Subdivision-specific expression of ZIF268 in the hippocampal formation of the macaque monkey

The hippocampal formation consists of the dentate gyrus, the hippocampus proper, the subicular complex and the entorhinal cortex. This structure is a major component of the medial temporal lobe, which is essential for memory formation. We investigated the expression of Zif268, a transcription factor regulated by physiological synaptic activity, in the monkey hippocampal formation. Immunoprecipitation with an anti-Zif268 antibody identified monkey Zif268 as an 86,000 molecular weight protein. In the subicular complex, the majority of neurons in the presubiculum were intensely immunopositive for Zif268 when stained with this antibody. A moderate number of Zif268-immunopositive neurons were located in the parasubiculum and the number of these neurons in the subiculum proper was smallest among the three subicular subdivisions. In the entorhinal cortex, layer- and subdivision-specific expression of Zif268 was observed. The rostral part of the entorhinal cortex contained many Zif268-immunopositive neurons in layer II, but immunopositive neurons were only sparsely present in deeper layers. By contrast, the caudal part of the entorhinal cortex contained many Zif268-immunopositive neurons in layer VI and a smaller number of those neurons in layer II. In the dentate gyrus, a few granule cells expressed Zif268. The hippocampus proper contained weakly immunostained neurons in CA1-CA3. No glial cells were immunostained by the anti-Zif268 antibody. Fos and Fos-related antigens were expressed only at very low levels in the examined areas. This study is the first report discussing the expression of immediate early genes in the primate hippocampal formation. Many Zif268-expressing neurons were observed in the presubiculum and layer II of the rostral part of the entorhinal cortex. These subdivision-specific patterns of Zif268 expression may reflect differences in synaptic activities in these regions.