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This Article Full Text Full Text (PDF) All Versions of this Article: 565/2/517    most recent jphysiol.2005.083436v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ichinose, T. Articles by Lukasiewicz, P. D. Search for Related Content PubMed PubMed Citation Articles by Ichinose, T. Articles by Lukasiewicz, P. D.

¹ Department of Ophthalmology and Visual Sciences, Department of Anatomy and Neurobiology, Washington University School of Medicine, 660 S. Euclid Avenue, St Louis, MO 63110, USA

Illumination of the receptive-field surround reduces the sensitivity of a retinal ganglion cell to centre illumination. The steady, antagonistic receptive-field surround of retinal ganglion cells is classically attributed to the signalling of horizontal cells in the outer plexiform layer (OPL). However, amacrine cell signalling in the inner plexiform layer (IPL) also contributes to the steady receptive-field surround of the ganglion cell. We examined the contributions of these two forms of presynaptic lateral inhibition to ganglion cell light sensitivity by measuring the effects of surround illumination on EPSCs evoked by centre illumination. GABA_C receptor antagonists reduced inhibition attributed to dim surround illumination, suggesting that this inhibition was mediated by signalling to bipolar cell axon terminals. Brighter surround illumination further reduced the light sensitivity of the ganglion cell. The bright surround effects on the EPSCs were insensitive to GABA receptor blockers. Perturbing outer retinal signalling with either carbenoxolone or cobalt blocked the effects of the bright surround illumination, but not the effects of dim surround illumination. We found that the light sensitivities of presynaptic, inhibitory pathways in the IPL and OPL were different. GABA_C receptor blockers reduced dim surround inhibition, suggesting it was mediated in the IPL. By contrast, carbenoxolone and cobalt reduced bright surround, suggesting it was mediated by horizontal cells in the OPL. Direct amacrine cell input to ganglion cells, mediated by GABA_A receptors, comprised another surround pathway that was most effectively activated by bright illumination. Our results suggest that surround activation of lateral pathways in the IPL and OPL differently modulate the sensitivity of the ganglion cell to centre illumination.

(Received 18 January 2005; accepted after revision 9 March 2005; first published online 10 March 2005)
Corresponding author P. D. Lukasiewicz: Department of Ophthalmology/Campus Box 8096, Washington University School of Medicine, 660 S. Euclid Avenue, St Louis, MO 63110, USA.  Email: lukasiewicz{at}vision.wustl.edu

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