Horizontal Cells In Carp Retina Research Articles

NMDA modulation of GABA transporter current in carp retinal horizontal cells

In the present study, the modulatory effect of NMDA on GABA transporter current was investigated on enzymatically isolated horizontal cells of carp retina. After application of NMDA (0.1 mM) for 50 s, the GABA transporter current elicited by GABA (1 mM) was decreased to 78.07 ± 3.10% ( n = 5) of the control level. When the extracellular Ca 2+ was removed from the Ringer's solution, the NMDA inhibitory effect on the GABA transporter current was eliminated. The suppression effect could be attenuated when the Ca 2+ release and Ca 2+ uptake of intracellular Ca 2+ store were blocked after the cell had been pre-incubated with 20 μM ryanodine plus 2 μM thapsigargin. Application of 10 mM BAPTA in intracellular solution also suppressed the NMDA modulation of GABA transporters. These results suggest that the activation of NMDA receptors inhibits GABA transporter-mediated current by affecting Ca 2+ processes in the retinal horizontal cells.

Strongly pH-Buffered Ringer's Solution Expands the Receptive Field Size of Horizontal Cells in the Carp Retina

By intracellular recordings, we studied the effects of pH buffering on the size of the receptive field and the extent of dye coupling of horizontal cells (HCs) in the light-adapted carp retina. These parameters were compared between data obtained in fortified Ringer's solution and those obtained in control bicarbonate Ringer's of the same pH (7.60). In Ringer's fortified with 10 mM HEPES or 15 mM Tris, the dye-coupling ratio of HCs increased by 71% and 70%, respectively. These fortified Ringer's solutions also depolarized the dark membrane potential and increased the light-evoked response. The HC receptive field profile could be described by the exponential decline in peak response amplitude to a slit of light moved tangentially from the recording electrode. Thus, the receptive field size was determined as a space constant proportional to (gj/gm)(1/2), where gj and gm denote gap and non-gap-junctional conductances. The HEPES- or Tris-fortified Ringer's significantly increased the space constant by 43% and 41%, respectively. Since dye coupling was increased in the fortified Ringer's, it is likely that gj increased more than gm as a result of alkalinization of the cytosol. Since HEPES has an aminosulfonate moiety, it has been assumed to close the hemi-channels of connexin 26, but the pH-buffering effects were essentially the same as those of Tris that has no aminosulfonate moiety. Therefore, it is unlikely that the closure of connexin 26 hemichannels is responsible for the change in the receptive field size of HCs.

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.

Modeling the pre- and post-synaptic components involved in the synaptic modification between cones and horizontal cells in carp retina

In retinal synapses between cones and luminosity type horizontal cells (LHC), it was previously found in this laboratory that repetitive red flashes progressively strengthened the LHC's response to red flash, whereas weakened the LHC's response to green flash; repetitive green flash remarkably depressed the LHC's red response, but caused little changes in the cell's green response. However, the detailed mechanisms underlying these phenomena are not entirely clear. In the present study, based on an ion-channel model described mainly in the form of Hodgkin-Huxley equations, possible mechanisms of the short-term synaptic modification are investigated. The simulation results suggest that: (1) the auto-enhancement effect might be induced by the Ca2+-dependent process on the post-synaptic AMPA receptors, which could lead to changes of the ionic channel's properties; (2) the asymmetric response to red- and green-flashes and the mutual-chromatic suppression effects might be attributed to the regulatory effects on the presynaptic glutamate release.

Functional N-Methyl-D-Aspartate Receptors Are Expressed in Cone-Driven Horizontal Cells in Carp Retina

Glutamate works as a major excitatory neurotransmitter in the vertebrate retina. Whole-cell recordings made from isolated carp cone horizontal cells (H1 cells) showed that N-methyl-D-aspartate (NMDA), co-applied with glycine, induced inward currents that were blocked by the NMDA receptor competitive antagonist D-2-amino-5-phosphonopentanoate (D-AP5) and 5,7-dichlorokynurenic acid (DCKA), a selective NMDA receptor antagonist acting at the glycine site on the NMDA receptor complex. Moreover, calcium imaging showed that NMDA caused a significant elevation of intracellular calcium levels ([Ca²⁺]_i) of H1 cells, which was also blocked by D-AP5. In contrast, neither inward currents nor changes in [Ca²⁺]_i could be induced by NMDA in rod horizontal cells (H4 cells). Intracellular recordings made from H1 cells in the isolated retina, superfused with Ringer’s containing 1 mM Mg²⁺, in the dark demonstrated that NMDA reduced the light-off overshoot of H1 cells. We therefore conclude that the functional NMDA receptor is expressed in carp H1 cells, from which this receptor has been thought to be absent, and this receptor may play a role in modulating cone-driven signal of horizontal cells in the dark.

Ca2+-permeable and Ca2+-impermeable AMPA receptors coexist on horizontal cells

Fura-2 fluorescent calcium imaging was used for analyzing the subtype of AMPA receptors in freshly dissociated horizontal cells of carp retina. Exogenous application of AMPA induced an increase of intracellular concentration of free Ca2+ ([Ca2+]i) in horizontal cells, while the [Ca2+]i increase was partly inhibited by nifedipine. The residual [Ca2+]i increase was completely eliminated by joro spider toxin-3, a blocker of Ca2+-permeable AMPA receptors. On the other hand, the application of pentobarbital, which blocked Ca2+-impermeable AMPA receptors, could also partly inhibit the increase of [Ca2+]i, implying that the application of AMPA induced the activation of both Ca2+-permeable and Ca2+-impermeable AMPA receptors and the consequent activation of voltage-gated Ca2+ channels. Taken together, these results suggested that Ca2+-permeable and Ca2+-impermeable AMPA receptors were coexpressed on horizontal cells.

Role of Ca2+ store in AMPA-triggered Ca2+ dynamics in retinal horizontal cells

Fura-2 fluorescent calcium imaging was applied to measure [Ca(2+)](i) in freshly dissociated horizontal cells of carp retina, and a model containing endoplasmic reticulum (ER) membrane processes and plasma membrane processes was constructed for quantitative analyses of the AMPA-triggered calcium dynamics. A transient increase followed by a sustained steady level of [Ca(2+)](i) was observed when 100 microM AMPA was applied, while the initial transient increase of [Ca(2+)](i) was suppressed by exogenously applied ryanodine. The model analyses results suggest that the AMPA-triggered calcium dynamics involves a number of cytoplasmic and endoplasmic processes that interact with each other. It also suggests that calcium store is an important part contributing to the transient calcium signal.

Dopamine effect on the stimulus pattern related changes in response characteristics of R/G horizontal cells in carp retina

Repetitive red flashes increased the R/G horizontal cells’ red response amplitude and induced a hyperpolarization of the cells’ dark membrane potential. These phenomena were eliminated in 6-OHDA pretreated retinas and restored by exogenous dopamine, which suggests the involvement of dopamine receptor activity changes instead of dopamine release changes. Furthermore, the phenomena persisted on D 1 receptor antagonist (SKF-83566) application, whereas they diminished on D 2 receptor antagonist (eticlopride) application, indicating that the mechanism is related to a D 2 receptor, possibly located on photoreceptors.

Zn 2+ differentially modulates signals from red- and short wavelength-sensitive cones to horizontal cells in carp retina

The effects of Zn 2+ were studied while recording intracellularly from L-type horizontal cells (LHCs) in the isolated, superfused carp retina. In darkness, 25 μM Zn 2+ hyperpolarized LHCs and potentiated responses of these cells to 500 nm flashes, but decreased those to 680 nm flashes. Zn 2+ did not change photopic electroretinographic P III responses. The differential modulation by Zn 2+ persisted when the Zn 2+-induced membrane hyperpolarization was compensated by lowering Ca 2+ concentration in the perfusate, but it was abolished in the presence of background illumination. Furthermore, the differential modulation no longer existed in the presence of bicuculline, suggesting the involvement of γ-aminobutyric acid A (GABA A) receptors. We speculate that the differential modulation may be a consequence of multiple changes caused by Zn 2+. Decreased glutamate release from the cone terminal by Zn 2+ results in a reduction of cone signals. Zn 2+ antagonizes GABA receptors on LHCs, leading to cone signal reduction. On the other hand, Zn 2+ may reduce the strength of the negative feedback from LHCs to cones by downregulating the activity of GABA receptors on the cone terminal, which causes a potentiation of LHC light responses. Cone- or wavelength-relevance of the Zn 2+-induced feedback strength change may account for the differential modulation.

Stimulus pattern related plasticity of synapses between cones and horizontal cells in carp retina.

Stimulus pattern related synaptic plasticity in the luminosity-type horizontal cell (LHC) of isolated carp retina was investigated. The major findings were: (1) repetitive red flashes progressively strengthened the synaptic connection between red-cone and LHC, whereas weakened that between green-cone and LHC; (2) repetitive green flashes remarkably depressed the LHC's red response, but caused little changes in the cell's green response. A competitive depression between different cone signals is suggested.

Suppression of spontaneous EPSCs on H1 horizontal cells in carp retina by a metabotropic glutamate receptor agonist

Suppression of spontaneous EPSCs on H1 horizontal cells in carp retina by a metabotropic glutamate receptor agonist

Effects of nitric oxide, light adaptation and APB on spectral characteristics of H1 horizontal cells in carp retina.

The spectral characteristics of cone-driven horizontal cells of H1 subtype (H1 HCs) receiving main synaptic input from red-sensitive cones were studied in light- and dark-adapted retinae of carp. The spectral sensitivity profile of H1 HCs in dark-adapted retinae was practically the same as the absorption spectrum of red-sensitive cones. Light-adaptation decreased the sensitivity preferentially in the short-wavelength (blue/green) region, resulting in a relative enhancement of the 617 nm peak. Application of nitric oxide (NO) donors, sodium nitroprusside (SNP) and S-nitrosoglutathione (SNOG or GSNO), or dopamine to dark-adapted retinae decreased the sensitivity preferentially in blue/green region, an effect similar to that of light-adaptation. Application of haemoglobin (Hb, an NO scavenger) or 2-amino-4-phosphonobutyrate (APB, a metabotropic glutamate receptor agonist), to light-adapted retinae increased the sensitivity preferentially in the blue/green region, an effect similar to dark-adaptation. The photoresponses of H1 HCs were univariant in dark-adapted retinae as well as Hb-treated light-adapted retinae. In light-adapted retinae with normal Ringer, however, the univariance did not hold. These results suggested that the photoresponses of H1 HCs to short-wavelength stimuli contain a depolarising (sign-reversing) component, which can be activated by light-adaptation or application of NO and dopamine, and inactivated by dark-adaptation or deprivation of NO or application of APB.

Glutathione depletion causes an uncoupling effect on retinal horizontal cells through oxidative stress

To investigate a physiological role of glutathione in the horizontal cells of carp retina, the gap junctional intercellular communication between horizontal cells was studied using the techniques of intracellular recording of light-induced responses and coupling of the fluorescence dye Lucifer Yellow. Intravitreal injection of 2.5 μmol l-buthionine sulfoximine, an inhibitor of glutathione synthesis, induced a dramatic reduction (20% of control) of retinal glutathione level two days after treatment. The low level of glutathione continued for a further four to five days, and thereafter gradually recovered to about 40% (20 days after injection) and 70% (50 days after injection) of the control level. The spatial properties of the photopic L-type horizontal cell response were examined by enlarging the diameter of the central spot and peripheral annulus over the recording point. In normal retinas, the response amplitude of horizontal cells was monotonically enhanced as the diameter of the spot increased (0.5–4.0 mm) and correspondingly the dye diffusion area was wide, as the injected Lucifer Yellow normally diffused to several neighboring cells. Treatment with l-buthionine sulfoximine significantly altered the spatial properties of horizontal cells by increasing the response amplitude to central spots and slightly decreasing that to peripheral annuli, which were observed by four days after injection. It also restricted intracellular Lucifer Yellow to one or two cells. Accompanying the recovery of the cellular level of glutathione, the spatial properties and dye coupling of horizontal cells were restored to normal. A time lag (two days) of initiation in retinal glutathione depletion and alteration of spatial or dye coupling properties of horizontal cells is discussed, together with reactive oxygen species accumulation.

Modulation of chromatic difference in receptive field size of H1 horizontal cells in carp retina: dopamine- and APB-sensitive mechanisms

Chromatic aspects of receptive field size in the H1 horizontal cell syncytium of the carp retina were investigated using spectral photostimuli (blue or red) presented in the form of either a pair of a small spot and annulus, or a narrow moving slit. In the light-adapted retina, the receptive field for the blue stimulus was found to be significantly smaller than that for the red, i.e. there was a chromatic difference in the receptive field size. During the course of dark adaptation, the overall receptive field size increased, but the chromatic difference decreased. Immediately after adaptation to bright light, the receptive field sizes were reduced significantly, but the chromatic difference increased, mainly due to a greater reduction in the receptive field for the blue stimulus. Application of dopamine (5 μM) to a dark-adapted retina gradually decreased the receptive field size for both colours, but the chromatic difference became larger, again due to a greater reduction in the receptive field size for the blue stimulus. 2-Amino-4-phosphonobutyrate (APB) applied to light-adapted retinae at a working concentration of 1 mM, greatly expanded the receptive field size and suppressed the chromatic difference due to the effect being greater for the receptive field for the blue stimulus. The effect of APB was slow and cumulative. On the other hand, intracellular injection of cGMP or dibutyryl-cGMP increased the chromatic difference in the receptive field size. It is suggested (i) that the chromatic difference in the receptive field size could be due to a cGMP-coupled, conductance-decreasing receptor mechanism activated by APB; and (ii) that the mechanism is associated with short-wavelength sensitive cone input to the H1 cells and operates in the light-adapted state of the retina.

Chromatic difference of postsynaptic current in H1 horizontal cells in carp retina

Chromatic difference of postsynaptic current in H1 horizontal cells in carp retina

Spectral plasticity of H1 horizontal cells in carp retina: independent modulation by dopamine and light-adaptation.

It was shown previously that the spectral sensitivity of luminosity/H1-type horizontal cells (HCs) in carp retinae reflects the absorption spectrum of red-sensitive cones for long wavelengths but can appear highly variable and "truncated' in the short-wavelength region of the spectrum. We have found that light-adaptation sharpened the red-sensitive spectral peak and decreased the blue/red response amplitude ratio (B/R ratio), mainly by decreasing the response to short-wavelength stimuli. The adaptation effect was more pronounced for red background light than for blue. During dark adaptation, the B/R ratio increased steadily. Exogenous dopamine (DA; 5 microM) changed the spectral response profile in a similar way to light-adaptation. However, the effect of light-adaptation in reducing the B/R ratio was still seen in retinae bathed in 5 microM DA. This effect of background adaptation was also recorded in retinae bathed in 37 microM haloperidol, as well as in retinae pretreated with 6-hydroxydopamine (i.e. DA-depleted). The results suggest that (i) short-wavelength-sensitive cones play a dynamic role in determining the spectral response profile of H1 HCs and (ii) spectral response characteristics are modulated independently by exogenous DA and an unknown endogenous neuromodulator which is activated by light-adaptation.

The short and long-term effects of temperature on the dynamic range of signalling in horizontal cells of carp retina

1. 1. Intracellular recordings of luminosity horizontal cell responses were made from retinas isolated from carp ( Cyprinus carpio) acclimated for at least three weeks to temperatures of 8, 16 and 26°C. 2. 2. Changing the temperature of the isolated retina resulted in an increase in the rate of rise and fall phases of horizontal responses and a reduction of response latency as temperature increased. 3. 3. The maximum amplitudes ( V max) of horizontal cell responses were reduced for low and high temperatures with a small, intermediate range over which the largest values of V max were recorded. 4. 4. The range of temperatures for which V max was maximum was found to be dependent on the temperature of acclimation in an adaptive manner.

Nitric oxide sharpens spectral sensitivity of H1 horizontal cells in carp retina

Nitric oxide sharpens spectral sensitivity of H1 horizontal cells in carp retina

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)

Dopamine decreases receptive field size of rod-driven horizontal cells in carp retina

Receptive field size of rod-driven horizontal cells (HCs) in the carp retina was measured by the spread of responses to the slit of light stimulus with changing the distance from the recording electrode and it was found to decay with a single exponential function. By perfusing 10 μM dopamine (DA) the length constant of rod-driven HCs was reduced to half and the response amplitude in the centre increased approximately two-fold, and the input resistance was markedly increased. This suggests that DA as a neuromodulator released from interplexiform cells could decouple the rod-driven HCs which had no direct synaptic contact with the interplexiform cells.