Figure 2.

Adult neurogenesis in laboratory rodents and its reduction across vertebrates and mammals. (A,B) Remarkable knowledge has been gathered on the cellular and molecular mechanisms regulating the activity of the neural stem cell niches which provide new neurons throughout life in mice and rats. These neurogenic niches are restricted to three small brain regions (A, green), and only the subventricular zone (in the lateral ventricle wall) and the subgranular zone (in the hippocampus) are considered “canonical” neurogenic sites leading to “complete” neurogenesis. (C) Comparative studies revealed that the amount of stem cell-related plasticity strongly depends on evolutionary constraints: Adult neurogenesis and reparative capacity dramatically decrease from non-mammalian vertebrates to mammals, and, to a lesser extent, among mammals. Among the latter, the reduction follows a trend from small, lissencephalic to large, gyrencephalic brains, becoming restricted to early postnatal stages. Modified from [46] (with permission of Elsevier), [70] and [71].