Broide R S, O'Connor L T, Smith M A, Smith J A, Leslie F M
Department of Pharmacology, College of Medicine, University of California, Irvine 92717, USA.
Neuroscience. 1995 Jul;67(1):83-94. doi: 10.1016/0306-4522(94)00623-d.
The distribution of alpha 7 messenger RNA expression was characterized in developing rat cortex and thalamus. Northern blot analysis of neonatal and adult cortex revealed a single messenger RNA transcript of 5.7 kb. Using in situ hybridization with both full length and short 35S-labeled alpha 7 riboprobes, a distinct transient expression of messenger RNA within sensory cortex and thalamus, during early postnatal development, was observed. alpha 7 transcripts were expressed in low levels as early as embryonic day 13 in the ventricular zone of the neocortex, and as early as embryonic day 15 in the thalamic neuroepithelium. A marked increase in messenger RNA levels was observed during the late prenatal period in both sensory and non-sensory regions of the cortex and thalamus. Moderate to high levels of messenger RNA were maintained into the first postnatal week, followed by a decline into adulthood. alpha 7 messenger RNA expression was significantly higher in the anterodorsal, lateral dorsal, ventral posterior medial and ventral posterior lateral thalamic nuclei of postnatal day 7 pups than in adult brains. Expression of messenger RNA within dorsal lateral geniculate, ventral lateral geniculate and medial geniculate did not show a significant reduction with age. Within the developing cortex, messenger RNA expression delineated the primary somatosensory, auditory and visual cortices in a unique laminar pattern that was consistently and significantly higher than in the adult in superficial layer VI. Higher levels of expression were also observed in retrosplenial cortex at postnatal day 7 than in the adult. Tangential sections through postnatal day 7 cortex revealed low levels of alpha 7 messenger RNA expression delineating the primary sensory areas in layer IV, corresponding to acetylcholinesterase-labeled thalamocortical afferents. However, these sensory areas exhibited higher levels of alpha 7 messenger RNA expression and were more clearly defined in layer VI, but not by acetylcholinesterase staining. The distribution of alpha 7 messenger RNA within the developing thalamocortical system parallels the distribution of alpha-bungarotoxin binding sites and suggests that the receptor is localized on both thalamic cells and their cortical target neurons. This transient and distinct pattern of distribution of the alpha 7 neuronal nicotinic receptor, which coincides with the major phase of thalamocortical development, suggests that it may play a functional role in the development of cortical circuitry.
对发育中的大鼠皮质和丘脑的α7信使核糖核酸（mRNA）表达分布进行了特征描述。对新生和成年皮质进行的Northern印迹分析显示有一条5.7 kb的单一信使核糖核酸转录本。使用全长和短的35S标记的α7核糖核酸探针进行原位杂交，观察到在出生后早期发育阶段，感觉皮质和丘脑中信使核糖核酸有明显的短暂表达。α7转录本早在胚胎第13天就在新皮质的脑室区低水平表达，早在胚胎第15天就在丘脑神经上皮中表达。在产前后期，皮质和丘脑的感觉和非感觉区域的信使核糖核酸水平都有显著增加。中等至高水平的信使核糖核酸持续到出生后第一周，随后下降至成年期。出生后第7天幼崽的前背侧、背外侧、腹后内侧和腹后外侧丘脑核中的α7信使核糖核酸表达明显高于成年大脑。背外侧膝状体、腹外侧膝状体和内侧膝状体中的信使核糖核酸表达并未随年龄增长而显著降低。在发育中的皮质内，信使核糖核酸表达以独特的分层模式描绘了主要的躯体感觉、听觉和视觉皮质，在表层VI中始终且显著高于成年皮质。出生后第7天的扣带回皮质中的表达水平也高于成年期。对出生后第7天皮质的切线切片显示，α7信使核糖核酸在IV层的表达水平较低，描绘了主要感觉区域，对应于乙酰胆碱酯酶标记的丘脑皮质传入纤维。然而，这些感觉区域在VI层中α7信使核糖核酸表达水平较高且更清晰界定，但不是通过乙酰胆碱酯酶染色。α7信使核糖核酸在发育中的丘脑皮质系统内的分布与α-银环蛇毒素结合位点的分布平行，表明该受体定位于丘脑细胞及其皮质靶神经元上。α7神经元烟碱受体这种短暂且独特的分布模式，与丘脑皮质发育的主要阶段一致，表明它可能在皮质回路的发育中发挥功能作用。
