Exploring the Intricacies of Neurogenic Niches: Unraveling the Anatomy and Neural Microenvironments

Abstract

Neurogenesis is the process of forming new neurons from neural stem cells (NSCs). In adults, this process takes place in specific areas of the brain, known as neurogenic niches. These regions have unique anatomical features that have been studied in animal models and in the human brain; however, there are differences between these models that need to be addressed. The most studied areas are the subventricular zone, the lateral and latero-dorsal walls of the lateral ventricles, and the dentate gyrus of the hippocampus (Hp), which are known as the canonical areas. Other, less-studied niches, such as the hypothalamus, the cerebellum, and the amygdala, are known as non-canonical areas. Anatomy occupies a relevant place in adult neurogenesis, in which the tissue architecture and cellular location are necessities for the interaction and release of diverse molecules that allow this phenomenon. The cell arrangement within the niche and the location of the niche itself are of particular relevance to the state in which the NSCs are found. Consequently, the majority of previous discoveries have been related to pathology. While many studies are based on animal models, discoveries related to neurogenesis in humans have also been made; however, in this case, opinions vary, leading to extensive controversy in recent years. In this review, we address the anatomical characteristics of the different brain regions to better understand their relationships within neurogenesis.

Keywords: adult neurogenesis; anatomy; nervous system; neural stem cells; neurogenic niches.

Figure 1

(A) Photograph of a coronal view of an adult human brain (genicocapsular section) showing the lateral wall of the lateral ventricle (red line and white arrows), the caudate nucleus (purple), the putamen (in green), and the two globus pallidus nuclei (internal and external, in yellow). (B) Drawing depicting a coronal section at genicocapsular level pointing out the lateral wall of the lateral ventricle (red line and white arrows), the caudate nucleus (purple), the putamen (in green), and the two globus pallidus nuclei (internal and external, in yellow). The enlarged region corresponds to the lateral wall of the lateral ventricle where the cytoarchitecture of the region can be observed. Astrocytes are represented in green, neurons in blue, oligodendrocytes in purple, neuroblasts in yellow, and finally ependymal cells are represented in pink.

Figure 2

Photograph of a coronal view of an adult human brain (retrolenticular section) showing the anterior and inferior horn of the lateral ventricles, exposing the hippocampus (enlarged region). The drawing shows the anatomical region occupied by the hippocampus.

Figure 3

Drawing of the anatomical features of the hippocampus in murine models. The enlarged region corresponds to the dentate gyrus (DG) of the hippocampus, where the proliferating zone corresponds to the subgranular zone (SGZ).

Figure 4

(A,B), drawings showing the cellular distribution in the hypothalamus and its different regions. Cells can be observed surrounding the third ventricle and distributed in a very specific way. Arc (arcuate nucleus); VMN (ventromedial nucleus); DMN (dorsomedial nucleus); PVN (periventricular nucleus); DHA (dorsal hypothalamic area); LHA (lateral hypothalamic area); AHA (anterior hypothalamic area).

Figure 5

(A) Photograph of a coronal view of an adult human brain at the pyramid level, showing the substantia nigra position (black arrows). (B) Drawing showing the substantia nigra (purple). 3V (Tirth ventricle); LV (lateral ventricle); SN (substantia nigra).