Brain Control of Olfaction via Top-down Regulation on Adult Neurogenesis

to glutamate before the establishment of synaptic connections with mitral cells at the more distal portions of their dendritic arbors (Panzanelli et al., 2009). In addition, olfactory deprivation differentially affects spine density in the distal and proximal dendritic domains, where respectively centripetal and centrifugal synaptic connections take place (Kelsch et al., 2009). Hence, the role of central brain activity is exceedingly likely to affect the fate of developing GCs, but the mechanisms of this effect have yet to be elucidated. Surprisingly, only a few reports have aimed to do so (Bauer et al., 2003; Cooper-Kuhn et al., 2004; Veyrac et al., 2005, 2009) and, although focusing on the local OB reveals why younger neurons may be preferable to older ones, the mechanisms by which the brain makes this choice can not be fully clarified without considering its feedback modulatory activity. Moreno et al. (2012) have recently shed new light on this issue and analyzed the interaction between centrifugal innervation and plasticity in the olfactory bulb in a sensory context meaningful for both. The authors investigated the involvement of the noradrenergic signaling in the olfactory perceptual learning, a form of learning in which previous experience like olfactory habituation allows discrimination between perceptually similar odorants. They showed that blocking the noradrenergic system during olfactory enrichment abolishes its positive effects on olfactory discriminatory ability while the stimulation of the noradrenergic system alone results in better performances in the discriminatory task. To complete the picture of the involvement of the noradrenergic system, they A commentary on