Abstract
The subiculum displays as much anatomical and physiological heterogeneity as the hippocampus. Recent studies suggest that the subiculum is also diverse in terms of gene expression. However, few studies have investigated the heterogeneity of the entire subiculum. To address this issue, we focused on fibronectin because its mRNA (FN1 mRNA) is expressed in the dorsal and ventral subiculum. We immunohistochemically characterized the intracellular expression of fibronectin in the entire subiculum along three axes (i.e., the dorsoventral, proximodistal, and superficial-deep axes). We first confirmed that FN1 mRNA is translated into protein inside cells. Moreover, we found that fibronectin was expressed evenly in the pyramidal cell layer of the dorsal subiculum, whereas in the ventral subicular pyramidal field, fibronectin was most concentrated in the superficial, distal corner. These results suggest that excitatory neurons labeled by fibronectin are more localized in the ventral subiculum than in the dorsal subiculum. Therefore, fibronectin may be useful as an indicator for studying the heterogeneity of principal cells in the subiculum.