Temporal mapping of adult-born granule cells integration in two major local inhibitory populations of the hippocampus.

AYELEN I GROISMAN; SUNG M YANG; ALEJANDRO F SCHINDER

Grenoble

Simposio; Neurodynamics Symposium; 2019

Grenoble Institut des Neurosciences

Adult neurogenesis provides a continuous pool of new granule cells (GCs) that participate in informationprocessing in the dentate gyrus of the hippocampus of all mammals, including humans. We studied how GCsbecome integrated toward maturation into the preexisting circuit of the adult mouse dentate gyrus. We chose twomajor population of GABAergic interneurons (INs) of the hippocampus: Parvalbumin expressing cells (PV) andSomatostatin expressing cells (SST). We combined optogenetics and acute slice electrophysiology to activate PVor SST and GCs, retrovirally labeled, at different stages of maturation and studied their connectivity in bothdirections, interneuron to GCs and viceversa. We built a temporal map of synaptogenesis for each IN populationand observed that connectivity between PV and GCs (input and output) reached maturation when GCs were >6weeks old. For SST, the inhibitory postsynaptic current increased gradually with GCs development, while the GCoutput connectivity developed much later (>11 weeks) compared to PV. We found that PV synapses onto GCswere located perisomatically and contributed to both feedforward and feedback inhibitory loops within the granulecell layer. In contrast, SST contacted GCs in proximal and distal dendrites and contributed only to feedbackinhibition. These data demonstrates that integration of new GCs within the preexistent dentate GABAergicnetwork is specific of each IN population and that adult neurogenesis promotes a long-term plasticity for circuitremodeling.