N-methyl-D-aspartate receptors (NR) regulate neuronal plasticity, migration and excitotoxicity. The subunit composition thereby determines specific channel properties. In the postnatal cerebellum, the NR2B subunit is expressed in migrating granule cells and afterwards replaced by NR2C. We have examined the cerebellar development of transgenic mice (NR2CB) in which NR2C was exchanged by NR2B (see Eisel et al, SFN 2001). In vivo histological analyzes indicated that the thickness of the external granule layer (EGL) was increased in NR2CB mice at P7 to P10. This tendency ceased by the second postnatal week. The thickness of the internal granule layer in NR2CB mice, on the other hand, was decreased from this time on. We then analyzed cerebellar development in slice cultures of P8 mice for up to 12 days in vitro (DIV). Immunostaining for TAG-1, an axonal marker expressed by migratory granule cells, was heavily detected up to DIV6 in wild-type slices and then declined progressively. At DIV12, only <20% of the sli...