Control of the Circadian Rhythm in Serotonin Content of the Rat Pineal Gland

In this article, Axelrod and several members of his laboratory reported their findings on circadian rhythms and the results of a series of experiments on the pineal glands of rats. The researchers found that the circadian rhythm was synchronized by exposure to light, but otherwise operated independent of it. However, exposure to constant light, or blinding the rats altogether, significantly altered their circadian rhythms.