The development and ultrastructure of previously dissociated foetal human cerebral cortical cells in vitro

Cells from foetal human cerebral cortex were mechanically dissociated and subsequently maintained in vitro for periods ranging between three and twenty-eight days. The ultrastructure of these cells at different stages of their development in culture was extensively examined. Nuclear and cytoplasmic features were extremely variable and a wide range of cell types was evidently represented. Of the three principal cell types found i.e. neurons, neuroglia and mesenchymal cells, only a minority of cells was classified with confidence, particularly during the first two weeks in culture. Extensive intercellular junctions of the adhaerens variety, common after 14 days in vitro were present at an earlier stage of development than synaptic profiles. First indications of synapse formation were observed after 21 days in vitro and after 24 days presynaptic sites filled with synaptic vesicles and with well defined presynaptic and postsynaptic thickenings were found. The significance of some of the features observed are both considered and discussed.