Polson Jaimie W, Mrljak Steven, Potts Patrick D, Dampney Roger A L
Department of Physiology and Institute for Biomedical Research, University of Sydney, NSW, Australia.
Auton Neurosci. 2002 Sep 30;100(1-2):10-20. doi: 10.1016/s1566-0702(02)00143-1.
Hypotension produces a reflex increase in the activity of sympathetic vasomotor nerves. Studies in anaesthetised animals have established that neurons in the rostral ventrolateral medulla (RVLM) that project directly to sympathetic vasomotor preganglionic neurons in the spinal cord are a critical component of the central pathways mediating this reflex response. There are also neurons in supramedullary regions (the A5 area in the pons and the paraventricular nucleus (PVN) in the hypothalamus), however, that project directly to the sympathetic vasomotor outflow. The aim of this study was to identify and map neurons within the A5 area and PVN, as well as in the RVLM, which may contribute to the reflex sympathoexcitatory response to a hypotensive challenge in conscious rabbits. In a preliminary operation, a retrogradely transported tracer was injected into a site centred on the intermediolateral cell column in the upper lumbar spinal cord. After a waiting period of at least 1 week, a moderate hypotension (decrease in arterial pressure of approximately 20 mm Hg) was induced in conscious rabbits for 60 min by continuous infusion of sodium nitroprusside. In confirmation of previous studies, hypotension resulted in the expression of Fos in the RVLM, the A5 area and PVN. There were also retrogradely labelled neurons in all these regions. In both the RVLM and A5 area, approximately 40% of the retrogradely labelled neurons were also immunoreactive for Fos. In contrast, in the PVN the proportion of retrogradely labelled neurons that were also Fos-positive was much less (approximately 6%). This study has demonstrated that, in the conscious rabbit, a significant proportion of spinally projecting neurons within discrete regions in the RVLM and A5 area are activated by hypotension (as indicated by Fos expression). In the PVN, only a very small proportion of spinally projecting neurons are activated by hypotension, and thus these neurons appear to be regulated primarily by inputs other than baroreceptor inputs.
低血压会引起交感缩血管神经活动反射性增强。对麻醉动物的研究表明，延髓头端腹外侧区（RVLM）中直接投射至脊髓交感缩血管节前神经元的神经元，是介导这种反射反应的中枢通路的关键组成部分。然而，在延髓以上区域（脑桥的A5区和下丘脑室旁核（PVN））也存在直接投射至交感缩血管传出神经的神经元。本研究的目的是识别并绘制A5区、PVN以及RVLM内可能参与清醒家兔对低血压刺激的反射性交感兴奋反应的神经元。在初次手术中，将一种逆行运输示踪剂注入上腰段脊髓中间外侧细胞柱中心部位。经过至少1周的等待期后，通过持续输注硝普钠在清醒家兔中诱导出中度低血压（动脉压降低约20 mmHg），持续60分钟。正如先前研究所证实的，低血压导致RVLM、A5区和PVN中Fos蛋白表达。在所有这些区域也有逆行标记的神经元。在RVLM和A5区，约40%的逆行标记神经元也对Fos蛋白呈免疫反应。相比之下，在PVN中，同时为Fos阳性的逆行标记神经元比例要小得多（约6%）。本研究表明，在清醒家兔中，RVLM和A5区离散区域内相当一部分投射至脊髓的神经元被低血压激活（以Fos蛋白表达为指标）。在PVN中，只有极少数投射至脊髓的神经元被低血压激活，因此这些神经元似乎主要受压力感受器输入以外的其他输入调控。
