Embryonic raphe neurons grafted in vitro on fetal spinal cord slices recognize specific target areas

Abstract

To investigate the characteristics of neurotropic signaling involved in specific target recognition by grafted embryonic serotonergic cells, we have developed an in vitro grafting model. Specific raphe nuclei (B1/B2 and B3) were respectively dissected from 14-day-old rat embryos, and partially dissociated cells were cocultured on spinal cord slices from 20-day-old fetuses. After serotonin immunodetection, neurite growth patterns were analyzed by standard photonic or confocal scanning microscopy. Computer reconstruction (maximal signal projection) was used to track individual neurites in spite of their changing depth levels. Whereas the direction and branching of the initial neurite segments did not seem to be significantly influenced by any specific environment, specific growth patterns were developed at some distance from the cell bodies, indicating that neurites are able to recognize their specific targets.