SAN2020

The piriform cortex (PC), main region of the olfactory cortex, receives afferent (bottom-up) sensory inputs from the olfactory bulb (OB) carrying odor information through the lateral olfactory tract (LOT); and extensive (top-down) inputs from higher-order areas such as the lateral entorhinal cortex (LEC). To understand the contribution of LEC to the processing of odors we study its functional connectivity to the posterior PC (pPC). We infected LEC with adeno-associated virus expressing channelrhodopsin under CamKIIa promoter to activate excitatory LEC afferents arriving to pPC. We recorded then, in acute brain slices, postsynaptic currents in different principal neurons of the pPC in response to photostimulation. We found that excitatory long-range projections coming from LEC differentially modulate the response to LOT stimulation along the layers of the pPC. Layer 3 deep pyramidal neurons appear to be more affected by LEC activation than layer 2 pyramidal neurons. On the other hand, we discovered that excitatory inputs from LEC recruit local inhibition, independent of the LOT evoked inhibition. This results in a different inhibitory dynamics only for layer 3 neurons. We did not find direct inhibitory long-range projection from LEC to pPC. To assess the role of LEC in the processing of odors in vivo, we are conducting experiments to photoinactivate it during an associative odor-context-reward task and evaluate the effect of LEC inhibition on this olfactory behavior.