DISTRIBUTION OF CALRETININ IMMUNOREACTIVITY IN THE MOUSE DENTATE GYRUS .1. GENERAL DESCRIPTION

Calretinin-containing elements were visualized with immunocytochemistr y in the adult mouse dentate gyrus (DG). In the ventral DG calretinin immunoreactive (CR-LR) large multipolar cells were clustered; they ext ended between two and four thick cylindrical dendrites which further b ranched into several thinner processes. Characteristic grape-like spin y appendages were occasionally observed on these thick and thinner den dritic processes. On the basis of these structural features these larg e CR-IR cells were identified as hilar messy cells. At the supragranul ar zone a dense CR-IR band was seen, where numerous CR-IR punctae and fibers were packed tightly among putative granule cell dendrites. In t he granule cell layer, especially at the dorsal DG, numerous faintly C R-IR cells were located at the interface with the hilus. They were tri angular in shape and neither calbindin D28k nor GABA positive, but wer e immunoreactive for highly polysialylated neural cell adhesion molecu le (NCAM-H) and thus considered as newly generated neurons. In the mol ecular layer CR-LR cells were also scattered; they were mainly located near the pial surface and the hippocampal fissure, small in size, ovo id in shape and usually gave rise to one very thin axon-like and one t hin cylindrical dendritic process. These cells were assumed to be Caja l-Retzius cells. Throughout the layers, that is, the molecular layer, the granule cell layer and the hilus, CR-IR multipolar and/or fusiform cells were encountered. They resembled those reported in the rat DG i n their structural features and usually extended smooth or varicose or sparsely spiny dendritic processes; some of them were confirmed to be GABA-like immunoreactive and/or glutamic acid decarboxylase immunorea ctive. The present study showed that CR immunoreactivity in the mouse DG differed significantly from that in the rat and monkey dentate gyri reported previously.