Melatonin receptor expression in the zebra finch brain and peripheral tissues

The circadian endocrine hormone melatonin plays a significant role in many physiological processes, such as modulating the sleep/wake cycle and oxidative stress. Melatonin is synthesized and secreted during the night by the pineal gland and released into the circulatory system. It binds to numerous membrane, cytosolic, and nuclear receptors in the brain and peripheral organs. Three G-protein-linked membrane receptors (Mel1A, Mel1B, and Mel1C) have been identified in numerous species. Considering the importance of this hormone and its receptors, this study looks at the location and rhythmicity of these three avian melatonin receptors using reverse transcriptase-polymerase chain reaction (RT-PCR) mRNA analysis techniques. This study shows successful partial cloning of the three receptors, and gene expression analysis reveals significant rhythms of the Mel1A receptor in the cerebellum, diencephalon, tectum opticum, telencephalon, and retina. Significant rhythms were found in the diencephalon, pineal gland, retina, tectum opticum, and cerebellum of the Mel1B receptor, whereas Mel1C appeared not to be rhythmically expressed in brain tissues studied. Mel1A, Mel1B, and Mel1C receptor mRNAs were also present in peripheral tissues, showing tissue-specific expression patterns.