GLUTAMATE-RECEPTOR SUBUNITS AT MOSSY FIBER-UNIPOLAR BRUSH CELL SYNAPSES - LIGHT AND ELECTRON-MICROSCOPIC IMMUNOCYTOCHEMICAL STUDY IN CEREBELLAR CORTEX OF RAT AND CAT

The present study provides a survey of the immunolocalization of ionot ropic glutamate receptor subunits throughout the rat and cat cerebella r cortex, with emphasis on the unipolar brush cell (UBC), a hitherto n eglected cerebellar cell that is densely concentrated in the granular layer of the vestibulocerebellum and that forms giant synapses with me ssy fibers. An array of nine previously characterized antibodies has b een used, each of which stained a characteristic profile of cerebellar cells. The UBCs of both rat and cat were strongly immunostained by an antibody against the ha-amino-3-hydroxy-5-methyl-4-isoxazolepropriona te ate (AMPA) receptor subunits, GluR2 and GluR3; were moderately immu nostained by a monoclonal antibody to kainate receptor subunits, GluR5 /6/7; were weakly immunostained by antibodies to NR1 subunits; and wer e not stained by antibodies to GluR1, GluR4, GluR6/7, KA-2, and NR2A/B . Postsynaptic densities of the giant massy fiber-UBC synapses were Gl uR2/3, GluR5/6/7, and NR1 immunoreactive. The other cerebellar neurons were all immunolabeled to some extent with the GluR2/3 and NR1 antibo dies. In addition, Purkinje cells were immunopositive for GluR1 and Gl uR5/6/7; granule cells were immunopositive for GluR5/6/7, GluR6/7, KA- 2, and NR2A/B. The Golgi-Bergmann glia was densely stained by GluR1 an d GluR4 antibodies, whereas astrocytes of the granular layer were stai ned by the GluR4 antiserum. Data provided herein may guide further ele ctrophysiological and pharmacological studies of cerebellar cells in g eneral and the UBCs in particular. (C) 1995 Wiley-Liss, Inc.