Serotonin synthesis from tryptophan by hypothalamic cells in serum-free medium culture

The hypothalamus of both adult and fetal rats contains a population of cells which can exhibit some features of serotoninergic (5-HT) neurons under certain circumstances. However, their neuronal serotoninergic nature is still controversial. In fact the presence of tryptophan hydroxylase activity has not yet been clearly established. This study attempted to verify whether [3H]5-HT can be synthesized from [3H]tryptophan ([3H]TRP) in hypothalamic cell cultures from 16-day-old fetuses. Data showed that [3H]5-HT was synthesized from [3H]TRP and the amounts of [3H]5-HT increased linearly as a function of time for 60 min. Pargyline markedly increased the quantities of [3H]5-HT and decreased those of [3H]5-hydroxyindole acetic acid, [3H]5-HT synthesis was inhibited by p-chlorophenylalanine, while α-methyl-p-tyrosine had no effect. The present biochemical study shows the presence of an intrinsic 5-HT neuronal system in the hypothalamus of the fetal rat.