Abstract
The continued addition of new neurons to mature olfactory circuits represents a remarkable mode of cellular and structural brain plasticity. However, the anatomical configuration of newly established circuits, the types and numbers of neurons that form new synaptic connections, and the effect of sensory experience on synaptic connectivity in the olfactory bulb remain poorly understood. Using in vivo electroporation and monosynaptic tracing, we show that postnatal-born granule cells form synaptic connections with centrifugal inputs and mitral/tufted cells in the mouse olfactory bulb. In addition, newly born granule cells receive extensive input from local inhibitory short axon cells, a poorly understood cell population. The connectivity of short axon cells shows clustered organization, and their synaptic input onto newborn granule cells dramatically and selectively expands with odor stimulation. Our findings suggest that sensory experience promotes the synaptic integration of new neurons into cell type-specific olfactory circuits.
Highlights
The mammalian brain ensures adaptive behavior through its large capacity for cellular and circuit plasticity
In the present study we combined genetic circuit tracing and in vivo labeling technologies to map monosynaptic connections made between postnatal-born granule cells and their presynaptic input neurons in mouse olfactory bulb
In addition to previous known connections with mitral/tufted cells, postnatalborn granule cells show extensive connectivity to short axon cells, and these short axon cell inputs contribute to clustered architecture in the olfactory bulb
Summary
The mammalian brain ensures adaptive behavior through its large capacity for cellular and circuit plasticity. The olfactory system possesses a large capacity for circuit plasticity through continued generation of new neurons in adult life. Such continuous incorporation of new neurons implies persistent, large-scale remodeling of synaptic connections, the nature of which is not well known. Groups of mitral/ tufted cells, as well as various interneurons, form connected networks that extend into all layers of the olfactory bulb [11]. These networks likely represent unitary modules for odor information processing [11,12,13,14] and may be functionally analogous to barrels in the somatosensory cortex or ocular dominance columns in the visual system
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