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The authors tested how prior odor enrichment affects the spontaneous discrimination of both preexposed and novel odors. Experimental rats were exposed to single odors or to pairs of similar or dissimilar odors for 1-hr periods twice daily over 20 days. Spontaneous discriminations between pairs of similar odors were tested before and after the odor exposure period using an olfactory habituation task. The authors found that (a) experimental rats did not spontaneously discriminate similar odor pairs before the exposure period, whereas they spontaneously discriminated them after the enrichment period, and (b) the improvement of performance was not selective for the odors used during enrichment. These results show that odor experience changes perception in the manner predicted based on other groups' electrophysiological experiments. Keywords: olfaction, spontaneous discrimination, olfactory enrichment

Noradrenaline contributes to olfactory-guided behaviors but its role in olfactory learning during adulthood is poorly documented. We investigated its implication in olfactory associative and perceptual learning using local infusion of mixed α1-β adrenergic receptor antagonist (labetalol) in the adult mouse olfactory bulb. We reported that associative learning, as opposed to perceptual learning, was not affected by labetalol infusions in the olfactory bulb. Accordingly, this treatment during associative learning did not affect the survival of bulbar adult-born neurons. Altogether, our results suggest that the noradrenergic system plays different parts in specific olfactory learning tasks and their neurogenic correlates.

Neural stem cells (NSC) persist in the adult mammalian brain, within the subventricular zone (SVZ). The endogenous mechanisms underpinning SVZ stem and progenitor cell proliferation are not fully elucidated. Vitamin K‐dependent proteins (VKDPs) are mainly secreted factors that were initially discovered as major regulators of blood coagulation. Warfarin ((S(−)‐3‐acetonylbenzyl)‐4‐hydroxycoumarin)), a widespread anticoagulant, is a vitamin K antagonist that inhibits the production of functional VKDP. We demonstrate that the suppression of functional VKDPs production, in vitro, by exposure of SVZ cell cultures to warfarin or, in vivo, by its intracerebroventricular injection to mice, leads to a substantial increase in SVZ cell proliferation. We identify the anticoagulant factors, protein S and its structural homolog Gas6, as the two only VKDPs produced by SVZ cells and describe the expression and activation pattern of their Tyro3, Axl, and Mer tyrosine kinase receptors. Both in vitro and in vivo loss of function studies consisting in either Gas6 gene invalidation or in endogenous protein S neutralization, provided evidence for an important novel regulatory role of these two VKDPs in the SVZ neurogenic niche. Specifically, we show that while a loss of Gas6 leads to a reduction in the numbers of stem‐like cells and in olfactory bulb neurogenesis, endogenous protein S inhibits SVZ cell proliferation. Our study opens up new perspectives for investigating further the role of vitamin K, VKDPs, and anticoagulants in NSC biology in health and disease. STEMCELLS2012; 30:719–731

Hedonic value is a dominant aspect of olfactory perception. Using optogenetic manipulation in freely behaving mice paired with immediate early gene mapping, we demonstrate that hedonic information is represented along the antero-posterior axis of the ventral olfactory bulb. Using this representation, we show that the degree of attractiveness of odors can be bidirectionally modulated by local manipulation of the olfactory bulb's neural networks in freely behaving mice.