Adult-generated hippocampal and neocortical neurons in macaques have a transient existence

Abstract

Previously we reported that new neurons are added to the hippocampus and neocortex of adult macaque monkeys. Here we compare the production and survival of adult-generated neurons and glia in the dentate gyrus, prefrontal cortex, and inferior temporal cortex. Twelve adult macaques were injected with the thymidine analogue BrdUrd, and the phenotypes of labeled cells were examined after 2 h, 24 h, 2 wk, 5 wk, 9 wk, and 12 wk by using the following immunocytochemical markers: for immature and mature neurons, class III ␤-tubulin (TuJ1); for mature neurons, neuronal nuclei; for astrocytes, glial fibrillary acidic protein; and for oligodendrocytes, 2 ,3 -cyclic nucleotide 3 phosphodiesterase. We found that the dentate gyrus had many more BrdUrd-labeled cells than either neocortical area. Furthermore, a greater percentage of BrdUrd-labeled cells expressed a neuronal marker in the dentate gyrus than in either neocortical area. The number of new cells in all three areas declined by 9 wk after BrdUrd labeling, suggesting that some of the new cells have a transient existence. BrdUrd-labeled cells also were found in the subventricular zone and in the white matter between the lateral ventricle and neocortex; some of the latter cells were double-labeled for BrdUrd and TuJ1. Adult neocortical neurogenesis is not restricted to primates. Five adult rats were injected with BrdUrd, and after a 3-wk survival time, there were cells double-labeled for BrdUrd and either TuJ1 or neuronal nuclei in the anterior neocortex as well as the dentate gyrus.

New Interneurons in the Adult Neocortex: Small, Sparse, but Significant?

“…Interestingly, the earliest reports of adult neurogenesis in these two regions also described new neurons in the adult neocortex (1;2). These early neocortical neurogenesis findings have been replicated in recent studies (3)(4)(5)(6)(7), but the existence of adult neurogenesis in the neocortex remains controversial, largely due to the existence of negative reports. In non-human primates, new neurons have been reported in prefrontal, inferior temporal, and posterior parietal cortex (3;6;7), though other groups have found no new neurons in the neocortex of adult primates, including humans (8)(9)(10)(11).…”

Chronic Social Stress Inhibits Cell Proliferation in the Adult Medial Prefrontal Cortex: Hemispheric Asymmetry and Reversal by Fluoxetine Treatment

“…The presence of newborn neurons has been reported in various neocortical areas of adult nonhuman primates (Gould et al, 1999(Gould et al, , 2001Bernier et al, 2002), but these findings have not been replicated by other investigators (Kornack and Rakic, 2001). Interestingly, a recent study came to the conclusion that GABAergic interneurons are generated in the neocortex of adult rats (Dayer et al, 2005).…”

Noncanonical Sites of Adult Neurogenesis in the Mammalian Brain

“…Spontaneous (constitutive) parenchymal neurogenesis can be considered a rare phenomenon in mammals, with its regional location being dependent on the animal species (reviewed in Bonfanti and Peretto 2011;Bonfanti 2013;and summarized in Table 1). Different examples of neurogenesis occurring outside of the two germinal-layer-derived neurogenic sites have been described in rodents (Dayer et al 2005;Kokoeva et al 2005), rabbits (Luzzati et al 2006;Ponti et al 2008), and monkeys (Gould et al 2001;Bernier et al 2002), with remarkable differences between closely related orders (e.g., rodents and lagomorphs: cf., for example, Dayer et al 2005;Luzzati et al 2006;Ohira et al 2010;Ponti et al 2008). Some of the differences and discrepancies among studies arise from technical issues, such as analysis of a proliferative marker (e.g., BrdU), colocalization with neuronal markers, or misconception about specific markers (e.g., PSA-NCAM labeling migrating cells and not newborn neurons).…”