Comparison of IEG induction patterns in response to two different odorants. Mice were sacrificed after the 30-min continuous exposure to the test odorant. (A, A’) Propionic acid activated several glomeruli specifically in the dorsal OB (arrowheads in A). Induced expression of Npas4 was observed only in the granule cell layer (A’, inset). (B, B’) A large number of glomeruli were activated by amyl acetate. Npas4 induction was apparent only in the granule cell layer (B’). (C-D’) Patterns of IEG induction in the AOB after odorant exposure. Arrowheads indicate c-fos induction in the granule cell layer of the AOB (C, D). Only a slight induction of Npas4 was observed in the AOB (C’, D’, insets). GL, Glomerular layer; M/T,Mitral/Tufted cell layer; GC, Granule cell layer; GrA, Granule cell layer of the AOB; EPlA, External plexiform layer of the AOB. Scale bar: 200 μm.