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L. Yin, R.G. Smith, P. Sterling, D.H. Brainard; Retinal Processing of Color Information in Guinea Pig . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4537.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The guinea pig (gp) has two classes of light sensitive cones (M and S), with more M cone pigment in superior retina than in inferior (Rohlich et al., 1994; Parry and Bowmaker, 2002). This may reflect systematic differences in the color of sky and ground. To probe the relation between retinal region and gp color vision, we studied (a) how the two classes of cone contribute to the responses of gp horizontal (H) and ganglion (G) cells and (b) how chromatic adaptation affects the responses of the two cell types. Methods: Responses of single cells to flickering 2 Hz spots modulated around an adapting background were recorded intracellularly (H cells, ∼2000 um spots) or extracellularly (brisk–transient G cells, ∼600 um spots) from in vitro whole mount albino gp retina. Cells were sampled from ∼3 mm superior and ∼3 mm inferior to the optic disk. The contribution of M– and S–cones to the responses of each cell were estimated from its responses to spots that modulated the two cone classes in different proportions. In making the estimates, we assumed that contrast from the two cone types is summed linearly and passed through a non–linear contrast–response function (LNL model). Two adapting backgrounds were used. The neutral background produced equal quantal absorption rates in the M and S cones. The chromatic background produced higher absorptions in the M cones by a factor of 2.6. The intensity of both backgrounds was chosen to saturate the rods. Results: The responses of both the H and brisk–transient G cells were well–described by the LNL model. Thus the cone inputs to each cell are characterized by an M/S weight w, such that the linear response component is w*Cm + (1–w)*Cs, where Cm and Cs denote M and S cone contrasts. M cone contribution was stronger in superior retina than inferior for both H and G cells (superior: mean H cell w = 0.70, mean G w = 0.75; inferior: mean H cell w = 0.29; mean G cell w = 0.27). Differences in M/S weight between H and G cells were small in both regions of retina. Changing the adapting background resulted in similar changes in M/S weight in H and G cells (superior: mean H cell w = 0.86, mean G cell w = 0.85; inferior: mean H cell w = 0.41; mean G cell w = 0.40.) Conclusions: Photopigment inhomogeneity in M/S cone ratio is preserved at the G cell level of guinea pig retina. The similarity of relative M/S weight between H and G cells suggests that most adaptation to uniform backgrounds occurs prior to the H cells, at least for the brisk–transient G cell pathway.
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