Doublecortin-Expressing Neurons in Chinese Tree Shrew Forebrain Exhibit Mixed Rodent and Primate-Like Topographic Characteristics.

Jia-Qi Ai,Xiao-Xin Yan,Chen Yang,Bo Zhang,Juan Jiang,Tian Tu,Ewen Tu,Rongcan Luo,Rui Bi,Yong-Gang Yao

doi:10.3389/fnana.2021.727883

Abstract

Doublecortin (DCX) is transiently expressed in new-born neurons in the subventricular zone (SVZ) and subgranular zone (SGZ) related to adult neurogenesis in the olfactory bulb (OB) and hippocampal formation. DCX immunoreactive (DCX+) immature neurons also occur in the cerebral cortex primarily over layer II and the amygdala around the paralaminar nucleus (PLN) in various mammals, with interspecies differences pointing to phylogenic variation. The tree shrews (Tupaia belangeri) are phylogenetically closer to primates than to rodents. Little is known about DCX+ neurons in the brain of this species. In the present study, we characterized DCX immunoreactivity (IR) in the forebrain of Chinese tree shrews aged from 2 months- to 6 years-old (n = 18). DCX+ cells were present in the OB, SVZ, SGZ, the piriform cortex over layer II, and the amygdala around the PLN. The numerical densities of DCX+ neurons were reduced in all above neuroanatomical regions with age, particularly dramatic in the DG in the 5–6 years-old animals. Thus, DCX+ neurons are present in the two established neurogenic sites (SVZ and SGZ) in the Chinese tree shrew as seen in other mammals. DCX+ cortical neurons in this animal exhibit a topographic pattern comparable to that in mice and rats, while these immature neurons are also present in the amygdala, concentrating around the PLN as seen in primates and some nonprimate mammals.

Highlights

Doublecortin (DCX) and other immature neuronal markers are commonly used for the characterization of adult neurogenesis, which predominantly occurs in the subventricular zone (SVZ) and subgranular zone (SGZ) to support cellular replacement in the olfactory bulb via the rostral migratory stream (RMS) and in the hippocampal dentate gyrus (DG) via radial migration (Seki and Arai, 1993, 1995; Nacher et al, 2001; Miller and Sahay, 2019; Abbott and Nigussie, 2020)
It should be noted that the lateral ventricle (LV) extended into the bulb as the olfactory ventricle (OV) in all the three age groups of tree shrews examined in the present study
We report here that DCX+ neurons occur in the amygdala in Chinese tree shrews, most densely distributed around its border to the white matter of the piriform cortex, which is consistent with the anatomical location of the paralaminar nucleus (PLN) in this species (Flügge et al, 1994)

Summary

Introduction

Doublecortin (DCX) and other immature neuronal markers are commonly used for the characterization of adult neurogenesis, which predominantly occurs in the subventricular zone (SVZ) and subgranular zone (SGZ) to support cellular replacement in the olfactory bulb via the rostral migratory stream (RMS) and in the hippocampal dentate gyrus (DG) via radial migration (Seki and Arai, 1993, 1995; Nacher et al, 2001; Miller and Sahay, 2019; Abbott and Nigussie, 2020). While virtually absent in rodents, these immature neurons are present over the neocortex in other species, with a linear density increased relative to brain size (La Rosa et al, 2020a)

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