GAD67-containing neurons in coronal sections of the developing hippocampal formation at E18 and E19. A, At E18, a prominent population of GAD67-containing neurons is present within the hippocampal marginal zone (hMZ). These GAD67-positive neurons appear to be in continuity with the GAD67-labeled neurons of the neocortical marginal zone (cMZ). Positively labeled neurons are also dispersed throughout the subplate (SP) and lower intermediate zone (LIZ). B, At higher magnification, the cell bodies of GAD67-containing neurons within the hippocampal marginal zone at E18 are clearly delineated. Several of the labeled neurons within this zone are located immediately adjacent to the developing pyramidal cell layer (P). The labeled structures in the lower left corner are red blood cells that exhibit endogenous peroxidase activity.C, At E19, GAD67-containing neurons now occupy positions within the CA1 and CA3 hippocampal marginal zones and the dentate marginal zone (dMZ). The positively labeled neurons appear as a single row in the dentate marginal zone. Scale bars: A, 100 μm; B, C, 50 μm.