Photoperiod modifies daily maps of light and dark sensitivity for N-acetyltransferase activity in pineal glands of 3-week old Gallus domesticus

Structures and molecules involved in generation and regulation of biological rhythms in vertebrates and invertebrates

Melatonin from the retina and the pineal gland functions in neuroendocrine hierarchies. Photoreceptors--eyes and extraretinal--detect light. Oscillators--pineal and suprachiasmatic nuclei--act as pacemakers. Driven neuroendocrine rhythms carry temporal hormone signals throughout the body. Light controls melatonin: light sets the phase of the melatonin rhythm and determines the duration of melatonin synthesis. By these means, circadian rhythms (e.g., in locomotor activity and body temperature) and seasonal rhythms (e.g., in reproduction) are controlled.

Light-induced plasma melatonin suppression in seasonal affective disorder

1. Subjects with seasonal affective disorder were exposed to 0, 500 and 1000 lux of white light for one hour beginning at 0300 hours. 2. Plasma samples were taken periodically and analysed for melatonin. 3. Plasma melatonin levels were suppressed by exposure to both 500 and 1000 lux light levels, suggesting that SAD patients show no neuroendocrine insensitivity to light but may show supersensitive responses to light.