scholarly journals Simulation of the Ephaptic Effect in the Cone--Horizontal Cell Synapse of the Retina

2013 ◽  
Vol 73 (2) ◽  
pp. 636-648 ◽  
Author(s):  
Carl L. Gardner ◽  
Jeremiah R. Jones ◽  
Steven M. Baer ◽  
Shaojie Chang
Keyword(s):  
Horizontal Cell ◽  
Cell Synapse ◽  
Ephaptic Effect

Photoreceptor to horizontal cell synaptic transfer in the Xenopus retina: modulation by dopamine ligands and a circuit model for interactions of rod and cone inputs

1989 ◽  
Vol 62 (4) ◽  
pp. 864-881 ◽  
Author(s):  
P. Witkovsky ◽  
S. Stone ◽  
D. Tranchina
Keyword(s):  
Horizontal Cell ◽  
Freeze Fracture ◽  
Circuit Model ◽  
Variable Degree ◽  
Cell Transfer ◽  
D2 Agonist ◽  
D1 Agonist ◽  
D2 Antagonists ◽  
Kinetics Of ◽  
Cell Synapse

1. In the Xenopus retina, the effects of selective D1 and D2 dopamine ligands on photoreceptor to horizontal cell transfer were studied by intracellular recording from horizontal cell axons. Rod and cone inputs to the horizontal cell were estimated by adjusting the intensities of red and green flashes to elicit equal rod tails. The resultant waveforms were digitized and subtracted, and their difference was taken to reflect solely cone input to the horizontal cell. 2. It was found that both D1 (SKF 38393) and D2 (LY 171555) agonists increased the amplitude and quickened the kinetics of cone-to-horizontal cell transfer; they also depolarized the horizontal cell by 8-10 mV. In contrast, either D1 or D2 agonists reduced the rod input to the horizontal cell without altering its kinetics. 3. Type D2 antagonists reduced and slowed the cone input and hyperpolarized the horizontal cell. D2 antagonists increased the rod input but left its kinetics unchanged. 4. Although both D1 and D2 agonists elicited qualitatively similar effects, the D1 agonist evoked a greater increase in the amplitude and a greater acceleration of the kinetics of the cone input than did the D2 agonist. Moreover, the action of the D1 agonist was blocked by SCH 23390 but not by spiroperidol or metoclopramide, whereas the reverse was true for the D2 agonist. These data indicate that D1 and D2 agonists probably act at different sites. 5. The pharmacologic findings are interpreted to indicate that dopamine ligands act primarily through the cone pathway and that rod-to-horizontal cell transfer is shunted to a variable degree. 6. An equivalent circuit model was developed for a spine-bearing portion of a horizontal cell axon of the Xenopus retina. Anatomic study shows that such spines branch, making contact with both rod and cone photoreceptor bases. Thus there are two conductance pathways in parallel for rod-to-horizontal cell and cone-to-horizontal cell transmission. The model is used to test the hypothesis that mutual shunting in the two pathways can account for the physiological effects observed. 7. The values of the purely resistive elements of the pathway are based on their dimensions. Membrane resistance was taken to be 5,000 omega/cm2 and axial resistance 200 omega/cm. The photoreceptor-to-horizontal cell synaptic battery was taken to be composed of glutamate-sensitive channels, with unitary channel conductance of 6 pS. Channel density was estimated from freeze-fracture data at 5,000 microns-2. A potassium battery and a glycine-sensitive synaptic input from an interplexiform cell were modeled to exist in parallel with the light-sensitive battery. 8. Dopamine was assumed to increase the conductance of the cone-to-horizontal cell synapse, but not to affect the conductance of the rod-to-to-horizontal cell synapse, consistent with physiological measures.(ABSTRACT TRUNCATED AT 400 WORDS)

The Open- and Closed-Loop Gain-Characteristics of the Cone/Horizontal Cell Synapse in Goldfish Retina

2000 ◽  
Vol 84 (3) ◽  
pp. 1256-1265 ◽  
Author(s):  
D. A. Kraaij ◽  
H. Spekreijse ◽  
M. Kamermans
Keyword(s):  
Synaptic Transmission ◽  
Negative Feedback ◽  
Horizontal Cell ◽  
Bipolar Cells ◽  
Horizontal Cells ◽  
Strongly Nonlinear ◽  
Highly Nonlinear ◽  
Gain Characteristic ◽  
Cell Synapse ◽  
Goldfish Retina

Under constant light-adapted conditions, vision seems to be rather linear. However, the processes underlying the synaptic transmission between cones and second-order neurons (bipolar cells and horizontal cells) are highly nonlinear. In this paper, the gain-characteristics of the transmission from cones to horizontal cells and from horizontal cells to cones are determined with and without negative feedback from horizontal cells to cones. It is shown that 1) the gain-characteristic from cones to horizontal cells is strongly nonlinear without feedback from horizontal cells, 2) the gain-characteristic between cones and horizontal cells becomes linear when feedback is active, and 3) horizontal cells feed back to cones via a linear mechanism. In a quantitative analysis, it will be shown that negative feedback linearizes the synaptic transmission between cones and horizontal cells. The physiological consequences are discussed.

scholarly journals Intracellular recordings from gecko photoreceptors during light and dark adaptation.

1975 ◽  
Vol 66 (5) ◽  
pp. 617-648 ◽  
Author(s):  
J Kleinschmidt ◽  
J E Dowling
Keyword(s):  
Membrane Potential ◽  
Dark Adaptation ◽  
Horizontal Cell ◽  
Intracellular Recordings ◽  
Receptor Sensitivity ◽  
Intensity Curve ◽  
Voltage Range ◽  
Voltage Change ◽  
Sensitivity Change ◽  
Compression Treatment

Intracellular recordings were obtained from rods in the Gekko gekko retina and the adaptation characteristics of their responses studied during light and dark adaptation. Steady background illumination induced graded and sustained hyperpolarizing potentials and compressed the incremental voltage range of the receptor. Steady backgrounds also shifted the receptor's voltage-intensity curve along the intensity axis, and bright backgrounds lowered the saturation potential of the receptor. Increment thresholds of single receptors followed Weber's law over a range of about 3.5 log units and then saturated. Most of the receptor sensitivity change in light derived from the shift of the voltage-intensity curve, only little from the voltage compression. Treatment of the eyecup with sodium aspartate at concentrations sufficient to eliminate the beta-wave of the electroretinogram (ERG) abolished initial transients in the receptor response, possibly indicating the removal of horizontal cell feedback. Aspartate treatment, however, did not significantly alter the adaptation characteristics of receptor responses, indicating that they derive from processes intrinsic to the receptors. Dark adaptation after a strongly adapting stimulus was similarly associated with temporary elevation of membrane potential, initial lowering of the saturation potential, and shift of the voltage-intensity curve. Under all conditions of adaptation studied, small amplitude responses were linear with light intensity. Further, there was no unique relation between sensitivity and membrane potential suggesting that receptor sensitivity is controlled at least in part by a step of visual transduction preceding the generation of membrane voltage change.

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