Labelling for GIRK1 in the hippocampus was weak at P0 (Fig. 1A) and more detectable at P5 (Fig. 1A), whereas it appeared only around P10 for GIRK2 and became strong at P15 (Fig. 1A). The first labelling for GIRK3 in the hippocampus was detected weakly at P5 and increased steadily until P60 (Fig. 2A). Densitometric measurements performed in the hippocampus demonstrated that, at all developmental stages, immunoreactivity for GIRK1, GIRK2 and GIRK3 was generally greatest within the CA1 region, CA3 region and molecular layer of the dentate gyrus, and lowest in the hilus (Figs 1B and C, and 2B). Furthermore, in all of those subregions of the hippocampus, GIRK1 and GIRK3 proteins increased from the lowest levels at P5-P10 to the highest level at P60, whereas GIRK2 expression remained relatively consistent, with only minor increases early on and levelling out after P15.
