Spatial arrangement of glomerular molecular-feature clusters in the odorant-receptor class domains of the mouse olfactory bulb.

The glomerular layer of the mammalian olfactory bulb (OB) forms odorant receptor (OR) maps. Each OR map is structurally and functionally compartmentalized into zones (dorsal and ventral) and domains (DI and DII in the dorsal zone). We previously reported that glomeruli with similar molecular receptive range properties formed molecular feature clusters at stereotypical positions in the rat OB. However, the spatial arrangement of the molecular feature clusters with regard to the OR zones and domains has not been systematically examined. In this study, we optically mapped the molecular feature clusters of glomeruli within the domain and zone framework of the OB using domain-visible class II GFP transgenic mice. In all mice examined, fatty acid-responsive cluster A was located in the lateral part of domain DI, whereas clusters B, C, and D were arranged in an anterior to posterior order within domain DII. We also found a new cluster of glomeruli that respond to fox odor trimethyl-thiazoline and its structural analogs (heterocyclic odorants that contain sulfur and nitrogen atoms within the ring). This cluster (named cluster J) was located posterior to cluster D within the DII domain. These results show that molecular feature clusters correspond to specific subsets of glomeruli in selective domains of the OR map, suggesting that the molecular feature clusters represent specific ORs that have similar molecular receptive range properties and functional roles.