Granule Cell Heterogeneity Between Blades of the Dentate Gyrus

Mayan Baues1, Laura Ewell1

1 IEECR, University of Bonn, Germany

The dentate gyrus (DG) is a sub-region of the hippocampus, which is thought to support memory formation through computations such as pattern separation. A sparse population of granule cells (GCs) in the DG show immediate early gene (IEG) expression after behavioral training. The majority of the IEG positive cells are located in the upper blade of the DG, indicating more cell activity in the upper blade. The physiological mechanism for the difference in activity levels between the blades is not known. Employing in vitro whole cell patch clamp experiments, we aimed to explore heterogeneity within GCs in mice by looking at their synaptic inputs, intrinsic properties, and their morphology. We did not find a general difference in EPSC to IPSC ratio (E/I ratio) between the blades (0.27 +/-0.15, n = 16, upper blade; 0.31 +/-0.16, n = 17, lower blade). Preliminary histological analysis revealed a better recovery for GCs in the upper blade. Of the recovered cells, we observed heterogeneity of GCs based on their dendritic morphology. We were able to differentiate between GCs with one (n = 13) and two (n = 6) primary dendrites. GCs with two primary dendrites trended toward having lower E/I ratios (p = 0.08). Correlating morphology with the intrinsic cell properties is ongoing. In conclusion, electrophysiological results alone did not reveal an overall difference in excitability between GCs in upper and lower blade, but preliminary classification based on morphology may reveal a subpopulation of GCs with a specific activity profile.