Evaluating Neural Activity of Retinal Ganglion Cells by Flash-evoked Intrinsic Signal Imaging in Macaque Retina

¹ Laboratory of Visual Physiology, National Institute of Sensory Organs, Meguro-ku, Tokyo, Japan; Laboratory for Integrative Neural Systems, Brain Science Institute, RIKEN, Saitama, Japan; Department of Ophthalmology, Kikkoman General Hospital, Chiba, Japan
² Laboratory of Visual Physiology, National Institute of Sensory Organs, Meguro-ku, Tokyo, Japan; Laboratory for Integrative Neural Systems, Brain Science Institute, RIKEN, Saitama, Japan
³ Division of Ophthalmology, Department of Visual Science, Nihon University School of Medicine, Tokyo, Japan
⁴ Department of Ophthalmology, Keio University School of Medicine, Tokyo, Japan
⁵ Laboratory for Integrative Neural Systems, Brain Science Institute, RIKEN, Saitama, Japan

^* To whom correspondence should be addressed. E-mail: tsunodakazushige{at}kankakuki.go.jp.

	Abstract

Purpose: Intrinsic signal imaging (ISI) detects light-induced micro-structural or metabolic changes in retinal tissues. Thus, activities of the rod and cone systems could be mapped topographically. However, there is no direct evidence on the cellular origin of the signals. The purpose of this study was to determine if and how the retinal ganglion cells (RGCs) contribute to the ISI. Methods: In anesthetized macaque monkeys, the properties of intrinsic signals were investigated by 1) simultaneous measurement of the retina and the primary visual cortex (V1) with different wavelengths of observation light; 2) measurement of the flash-induced blood flow changes by laser Doppler flowmetry, and 3) intravitreal injection of tetrodotoxin (TTX). Results: Slow components of the ISI well correspond to the flash-induced blood flow increase. The intrinsic signals of the posterior retina are partially decreased and the signal of the optic disc is completely abolished by an intravitreal injection of tetrodotoxin (TTX) at a concentration that should reduce the neural activities of RGCs. The intrinsic signal at the fovea did not change significantly following the TTX injection. Conclusions: Not only the photoreceptors in the outer retina but the RGCs in the inner retina are major contributors to the intrinsic signals, and that the activity of the RGCs can be mapped by using both the fast and slow components of the signal in the posterior retina. The functional organization of the RGC layer has not been objectively mapped, and our results indicate that the ISI has the potential to do this.

Key Words: ganglion cell, retinal blood flow, image analysis

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