Retinal serotonin, eye growth and myopia development in chick

Area of Science:

• Ophthalmology
• Neuroscience
• Developmental Biology

Background:

• Myopia, or short-sightedness, is linked to excessive eye growth.
• Serotonin (5-hydroxytryptamine, 5-HT) influences retinal processing, intraocular pressure, and blood vessels within the eye.
• The specific role of retinal serotonin in regulating eye growth remains largely undetermined.

Purpose of the Study:

• To investigate the role of the retinal serotonin system in regulating eye growth, specifically in the context of myopia.
• To assess the impact of serotonin receptor antagonists and serotonin itself on experimentally induced myopia in chicks.

Main Methods:

• Myopia was induced in 7-day-old chicks using lens-induced myopia (LIM) and form deprivation (FDM).
• Intravitreal injections of serotonin receptor antagonists, a selective 5-HT(2) antagonist, or serotonin were administered daily.
• Serotonin and tyrosine hydroxylase positive neurons were counted, and their relative density was determined to account for changes in eye size.

Main Results:

• A combination of 5-HT receptor antagonists significantly inhibited LIM by approximately 50%, while FDM was unaffected.
• A selective 5-HT(2) antagonist showed a less pronounced inhibitory effect on LIM.
• High doses of serotonin appeared to be inhibitory to LIM, contrasting with a potential stimulatory role at lower doses.
• Lens-induced myopia eyes exhibited a 12.5% increase in serotonin-containing amacrine cells in the central retina.

Conclusions:

• Modulating the serotonin system can influence the eye growth process, particularly in lens-induced myopia.
• Serotonin appears to have a complex, potentially dual role (stimulatory and inhibitory) in myopia development.
• The precise function of serotonin within the mechanisms of eye growth regulation requires further investigation.