Identification of NeuN immunopositive cells in the adult mouse subventricular zone

In the adult rodent subventricular zone (SVZ), there are neural stem cells (NSCs) and the specialized neurogenic niche is critical to maintain their stemness. To date, many cellular and noncellular factors that compose the neurogenic niche and markers to identify subpopulations of Type A cells have been confirmed. In particular, neurotransmitters regulate adult neurogenesis and mature neurons in the SVZ have been only partially analyzed. Moreover, Type A cells, descendants of NSCs, are highly heterogeneous and more molecular markers are still needed to identify them. In the present study, we systematically classified NeuN, commonly used as a marker of mature and immature post‐mitotic neurons, immunopositive (+) cells within the adult mouse SVZ. These SVZ‐NeuN+ cells (SVZ‐Ns) were mainly classified into two types. One was mature SVZ‐Ns (M‐SVZ‐Ns). Neurochemical properties of M‐SVZ‐Ns were similar to those of striatal neurons, but their birth date and morphology were different. M‐SVZ‐Ns were generated during embryonic and early postnatal stages with bipolar peaks and extended their processes along the wall of the lateral ventricle. The second type was small SVZ‐Ns (S‐SVZ‐Ns) with features of Type A cells. They expressed not only markers of Type A cells, but also proliferated and migrated from the SVZ to the olfactory bulb. Furthermore, S‐SVZ‐Ns could be classified into two types by their spatial locations and glutamic acid decarboxylase 67 expression. Our data indicate that M‐SVZ‐Ns are a new component of the neurogenic niche and S‐SVZ‐Ns are newly identified subpopulations of Type A cells.