Co-localization of calretinin and calbindin in distinct cells in the hippocampal formation of the rat

We studied the distribution of the calcium binding proteins calretinin and calbindin in the hippocampal formation of the rat brain by means of double-label immunofluorescence - confocal laser scanning microscopy. Colocalization of calretinin and calbindin occurred mostly in large neurons located in the alveus and stratum oriens of field CA1. Some double-labeled cells were observed in the transition area between field CA1 and the subiculum. Finally, double-labeled cells were present in the deep layer of the ventral subiculum. The cells in field CA1 co-expressing both proteins resemble neurons which in neurophysiological experiments by others have been identified as O-LM cells. and we believe that these co-expressing cells should be considered a distinct subpopulation of the calretinin and calbindin populations of GABAergic hippocampal interneurons. (C) 2001 Elsevier Science B.V. All rights reserved.