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Chronobiology International
The Journal of Biological and Medical Rhythm Research
Volume 26, 2009 - Issue 8
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Research Papers

EARLY PROGRAMMING OF ASTROCYTE ORGANIZATION IN THE MOUSE SUPRACHIASMATIC NUCLEI BY LIGHT

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Pages 1545-1558 | Received 22 May 2009, Accepted 05 Jul 2009, Published online: 23 Dec 2009
 

Abstract

The principal pacemaker in mammals, controlling physiology and behavior, is located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Early photic experience has long-term effects on the animal's rhythmic behavior, as indicated by alterations in the phase shift induced by a light pulse, and in the expression of the circadian rhythm of locomotor activity under light-dark (LD), constant light (LL), and constant darkness (DD) environments. However, the brain substrates targeted by early light have not yet been identified. Possible candidates are astrocytes, as they develop postnatally in parallel to the circadian system, and are involved in SCN function by modulating intercellular communication and mediating photic input. Here, we reared three groups of mice under different light environments (LD, LL, and DD) during the suckling period. Later on, all mice were entrained to LD, and we determined associated astrocytic modifications by examining the expression of glial fibrillary acidic protein (GFAP) in the SCN. We observed that although LL-reared mice showed lowest GFAP expression in the SCN, as determined by quantification of immunostaining levels, the number of GFAP-positive cells was highest in this group, suggesting structural remodelling of SCN astrocytes by early light experience. These results indicate the postnatal light environment has long-term effects on the astrocytic population of the SCN. We argue that these neurochemical and structural alterations may affect clock function, which may in turn modify animal behavior (Author correspondence: [email protected], [email protected]).

ACKNOWLEDGMENTS

This work was supported by funding from the Research Councils UK, and the Biotechnology and Biological Sciences Research Council (BBSRC) to MMC. NMM was a recipient of a Nuffield Science Undergraduate Research Bursary.

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