Department of Physiology, Georgia Health Sciences University, Augusta, GA 30912, USA.
J Neuroendocrinol. 2012 Feb;24(2):378-92. doi: 10.1111/j.1365-2826.2011.02243.x.
In addition to their peripheral vasoactive effects, accumulating evidence supports an important role for endothelins (ETs) in the regulation of the hypothalamic magnocellular neurosecretory system, which produces and releases the neurohormones vasopressin (VP) and oxytocin (OT). Still, the precise cellular substrates, loci and mechanisms underlying the actions of ETs on the magnocellular system are poorly understood. In the present study, we combined patch-clamp electrophysiology, confocal Ca(2+) imaging and immunohistochemistry to study the actions of ETs on supraoptic nucleus (SON) magnocellular neurosecretory neurones and astrocytes. Our studies show that ET-1 evoked rises in Ca(2+) levels in SON astrocytes (but not neurones), an effect largely mediated by the activation of ET(B) receptors and mobilisation of thapsigargin-sensitive Ca(2+) stores. The presence of ET(B) receptors in SON astrocytes was also verified immunohistochemically. ET(B) receptor activation either increased (75%) or decreased (25%) SON firing activity, both in VP and putative OT neurones, and these effects were prevented when slices were preincubated in glutamate receptor blockers or nitric oxide synthase blockers, respectively. Moreover, ET(B) -mediated effects in SON neurones were also prevented by a gliotoxin compound, and when changes in Ca(2+) were prevented with bath-applied BAPTA-AM or thapsigargin. Conversely, intracellular Ca(2+) chelation in the recorded SON neurones failed to block ET(B) -mediated effects. In summary, our results indicate that ET(B) receptor activation in SON astrocytes induces the mobilisation of Ca(2+) , likely resulting in the activation of glutamate and nitric oxide signalling pathways, evoking in turn excitatory and inhibitory SON neuronal responses, respectively. Taken together, our study supports an important role for astrocytes in mediating the actions of ETs on the magnocellular neurosecretory system.
除了它们的外周血管活性作用外，越来越多的证据支持内皮素（ETs）在调节下丘脑大细胞神经分泌系统中的重要作用，该系统产生和释放神经激素血管加压素（VP）和催产素（OT）。然而，ET 对大细胞系统作用的确切细胞底物、部位和机制仍知之甚少。在本研究中，我们结合膜片钳电生理学、共聚焦 Ca(2+)成像和免疫组织化学研究了 ET 对视上核（SON）大细胞神经分泌神经元和星形胶质细胞的作用。我们的研究表明，ET-1 可引起 SON 星形胶质细胞（而非神经元）内 Ca(2+) 水平升高，这种作用主要是通过激活 ET(B)受体和动员 thapsigargin 敏感的 Ca(2+)库来介导的。SON 星形胶质细胞中也存在 ET(B)受体，这一点也通过免疫组织化学得到了验证。ET(B)受体激活可增加（75%）或减少（25%）VP 和假定的 OT 神经元中的 SON 放电活动，并且当切片分别用谷氨酸受体阻滞剂或一氧化氮合酶阻滞剂预孵育时，这些作用被阻止。此外，用神经胶质毒素化合物和当用浴中应用 BAPTA-AM 或 thapsigargin 阻止 Ca(2+) 变化时，ET(B) 介导的 SON 神经元中的作用也被阻止。相反，记录的 SON 神经元中的细胞内 Ca(2+)螯合未能阻断 ET(B) 介导的作用。总之，我们的结果表明，SON 星形胶质细胞中 ET(B)受体的激活诱导 Ca(2+) 的动员，可能导致谷氨酸和一氧化氮信号通路的激活，从而分别引发兴奋性和抑制性 SON 神经元反应。综上所述，我们的研究支持星形胶质细胞在介导 ET 对大细胞神经分泌系统的作用中的重要作用。
