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. Author manuscript; available in PMC: 2012 Dec 1.
Published in final edited form as: Neuroscience. 2011 Oct 8;197:1–7. doi: 10.1016/j.neuroscience.2011.10.005

Figure 2.

Figure 2

New model of placental contributions to the fetal brain and blood 5-HT. A, the source of 5-HT in the embryonic forebrain changes over time, from an early exogenous (placental) source to a later endogenous (dorsal raphe serotonergic neurons) source. This switch during development allows the embryo brain to progressively become dependent on its own production of 5-HT. DR, dorsal raphe; DT, dorsal thalamus; ctx, cortex. B, The placenta synthesizes 5-HT and 5-HTP from maternal blood tryptophan. This placental 5-HT (red color) is a source of 5-HT to the forebrain during an early phase of development (E10 to E15). Later (E16 to birth), the main source of 5-HT is provided by conversion of maternal tryptophan in hindbrain DR neurons and their axons throughout the forebrain.