CONICET | Buscador de Institutos y Recursos Humanos

The addition of adult-born dentate granule cells (GCs) in the dentate gyrus is a unique form of network plasticity. GCs develop and integrate into the local networks in a process that lasts several weeks. It has been shown that the level of local networks activity has a positive impact on the maturation speed of adult-born GCs. Here we show that developing GCs in the adult mouse hippocampus display a critical period whereby they are prone to activity modulation long before they acquire cortical excitatory inputs. A brief exposure to an enriched environment (EE) of immature GCs undergoing this critical period for two days, accelerated their functional integration. Furthermore, direct in vivo depolarization of young GCs during the critical period using synthetic DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) was sufficient to also accelerate dendritic growth. In addition, activation of mature GCs by means of the hM3Dq receptor was used to monitor the influence of local circuits on developing GCs. Indeed, in vivo chemogenetic activation of a limited population of mature GCs accelerated the integration of developing GCs. Slice recordings showed that mature GCs recruit GABAergic feedback mediated by parvalbumin interneurons (PV-INs) that depolarizes developing GCs. Accordingly, chemogenetic stimulation of PV-INs accelerated GC integration, while inactivation of PV-INs prevented the effects of EE. In agreement with recent works we propose that PV-INs are responsible of controlling neuronal maturation. Our results suggest that during EE exposure, mature GCs activate PV-INs, which, in turn, ?prime? young GCs promoting their functional recruitment through a disynaptic feedback loop.