Melatonin modulates intercellular communication among immortalized rat suprachiasmatic nucleus cells

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Title: Melatonin modulates intercellular communication among immortalized rat suprachiasmatic nucleus cells
Author: Cox, Kimberly Yvonne
Abstract: The mammalian brain contains a regulatory center in the diencephalic region known as the hypothalamus that plays a critical role in physiological homeostasis , and contains a variety of centers for behavioral drives , such as hunger and thirst . Located deep within the hypothalamus is the suprachiasmatic nucleus (SCN ) , or the master biological clock , that organizes rhythmic physiology and behavior , such that critical events take place at the most appropriate time of the day or night and in the most appropriate temporal , phase relationships . Cell -to -cell communication is essential for conveying inputs to and outputs from the SCN . The goal of the present study was to use an immortalized neural cell line (SCN2 .2 ) , derived from the presumptive anlage of the rat suprachiasmatic nucleus , as an in vitro model system to study intercellular communication among SCN cells . I tested whether the pineal neurohormone melatonin could modulate cell -to -cell signaling , via both dye coupling (gap junctional communication ) and calcium waves (ATP -dependent gliotransmission ) . I also tested whether extracellular ATP could influence the spread of calcium waves in SCN2 .2 cells . Lastly , the ability of extracellular ATP to modulate SCN physiological responses to melatonin in SCN2 .2 cells was examined . I show that melatonin at a physiological concentration (nM ) reduced dye coupling (gap junctional communication ) in SCN2 .2 cells , as determined by a scrape loading procedure employing the fluorescent dye lucifer yellow . Melatonin caused a significant reduction in the spread of calcium waves in cycling SCN2 .2 cultures as determined by ratiometric calcium imaging with Fura -2 AM , a calcium sensitive indicator dye . This reduction was greatest when an endogenous circadian rhythm in extracellular ATP accumulation , determined by luciferase assay , was at its trough or lowest extracellular concentration . In addition , melatonin and ATP interacted in the regulation of gliotransmission (calcium waves ) , and this interaction was also specific to particular phases of the endogenous SCN physiological rhythmicity . Thus , I have established that a complex interaction exists between established melatonin signaling pathways and this newly discovered ATP accumulation rhythm , with the mechanisms underlying this relationship linked to endogenous cycling of SCN cellular physiology .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2436
Date: 2009-05-15

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Melatonin modulates intercellular communication among immortalized rat suprachiasmatic nucleus cells. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2436 .

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