SummaryTwo populations of oligodendrogenic progenitors co-exist within the corpus callosum (CC) of the adult mouse. Local, parenchymal oligodendrocyte progenitor cells (pOPCs) and progenitors generated in the subependymal zone (SEZ) cytogenic niche. pOPCs are committed perinatally and retain their numbers through self-renewing divisions, while SEZ-derived cells are relatively “young,” being constantly born from neural stem cells. We compared the behavior of these populations, labeling SEZ-derived cells using hGFAP:CreErt2 mice, within the homeostatic and regenerating CC of the young-adult and aging brain. We found that SEZ-derived oligodendroglial progenitors have limited self-renewing potential and are therefore not bona fide OPCs but rather “oligodendroblasts” more similar to the neuroblasts of the neurogenic output of the SEZ. In the aged CC their mitotic activity is much reduced, although they still act as a “fast-response element” to focal demyelination. In contrast to pOPCs, they fail to generate mature myelinating oligodendrocytes at all ages studied.

Postnatal brain neural stem and progenitor cells (NSPCs) cluster in anatomically inaccessible stem cell niches, such as the subependymal zone (SEZ). Here, we describe a method for the isolation of NSPCs from live animals, which we term ''milking.'' The intracerebroventricular injection of a release cocktail, containing neuraminidase, integrin-b1-blocking antibody, and fibroblast growth factor 2, induces the controlled flow of NSPCs in the cerebrospinal fluid, where they are collected via liquid biopsies. Isolated cells retain key in vivo selfrenewal properties and their cell-type profile reflects the cell composition of their source area, while the function of the niche is sustained even 8 months post-milking. By changing the target area more caudally, we also isolate oligodendrocyte progenitor cells (OPCs) from the corpus callosum. This novel approach for sampling NSPCs and OPCs paves the way for performing longitudinal studies in experimental animals, for more in vivo relevant cell culture assays, and for future clinical neuro-regenerative applications.