Neurons in very few CNS populations continue to be produced during adulthood. The goal of our research is to understand the function of this adult neurogenesis by studying the regulation of neuronal precursor proliferation and survival. This year we published an investigation of the naturally occurring death of newborn granule neurons in the adult dentate gyrus, a part of the hippocampal region in which large numbers of new neurons are born throughout adulthood. We examined the effects of a rapidly learned, natural learning task on survival of newborn neurons in the dentate gyrus. We found that one day of training on this task increased new neuron survival while two days of training decreased survival. This switch from increased survival to increased cell death may provide a mechanism for storing information temporarily in the hippocampus and discarding cells when their stored information is no longer needed, in order to make space for new completely naive neurons. Additionally, we found evidence that new neurons are born in the adult rodent cortex and striatum. We identified the new neurons in both of these regions as interneurons, based on their small size and expression of the GABA synthesizing enzyme GAD 65, calretinin, and calbindin (in neocortex only). We found evidence suggesting that the new striatal neurons are generated from precursor cells located within the subventricular zone, a known source of new neurons in the adult brain. However, the new neocortical neurons did not appear to migrate into the cortex from the subventricular zone. Instead, our data suggest that these new neurons are generated from NG2 expressing cells, formerly believed to be oligodendrocyte-specific progenitors, within the neocortex itself.
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