Progenitor cells from the CA3 region of the embryonic day 19 rat hippocampus generate region‐specific neuronal phenotypes in vitro

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Abstract
Progenitor cells that endure in different regions of the CNS after the initial neurogenesis can be expanded in culture and used as a source of donor tissue for grafting in neurodegenerative diseases. However, the proliferation and differentiation characteristics of residual neural progenitor cells from distinct regions of the CNS are mostly unknown. This study elucidated the characteristics of progenitor cells that endure in the CA3 region of the hippocampus after neurogenesis, by in vitro analyses of cells that are responsive to epidermal growth factor (EGF) or fibroblast growth factor‐2 (FGF‐2) in the embryonic day 19 (E19) rat hippocampus. Isolated cells from the E19 CA3 region formed neurospheres in the presence of either EGF or FGF‐2, but the yield of neurospheres was greater with FGF‐2 exposure. Differentiation cultures revealed a greater yield of neurons from FGF‐2 neurospheres (60%) than from EGF neurospheres (35%). Exposure to brain‐derived neurotrophic factor (BDNF) enhanced the yield of neurons from EGF neurospheres but had no consequence on FGF‐2 neurospheres. A large number of neurons from EGF/FGF‐2 neurospheres demonstrated clearly palpable morphological features of CA3 pyramidal neurons and lacked γ‐aminobutyric acid (GABA) expression. However, a fraction of neurons (17–20%) from EGF/FGF‐2 neurospheres expressed GABA, and exposure to BDNF increased the number of GABAergic neurons (30%) from EGF neurospheres. Neurons from EGF/FGF‐2 neurospheres also contained smaller populations of calbindin‐ and calretinin‐positive interneuron‐like cells. Thus, progenitor cells responsive to FGF‐2 are prevalent in the CA3 region of the E19 rat hippocampus and give rise to a greater number of neurons than progenitor cells responsive to EGF. However, both FGF‐2‐ and EGF‐responsive progenitor cells from E19 CA3 region are capable of giving rise to CA3 field‐specific phenotypic neurons. These results imply that progenitor cells that persist in the hippocampus after neurogenesis remain regionally restricted and hence retain their ability to give rise to region‐specific phenotypic neurons even after isolation and expansion in vitro.