Postnatal neurogenesis provides an opportunity to understand how newborn neurons functionally integrate into circuits to restore lost function. Newborn olfactory sensory neurons (OSNs) wire into highly organized olfactory bulb (OB) circuits throughout life, enabling lifelong plasticity and regeneration. Immature OSNs can form functional synapses capable of evoking firing in OB projection neurons. However, what contribution, if any, immature OSNs make to odor processing is unknown. Indeed, because immature OSNs can express multiple odorant receptors, any input that they do provide could degrade the odorant selectivity of input to OB glomeruli. Here, we used a combination of in vivo 2-photon calcium imaging, optogenetics, electrophysiology and behavioral assays to show that immature OSNs provide odor input to the OB, where they form monosynaptic connections with excitatory neurons. Importantly, immature OSNs responded as selectively to odorants as mature OSNs. Furthermore, mice successfully performed odor detection tasks using sensory input from immature OSNs alone. Immature OSNs responded more strongly to low odorant concentrations but their responses were less concentration dependent than those of mature OSNs, suggesting that immature and mature OSNs provide distinct odor input streams to each glomerulus. Together, our findings suggest that sensory input mediated by immature OSNs plays a previously unappreciated role in olfactory-guided behavior.
Activity plays a role in eliminating olfactory sensory neurons expressing multiple odorant receptors in the mouse septal organ
