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F.A. Rocha, C.A. Saito, L.C. L. Silveira, J.M. de Souza, D.F. Ventura; Color Coding With UV Input in the Inner Retina of the Turtle (Pseudemys scripta elegans) . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3767.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the influence of the ultraviolet (UV) input in the chromatic responses of inner retina neurons of the turtle and to describe the types of color–coding mechanisms envolved.
Intracellular recordings were made in everted eyecup preparations of the turtle Pseudemys scripta elegans. The retina was superfused with oxygenated Ringer’s solution (pH 7.5) and stimulated with spots of light centered in the receptive field, and/or with annuli. Stimuli of equal numbers of quanta of UV (370nm), blue (450nm), green (540nm), and red (620nm) light, were presented at three intensities (see Ventura et al., 1999). In the same experiment, neurobiotin was injected iontoforetically after recording. Afterwards, the retina was disected, fixed for 1 hour in 4% paraformaldehyde in 0.1M phosphate buffer and incubated in Cy3–streptavidin. The retina was then mounted on a glass slide and visualized using confocal microscopy.
Recordings were obtained in a total of 42 neurons of the turtle inner retina, 16 of which were spectrally opponent. Among these there were four amacrine (9%) and 12 ganglion cells (28%). Many responses showed a very intricate picture with a variety of response types and a potential for complex processing of chromatic stimuli, with intensity– and wavelength–dependent response components. Among the 12 ganglion cells with color opponency, seven different combinations of opponency were found in the center of the receptive field: UVBG+R–; GR+UVB–; R+UVBG–; BGR+UV–; B+UVGR–; UVRG+B–; UV+BGR–. Among the four amacrine cells, we found three different types of chromatic opponency: BGR+UV–, with fast transient responses; GR+UVB–; and UVBG+ R–. This third amacrine cell type was identified as an A23b amacrine cell (Ammermüller and Kolb, 1995). It should be noted that there was one ganglion cell and also an amacrine cell, with OFF responses to UV light and ON responses to the rest of the spectrum.
Previous work on chromatic processing in the inner retina of the turtle, which included UV stimulation had identified eight types of chromatically opponent ganglion cells and two of amacrine cells (Ventura et al., 1999, 2001). We now add two new types of chromatic opponency in ganglion cells and two new amacrine cell types with chromatic opponency involving the UV channel. We also identified morphologically (A23b) an amacrine cell type whose electrophysiology had been previously described.
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