Control of 5-hydroxytryptophan Decarboxylase Activity in the Rat Pineal Gland by Sympathetic Nerves.

The mammalian pineal gland is rich in serotonin content and this amine is present in high concentration within the sympathetic nerve endings of this organ (Quay and Halevy, 1962; Bertler et al., 1963). Sympathetic denervation of the pineal gland results in a 50% decrease in its serotonin content (Bertler et al., 1963; Pellegrino de Iraldi et al., 1963). Recently it has been demonstrated that the pineal gland has the highest concentration of 5-hydroxytryptophan decarboxylase, the enzyme which forms serotonin, of all mammalian tissues examined (Snyder and Axelrod, 1964a). An important role of serotonin in the pineal gland is to serve as a precursor for the gonadal inhibiting hormone, melatonin (Axelrod and Weissbach, 1960; Weissbach et al., 1960; Wurtman et al., 1963a). The synthesis of melatonin as well as the concentration of serotonin has been shown to be influenced by environmental lighting (Wurtman et al., 1963b; Quay, 1963). Ariens-Kappers (1960) has demonstrated that the rat pineal gland is largely or wholly innervated by sympathetic nerves whose cell bodies are located in the superior cervical ganglia. The effects of changes in environmental lighting on the melatonin synthesizing enzyme in the pineal gland have been shown to be mediated by its sympathetic innervation (Wurtman et al., 1964). The experiments described here will demonstrate that the sympathetic nerves to the pineal gland as well as environmental lighting markedly influence the activity of pineal 5-hydroxytryptophan decarboxylase (5-HTPD).