Impact of oral melatonin on the electroretinogram cone response

Anne-Marie Gagné,Serge G Rosolen,Konstantin V Danilenko,Marc Hébert

doi:10.1186/1740-3391-7-14

Abstract

BackgroundIn the eye, melatonin plays a role in promoting light sensitivity at night and modulating many aspects of circadian retinal physiology. It is also an inhibitor of retinal dopamine, which is a promoter of day vision through the cone system. Consequently, it is possible that oral melatonin (an inhibitor of retinal dopamine) taken to alleviate circadian disorders may affect cone functioning. Our aim was to assess the impact of melatonin on the cone response of the human retina using electroretinography (ERG).MethodsTwelve healthy participants aged between 18 to 52 years old were submitted to a placebo-controlled, double-blind, crossover, and counterbalanced-order design. The subjects were tested on 2 sessions beginning first with a baseline ERG, followed by the administration of the placebo or melatonin condition and then, 30 min later, a second ERG to test the effect.ResultsFollowing oral melatonin administration, a significant decrease of about 8% of the cone maximal response was observed (mean 6.9 μV ± SEM 2.0; P = 0.0065) along with a prolonged b-wave implicit time of 0.4 ms ± 0.1, 50 minutes after ingestion.ConclusionOral melatonin appears to reach the eye through the circulation. When it is administered at a time of day when it is not usually present, melatonin appears to reduce input to retinal cones. We believe that the impact of melatonin on retinal function should be taken into consideration when used without supervision in chronic self-medication for sleep or circadian disorder treatment.

Highlights

In the eye, melatonin plays a role in promoting light sensitivity at night and modulating many aspects of circadian retinal physiology
Considering that melatonin feeds back to the suprachiasmatic nucleus (SCN), site of the internal clock, where melatonin receptors are located [2], it is suggested that melatonin may be a regulatory hormone of darkness for the SCN
Retinal melatonin appears to play a role in promoting light sensitivity at night and modulating many aspects of circadian retinal physiology such as rod disk shedding [12,13]

Summary

Introduction

Melatonin plays a role in promoting light sensitivity at night and modulating many aspects of circadian retinal physiology It is an inhibitor of retinal dopamine, which is a promoter of day vision through the cone system. Retinal melatonin appears to play a role in promoting light sensitivity at night and modulating many aspects of circadian retinal physiology such as rod disk shedding [12,13]. Beside melatonin, it has been shown in avian retina that dopamine is produced from specific amacrine cells [14] and in a circadian rhythm manner in the rat retina [15]. Melatonin is thought to promote night vision (rod pathway)[19] whereas dopamine appears to promote day vision (cone pathway) [16]

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