cGMP modulates stem cells differentiation to neurons in brain in vivo

During brain development neural stem cells may differentiate to neurons or to other cell types. The aim of this work was to assess the role of cGMP (cyclic GMP) in the modulation of differentiation of neural stem cells to neurons or non-neuronal cells. cGMP in brain of fetuses was reduced to 46% of controls by treating pregnant rats with nitroarginine-methylester (l-NAME) and was restored by co-treatment with sildenafil.Reducing cGMP during brain development leads to reduced differentiation of stem cells to neurons and increased differentiation to non-neuronal cells. The number of neurons in the prefrontal cortex originated from stem cells proliferating on gestational day 14 was 715±14/mm2 in control rats and was reduced to 440±29/mm2 (61% of control) in rats treated with l-NAME. In rats exposed to l-NAME plus sildenafil, differentiation to neurons was completely normalized, reaching 683±11 neurons/mm2. In rats exposed to sildenafil alone the number of cells labelled with bromodeoxyuridine (BrdU) and NeuN was 841±16/mm2. In prefrontal cortex of control rats 48% of the neural stem cells proliferating in gestational day 14 differentiate to neurons, but only 24% in rats exposed to l-NAME. This was corrected by sildenafil, 40% of cells differentiate to neurons. Similar results were obtained for neurons proliferating during all developmental period. Treatment with l-NAME did not reduce the total number of cells labelled with BrdU, further supporting that l-NAME reduces selectively the differentiation of stem cells to neurons. Similar results were obtained in hippocampus. Treatment with l-NAME reduced the differentiation of neural stem cells to neurons, although the effect was milder than in prefrontal cortex. These results support that cGMP modulates the fate of neural stem cells in brain in vivo and suggest that high cGMP levels promote its differentiation to neurons while reduced cGMP levels promote differentiation to non-neuronal cells.