Analysis of proliferating neuronal progenitors and immature neurons in the human hippocampus surgically removed from control and epileptic patients

Adult neurogenesis in the mammalian hippocampus is a well-known phenomenon. However, it remains controversial as to what extent adult neurogenesis actually occurs in the adult human hippocampus, and how brain diseases, such as epilepsy, affect human adult neurogenesis. To address these questions, we analyzed immature neuronal marker-expressing (PSA-NCAM+) cells and proliferating neuronal progenitor (Ki67+/HuB+/DCX+) cells in the surgically removed hippocampus of epileptic patients. In control patients, a substantial number of PSA-NCAM+ cells were distributed densely below the granule cell layer. In epileptic patients with granule cell dispersion, the number of PSA-NCAM+ cells was reduced, and aberrant PSA-NCAM+ cells were found. However, the numbers of Ki67+/HuB+/DCX+ cells were very low in both control and epileptic patients. The large number of PSA-NCAM+ cells and few DCX+/HuB+/Ki-67+ cells observed in the controls suggest that immature-type neurons are not recently generated neurons, and that the level of hippocampal neuronal production in adult humans is low. These results also suggest that PSA-NCAM is a useful marker for analyzing the pathology of epilepsy, but different interpretations of the immunohistochemical results between humans and rodents are required.