Functional maturation and experience-dependent plasticity in adult-born olfactory bulb dopaminergic neurons

Continued integration of new neurons persists in only a few areas of the adult mouse brain. In the olfactory bulb (OB), immature adult-born neurons respond differently to olfactory stimuli compared to their more mature counterparts, and have heightened levels of activity-dependent plasticity. These distinct functional features are thought to bestow unique properties onto existing circuitry. OB interneurons, including those generated through adult neurogenesis, consist of a set of highly distinct subtypes. However, we do not currently know the different cell-type-specific mechanisms underlying their functional development and plastic potential. Here, we specifically characterised electrophysiological maturation and experience-dependent plasticity in a single, defined subtype of adult-born OB neuron: dopaminergic cells. We selectively live-labelled both adult-born and resident dopaminergic cells, and targeted them for whole-cell patch-clamp recordings in acute mouse OB slices. Surprisingly, we found that from the time - at [~]1 month of cell age - that live adult-born dopaminergic neurons could first be reliably identified, they already possessed almost fully mature intrinsic firing properties. We saw significant maturation only in increased spontaneous activity and decreased medium afterhyperpolarisation amplitude. Nor were adult-born dopaminergic cells especially plastic. In response to brief sensory deprivation via unilateral naris occlusion we observed no maturation-specific plastic alterations in intrinsic properties, although we did see deprivation-associated increases in spike speed and amplitude across all adult-born and resident neurons. Our results not only show that adult-born OB dopaminergic cells rapidly functionally resemble their pre-existing counterparts, but also underscore the importance of subtype identity when describing neuronal maturation and plasticity.