A developmental study of the effects of 5,7-dihydroxytryptamine on regional tryptophan hydroxylase in rat brain.

Tryptophan hydroxylase activity rises rapidly after birth in 5 distinct regions of the rat CNS. Near-adult levels of activity are recorded by 22 days of age in the cell-body rich regions of the brainstem and by 42 days in the terminal-rich areas, hypothalamus and remaining forebrain. The intracisternal injection of 40 mug 5,7-dihydroxytryptamine on day 2 after birth results in a near-total depletion of tryptophan hydroxylase in all CNS regions analyzed 6 or 12 days after drug administration. Enzyme activity recovers (to 11-24% of age matched controls) between day 12 and 20 after 5,7-dihydroxytryptamine in hypothalamus, midbrain and pons medulla oblongata. The growth of 5,7-DHT-treated animals is retarded between 3 and 40 days after drug administration.