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| This page describes the in vitro primate retinal preparation that we use and shows some of the discoveries we have made using the technique. |
 First, the retina is carefully peeled out of the inside of a living primate donor eye. Five cuts allow the retina to be flattened and glued to the bottom of a glass recording chamber with the ganglion cell-side up (shown to the right).
It is kept alive by continuously bathing it in synthetic spinal fluid and heating it to normal body temperature. |
 The recording chamber is placed on the stage of a light microscope. The microscope can be set to one of two configurations.
Visual stimuli produced by a digital video projector can be imaged directly onto the retina using a custom optical system or the retina can be viewed through the microscope. |
 Although the retina is transparent, the experimenter can view retinal cells by applying dyes that stain various types of cells without damaging them.
Once they are found they can be targeted for penetration by an intracellular electrode. Then the microscope configuation is switched and the electrical responses of the cell are measured during the presenation of various visual stimuli. Each recorded cell is filled with a permanent stain so that it can be examined in detail after the experiment. |
| Color Vision - What is the retinal circuitry that underlies blue/yellow color vision? |
 In 1994, Dacey and Lee described a unique small bistratified ganglion cell. The in vitro retinal preparation allowed them to microscopically select individual cells for intracellular recording, carefully characterize their responses to chromatic stimuli, and fill them with a stain for detailed anatomical examination after the experiment. |
 The recordings showed that the cells were excited by flashing blue lights which stimulated the S-cones and inhibitied by flashing yellow lights that stimulated the M- and L-cones.
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| Spatial Vision - Where does the receptive field surround come from? |
 Ganglion cells exhibit a classical center-surround receptive field organization. We conducted a series of experiments to figure out what cells provide the lateral inhibition that creates the receptive field surround of primate ganglion cells. |
| We measured the receptive field structure of parasol ganglion cells under two conditions. First, we used cobalt or carbenoxolone to attenuate the contribution from horizontal cells. Then we applied drugs to block the inhibition from GABA released by amacrine cells. The surround response disappeared when horizontal cells were blocked but not when amacrine cells were blocked.
The effect is easy to see if you measure the cell's responses to a flashing spot, which stimulates the center, and a flashing annulus, which stimulates the surround, under both conditions. |
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| These results suggest that the surrounds of light-adapted parasol ganglion cells are generated primarily by non-GABAergic horizontal cell feedback, with a small contribution from GABAergic amacrine cells.
The results of this study were published in the Journal of Neuroscience. The Classical Receptive Field Surround of Primate Parasol Ganglion Cells Is Mediated Primarily by a Non-GABAergic Pathway. M. J. McMahon, O.S. Packer & D. M. Dacey (2004), Journal of Neuroscience, 24(15) 3736-3745. Pubmed [pdf] |
| Contact Matt McMahon • Copyright 2003 © Matthew J. McMahon. All rights reserved. last modified 6/27/2004 |