Nouel D, Faure M P, St Pierre J A, Alonso R, Quirion R, Beaudet A
Montreal Neurological Institute and Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada, H3A 2B4.
J Neurosci. 1997 Mar 1;17(5):1795-803. doi: 10.1523/JNEUROSCI.17-05-01795.1997.
Two G-protein-coupled receptors for the tridecapeptide neurotensin (NT) have been identified and cloned in mammalian brain: a high-affinity (Kd = 0.3 nM) receptor, sensitive to the antagonist SR 48692 but insensitive to levocabastine, and a lower-affinity (Kd = 2-4 nM) receptor, sensitive to levocabastine but with poor affinity for SR 48692. Although there is good evidence that the high-affinity site is predominantly expressed in neurons, little is known of the cellular localization of the low-affinity receptor. In the present study, we identify by confocal microscopy selective levocabastine-sensitive, SR 48692-resistant binding of a fluorescent derivative of NT (fluo-NT) to a subpopulation of glial fibrillary acidic protein-immunoreactive glial cells grown in culture from the midbrain and cerebral cortex of embryonic and neonatal rats, respectively. We also demonstrate, by combining fluo-NT detection with tyrosine hydroxylase immunofluorescence, that these glial binding sites are differentially regulated from the SR 48692-sensitive NT receptor expressed in the same cultures by mesencephalic dopamine neurons. Whereas the latter undergoes rapid ligand-induced internalization followed by centripetal mobilization of ligand-receptor complexes from processes to perikarya and from perikaryal periphery to cell center, the former induces the formation of cell-surface clusters that fail to internalize. It is concluded that NT may exert its effects on both neurons and astrocytes in the CNS. Whereas NT neural signaling is exerted through high-affinity receptors and may be partly effected through internalization of receptor-ligand complexes, glial signaling is exerted through low-affinity NT receptors and appears to be transduced exclusively at the level of the plasma membrane.
在哺乳动物大脑中已鉴定并克隆出两种针对十三肽神经降压素（NT）的G蛋白偶联受体：一种高亲和力（Kd = 0.3 nM）受体，对拮抗剂SR 48692敏感，但对左卡巴斯汀不敏感；另一种低亲和力（Kd = 2 - 4 nM）受体，对左卡巴斯汀敏感，但对SR 48692亲和力较差。尽管有充分证据表明高亲和力位点主要在神经元中表达，但对低亲和力受体的细胞定位了解甚少。在本研究中，我们通过共聚焦显微镜鉴定出，NT的荧光衍生物（fluo-NT）能选择性地与分别从胚胎和新生大鼠中脑及大脑皮质培养的胶质纤维酸性蛋白免疫反应性胶质细胞亚群结合，这种结合对左卡巴斯汀敏感、对SR 48692耐药。我们还通过将fluo-NT检测与酪氨酸羟化酶免疫荧光相结合证明，这些胶质细胞结合位点与同一培养物中中脑多巴胺神经元表达的对SR 48692敏感的NT受体受到不同的调节。后者在配体诱导下迅速内化，随后配体 - 受体复合物从突起向胞体、从胞体周边向细胞中心进行向心性移动，而前者则诱导形成不能内化的细胞表面簇。结论是，NT可能在中枢神经系统中对神经元和星形胶质细胞都发挥作用。NT的神经信号传导是通过高亲和力受体进行的，可能部分通过受体 - 配体复合物的内化来实现，而胶质细胞信号传导则通过低亲和力NT受体进行，并且似乎仅在质膜水平进行转导。
