The development of the hippocampal network requires neuronal activity, which is shaped by the differential expression and sorting of a variety of neurotransmitter receptors and ion channels. Parallel to their maturation, hippocampal neurons undergo a distinct development of their neurotransmitter receptor/ion channel profiles. Specific neurotransmitter receptors and ion channel subunits are developmentally regulated in the hippocampus, in a parallel process in the establishment and maturation of synaptic contacts (Luján et al., 2005). However, data regarding the exact temporal expression of GIRK channels are scarce. Here, the use of high-resolution immunoelectron microscopy yielded novel findings about the differential trafficking of GIRK1, GIRK2 and GIRK3 to the dendritic compartments as a function of age. Thus, during the first week of postnatal development, GIRK1 and GIRK2 were largely expressed in the somata of CA1 pyramidal neurons, almost entirely intracellular in association with the 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),
