Comparing adult hippocampal neurogenesis in mammalian species and orders: influence of chronological age and life history stage

Abstract

Adult hippocampal neurogenesis is a prominent event in rodents. In species with longer life expectancies, newly born cells in the adult dentate gyrus of the hippocampal formation are less abundant or can be completely absent. Several lines of evidence indicate that the regulatory mechanisms of adult neurogenesis differ between short- and long-lived mammals. After a critical appraisal of the factors and problems associated with comparing different species, we provide a quantitative comparison derived from seven laboratory strains of mice (BALB, C57BL/6, CD1, outbred) and rats (F344, Sprague-Dawley, Wistar), six other rodent species of which four are wild-derived (wood mouse, vole, spiny mouse and guinea pig), three non-human primate species (marmoset and two macaque species) and one carnivore (red fox). Normalizing the number of proliferating cells to total granule cell number, we observe an overall exponential decline in proliferation that is chronologically equal between species and orders and independent of early developmental processes and life span. Long- and short-lived mammals differ with regard to major life history stages; at the time points of weaning, age at first reproduction and average life expectancy, long-lived primates and foxes have significantly fewer proliferating cells than rodents. Although the database for neuronal differentiation is limited, we find indications that the extent of neuronal differentiation is subject to species-specific selective adaptations. We conclude that absolute age is the critical factor regulating cell genesis in the adult hippocampus of mammals. Ontogenetic and ecological factors primarily influence the regulation of neuronal differentiation rather than the rate of cell proliferation.

Microbats appear to have adult hippocampal neurogenesis, but post-capture stress causes a rapid decline in the number of neurons expressing doublecortin

“…Studies of adult neurogenesis in wild-living mammals are becoming more common due to the need to understand this process in relation to normal life-history parameters (Bartkowska et al 2010;Amrein et al, 2011;Kempermann, 2012;Patzke et al 2013;Chawana et al, 2013;Cavegn et al, 2013). The investigation of wild-living mammals may provide a broader understanding of the dynamics and mechanisms influencing adult neurogenesis for species in their natural habitat and ultimately reveal potential reasons for the presence of adult neurogenesis in the mammalian brain.…”

Effect of Cholesterol Enriched or Fatty-Acid Diets on Cholesterol and Lipid Levels in Young Wistar Rats

“…Rats had a compatible metabolic rate of clearance, and are physiologically close to humans, whereas mice have faster metabolic rate of clearance than humans. Additionally the rat genome is much closer to human than mice, and this genetic closeness makes the rat model more appropriate to evaluate the effects of the diet and compare it to human being [12] [13] [14]. Another advantage of this animal strain is that prolonged times consuming high cholesterol diets does not promote arteriosclerosis, allowing longer periods of treatment [15] [16].…”

“…Due to these important antecedents we wanted to compare in separate animal cohorts the effect of a cholesterol enriched diet (CED) or a fatty-acid diet (FAD) on the levels of cholesterol and lipids in a Wistar rat model since we considered important to establish physiological changes induced by diet that could precede the onset of dementias and other diseases related to dietary habits. Particularly we were interested in this animal model, due to its metabolic characteristics, which are closer to human than mouse [10] [11] [12]. Rats had a compatible metabolic rate of clearance, and are physiologically close to humans, whereas mice have faster metabolic rate of clearance than humans.…”

Memory consolidation — Mechanisms and opportunities for enhancement

“…Ageing is accompanied by a decrease in neurogenesis in animals [79,80], and imaging in humans demonstrates that hippocampal volume is decreased with age [81]. Exercise, however, can ameliorate this -it improves spatial memory that normally deteriorates with age [77], and there is larger hippocampal volume in older adults with higher fitness [76].…”