Proximodistal Organization of the CA2 Hippocampal Area

• Main Authors: Ivan Fernandez-Lamo, Daniel Gomez-Dominguez, Alberto Sanchez-Aguilera, Azahara Oliva, Aixa Victoria Morales, Manuel Valero, Elena Cid, Antal Berenyi, Liset Menendez de la Prida
• Format: Article
• Language: English
• Published: Elsevier 2019-02-01
• Series: Cell Reports
• Online Access: http://www.sciencedirect.com/science/article/pii/S2211124719300890

Summary: The proximodistal axis is considered a major organizational principle of the hippocampus. At the interface between the hippocampus and other brain structures, CA2 apparently breaks this rule. The region is involved in social, temporal, and contextual memory function, but mechanisms remain elusive. Here, we reveal cell-type heterogeneity and a characteristic expression gradient of the transcription factor Sox5 within CA2 in the rat. Using intracellular and extracellular recordings followed by neurochemical identification of single cells, we find marked proximodistal trends of synaptic activity, subthreshold membrane potentials, and phase-locked firing coupled to theta and gamma oscillations. Phase-shifting membrane potentials and opposite proximodistal correlations with theta sinks and sources at different layers support influences from different current generators. CA2 oscillatory activity and place coding of rats running in a linear maze reflect proximodistal state-dependent trends. We suggest that the structure and function of CA2 are distributed along the proximodistal hippocampal axis. : The CA2 region of the hippocampus has distinctive molecular, physiological, and connectivity properties. Fernandez-Lamo et al. provide data supporting a proximodistal functional organization of this region in the rat. Keywords: cell type, theta, gamma, PCP4, Sox5