At P0 and P5, GIRK2 was expressed intensely in the principal cells of all hippocampal subregions, with stronger labelling seen in the dendritic layers (Fig. 4B1 and B2) as compared with GIRK1. During the second postnatal week (P10), principal cell layers of areas CA1 and CA3, and the dentate gyrus displayed relatively weak labelling, whereas more intense labelling was found in the dendritic layers, particularly in the CA3 and molecular layer of dentate (Fig. 4B3). At P15 and P21, the pattern of GIRK2 immunolabelling was similar, but stronger than that observed at P10, only showing a stronger signal in the stratum lacunosum–moleculare of the CA1 region (Fig. 4B4 and B5). At P60, immunolabelling for GIRK2 was strong in the stratum lacunosum–moleculare in the CA1 region, whereas the stratum radiatum showed an uneven labelling with moderate intensity in the proximal half and high intensity in the distal half, and the stratum oriens showed moderate intensity (Fig. 4B6). In the CA3 region, GIRK2 immunoreactivity was strongest in the strata oriens, radiatum and lacunosum–moleculare, compared with the more moderate expression in the stratum
