IMMATURE NEURONAL CELLS ACCUMULATE DIFFERENTLY IN THE HIPPOCAMPAL DENTATE GYRUS OF DIFFERENT MAMMALS AFTER SLOWING DOWN OF CELL DIVISION

Adult neurogenesis extension, rate, time course and functions can be quite heterogeneous among mammals. In general, small-brained, lissencephalic species have high rates, lifelong production of neurons, whereas a decline in neurogenic processes is observed in large, gyrencephalic brains. In the human hippocampus results are controversial: many cells expressing the cytoskeletal marker of immaturity doublecortin (DCX) are detectable, in contrast with very low levels of cell division and stem cell niche disappearance. The recent demonstration that populations of prenatally generated, “immature” neurons can persistently express DCX in adulthood (thus remaining in an undifferentiated state for long periods) open the hypothesis that immature-like neurons might also be present in neurogenic sites. Here, the Optical Fractionator with StereoInvestigator software was used to estimate the number of granule cells, DCX+ and Ki-67+ antigen cells in the dentate gyrus of mouse, rabbit, cat, sheep. We found significant difference in the relationship between cell division and occurrence of DCX+ cells, with accumulation of immature cells in hippocampi of large-brained species characterized by low cell division rate. Detection of maturity/immaturity markers revealed a more stable pattern among species. Our results suggest that in the hippocampus of gyrencephalic mammals, immature-like neurons can persist after reduction of cell division.