Spontaneous calcium transients in the immature adult-born neurons of the olfactory bulb

Spontaneous neuronal activity and concomitant intracellular Ca²⁺ signaling are abundant during early perinatal development and are well known for their key role in neuronal proliferation, migration, differentiation and wiring. However, much less is known about the in vivo patterns of spontaneous Ca²⁺ signaling in immature adult-born cells. Here, by using two-photon Ca²⁺ imaging, we analyzed spontaneous in vivo Ca²⁺ signaling in adult-born juxtaglomerular cells of the mouse olfactory bulb over the time period of 5 weeks, from the day of their arrival in the glomerular layer till their stable integration into the preexisting neural network. We show that spontaneous Ca²⁺ transients are ubiquitously present in adult-born cells right after their arrival, require activation of voltage-gated Na⁺ channels and are little sensitive to isoflurane anesthesia. Interestingly, several parameters of this spontaneous activity, such as the area under the curve, the time spent in the active state as well as the fraction of continuously active cells show a bell-shaped dependence on cell’s age, all peaking in 3–4 weeks old cells. This data firmly document the in vivo presence of spontaneous Ca²⁺ signaling during the layer-specific maturation of adult-born neurons in the olfactory bulb and motivate further analyses of the functional role(s) of this activity.