Selective cell association of catecholamine neurons in brain aggregates in vitro.

Brain tissues (aggregates) were reconstructed in vitro from dissociated single cell suspensions derived from 12- to 18-day embryonic mouse midbrain containing the substantia nigra. The application of the Falck-Hillarp histofluorescence method to these cell systems allows the visualization and identification of this specific population of developing catecholamine (CA) neurons during their reassembly, differentiation and histogenetic patterning in vitro. CA neurons are unselectively distributed in the initial dissociated cell suspension and in the reaggregating tissue up to 24 h. By 48 h the CA neurons have selectively associated into small clusters which further coalesce into a thick and elongated band along one margin of the aggregate by 96 h. This structure is similar in organization to the morphology exhibited by substantia nigra neurons in situ during their migratory phase in normal development. In addition, the differentiated neurons observed in the later aggregates appear to produce normal processes. Catecholamine analyses show a significant increase in dopamine and noradrenaline levels during the process of differentiation and histogenetic organization in vitro.