Circadian rhythms are biological oscillations, that perpetuate themselves even in the
absence of “zeitgebers” (external time cues), with a period of
approximately 24 hours. The master pacemaker is the suprachiasmatic nucleus
(SCN) of the hypothalamus. The SCN is entrained by environmental factors,
particularly light, to the 24-hour light-dark cycle by the Earth’s rotation.
Peripheral circadian oscillators, located in multiple cell types and tissues, are
controlled by signals arising from the SCN and from the environment, particularly
food intake, hormonal signals and body-temperature fluctuations. Circadian
rhythmicity is observable in almost every cell of living organisms including humans
and, for example in cell cultures, these rhythms persist even without the SCN [1]
[2].
Key words
Attention-deficit/hyperactivity disorder(ADHD) - Circadian rhythm - Molecular biology - Neurotransmitters - Fibroblast cell culture
