215 | Activity-dependent synaptogenesis in mossy fiber terminals from adult-born granule cells

Neural Circuits and Systems Neuroscience

Author: Violeta Lopez Sonnabend | Email: violetalopezsonnabend@gmail.com

Violeta López-Sonnabend , Andrea Aguilar-Arredondo , Alejandro F. Schinder

1° Laboratorio de Plasticidad Neuronal, Fundación Instituto Leloir

Neurogenesis occurs in the dentate gyrus (DG) of the adult mammalian hippocampus and is involved in spatial encoding and learning. Cohorts of adult-born granule cells (aGCs) are continually added into the DG in a highly regulated process. Projections of aGCs contact interneurons in the hilus as well as pyramidal cells in CA3. Electron microscopy studies have shown that boutons of young aGCs establish new connections on dendritic spines of pyramidal cells already occupied by mossy fiber terminals of mature GCs, leading to postsynaptic spines in contact with multiple boutons. In mature aGCs, the majority of synapses are formed by single boutons. It has been proposed that the more active synapses are more likely to remain connected, suggesting an activity-dependent competition among presynaptic terminals. To test this hypothesis, we aimed to compare the structure of presynaptic terminals in cohorts of aGCs growing under chronic conditions of enhanced activity or electrical silencing in vivo. Preliminary data suggests that aGCs developing in conditions of high activation tend do display more complex presynaptic boutons compared to those that grow under electrical silencing. Moreover, terminals of mature aCGs located in close proximity of active young aGCs show smaller terminals, which hints in favor of synaptic competition. Current experiments are underway to determine whether aGCs at different developmental stages display distinct sensitivity to activity-dependent competition.