[Proceedings: Effect of glutamate on retinal horizontal cells].
Explore the source record for details and available documents.
Animals↗
SEARCH · PubMed Health
Results for “Retinal Horizontal Cells”
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
[Submicroscopic morphology and structural interrelations of receptor and horizontal retinal cells in a series of lower vertebrates].
Explore the source record for details and available documents.
Animals↗
[Ionic mechanisms of the nonlinearity of retinal horizontal cell membranes].
Changes in ionic conductivity underlying the nonlinearity a voltage-current curve of the nonsynaptic membrane of horizontal cells were investigated in experiment on goldfish and turtle retina. The measurements were made under conditions when conductivity of a subsynaptic membrane was minimal, i.e. when the retina was illuminated with bright light or synaptic transmission from photoreceptors was blocked with Co2+. An increase in [K+] led to depolarization and diminution os steepness i a hyperpolarizing part of the voltage-current curve; a decrease in K+ evoked an opposite effect. A decrease in [C1-] did not change both the membrane potential and the shape of the voltage-current curve. Substitution of Na+ by tris or choline did not evoke a reliable change in the membrane potential, and produce only a slight change in the shape of he current-voltage curve. It is concluded that the membrane is permeable for K+; permeability for C1- is absent or small; permeability for Na + is small too. Ba2+ (2-5 mM) increased the steepness of the hyperpolarizing part of the voltage current curve, and the curve became more linear. It is concluded that the nonlinearity is determined mainly by potential-dependent k+-channels whose conductivity increases with hyperpolarization, and Ba2+ blocks this increase in permeability. An increase in Ca2+ from 1 to 20 mM enhanced the steepness of the depolarizing part of the voltage-current curved without altering the hyperpolarizing part. It is supposed that the horizontal cell membrane has potential-dependent Ca2+- channels whose conductivity increases with depolarization.
Animals↗
[Study of the electrical properties of retinal horizontal cell syncytia by the technic of uniform polarization].
For uniform polarization of syncytial or cable structures at a large area with current passed via extracellular electrodes the extracellular longitudinal gradient of potential must be proportional to distance from the edge of preparation. In this paper the profile of conducting plate was found analytically which allows to obtain such a distribution of potentials. The profile is formed by hyperbola and its orthogonal asymptotes. Two polarizing electrodes are applied to places where the hyperbola is near to asymptotes. On the surfaces formed by asymptotes the gradient of potential is proportional to distance from intersection of these surfaces. Such a conducting plate was made as cavity in plexiglas filled by Ringer solution in agar. The plate was used for obtaining the voltage-current curves of horizontal cell membrane in gold fish retina. The area of uniform polarization was 4-5 mm long. Measurements inside this area allowed to determine the space constant of horizontal cell layer. The space constant measured in bright light (when resistance of subsynaptic membrane is high) depends on the membrane potential, being high (approximately 1,5 mm) during depolarization and low (0,2-0,4 mm) during hyperpolarization.
Animals↗
Two components of GABA-induced currents in catfish retinal horizontal cells.
In cone-driven horizontal cells dissociated from the catfish retina, we recorded GABA-induced currents by using a whole-cell voltage-clamp technique. The current consisted of two components. The major component was blocked by picrotoxin, but not by bicuculline, and was identified as a current flowing through the GABAC receptor channel. The second minor component was identified as a current carried by an electrogenic GABA transporter.
Animals↗
Retinal horizontal cells: old cells, old experiments, new results.
The study of neural interactions in the vertebrate retina carried out after the pioneering studies of Svaetichin has provided important information on the functioning of nerve circuits in the central nervous system. Recently we have investigated the effects of changes of divalent cation concentration on the synaptic transmission between cones and horizontal cells of the turtle retina. Our results seemed apparently in contrast with the classical Ca2(+)-hypothesis of chemical synaptic transmission. Application of low Ca2+ media resulted in a recovery of synaptic transmission after application of divalent cations such as Ca2+, Zn2+ and Ni2+ traditionally considered as Ca2+ channel antagonists. Moreover, in the absence of exogenous divalent cations, low Ca2+ could result in an increase of transmitter release particularly if Mg2+ was omitted from the perfusing medium. These apparently paradoxical results can be reconciled with the postulates of the Ca2(+)-hypothesis of synaptic transmission by taking into account the effects of divalent cations on the fixed charges present at the external surface of cell membrane. It is possible that a similar interpretation could also account for the so-called "Ca2(+)-independent" transmission in other structures of the nervous system.
Animals↗
Antibody to keyhole limpet hemocyanin labels retinal horizontal cells in some amphibians, but not in others.
Antibody to keyhole limpet hemocyanin (KLH) reacts with putative horizontal cells in anuran amphibians of the superfamily Bufonoidea. The reactive epitope appears to be located on the cell membrane. No KLH-like immunoreactivity was observed in the outer plexiform layer (OPL) of anurans not members of this superfamily, nor in the OPL of urodeles or other vertebrates. Thus KLH-like immunoreactivity in the OPL provides a tool for assessing phylogenetic relationships within anurans.
Amphibians↗
Afferents and homotypic neighbors regulate horizontal cell morphology, connectivity, and retinal coverage.
Horizontal cells are inhibitory interneurons with laterally oriented dendrites that overlap one another, contacting the pedicles of cone photoreceptors. Because of their regular spacing, the network of horizontal cells provides a uniform coverage of the retinal surface. The developmental processes establishing these network properties are undefined, but cell-intrinsic instructions and interactions with other cells have each been suggested to play a role. Here, we show that the intercellular spacing of horizontal cells is essentially independent of genetic background and is predicted by local density, suggesting that horizontal cell positioning is modulated by proximity to other horizontal cells. Dendritic field area compensates for this variation in intercellular spacing, maintaining constant dendritic coverage between strains. Functional dendritic overlap is achieved anatomically at the level of the pedicles, where horizontal cells interact with one another to establish their connectivity: the number of dendritic terminals contacting a pedicle changes, reciprocally, between neighboring horizontal cells during development based on their relative proximity to each pedicle. Cellular morphology is also shown to be regulated by the afferents themselves: afferent elimination before innervation does not alter dendritic field size nor stratification but compromises dendritic branching and prevents terminal formation. Afferent and homotypic interactions therefore generate the morphology, spacing, and connectivity of horizontal cells underlying their functional coverage of the retina.
Animals↗
Dark- and light-induced changes in coupling between horizontal cells in mammalian retina.
Retinal horizontal cells exhibit large receptive fields derived from their extensive electrical coupling by means of gap junctions. The conductance of these gap junctions seems to be regulated by dopamine acting through a cAMP-mediated cascade. There is now abundant evidence that extracellular dopamine levels vary with changes in ambient light intensity, suggesting that changes in the dark/light adaptational state of the retina can modulate coupling between horizontal cells. We studied this question in the mammalian retina by determining the effects of ambient light levels, in the form of changing background light intensity, on the coupling profiles of A- and B-type horizontal cells in the rabbit. Changes in coupling were assessed by measurements of the space constants of the syncytium formed by horizontal cells and the intercellular spread of the biotinylated tracer Neurobiotin. Our results indicate that dark-adapted horizontal cells show relatively weak coupling. However, presentation of background lights as dim as one-quarter log unit above rod threshold resulted in increases in both the averaged extent of tracer coupling and space constants of A- and B-type horizontal cells. Coupling expanded further as background light intensities were increased by 1-1.5 log units, after which additional light adaptation brought about an uncoupling of cells. Coupling reached its minimum at light intensities about 3 log units above rod threshold, after which, with further light adaptation, it stabilized at levels close to those seen in dark-adapted retinas. Our results indicate that electrical coupling between mammalian horizontal cells is modulated dramatically by changes in the adaptational state of the retina: coupling is maximized under dim ambient light conditions and diminishes as the retina is dark or light adapted from this level.
Adaptation, Ocular↗
Effects of nitric oxide on horizontal cells in the rabbit retina.
Retinal horizontal cells display large receptive fields as a result of extensive electrical coupling via gap junctions. There is abundant evidence that these gap junctions are dynamically regulated by changes in the adaptational state of the retina. The neuromodulator dopamine appears to play a major role in regulating gap junctional conductances of horizontal cells. Emerging evidence indicates that nitric oxide (NO) also acts as a neuromodulator in the retina and, more specifically, regulates the coupling between horizontal cells. In the present study, we examined the effects of a nitric oxide, and its secondary messenger cGMP, on electrical and tracer coupling between A-type and between B-type horizontal cells in the rabbit retina. Application of the NO donors S-nitroso-N-acetylpenicillamine (SNAP) or sodium nitroprusside (SNP) significantly reduced the coupling between horizontal cells as evidenced by a decrease in their space constants, annulus-to-small spot response ratios, and the extent of tracer coupling following injection with Neurobiotin. Further, application of SNP eliminated the increase in coupling of horizontal cells normally seen with exposure to dim background illumination. Application of 8-bromo-cGMP produced effects similar to those of the NO donors, consistent with the idea that the uncoupling actions of NO were mediated via a cGMP cascade. In addition, the NO donors and cGMP augmented the responsiveness of A- and B-type cells to both small and large spots of light. This augmentation appeared to be due to secondary effects on photoreceptor transduction and/or photoreceptor-to-horizontal cell synaptic efficacy that were distinct from the actions on gap junctions. Our results suggest that NO may mediate changes in coupling between horizontal cells related to the adaptational state of the mammalian retina.
Adaptation, Ocular↗
A comparison of release kinetics and glutamate receptor properties in shaping rod-cone differences in EPSC kinetics in the salamander retina.
Synaptic transmission from cones is faster than transmission from rods. Using paired simultaneous recordings from photoreceptors and second-order neurones in the salamander retina, we studied the contributions of rod-cone differences in glutamate receptor properties and synaptic release rates to shaping postsynaptic responses. Depolarizing steps evoked sustained calcium currents in rods and cones that in turn produced transient excitatory postsynaptic currents (EPSCs) in horizontal and OFF bipolar cells. Cone-driven EPSCs rose and decayed faster than rod-driven EPSCs, even when comparing inputs from a rod and cone onto the same postsynaptic neurone. Thus, rod-cone differences in EPSCs reflect properties of individual rod and cone synapses. Experiments with selective AMPA and KA agonists and antagonists showed that rods and cones both contact pharmacologically similar AMPA receptors. Spontaneous miniature EPSCs (mEPSCs) exhibited unimodal distributions of amplitude and half-amplitude time width and there were no rod-cone differences in mEPSC properties. To examine how release kinetics shape the EPSC, we convolved mEPSC waveforms with empirically determined release rate functions for rods and cones. The predicted EPSC waveform closely matched the actual EPSC evoked by cones, supporting a quantal release model at the photoreceptor synapse. Convolution with the rod release function also produced a good match in rod-driven cells, although the actual EPSC was often somewhat slower than the predicted EPSC, a discrepancy partly explained by rod-rod coupling. Rod-cone differences in the rates of exocytosis are thus a major factor in producing faster cone-driven responses in second-order retinal neurones.
Animals↗
A comparison of receptive field and tracer coupling size of horizontal cells in the rabbit retina.
The large receptive fields of retinal horizontal cells are thought to reflect extensive electrical coupling via gap junctions. It was shown recently that the biotinylated tracers, biocytin and Neurobiotin, provide remarkable images of coupling between many types of retinal neuron, including horizontal cells. Further, these demonstrations of tracer coupling between horizontal cells rivaled the size of their receptive fields, suggesting that the pattern of tracer coupling may provide some index of the extent of electrical coupling. We studied this question by comparing the receptive field and tracer coupling size of dark-adapted horizontal cells recorded in the superfused, isolated retina-eyecup of the rabbit. Both the edge-to-edge receptive field and space constants (lambda) were computed for each cell using a long, narrow slit of light displaced across the retinal surface. Cells were subsequently labeled by iontophoretic injection of Neurobiotin. The axonless A-type horizontal cells showed extensive, homologous tracer coupling in groups greater than 1000 covering distances averaging about 2 mm. The axon-bearing B-type horizontal cells were less extensively tracer coupled, showing homologous coupling of the somatic endings in groups of about 100 cells spanning approximately 400 microns and a separate homologous coupling of the axon terminal endings covering only about 275 microns. Moreover, we observed a remarkable, linear relationship between the size of the receptive fields of each of the three horizontal cell endings and the magnitude of their tracer coupling. Our findings suggest that the extent of tracer coupling provides a strong, linear index of the magnitude of electrical current flow, as derived from receptive-field measures, across groups of coupled horizontal cells. These data thus provide the first direct evidence that the receptive-field size of horizontal cells is related to the extent of their coupling via gap junctions.
Animals↗
Acidification decouples gap junctions but enlarges the receptive field size of horizontal cells in carp retina.
The receptive field size of retinal horizontal cells is much larger than their dendritic field size due to gap junctional coupling between the same sub-types of cell. Thus, horizontal cells form syncytia by electrical coupling. The basic receptive field profile of horizontal cells can be described by an exponential function based on measurement of responses to a slit of light moved tangentially from a recording electrode. The space constant of this exponential function is proportional to (g(s)/g(m))(1/2), where g(s) and g(m) represent gap junctional conductance and non-gap junctional conductance, respectively. Acidifying the superfusing solution by lowering the pH from 7.60 to 7.30 decreased the dye-coupling, hyperpolarised the resting membrane potential and reduced the photoresponses of H1 type horizontal cells. Surprisingly, however, the receptive field size expanded significantly. Raising the pH from 7.30 to 7.60 or 7.90 produced opposite effects. These results were consistent with alkaline extracellular pH producing a greater increase in g(m) than in g(s) and enhancing release of transmitter from cones acting upon horizontal cells.
Animals↗
Adult human retinal neurons in culture: Physiology of horizontal cells.
PURPOSE: Adult postmortem human retinal neurons in long-term monolayer cultures were recorded to characterize the voltage- and transmitter-gated currents in putative human horizontal cells (HCs). METHODS: Enzymatically and mechanically dissociated human retinal cells were seeded on polylysine and laminin- coated coverslips. Cells were identified by immunocytochemistry with cell type-specific antibodies and recorded with the patch-clamp technique. RESULTS: Immunostaining and responses to voltage steps confirmed the survival of various retinal cell types. Horizontal cells were identified by their specific glutamate-modulated anomalous rectifier K+ current conductance. This identification was further confirmed by subsequent immunolabeling of dye-labeled recorded cells with an anti-parvalbumin antibody that selectively stained HCs in frozen human retinal sections. Horizontal cells generated voltage-gated currents classically observed in HCs from fish to mammals: a transient outward K+ current, a sustained outward K+ current, and an L-type (Ca2+ current. Na+ currents were observed in only a few HCs. As in other species, glutamate, gamma-aminobutyric acid (GABA), and glycine generated responses mediated by the activation of kainate/(RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), GABA(A), and glycine receptors, respectively. CONCLUSIONS: Various human retinal cell populations survive in vitro as indicated by immunolabeling with specific cell markers and by the diversity of responses to voltage steps. Human HCs exhibited extensive physiological similarities to HCs from other vertebrate species and a maintained expression of parvalbumin. These results constitute a comprehensive analysis of voltage- and transmitter-gated currents in a primate retinal neuron and validate the use of long-term monolayer culture of adult human neurons as a novel in vitro model for the study of human vision.
Aged↗
Blocking AMPA receptor desensitization prolongs spontaneous EPSC decay times and depolarizes H1 horizontal cells in carp retinal slices.
Desensitization of H1 horizontal cell (H1 HC) glutamate receptors was investigated in carp retinal slices using cyclothiazide (CTZ), an inhibitor of AMPA receptor desensitization. 100 microM CTZ depolarized H1 HCs and increased the amplitude of light responses, without any prominent changes in their kinetics. Spontaneous EPSCs (sEPSCs) in H1 HCs were observed in the presence of 2.5 mM heptanol, an uncoupling agent of gap junctions. 20 microM GYKI52466 (an AMPA receptor antagonist) blocked the sEPSCs, consistent with the sEPSCs being mediated by AMPA receptors. 100 microM cobalt suppressed the frequency of sEPSCs without changing their mean peak amplitude, suggesting that calcium-dependent transmitter release from cones was not affected by heptanol. CTZ increased the total inward charge transferred per sEPSC by increasing the sEPSC decay time constant twofold, without any significant change in their frequency and mean peak amplitude. This suggests that the depolarizing effect of CTZ on H1 HCs was due to blocking desensitization of AMPA receptors, increasing the inward current induced by glutamate released from cone synaptic terminals. The desensitization of glutamate receptors may function to extend the dynamic range of H1 HC light responses.
Animals↗
Voltage-gated currents of rabbit A- and B-type horizontal cells in retinal monolayer cultures.
In monolayer cultures prepared from immature early postnatal rabbit retina, small populations of neurons can be demonstrated to differentiate into apparently mature A- and B-type horizontal cells. Using whole-cell, single-channel, patch-clamp recording techniques, we have analyzed the pattern of voltage-gated conductances expressed by mammalian horizontal cells under these conditions. A total of six different voltage-dependent ionic currents were recorded. Tetrodotoxin-sensitive fast sodium inward currents (INa) were found in 81% of the A-type and 90% of the B-type cells. Inward calcium currents could be demonstrated in all cells tested after blockade of other conductances. Two types of outward potassium currents with properties of the 4-aminopyridine-sensitive transient IA and the tetraethylammonium sensitive delayed rectifier IK, respectively, could be characterized in whole-cell recordings. An inward rectifying potassium current (Ianom) typical for horizontal cells was activated in response to hyperpolarizing voltage steps. These types of currents have also been described in dissociated adult horizontal cells from lower vertebrates and cat. With single-channel recordings on inside-out patches excised from B-type cells, an additional Ca(2+)-dependent current (IK(Ca)) was observed which, so far, has not been described in horizontal cells developing in situ. Our results demonstrate that cultured rabbit horizontal cells express a set of voltage-gated currents which largely, but not completely, corresponds to that described in situ for horizontal cells of other species. The culture system will allow further investigation of developmental and functional aspects of mammalian horizontal cells.
Animals↗
A non-canonical photopigment, melanopsin, is expressed in the differentiating ganglion, horizontal, and bipolar cells of the chicken retina.
Vertebrate melanopsin is a photopigment in the eye, required for photoentrainment. Melanopsin is more closely related to opsin proteins found in invertebrates, than to the other photo-pigments. Although the invertebrate melanopsin-like protein is localized in rhabdomeric photoreceptors in the invertebrate eye, it has been shown to be expressed in a subset of retinal ganglion cells in the mouse and in horizontal cells in the frog, indicating its diversified expression pattern in vertebrates. Here we show that two types of melanopsin transcripts are expressed in the developing chicken retina. Melanopsin is firstly expressed by a small subset of ganglion cells, and then prominently expressed by horizontal cells and later by bipolar cells in the developing chicken retina. This suggests that a subset of ganglion, horizontal, and bipolar cells in the chicken retina may have rhabdomeric properties in their origins.
Amino Acid Sequence↗
Foxn4 controls the genesis of amacrine and horizontal cells by retinal progenitors.
During vertebrate retinogenesis, seven classes of cells are specified from multipotent progenitors. To date, the mechanisms underlying multipotent cell fate determination by retinal progenitors remain poorly understood. Here, we show that the Foxn4 winged helix/forkhead transcription factor is expressed in a subset of mitotic progenitors during mouse retinogenesis. Targeted disruption of Foxn4 largely eliminates amacrine neurons and completely abolishes horizontal cells, while overexpression of Foxn4 strongly promotes an amacrine cell fate. These results indicate that Foxn4 is both necessary and sufficient for commitment to the amacrine cell fate and is nonredundantly required for the genesis of horizontal cells. Furthermore, we provide evidence that Foxn4 controls the formation of amacrine and horizontal cells by activating the expression of the retinogenic factors Math3, NeuroD1, and Prox1. Our data suggest a model in which Foxn4 cooperates with other key retinogenic factors to mediate the multipotent differentiation of retinal progenitors.
Age Factors↗