The brain processes sensory information to translate stimulus features into appropriate behavioral outputs. In the olfactory system, odor information is initially represented as a topographic, chemotopic map in the olfactory bulb (OB). In zebrafish, for example, bile acids (putative social cues) and amino acids (potent feeding cues) activate medial and lateral OB, respectively. Our transgenic approach revealed two segregated neural pathways from the olfactory epithelium to mutually exclusive glomeruli in the medial and lateral OB, which are quite likely to be responsible for coding different classes of odor information (e.g. pheromones and odorants). How is the odor map transmitted from the OB to higher brain centers? We recently addressed this issue by using a genetic single-neuron labeling technique in zebrafish. Tracing OB output neurons at single-cell resolution revealed coarse topography of their projections in some target areas but highly distributive projections in the main telencephalic target area, Dp (putative homolog of mammalian piriform cortex). These results suggest that the topographic odor map in the OB is not maintained intact, but reorganized in higher brain centers, presumably according to odor qualities relevant to behavioral functions. The logic of odor information coding employed by higher olfactory centers will be discussed.
奈良先端科学技術大学院大学