Adult-Born Hippocampal Neurons Are More Numerous, Faster Maturing, and More Involved in Behavior in Rats than in Mice

Abstract

Neurons are born throughout adulthood in the hippocampus and show enhanced plasticity compared with mature neurons. However, there are conflicting reports on whether or not young neurons contribute to performance in behavioral tasks, and there is no clear relationship between the timing of maturation of young neurons and the duration of neurogenesis reduction in studies showing behavioral deficits. We asked whether these discrepancies could reflect differences in the properties of young neurons in mice and rats. We report that young neurons in adult rats show a mature neuronal marker profile and activity-induced immediate early gene expression 1-2 weeks earlier than those in mice. They are also twice as likely to escape cell death, and are 10 times more likely to be recruited into learning circuits. This comparison holds true in two different strains of mice, both of which show high rates of neurogenesis relative to other background strains. Differences in adult neurogenesis are not limited to the hippocampus, as the density of new neocortical neurons was 5 times greater in rats than in mice. Finally, in a test of function, we find that the contribution of young neurons to fear memory is much greater in rats than in mice. These results reveal substantial differences in new neuron plasticity and function between these two commonly studied rodent species.

Spatial learning sculpts the dendritic arbor of adult-born hippocampal neurons

“…Interestingly, these treatments did not disrupt basal neurogenesis, a finding consistent with some (35), but not all, previous studies (36,37). The discrepancy between these studies might be related to differences in drug regimens, species, strains, and sex, all of which are known to influence neurogenesis (2,38). The lack of effect on basal neurogenesis in the present study indicates specific impairment of learning-driven activity mediated by NMDAR activity.…”

“…At a later developmental stage, adult-born neurons express NMDARs (19,37) and functional glutamatergic afferents that have been described to occur in mice toward the end of the second week after birth (30,31). However, it has been recently shown that adult-born neuron maturation and functional recruitment into the dentate network is faster in rats compared with mice (38) and that glutamatergic afferents arrive earlier in rats, when newborn neurons are 10 days old (40), a time window consistent with our data. Thus, learning may accelerate the maturation of adult-born neurons by inducing proneural genes and/or by accelerating the arrival of glutamatergic inputs and their functional integration into the network, as has been described during epileptic crises (32).…”

BDNF-stimulated intracellular signalling mechanisms underlie exercise-induced improvement in spatial memory in the male Wistar rat

“…Cell proliferation has been shown to increase after as little as three days of voluntary exercise in mice, becoming statistically significant only after 10 days [45]. However, there is some evidence that the stages of neurogenesis occur at a different rate in rats than in mice [46]. Our results demonstrate that cell division is increased in the dentate gyrus with as little as one week of forced exercise; however, it is unlikely that this contributes to the observed improvements in spatial memory.…”

Axonal ribosomes and mRNAs associate with fragile X granules in adult rodent and human brains

“…Adult neurogenesis is more robust in rats than mice (33). Thus it is possible that the interspecies differences in FXG expression in the hippocampus (Figs.…”