Development of a feedback circuit for input specification in adult-born dentate granule cells

TEMPRANA SG; MONGIAT LA; YANG SM; TRINCHERO MF; ALVAREZ DD; KROPFF E; GIACOMINI D; BELTRAMONE N; LANUZA GM; SCHINDER AF

Córdoba

Congreso; Annual meeting of argentine society for neuroscience; 2014

Society for Research in Neuroscience

Adult neurogenesis provides a continuous pool of new granule cells (GCs) to the dentate gyrus (DG) of thehippocampus. The specific contribution of adult-born GCs to the hippocampal network remains unknown. New GCsdevelop and mature over several weeks; during this process they become integrated in the preexisting network.Immature GCs become highly active due to their low spiking threshold that renders low input specificity, shiftingupon maturation towards sparse activity as a consequence of their high spiking threshold. The impact of this dualfunction in the circuit remains unclear, and it will be determined by the output networks activated by new neurons atdifferent stages of maturation. We have used optogenetics to map the networks activated by adult-born GCs. Mossyfibers, the axons of GCs, would typically activate interneurons in the hilus and CA3 region, as well as CA3 pyramidalcells. We found that as adult-born GCs transition towards fully mature stages they acquire the capacity to exert apowerful feedback inhibition onto the granule cell layer through the activation of local GABAergic interneurons inthe polymorphic region. In addition, they activate distal CA3 targets that elicit feed-forward GABAergic inhibitionand excitation of CA3 pyramidal cells. We are currently aiming to refine the identification of individual populationsof GABA interneurons that participate in this process at the proximal and distal regions.