Synaptogenesis of adult-born dentate granule cells onto CA3 pyramidal neurons using optogenetics

TEMPRANA, SG; SCHINDER, AF; MONGIAT, LA

Huerta Grande, Cordoba

Congreso; XXVII Congreso anual de la Sociedad Argentina de Investigación en Neurociencia; 2012

Sociedad Argentina de Investigación en Neurociencia

The dentate gyrus generates new dentate granule cells (DGCs) through life. In the adult mouse development and integration of new DGCs takes 6-8 weeks. Whereas afferent synaptogenesis to new DGCs has been extensively characterized, the efferent connectivity remains poorly understood. Previous studies showed that presynaptic terminals onto hilar interneurons are morphologically mature by four weeks, whereas mossy buttons onto CA3 pyramidal neurons remain immature at that neuronal age. These results lead us to hypothesize that immature DGCs initially contact proximal GABAergic interneurons and only later synapse onto distal pyramidal cells. To test this hypothesis we employed retroviral transduction of adult-born DGCs with channelrhodopsin-2 and performed electrophysiological recordings of postsynaptic currents in CA3 pyramidal cells elicited by optical stimulation with a 472 nm laser in acute slices from adult mice. Single pulses or trains of brief blue light stimuli evoked monosynaptic excitatory postsynaptic currents and disynaptic inhibitory postsynaptic currents in 4-6 week old DGCs. Further characterization of the amplitude, kinetics and plasticity of these responses will be performed in order to study the excitation/inhibition balance exerted by developing DGCs in CA3 pyramidal cells.