Drolet G, Van Bockstaele E J, Aston-Jones G
Department of Mental Health Sciences, Hahnemann University, Philadelphia, Pennsylvania 19102-1192.
J Neurosci. 1992 Aug;12(8):3162-74. doi: 10.1523/JNEUROSCI.12-08-03162.1992.
Substantial evidence indicates that the noradrenergic nucleus locus coeruleus (LC) is a key target of endogenous opioid neurons, and an important structure in mediating opiate effects. However, the detailed distribution of opioid fibers and terminals in the LC, and the sources of its opioid innervation are unknown. In the present study, the enkephalin innervation of the LC was investigated in the rat using an antibody directed against the extended enkephalin peptide Met-enkephalin-Arg6-Gly7-Leu8 (ENK), which is derived exclusively from the enkephalin precursor proenkephalin A. An antibody directed against tyrosine hydroxylase (TH), the synthetic enzyme for catecholaminergic neurons, was also applied to the same tissue sections to delineate LC neurons and their dendrites. Enkephalin fibers in the LC were dense and highly varicose. In horizontal sections, ENK-like-immunoreactive (ENK-ir) fibers of considerable length coursed throughout the rostrocaudal orientation of the LC proper, whereas in frontal sections ENK-ir processes appeared punctate, suggesting a rostrocaudal orientation. Dense ENK-ir fibers were also identified in the rostromedial and caudal juxtaependymal pericoerulear regions where extranuclear dendrites of LC neurons are extensive. As previously reported, there were no ENK-ir neurons in the LC nucleus proper, but such cells were present in neighboring structures such as the parabrachial, sphenoid, and Barrington's nuclei as well as in the central gray and in the subcoeruleus area. ENK-ir neurons were also present in nuclei of the rostral medulla reported to be major afferents of the LC, the nucleus prepositus hypoglossi (PrH), and the nucleus paragigantocellularis (PGi). In the dorsomedial medulla, numerous ENK-ir neurons were identified in the medial aspect of the PrH and along the medial longitudinal fasciculus in the perifascicular reticular formation. In the ventrolateral medulla, ENK-ir neurons were distributed in a conical caudorostral column throughout the PGi. Retrograde transport of a WGA-colloidal gold conjugate (WGA-apoHRP-Au) from LC, combined with immunohistochemistry for ENK in the same tissue sections, revealed that LC afferents in the PGi and PrH were interdigitated with ENK-ir neurons. Furthermore, an unexpectedly high incidence of doubly labeled neurons were identified in both PGi and PrH. Overall, 57% and 56% of the LC-projecting neurons in PGi and PrH, respectively, were also immunoreactive for ENK, suggesting that enkephalinergic neurons of PGi and PrH are major afferents to noradrenergic LC neurons.
大量证据表明，去甲肾上腺素能蓝斑核（LC）是内源性阿片样物质神经元的关键靶点，也是介导阿片类药物作用的重要结构。然而，LC中阿片样物质纤维和终末的详细分布及其阿片样物质神经支配的来源尚不清楚。在本研究中，使用针对延伸的脑啡肽肽甲硫氨酸脑啡肽-精氨酸6-甘氨酸7-亮氨酸8（ENK）的抗体，在大鼠中研究了LC的脑啡肽神经支配，该抗体仅来源于脑啡肽前体前脑啡肽A。还将针对酪氨酸羟化酶（TH）（儿茶酚胺能神经元的合成酶）的抗体应用于相同的组织切片，以描绘LC神经元及其树突。LC中的脑啡肽纤维密集且高度曲张。在水平切片中，相当长的ENK样免疫反应性（ENK-ir）纤维在LC本体的整个 rostrocaudal 方向上走行，而在额状切片中，ENK-ir 突起呈点状，表明为 rostrocaudal 方向。在 LC 神经元核外树突广泛的 rostromedial 和尾侧室周蓝斑旁区域也发现了密集的 ENK-ir 纤维。如先前报道，LC 核本体内没有 ENK-ir 神经元，但在相邻结构如臂旁核、蝶骨核和巴林顿核以及中央灰质和蓝斑下区域存在此类细胞。ENK-ir 神经元也存在于据报道是 LC 的主要传入神经的延髓头端核、舌下前置核（PrH）和巨细胞旁核（PGi）中。在延髓背内侧，在 PrH 的内侧和束状网状结构中沿内侧纵束发现了许多 ENK-ir 神经元。在延髓腹外侧，ENK-ir 神经元分布在整个 PGi 的一个锥形尾头柱中。从 LC 逆行转运 WGA-胶体金结合物（WGA-apoHRP-Au），并结合在相同组织切片中对 ENK 的免疫组织化学，显示 PGi 和 PrH 中的 LC 传入神经与 ENK-ir 神经元相互交错。此外，在 PGi 和 PrH 中都发现了意外高比例的双标记神经元。总体而言，PGi 和 PrH 中分别有57%和56%投射到 LC 的神经元也对 ENK 有免疫反应，这表明 PGi 和 PrH 的脑啡肽能神经元是去甲肾上腺素能 LC 神经元的主要传入神经。
