Spatio-temporal pattern of efferent connectivity of adult-born dentate granule cells

SILVIO GABRIEL TEMPRANA ; LUCAS A MONGIAT; ALEJANDRO F SCHINDER

Huerta Grande - Cordoba

Congreso; Reunión Anual Sociedad Argentina de Investigación en Neurociencia; 2011

Sociedad Argentina de Investigación en Neurociencia

Adult neurogenesis provides a continuous pool of new dentate granule cells (DGCs) to the hippocampus. The maturation process of adult-born DGCs takes from six to eight weeks. Whereas the development of afferents to new DGCs has been extensively characterized, the pattern of efferent connectivity remains poorly understood. In the adult hippocampus, mossy fibers grow through the hilus to reach pyramidal cells in the CA3 region. This led us to hypothesize that mossy fibers of immature DGCs primarily innervate proximal GABAergic interneurons and lately they synapse on pyramidal cells. To test this hypothesis we retrovirally transduced adult-born DGCs to express channelrhodopsin-2 (ChR2). Newborn DGCs were stimulated by flashes of blue light in order to characterize their connectivity by recording on putative postsynaptic targets in acute slices. Preliminary recordings on pyramidal neurons suggest that 6 to 8-week-old DGCs project functional monosynaptic contacts as evidenced by evoked glutamatergic EPSCs. Moreover, light stimulation also evoked disynaptic IPSCs on pyramidal neurons. These results suggest that adult-born DGCs perform functional synaptic connections on CA3 neurons by 6 weeks. We are currently investigating the functional output connectivity of younger DGCs.