Eckersell C B, Popper P, Micevych P E
Department of Neurobiology, School of Medicine, and the Laboratory of Neuroendocrinology, Brain Research Institute, University of California Los Angeles, Los Angeles, California 90095-1763, USA.
J Neurosci. 1998 May 15;18(10):3967-76. doi: 10.1523/JNEUROSCI.18-10-03967.1998.
The mu-opioid receptor (mu-OR), like most G-protein-coupled receptors, is rapidly internalized after agonist binding. Although opioid peptides induce internalization in vivo, there are no studies that demonstrate mu-OR internalization in response to natural stimuli. In this study, we used laser-scanning microscopy to demonstrate that estrogen treatment induces the translocation of mu-OR immunoreactivity (mu-ORi) from the membrane to an internal location in steroid-sensitive cell groups of the limbic system and hypothalamus. Estrogen-induced internalization was prevented by the opioid antagonist naltrexone, suggesting that translocation was largely dependent on release of endogenous agonists. Estrogen treatment also altered the pattern of mu-ORi at the bright-field light microscopic level. In the absence of stimulation, the majority of immunoreactivity is diffuse, with few definable mu-OR+ cell bodies or processes. After stimulation, the density of distinct processes filled with mu-ORi was significantly increased. We interpreted the increase in the number of mu-OR+ processes as indicating increased levels of internalization. Using this increase in the density of mu-OR+ fibers, we showed that treatment of ovariectomized rats with estradiol benzoate induced a rapid and reversible increase in the number of fibers. Significant internalization was noted within 30 min and lasted for >24 hr after estrogen treatment in the medial preoptic nucleus, the principal part of the bed nucleus, and the posterodorsal medial amygdala. Naltrexone prevented the increase of mu-OR+ processes. These data imply that estrogen treatment stimulates the release of endogenous opioids that activate mu-OR in the limbic system and hypothalamus providing a "neurochemical signature" of steroid activation of these circuits.
与大多数G蛋白偶联受体一样，μ-阿片受体（mu-OR）在激动剂结合后会迅速内化。尽管阿片肽在体内可诱导内化，但尚无研究表明mu-OR会因自然刺激而发生内化。在本研究中，我们使用激光扫描显微镜来证明雌激素处理可诱导mu-OR免疫反应性（mu-ORi）从膜转运至边缘系统和下丘脑的类固醇敏感细胞群中的内部位置。阿片拮抗剂纳曲酮可阻止雌激素诱导的内化，这表明转运在很大程度上依赖于内源性激动剂的释放。雌激素处理还改变了明视野光学显微镜水平下mu-ORi的模式。在无刺激的情况下，大多数免疫反应性是弥散的，几乎没有可明确界定的mu-OR+细胞体或突起。刺激后，充满mu-ORi的明显突起的密度显著增加。我们将mu-OR+突起数量的增加解释为内化水平升高的指标。利用mu-OR+纤维密度的这种增加，我们表明用苯甲酸雌二醇处理去卵巢大鼠可诱导纤维数量迅速且可逆地增加。在内侧视前核、终纹床核主要部分和杏仁核后内侧背核中，雌激素处理后30分钟内即出现明显的内化，且持续超过24小时。纳曲酮可阻止mu-OR+突起的增加。这些数据表明，雌激素处理可刺激内源性阿片类物质的释放，这些物质激活边缘系统和下丘脑的mu-OR，从而提供这些神经回路类固醇激活的“神经化学特征”。
