[Serotonin as a neurotrophic factor in the fetal brain: binding, capture and release in centers of axonal growth]

Currently serotonin (5-HT) is recognized as one of the classic neurotransmitters in the adult brain. Results from our laboratory have suggested a trophic role of 5-HT in the fetal brain. Stimulation of 5-HT synthesis during gestation with its precursor, L-tryptophan, has shown the existence of biosynthetic machinery for this amine in the fetal brain. Attempts to demonstrate directly a molecular recognizing system for 5-Ht in the fetal brain have not been conclusive until now. We have profited of a special preparation of axonal growth cones (AGC) derived from neuroblasts of the rat fetal brain. In this neuronal structures actively differentiating we were able to demonstrate a high-affinity and saturable uptake system for 5-HT and the possibility of a regulated release of the amine. In postnatal AGC the 5-Ht uptake has similar kinetics to the adult, whereas fetal AGC have a transitional uptake kinetics with a higher Vmax for the amine. Also in these structures we demonstrated, directly, for the first time, a specific binding system for (3H) 5-HT, saturable, reversible and of high affinity. Altogether, these results strongly support the hypothesis of an important trophic role of 5-HT during neurogenesis.