Reduction in OR expression does not prevent axons from correctly targeting the OB. I7+ axons normally form a medial glomerulus in the OB near the ventral midline (arrow in a). In β3GnT2−/− mice, there are insufficient numbers of I7+ axons to form a glomerulus but individual axon targets an identically positioned medial glomerulus (arrow). Synaptophysin (red) staining in A and B suggest that WT and null glomeruli contain functionally active connections. mOR28 is expressed on clusters of neurons in the ventral OE and is heavily expressed on dendrites on the luminal surface of the OE. In null OE’s (D), the number of mOR28+ neurons is greatly reduced compared to OEs (C). mOR28+ axons normally form a medial glomerulus in the caudal OB near the ventral midline (arrow in E). Very few mOR28+ axons can be found targeting this glomerulus in β3GnT2−/− OBs (arrow in F, see inset). Scale bar = 50 μM in all panels.