Exploring Retinal Neuron Responses to Defocused Images in the Mouse Retina

Abstract

Purpose
Although myopia, or nearsightedness, is a health problem worldwide, the mechanisms of its development remain unknown. It is hypothesized that refractive errors could result from the impact of defocused visual signals on various types of retinal neurons. This research study aimed to explore whether defocused images influence the signaling processes of individual types of retinal ganglion cells, specifically alpha retinal ganglion cells (αRGCs), as well as dopaminergic Amacrine Cells (Dopaminergic ACs), AII ACs, and Horizontal Cells (HCs). Additionally, the study examined the role of connexin 36 gap junctions (Cx36 GJs) in modulating these effects.
Methods
Several strains of mice, C57BL/6, KCNG-YFP, EGR-1, Fam81a, and Cx36-knockout, were used in this study. A custom-made device was used to project defocused images onto the retina under the microscope. Mightex 1000 generated light bars, annulus, and spots of varying sizes. Biophysical response of αRGCs, DACs, AII ACs, and HCs were recorded by patch clamp in flat-mounted retinas. Intracellular dye injection and confocal microscopy were then applied to confirm and study the morphology of neurons in the mouse retinas. The Generalized linear model (GLM) was used to predict RGC responses in normal and lens-induced myopic mice in order to study the myopic retina. Additionally, stretched soma and retinas were investigated to simulate myopic conditions. Gap junction blocker-Meclofenamic acid (MFA, 100μM), was applied to the retinas to study the impact of uncoupling AII ACs.
Study 1. This study investigated whether the biophysical characteristics of alpha retinal ganglion cells (αRGCs) differ between normal Cx36 knockout mice and those with lens-induced myopia (LIM) retinas. The study applied a generalized linear model (GLM) to predict the coding efficiency between focused and defocused images of RGCs in these mice.
Study 2. This study explored whether there are differences in the biophysical responses of alpha retinal ganglion cells (αRGCs) between focused and defocused image stimuli and to observe whether there is a difference in biophysical responses when the soma and retinas were stretched to mimic myopic conditions in both normal and Cx36 KO mice.
Study 3 This study investigated whether dopaminergic ACs and AII ACs demonstrated differences in their responses to focused versus defocused images. To uncouple the coupling between AII ACs, gap junction blocker was applied.
Study 4. The study investigated whether there are differences in the biophysical responses of horizontal cells (HCs) to focused and defocused images.
Summary
The neurons in the retina, such as αRGCs, HC, AII ACs, and dopaminergic ACs, can exhibit different responses to focused or defocused images. Gap junctions within retinal circuits might have a significant impact on the development of visually induced myopia.

Date of Award	13 Nov 2024
Original language	English
Awarding Institution	The Hong Kong Polytechnic University
Supervisor	Feng Pan (Chief supervisor), Yan Yin Tse (Co-supervisor) & Chi Ho To (Co-supervisor)