The suprachiasmatic nucleus of the domestic chicken, Gallus domesticus

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Title: The suprachiasmatic nucleus of the domestic chicken, Gallus domesticus
Author: Cantwell, Elizabeth Layne
Abstract: The avian circadian system is composed of multiple inputs , oscillators and outputs . Among its oscillators is a hypothalamic structure presumed to be homologous to the primary circadian pacemaker in mammals , the suprachiasmatic nucleus (SCN ) . The SCN in avian species is poorly defined : two structures in the hypothalamus , the medial SCN (mSCN ) and visual SCN (vSCN ) , have been referred to in the literature as the SCN . The present studies were designed to answer one central question : where is the avian homolog to the mammalian SCN ? Uptake of 2 -[14C] -deoxyglucose (2DG ) , an indicator of glucose metabolism , fluctuates in the mSCN and vSCN in both a daily and circadian manner . These data indicate a possible role in the circadian system for both the vSCN and the mSCN . Additionally , several visual structures display daily fluctuations of 2DG uptake , two of which exhibit circadian variations , supporting previous studies indicting circadian regulation of the visual system . Efferents and afferents of the mSCN and vSCN were identified and compared to those of rodents . While the mSCN bears a stronger resemblance to the rodent SCN in its efferent connections than the vSCN , afferents of both are comparable . The total number of mSCN and vSCN neuronal connections far exceeds that of the rodent SCN . A subset of these connections is strikingly similar to those of the rodent SCN , while others are found to connect these two nuclei to the visual system . These data further support the involvement of both the mSCN and vSCN in the circadian and visual systems . Suprachiasmatic organization was addressed using classical techniques . Though loosely similar in location to the mammalian SCN , the mSCN is cyto - and chemoarchitecturally different , while the vSCN bears more similarity to the mammalian SCN in this regard . A unique astrocytic bridge exists between the mSCN and vSCN , suggesting a role for astrocytes in the circadian system . Finally , the vSCN efferent to the medial nucleus of Edinger -Westphal was verified using a technique that may advance future studies of avian of circadian organization . The current data and the available literature were considered in the development of a working model of the avian SCN .
URI: http : / /hdl .handle .net /1969 .1 /4655
Date: 2007-04-25

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The suprachiasmatic nucleus of the domestic chicken, Gallus domesticus. Available electronically from http : / /hdl .handle .net /1969 .1 /4655 .

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