Mossy fiber plasticity of adult born dentate granule cells take weeks to mature in vivo

SCHINDER, A. F.; KROPFF, E.; MUGNAINI, M.; PIATTI, V. C.

Córdoba

Congreso; XXXIII Congress of the Argentine Society for Research in Neuroscience; 2018

New granule cells (GCs) of the hippocampus are constantly incorporated duringmammalian adulthood. Ex vivo studies showed that four-week-old GCs (young) aretransiently hyper-plastic, excitable and poorly coupled to feedback inhibitoryloops. In agreement with this notion, young cells showenhanced synaptic plasticity on their main output, pyramidal cells in the CA3 region,visualized upon induction of long term potentiation in anesthetized mice. Our aim is to investigate output properties of developing adult-bornGCs under physiological conditions on free-moving mice. We hypothesizedthat young GCs would be more likely to activate CA3 network than old GCs. We implantedarrays of optotrodes in transgenic adult mice and stimulated new GCs expressingchannelrhodopsin-2 at different frequencies and variable laser intensities tostimulate GC cohorts through their development, while simultaneously recording CA3activity. We found that young GC activation evoke scarce spiking events in singlecell recordings and small local field potential responses in CA3.  Both spiking and field potentials increasesubstantially as GCs become mature. Interestingly, frequency facilitation of the postsynaptic responseappeared by the fifth week and increased consistently until reaching neuronalmaturation. This prolonged process of mossy fiber maturation may offer criticalwindows of network plasticity, which might be a crucial network propertycontributed by adult neurogenesis.