Postnatal developmental changes of tryptophan hydroxylase activity in serotonergic cell bodies and terminals of rat brain.

Tryptophan hydroxylase (TPH) is the rate limiting enzyme in serotonin biosynthesis, so its development is very important to the functional maturation of the serotonergic neurons. In the present study, we examined changes of TPH activity in serotonergic cell bodies and terminals of rat brain during postnatal development. TPH activity reached its peak in the cell body regions at 24 days after birth, while the enzyme activity in a terminal region rose to its plateau at day 30. TPH activity in adult rat is the highest in nucleus raphe dorsalis, then nucleus raphe centralis and hypothalamus in a decreasing order.