Influence of atropine on retinal signaling in a mouse model

Title: Low dose atropine might affect alpha ganglion cell signalling in the mouse retina

Authors: Qin Wang (1), Feng Pan (1,2)

1. The Hong Kong Polytechnic University, Kowloon, Hong Kong
2. Centre for Eye and Vision Research Limited, Hong Kong, Hong Kong

Reference: ARVO 2021 Abstract

This study explored the impact of atropine on retinal ganglion cells (RGCs) in the mouse retina through topical and direct exposure. Firstly, on corneal application, the concentration that reached the retina was 400 times less. Secondly, on direct application to the retina, results show that low concentration atropine did not change the morphology and most of the biophysical properties of the RCG’s in the mouse retina. Higher concentrations of atropine (more than 0.3%) inhibited the light-evoked spike responses and increases the tonic firing of RGC’s. ON responses were induced in certain OFF alpha RGC’s by atropine from low to high concentrations in a dose-response effect. This was abolished by GABA, confirming this biochemical action of atropine. The impact of changes in retinal signaling found here are unknown when translated to humans: this study involved short term, high concentration, direct retinal exposure to atropine whereas in humans the exposure is long term, in very low concentration via topical administration. 

What this means for your clinical practice: at the moment, this research doesn't translate to any changes in atropine prescribing. It is uncertain if these findings may help to illuminate a possible mechanism or unintended impact of atropine - good thing or bad thing? The concentration of atropine reaching a human retina would be a minute fraction of that tested directly on the retina here. It does indicate that we have more to learn about the mechanism and long-term impact of atropine.

Purpose: Atropine was used to retard myopia progression in clinic, while its effect on retina is unclear. Therefore, we explored the impact of atropine from concentrations 0.05 µM to 500 µM on retinal ganglion cells (RGCs) in the mouse retina.

Methods: Adult C57BL/6J mice, Kcng4-YFP mice, Cx36-knockout mice were used in this study. Retinas (n=5) were removed and immersed in 800 µM (0.05%) atropine sulfate for 30 minutes and liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to detect atropine concentration in retina. Alpha RGCs (n=10) were injected with Neurobiotin to show morphology. In electrophysiological recording, retinas were directly applied in atropine and stimulated with 525nm full-field light. ON (n=5) and OFF αRGCs (n=5) were applied with 0 µM, 100 µM, 300 µM, 500 µM atropine subsequently for does-dependent test. For time and concentration-dependent test, alpha RGCs were recorded before and after application of 0.05 µM (n=8), 0.5 µM (n=8), 10 µM (n=8), 100 µM (n=9) atropine respectively.

Results: Around 400-fold reduction was detected in retina after 800 µM atropine applied in cornea and choroid side (1960.0 ± 524.2nmol/L). No morphological changes were observed after superfusion in 1µM atropine for 30 minutes. Atropine over 100µM had a does-dependent inhibition effect on light-evoked response in ON αRGCs (300 µM p=0.048, 500 µM p=0.001) and OFF αRGCs (300 µM p=0.048, 500µM p=0.003). Application of 100 µM, 10 µM, 0.5 µM, 0.05 µM atropine had no effect on spike frequency and time latency of original ON or OFF light-evoked responses. Synchronized firing pattern between OFF RGCs was not changed in 0.5 µM atropine. However, ON responses were induced in certain OFF αRGCs (20% in 0.05µM, 37% in 0.5µM, 40% in 10µM, 33% in 100µM). Atropine of 50µM extended the threshold of joint inter-spike interval (ISI) distribution of αRGCs.

Conclusions: Atropine of high concentration had inhibition effect on αRGCs firing response, while low-dose atropine did not interfere with spike frequency, synchronized pattern, and threshold of joint ISI distribution of ON and OFF αRGCs. However, atropine induced ON responses from certain OFF RGCs, which suggested unintended consequences on retinal information processing.

Layman Abstract: Atropine is used to retard myopia progression in children and low-dose atropine was adopted to avoid side effects. Our study explored the effect of atropine on retinal ganglion cells (RGCs) over a range of concentrations in mouse retina. Although low-dose atropine had few effect on most of RGCs, it could induce ON responses from certain OFF RGCs. This may suggest the unintended consequences of atropine on retinal information processing.

Disclosures: Qin Wang, None; Feng Pan, None