In Vivo Whole Cell Recordings of Excitatory Input onto Subicular Neurons in Freely Moving Mice

Hiroshi kaneko1, Pavol Bauer1, Stefan Remy1

1 Leibniz Institute for Neurobiology

The subiculum is the major output structure of the hippocampal formation and plays an important role in learning and memory and spatial navigation. Subicular neurons receive excitatory synaptic input containing spatial and non-spatial information from entorhinal cortex and CA1 and convert these inputs into spatially tuned output. On the synaptic input level, it is not known, if the spatial tuning of subicular neurons derives from predominant input from neurons with identical spatial tuning. Alternatively it could be equally distributed along different spatial locations and tuned via synaptic plasticity/dendritic nonlinearities. Moreover, it is not known whether the behavioral state of an animal is represented by the cumulative synaptic input of individual neurons.

To investigate this, we measured excitatory postsynaptic currents (EPSCs) in subicular neurons in freely moving mice using the whole cell patch clamp configuration. Simultaneously, the behavior of the mice was recorded with a time of flight camera. From the recorded video we then extracted the position, speed as well as the head-direction with use of the DeepLabCut pose estimation toolbox.

We present data from 8 neurons recorded from 7 mice that performed between 2 min and 8 min in whole-cell voltage clamp configuration together with deep behavioral observation. Preferred speed-, the head directional and place-tuning of cumulative EPSCs were observed. However, several other neurons exhibited no apparent spatial and behavioral tuning. Taken together, we provide experimental evidence for a preselection of similarly tuned input at a spatial location, which could be due to plasticity process.