Beyond the Hippocampus and the SVZ: Adult Neurogenesis Throughout the Brain

Abstract

Convincing evidence has repeatedly shown that new neurons are produced in the mammalian brain into adulthood. Adult neurogenesis has been best described in the hippocampus and the subventricular zone (SVZ), in which a series of distinct stages of neuronal development has been well characterized. However, more recently, new neurons have also been found in other brain regions of the adult mammalian brain, including the hypothalamus, striatum, substantia nigra, cortex, and amygdala. While some studies have suggested that these new neurons originate from endogenous stem cell pools located within these brain regions, others have shown the migration of neurons from the SVZ to these regions. Notably, it has been shown that the generation of new neurons in these brain regions is impacted by neurologic processes such as stroke/ischemia and neurodegenerative disorders. Furthermore, numerous factors such as neurotrophic support, pharmacologic interventions, environmental exposures, and stem cell therapy can modulate this endogenous process. While the presence and significance of adult neurogenesis in the human brain (and particularly outside of the classical neurogenic regions) is still an area of debate, this intrinsic neurogenic potential and its possible regulation through therapeutic measures present an exciting alternative for the treatment of several neurologic conditions. This review summarizes evidence in support of the classic and novel neurogenic zones present within the mammalian brain and discusses the functional significance of these new neurons as well as the factors that regulate their production. Finally, it also discusses the potential clinical applications of promoting neurogenesis outside of the classical neurogenic niches, particularly in the hypothalamus, cortex, striatum, substantia nigra, and amygdala.

Cell Proliferation in the Piriform Cortex of Rats with Motor Cortex Ablation Treated with Growth Hormone and Rehabilitation

“…Classically, in the adult brain, the two best known and most studied neurogenic niches are the subgranular region of the dentate gyrus of the hippocampus (SGZ) and the subventricular zone of the lateral ventricles (SVZ). However, cell proliferation has also been detected in the brain in other areas, such as the hypothalamus, the amygdala or the piriform cortex [ 70 , 71 ]. In the latter, doublecortin positive cells (DCX+) (a marker of neurogenesis) have been detected.…”

Amygdala Allostasis and Early Life Adversity: Considering Excitotoxicity and Inescapability in the Sequelae of Stress

“…Connected to heterogeneity, volumetric growth during development varies across subnuclei, but is driven by an increase in neurons of the basal nuclei and lateral nucleus. Other subnuclei of the amygdala (i.e., the paralaminar region) gradually loses putative newly generated/differentiated neurons, suggesting a proliferative role (or migration pathway) akin to subventricular zones of neighboring structures (Chareyron et al, 2012;Avino et al, 2018;Jurkowski et al, 2020). Related to allostatic, inverted-U patterns, allostatic load translates roughly to "a new normal" and is the detrimental physiological consequence caused by sustained excessive activation of stress-responsive systems (Danese and McEwen, 2012); this is commonly caused by chronic or repeated exposure to psychosocial stressors.…”

Loss of Active Neurogenesis in the Adult Shark Retina

“…Adult neurogenesis recapitulates to some extent the neurogenic process occurring in early development, but certain regulatory mechanisms are unique to the process in adults. Moreover, adult neurogenesis via these neurogenic niches is highly dependent on species and CNS regions, i.e., different types of progenitors with different neurogenic potentials have been described depending on the neurogenic niche (Docampo-Seara et al, 2020 and references therein; Jurkowski et al, 2020 ).…”