Figure 2. Labeling of different subpopulations of OB projection neurons using in utero electroporation. A, Coronal sections of the OBs from adult mice in which electroporations were performed at E11 (A1) or E12 (A2). GFP is expressed only in mitral and tufted cells. IUE@E12 preferentially labeled mitral cells in the ventrolateral part of the OB. B, Quantification of mitral and tufted cells in the OB. Cells that have GFP+ somata in the MCL and EPL were defined as mitral cells (marked with asterisks) and tufted cells (marked with plus signs), respectively. C, Ratios of mitral cells to tufted cells calculated from IUE@E11 (n = 5) and IUE@E12 (n = 7) OBs are shown with box plots. D–F, Projection of GFP+ axons to the anterior (D1, E1, F1) and posterior (D2, E2, F2) part of the olfactory cortex in the IUE@E11 (E) and IUE@E12 brain (F). Reference brain regions observed in E, F are cited from a mouse brain atlas (Paxinos and Franklin, 2001). GFP+ axons are seen in the anterior PIR of both IUE@E11 (E1) and IUE@E12 (F1) brains, whereas only the IUE@E11 brain has a significant GFP signal in the posterior PIR (E2, F2). Scale bars: 200 μm (A), 50 μm (B), and 500 μm (E, F). EPL: external plexiform layer; MCL: mitral cell layer; CC: corpus callosum; AC: anterior commissure; LOT: lateral olfactory tract; PIR: piriform cortex; OT: olfactory tubercle; LV: lateral ventricle; COApl and COApm: posterolateral and posteromedial cortical amygdala; ENTl: lateral entorhinal cortex.