Emerging new sites for adult neurogenesis in the mammalian brain: a comparative study between the hypothalamus and the classical neurogenic zones.

In adult mammalian brain, two main germinative regions located in the subventricular zone of the lateral ventricle and in the subgranular cell layer of the hippocampal dentate gyrus have been considerably documented and are still under intense scrutiny. However, new neuron formation has recently been reported in various other brain areas including the hypothalamus. This central structure, responsible for the control of many major neuroendocrine functions such as reproduction, expresses high levels of PSA-NCAM and nestin, both proteins being involved in structural and morphological plasticity mechanisms. Cell proliferation and new neuron production have been demonstrated in the adult hypothalamus of numerous species, although not hitherto described in non-human primates and humans. Similarly to the subventricular zone and in the subgranular cell layer, the adult hypothalamic neurogenesis process is subject to dynamic regulation by various physiological and pharmacological signals. Several pieces of evidence support the hypothesis that a stem cell niche-like architecture exist in the hypothalamus region lining the third ventricle thereby enabling adult neural stem cells to continuously generate neurons in vivo throughout life. Furthermore, recent data indicating that new hypothalamic neurons may become functionally implicated in sensory information processing endorse the assumption that the hypothalamus might be a neurogenic region.