GAD67-containing neurons in coronal sections of the developing hippocampal formation at E21 and P1. A, At E21, the cell bodies of GAD67-containing neurons are less evident than at E20, but a plexus of GAD67-containing processes now occupies a substantial portion of the hippocampal and dentate marginal zones (hMZ and dMZ). B, By P1, the GAD67-containing fine fibers with periodic varicosities are extensive. The GAD67 fibers with occasional swellings occupy a large portion of the presumptive hippocampal and dentate dendritic fields, the strata radiatum and lacunosum/moleculare (R/LM) and dentate molecular layer (M). Many of these terminal-like structures lie immediately adjacent to the pyramidal (P) and granule (G) cell layers. Scale bars: A, 100 μm;B, 50 μm.