Abstract
Vasoactive intestinal peptide (VIP) is a 28 amino acid polypeptide that is a modulator of neurodevelopment. High levels of VIP and its receptors have been found in postnatal mammalian hippocampus and are influenced by different physiological and pathological conditions such as exercise, stress, spatial learning and epilepsy, which also affect hippocampal neurogenesis. We are investigating the hypothesis that VIP modulates the survival, proliferation and differentiation of stem cells and their progeny in the postnatal hippocampus. We have investigated the effect of VIP alone or in conjunction with NPY or FGF-2 in primary hippocampal neuronal cultures from postnatal rats (P7–9). Bromodeoxyuridine (BrdU) and Ki-67 were used as markers of cell proliferation. Ara-C was used to inhibit cell proliferation. Quantification of cell death was achieved using the nuclear stain 4?,6-diamidino-2-phenylindole (DAPI) and the cell death marker propidium iodide (PI). Immunohistochemistry was used to phenotype cells for nestin, GFAP, and class-III beta-tubulin. We have shown that VIP enhances the survival of postnatal nestin positive hippocampal stem cells and their progeny in a dose dependent manner. At micromolar concentrations, VIP increased cell proliferation and the labelling index. However, at nanomolar concentrations, we observed a purely trophic effect on both mitotic and non-mitotic cells. When cells were exposed to VIP in conjunction with the mitogens NPY or FGF-2, VIP abolished and decreased their proliferative effects respectively. Interestingly, the proportion of neuroblasts increased under VIP plus NPY conditions while the number of progenitor cells increased under VIP plus FGF-2 conditions. We conclude that VIP may be an important trophic factor for hippocampal neurogenesis and interacts with NPY and FGF-2 to modulate the proliferation of stem cells and the survival of their progeny. We suggest that these neuropeptides and others provide a novel control system for postnatal hippocampal neurogenesis depending on their differential release.
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