Adult Neurogenesis in the Mammalian Hypothalamus: Impact of Newly Generated Neurons on Hypothalamic Function

In mammals, adult neurogenesis was first demonstrated in the subventricular zone of the lateral ventricle (SVZ) and the dentate gyrus of the hippocampal formation. Further research showed that adult neurogenesis persists in other brain structures, such as the cerebral cortex, piriform cortex, striatum, amygdala, and hypothalamus. However, the origin of newly generated cells in these structures is not clear. Accumulating evidence indicates that newly generated neurons in the striatum or amygdala are derived from the SVZ, while in the adult hypothalamus, the proliferation of progenitor cells occurs in the ependymal cells lining the third ventricle, which give rise to new neurons. The heterogeneous cellular organization of the ependymal layer of the hypothalamus leads to different conclusions regarding the type of hypothalamic progenitor cells. In addition, adult hypothalamic neurogenesis occurs at low levels. Based on comparative and functional approaches, we synthesize the knowledge of newly generated cells in the adult hypothalamus. The aim of this review is to provide new insights on adult neurogenesis in the mammalian hypothalamus, with particular attention given to marsupial species. We highlight the number of adult-born neurons in various hypothalamic nuclei, debating whether their low number has an impact on hypothalamic function.