Twenty-four-hour rhythms in cerebral and brainstem contents of 5-hydroxytryptamine in a turtle, Pseudemys scripta elegans

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.

Serotonin in the control of the sleep-like states in frogs

It has been established that brain serotonin (5-HT) is involved in the control of behavioral phenomena in amphibians. The transition of frogs from active wakefulness to sleep-like states was accompanied by alteration of brain 5-HT metabolism, i.e., in sleep-like state with plastic muscle tone 5-hydroxyindoleacetic acid (5-HIAA) level was reduced and in sleep-like state with rigid muscle tone both brain 5-HIAA and 5-HT were decreased. An experimental decrease of brain 5-HT level by inhibition of its biosynthesis by p-chlorophenylalanine (200 mg/kg) induced the sleep-like state of catatonic type, i.e., the state which was characterized by lowered brain 5-HT.