Diversity of the calretinin immunoreactivity in the dentate gyrus of gerbils, hamsters, guinea pigs, and laboratory shrews.

We have recently reported that calretinin (CR) immunoreactivity in the mouse dentate gyrus (DG) is prominently different from that in the rat and monkey dentate gyrus. The CR-immunoreactive (IR) neuronal components characteristic of mouse DG were (1) mossy cells in the ventral hilus, (2) punctate elements in the inner molecular layer, (3) Cajal-Retzius cells in the molecular layer, and (4) immature granule cells at the basal part of the granule cell layer, which were also IR for highly polysialylated neural cell adhesion molecule. In this study, we examine the CR-IR elements in the DG of the gerbil, hamster, guinea pig, and laboratory shrew, and compare them with those of the rat, monkey, and mouse, reported previously. We show that mossy cells are distributed throughout the dorsoventral axis in all these animals, but mossy cells in the ventral hilus of the hamster, gerbil, and laboratory shrew are CR-IR, resembling those of the mouse, whereas mossy cells of the guinea pig are CR negative, like those of the rat. The inner molecular layer, the target zone of mossy cells, was observed to contain CR-IR punctae in the hamster, gerbil, and laboratory shrew, which corresponds to the CR immunoreactivity of the mossy cells. In addition, we observed CR-IR presumed Cajal-Retzius cells in all animals examined. On the other hand, CR-IR immature granule cells were encountered in the laboratory shrew, but not in other animals. The present study reveals prominent species differences in the CR-IR elements of the DG. Copyright 1999 Wiley-Liss, Inc.