Delayed axonal development of dentate granule cells born in aging mice

SULKES JN; TRINCHERO MF; SCHINDER AF

Mar del Plata

Congreso; Annual meeting of argentine society for neuroscience; 2015

Society for Research in Neuroscience

Neural progenitor cells of the adult hippocampus can differentiate and develop into fullyfunctional dentate granule cells (DGCs). During aging low levels of neurogenesis have beenreported. In recent work from our laboratory, analysis of dendritic tree length and spine densityindicated that an aged niche imposes a largely decreased rate of maturation of new DGCs. Weinvestigated if this effect could also be exerted on axonal development. To address this problemwe injected a GFP-expressing retrovirus in 2 (2M) and 5 month-old (5M) mice to visualize DCGsborn in adult hippocampus. We then analyzed the number of secondary branches includingcontacts in the hilus. During the first weeks of axonal development the 5M group presented alower number of secondary branches compared to 2M mice. However, the number of hilarcontacts remained constant. This observation suggests that aging affects axonal branching inDGCs born in aging mice. We then asked if aging modifies functional connections betweennewborn DGCs and their postsynaptic targets in the hilus. To answer this question we used aretrovirus expressing the synthetic g-coupled receptor hM3Dq to activate newborn DGCs in theaged hippocampus in vivo, and quantified c-Fos+ cells in the hilus. Mature adult-born DGCsfrom both 2M and 5M groups were able to activate similar numbers of postsynaptic targets. Thisindicates that despite the delayed axonal development, they both reach the same level ofconnectivity upon maturation.