Rewiring the olfactory bulb: changes in odor maps following recovery from nerve transection.

Recent studies have shown that axons from olfactory receptor subtypes converge onto glomeruli in fixed positions within the olfactory bulb. Different receptor subtypes project to different glomeruli, forming a spatial distribution of odor information or 'odor maps'. Olfactory receptor neurons are continuously replaced throughout the life span of an animal, yet they preserve this highly localized mapping of receptor subtypes. In this study we used a transgenic mouse (P2-IRES-tau-lacZ) to map axons from a single receptor subtype (P2 receptors) in order to determine if regenerating axons were able to re-establish the P2 receptor map following nerve transection. Results confirm that P2 receptor axons retain their capacity to grow back to the olfactory bulb and converge onto glomeruli following nerve transection. However, the location and number of convergence sites was significantly altered compared to the control map. This change in the spatial distribution of axons alters the topography of odor mapping and has important implications for the processing of olfactory information. Findings from this study may explain why animals recovering from nerve injury require odor training before odor discrimination is restored. Future studies of olfactory receptor mapping could prove helpful in planning strategies to rewire connections in the brain and to restore function following injury or neurological disease.