Adult neurogenesis and gliogenesis in the dorsal and ventral canine hippocampus

Dentate gyrus (DG) of the mammalian hippocampus gives rise to new neurons and astrocytes all through adulthood. Canine hippocampus presents many similarities in fetal development, anatomy, and physiology with human hippocampus, establishing canines as excellent animal models for the study of adult neurogenesis. In the present study, BrdU-dated cells of the structurally and functionally dissociated dorsal (dDG) and ventral (vDG) adult canine DG were comparatively examined over a period of 30 days. Each part's neurogenic potential, radial glia-like neural stem cells (NSCs) proliferation and differentiation, migration, and maturation of their progenies were evaluated at 2, 5, 14, and 30 days post BrdU administration, with the use of selected markers (glial fibrillary acidic protein, doublecortin, calretinin and calbindin). Co-staining of BrdU+ cells with NeuN or S100B permitted the parallel study of the ongoing neurogenesis and gliogenesis. Our findings reveal the comparatively higher populations of residing granule cells, proliferating NSCs and BrdU+ neurons in the dDG, whereas newborn neurons of the vDG showed a prolonged differentiation, migration, and maturation. Newborn astrocytes were found all along the dorso-ventral axis, counting however for only 11% of newborn cell population. Comparative evaluation of adult canine and rat neurogenesis revealed significant differences in the distribution of resident and newborn granule cells along the dorso-ventral axis, division pattern of adult NSCs, maturation time plan of newborn neurons, and ongoing gliogenesis. Concluding, spatial and temporal features of adult canine neurogenesis are similar to that of other gyrencephalic species, including humans, and justify the comparative examination of adult neurogenesis across mammalian species.