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C. L. Passaglia, W. F. Heine; Spatial Frequency Response of Rat Retinal Ganglion Cells. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1421.
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© ARVO (1962-2015); The Authors (2016-present)
Rodents have become a popular animal model for studying assorted ocular disorders. Much work has been done characterizing the anatomical properties of rat retinal neurons with relatively little effort being spent on quantitative analyses of their physiological properties. In this study we examine the spatial receptive fields of different types of rat retinal ganglion cells (RGCs). Our results provide a foundation for investigating in rats the effects of retinal pathophysiology on spatial information processing.
Male retired-breeder Brown Norway rats were anesthetized with a continuous infusion of ketamine/xylazine and placed in a stereotaxic device. Sinusoidal gratings of various spatial frequency were displayed on a cathode-ray tube with a frame rate of 100 Hz and mean luminance of 26 cd/m2. The gratings drifted or reversed contrast at 2 Hz. A tungsten-in-glass microelectrode was positioned in the optic tract to record single RGC fiber activity. The fundamental and second harmonic responses to a reversing grating of high spatial frequency were used to calculate the degree of nonlinearity. Spatial tuning curves were measured at various orientations and fitted to a two dimensional Difference of Gaussian (DOG) model.
We demonstrate the presence of linear and nonlinear RGCs which appear analogous to X and Y cells found in other mammals. The spatial frequency response of many of these cells was unimodal and showed orientation bias. Some cells displayed bimodal tuning curves, indicating a more complex receptive field structure. The DOG model provided estimates of center and surround receptive field properties of cells with unimodal tuning curves. A modified DOG consisting of two center regions was able to capture the receptive field properties of cells with bimodal tuning curves.
Rat RGC receptive field properties share similarities with those of cats and other mammals, including center-surround organization, some orientation sensitivity, and linear and nonlinear spatial summation. Differences are that the center and surround of rat X and Y cells are comparable in size and strength.
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