CLOCKING ON
It has been clearly established that a structure in the
hypothalamus of the mammalian brain, called the
suprachiasmatic nucleus (SCN), contains a ‘daily
clock’, which generates near 24 hour (i.e. circadian)
rhythmic variations in both physiology and behaviour.
This clock is synchronised to changes in environmental
illumination (i.e. day/night variations) by light
information, which is conveyed directly to the SCN by
a specialised input from the eye. The SCN neurons
send clock information to the rest of the brain and
body via nerve pathways and secretion of particular
chemicals. The SCN is composed of different cell
types, differentiated in part on the basis of the kinds
of neurochemicals that they make as well as their
location within the SCN. Further, some SCN cells
contain the necessary molecular apparatus to function
as single cell timekeepers (‘clock cells’), whereas
others lack this property. Key to progressing with
research is to be able to identify clock cells and the
chemicals via which they communicate to one another
as well as the rest of the brain.
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