The Development of Circadian Rhythms in Human Infants

melatonin is measured in the blood circulating volume, it is a direct measure of the
quantity of melatonin produced.
The secretion of melatonin is under direct control of the suprachiasmatic nucleus
(SCN). Information about darkness and light is relayed to the SCN from the retina,
via specialist nerve pathway called the retinohypothalamic fibres. During the day,
bright lights inhibit melatonin production. It reaches maximum concentrations during
periods of darkness (Reiter, 1991).
1.6.2 Actions of Melatonin
A major role of melatonin involves determination of circadian rhythmicity. Body
temperature and night time sleep, are directly influenced by levels of melatonin within
the body.
In animal studies, melatonin has also been identified as a potent free radical scavenger
with anti-oxidative properties. Its mode of action is thought to be related to enhancing
the amount of detectable specific active enzymes. There is little data on how this
translates in the human body as reviewed by Claustrat (Claustrat et al., 2005).
Melatonin is also thought to have a role in immunity by being involved in some way
in the interaction between the immune system and the central nervous system
(Cardinali & Pévet, 1998, Guerrero & Reiter, 2002, Claustrat et al., 2005). It is
involved with T helper cell recruitment. It also is thought to increase natural killer
cell activity. Some work suggests that it works in direct opposition to steroid induced
immunosuppression and prevents T cell death (Shneerson, 2005). The exact
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