To evaluate the developmental expression profile of synaptic GIRK-containing channels, we performed quantitative postembedding immunogold labelling, and examined GIRK1, GIRK2 and GIRK3 at asymmetric synapses of CA1 pyramidal neurons in the stratum radiatum during postnatal development (Table 2). GIRK1 was detected at perisynaptic and/or extrasynaptic sites of the dendritic spines but never along the main body of the postsynaptic density (PSD) at any developmental age analysed (Fig. 7A-C). GIRK2 and GIRK3, however, were observed along the PSD at all developmental ages, each displaying different patterns. At P5, GIRK2 immunoparticles were detected at low levels along the PSD (1.03 ± 0.11 immunoparticles/labelled synapse; Fig. 7D; Table 2), increased by P15 (1.84 ± 0.11 immunoparticles/labelled synapse, p < 0.05; Fig. 7E) and were highest at P60 (2.51 ± 0.12 immunoparticles/labelled synapse, p < 0.05; Fig. 7F). In contrast, we observed a similar number of GIRK3 immunoparticles per synapse and percentage of synapses labelled at all ages studied (P5, 1.47 ± 0.11 immunoparticles/labelled synapse; P15, 1.53 ± 0.11 immunoparticles/labelled synapse; P60, 1.54 ± 0.12 immunoparticles/labelled synapse; Fig. 7G-I, Table 2). We used anti-PSD-95
