Hungarian Brain Research Program(NAP2022-I-1/2022)
International Research Scholar Program of the Howard Hughes Medical Institute(55008740)
European Research Council Consolidator Grant(ERC-CoG 771849)
European Research Council Advanced Grant(ERC-AG 787157)
Neuronal activity in the hippocampus creates a cognitive map of space that is essential
for navigation. In any given environment, a fraction of hippocampal pyramidal cells
(PCs) is active at specific locations (place cells), others are sparsely active without
spatial tuning, and a significant proportion of the PCs is entirely silent. The mechanisms
underlying the vastly different activities of PCs in the rodent hippocampal CA1 area
are unknown. Here, we measured the in vivo activity of CA1 PCs using two-photon [Ca2+]
imaging in head-restrained mice during navigation in a virtual corridor and then performed
in vitro patch-clamp recording to probe their intrinsic electrical properties and
anatomical investigation to characterize their input synapses. The active and passive
electrical properties of PCs were similar between PCs with different prior in vivo
activities. Perisomatic inhibitory synapse density was also comparable among PCs.
The average dendritic spine density and spine head area did not correlate with the
mean in vivo activity of PCs, but the size of the spines of place cells was significantly
larger compared to that of silent cells. Our results are consistent with excitatory
synaptic plasticity as a major mechanism underlying spatially tuned activity of place
cells in hippocampal networks.
