Rhythms in neurotransmitter turnover: focus on the serotonergic system.

Circadian rhythms in the turnover of many neurotransmitters (e.g. serotonin, noradrenaline, melatonin, substance P, neuropeptide Y) are well known, but the mechanisms responsible for the rhythms in these transmitter systems are less well understood. One of the most extensively studied neurotransmitter systems, in terms of circadian rhythms, is the serotonergic system. This article has therefore focused on this system in order to highlight the approaches that have been taken and the possible mechanisms that may be involved in controlling the rhythmic nature of serotonergic neuronal function, and in particular, neurotransmitter release and metabolism.