Conditional labeling of newborn granule cells to visualize their integration into established circuits in hippocampal slice cultures

The dentate gyrus continues to produce new granule cells throughout life. Understanding the mechanisms underlying their integration into the pre-existing hippocampal circuitry is of crucial importance. In the present study, we developed an approach allowing visual tracking of newborn granule cells in hippocampal organotypic slices. By crossing neurogenin 2 (Ngn2-CreER) with Cre-reporter mice expressing YFP or GFP reporter genes, it was possible to observe living cells after treating slice cultures with 4-hydroxytamoxifen to induce Cre recombinase activation. Colocalization of GFP with the mitotic marker BrdU demonstrated that the GFP-expressing granule cells were born in vitro. They mature and integrate normally into the hippocampal circuitry, as shown using morphological and electrophysiological techniques. This ex vivo approach therefore offers a highly accessible model to study the effects of long-term treatments on maturation and integration of newborn granule cells.