Group I metabotropic glutamate receptors are differentially expressed by two populations of olfactory bulb granule cells

Abstract

In the main olfactory bulb, several populations of granule cells (GCs) can be distinguished based on the soma location either superficially, interspersed with mitral cells within the mitral cell layer (MCL), or deeper, within the GC layer (GCL). Little is known about the physiological properties of superficial GCs (sGCs) vs. deep GCs (dGCs). Here, we used patch-clamp recording methods to explore the role of Group I metabotropic glutamate receptors (mGluRs) in regulating the activity of GCs in slices from wildtype and mGluR −/− mutant mice. In wildtype mice, bath application of the selective Group I mGluR agonist DHPG depolarized and increased the firing rate of both GC subtypes. In the presence of blockers of fast synaptic transmission (APV, CNQX, gabazine), DHPG directly depolarized both GC subtypes. The two GC subtypes responded differentially to DHPG in mGluR1−/− and mGluR5−/− mice, however. DHPG depolarized sGCs in slices from mGluR5−/− mice, but it had no effect on sGCs in slices from mGluR1−/− mice. By contrast, DHPG depolarized dGCs in slices from mGluR1−/− mice, but it had no effect on dGCs in slices from mGluR5−/− mice. Previous studies have shown that mitral cells express mGluR1, but not mGluR5. The results suggest that sGCs are more similar to mitral cells than dGCs in terms of mGluR expression. Support: Whitehall Foundation, Howard Univ. New Faculty Research Program, Biomedical Research Foundation of Northwest Louisiana, and U.S. PHS grants 2-S06-GM08016-36 (NIGMS/NIH) and DC03195.