生物谷报道：近期的证据表明抗抑郁剂可以促使成熟的海马（掌管记忆的大脑区域）中形成新的神经元。这些发现激起了人们对成熟神经发生的兴趣，并且也提出了这样一个问题：新神经元也能在成熟大脑中与思考和情绪混乱（抑郁和焦虑）有关的区域中萌发。
现在，来自美国国家卫生研究院（NIH）的智力健康研究院（NIMH）的研究人员在成熟的大鼠皮层中发现了通过神经递质GABA（gamma-aminobutyric acid）（一种能够抑制神经元活动的神经递质）来交流的新生神经元。在皮层中，这种新神经元似乎源自本地的、先前未知的前体细胞，而不是由从其他地方迁移来的细胞形成。研究人员将这些发现公布在2005年1月31日的Journal of Cell Biology(JCB)上。
NIMH研究组利用了更多的标记物来追踪新生的神经元并且确定出它们分泌的神经递质的类型。这些标记物利用抗体对特定蛋白的亲和力使特殊的细胞类型带上指示颜色密码。研究人员发现大鼠大脑皮层和纹状体正在产生新的、广泛散布的小细胞即中间神经元。这种神经元能够制造和分泌GABA。这种新的中间神经元与海马和嗅球中的细胞很相似，并且产生的频率也相似。中间神经元被认为在调节较大类型的神经元中起到一定的作用。
由于抗抑郁剂能够促进成熟海马区域的神经形成，因此它们可能对皮层有相似的作用。但是有关新神经元的调节和可能的功能问题还有待进一步研究.
JCB在本期也给出了精彩的评论，全文如下：
Neurogenesis in the adult brain is generally considered to be restricted to the hippocampus and olfactory bulb—ancient parts of the brain that are found even in nonmammalian species. A few publications suggested that the neocortex—a well-developed region in primates that is implicated in higher thought—also supports neurogenesis. These reports have been met with skepticism, as other groups have been unable to replicate the findings. On page 415, Dayer et al. bolster the evidence for proliferating neurons in regions beyond the hippocampus and olfactory bulb.The authors used a battery of neuronal markers to confirm that neurogenesis exists in the neocortex. Although difficult to find in the sparsely populated expanse of the cortex, replicating cells with markers of neuronal precursors were present in the adult rat neocortex. Their numbers suggest that these interneurons in the cortex turnover as rapidly as granule cells in the hippocampus, where up to 6% of the cells are replaced within a month.
The various markers that the authors used also revealed for the first time that the neocortical precursors produce GABAergic interneurons, which are small inhibitory neurons that regulate the larger pyramidal cells of the cortex. Because most neurons in the cortex are pyramidal cells, which are large and unmistakably neuronal, the new interneurons can be easily overlooked or mistaken for glial cells.
The precursors originate from within the cortex itself, rather than migrating from the subventricular zone (SVZ), which provides new neurons to the olfactory bulb. The authors did note, however, that some SVZ precursors also found their way to the striatum—a region associated with motor skill learning—where they formed interneurons.
Depression has been correlated with decreased hippocampal neurogenesis and a decrease in small cells in the neocortex that look like glia. The new findings hint that some of those missing cells may be newly born interneurons and suggest that neurogenesis in the cortex will be an important event to examine in disease states and old age.
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