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 i mmunohistochemically during development of the rat cerebellum GluR2/3 immunoreactivity appeared by postnatal day PO in somata of Purkinje ce lls. Throughout P7, P15, P20 and adulthood, GluR2/3 immunoreactivity w as found in the entire Purkinje cell dendritic arbor reaching to the e xternal 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 t he multi-layered Purkinje cell somata. By P15, NR1 was prominent in Pu rkinje cell somata and Golgi cells. The reaction product extended into the primary main dendrite of Purkinje cells. By P21, stellate and bas ket cells had intense reactivity throughout the molecular layer and re active large-diameter dendrites of Golgi cells projected toward the mo lecular layer. Granule cells remained very weak among strongly reactiv e Golgi cell somata and dendrites. Ultrastructural immunohistochemistr y revealed NR1 reaction product in Purkinje cell somata, in stellate c ell somata and dendrites and on postsynaptic membranes of scattered sp ines throughout the molecular layer. The later appearance and restrict ed location of NR1 in somata and proximal dendrites of Purkinje cells contrasted markedly with GluR2/3 which appeared before birth and remai ned prominent throughout Purkinje cell dendritic arbors of adults. The time of NR1 expression correlated with the generation of granule cell s, their synaptogenesis on Purkinje cells, the formation of stellate/b asket cells and the shift of climbing fibre synapses from distal to pr oximal dendrites. The developmental appearance of stellate/basket cell s and Golgi cells as well as their high reactivity remaining into adul thood suggest that these inhibitory molecular and granular layer inter neurons are the principal targets of glutamate axons serving NR1 synap tic properties while Purkinje cells and brush type granule cells are t argets for glutamate connections with GluR2/3 characteristics. (C) 199 7 IBRO. Published by Elsevier Science Ltd.