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

SILVIO GABRIEL TEMPRANA; LUCAS A MONGIAT; YANG SUN MING; MARIELA F TRINCHERO; ALVAREZ DIEGO D; EMILIO KROPFF; GIACOMINI D; BELTRAMONE N; LANUZZA G; ALEJANDRO F SCHINDER

Huerta Grande, Cordoba

Congreso; Sociedad Argentina de Investigación en Neurociencias - XXIX Annual Meeting; 2014

Sociedad Argentina de Investigación en Neurociencias

Adult neurogenesis provides a continuous pool of new granule cells (GCs) to the dentate gyrus (DG) of the hippocampus. The specific contribution of adult-born GCs to the hippocampal network remains unknown. New GCs develop 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, shifting upon maturation towards sparse activity as a consequence of their high spiking threshold. The impact of this dual function in the circuit remains unclear, and it will be determined by the output networks activated by new neurons at different stages of  maturation. We have used optogenetics to map the networks activated by adult-born GCs. Mossy fibers, the axons of GCs, would typically activate interneurons in the hilus and CA3 region, as well as CA3 pyramidal cells. We found that as adult-born GCs transition towards fully mature stages they acquire the capacity to exert a powerful feedback inhibition onto the granule cell layer through the activation of local GABAergic interneurons in the polymorphic region. In addition, they activate distal CA3 targets that elicit feed-forward GABAergic inhibition and excitation of CA3 pyramidal cells. We are currently aiming to refine the identification of individual populations of GABA interneurons that participate in this process at the proximal and distal regions.