Spatial Organization of the Components of the Serotonergic System in the Early Mouse Development

Serotonin is a regulator of early embryonic development and has a complete functional system in preimplantation mammalian embryos. In the present work, the spatial distribution of serotonin, the vesicular monoamine transporter VMAT2, and the 5-HT_1D and 5-HT_2A receptors at different stages of early embryonic development was described. Serotonin, the VMAT2 transporter, and the 5-HT_1D receptor are visualized in the cortical compartment of cells, whereas the 5-HT_2A receptor has a more even distribution throughout the cytoplasm. The comparison showed that there were no statistically significant differences between the immunoreactive particle sizes of serotonin and the VMAT2 transporter, suggesting the presence of vesicles in which serotonin accumulates with the involvement of VMAT2 for further intercellular signal transduction. Moreover, the patterns of immunoreactivity of the two serotonin receptors, 5-HT_1D and 5-HT_2A, differ markedly, which may indicate that they simultaneously serve different functions in early embryogenesis.