The hippocampus is involved in declarative memory and produces new neurons throughout adulthood. Numerous experiments have been aimed at testing the possibility that adult neurogenesis is required for learning and memory. However, progress has been encumbered by the fact that abating adult neurogenesis usually affects other biological processes, confounding the interpretation of such experiments. In an effort to circumvent this problem, we used a reverse approach to test the role of neurogenesis in hippocampus-dependent learning, exploiting the low levels of adult neurogenesis in the MRL/MpJ strain of mice compared with other mouse strains. We observed that adult MRL/MpJ mice produce 75% fewer new neurons in the dentate gyrus than age-matched C57BL/6 mice. Learning-induced synaptic remodeling, spatial learning, and visual recognition learning were reduced in MRL/MpJ mice compared with C57BL/6 mice. When MRL/MpJ mice were allowed unlimited access to running wheels, neurogenesis along with spatial learning and visual recognition learning were increased to levels comparable to those in running C57BL/6 mice. Together, these results suggest that adult neurogenesis is correlated with spatial learning and visual recognition learning, possibly by modulating morphological plasticity in the dentate gyrus.
(c) 2009 Wiley-Liss, Inc.