Olfactory information perceived in the nose is transferred and processed in the olfactory bulb of the brain. Development of the afferent projection from this first-order olfactory center is being studied, using knockout mice for various axon guidance molecules and their receptors.
Ventral aspects of three mouse embryonic brains with different genotypes. Olfactory bulb axons are labeled in blue. Left: In the wild-type brain, olfactory bulb axons are bundled together and run in a stereotyped projection route. Middle & Right: in mutant brains for axon guidance molecules, many of the axons ectopically grow and make aberrant projections.