Study of dentate gyrus engram cells supporting different associative memories.

MARIA SOL RAMOS; ANTONIA MARIN BURGIN; NOEL FEDERMAN

Congreso; XXXVII Congress of the Argentine Society for Research in Neuroscience (SAN). Buenos Aires; 2022

The ability to store new information through a process of learning and retrieve it over time is an essential property of the brain. This information is thought to be encoded by sparse but defined populations of neurons that are synchronously activated during learning, so-called engram cells. The dentate gyrus (DG) of the hippocampus plays a key role in memory formation and generates new adult-born granule cells (abGCs) throughout life. We are conducting experiments training mice to perform a GO/NO GO discrimination task in distinct virtual reality environments. In head-fixed conditions, water restricted mice learn to drink water or not depending on distinct cues presented in a virtual corridor. Animals are trained only with contextual cues or are trained to learn an odor-context association as a prediction of the reward. We show that animals reached to criterion within around 6 sessions showing changes in distinct behavioral variables. In order to study engram cells, we used cfos tTA mice injected with AAV9-TRE-GFP in the DG to label activated neurons. We characterized memory engrams using confocal imaging and ex-vivo electrophysiological recordings. We recorded miniature postsynaptic currents on activated and non-activated cells of expert animals. Furthermore, we evaluated the contribution of abGCs to the engram by analizing their activation using confocal microscopy. In addition, we reversibly inactivate abGCs of expert animals using a chemogenetic DREADDs approach.