Somatodendritic HCN channels in hippocampal OLM cells revealed by a convergence of computational models and experiments

Determining details of spatially extended neurons is a challenge that needs to be overcome. The oriens-lacunosum/moleculare (OLM) interneuron has been implicated as a critical controller of hippocampal memory making it essential to understand how its biophysical properties contribute to function. We previously used computational models to show that OLM cells exhibit theta spiking resonance frequencies that depend on their dendrites having hyperpolarization-activated cation channels (h-channels). However, whether OLM cells have dendritic h-channels is unknown. We performed a set of whole-cell recordings of OLM cells from mouse hippocampus and constructed multi-compartment models using morphological and electrophysiological parameters extracted from the same cell. The models matched experiments only when dendritic h-channels were present. Immunohistochemical localization of the HCN2 subunit confirmed dendritic expression. These models can be used to obtain insight into hippocampal function. Our work shows that a tight integration of model and experiment tackles the challenge of characterizing spatially extended neurons.