Abstract
In the mouse olfactory bulb, neural map topography is largely established by axon–axon interactions of olfactory sensory neurons (OSNs). However, to make the map functional, the OSNs must make proper connections to second-order neurons, the mitral cells. How do the mitral-cell dendrites find their partner glomeruli for synapse formation with OSN axons? Here, we analyze dendrite connections of mitral cells in various mutant mice in which glomerular formation is perturbed. Our present results support the proximity model, whereby mitral cells tend to connect primary dendrites to the nearest neighboring glomeruli regardless of their odorant receptor identities. The physical location of glomeruli rather than the odorant-receptor specificity appears to play a key role in matching mitral cells with their partner OSN axons.
Highlights
In the mouse olfactory bulb, neural map topography is largely established by axon–axon interactions of olfactory sensory neurons (OSNs)
Odorous information detected in the olfactory epithelium is converted to a two-dimensional map of activated glomeruli in the olfactory bulb, enabling the brain to discriminate a variety of odorants[8]
Our present results indicate that mitral-cell dendrites find their partner OSNaxons based on their proximity to the target glomeruli without regard to odorant-receptor specificity, tending to connect to the nearby glomerulus
Summary
In the mouse olfactory bulb, neural map topography is largely established by axon–axon interactions of olfactory sensory neurons (OSNs). In the olfactory systems of the fly and nematode, projection neurons are prespecified by the cell lineage and birth order to form synapses with incoming axons of olfactory receptor neurons (ORNs)[10,11,12,13] This genetically-programmed pre-specification of ORNs generates hard-wired circuits that induce stereotyped innate odor responses. One possibility is that OSN axons and mitral-cell dendrites recognize the partners’ identity when the matching is taking place If this is the case, the identity of OSNs is likely established by the expressed odorant receptor species. Mitral-cell dendrites may find their partner OSN axons based on their proximity to the target glomeruli without regard to odorantreceptor specificity If this is the case, it is important for mitral cells to migrate to proper locations in the olfactory bulb to make the circuit functional[19].
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