rough endoplasmic reticulum. This early postnatal distribution was distinct from later stages when GIRK1 and GIRK2 migrate into dendritic shafts and spines of CA1 pyramidal neurons, and in the adult they are mainly localized to spines (Koyrakh et al., 2005), consistent with previous studies (Drake et al., 1997; Lüscher et al., 1997; Ponce et al., 1996). Although GIRK3 generally followed this spatial and temporal distribution pattern at postsynaptic sites, it appears to have a preferential localization at presynaptic sites in glutamatergic terminals establishing synapses with CA1 neurons during development, as also suggested in culture neurons (Grosse et al., 2003). This presynaptic localization of GIRK channel subunits is consistent with previous morphological (Marker et al., 2005; Morishige et al., 1996; Ponce et al., 1996) and functional (Fernández-Alacid et al., 2009) observations, although the relevance of GIRK3 in axon terminals in the hippocampus is still unknown.
