Interactions of neurons and astrocytes during growth and development of human fetal brain in vitro

Morphologic details of interactions between neurons and astrocytes from human fetal cerebrum during the early phases of in vitro growth in dissociated cultures are described. There is an intimate relationship between these two cell types characterized by aggregation of neurons along the surface of the soma and processes of astrocytes and subsequent migration along astrocytic processes. Neurons form long processes that establish contact with other astrocytes. The occurrence of these features in dissociated cultures strengthens the significance of similar findings observed in the outgrowth of organotypic cultures. Dissociated cultures establish, furthermore, that the production and growth of neurites and survival of neurons during this early period in vitro are dependent upon the development of this close relationship with astrocytes. Another feature of this cellular interaction observed at the ultrastructural level in organotypic cultures is the development of an unusual type of junction between neurites and astrocytes, characterized by deposition of intermembranous electron-dense material. The findings suggest that the relationship between neurons and astrocytes is an important aspect of neural ontogenesis and lend further support to the thesis that astocytes play a role in neuronal migration and differentiation. The combined criteria for identification of neurons and astrocytes in culture based upon multiple procedures, including bright field stains, phase contrast microscopy, electron microscopy, and immunofluorescence are also reviewed in detail.