Circadian Serotonin Rhythm Control: Sympathetic and Nonsympathetic Pathways in Rat Pineals of Different Ages

Abstract

Immature rats (15–20 days) maintained in a 14 :10 hr light: dark cycle, and sacrificed at 1:00 and 11:00 PM, showed a circadian rhythm in pineal serotonin levels. When pineals of similar animals were sympathectomized by bilateral superior cervical ganglionectomy the serotonin rhythm persisted. Thus, in contrast to the adult, the serotonin rhythm in the immature pineal is independent of sympathetic innervation. At 60 days of age there was no rhythm in sympathectomized pineals; thus, the nerve dependent serotonin rhythm of the adultwas already established. When ganglionectomized immature rats were kept in constant light or in constant dark, the rhythm was abolished. Diurnal lighting, therefore, is important maintain the nerve independent serotonin rhythm of the immature rat. In contrast, the rhythm in the adult rat persists in constant dark. The mechanism controlling circadian serotonin rhythm in immature rats may be very different from that in adult animals. Ontogeny of the rhythm is proposed and discussed. (Endocrinology85: 846, 1969)