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Y. Okawa, T. Fujikado, T. Miyoshi, Y. Hirohara, T. Mihashi, Y. Tano; Contribution of Retinal Ganglion Cell Activity to Intrinsic Signals. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3845.
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© ARVO (1962-2015); The Authors (2016-present)
Origins of intrinsic signals were not well defined in optical imaging of retina. Recently, Ts'o reported that the inhibition of action potentials of retinal ganglion cells (RGCs) by tetrodotoxin (TTX) did not induce significant changes of retinal intrinsic signals using light stimulation (ARVO 2006). In this study, we studied the retinal intrinsic signals caused by activating RGCs selectively by retrograde electrical stimulation, and examined if the activity of RGCs contributes to retinal intrinsic signals or not.
Three eyes of three cats were studied under general anesthesia. RGCs were stimulated retrogradely with electrical currents between two electrodes placed on both sides of optic chiasma. Monophasic pulses of 0.05 msec duration and 2.5-5.0 mA intensity were applied for 4 seconds with frequency of 100Hz. Fundus images with near-infrared light (800-880 nm) were obtained in every 20 msec for 26 seconds between 2 seconds before and 20 seconds after stimulation. To improve S/N ratio, the images of 20 consecutive recordings were averaged. Two-dimensional topography was constructed by subtracting images before stimulation from those after stimulation. Same experiments were carried out with TTX injected intravitreally.
We were able to detect the change of light-reflectance in optic disc (-1.27%), retina (-0.61%), and blood vessels (-1.23%) with a current of 2.5mA. These intrinsic signals increased with stimulating current intensities and disappeared with TTX application (-0.58%, -0.52% and -0.72% respectively).
Intrinsic signals caused by retrograde electrical activation of RGCs alone was able to be detected clearly. RGCs may contribute to intrinsic signals to some extent in light stimulation.
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