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

Abstract

domains and show early synaptic responses 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 den-dritic domains, where respectively centrip-etal 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 mecha-nisms by which the brain makes this choice can not be fully clarified without consider -ing its feedback modulatory activity.Moreno et al. (2012) have recently shed new light on this issue and analyzed the interaction between centrifugal innerva-tion and plasticity in the olfactory bulb in a sensory context meaningful for both. The authors investigated the involvement of the noradrenergic signaling in the olfac-tory perceptual learning, a form of learning in which previous experience like olfactory habituation allows discrimination between perceptually similar odorants.They showed that blocking the noradr-energic system during olfactory enrichment abolishes its positive effects on olfactory dis-criminatory ability while the stimulation of the noradrenergic system alone results in better performances in the discriminatory task. To complete the picture of the involve-ment of the noradrenergic system, they