Adult Striatal Neurogenesis-A Comparative Approach Between Pigeons, Mice, Macaques, and Human.

Adult neurogenesis describes the formation of new neurons in the adult brain, a process that is fundamental to related functions, particularly in the hippocampus. Although studies reported adult striatal neurogenesis in humans, the phenomenon is still understudied in those regions. Thus, to gain a deeper understanding in different species, the expression of neurogenic markers was quantitatively analyzed in striatal subregions of pigeons and mice. Further, in macaques and human a detailed analysis of the subventricular zone (SVZ) was performed and the human caudate nucleus was qualitatively examined. The results show higher neuronal plasticity in striatal subregions of pigeons compared to mice, as reflected by higher numbers of Bromodeoxyuridine (BrdU)+, BrdU+/Doublecortin+, Doublecortin+, and BrdU+/Neuronal nuclei marker+ cells. Analysis of BrdU+/glial fibrillary acidic protein (GFAP)+ signals indicated further higher gliogenesis/potential stem cell division in pigeons. As newborn striatal neurons may arise from stem cell niches in the SVZ, active proliferation was analyzed with (sex determining region Y)-box 2, GFAP, and Ki-67 in macaques and humans. Specific subdivisions of the SVZ were identified, with GFAP and Ki-67 differentially distributed. Additionally, signs of persistent neuronal plasticity were observed with Doublecortin+ cells in the human caudate nucleus but not in the macaque. The higher levels of striatal adult neurogenesis in pigeons and perspectives of useful methods may encourage the use of birds to investigate the functional role of this phenomenon and may facilitate our understanding of neuronal plasticity even in the human striatum in the future.