Rod and Cone Contributions to Horizontal Cell Light Responses in the Mouse Retina

Jul 4, 2008The Journal of neuroscience : the official journal of the Society for Neuroscience

How Rod and Cone Cells Influence Light Responses in Mouse Retinal Horizontal Cells

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Abstract

Horizontal cells in the mouse retina receive inputs from both rod and cone photoreceptors.

Horizontal cell bodies and axon terminals integrate signals from both types of photoreceptors.
Rod and cone inputs are transmitted via connexin36 gap junctions.
Signal transmission appears to be unidirectional, moving from the horizontal cell body to the axon terminal.
Cone function can be isolated in studies by using a specific mouse model lacking cone channels.
The interaction of rod and cone signals is important for adapting photoreceptor sensitivity to light conditions.

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Mammalian B-type horizontal cells make contact with both photoreceptor types: the dendrites contact cone photoreceptors, whereas the axon terminal processes contact rods. Despite their distinct synaptic contacts, horizontal cell somata and axon terminals receive a mixture of rod and cone inputs. Interaction of the two photoreceptor systems is essential for adaptation of photoreceptor sensitivity to different levels of background illumination, and horizontal cells play a key role in this adaptation. In this study, we used transgenic mouse lines to examine the contributions of rod and cone photoreceptor inputs to horizontal cell light responses in the mouse retina: rod signals were isolated by recording intracellularly from horizontal cells in a mouse lacking the cone cyclic nucleotide-gated channel, which lacks cone function, and cone signals were assessed using the rhodopsin knock-out mouse, which is a model for pure cone function. We found that both horizontal cell compartments receive a mixture of inputs from both photoreceptor types. To determine whether these inputs arrive via the long axon connecting the compartments or by way of rod-cone gap junctional coupling, we assessed the rod and cone contributions to horizontal cell somatic and axon terminal light responses in the connexin36-deficient mouse retina, which lacks rod-cone coupling. Our results confirm that rods and cones are coupled by connexin36, and suggest that signal transmission along the axon is unidirectional: signals are passed from horizontal cell soma to axon terminal but not from axon terminal to soma.

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Rod and Cone Contributions to Horizontal Cell Light Responses in the Mouse Retina

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