Gebke E, Müller A R, Jurzak M, Gerstberger R
Max-Planck-Institute for Physiological and Clinical Research, W. G. Kerckhoff-Institute, Bad Nauheim, Germany.
Neuroscience. 1998 Jul;85(2):509-20. doi: 10.1016/s0306-4522(97)00601-5.
The subfornical organ and organum vasculosum laminae terminalis represent neuroglial circumventricular organ structures bordering the anterior third cerebral ventricle. Owing to the absence of the blood-brain barrier, the cellular elements of the subfornical organ and the organum vasculosum laminae terminalis can be reached by circulating messenger molecules transferring afferent information. As demonstrated for the control of extracellular fluid composition, the circulating hormone angiotensin II acts on these sensory circumventricular organs to induce drinking, elevated peripheral resistance and neurohypophyseal hormone release via interaction with membrane-spanning receptor proteins. To characterize the cell-specific distribution of angiotensin II receptors within the circumventricular organs, primary cell cultures derived from the subfornical organ or organum vasculosum laminae terminalis of five- to six-day-old rat pups were used to measure alterations in intracellular calcium at the single cell level. Neurons and astrocytes were identified by immunocytochemical staining for specific marker proteins. Bath application of angiotensin II (10(-10)-10(-6) M) dose-dependently induced calcium transients in neurons (19.6%) and astrocytes (15.7%), and angiotensin II threshold concentrations to elicit intracellular calcium signalling proved to be one order of magnitude higher in astrocytes as compared to neurons (10(-9) M). At angiotensin II concentrations higher than 10(-7) M, pronounced desensitization of the angiotensin II receptor occurred. Employing the angiotensin II receptor antagonists losartan (DUP-753; AT1-receptor) and PD-123319 (AT2-receptor), exclusive expression of the AT1 receptor subtype coupled to intracellular calcium concentration signalling could be demonstrated for neurons and astrocytes. In all cells examined, the angiotensin II-evoked increase in intracellular calcium concentrations could be fully suppressed in the absence of extracellular calcium. Co-activation by angiotensin II and other agents (vasopressin, its fragment 8-arginine-vasopressin(4-9), oxytocin, endothelin) was indicated for subfornical organ neurons and organum vasculosum laminae terminalis astrocytes.
穹窿下器和终板血管器是毗邻第三脑室前1/3的神经胶质室周器官结构。由于缺乏血脑屏障，循环中的信使分子可接触到穹窿下器和终板血管器的细胞成分，从而传递传入信息。如在细胞外液成分控制方面所示，循环激素血管紧张素II作用于这些感觉性室周器官，通过与跨膜受体蛋白相互作用诱导饮水、外周阻力升高及神经垂体激素释放。为了表征血管紧张素II受体在室周器官内的细胞特异性分布，使用了来自5至6日龄大鼠幼崽的穹窿下器或终板血管器的原代细胞培养物，在单细胞水平上测量细胞内钙的变化。通过对特定标记蛋白进行免疫细胞化学染色来鉴定神经元和星形胶质细胞。浴用血管紧张素II（10⁻¹⁰ - 10⁻⁶ M）剂量依赖性地诱导神经元（19.6%）和星形胶质细胞（15.7%）出现钙瞬变，与神经元相比，星形胶质细胞引发细胞内钙信号的血管紧张素II阈值浓度高一个数量级（10⁻⁹ M）。在血管紧张素II浓度高于10⁻⁷ M时，血管紧张素II受体出现明显脱敏。使用血管紧张素II受体拮抗剂氯沙坦（DUP - 753；AT1受体）和PD - 123319（AT2受体），可证明神经元和星形胶质细胞中与细胞内钙浓度信号传导偶联的AT1受体亚型的特异性表达。在所有检测的细胞中，在无细胞外钙的情况下，血管紧张素II引起的细胞内钙浓度升高可被完全抑制。穹窿下器神经元和终板血管器星形胶质细胞存在血管紧张素II与其他因子（血管加压素、其片段8 - 精氨酸血管加压素(4 - 9)、催产素、内皮素）的共同激活。
