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M.J. McMahon, O. Packer, D.M. Dacey; Circuitry of the Parasol Ganglion Cell Receptive Field Surround . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3236.
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Purpose: Many drugs alter the spatial organization of receptive fields. Carbenoxolone blocks horizontal cell feedback to cones in fish (Kamermans et al. 01). Cobalt inhibits the surrounds of bipolar and ganglion cells and prevents injected horizontal cell current from driving ganglion cells in turtle (Vigh & Witkovsky 99). TTX and picrotoxin attenuate the surround of ganglion cells in salamander (Cook & McReynolds 98) and rabbit (Taylor 99, Flores-Herr et al. 01). Our purpose was to compare the effects of these drugs on spatial receptive field organization in primate parasol ganglion cells. Methods: Intracellular recordings were made from parasol ganglion cells in an in vitro preparation of the intact macaque monkey retina. Responses to drifting sine wave gratings and flickering spots and annuli were used to make quantitative estimates of the strength of the receptive field center and surround. Measurements were made before, during, and after the application of cobalt chloride (75-300 µM), carbenoxolone (100 µM), picrotoxin (100 µM), TTX (0.5 µM), and GABA (200-500 µM). Results: Cobalt chloride attenuated the surround much more than the center. Relative surround strength decreased by 69% (n=22, SEM=5%). Carbenoxolone produced similar results, with surround strength decreasing by 73% (n=10, SEM=7%). Picrotoxin did not significantly reduce surround strength (n=13) but it altered the temporal dynamics by attenuating the membrane potential rebound following stimulus offset. TTX reduced surround strength 11% (n=12, SEM=7%) and eliminated spikes, but did not significantly alter the temporal dynamics. GABA hyperpolarized the cells and decreased the baseline membrane potential variance. It reduced surround strength by 17% (SEM=7%) in 7 cells and abolished the entire response of 4 others. Conclusions: Cobalt and carbenoxolone, which are thought to modulate signals in the outer retina, severely attenuate the spatial receptive field surround. Blocking or saturating GABAergic neurotransmission caused only a small attenuation of the receptive field surround. This data is consistent with the hypothesis that the spatial receptive field surround of parasol ganglion cells in macaque monkey retina is generated mostly by horizontal cell feedback mechanisms, with a small contribution from GABAergic cells of the inner retina.
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