Abstract
BackgroundIt has recently been proposed that adult-born neurons in the olfactory bulb, whose survival is modulated by learning, support long-term olfactory memory. However, the mechanism used to select which adult-born neurons following learning will participate in the long-term retention of olfactory information is unknown. We addressed this question by investigating the effect of bulbar consolidation of olfactory learning on memory and neurogenesis.Methodology/Principal FindingsInitially, we used a behavioral ecological approach using adult mice to assess the impact of consolidation on neurogenesis. Using learning paradigms in which consolidation time was varied, we showed that a spaced (across days), but not a massed (within day), learning paradigm increased survival of adult-born neurons and allowed long-term retention of the task. Subsequently, we used a pharmacological approach to block consolidation in the olfactory bulb, consisting in intrabulbar infusion of the protein synthesis inhibitor anisomycin, and found impaired learning and no increase in neurogenesis, while basic olfactory processing and the basal rate of adult-born neuron survival remained unaffected. Taken together these data indicate that survival of adult-born neurons during learning depends on consolidation processes taking place in the olfactory bulb.Conclusion/SignificanceWe can thus propose a model in which consolidation processes in the olfactory bulb determine both survival of adult-born neurons and long-term olfactory memory. The finding that adult-born neuron survival during olfactory learning is governed by consolidation in the olfactory bulb strongly argues in favor of a role for bulbar adult-born neurons in supporting olfactory memory.
Highlights
In mammals, olfactory information is memorized through activation of a combination of cerebral structures, including the olfactory bulb (OB), piriform cortex and, depending on the required task, the hippocampus and amygdala [1,2,3,4,5,6]
The present results show that neurogenesis was increased in the OB of the group which underwent the spaced training, when there was sufficient time for consolidation to occur
Consistent with performances observed in spatial learning during spaced or massed training [35], we found that less trials were required for learning acquisition during a spaced versus a massed paradigm
Summary
Olfactory information is memorized through activation of a combination of cerebral structures, including the olfactory bulb (OB), piriform cortex and, depending on the required task, the hippocampus and amygdala [1,2,3,4,5,6]. The main effectors of plasticity of the bulbar network are thought to be the inhibitory granule cells which regulate output of the olfactory message through reciprocal synapses with the mitral cells [20] Taken together, these data suggest that the OB has a central role in processing the olfactory signal in relation to its context and significance and so to memorizing it. The mechanism used to select which adult-born neurons following learning will participate in the long-term retention of olfactory information is unknown. We addressed this question by investigating the effect of bulbar consolidation of olfactory learning on memory and neurogenesis
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