Recent studies have shown that the hippocampus can influence neurogenesis in the adult dentate gyrus but little is known about the mechanism through which this occurs and the circuitry involved. In the subgranular zone of the adult dentate gyrus, neurogenesis involves a series of differentiation steps from radial glia-like stem/progenitor cells to transiently amplifying neuronal progenitor cells to postmitotic neurons.
A study by researchers from the Stanford University found that transient amplified neuronal progenitor cells receive direct excitatory inputs from the hippocampal GABAergic circuitry. This paper provides both in vitro and in vivo data to support the conclusion that this GABAergic excitation to dividing progenitor cells promotes activity-dependent neuronal differentiation.
The mandala-like composition on the cover depicts the sophisticated complication of adult hippocampal neurogenesis. The system in which many proliferating cells firmly support the differentiation of each functional neuron is symbolized by the concentric alignment of the photographs of cells, which includes radial glia-like stem/progenitor (type-1) cells, transiently amplifying neuronal progenitor (type-2) cells, immature neurons, and mature neurons. Research from the University of Tokyo elucidates a part of the mechanisms underlying neuronal differentiation of type-2 cells, which is a direct involvement of the hippocampal GABAergic system. This work reveals that GABAergic, but not glutamatergic, inputs depolarize type-2 cells, promoting activity-dependent neuronal differentiation.
Earlier research suggested that there is extensive evidence indicating that new neurons are generated in the dentate gyrus of the adult mammalian hippocampus, a region of the brain that is important for learning and memory. However, it was not known whether these new neurons become functional, since the methods used to study adult neurogenesis were limited to fixed tissue. They reported that newly generated cells in the adult mouse hippocampus have neuronal morphology and can display passive membrane properties, action potentials and functional synaptic inputs similar to those found in mature dentate granule cells. These findings demonstrated that newly generated cells mature into functional neurons in the adult mammalian brain.
Another earlier study from Rockefeller University showed that astrocytes give rise to new neurons in the adult mammalian hippocampus which demonstrated that stem cells are essential to understanding how tissues continue to generate new cells in the adult vertebrate brain throughout life.
Neuron, Vol 47, 775-777, 15 September 2005
Neuron, Vol 47, 803-815, 15 September 2005
Nature 415, 1030-1034 (28 February 2002)
The Journal of Neuroscience, September 15, 2001, 21(18):7153-7160
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