NEUROBIOLOGY OF ENDOMORPHINS IN SPINAL DORSAL HORN

脊髓中的胶状质（SG）神经元是初级传入的主要终止部位，其中许多神经元支配伤害感受器。内源性阿片类药物或合成化合物被认为产生其抗伤害感受器。内源性阿片或合成化合物被认为是通过与SG神经元上的阿片受体亚型相互作用来产生其抗伤害性感受。两个最近分离的四肽内吗啡肽（Endo）1和2被认为是阿片受体μ亚型的内源性配体。初步结果表明，内吗啡样免疫反应（Endo-LI）亚型阿片受体。初步结果表明，内吗啡样免疫反应（Endo-LI）定位于致密的神经纤维网络在大鼠背角的浅层。因此，大鼠背角提供了一个独特的机会，以测试的假设，内-1/内-2内源性释放，它可以调节SG神经元的活动。将讨论两个主要问题。首先，利用放射性微探针技术，在麻醉大鼠体内或离体大鼠脊髓中评价内源性内吗啡肽的释放。电刺激后爪的疼痛刺激的传入纤维将用于评估在这些条件下内吗啡肽释放是否改变。第二，将使用全细胞膜片记录技术来研究Endo对大鼠脊髓横片单个SG神经元的细胞作用和潜在的信号转导机制。 我们的初步结果表明，Endo抑制SG神经元的活动，通过超极化膜和/或衰减突触传递。在本研究中，将从电生理学和电生理学的角度来评价Endo在突触前和突触后的作用。将检查可能是Endo超极化作用基础的K+通道亚型。类似地，将评价与突触前阿片受体偶联的Ca2+和/或K+通道的亚型，其可能介导Endo的突触抑制作用。本项目的长期目标是提高我们目前对这类新的阿片肽对背角神经元作用的部位和机制的理解，目的是开发一类具有治疗潜力的新型阿片化合物。

Substantia gelatinosa (SG) neurons in the spinal cord are the principal site of termination of primary afferents, many of which innervate nociceptors. Endogenous opiates or synthetic compounds are thought to produce their anti-nociceptors. Endogenous opiates or synthetic compounds are thought to produce their anti-nociception by interacting with subtypes of opiate receptors on SG neurons. Two recently isolated tetrapeptides endomorphin (Endo) 1 and 2 are believed to be the endogenous ligand for the mu-subtype of opioid receptors. Preliminary results showed endomorphin-like immunoreactivity (Endo-LI) subtype of opioid receptors. Preliminary results showed that endomorphin-like immunoreactivity (Endo-LI) is localized to dense networks of nerve fibers in the superficial layers of the rat dorsal horn. Thus, the rat dorsal horn offers a unique opportunity to test the hypothesis that Endo-1/Endo-2 is released endogenously and that it may modulate the activity of SG neurons. Two major issues will be addressed. First, release of endogenous of endogenous endomorphins will be evaluated in anesthetized rats in vivo or isolated rat spinal cords in vitro by the radioactive microprobe techniques. Electrical stimulation of afferent fibers of painful stimulus to the hindpaw will be employed to evaluate whether or not endomorphin release is altered under these conditions. Second, whole-cell patch recording techniques will be used to study the cellular action and the signal transduction mechanism underlying the action of Endo on single SG neurons in rat transverse spinal cord slices. Our preliminary results show that Endo inhibits the activity of SG neurons by hyperpolarizing the membrane and/or attenuating synaptic transmission. In this proposal, the pre- and post-synaptic actions of Endo will be evaluated electrophysiologically and pharmacologically. The subtype(s) of K+ channels that may underlie the hyperpolarizing action of Endo will be examined. Similarly, the subtype(s) of Ca2+ and/or K+ channels coupled to the presynaptic opiate receptor that may mediate the synaptic depressant action of Endo will be evaluated. The long term goal of this project is to improve our current understanding of the site and mechanism of action of this new class of opioid peptides on dorsal horn neurons, with the aim toward developing a novel class of opiate compounds with therapeutic potentials.