Peptide hormone exendin-4 stimulates subventricular zone neurogenesis in the adult rodent brain and induces recovery in an animal model of Parkinson's disease

We investigated the effects of exendin-4 on neural stem/progenitor cells in the subventricular zone of the adult rodent brain and its functional effects in an animal model of Parkinson's disease. Our results showed expression of GLP-1 receptor mRNA or protein in the subventricular zone and cultured neural stem/progenitor cells isolated from this region. In vitro, exendin-4 increased the number of neural stem/progenitor cells, and the number of cells expressing the neuronal markers microtubule-associated protein 2, beta-III-tubulin, and neuron-specific enolase. When exendin-4 was given intraperitoneally to naive rodents together with bromodeoxyuridine, a marker for DNA synthesis, both the number of bromodeoxyuridine-positive cells and the number of neuronal precursor cells expressing doublecortin were increased. Exendin-4 was tested in the 6-hydroxydopamine model of Parkinson's disease to investigate its possible functional effects in an animal model with neuronal loss. After unilateral lesion and a 5-week stabilization period, the rats were treated for 3 weeks with exendin-4. We found a reduction of amphetamine-induced rotations in animals receiving exendin-4 that persisted for several weeks after drug administration had been terminated. Histological analysis showed that exendin-4 significantly increased the number of both tyrosine hydroxylase- and vesicular monoamine transporter 2-positive neurons in the substantia nigra. In conclusion, our results show that exendin-4 is able to promote adult neurogenesis in vitro and in vivo, normalize dopamine imbalance, and increase the number of cells positive for markers of dopaminergic neurons in the substantia nigra in a model of Parkinson's disease. (C) 2007 Wiley-Liss, Inc.