Adult born dentate granule cells evoke CA3 activity with a gain that increases along maturation

ALEJANDRO SCHINDER; MATIAS MUGNAINI; EMILIO KROPFF; VERONICA PIATTI

Congreso; Reunion anual de la Sociedad Argentina de Neurociencias; 2019

Hippocampal granule cells (GCs) are among the few neurons that are born throughoutmammalian lifespan. It has been shown that young adult born GCs (4 weeks old) aretransiently hyperplastic and excitable compared to mature ones (8 weeks old). While theirinputs are well characterized, only a few studies address the maturation of GCs outputs.Here we aim to investigate the influence of developing adult born GCs on CA3, its maintarget. We hypothesize that evoked activity in CA3 reflects transient properties of youngGCs. To explore this possibility, we performed optical stimulation of a cohort of adult bornGCs expressing channelrhodopsin-2 in awake behaving mice while recording neuronalactivity in CA3. We used different frequencies of stimulation at variable laser intensities tostimulate young and mature GCs.We found that mature GCs recruit more CA3 single unit activity, with frequency dependentfacilitation. Evoked local field potentials followed a similar pattern. Interestingly, a smallsubset of putative pyramidal CA3 cells presented significantly high spiking levels as long as50 ms after the light pulse. Only mature GCs were able to evoke this sustained activity. Isthis persistent excitability caused by attractor dynamics? Do adult born neurons reshape dearchitecture of recurrent CA3 networks? These results open new challenges regarding thefunction of adult hippocampal neurogenesis and mnemonic networks dynamics dependenton the neurogenic niche.