The present study provides a survey of the immunolocalization of ionotropic 
glutamate receptor subunits throughout the rat and cat cerebellar cortex, with 
emphasis on the unipolar brush cell (UBC), a hitherto neglected cerebellar cell 
that is densely concentrated in the granular layer of the vestibulocerebellum 
and that forms giant synapses with mossy fibers. An array of nine previously 
characterized antibodies has been 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 
alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate (AMPA) receptor subunits, 
GluR2 and GluR3; were moderately immunostained by a monoclonal antibody to 
kainate receptor subunits, GluR5/6/7; were weakly immunostained by antibodies to 
NR1 subunits; and were not stained by antibodies to GluR1, GluR4, GluR6/7, KA-2, 
and NR2A/B. Postsynaptic densities of the giant mossy fiber-UBC synapses were 
GluR2/3, GluR5/6/7, and NR1 immunoreactive. The other cerebellar neurons were 
all immunolabeled to some extent with the GluR2/3 and NR1 antibodies. In 
addition, Purkinje cells were immunopositive for GluR1 and GluR5/6/7; granule 
cells were immunopositive for GluR5/6/7, GluR6/7, KA-2, and NR2A/B. The 
Golgi-Bergmann glia was densely stained by GluR1 and GluR4 antibodies, whereas 
astrocytes of the granular layer were stained by the GluR4 antiserum. Data 
provided herein may guide further electrophysiological and pharmacological 
studies of cerebellar cells in general and the UBCs in particular.