Generation of GABA-synthesizing nerve cells cultured from embryonic cortex cerebri of mice with and without cell-to-cell contacts.

Neuroblasts, growing from cerebral cortices of embryonic mice, Theiler stages 16, 19, 20, 21, 23 and 24 (embryonic days (ed) 10, 11 1/2, 12, 13, 15 and 16) were cultured in plasma clot and serum-containing MEM-medium in whole-mount cultures, suspension cultures or single-cell cultures. In whole-mount cultures, cell connections were preserved, allowing continuity of cell interactions in vivo and in vitro. In suspension cultures cell adherences and contacts were interrupted by the dissociation procedure. However, contacts re-establish when cells re-aggregate. In single-cell cultures, neuroblasts were cultured without cell-to-cell contacts, and were deprived of potentially mediating cell interactions. Individual features of these cells supposedly reflected both the effect of the medium-derived environment and the state of their intrinsic program at the time of culturing. The neuroblasts' potential for differentiation into GABAergic neurons was studied in all three kinds of culture. GABAergic neurons developed in both tissue samples and suspension cultures, in small numbers from 11 1/2-day-old embryos (stage 19), but in increasing numbers in cortices of advanced ages. GABA immuno-reactivity starts at day 3 in vitro and persists throughout the whole culture period of up to 26 days. Neuroblasts developed in sufficient numbers without cell-to-cell contacts at the earliest in cultures from 12-day-old embryos (stage 20). At that time a few nerve cells expressed GABA after 3 days in vitro. Immunoreactivity increased and persisted until at least day 9. These results indicate that the GABAergic phenotype is expressed irrespective of whether physical cell-to-cell contacts are present or not. Moreover, differences are apparent in the intrinsic program of neuroepithelial cells prior to their display in vivo.