Effect of Continuous Light and Darkness on Hydroxyindole-O-Methyltransferase and 5-Hydroxytryptophan Decarboxylase Activities in the Japanese Quail

Abstract

Hydroxyindole-O-methyltransferase (HIOMT), the melatonin forming enzyme, and 5-hydroxytryptophan decarboxylase (5- HTPD), the serotonin forming enzyme, were measured in the pineal gland (HIOMT and 5- HTPD) and hypothalamus (5-HTPD) in mature female Japanese quail maintained on a 16-hr daily photoperiod and after 5-day exposure to continuous light and darkness. HIOMT was inhibited by exposure to continuous darkness but not influenced by continuous light. Pineal 5- HTPD activity was increased by exposure to continuous darkness but not significantly decreased by exposure to continuous light. These changes in both pineal HIOMT and 5-HTPD activities in response to photoperiod are opposite to those reported in the rat. Hypothalamic 5- HTPD, also measured in the same birds, was found to be increased by exposure to both continuous light and darkness. (Endocrinology86: 1441, 1970)