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Science 22 December 2006:
Vol. 314. no. 5807, pp. 1941 - 1944
DOI: 10.1126/science.1132009
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Reports

Characterizing a Mammalian Circannual Pacemaker

Gerald A. Lincoln,1* Iain J. Clarke,2 Roelof A. Hut,3 David G. Hazlerigg4

Many species express endogenous cycles in physiology and behavior that allow anticipation of the seasons. The anatomical and cellular bases of these circannual rhythms have not been defined. Here, we provide strong evidence using an in vivo Soay sheep model that the circannual regulation of prolactin secretion, and its associated biology, derive from a pituitary-based timing mechanism. Circannual rhythm generation is seen as the product of the interaction between melatonin-regulated timer cells and adjacent prolactin-secreting cells, which together function as an intrapituitary "pacemaker-slave" timer system. These new insights open the way for a molecular analysis of long-term timing mechanisms.

1 Centre for Reproductive Biology, University of Edinburgh, The Queen's Medical Research Institute, Edinburgh, Scotland.
2 Department of Physiology, Monash University, Melbourne, Australia.
3 Department of Chronobiology, University of Groningen, Haren, Netherlands.
4 School of Biological Sciences, University of Aberdeen, Aberdeen, Scotland.

* To whom correspondence should be addressed. E-mail: g.lincoln{at}hrsu.mrc.ac.uk

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