THE BRAIN TRYPTOPHAN-HYDROXYLASE ACTIVITY IN THE SLEEP-LIKE STATES INFROG

The activity of the rate-limiting enzyme of serotonin biosynthesis, tr yptophan hydroxylase, was determined in the brain stem in active awake frogs, and frogs in three sleep-like states: with plastic muscle tone (SLS-1), with rigid muscle tone (SLS-2), and with relaxed muscle tone (SLS-3). Significant decrease in the enzyme activity has been found i n frogs in SLS-1 and SLS-2 compared to awake animals. The development in frogs a cataleptic-like immobility after treating the animals with rhythmic lighting was accompanied with a decrease in the brain tryptop han hydroxylase activity. These results provide strong evidence for th e involvement of the brain serotonin in frogs in the control of evolut ionary ancient sleep-like states, probably by the regulation of muscle tone.