SP–SR interneurones: A novel class of neurones of the CA2 region of the hippocampus
Article first published online: 19 MAR 2012
Copyright © 2012 Wiley Periodicals, Inc.
Volume 22, Issue 8, pages 1758–1769, August 2012
How to Cite
Mercer, A., Botcher, N. A., Eastlake, K. and Thomson, A. M. (2012), SP–SR interneurones: A novel class of neurones of the CA2 region of the hippocampus. Hippocampus, 22: 1758–1769. doi: 10.1002/hipo.22010
- Issue published online: 11 JUL 2012
- Article first published online: 19 MAR 2012
- Manuscript Accepted: 30 JAN 2012
- Medical Research Council (MRC). Grant Number: G0401248
- Biotechnology and Biological Sciences Research Council (BBSRC). Grant Number: BB/G008639/1
- bistratified cells;
The CA2 region of the hippocampus has distinctive properties and inputs and may be linked with the pathology of specific psychiatric and neurological disorders. It is, therefore, important to understand CA2 circuitry and its involvement in the circuitry of the hippocampus. Properties of CA2 basket cells have been reported. However, other classes of CA2 interneurones with cell bodies located in stratum pyramidale remained to be described. In this study, the unusual axonal arbors of a novel subclass of dendrite-preferring CA2 interneurones whose somata are located in the pyramidal cell layer was revealed following intracellular recordings and biocytin labeling. One to four apical dendrites emerged from the soma, branched in stratum radiatum (SR) forming a tuft, but rarely penetrated stratum lacunosum-moleculare (SLM). One or two basal dendrites branched close to the soma, the branches extended through stratum oriens (SO) and often reached the alveus. Unlike CA2 bistratified cells, the axons of these cells arborized almost exclusively in SR with few, if any, branches extending to stratum pyramidale (SP), SO, or SLM. These interneurones again, unlike bistratified cells, were immunonegative for parvalbumin and cholecystokinin. Electrophysiologically, they were similar to some CA2 basket and bistratified cells in that they presented a “sag” in response to hyperpolarizing current injections and displayed spike frequency adaptation. They targeted the apical dendrites of neighboring CA2 pyramidal cells and received inputs from them. © 2012 Wiley Periodicals, Inc.