Dodge J T, Bevan R D, Bevan J A
Department of Pharmacology, College of Medicine, University of Vermont, Burlington 05405-0068.
Circ Res. 1994 Nov;75(5):916-25. doi: 10.1161/01.res.75.5.916.
The density and nerve varicosity-smooth muscle cell separation of rabbit cerebral and ear arterial beds were compared. The rabbit middle cerebral artery and three of its successive branches and a comparable-sized ear artery and two branches were perfusion-fixed for electron microscopy and analyzed by quantitative morphometric procedures. The purpose was to determine if there are structural correlates to previously observed differences in the sympathetic control of these two vascular systems. The in vitro contractile response of isolated artery segments to electrical field stimulation of their intramural nerves is considerably less in cerebral arteries compared with the similar-sized ear arteries. Furthermore, in the cerebral but not the ear circulation, there is progressive diminution of the neurogenic response with successive branching. Although the total varicosity densities of the major ear and brain arteries studied are similar, and this parameter stays fairly constant with successive branching of the ear, it falls off considerably in the cerebral vessels. There is a significant difference in densities between the two vascular beds when "bare" varicosities located < 1 micron from the medial smooth muscle are compared. The second-order branch of the ear artery has an average of 18 bare varicosities per 500-micron circumference, and the corresponding cerebral vessel has only 2.8 bare varicosities per 500-micron circumference. The mean bare varicosity-smooth muscle cell separation (mean +/- SEM) is significantly (P < .05) less in the ear (1.18 +/- 0.06 microns) than in the cerebral arteries (4.95 +/- 0.23 microns). This is true of all vessels studied. Fifty-nine percent of the bare varicosities in the ear arteries are < 1 micron from the smooth muscle cells, and 1.2% are more distant than 5 microns. These values for cerebral vessels are 9.5% and 37%, respectively. In the ear vessels, 25% of the bare varicosities make close neuromuscular contact (within 500 nm of the smooth muscle), whereas only 3% do so in cerebral vessels; in cerebral compared with ear vessels, the percentage becomes significantly less with branching. These structural features of brain vessels, taken together with the lower sensitivity to and the diminished capacity to respond to norepinephrine, probably account for their weak neurogenic control. The results indicate that the cerebral circulation of the rabbit receives a sympathetic innervation that is relatively ineffective in altering cerebrovascular tone.
比较了兔脑动脉床和耳动脉床的密度以及神经膨体与平滑肌细胞的间距。将兔大脑中动脉及其三个连续分支，以及一条大小相当的耳动脉及其两个分支进行灌注固定，用于电子显微镜观察，并通过定量形态学方法进行分析。目的是确定这两个血管系统在交感神经控制方面先前观察到的差异是否存在结构上的相关性。与大小相似的耳动脉相比，离体动脉段对其壁内神经进行电场刺激的体外收缩反应在脑动脉中明显较小。此外，在脑循环而非耳循环中，随着分支的增加，神经源性反应逐渐减弱。虽然所研究的主要耳动脉和脑动脉的总膨体密度相似，并且该参数在耳动脉连续分支时保持相当恒定，但在脑血管中却显著下降。当比较距内侧平滑肌小于1微米的“裸露”膨体时，两个血管床的密度存在显著差异。耳动脉的二级分支每500微米周长平均有18个裸露膨体，而相应的脑血管每500微米周长只有2.8个裸露膨体。平均裸露膨体与平滑肌细胞的间距（平均值±标准误）在耳动脉（1.18±0.06微米）中显著（P<0.05）小于脑动脉（4.95±0.23微米）。所有研究的血管都是如此。耳动脉中59%的裸露膨体距平滑肌细胞小于1微米，1.2%的裸露膨体距平滑肌细胞超过5微米。脑血管的这些值分别为9.5%和37%。在耳血管中，25%的裸露膨体形成紧密的神经肌肉接触（距平滑肌500纳米以内），而在脑血管中只有3%形成紧密接触；与耳血管相比，脑血管中随着分支增加，这一比例显著降低。脑血管的这些结构特征，连同对去甲肾上腺素较低的敏感性和较弱的反应能力，可能解释了它们较弱的神经源性控制。结果表明，兔的脑循环接受的交感神经支配在改变脑血管张力方面相对无效。
