The proximodistal axis is considered a major organizationalprinciple of the hippocampus. At the interfacebetween the hippocampus and other brainstructures, CA2 apparently breaks this rule. The regionis involved in social, temporal, and contextualmemory function, but mechanisms remain elusive.Here, we reveal cell-type heterogeneity and a characteristicexpression gradient of the transcription factorSox5 within CA2 in the rat. Using intracellularand extracellular recordings followed by neurochemicalidentification of single cells, we find markedproximodistal trends of synaptic activity, subthresholdmembrane potentials, and phase-locked firingcoupled to theta and gamma oscillations. Phaseshiftingmembrane potentials and opposite proximodistalcorrelations with theta sinks and sources atdifferent layers support influences from different currentgenerators. CA2 oscillatory activity and placecoding of rats running in a linear maze reflect proximodistalstate-dependent trends. We suggest thatthe structure and function of CA2 are distributedalong the proximodistal hippocampal axis.
展开▼
