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M. H. Karakossian, E. E. Sutter, W. A. Hare; Multifocal Stimulus Characterization of GABAA-ergic Contribution to Retinal Ganglion Cell Receptive Field Organization. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1407.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize, using multifocal stimulation, the contribution of GABAA receptors to receptive field properties of retinal ganglion cells (RGC).
We used simultaneous recordings of the electroretinogram (ERG) and single unit RGC responses in an ex vivo dark-adapted rabbit retina. Responses to diffuse and multifocal stimuli were used to characterize RGC response properties. Multifocal stimulation and recording was performed using VERIS (EDI, Redwood City, CA). RGC receptive field properties were probed using a stimulus array consisting of 241 hexagonal elements of equal size and subtending a total area of 2.5mm in diameter at the retinal surface. RGC responses were grouped in concentric rings and the length constant for spatial summation was obtained by fitting responses with an analytical (sigmoidal) function. GABAA-ergic activity was blocked by bath application of 5 µM gabazine.
Application of gabazine was associated with an increased receptive field size for OFF RGCs (50.92±12.57%, p<0.05, N=6). The length constant for spatial summation was increased from an average of 114µm (control) to 179µm (gabazine). This effect was statistically significant (p<0.05, N=6; Generalized Estimating Equations model of Repeated Measures) and was reversible following gabazine washout. In all cells tested, an ON response was revealed in the presence of gabazine. Gabazine also decreased the time-to-peak of ERG b-wave responses to dim diffuse flash stimuli (-8.77 ± 2.89%, p<0.05, N=5) but had no effect on b-wave amplitude (-5.12 ± 10.78%, p>0.05, N=5).
Our results demonstrate that multifocal stimulation provides a useful method for characterization of RGC receptive field organization.
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