The development of pineal serotonin content from birth to age 50 days is described. In pineal glands of newborn rats serotonin is barely detectable; its presence was clearly established in 3-day-old rats. A circadian rhythm in pineal serotonin content was found not only in young rats maintained in diurnal lighting conditions but also in rats kept from birth in continuous darkness. Hence light or an environmental light-dark cycle is not essential for the induction of a serotonin rhythm after birth. In rats exposed to constant light no rhythm was found but it appeared when these rats were transferred to a diurnal lighting regime. © 1971.
Illnerová, H. (1971). Effect of environmental lighting on serotonin rhythm in rat pineal gland during postnatal development. Life Sciences, 10(10 PART 1), 583–590. https://doi.org/10.1016/0024-3205(71)90044-0