganglion cells were reduced by the 5-HT2 antagonist or the 5-HT1A agonist, the membrane potential and the light responses of horizontal cells and the b-wave of the ERG were simultaneously unaffected. However, the drugs blocked current-driven ganglion cell spike activity induced by current injections into nearby horizontal cells. These results are discussed with respect to the site of action of these serotonin drugs and with respect to the circuitry of serotonergic neurons.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1994

Effects of prolonged darkness on light responsiveness and spectral sensitivity of cone horizontal cells in carp retina in vivo.

Light responses of cone- and rod-driven horizontal cells were recorded intracellularly from opened eyes of intact, immobilized carp and the effects of prolonged darkness on these cells were examined. When the retina was left in the dark, responses of cone horizontal cells to a moderate test flash presented once every 10 min gradually and steadily decreased in size (dark suppression effect). Following a repetitive presentation of the test flash, the light responsiveness of the cells was enhanced. In contrast, the rod horizontal cells did not show the dark suppression effect and the light responsiveness of these cells increased in the dark. Effects of prolonged darkness on the spectral sensitivity of L-type and R/G-type cone horizontal cells were also studied. The spectral sensitivity of L-type cells, determined just after background illumination was extinguished, agreed reasonably well with that of red-sensitive (R-) cones, but it matched better that of green-sensitive (G-) cones when determined in prolonged darkness. We further show that depolarizing responses of R/G-type cone horizontal cells to long-wavelength flashes, driven by R-cones, were abolished after prolonged darkness. Taken together, these results suggest that input from R-cones converging onto the cone horizontal cells is more significantly suppressed after prolonged dark adaptation than input from G-cones. Due to the suppression of the R-cone input, enhancement of responses of the L-type cone horizontal cells to long-wavelength stimulation in the presence of a green background light was no longer seen after prolonged darkness.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

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.

Animals↗

PubMed1977

Effects of alcohol on ganglion cell receptive field properties and sensitivity in the frog retina.

Previous results have shown that alcohol has an effect on vision and on the excitability of retinal neurons. Action potentials of single ganglion cells were recorded by microelectrodes in opened and excised eyes from frogs (Rana temporaria L.). Histologically two types of synapses have been described in the retina: conventional synapses and synapses with a ribbon or bar shaped component surrounded by a rather uniform layer of synaptic vesicles. The "ribbon synapses" are presynaptic contacts in receptor and bipolar cells while horizontal and amacrine cells have conventional synapses. Tests with ethanol doses up to 0.2% indicated stronger effects on the conventional synapses than on the ribbon synapses. Alcohol decreased or abolished the lateral inhibition ( inhibitory surround) mediated by the amacrine cells and depressed the signals from the green rods, which apparently are mediated by horizontal cells. Further alcohol decreased the sensitivity of the signals from the completely dark-adapted red rods in the retina, and increased the sensitivity of the cone-mediated responses for class 3 and deviating class 4 cells, when measured against a background light. Alcohol also increased the latency of the response up to 55 msec. depending on the size of the stimulus field.

Animals↗

PubMed1992

Development of the glutamate system in rabbit retina.

We have investigated two characteristics of the glutamate system in the developing rabbit retina. 1) Glutamate immunoreactivity was observed at birth within developing processes of four cell types; two of which, photoreceptors and ganglion cells, are known to be glutamatergic in the adult. Two other cell types, type A horizontal cells and amacrine cells, are immunoreactive to both glutamate and GABA at birth, suggesting that endogenous pools of glutamate in GABAergic neurons serve as precursor for GABA synthesis. Thus it appears that endogenous glutamate pools are present within neurons prior to synaptogenesis as part of the early expression of either the glutamate or GABA transmitter phenotype. 2) Analysis of 3H-glutamate metabolism during retinal development showed that rapid conversion of glutamate to glutamine does not occur until the second postnatal week, coincident with the expression of Muller (glial) cell activity. In the absence of glial metabolism in the neonate, extracellular concentrations of glutamate remain relatively high and are likely to have major effects on neuronal maturation.

Aging↗

PubMed1977

Spreading depression in isolated carp retina.

(1) Spreading depression (SD) could be elicited in isolated carp retina by KCI application, the concomitants of which were similar to those described in other vertebrates. (2) The threshold for generating SD was greatly reduced by brief immersion of the retina in low ci-ringer's solutions. The properties of SD waves were almost the same with treated and untreated retinas, except for intervals. (3) Extracellular negative potential shifts during SD, averaging 4.6 mV in amplitude and 27 sec in duration, were recorded in whole retinal layers with the maximum amplitude about at the inner plexiform layer. (4) The PIII potential of the local electroretinogram was virtually unaffected by SD. (5) Both L-and C-type S-potentials could be evoked with increase of 20-40% in amplitude around the peak of slow membrane depolarizations (mean value of maximal amplitude 5.8 mV) during SD in horizontal cells. (6) Increase in spike number was observed in both on-and off-center ganglion cells before and after the spike cessation during SD in the untreated retina. However, the off-discharges, which were a unique response to light in the immersed retina, only decreased during SD.

Animals↗

PubMed1989

An eyecup slice preparation for intracellular recording in vertebrate retinas.

This report describes a new preparation for intracellular recording from the vertebrate retina, the eyecup slice preparation. It consists of a small (2 X 5 mm) strip cut from the posterior wall of the eye and thereby keeps the sclera, pigment epithelium and neural retina in place. Initial results are presented here for two vertebrates: the turtle, Pseudemys scripta elegans, and the toad, Bufo marinus. With conventional microscopy, the histological layers of the retina can be resolved, as well as individual photoreceptors, to provide landmarks for intracellular recording. When superfused, the eyecup slice remains in good condition for many hours and yields intracellular recordings of good quality and stability. Recordings of the light-evoked responses of cones and horizontal cells show that the slice is large enough to preserve the characteristic spatial interactions mediated by the laterally coursing neural networks of the distal retina. Recordings from rods show that full dark adaptation is achieved. Thus, photochemical dark adaptation as well as other normal cellular interactions between the neural retina and pigment epithelium can be preserved in this preparation, in contrast to isolated retinal slice preparations. The eyecup slice preparation might be particularly useful for work on mammalian retinas.

Adaptation, Physiological↗