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The Journal of Neuroscience, January 9, 2008, 28(2):456-464; doi:10.1523/JNEUROSCI.2735-07.2008

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Behavioral/Systems/Cognitive
Effects of pH Buffering on Horizontal and Ganglion Cell Light Responses in Primate Retina: Evidence for the Proton Hypothesis of Surround Formation

Christopher M. Davenport,^1,2 Peter B. Detwiler,² and Dennis M. Dacey^3,4

¹Neurobiology and Behavior Graduate Program, Departments of ²Physiology and Biophysics and ³Biological Structure, and the ⁴Washington National Primate Research Center, University of Washington, Seattle, Washington 98195

Correspondence should be addressed to Dennis Dacey, Department of Biological Structure, Box 357420, University of Washington, Seattle, WA 98195-7420. Email: dmd{at}u.washington.edu

Negative feedback from horizontal cells to cone photoreceptors is regarded as the critical pathway for the formation of the antagonistic surround of retinal neurons, yet the mechanism by which horizontal cells accomplish negative feedback has been difficult to determine. Recent evidence suggests that feedback uses a novel, non-GABAergic pathway that directly modulates the calcium current in cones. In non-mammalian vertebrates, enrichment of retinal pH buffering capacity attenuates horizontal cell feedback, supporting one model in which feedback occurs by horizontal cell modulation of the extracellular pH in the cone synaptic cleft. Here we test the effect of exogenous pH buffering on the response dynamics of H1 horizontal cells and the center-surround receptive field structure of parasol ganglion cells in the macaque monkey retina. Enrichment of the extracellular buffering capacity with HEPES selectively attenuates surround antagonism in parasol ganglion cells. The H1 horizontal cell light response includes a slow, depolarizing component that is attributed to negative feedback to cones. This part of the response is attenuated by HEPES and other pH buffers in a dose-dependent manner that is correlated with predicted buffering capacity. The selective effects of pH buffering on the parasol cell surround and H1 cell light response suggests that, in primate retina, horizontal cell feedback to cones is mediated via a pH-dependent mechanism and is a major determinant of the ganglion cell receptive field surround.

Key words: retina; horizontal cell; ganglion cell; feedback; surround; proton

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Received June 15, 2007; revised Oct. 17, 2007; accepted Nov. 16, 2007.

Correspondence should be addressed to Dennis Dacey, Department of Biological Structure, Box 357420, University of Washington, Seattle, WA 98195-7420. Email: dmd{at}u.washington.edu

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