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.