EXPRESSION OF AMPA-GLUTAMATE RECEPTOR-B SUBUNIT IN RAT HIPPOCAMPAL GABAERGIC NEURONS

The physiological properties of alpha-amino-3-hydroxy-5-methyl-4-isoxa zole propionic acid (AMPA)-type glutamate receptor (GluR) channels are determined by their subunit composition. In particular, the expressio n of the GluR-B subunit determines the divalent ion selectivity of the channel. We studied the distribution of GluR-B mRNA and protein in ad ult rat hippocampal GABAergic neurons combining non-radioactive in sit u hybridization with immunocytochemistry. The majority of GABAergic hi ppocampal neurons were GluR-B mRNA-positive, but overall the levels of GluR-B transcript were lower than in pyramidal and granule cells, whi ch showed the highest hybridization signal. The different GluR-B mRNA expression levels in GABAergic versus principal neurons were also obse rved at the protein level. There was a paucity of GluR-B/C immunoreact ivity in the vast majority of somata of the GABAergic neurons studied, which contrasted with the strong expression of GluR-B/C proteins in t he hippocampal principal neurons, Our results demonstrate the general low expression of the GluR-B subunit mRNA and GluR-B/C proteins in GAB Aergic hippocampal neurons. Considering the dominant role of the GluR- B subunit in determining the divalent ion permeability of the receptor , it is likely that most GABAergic neurons express AMPA receptor chann els with different calcium permeabilities.