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Cell type-specific genetic and optogenetic tools reveal hippocampal CA2 circuits
Keigo Kohara1, Michele Pignatelli2, Alexander J Rivest2
1RIKEN-MIT Center for Neural Circuit Genetics at the Picower Institute for Learning and Memory, Department of Biology and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA. keigo@mit.edu
Nature Neuroscience
|December 17, 2013
Summary
New research reveals that dentate gyrus cells project to the CA2 region, forming a novel circuit for memory. This discovery updates our understanding of the entorhinal-hippocampal network
Area of Science:
- Neuroscience
- Memory Research
- Hippocampal Circuitry
Background:
- The entorhinal-hippocampal network is crucial for episodic memory.
- Traditionally, ECII→DG→CA3→CA1 and ECIII→CA1 circuits were considered primary memory substrates.
- The role of the CA2 region in memory circuits is newly emerging.
Purpose of the Study:
- To investigate previously unknown functional inputs to the CA2 hippocampal region.
- To elucidate the connectivity of the CA2 region within the entorhinal-hippocampal network.
- To challenge existing models of hippocampal memory circuits.
Main Methods:
- Utilized cell type-specific transgenic mouse lines.
- Employed optogenetics for precise neural circuit manipulation.
- Performed patch-clamp recordings to assess synaptic function.
Main Results:
- Identified functional monosynaptic inputs from dentate gyrus (DG) cells to CA2 pyramidal cells.
- Demonstrated abundant longitudinal projections from DG to CA2.
- Revealed that CA2 preferentially projects to the deep CA1 sublayer, distinct from CA3.
- Found no direct projections from entorhinal cortex layer III (ECIII) to CA2.
Conclusions:
- Established a novel trisynaptic circuit involving DG→CA2→CA1.
- Revised the understanding of information flow within the entorhinal-hippocampal memory network.
- Highlighted the significant, previously unrecognized role of the CA2 region in learning and memory.
