CHANGES IN SUBCELLULAR-LOCALIZATION OF METABOTROPIC GLUTAMATE-RECEPTOR SUBTYPES DURING POSTNATAL-DEVELOPMENT OF MOUSE THALAMUS

High resolution immunoelectron microscopy was used to study subcellula r localization patterns of three metabotropic glutamate receptor subty pes (mGluR1 alpha, mGluR5, and mGluR2/3) during postnatal development of mouse ventral posterior (TP) thalamic nucleus. Immunoreactivity for all three mGluRs was detected from birth (postnatal day 0, PO), but; mGluR1 alpha showed dramatic changes in localization with age. In the first postnatal week, mGluR1 alpha immunoreactivity was mainly found i n proximal dendrites and somata and not usually associated with synapt ic contacts. From the second postnatal week, it became concentrated in distal dendrites and preferentially associated with corticothalamic ( RS) synapses. mGluR5 immunoreactivity was weaker than mGluR1 alpha imm unoreactivity at all postnatal ages and showed a similar change in sub cellular distribution to that of mGluR1 alpha. It was also localized i n astrocytic processes, mGluR2/3 immunoreactivity was mainly localized in astrocytic processes surrounding neuronal somata and synapses and this pattern was consistently maintained through all postnatal ages. A small number of presynaptic axon terminals were labeled for mGluR2/3 immunoreactivity and formed asymmetrical synapses. This study demonstr ates that Group I mGluR proteins (mGluR1 alpha and mGluR5) become redi stributed in association with the development of corticothalamic funct ion as demonstrated physiologically, whereas Group II mGluR proteins ( mGluR2/3) are mainly associated with neuroglia. (C) 1998 Wiley-Liss, I nc.