Erg1, but not erg3, is located in PV-containing interneurons throughout the hippocampus, but both are coexpressed in CA1 pyramidal cells. A–G, ISH using erg1 antisense probe. A, Erg1 expression within the CA1 pyramidal cell layer and scattered cells throughout the hippocampus.B–D, Dual labeling for erg1 and PV in the CA1 subfield.B, Bright-field image of erg1-positive neurons.C, Immunofluorescent detection of PV-reactive interneurons found on the margin of the CA1 pyramidal cell layer.D, Overlay of C and D with erg1 pseudocolored green. Note that many of the strongly labeled neurons in B are also PV positive (B–D, arrows). E–G, Dual labeling for erg1 and PV in the CA3 hippocampal subfield.E, Erg1 expression is found in the pyramidal cell layer and stratum radiatum. F, PV immunoreactive interneurons in the CA3 (arrows). G, Overlay ofE and F with erg1 pseudocoloredgreen. Note less erg1 expression in the CA3 pyramidal cell layer as compared with the CA1 (compare green cells in D and G). Similar to the CA1, several PV-positive neurons also expressed erg1 (E–G,arrows). However, not all erg1-positive neurons located outside the pyramidal cell layer were PV positive (E,G, arrowheads). H–N, ISH using erg3 antisense probe. H, Erg3 expression was very strong and concentrated on the CA1 hippocampal subfield.I–N, Dual labeling of erg3 transcripts and PV-immunoreactive interneurons in the CA1. I, Erg3 expression was located within the pyramidal cell layer of the CA1, but not in scattered cells located outside as observed using erg1 probe (compare B and I).J, Immunolocalization of PV+ interneurons located along the CA1 pyramidal cell layer. K, Overlay ofI and J with erg3 pseudocoloredgreen. L–M, High magnification ofI–K, respectively, showing that erg3 labeling does not colocalize with PV (arrows). Scale bar (shown inN): A, 1000 μm;B–G, I–K, 100 μm;H, 810 μm; L–N, 50 μm.