Density of iNOS- and Iba1-positive cells in the olfactory nerve (
), glomerular (
) and granule layers (
) in the unperturbed and bacterial challenged olfactory bulbs (A). These layers show a significant increase in the number of iNOS-positive cells in response to bacterial challenge (black bars) compared to those in the untreated control olfactory bulb (grey bars), 4.5 fold increase in the ONL + GmL and 2.8 fold increase in the GrL. However there is no significant increase in the number of Iba1-positive cells between the untreated olfactory bulb (bars with vertical lines) and S. aureus-exposed olfactory bulb (bars with horizontal lines). Error bars represent SEM. **p < 0.01. Fluorescence microscopy shows activated microglia with hypertrophied cell bodies and ramifying processes, and demonstrating co-localisation of Iba1 and tomato lectin (TL) in S.aureus-exposed olfactory bulb (B, C). Microglia (green: TL) expressing iNOS (red) in the vicinity of the mitral cell layer (MCL) in S.aureus-exposed olfactory bulb (D). No apparent staining for iNOS is observed in a similar area in this saline-treated olfactory bulb (E). NY = Nuclear yellow; EPL = external plexiform layer. Scale bar = 25 μm (B,C), 50 μm (D,E).