Distribution of glutamate receptors GluR 2/3 and NR1 in the developing rat cerebellum

The distribution of glutamate receptors GluR2/3 and NR1 was analysed immunohistochemically during development of the rat cerebellum. GluR2/3 immunoreactivity appeared by postnatal day P0 in somata of Purkinje cells. Throughout P7, P15, P20 and adulthood, GluR2/3 immunoreactivity was found in the entire Purkinje cell dendritic arbor reaching to the external granular layer and, by P15, the surface of the cerebellum. By P7, the granular layer revealed scattered, mildly reactive, cells. NR-1 immunoreactivity first gained prominence about P7 in the region of the multi-layered Purkinje cell somata. By P15, NR1 was prominent in Purkinje cell somata and Golgi cells. The reaction product extended into the primary main dendrite of Purkinje cells. By P21, stellate and basket cells had intense reactivity throughout the molecular layer and reactive large-diameter dendrites of Golgi cells projected toward the molecular layer. Granule cells remained very weak among strongly reactive Golgi cell somata and dendrites. Ultrastructural immunohistochemistry revealed NR1 reaction product in Purkinje cell somata, in stellate cell somata and dendrites and on postsynaptic membranes of scattered spines throughout the molecular layer. The later appearance and restricted location of NR1 in somata and proximal dendrites of Purkinje cells contrasted markedly with GluR2/3 which appeared before birth and remained prominent throughout Purkinje cell dendritic arbors of adults. The time of NR1 expression correlated with the generation of granule cells, their synaptogenesis on Purkinje cells, the formation of stellate/baske cells and the shift of climbing fibre synapses from distal to proximal dendrites. The developmental appearance of stellate/basket cells and Golgi cells as well as their high reactivity remaining into adulthood suggest that these inhibitory molecular and granular layer interneurons are the principal targets of glutamate axons serving NR1 synaptic properties while Purkinje cells and brush type granule cells are targets for glutamate connections with GluR2/3 characteristics.