Integration of CA1 inputs in subicular neurons

Dennis Dalügge1, Pavol Bauer1, Stefan Remy1

1 Neuronal Networks Group, German Center for Neurodegenerative Diseases, Sigmund-Freud-Str. 27, 53127 Bonn, Germany

As main output structure of the hippocampus, the subiculum has a central role in distributing hippocampally processed. To achieve this, subicular neurons integrate multiple spatially tuned inputs and generate a dense information-rich output. The mechanisms by which this input-output transformation is performed are largely unknonwn. The subiculum receives spatially tuned input from the CA1 area. We first investigated where on the dendritic tree these and other inputs are received. Then, we investigated, how subicular neurons integrate the CA1 input into their spatially tuned output firing. To this end, we performed somatic in-vivo calcium imaging of subicular neurons while mice performed on a linear treadmill with spatial somatosensory and visual cues. Furthermore, CA1 neurons were transfected with the inhibitory DREAD (hM4D(Gi)). Together with direct application of CNO through the hippocampal window, CA1 input to subicular neurons was reduced. We used cross-correlation between the two, pre- and post- CNO application, sessions to follow individual cells over time. Our preliminary results show diverse changes in place related firing of individual subicular neurons. Subicular place scores decreased and place field size either decreased or increased with the reduction of CA1 input. We concluded, that subicular neurons integrate input representing multiple spatially circumscribed CA1 place fields and convert them to a single spatially more distributed place field.