Region-Specific Adult Neural Stem Cell Niches of the Mediobasal Hypothalamus and Medulla Oblongata.

The presence of neural stem cells (NSCs) of the subventricular and subgranular zone in the adult mammalian brain has been the focus of much attention; however, these high-function centers have low regenerative ability in response to brain damage. In this review, we focus on the mediobasal hypothalamus (MBH)-a diencephalic region lining the floor of the third ventricle-and the medulla oblongata, a brainstem structure. Both contain niche-like glial populations with context-dependent neurogenic and gliogenic potential. These evolutionarily conserved regions contain neural circuits essential for life support and display high regenerative capacity in lower vertebrates. Recently, NSCs and neural progenitor cells (NPCs) have been reported in the MBH, including the arcuate nucleus and median eminence. Mediobasal hypothalamic tanycytes, with proximal cell bodies facing the third ventricle and distal cellular processes toward the parenchyma, are identified as NSCs that supply various progenitor and ependymal cells. Neural circuits of the MBH exhibit relatively regenerative capability with near-complete or alternative neuronal circuit reorganization after hypothalamic neuronal damage. In the medulla oblongata, there are two types of NSCs: astrocyte-like NSCs in the area postrema and tanycyte-like NSCs in the central canal facing the cerebrospinal fluid. Astrocyte-like NSCs exhibit relatively active proliferation, whereas tanycyte-like NSCs are almost quiescent. Monosodium glutamate selectively induces neuronal cell death in the area postrema, and NPCs proliferate and differentiate into mature neurons, resulting in near-complete restoration of neuronal density. Experimental autoimmune encephalomyelitis causes demyelination in the medulla oblongata, and NSCs partially restore the density of oligodendrocytes. Thus, recent studies indicate that the adult MBH and medulla oblongata exhibit context-dependent regenerative responses, supplying new neurons and oligodendrocytes in response to brain damage.