Title
Drift-diffusion simulation of the ephaptic effect in the triad synapse of the retina.
Abstract
Experimental evidence suggests the existence of a negative feedback pathway between horizontal cells and cone photoreceptors in the outer plexiform layer of the retina that modulates the flow of calcium ions into the synaptic terminals of cones. However, the underlying mechanism for this feedback is controversial and there are currently three competing hypotheses: the ephaptic hypothesis, the pH hypothesis, and the GABA hypothesis. The goal of this investigation is to demonstrate the ephaptic hypothesis by means of detailed numerical simulations. The drift-diffusion (Poisson-Nernst-Planck) model with membrane boundary current equations is applied to a realistic two-dimensional cross-section of the triad synapse in the goldfish retina to verify the existence of strictly electrical feedback, as predicted by the ephaptic hypothesis. The effect on electrical feedback from the behavior of the bipolar cell membrane potential is also explored. The computed steady-state cone calcium transmembrane current-voltage curves for several cases are presented and compared with experimental data on goldfish. The results provide convincing evidence that an ephaptic mechanism can produce the feedback effect seen in experiments. The model and numerical methods presented here can be applied to any neuronal circuit where dendritic spines are invaginated in presynaptic terminals or boutons.
Year
DOI
Venue
2015
10.1007/s10827-014-0531-7
Journal of Computational Neuroscience
Keywords
Field
DocType
Synapse,Retina,Ephaptic effect,Drift-diffusion model
Membrane potential,Neuroscience,Synapse,Dendritic spine,Retina,Ephaptic coupling,Outer plexiform layer,Negative feedback,Voltage-dependent calcium channel,Mathematics
Journal
Volume
Issue
ISSN
38
1
0929-5313
Citations 
PageRank 
References 
2
0.39
2
Authors
4
Name
Order
Citations
PageRank
Carl L. Gardner12812.81
Jeremiah R. Jones230.90
Steven M. Baer330.90
Sharon M. Crook47712.01