Melatonin signaling that breaks the usual nighttime pattern in trout eye

Light increases the activity and abundance of retinal AANAT1 in trout while decreasing pineal AANAT2 levels.

• Pineal melatonin synthesis typically increases at night across vertebrates due to heightened AANAT activity.
• In trout, retinal melatonin synthesis patterns differ, with AANAT1 activity peaking during the day instead of the night.
• Light exposure raises the levels and activity of retinal AANAT1, while darkness reduces it, contrasting with pineal AANAT2 activity.
• Retinal AANAT protein and activity demonstrate rhythmic changes that are out of phase with retinal AANAT1 mRNA levels.
• These findings suggest that retinal melatonin behavior in trout may represent an adaptation for photoadaptation or detoxification.

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