GAD67-containing neurons in coronal sections of the developing hippocampal formation at E20. A, At E20, GAD67-containing cell bodies within the hippocampal and dentate marginal zones (hMZ and dMZ) are even more striking and abundant than at earlier ages (compare with Fig.1B, C). Within the dentate marginal zone, many of the positively labeled cells are concentrated slightly above the outer border of the developing granule cell layer (G). Labeled neurons extend throughout the hippocampal marginal zone and form a clear border with the immediately adjacent pyramidal cell layer (P). B, A high-magnification photomicrograph of the CA1 and dentate marginal zones shown in A demonstrates the morphology of the GAD67-immunoreactive cells within these regions. The labeled neurons have variable sizes and shapes and process orientations, but several within the dentate marginal zone exhibit fusiform shapes, are aligned with their long axis parallel to the granule cell layer, and possess horizontally oriented processes (arrows). The close proximity of the GAD67-containing neurons to the pyramidal (P) and granule (G) cell body layers is also evident. Scale bars: A, 50 μm; B, 25 μm.