Odorant (amyl acetate) exposure induced the expression of IEGs in the mouse OB. Mice were exposed to overhead airflow for 2 h and then to the test odorant (amyl acetate) for 25 min (5-min exposures with 5-min intervals). The ISH of coronal sections of OB indicated low expression levels of ten IEGs in mice immediately after the 2-h air exposure, (Odorant (−), A1-J1, A1’-J1’). All these ten IEGs were induced in the mouse OB after 30 min of odor onset (AA 25 min, air 5 min, A2-J2, A2’-J2’). Boxed areas in A1-J1 and A2-J2 are magnified in A1’-J1’ and A2’-J2’, respectively. Inset in H2’ is a magnified view of the boxed area. Odor-evoked induction of IEG expression was transient and expression levels of most of the IEGs declined within 60 min of initial odorant exposure (AA 25 min, air 35 min, A3-J3). Arrows indicate GL, black arrowheads indicate M/T and green arrowheads indicate GC. AA, amyl acetate; GL, Glomerular layer; M/T, Mitral/Tufted cell layer; GC, Granule cell layer. D, Dorsal; V, Ventral; M, Medial; L, Lateral. Scale bars: (A1-J3) 200 μm, (A1’-J2’) 50 μm.