Dun N J, Dun S L, Wu S Y, Williams C A, Kwok E H
Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, Tenn. 37614, USA.
J Biomed Sci. 2000 May-Jun;7(3):213-20. doi: 10.1007/BF02255468.
Endomorphin (Endo) 1 and 2, two tetrapeptides isolated from the bovine and human brain, have been proposed to be the endogenous ligand for the mu-opiate receptor. A multi-disciplinary study was undertaken to address the issues of localization, release and biological action of Endo with respect to the rat dorsal horn. First, immunohistochemical studies showed that Endo-1- or Endo-2-like immunoreactivity (Endo-1- or Endo-2-LI) is selectively expressed in fiber-like elements occupying the superficial layers of the rat dorsal horn, which also exhibit a high level of mu-opiate receptor immunoreactivity. Second, release of immunoreactive Endo-2-like substances (irEndo) from the in vitro rat spinal cords upon electrical stimulation of dorsal root afferent fibers was detected by the immobilized antibody microprobe technique. The site of release corresponded to laminae I and II where the highest density of Endo-2-LI fibers was localized. Lastly, whole-cell patch clamp recordings from substantia gelatinosa (SG) neurons of rat lumbar spinal cord slices revealed two distinct actions of exogenous Endo-1 and Endo-2: (1) depression of excitatory and/or inhibitory postsynaptic potentials evoked by stimulation of dorsal root entry zone, and (2) hyperpolarization of SG neurons. These two effects were prevented by the selective mu-opiate receptor antagonist beta-funaltrexamine. The localization of endomorphin-positive fibers in superficial layers of the dorsal horn and the release of irEndo upon stimulation of dorsal root afferents together with the observation that Endo inhibits the activity of SG neurons by interacting with mu-opiate receptors provide additional support of a role of Endo as the endogenous ligand for the mu-opiate receptor in the rat dorsal horn.
内吗啡肽（Endo）1和2是从牛和人脑中分离出的两种四肽，被认为是μ-阿片受体的内源性配体。我们开展了一项多学科研究，以探讨内吗啡肽在大鼠背角的定位、释放及生物学作用相关问题。首先，免疫组织化学研究表明，内吗啡肽-1或内吗啡肽-2样免疫反应性（Endo-1-或Endo-2-LI）在占据大鼠背角浅层的纤维样成分中选择性表达，这些成分也表现出高水平的μ-阿片受体免疫反应性。其次，通过固定化抗体微探针技术检测了电刺激背根传入纤维时体外大鼠脊髓中免疫反应性内吗啡肽-2样物质（irEndo）的释放。释放部位对应于内吗啡肽-2-LI纤维密度最高的I层和II层。最后，大鼠腰段脊髓切片的胶状质（SG）神经元的全细胞膜片钳记录揭示了外源性内吗啡肽-1和内吗啡肽-2的两种不同作用：（1）抑制刺激背根进入区诱发的兴奋性和/或抑制性突触后电位，（2）使SG神经元超极化。这两种效应均被选择性μ-阿片受体拮抗剂β-芬太尼酰苯胺阻断。背角浅层内吗啡肽阳性纤维的定位、刺激背根传入纤维时irEndo的释放，以及内吗啡肽通过与μ-阿片受体相互作用抑制SG神经元活性的观察结果，为内吗啡肽作为大鼠背角μ-阿片受体的内源性配体发挥作用提供了额外支持。
