Two mirror-image sensory maps with domain organization in the mouse main olfactory bulb.

The glomerular sheet in the olfactory bulb (OB) provides an olfactory sensory map identifying which odorant receptors (ORs) in the nose are activated by inhaled odorants. How are the glomeruli spatially arranged in the OB? Using OCAM and neuropilin-1 (NP1) as molecular markers for target glomeruli of distinct subsets of olfactory axons, we demonstrate here that glomeruli are parceled into topographically distinct domains. Spatial arrangement of these domains suggests that each OB contains two mirror-image maps of the glomeruli. In situ hybridization shows that the glomeruli representing the same OR are symmetrically arranged; one in a domain in the lateral hemisphere and the other in a corresponding domain in the medial hemisphere of the OB. These results suggest that OB contains two symmetrical OR maps with similar domain organization.