Maternal influences on tryptophan hydroxylase activity in embryonic rat brain

Maternal treatment with p-chlorophenylalanine strongly inhibits brain tryptophan hydroxylase (TPH) activity in the embryo, whereas administration of tryptophan significantly elevates the activity of this enzyme. Maternal stress, glucocorticoid injections, or a corn diet (low in tryptophan) do not change embryonic TPH activity, however. Since TPH is thought to be rate-limiting for serotonin (5-HT) synthesis in the developing animal as well as in the adult altered TPH activity as a result of maternal influences could change 5-HT synthesis in the embryo. If 5-HT is a developmental signal in the early differentiation of specific neurons during embryogenesis, as previously suggested, such maternal influences could affect this process, resulting in altered neuronal genesis in those brain regions receiving a serotonergic innervation.