Nomura S, Ding Y Q, Kaneko T, Li J L, Mizuno N
College of Medical Technology, Kyoto University, Japan.
Neuroscience. 1996 Jul;73(1):277-86. doi: 10.1016/0306-4522(96)00027-9.
mu-Opioid receptor, the opioid receptor that shows the highest affinity for morphine, appears to induce a variety of side-effects, at least partly, directly through the mu-opioid receptor on neurons constituting the autonomic part of the vagus nerve. Thus, in the present study, location of mu-opioid receptor-like immunoreactivity in the central components of the autonomic part of the vagus nerve was examined in the rat. The intense immunoreactivity was observed light microscopically in the neuropil of the commissural subnucleus and the dorsal part of the medial subnucleus of the nucleus of the solitary tract, and in the neuropil of the rostral half of the ambiguus nucleus. The immunoreactivity was moderate in the neuropil of the rostral and lateral subnuclei and ventral part of the medial subnucleus of the nucleus of the solitary tract, and weak in the neuropil of the dorsal motor nucleus of the vagus nerve. In the nodose ganglion, many neurons of various sizes (17-48 microns in soma diameter) showed moderate immunoreactivity. After unilateral vagotomy at a level proximal to the nodose ganglion, the immunoreactivity in the ipsilateral ambiguus nucleus was apparently reduced within 48 h of the operation, and completely disappeared by the seventh day after the operation. In the nucleus of the solitary tract and dorsal motor nucleus of the vagus nerve, the reduction of immunoreactivity after the ganglionectomy was detectable on the fourth day after the operation, and became readily apparent by the seventh day after the operation; the immunoreactivity, none the less, still remained on the 10th day after the operation. Electron microscopically, the immunoreactivity in the ambiguus nucleus was seen mainly on dendritic profiles and additionally on somatic ones; no immunoreactivity was detected in axonal profiles. The immunoreactivity in the dorsal motor nucleus of the vagus nerve was observed only on dendritic profiles. The immunoreactivity in the nucleus of the solitary tract was seen on axonal and dendritic profiles, but not on somatic profiles. The immunoreactive axon terminals in the nucleus of the solitary tract were filled with spherical synaptic vesicles and made asymmetric synapses with dendritic profiles. The results indicate that the mu-opioid receptor in the central components of the autonomic part of the vagus nerve is located on dendrites and cell bodies of efferent neurons in the ambiguus, on dendrites of efferent neurons in the dorsal motor nucleus, and on axons which arise from nodose ganglion neurons and terminate in the nucleus of the solitary tract. The receptors on these structures may constitute the targets of enkephalin-containing and beta-endorphin-containing afferent axons arising from brainstem neurons. The receptors on the axon terminals of nodose ganglion neurons may be involved in regulation of the release of neurotransmitters and/or neuromodulators.
μ-阿片受体是对吗啡显示出最高亲和力的阿片受体，它似乎至少部分地通过迷走神经自主部分的神经元上的μ-阿片受体直接诱发多种副作用。因此，在本研究中，检测了大鼠迷走神经自主部分中枢成分中μ-阿片受体样免疫反应性的定位。在孤束核连合亚核和内侧亚核背侧部分的神经毡中，以及疑核 Rostral 半部分的神经毡中，光镜下观察到强烈的免疫反应性。在孤束核 Rostral 和外侧亚核以及内侧亚核腹侧部分的神经毡中，免疫反应性中等，而在迷走神经背运动核的神经毡中较弱。在结状神经节中，许多大小各异（胞体直径为 17 - 48 微米）的神经元显示出中等免疫反应性。在结状神经节近端水平进行单侧迷走神经切断术后，同侧疑核中的免疫反应性在术后 48 小时内明显降低，并在术后第 7 天完全消失。在孤束核和迷走神经背运动核中，神经节切除术后免疫反应性的降低在术后第 4 天可检测到，并在术后第 7 天变得明显；然而，免疫反应性在术后第 10 天仍然存在。电镜下，疑核中的免疫反应性主要见于树突轮廓，也见于胞体轮廓；在轴突轮廓中未检测到免疫反应性。迷走神经背运动核中的免疫反应性仅见于树突轮廓。孤束核中的免疫反应性见于轴突和树突轮廓，但不见于胞体轮廓。孤束核中免疫反应性轴突终末充满球形突触小泡，并与树突轮廓形成不对称突触。结果表明，迷走神经自主部分中枢成分中的μ-阿片受体位于疑核传出神经元的树突和胞体上、背运动核传出神经元的树突上，以及起源于结状神经节神经元并终止于孤束核的轴突上。这些结构上的受体可能构成来自脑干神经元的含脑啡肽和含β-内啡肽传入轴突的靶点。结状神经节神经元轴突终末上的受体可能参与神经递质和/或神经调质释放的调节。
