To study the regulation of adult neurogenesis and its relationship to behavior, we use rodents, mice and rats, which show adult neurogenesis in the same regions as primates. This year we examined regional differences in birth and activation of new hippocampal granule neurons. Hippocampal function varies in a subregion-specific fashion: spatial processing is thought to rely? on the dorsal hippocampus, while anxiety-related behavior relies more on the ventral hippocampus. We found that the rate of neurogenesis is higher in the dorsal portion than the ventral portion of the adult rat dentate gyrus. We then used c-fos, a protein with activity-dependent expression, to examine the activation of granule cells after a hippocampus-dependent task, the Morris water maze. We found that activation of the granule cell population as a whole (cells of all ages) is higher in the dorsal than the ventral dentate gyrus. However, activation of young granule cells, born in adulthood, is higher in the ventral dentate gyrus than in the dorsal region. Interestingly, activation of the granule cell population as a whole was equivalent whether rats learned to find a hidden platform in water maze-trained or simply explored the maze with no task, yet young granule cells were only activated in the learning condition. These results provide new evidence that hippocampally-relevant experience activates young and mature neurons in different dentate gyrus subregions and with different specificity, and in turn suggest that adult-born neurons may play a specific role in anxiety-related behavior or other non-spatial aspects of hippocampal function. We have also collaborated with SBSG (NIAAA) on several studies of the relationship between stress, antidepressants, adult neurogenesis, and behavior. In one, we found that the Neuropeptide Y Y1 receptor subtype is not required for the increase in adult neurogenesis in the dentate gyrus observed with antidepressant treatment.
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