Running wild: neurogenesis in the hippocampus across the lifespan in wild and laboratory-bred Norway rats.

The dogmatic view that new neurons are not produced in the adult mammalian brain has been overturned in light of mounting evidence that neurogenesis continues to occur within two neurogenic niches, the subventricular zone and the hippocampus. In mammals, new neurons are incorporated into the hippocampus throughout life and are influenced by environmental and genetic factors. Most studies use captive-bred animals, and no previous studies have examined neurogenesis in free-living rats despite the common use of laboratory rats. In particular, exercise upregulates neurogenesis in the hippocampus and exercise levels would certainly differ between wild and captive populations. Therefore, it is unclear whether results from captive populations can be generalized to natural populations or reflect variations from an artificial and inappropriate "baseline" level. To address this, we compared levels of cell proliferation and the number of immature neurons (using the endogenous markers Ki67 and doublecortin, respectively) in captured wild juvenile and adult Norway rats to three captive strains (Sprague-Dawley, Long-Evans, and Brown Norway) of the same species. Here, we show that the level of cell proliferation and young immature neuron survival in the dentate gyrus of juvenile wild rats is significantly higher than in Sprague-Dawley rats, but not Long-Evans or Brown Norway rats. However, cell proliferation and the number of immature neurons in the hippocampus of adult wild rats are within the normal range of captive-bred rats at all adult ages examined. This finding is surprising given the dissimilar environments, including stressors and opportunities for exercise, encountered by each population.

Epp JR ，Barker JM ，Galea LA 《-》

Hippocampus-dependent strategy choice predicts low levels of cell proliferation in the dentate gyrus.

Epp JR ，Galea LA 《-》

Strain differences in neurogenesis and activation of new neurons in the dentate gyrus in response to spatial learning.

Adult neurogenesis continues throughout life in the mammalian hippocampus and evidence suggests that adult neurogenesis is involved in hippocampus-dependent learning and memory. Numerous studies have demonstrated that spatial learning enhances neurogenesis in the hippocampus but few studies have examined whether enhanced neurogenesis is related to enhanced activation of new neurons in response to spatial learning. Furthermore, the majority of these studies have utilized Sprague-Dawley (SD) rats. However, Long-Evans and Sprague-Dawley rats have been reported to have different learning abilities. In order to determine whether these strains exhibit a similar enhancement of neurogenesis and new neuronal activation in response to spatial learning we tested both strains in a hippocampus-dependent or hippocampus-independent version of the Morris water task (MWT) and then compared levels of neurogenesis and activation of these new cells in the hippocampus. Here we show that despite equivalent performance in the MWT, spatial learning produced a different effect on neurogenesis in each strain. Spatial learning increased cell survival and the number of immature neurons in SD rats compared to cage control and cue-trained rats. In Long-Evans (LE) rats however, spatial learning increased cell survival (BrdU-labeling) but did not increase the number of immature neurons (doublecortin-labeling). Furthermore, we report here an intriguing difference in the activation of new neurons (using the immediate early gene product zif268) in SD versus LE rats. In SD rats we show that spatial learning increases the percentage of doublecortin-labeled cells that are activated during a probe trial. Conversely, in LE rats spatial learning increased the activation of BrdU-labeled but not doublecortin-labeled cells. This interesting difference suggests that different ages or maturational stages of cells are recruited by spatial learning in the two strains. These findings may lead to a better understanding of how and why neurogenesis is regulated by spatial learning.

Epp JR ，Scott NA ，Galea LA 《-》

Differences in immunoreactivities of Ki-67 and doublecortin in the adult hippocampus in three strains of mice.

Kim JS ，Jung J ，Lee HJ ，Kim JC ，Wang H ，Kim SH ，Shin T ，Moon C ... -  《-》

Dynamics of neurogenesis in the dentate gyrus of adult rats.

McDonald HY ，Wojtowicz JM 《NEUROSCIENCE LETTERS》