Fig. 5. Morphology and migration properties of cells released from the PSB or MGE explants in culture. (A-G) Cell migration and axonal outgrowth from stage 14 (A), 16 (B) and 18 (C) telencephalic turtle explants cultured on a laminin substrate. Explants prepared from the DC, DVR, PSB, LGE or MGE were cultured for 2 days and stained for GABA or ß-tubulin (TuJ1). Large numbers of GABAergic neurons migrated from MGE explants at stage 14 and 16, and from LGE explants at stage 18. PSB explants released a significant number of cells from stage 14 to 18. Cells around the DVR and cortical explants were always few in number. Long and dense axons were only observed around pallial explants. At high magnification, cells released from PSB (D) explants show longer neurites and larger somas than cells released from MGE (E) explants, which show large growth cones. (F) Summary of semi-quantitative analysis of the cell migration and axonal outgrowth (by the method explained in Fig. 4 legend). At least six explants of the same origin were analyzed at each stage. (G) Diagrams showing lateral views of stage 16 and 18 hemispheres summarizing the origin of explants that released migrating cells in vitro. Regions in dark gray released high cell densities, those in light gray released few cells. As development proceeds, LGE and PSB explants produce more cells, whereas this capacity decreased in the MGE. (H-I'') CMFDA placement (asterisk) in the PSB (H) of a stage 16 slice labeled cells with thick leading neurites and frequent bifurcations (H', arrows). Placement in the MGE (I) of a stage 16 slice labeled densely packed cells that showed simpler and thinner neurites (I'). GABA immunostaining (red in H'',I'') revealed numerous processes and cell bodies in slices. In optical sections obtained with confocal microscopy at the surface of each slice (H'',I''), a significant proportion of cells labeled from the PSB or MGE with CMFDA are GABA-immunopositive (arrowheads). Scale bars: 50 µm in C,D,H-I''; 100 µm in E.