Differential feed-forward inhibition generates division of labor of developing and mature granule cells in the adult hippocampus

PARDI M. BELÉN; OGANDO MORA B.; SCHINDER ALEJANDRO F.; MARIN-BURGIN ANTONIA

Congreso; XXX Congreso SAN; 2015

Adult neurogenesis provides the dentate gyrus (DG) of the hippocampus with constantly renewing pools of immature granule cells (GC) with unique properties. In the present work we address the specific contribution of immature GC to encoding of information arriving to the hippocampus. We injected a retrovirus to express RFP in dividing hippocampal cells and recognize immature four week old GC (4wpiGC) in acute hippocampal slices four weeks later. We stimulated the medial perforant path with a monopolar electrode with trains at physiological frequencies (1 Hz, 10 Hz, 20 Hz and 40 Hz) and recorded activation from 4wpiGC and mature GC with loose-patch. Results show that spike trains arriving to the DG at different frequencies are channeled into two populations of neurons with variable frequency-filter gains and temporal fidelity: Immature GC respond to a wider range of afferent stimuli arriving at 1-40 Hz, whereas mature GC are less effective in following higher frequencies; mature GC, on the other hand, show a higher temporal fidelity than 4wpiGC. Whole cell recordings of stimuli evoked excitation and inhibition indicate that activation differences are mainly dictated by feed forward inhibition, which predominantly restricts mature GC and time locks their spiking. Thus, adult neurogenesis provides pools of GC that escape form feed-forward inhibition and can reliably transit incoming frequency, while mature GC are precise at informing the beginning of the stimulus.