Neurogenesis occurs continuously in the forebrain of adult mammals, but the functional importance of adult neurogenesis is still unclear. Here, using a genetic labeling method in adult mice, we found that continuous neurogenesis results in the replacement of the majority of granule neurons in the olfactory bulb and a substantial addition of granule neurons to the hippocampal dentate gyrus. Genetic ablation of newly formed neurons in adult mice led to a gradual decrease in the number of granule cells in the olfactory bulb, inhibition of increases in the granule cell number in the dentate gyrus and impairment of behaviors in contextual and spatial memory, which are known to depend on hippocampus. These results suggest that continuous neurogenesis is required for the maintenance and reorganization of the whole interneuron system in the olfactory bulb, the modulation and refinement of the existing neuronal circuits in the dentate gyrus and the normal behaviors involved in hippocampal-dependent memory.
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We thank P. Soriano, F. Costantini and C. Lobe for materials, and K. Nakanishi, N. Tsunekawa, M. Hayashi, M. Fujioka, H. Kohda and K. Okamoto-Furuta for technical help. This work was supported by Grants-in-aid from the Ministry of Education, Culture, Sports, Science and Technology of Japan. I.I. was supported by the 21st Century Center of Excellence Program of the Ministry of Education, Culture, Sports, Science and Technology of Japan and Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists.
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Imayoshi, I., Sakamoto, M., Ohtsuka, T. et al. Roles of continuous neurogenesis in the structural and functional integrity of the adult forebrain. Nat Neurosci 11, 1153–1161 (2008) doi:10.1038/nn.2185
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