The Pineal Organ, Its Hormone Melatonin, and the Photoneuroendocrine System

摘要: The vertebrate pineal organ rhythmically synthesizes and secretes melatonin during nighttime forms an essential component of the photoneuroendocrine system which allows humans animals to measure keep time. Regulation biosynthesis depends on signals from photoreceptors perceiving transmitting environmental light stimuli endogenous oscillators generating a circadian rhythm is independent any time cue (zeitgeber). In nonmammalian species responsible for regulating reside within itself. several (e.g., lamprey, zebra fish, house sparrow, chicken) also capable rhythms thus serves all key functions system: photoreception, generation, production neurohormones. These may even be accomplished by single "photoneuroendocrine" cell. mammals has lost both direct sensitivity capacity rhythms, regulated retinal oscillator located in suprachiasmatic nucleus hypothalamus. Due this spatial separation comprises neuronal neuroendocrine pathways interconnect its components. involve circuits central peripheral nervous systems, as important final link noradrenergic sympathetic nerve fibers. appears major target mammals. hormone involved feedback loop mammalian system. present comparative contribution considers, after short survey classical findings phylogenetic development gross anatomy complex, cytoevolutionary cell biological aspects various types pinealocytes well afferent efferent innervation (pinealofugal pinealopetal pathways). Moreover, emphasis placed receptor mechanisms, second messenger systems (Ca2+ cyclic AMP), transcription factors (e.g, CREB ICER), their roles regulation biosynthesis. Finally, action, targets, receptors are dealt with. synoptic approach contribution, combines anatomical ultrastructural with molecular results, confirms functional significance melatonin-synthesizing stresses importance model study signal transduction mechanisms cells.