Department of Anatomy, Histology and Embryology, K.K. Leung Brain Research Center, Fourth Military Medical University, Xi'an, PR China.
Cells Tissues Organs. 2011;193(6):404-16. doi: 10.1159/000321403. Epub 2010 Dec 2.
To gain better insight into the ontogenic function of enkephalin (ENK) in the spinal cord, it is necessary to have a clear picture of the developing pattern of the ENKergic neurons. To address this question, we used transgenic mice which reveal ENKergic neurons easily by expressing enhanced green fluorescent protein (GFP) under the specific transcriptional control of the preproenkephalin (PPE) gene. GFP-positive neurons first appeared at embryonic day (E) 11.5 in the ventromedial part of the cervical ventral gray matter. At E13, they were mainly present in the intermediate zone. Thereafter, GFP-positive neurons increased progressively in number and extended from ventral to dorsal regions. Quantitative analysis showed that GFP-positive neurons peaked in number at postnatal day (P) 7 at the cervical level. The number of GFP-positive neurons reached a peak at P3 at the lumbar level. At P21, the distribution pattern of GFP immunoreactivity was similar to that in the adult spinal cord. Double-labeling results showed that about one-third of the total γ-aminobutyric acid cell population colocalized with GFP: 34.9 ± 3.5% at E16 and 32.4 ± 3.7% at P3. Double-labeled neurons accounted for nearly half of the GFP-positive neurons: 42.4 ± 2.4% at E16 and 44.1 ± 2.9% at P3. Taken together, the present results suggest that ENKergic neurons develop according to a rostrocaudal and ventrodorsal gradient. These results have broad implications for understanding the functional roles of ENKergic neurotransmission in the developing spinal cord.
为了更深入地了解脑啡肽（ENK）在脊髓中的发育功能，有必要清楚地了解 ENK 能神经元的发育模式。为了解决这个问题，我们使用了转基因小鼠，这些小鼠通过在 preproenkephalin（PPE）基因的特定转录控制下表达增强型绿色荧光蛋白（GFP），很容易显示出 ENK 能神经元。GFP 阳性神经元最早于胚胎第 11.5 天（E）出现在颈前灰的腹内侧部分。在 E13 时，它们主要存在于中间区。此后，GFP 阳性神经元的数量逐渐增加，并从腹侧延伸到背侧区域。定量分析显示，GFP 阳性神经元在颈段的出生后第 7 天（P）达到数量峰值。在腰段，GFP 阳性神经元的数量在 P3 时达到峰值。在 P21 时，GFP 免疫反应的分布模式与成年脊髓相似。双标记结果表明，约三分之一的总 γ-氨基丁酸细胞群体与 GFP 共定位：E16 时为 34.9±3.5%，P3 时为 32.4±3.7%。双标记神经元占 GFP 阳性神经元的近一半：E16 时为 42.4±2.4%，P3 时为 44.1±2.9%。总之，这些结果表明，ENK 能神经元的发育遵循头尾和腹背梯度。这些结果对于理解发育中脊髓中 ENK 能神经传递的功能作用具有广泛的意义。
